Agriculture could suffer the water stress induced by climate change. Because climate warming affects global hydrological cycles, it is vital to explore the effect of tree transpiration, as an important component of te...Agriculture could suffer the water stress induced by climate change. Because climate warming affects global hydrological cycles, it is vital to explore the effect of tree transpiration, as an important component of terrestrial evapotranspiration, on the environment. Thermal dissipation probes were used to measure xylem sap flux density of a Schima superba plantation in the urban area of Guangzhou City, South China. Stand transpiration was calculated by mean sap flux density times total sapwood area. The occurrence of the maximum sap flux density on the daily scale was later in wet season than in dry season. The peak of daily sap flux density was the highest of 59 g m-2 s^-1 in July and August, and the lowest of 28 g m-2 s-1 in December. In the two periods (November 2007-October 2008 and November 2008-October 2009), the stand transpiration reached 263.2 and 291.6 ram, respectively. During our study period, stand transpiration in wet season (from April to September) could account for about 58.5 and 53.8% of the annual transpiration, respectively. Heat energy absorbed by tree transpiration averaged 1.4×10s and 1.6×10s kJ per month in this Schima superba plantation with the area of 2 885 m2, and temperature was reduced by 4.3 and 4.7℃ s^-1 per 10 m3 air.展开更多
Experimental investigation is performed to investigate the cooling characteristics in the front zone of effusion configuration. Effects of blowing ratio,multi-hole arrangement mode,hole-to-hole pitch and jet orientati...Experimental investigation is performed to investigate the cooling characteristics in the front zone of effusion configuration. Effects of blowing ratio,multi-hole arrangement mode,hole-to-hole pitch and jet orientation angle on the adiabatic film cooling effectiveness are concentrated on. The results show that the film layer displays an obvious"developing"feature in the front zone of effusion cooling scheme,for either the staggered or inline multi-hole arrangement. The varying gradient of the laterally-averaged adiabatic cooling effectiveness along the streamwise direction is greater for the staggered arrangement than that for the inline arrangement. The holes array arranged in staggered mode with small hole-tohole pitches is in favor of obtaining developed film coverage layer rapidly.展开更多
Based on the analysis and comparison of soil temperature, thermal regime and permafrost table under the experimental embankment of crushed rock structures in Beiluhe, results show that crushed rock structures provide ...Based on the analysis and comparison of soil temperature, thermal regime and permafrost table under the experimental embankment of crushed rock structures in Beiluhe, results show that crushed rock structures provide an extensive cooling effect, which produces a rising permafrost table and decreasing soil temperatures. The rise of the permafrost table under the embankment ranges from an increase of 1.08 m to 1.67 m, with an average of 1.27 m from 2004 to 2007. Mean annual soil temperatures under the crushed rock layer embankment decreased significantly from 2005 to 2007, with average decreases of ?1.03 °C at the depth of 0.5 m, ?1.14 °C at the depth of 1.5 m, and ?0.5 °C at the depth of 5 m. During this period, mean annual soil temperatures under the crushed rock cover embankment showed a slight decrease at shallow depths, with an average decrease of ?0.2 °C at the depth of 0.5 m and 1.5 m, but a slight rise at the depth of 5 m. After the crushed rock structures were closed or crammed with sand, the cooling effect of the crushed rock layer embankment was greatly reduced and that of the crushed rock cover embankment was just slightly reduced.展开更多
With the completion of the Qinghai-Tibetan Railway,economic development of related areas has been greatly accelerated.This,in return,calls for building or upgrading more roadways,especially high-grade roadways.In cold...With the completion of the Qinghai-Tibetan Railway,economic development of related areas has been greatly accelerated.This,in return,calls for building or upgrading more roadways,especially high-grade roadways.In cold regions,the thawing of permafrost can induce settlement damage of and even failure to railway (or roadway) embankments.Thermosyphons (self-powered refrigera-tion devices that are used to help keep the permafrost cool) have proved effective in mitigating thaw settlement by maintaining the thermal stability of the embankments.However,for high-grade roadway embankments of great width,stabilizing or cooling ef-fects of traditional geotechnological measures may be limited.To enhance the cooling effect of thermosyphons,an L-shaped thermosyphon was designed.A laboratory test was carried out to study the combined cooling effect of the L-shaped thermosyphon and thermal insulation applying to roadbed construction.The angle between the evaporator and condenser sections of the L-shaped thermosyphon is 134 degrees,and the L-shaped thermosyphon was inserted into the soil at an angle of 5 degrees with the road surface.The tested results show that the L-shaped thermosyphon is effective in removing heat from a roadway in winter.When the ambient air temperature is lower than the soil temperature,the thermosyphon is active and extracts the heat in the soil around it.When the ambient air temperature is higher than the soil temperature,the thermosyphon is inactive,and no heat is in-jected into the soil through the L-shaped thermosyphon.Compared to embankments with straight thermosyphons,the inner parts of the embankments with L-shaped thermosyphons were significantly cooled.It is hoped that the present study would be useful to the application of L-shaped thermosyphons in the construction of high-grade roadways in cold regions.展开更多
It is claimed that open spaces in cities, such as parks, have an urban cooling effect. However, the relationship between urban parks and adjacent districts is still not explicit. In order to clarify the interaction be...It is claimed that open spaces in cities, such as parks, have an urban cooling effect. However, the relationship between urban parks and adjacent districts is still not explicit. In order to clarify the interaction between urban parks and their urban surroundings, this paper takes the Temple of Heaven Park (THP) as an example of a park station and focuses on analyzing the differences with a nearby urban station.THP is located in the center of Beijing, and the nearest urban station is Tian An Men. It is interesting that the cooling effect of THP reaches a peak and remains stable when its city background urban heat island (UHI) varies within a given range, but becomes unstable when the UHI goes beyond the range. This is called an enhanced cooling effect in this paper. As a result, the UHi intensities (UHIIs) are calculated in order to comprehend the role of the park cooling effect in the urban heating characteristics of Beijing. By comparison with five other park-district pairs, this paper attempts to identify the causes of the enhanced cooling effect. It is found that six park-district pairs consistently demonstrate a persistently stronger cooling rate during the night, and that the water coverage might be a key factor in enhancing the park cooling effect. Based on further investigation of the influence of surrounding UHIs on the park cooling effect, it is found that the UHII differences in park-district pairs show quasi-linear changes within a given range as the UHli of the surrounding district increases.展开更多
