An engineering approach for the calculation of the specific heat energy needed for melting of the ice, which is created from the freezing of hygroscopically bounded water in the wood, qbw, has been suggested. The appr...An engineering approach for the calculation of the specific heat energy needed for melting of the ice, which is created from the freezing of hygroscopically bounded water in the wood, qbw, has been suggested. The approach, together with the equation that presents it, includes mathematical descriptions of the density of frozen wood in the hygroscopic diapason, Pw, and of the specific heat capacity of the ice formed from the bounded water in the wood, cbw for the calculation of Pw, cbw and qbw according to the suggested approach a software program has been prepared in the calculation environment of Visual Fortran. Using the program computations have been carried out for the determination ofpw, cbw and qbw, of oak, pine, beech and poplar frozen wood with initial temperature in the range from -20℃ to -2℃, at which the thawing of the ice from the bounded water is completed, and with moisture content in the hygroscopic range during wood defrosting. Based on the obtained results, a very simple and easy for use equation for the calculation of qbw depending only on the wood moisture content and on the content of non-frozen water in the wood at given initial wood temperature has been suggested.展开更多
On the basis of information from the project ＂Land-surface Processes and their Experimental Study on the Chinese Loess Plateau＂, we analyzed differences in land-surface water and heat processes during the main dry a...On the basis of information from the project ＂Land-surface Processes and their Experimental Study on the Chinese Loess Plateau＂, we analyzed differences in land-surface water and heat processes during the main dry and wet periods of the semiarid grassland growing season in Yuzhong County, as well as the influences of these environmental factors. Studies have shown that there are significant differences in changes of land-surface temperature and humidity during dry and wet periods. Daily average normalized temperature has an overall vertical distribution of ＂forward tilting＂ and ＂backward tilting＂ during dry and wet periods, respectively. During the dry period, shallow soil above 20-cm depth is the active temperature layer. The heat transfer rate in soil is obviously different during dry and wet periods. During the dry period, the ratio of sensible heat flux to net radiation （H/Rn） and the value of latent heat flux to net radiation （LE/Rn） have a linear relationship with 5-cm soil temperature; during the wet period, these have a nonlinear relationship with 5-cm soil temperature, and soil temperature of 16℃ is the critical temperature for changes in the land-surface water and heat exchange trend on a daily scale. During the dry period, H/Rn and LE/Rn have a linear relationship with soil water content. During the wet period, these have a nonlinear relationship with 5-cm soil water content, and 0.21 m^3 m^-3 is the critical point for changes in the land-surface water and heat exchange trend at daily scale. During the dry period, for vapor pressure deficit less than 0.7 kPa, H/Rn rises with increased vapor pressure deficit, whereas LEIRn decreases with that increase. When that deficit is greater than 0.7 kPa, both H/Rn and LE/Rn tend to be constant. During the wet period, H/Rn increases with the vapor pressure deficit, whereas LE/Rn decreases. The above characteristics directly reflect the effect of differences in land-surface environmental factors during land-surface water and heat exchange processes, and indirectly reflect the influences of cloud precipitation processes on those processes.展开更多
Over 100 human thermal indices have been developed to predict the combined thermal impact on the body.In principle,these indices based on energy thermal budget equations should not only be the most complex but also be...Over 100 human thermal indices have been developed to predict the combined thermal impact on the body.In principle,these indices based on energy thermal budget equations should not only be the most complex but also be the most accurate.However,the simple indices based on algebraic or statistical models[e.g.,the wet-bulb globe temperature(WBGT)]continue to be the most popular.A new heat stress index,the enthalpy dry-bulb temperature(EnD)for indoor environments is developed and validated in this study.The EnD index is unique in that it uses the air specific enthalpy,not the wet-bulb temperature,to measure the latent heat transfer from the skin to the surrounding environment.Theoretically,the EnD index can be treated as the equivalent temperature based on the convective heat transfer coefficient h_(c).Comparison is made between the EnD index and the widely used WBGT index based on the experimental data taken from three independent studies available in the scientific literature.The results show that the EnD index can reduce the overestimation of the dry-bulb air temperature and thus reduce heat stress in most cases,especially for hot and humid environments.It can be concluded that the EnD index has the potential to replace the WBGT index as the standard heat stress index in the future.展开更多