One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, the...One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, their effects might not meet large-width expressway requirements. The convection-intensifying composite embankment composed of perforated ventilation ducts and crushed-rock layers was numerically studied to investigate its cooling effects. Adopting a numerical model, the temperature fields for two kinds of composite embankment with and without air doors were analyzed considering air flow and heat transfer characteristics in porous media. The results show that wind velocity in the crushed-rock zone is intensified by the perforated ventilation duct. The underlying permafrost temperature obviously decreases, and the 0 °C isotherm position rises significantly due to composite embankment. The composite embankment with air doors is more effective than that without air doors. Therefore, the new convection-intensifying composite embankment is potentially a highly efficient cooling measure for construction in permafrost regions.展开更多
Film cooling is introduction of a secondary fluid (coolant or injected fluid) at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immed...Film cooling is introduction of a secondary fluid (coolant or injected fluid) at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immediate region of injection but also downstream region. This paper numerically investigated the film cooling effectiveness on two types of hole geometries which are cut-shaped hole and antivortex hole. The 3D computational geometries are modeled with a single 30 deg angled hole on a flat surface. The different blowing ratios of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5 and k-Epsilon turbulence model are used in this study. A two dimensional distribution of film cooling effectiveness in the downstream region of the cooling hole is performed. A comparison of spanwise averaged effectiveness is also performed in the field starts from center point of hole to X/D=-30.展开更多
The heat convection of fluid inside the ballast layer and ripped-rock layer,which are re-garded as porous media in railway embankment,is a process of heat and mass transfer.At present,the ripped-rock embankment,as a n...The heat convection of fluid inside the ballast layer and ripped-rock layer,which are re-garded as porous media in railway embankment,is a process of heat and mass transfer.At present,the ripped-rock embankment,as a new type of embankment structure,has widely been used in the construction of Qinghai-Tibetan railway.However,because its ripped-rock layer is almost open in two bilateral boundaries and closed at top and bottom,and air can flow into/out of the ballast layer and ripped-rock layer,the convection and transfer heat patterns are very complicated in the embankment.Therefore,based on the temperature and geology conditions of the Qinghai-Tibetan Plateau,a nu-merical approach of the unsteady two-dimensional continuity,momentum(non-Darcy flow)and en-ergy equations of heat convection for incompressible fluid in porous media is provided to analyze the velocity and temperature characteristics of the ripped-rock embankment with different embankment heights under open boundary condition for the coming 50 years in this paper.The calculated results indicate that,due to the influence of the outside wind,the convective heat transfer mainly relies on the forced convection in the open ripped-rock embankment.Even if the air temperature will be warmed up by 2.6℃in the coming 50 years,it still has a better cooling effect on the underlying soils and a low temperature frozen-soil core is formed in the permafrost below it if the embankment is constructed in the regions whose present mean annual air temperature is?4.0℃.Furthermore,the cooling effect of high ripped-rock embankment is better than that of low embankment.This is because the wider bot-tom of high embankment has a more influence dimension on the underlying frozen soil.However,cardinal winds on the Qinghai-Tibetan Plateau disturb its convection pattern,so that an asymmetric temperature distribution occurs under high embankment and it is possible to induce a transverse un-even deformation of embankment,but no similar situation occurs under low embankment.This asymmetric temperature field problem should be considered when ripped-rock embankment is de-signed and constructed.展开更多
With the sea surface observations from ICOADS for the years 1960-2002, the conditions of coohng, evaporauon anu water vapol transportation are analyzed and compared for the formation of seasonal sea fog in April-July ...With the sea surface observations from ICOADS for the years 1960-2002, the conditions of coohng, evaporauon anu water vapol transportation are analyzed and compared for the formation of seasonal sea fog in April-July in the Huanghai Sea. It is found that sea surface cooling is always existent during the fog seasons while sea surface evaporation only appears in April-June in the Huanghai Sea. Local evaporation alone is not sufficient to form fogs though it may lead to light ones. Water vapor transported from the low-latitudes accomplished by specific synoptic systems is the most important condition for sea fog formation. In general, the moistening effect is more important than the cooling one.展开更多
A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness...A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness,under a wide blowing ratio range(M=0.25–1.5).Three kinds of holes(Cylindrical Hole(CH),Fan-Shaped Hole(FSH),and Crater-Shaped Hole(CSH))are taken into consideration.The SDR shows an inherent affecting mechanism on the mutual interaction of jet-in-crossflow.It aggravates the lateral spreading of cooling jet and thus improves the film cooling uniformity significantly,regardless of film-hole shape and blowing ratio.When the blowing ratio is beyond 1.0,the combined effect of shaped holes and SDR on improving film cooling effectiveness behaves more significantly.It is suggested that FSH-SDR is a most favorable film cooling scheme.For FSH-SDR case,the spatially-averaged film cooling effectiveness is increased monotonously with the increase of blowing ratio,among the present bowing ratio range.展开更多
Three-dimensional numerical computations are conducted to investigate the effects of the blowing ratio and corrugation geometry on the adiabatic film cooling effectiveness as well as the heat transfer coefficient over...Three-dimensional numerical computations are conducted to investigate the effects of the blowing ratio and corrugation geometry on the adiabatic film cooling effectiveness as well as the heat transfer coefficient over a transverse corrugated surface.It is noticeable that the adiabatic wall temperature on the wavy valley of the transverse corrugated surface is relatively lower than that on the wavy peak.Surface corrugation has a relatively obvious influence on the laterallyaveraged adiabatic film cooling effectiveness in the region where the effusion film layer is developed,but has little influence in the front region.Compared to a flat surface,the transverse corrugated surface produces a smaller adiabatic film cooling effectiveness and a higher heat transfer coefficient ratio.The effusion cooling difference between the flat and corrugated surfaces behaves more obviously under a small aspect ratio of the wavy corrugation.展开更多
The film cooling effectiveness of two turbine blades at different turbulence intensities(0.62%and 16.00%)and mass flux ratios(2.91%,5.82%,8.73%and 11.63%)is studied by using the Pressure-Sensitive Paint(PSP)measuremen...The film cooling effectiveness of two turbine blades at different turbulence intensities(0.62%and 16.00%)and mass flux ratios(2.91%,5.82%,8.73%and 11.63%)is studied by using the Pressure-Sensitive Paint(PSP)measurement technique.There are a baseline and an improved turbine blade in current work,and their film cooling hole position distribution is the same.But the hole shape on suction surface and pressure surface is changed from cylindrical hole(baseline)to laid-back fan-shaped hole(improved blade).Both blades have 5 rows of cylindrical holes at the leading edge and 4 rows of cooling-holes on the suction surface and the pressure surface.The experimental results show that the film cooling effectiveness of the improved blade is much better than the baseline.The increase in turbulence intensity will reduce the cooling effectiveness on the surface of turbine blade,but the effect of turbulence intensity becomes weaker with an increase in the mass flux ratio.Compared with the multiple rows of cylindrical holes,the cooling effectiveness of shaped holes is more influenced by the turbulence intensity at low mass flux ratio.展开更多
The data obtained through the roadbed surface thermal regime experiment (ROBSTREX), which was carried out at Beiluhe test section of Qinghai-Tibetan Railway from October to December in 2002, were used to estimate the ...The data obtained through the roadbed surface thermal regime experiment (ROBSTREX), which was carried out at Beiluhe test section of Qinghai-Tibetan Railway from October to December in 2002, were used to estimate the cooling effect of ballast revetment on the roadbed. The results show that both riprap rock ballast revetment and crushed stone ballast revetment can reduce the temperature of the roadbed. But the cooling effect of riprap rock ballast revetment is better than that of crushed stone ballast revetment when the temperature of roadbed is higher. The cooling effect of crushed stone ballast revetment is better than that of riprap rock ballast revetment when the temperature of the roadbed is lower, especially at deeper roadbed layers. In the frozen season, the heat release from the roadbed also shows that the cooling effect of ballast revetment on the roadbed is obvious, and the cooling effect of crushed stone-ballast revetment on the roadbed is much evident than that of riprap rock ballast revetment.展开更多
This paper describes the numerical study on film cooling effectiveness and aerodynamic loss due to coolant and main stream mixing for a turbine guide vane. The effects of blowing ratio, mainstream Mach number, surface...This paper describes the numerical study on film cooling effectiveness and aerodynamic loss due to coolant and main stream mixing for a turbine guide vane. The effects of blowing ratio, mainstream Mach number, surface curvature on the cooling effectiveness and mixing loss were studied and discussed. The numerical results show that the distributions of film cooling effectiveness on the suction surface and pressure surface at the same blowing ratio(BR) are different due to local surface curvature and pressure gradient. The aerodynamic loss features for film holes on the pressure surface are also different from film holes on the suction surface.展开更多
Experimental investigations were performed on the overall cooling effectiveness η of a flat effusion wall over a wide range of blowing ratio(M=0.47~5.27).The effusion wall had a staggered multi-hole pattern typical ...Experimental investigations were performed on the overall cooling effectiveness η of a flat effusion wall over a wide range of blowing ratio(M=0.47~5.27).The effusion wall had a staggered multi-hole pattern typical of gas turbine combustor application,with a ratio of hole pitch to row spacing P/S=1∶2,a porosity PS/d2=72,and an inclination angle α=30°.The current paper documented distribution of the overall cooling effectiveness on the wall surface,based on infrared imaging of the 2-D surface temperature field.Experimental results indicate:(1) The overall η increases along with the streamwise distance for the wide range of M due to the superposition effect of the multi-row film cooling.(2) The overall η substantially benefits from the multi-hole inside convective cooling.The hole convective cooling not only complements the weakest film protection at initial rows but also helps mitigate the temperature gradient.(3) The overall η increases asymptotically with increasing M,unlike adiabatic η mostly published in the past,which decreased after M reached a specific level.The current work showcased the end cooling outcome jointly driven by the filming cooling mechanism and the hole inside convective cooling mechanism.展开更多
As one of the most important developments in air cooling technology for hot parts of the aero-engine, film cool- ing technology has been widely used. Film cooling hole structure exists mainly in areas that have high t...As one of the most important developments in air cooling technology for hot parts of the aero-engine, film cool- ing technology has been widely used. Film cooling hole structure exists mainly in areas that have high temperature, uneven cooling effectiveness issues when in actual use. The first stage turbine vanes of the aero-engine consume the largest portion of cooling air, thereby the research on reducing the amount of cooling air has the greatest potential. A new stopped slot film cooling vane with a high cooling effectiveness and a high cooling uniformity was researched initially. Through numerical methods, the affecting factors of the cooling effectiveness of a vane with the stepped slot film cooling structure were researched. This paper focuses on the cooling effectiveness and the pressure loss in different blowing ratio conditions, then the most reasonable and scientific structure parameter can be obtained by analyzing the results. The results show that 1.0 mm is the optimum slot width and 10.0 is the most reasonable blowing ratio. Under this condition, the vane achieved the best cooling result and the highest cooling effectiveness, and also retained a low pressure loss.展开更多