Freezing is the most common method used to preserve and minimize loss in quality of catfish during storage. Since freezing is a heat transfer process, the design and selection of freezing equipment require knowledge o...Freezing is the most common method used to preserve and minimize loss in quality of catfish during storage. Since freezing is a heat transfer process, the design and selection of freezing equipment require knowledge of thermophysical properties such as freezing temperature, enthalpy of freezing, unfreezable water and specific heat. Channel catfish thermophysical properties at freezing temperature were determined using differential scanning calorimetry. Using the combination of Raoult＇s law and Classius-Clapeyron equations, the amount of unfreezable （bound water） was estimated to be 0.129 g H20 g^-1 During freezing （or melting）, the specific heat increased from about 1.5 J g^-1 ℃^-1 to about 30.6 J g^-1 ℃^-1 It was found that freezing of catfish occur over a wide temperature range with the peak and incident freezing temperatures occurring at temperatures of-1.88 ℃ and -6.10 ℃, respectively. About 250 J g^-1 of heat have to be removed from catfish when it is to be frozen to -40 ℃. The implication is that any system that will be designed to freeze catfish must be able to remove 250 J g^-1 of heat.展开更多
Based on a one-dimensional eddy diffusion model,a model to study the water mass and energy exchange between the water body(such as lake and wetland) and the atmosphere is developed,which takes the phase change process...Based on a one-dimensional eddy diffusion model,a model to study the water mass and energy exchange between the water body(such as lake and wetland) and the atmosphere is developed,which takes the phase change process due to the seasonal melting and freezing of water and the convection mixing process of energy caused by temperature stratification into consideration. The model uses enthalpy instead of temperature as predictive variable,which will help to deal with the phase change process and to design an efficient numerical scheme for obtaining the solution more easily. The performance of the model and the rationality of taking convection mixing into the consideration are validated by using observed data of Kinneret Lake in Israel and Lower Two Medicine Lake in Montana State in America. The comparison of model results with observed data indicates that the model presented here is capable of describing the physical process of water mass and energy between the water body(lake and wetland) and atmosphere. Comparison of the result from wetland with shallow and deep lakes under the same forcing conditions shows that the evaporation from wetland is much greater than that from lakes,which accords with the real observation fact and physical mechanism.展开更多
To ensure the long-term service performance of infrastructure such as railways,highways,airports and oil pipelines built on permafrost slope wetland sites,it is imperative to systematically uncover the long-term heat-...To ensure the long-term service performance of infrastructure such as railways,highways,airports and oil pipelines built on permafrost slope wetland sites,it is imperative to systematically uncover the long-term heat-water changes of soil in slope wetlands environment under climate warming.More specifically,considering valuable field data from 2001 to 2019,the long-term heat and water changes in active layers of the slope wetland site along the Qinghai-Xizang Railway(QXR)are illustrated,the effect of thermosyphon measures in protecting the permafrost environment is evaluated,and the influences of climate warming and hydrological effects on the stability of slope wetland embankments are systematically discussed.The permafrost at the slope wetland site is rapidly degrading,demonstrating a reduction in active layer thickness of>3.7 cm per year and a permafrost temperature warming of>0.006℃ per year.The thermosiphon embankment developed by QXR has a specific cooling period;thus,to mitigate the long-term impacts of climate warming on the thermal stability of permafrost foundation,it is essential to implement strengthening measures for the thermosiphon embankment,such as adding a crushed-rock layer or sunshade board on the slope of thermosiphon embankment to creating a composite cooling embankment.Short-term seasonal groundwater seepage intensifies frost damage to the slope wetland embankment,while long-term seasonal supra-permafrost water and groundwater seepage exacerbates uneven transverse deformation of slope wetland embankment.Long-term climate warming and slope effects have altered the surface water and groundwater hydrological processes of slope wetlands,potentially leading to an increased occurrence of slope embankment instability.These results are crucial for improving our understanding of heat and water variation processes in the active layer of slope wetland sites located in permafrost regions and ensuring long-term service safety for the QXR.展开更多
文摘An engineering approach for the calculation of the specific heat energy needed for melting of the ice, which is created from the freezing of hygroscopically bounded water in the wood, qbw, has been suggested. The approach, together with the equation that presents it, includes mathematical descriptions of the density of frozen wood in the hygroscopic diapason, Pw, and of the specific heat capacity of the ice formed from the bounded water in the wood, cbw for the calculation of Pw, cbw and qbw according to the suggested approach a software program has been prepared in the calculation environment of Visual Fortran. Using the program computations have been carried out for the determination ofpw, cbw and qbw, of oak, pine, beech and poplar frozen wood with initial temperature in the range from -20℃ to -2℃, at which the thawing of the ice from the bounded water is completed, and with moisture content in the hygroscopic range during wood defrosting. Based on the obtained results, a very simple and easy for use equation for the calculation of qbw depending only on the wood moisture content and on the content of non-frozen water in the wood at given initial wood temperature has been suggested.