Different fragments of a hot-rolled and homogenized Cu–Zn–Al shape memory alloy(SMA) were subjected to thermal cycling by means of a differential scanning calorimetric(DSC) device. During thermal cycling, heatin...Different fragments of a hot-rolled and homogenized Cu–Zn–Al shape memory alloy(SMA) were subjected to thermal cycling by means of a differential scanning calorimetric(DSC) device. During thermal cycling, heating was performed at the same constant rate of increasing temperature while cooling was carried out at different rates of decreasing temperature. For each cooling rate, the temperature decreased in the same thermal interval. During each cooling stage, an exothermic peak(maximum) was observed on the DSC thermogram. This peak was associated with forward martensitic transformation. The DSC thermograms were analyzed with PROTEUS software: the critical martensitic transformation start(Ms) and finish(Mf) temperatures were determined by means of integral and tangent methods, and the dissipated heat was evaluated by the area between the corresponding maximum plot and a sigmoid baseline. The effects of the increase in cooling rate, assessed from a calorimetric viewpoint, consisted in the augmentation of the exothermic peak and the delay of direct martensitic transformation. The latter had the tendency to move to lower critical transformation temperatures. The martensite plates changed in morphology by becoming more oriented and by an augmenting in surface relief, which corresponded with the increase in cooling rate as observed by scanning electron microscopy(SEM) and atomic force microscopy(AFM).展开更多
This article presents the data about heat transfer coefficient ratios, film cooling effectiveness and heat loads for the injection through cylindrical holes, 3-in-1 holes and fanned holes in order to characterize the ...This article presents the data about heat transfer coefficient ratios, film cooling effectiveness and heat loads for the injection through cylindrical holes, 3-in-1 holes and fanned holes in order to characterize the film cooling performance downstream of a row of holes with 45° inclination and 3 hole spacing apart. The trip wire is placed upstream at a distance of 10 times diameter of the cooling hole from the hole center to keep mainstream fully turbulent. Both inlet and outlet of 3-in-1 holes have a 15° lateral expansion. The outlet of fanned holes has a lateral expansion. CO2 is applied for secondary injection to obtain a density ratio of 1.5. Momentum flux ratio varies from 1 to 4. The results indicate that the increased momentum flux ratio significantly increases heat transfer coefficient and slightly improve film cooling effectiveness for the injection through cylindrical holes. A weak dependence of heat transfer coefficient and film cooling effectiveness, respectively, on momentum flux ratio has been identified for the injection through 3-in-1 holes. The in- crease of the momentum flux ratio decreases heat transfer coefficient and significantly increases film cooling effectiveness for the injection through fanned holes. In terms of the film cooling performance, the fanned holes are the best while the cylindrical holes are the worst among the three hole shapes under study.展开更多
The characteristics of the urban heat island effect and the climate change in Shanghai and its possible mechanism are analyzed based on monthly meteorological data from 1961 to 1997 at 16 stations in Shanghai and its ...The characteristics of the urban heat island effect and the climate change in Shanghai and its possible mechanism are analyzed based on monthly meteorological data from 1961 to 1997 at 16 stations in Shanghai and its adjacent areas. The results indicate that Shanghai City has the characteristics of a heat island of air temperature and maximum and minimum air temperature, a cold island of surface soil temperature, a weak rainy island of precipitation, and a turbid island of minimum visibility and aerosols, with centers at or near Longhua station (the urban station of Shanghai). Besides theses, the characteristics of a cloudy island and sunshine duration island are also obvious, but their centers are located in the southern part of the urban area and in the southern suburbs. A linear trend analysis suggests that all of the above urban effects intensified from 1961 to 1997. So far as the heat island effect is concerned, the heat island index (difference of annual temperature between Longhua and Songjiang stations) strengthens (weakens) as the economic development increases (decreases). The authors suggest that the heating increase caused by increasing energy consumption due to economic development is a main factor in controlling the climate change of Shanghai besides natural factors. On the other hand, increasing pollution aerosols contribute to the enhancement of the turbid island and cooling. On the whole, the heating effect caused by increasing energy consumption is stronger than the cooling effect caused by the turbid island and pollution aerosols.展开更多
The experimental study focuses on the heat flux on a double cone blunt body in the presence of tangential-slot super- sonic injection into hypersonic flow. The tests are conducted in a contoured axisymmetric nozzle wi...The experimental study focuses on the heat flux on a double cone blunt body in the presence of tangential-slot super- sonic injection into hypersonic flow. The tests are conducted in a contoured axisymmetric nozzle with Mach numbers of 7.3 and 8.1, and the total temperature is about 900 K. The injection Mach number is 3.2, and total temperature is 300 K. A constant voltage circuit is developed to supply the temperature detectors instead of the normally used constant current circuit. The schlieren photographs are presented additionally to visualize the flow and help analyze the pressure relationship between the cooling flow and the main flow. The dependence of the film-cooling effectiveness on flow parameters, i.e. the blow ratio, the convective Mach number, and the attack angle, is determined. A semi-empirical formula is tested by the present data, and is improved for a better correlation.展开更多
基金supported by the National Natural Science Foundation of China(41030638,31170673 and 41275169)the Provincial Natural Science Foundation of Guangdong,China(S2012020010933)
文摘Agriculture could suffer the water stress induced by climate change. Because climate warming affects global hydrological cycles, it is vital to explore the effect of tree transpiration, as an important component of terrestrial evapotranspiration, on the environment. Thermal dissipation probes were used to measure xylem sap flux density of a Schima superba plantation in the urban area of Guangzhou City, South China. Stand transpiration was calculated by mean sap flux density times total sapwood area. The occurrence of the maximum sap flux density on the daily scale was later in wet season than in dry season. The peak of daily sap flux density was the highest of 59 g m-2 s^-1 in July and August, and the lowest of 28 g m-2 s-1 in December. In the two periods (November 2007-October 2008 and November 2008-October 2009), the stand transpiration reached 263.2 and 291.6 ram, respectively. During our study period, stand transpiration in wet season (from April to September) could account for about 58.5 and 53.8% of the annual transpiration, respectively. Heat energy absorbed by tree transpiration averaged 1.4×10s and 1.6×10s kJ per month in this Schima superba plantation with the area of 2 885 m2, and temperature was reduced by 4.3 and 4.7℃ s^-1 per 10 m3 air.
基金Supported by the National Natural Science Foundation of China(51276090)
文摘Experimental investigation is performed to investigate the cooling characteristics in the front zone of effusion configuration. Effects of blowing ratio,multi-hole arrangement mode,hole-to-hole pitch and jet orientation angle on the adiabatic film cooling effectiveness are concentrated on. The results show that the film layer displays an obvious"developing"feature in the front zone of effusion cooling scheme,for either the staggered or inline multi-hole arrangement. The varying gradient of the laterally-averaged adiabatic cooling effectiveness along the streamwise direction is greater for the staggered arrangement than that for the inline arrangement. The holes array arranged in staggered mode with small hole-tohole pitches is in favor of obtaining developed film coverage layer rapidly.
基金supported by The Outstanding Youth Foundation Project, National Natural Science Foundation of China (Grant No. 40625004) the grant of the Western Project Program of the Chinese Academy of Sciences (No. KZCX2-XB2-10)
文摘Based on the analysis and comparison of soil temperature, thermal regime and permafrost table under the experimental embankment of crushed rock structures in Beiluhe, results show that crushed rock structures provide an extensive cooling effect, which produces a rising permafrost table and decreasing soil temperatures. The rise of the permafrost table under the embankment ranges from an increase of 1.08 m to 1.67 m, with an average of 1.27 m from 2004 to 2007. Mean annual soil temperatures under the crushed rock layer embankment decreased significantly from 2005 to 2007, with average decreases of ?1.03 °C at the depth of 0.5 m, ?1.14 °C at the depth of 1.5 m, and ?0.5 °C at the depth of 5 m. During this period, mean annual soil temperatures under the crushed rock cover embankment showed a slight decrease at shallow depths, with an average decrease of ?0.2 °C at the depth of 0.5 m and 1.5 m, but a slight rise at the depth of 5 m. After the crushed rock structures were closed or crammed with sand, the cooling effect of the crushed rock layer embankment was greatly reduced and that of the crushed rock cover embankment was just slightly reduced.
基金supported by National Natural Science Foundation of China (Grant No.40730736 and No.40601023)the National Hi-Tech Research and Development Plan (2008AA11Z103)the Western Project Program of the Chinese Academy of Sciences (No.KZCX2-XB2-10)
文摘With the completion of the Qinghai-Tibetan Railway,economic development of related areas has been greatly accelerated.This,in return,calls for building or upgrading more roadways,especially high-grade roadways.In cold regions,the thawing of permafrost can induce settlement damage of and even failure to railway (or roadway) embankments.Thermosyphons (self-powered refrigera-tion devices that are used to help keep the permafrost cool) have proved effective in mitigating thaw settlement by maintaining the thermal stability of the embankments.However,for high-grade roadway embankments of great width,stabilizing or cooling ef-fects of traditional geotechnological measures may be limited.To enhance the cooling effect of thermosyphons,an L-shaped thermosyphon was designed.A laboratory test was carried out to study the combined cooling effect of the L-shaped thermosyphon and thermal insulation applying to roadbed construction.The angle between the evaporator and condenser sections of the L-shaped thermosyphon is 134 degrees,and the L-shaped thermosyphon was inserted into the soil at an angle of 5 degrees with the road surface.The tested results show that the L-shaped thermosyphon is effective in removing heat from a roadway in winter.When the ambient air temperature is lower than the soil temperature,the thermosyphon is active and extracts the heat in the soil around it.When the ambient air temperature is higher than the soil temperature,the thermosyphon is inactive,and no heat is in-jected into the soil through the L-shaped thermosyphon.Compared to embankments with straight thermosyphons,the inner parts of the embankments with L-shaped thermosyphons were significantly cooled.It is hoped that the present study would be useful to the application of L-shaped thermosyphons in the construction of high-grade roadways in cold regions.