基金supported by the National Basic Research Program of China(Grant No.2013CB430206,2012CB955304)National Natural Science Foundation of China(Grant Nos.41075008,40830957,41275118)+2 种基金China Postdoctoral Science Special Foundation(Grant No.2013T60901)China Postdoctoral Science Foundation(Grant No.20110490854)the Ten Talents Program of Gansu Meteorology Bureau
文摘On the basis of information from the project ＂Land-surface Processes and their Experimental Study on the Chinese Loess Plateau＂, we analyzed differences in land-surface water and heat processes during the main dry and wet periods of the semiarid grassland growing season in Yuzhong County, as well as the influences of these environmental factors. Studies have shown that there are significant differences in changes of land-surface temperature and humidity during dry and wet periods. Daily average normalized temperature has an overall vertical distribution of ＂forward tilting＂ and ＂backward tilting＂ during dry and wet periods, respectively. During the dry period, shallow soil above 20-cm depth is the active temperature layer. The heat transfer rate in soil is obviously different during dry and wet periods. During the dry period, the ratio of sensible heat flux to net radiation （H/Rn） and the value of latent heat flux to net radiation （LE/Rn） have a linear relationship with 5-cm soil temperature; during the wet period, these have a nonlinear relationship with 5-cm soil temperature, and soil temperature of 16℃ is the critical temperature for changes in the land-surface water and heat exchange trend on a daily scale. During the dry period, H/Rn and LE/Rn have a linear relationship with soil water content. During the wet period, these have a nonlinear relationship with 5-cm soil water content, and 0.21 m^3 m^-3 is the critical point for changes in the land-surface water and heat exchange trend at daily scale. During the dry period, for vapor pressure deficit less than 0.7 kPa, H/Rn rises with increased vapor pressure deficit, whereas LEIRn decreases with that increase. When that deficit is greater than 0.7 kPa, both H/Rn and LE/Rn tend to be constant. During the wet period, H/Rn increases with the vapor pressure deficit, whereas LE/Rn decreases. The above characteristics directly reflect the effect of differences in land-surface environmental factors during land-surface water and heat exchange processes, and indirectly reflect the influences of cloud precipitation processes on those processes.
文摘Over 100 human thermal indices have been developed to predict the combined thermal impact on the body.In principle,these indices based on energy thermal budget equations should not only be the most complex but also be the most accurate.However,the simple indices based on algebraic or statistical models[e.g.,the wet-bulb globe temperature(WBGT)]continue to be the most popular.A new heat stress index,the enthalpy dry-bulb temperature(EnD)for indoor environments is developed and validated in this study.The EnD index is unique in that it uses the air specific enthalpy,not the wet-bulb temperature,to measure the latent heat transfer from the skin to the surrounding environment.Theoretically,the EnD index can be treated as the equivalent temperature based on the convective heat transfer coefficient h_(c).Comparison is made between the EnD index and the widely used WBGT index based on the experimental data taken from three independent studies available in the scientific literature.The results show that the EnD index can reduce the overestimation of the dry-bulb air temperature and thus reduce heat stress in most cases,especially for hot and humid environments.It can be concluded that the EnD index has the potential to replace the WBGT index as the standard heat stress index in the future.