基金supported by the National Natural Science Foundation of China[grant number 41375069]National Basic Research Program of China[grant number 2012CB957804]Young Talent Programming of China Meteorological Administration
文摘It is claimed that open spaces in cities, such as parks, have an urban cooling effect. However, the relationship between urban parks and adjacent districts is still not explicit. In order to clarify the interaction between urban parks and their urban surroundings, this paper takes the Temple of Heaven Park (THP) as an example of a park station and focuses on analyzing the differences with a nearby urban station.THP is located in the center of Beijing, and the nearest urban station is Tian An Men. It is interesting that the cooling effect of THP reaches a peak and remains stable when its city background urban heat island (UHI) varies within a given range, but becomes unstable when the UHI goes beyond the range. This is called an enhanced cooling effect in this paper. As a result, the UHi intensities (UHIIs) are calculated in order to comprehend the role of the park cooling effect in the urban heating characteristics of Beijing. By comparison with five other park-district pairs, this paper attempts to identify the causes of the enhanced cooling effect. It is found that six park-district pairs consistently demonstrate a persistently stronger cooling rate during the night, and that the water coverage might be a key factor in enhancing the park cooling effect. Based on further investigation of the influence of surrounding UHIs on the park cooling effect, it is found that the UHII differences in park-district pairs show quasi-linear changes within a given range as the UHli of the surrounding district increases.
基金the financial support of the National Natural Science Foundation of China (No. 41121061)the National Basic Research Program (973) of China (Nos. 2012CB026101 and 2011CB013505)+1 种基金the Western Project Program of the Chinese Academy of Sciences (No. KZCX2-XB3-19)the Open Fund of State Key Laboratory of Frozen Soil Engineering (No. SKLFSE201209)
文摘One of the main construction problems in permafrost regions is protecting permafrost thermal stability. Although ventilating ducts and crushed-rock layers were successfully used in railway embankment construction, their effects might not meet large-width expressway requirements. The convection-intensifying composite embankment composed of perforated ventilation ducts and crushed-rock layers was numerically studied to investigate its cooling effects. Adopting a numerical model, the temperature fields for two kinds of composite embankment with and without air doors were analyzed considering air flow and heat transfer characteristics in porous media. The results show that wind velocity in the crushed-rock zone is intensified by the perforated ventilation duct. The underlying permafrost temperature obviously decreases, and the 0 °C isotherm position rises significantly due to composite embankment. The composite embankment with air doors is more effective than that without air doors. Therefore, the new convection-intensifying composite embankment is potentially a highly efficient cooling measure for construction in permafrost regions.
文摘Film cooling is introduction of a secondary fluid (coolant or injected fluid) at one or more discrete locations along a surface exposed to a high temperature environment to protect that surface not only in the immediate region of injection but also downstream region. This paper numerically investigated the film cooling effectiveness on two types of hole geometries which are cut-shaped hole and antivortex hole. The 3D computational geometries are modeled with a single 30 deg angled hole on a flat surface. The different blowing ratios of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5,5 and k-Epsilon turbulence model are used in this study. A two dimensional distribution of film cooling effectiveness in the downstream region of the cooling hole is performed. A comparison of spanwise averaged effectiveness is also performed in the field starts from center point of hole to X/D=-30.
基金This research was supported by the National Science Fund for Distinguished Young Scholars of China(Grant No.40225001)the Foundation of"Excellent Hundred Talent Plan"of the Chinese Academy of Sciences(to Dr.Y.M.Lai)+1 种基金the CAS Special Fund for the authot of the"National Excellent PhD Dissertation"(to Dr.Y.M.Lai)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KZCX1-SW-04).
文摘The heat convection of fluid inside the ballast layer and ripped-rock layer,which are re-garded as porous media in railway embankment,is a process of heat and mass transfer.At present,the ripped-rock embankment,as a new type of embankment structure,has widely been used in the construction of Qinghai-Tibetan railway.However,because its ripped-rock layer is almost open in two bilateral boundaries and closed at top and bottom,and air can flow into/out of the ballast layer and ripped-rock layer,the convection and transfer heat patterns are very complicated in the embankment.Therefore,based on the temperature and geology conditions of the Qinghai-Tibetan Plateau,a nu-merical approach of the unsteady two-dimensional continuity,momentum(non-Darcy flow)and en-ergy equations of heat convection for incompressible fluid in porous media is provided to analyze the velocity and temperature characteristics of the ripped-rock embankment with different embankment heights under open boundary condition for the coming 50 years in this paper.The calculated results indicate that,due to the influence of the outside wind,the convective heat transfer mainly relies on the forced convection in the open ripped-rock embankment.Even if the air temperature will be warmed up by 2.6℃in the coming 50 years,it still has a better cooling effect on the underlying soils and a low temperature frozen-soil core is formed in the permafrost below it if the embankment is constructed in the regions whose present mean annual air temperature is?4.0℃.Furthermore,the cooling effect of high ripped-rock embankment is better than that of low embankment.This is because the wider bot-tom of high embankment has a more influence dimension on the underlying frozen soil.However,cardinal winds on the Qinghai-Tibetan Plateau disturb its convection pattern,so that an asymmetric temperature distribution occurs under high embankment and it is possible to induce a transverse un-even deformation of embankment,but no similar situation occurs under low embankment.This asymmetric temperature field problem should be considered when ripped-rock embankment is de-signed and constructed.
文摘With the sea surface observations from ICOADS for the years 1960-2002, the conditions of coohng, evaporauon anu water vapol transportation are analyzed and compared for the formation of seasonal sea fog in April-July in the Huanghai Sea. It is found that sea surface cooling is always existent during the fog seasons while sea surface evaporation only appears in April-June in the Huanghai Sea. Local evaporation alone is not sufficient to form fogs though it may lead to light ones. Water vapor transported from the low-latitudes accomplished by specific synoptic systems is the most important condition for sea fog formation. In general, the moistening effect is more important than the cooling one.
基金financial support for this project from the National Natural Science Foundation of China(No.U1508212)National Science and Technology Major Projects(Nos.2017-Ⅲ-0011-0025 and 2017-Ⅲ0011-0037)。
文摘A numerical investigation and experimental validation is performed to address deeper insights into the combined effect of shaped holes and Sand-Dune-shaped upstream Ramp(SDR)on enhancing the film cooling effectiveness,under a wide blowing ratio range(M=0.25–1.5).Three kinds of holes(Cylindrical Hole(CH),Fan-Shaped Hole(FSH),and Crater-Shaped Hole(CSH))are taken into consideration.The SDR shows an inherent affecting mechanism on the mutual interaction of jet-in-crossflow.It aggravates the lateral spreading of cooling jet and thus improves the film cooling uniformity significantly,regardless of film-hole shape and blowing ratio.When the blowing ratio is beyond 1.0,the combined effect of shaped holes and SDR on improving film cooling effectiveness behaves more significantly.It is suggested that FSH-SDR is a most favorable film cooling scheme.For FSH-SDR case,the spatially-averaged film cooling effectiveness is increased monotonously with the increase of blowing ratio,among the present bowing ratio range.
文摘Three-dimensional numerical computations are conducted to investigate the effects of the blowing ratio and corrugation geometry on the adiabatic film cooling effectiveness as well as the heat transfer coefficient over a transverse corrugated surface.It is noticeable that the adiabatic wall temperature on the wavy valley of the transverse corrugated surface is relatively lower than that on the wavy peak.Surface corrugation has a relatively obvious influence on the laterallyaveraged adiabatic film cooling effectiveness in the region where the effusion film layer is developed,but has little influence in the front region.Compared to a flat surface,the transverse corrugated surface produces a smaller adiabatic film cooling effectiveness and a higher heat transfer coefficient ratio.The effusion cooling difference between the flat and corrugated surfaces behaves more obviously under a small aspect ratio of the wavy corrugation.
基金supported by the National Natural Science Foundation of China(No.51936008)the Shaanxi Science Foundation for Distinguished Young Scholars(No.2021JC-11)+1 种基金the National Science and Technology Major Project(No.2017-III-0003-0027)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX2021074)。
文摘The film cooling effectiveness of two turbine blades at different turbulence intensities(0.62%and 16.00%)and mass flux ratios(2.91%,5.82%,8.73%and 11.63%)is studied by using the Pressure-Sensitive Paint(PSP)measurement technique.There are a baseline and an improved turbine blade in current work,and their film cooling hole position distribution is the same.But the hole shape on suction surface and pressure surface is changed from cylindrical hole(baseline)to laid-back fan-shaped hole(improved blade).Both blades have 5 rows of cylindrical holes at the leading edge and 4 rows of cooling-holes on the suction surface and the pressure surface.The experimental results show that the film cooling effectiveness of the improved blade is much better than the baseline.The increase in turbulence intensity will reduce the cooling effectiveness on the surface of turbine blade,but the effect of turbulence intensity becomes weaker with an increase in the mass flux ratio.Compared with the multiple rows of cylindrical holes,the cooling effectiveness of shaped holes is more influenced by the turbulence intensity at low mass flux ratio.
文摘The data obtained through the roadbed surface thermal regime experiment (ROBSTREX), which was carried out at Beiluhe test section of Qinghai-Tibetan Railway from October to December in 2002, were used to estimate the cooling effect of ballast revetment on the roadbed. The results show that both riprap rock ballast revetment and crushed stone ballast revetment can reduce the temperature of the roadbed. But the cooling effect of riprap rock ballast revetment is better than that of crushed stone ballast revetment when the temperature of roadbed is higher. The cooling effect of crushed stone ballast revetment is better than that of riprap rock ballast revetment when the temperature of the roadbed is lower, especially at deeper roadbed layers. In the frozen season, the heat release from the roadbed also shows that the cooling effect of ballast revetment on the roadbed is obvious, and the cooling effect of crushed stone-ballast revetment on the roadbed is much evident than that of riprap rock ballast revetment.
基金financially supported by the National Natural Science Foundation of China through Grant No.51336007
文摘This paper describes the numerical study on film cooling effectiveness and aerodynamic loss due to coolant and main stream mixing for a turbine guide vane. The effects of blowing ratio, mainstream Mach number, surface curvature on the cooling effectiveness and mixing loss were studied and discussed. The numerical results show that the distributions of film cooling effectiveness on the suction surface and pressure surface at the same blowing ratio(BR) are different due to local surface curvature and pressure gradient. The aerodynamic loss features for film holes on the pressure surface are also different from film holes on the suction surface.
文摘Experimental investigations were performed on the overall cooling effectiveness η of a flat effusion wall over a wide range of blowing ratio(M=0.47~5.27).The effusion wall had a staggered multi-hole pattern typical of gas turbine combustor application,with a ratio of hole pitch to row spacing P/S=1∶2,a porosity PS/d2=72,and an inclination angle α=30°.The current paper documented distribution of the overall cooling effectiveness on the wall surface,based on infrared imaging of the 2-D surface temperature field.Experimental results indicate:(1) The overall η increases along with the streamwise distance for the wide range of M due to the superposition effect of the multi-row film cooling.(2) The overall η substantially benefits from the multi-hole inside convective cooling.The hole convective cooling not only complements the weakest film protection at initial rows but also helps mitigate the temperature gradient.(3) The overall η increases asymptotically with increasing M,unlike adiabatic η mostly published in the past,which decreased after M reached a specific level.The current work showcased the end cooling outcome jointly driven by the filming cooling mechanism and the hole inside convective cooling mechanism.