文摘Freezing is the most common method used to preserve and minimize loss in quality of catfish during storage. Since freezing is a heat transfer process, the design and selection of freezing equipment require knowledge of thermophysical properties such as freezing temperature, enthalpy of freezing, unfreezable water and specific heat. Channel catfish thermophysical properties at freezing temperature were determined using differential scanning calorimetry. Using the combination of Raoult＇s law and Classius-Clapeyron equations, the amount of unfreezable （bound water） was estimated to be 0.129 g H20 g^-1 During freezing （or melting）, the specific heat increased from about 1.5 J g^-1 ℃^-1 to about 30.6 J g^-1 ℃^-1 It was found that freezing of catfish occur over a wide temperature range with the peak and incident freezing temperatures occurring at temperatures of-1.88 ℃ and -6.10 ℃, respectively. About 250 J g^-1 of heat have to be removed from catfish when it is to be frozen to -40 ℃. The implication is that any system that will be designed to freeze catfish must be able to remove 250 J g^-1 of heat.
基金the National Natural Science Foundation of China (Grant Nos. 40575043 and 40605024) and KZCX-sw-229
文摘Based on a one-dimensional eddy diffusion model,a model to study the water mass and energy exchange between the water body(such as lake and wetland) and the atmosphere is developed,which takes the phase change process due to the seasonal melting and freezing of water and the convection mixing process of energy caused by temperature stratification into consideration. The model uses enthalpy instead of temperature as predictive variable,which will help to deal with the phase change process and to design an efficient numerical scheme for obtaining the solution more easily. The performance of the model and the rationality of taking convection mixing into the consideration are validated by using observed data of Kinneret Lake in Israel and Lower Two Medicine Lake in Montana State in America. The comparison of model results with observed data indicates that the model presented here is capable of describing the physical process of water mass and energy between the water body(lake and wetland) and atmosphere. Comparison of the result from wetland with shallow and deep lakes under the same forcing conditions shows that the evaporation from wetland is much greater than that from lakes,which accords with the real observation fact and physical mechanism.
基金This research was supported by the Second Tibetan Plateau Scientific Expedition and Research Program(STEP)(2021QZKK0205)the National Natural Science Foundation of China(41901082).
文摘To ensure the long-term service performance of infrastructure such as railways,highways,airports and oil pipelines built on permafrost slope wetland sites,it is imperative to systematically uncover the long-term heat-water changes of soil in slope wetlands environment under climate warming.More specifically,considering valuable field data from 2001 to 2019,the long-term heat and water changes in active layers of the slope wetland site along the Qinghai-Xizang Railway(QXR)are illustrated,the effect of thermosyphon measures in protecting the permafrost environment is evaluated,and the influences of climate warming and hydrological effects on the stability of slope wetland embankments are systematically discussed.The permafrost at the slope wetland site is rapidly degrading,demonstrating a reduction in active layer thickness of>3.7 cm per year and a permafrost temperature warming of>0.006℃ per year.The thermosiphon embankment developed by QXR has a specific cooling period;thus,to mitigate the long-term impacts of climate warming on the thermal stability of permafrost foundation,it is essential to implement strengthening measures for the thermosiphon embankment,such as adding a crushed-rock layer or sunshade board on the slope of thermosiphon embankment to creating a composite cooling embankment.Short-term seasonal groundwater seepage intensifies frost damage to the slope wetland embankment,while long-term seasonal supra-permafrost water and groundwater seepage exacerbates uneven transverse deformation of slope wetland embankment.Long-term climate warming and slope effects have altered the surface water and groundwater hydrological processes of slope wetlands,potentially leading to an increased occurrence of slope embankment instability.These results are crucial for improving our understanding of heat and water variation processes in the active layer of slope wetland sites located in permafrost regions and ensuring long-term service safety for the QXR.