基金supported by funds form National natural science foundation of China(Grant No.50976008)
文摘As one of the most important developments in air cooling technology for hot parts of the aero-engine, film cool- ing technology has been widely used. Film cooling hole structure exists mainly in areas that have high temperature, uneven cooling effectiveness issues when in actual use. The first stage turbine vanes of the aero-engine consume the largest portion of cooling air, thereby the research on reducing the amount of cooling air has the greatest potential. A new stopped slot film cooling vane with a high cooling effectiveness and a high cooling uniformity was researched initially. Through numerical methods, the affecting factors of the cooling effectiveness of a vane with the stepped slot film cooling structure were researched. This paper focuses on the cooling effectiveness and the pressure loss in different blowing ratio conditions, then the most reasonable and scientific structure parameter can be obtained by analyzing the results. The results show that 1.0 mm is the optimum slot width and 10.0 is the most reasonable blowing ratio. Under this condition, the vane achieved the best cooling result and the highest cooling effectiveness, and also retained a low pressure loss.
基金supported by the project PN-II-ID-PCE-2012-4-0033,contract 13/2013
文摘Different fragments of a hot-rolled and homogenized Cu–Zn–Al shape memory alloy(SMA) were subjected to thermal cycling by means of a differential scanning calorimetric(DSC) device. During thermal cycling, heating was performed at the same constant rate of increasing temperature while cooling was carried out at different rates of decreasing temperature. For each cooling rate, the temperature decreased in the same thermal interval. During each cooling stage, an exothermic peak(maximum) was observed on the DSC thermogram. This peak was associated with forward martensitic transformation. The DSC thermograms were analyzed with PROTEUS software: the critical martensitic transformation start(Ms) and finish(Mf) temperatures were determined by means of integral and tangent methods, and the dissipated heat was evaluated by the area between the corresponding maximum plot and a sigmoid baseline. The effects of the increase in cooling rate, assessed from a calorimetric viewpoint, consisted in the augmentation of the exothermic peak and the delay of direct martensitic transformation. The latter had the tendency to move to lower critical transformation temperatures. The martensite plates changed in morphology by becoming more oriented and by an augmenting in surface relief, which corresponded with the increase in cooling rate as observed by scanning electron microscopy(SEM) and atomic force microscopy(AFM).
文摘This article presents the data about heat transfer coefficient ratios, film cooling effectiveness and heat loads for the injection through cylindrical holes, 3-in-1 holes and fanned holes in order to characterize the film cooling performance downstream of a row of holes with 45° inclination and 3 hole spacing apart. The trip wire is placed upstream at a distance of 10 times diameter of the cooling hole from the hole center to keep mainstream fully turbulent. Both inlet and outlet of 3-in-1 holes have a 15° lateral expansion. The outlet of fanned holes has a lateral expansion. CO2 is applied for secondary injection to obtain a density ratio of 1.5. Momentum flux ratio varies from 1 to 4. The results indicate that the increased momentum flux ratio significantly increases heat transfer coefficient and slightly improve film cooling effectiveness for the injection through cylindrical holes. A weak dependence of heat transfer coefficient and film cooling effectiveness, respectively, on momentum flux ratio has been identified for the injection through 3-in-1 holes. The in- crease of the momentum flux ratio decreases heat transfer coefficient and significantly increases film cooling effectiveness for the injection through fanned holes. In terms of the film cooling performance, the fanned holes are the best while the cylindrical holes are the worst among the three hole shapes under study.
基金supported the National Natural Science Foundation of China under Grant No.49899270.
文摘The characteristics of the urban heat island effect and the climate change in Shanghai and its possible mechanism are analyzed based on monthly meteorological data from 1961 to 1997 at 16 stations in Shanghai and its adjacent areas. The results indicate that Shanghai City has the characteristics of a heat island of air temperature and maximum and minimum air temperature, a cold island of surface soil temperature, a weak rainy island of precipitation, and a turbid island of minimum visibility and aerosols, with centers at or near Longhua station (the urban station of Shanghai). Besides theses, the characteristics of a cloudy island and sunshine duration island are also obvious, but their centers are located in the southern part of the urban area and in the southern suburbs. A linear trend analysis suggests that all of the above urban effects intensified from 1961 to 1997. So far as the heat island effect is concerned, the heat island index (difference of annual temperature between Longhua and Songjiang stations) strengthens (weakens) as the economic development increases (decreases). The authors suggest that the heating increase caused by increasing energy consumption due to economic development is a main factor in controlling the climate change of Shanghai besides natural factors. On the other hand, increasing pollution aerosols contribute to the enhancement of the turbid island and cooling. On the whole, the heating effect caused by increasing energy consumption is stronger than the cooling effect caused by the turbid island and pollution aerosols.
基金Project supported by the National Natural Science Foundation of China(Grant No.11172326)the Scientific Research Program of National University of Defense Technology,China(Grant No.0100010112001)
文摘The experimental study focuses on the heat flux on a double cone blunt body in the presence of tangential-slot super- sonic injection into hypersonic flow. The tests are conducted in a contoured axisymmetric nozzle with Mach numbers of 7.3 and 8.1, and the total temperature is about 900 K. The injection Mach number is 3.2, and total temperature is 300 K. A constant voltage circuit is developed to supply the temperature detectors instead of the normally used constant current circuit. The schlieren photographs are presented additionally to visualize the flow and help analyze the pressure relationship between the cooling flow and the main flow. The dependence of the film-cooling effectiveness on flow parameters, i.e. the blow ratio, the convective Mach number, and the attack angle, is determined. A semi-empirical formula is tested by the present data, and is improved for a better correlation.