The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the...The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the HCFC (hydro-chloro-floro-carbon) refrigerant and little attention has been paid to comparative study on sizing capillary tube for retrofitted HFC (hydro-floro-carbon) refrigerant. In this paper, the adiabatic flow in capillary tube is analyzed and modeled for retrofitting of HFC-407C refrigerant in a machine tool cooler system. A computer code including determining the length of sub-cooled flow region and the two phase region of capillary tube is developed. Comparative study of HCFC-22 and HFC-407C in a capillary tube is derived and conducted to simplify the traditional trial-and-error method of predicting the length of capillary tubes. Besides, experimental investigation is carried out by field tests to verify the simulation model and cooling performance of the machine tool cooler system. The results from the experiments reveal that the numerical model provides an effective approach to determine the performance data of capillary tube specific for retrofitting a HFC-407C machine tool cooler. The developed machine tool cooler system is not only directly compatible with new HFC-407C refrigerant, but can also perform a cost-effective temperature control specific for industrial machines.展开更多
The tests on the thermoelectric shock of semiconductor coolers show that the life of semiconductor coolers follows the Weibull distribution. After the early failed devices are removed, the failure rule of the devices ...The tests on the thermoelectric shock of semiconductor coolers show that the life of semiconductor coolers follows the Weibull distribution. After the early failed devices are removed, the failure rule of the devices can be described as an exponential distribution. The main failure mode is tile crack between electric couple material and welding pad. The failure mechanism is the orientated incline and easy splitting of the thermoelectric materials and the stress of substrate deformation due to the temperature difference between the two sides of the cooler. The reliability of the devices can be improved by using multi-layer metalization in electric couple welding.展开更多
The presence of water molecules in the air can impact how super cool broadband radiative coolers behave.Higher humidity in the lower atmosphere traps infrared radiation,reducing heat sent back to outer space.In this s...The presence of water molecules in the air can impact how super cool broadband radiative coolers behave.Higher humidity in the lower atmosphere traps infrared radiation,reducing heat sent back to outer space.In this study,a mesoscale urban climate model is used to evaluate the newly developed super cool materials with broadband emissivity not selective in atmospheric window as an arsenal for urban heat management of tropical wet and dry cities like Kolkata.The results suggest that the energy balance over urban domain has substantially been altered by the city scale deployment of super cool broadband radiative cooling materials on the building rooftop.Bowen ratio and evaporative fraction values were found decreasing and increasing,respectively with a positive directional polynomial(R2=0.968)relationship,after the implementation of super cool broadband radiative cooling materials and in comparison,to the unmitigated scenario.At high solar hour(14:00 LT),additional thermal variables of urban domain such as 2 m air temperature,surface skin temperature,urban canopy temperature,and roof surface temperature decrease by 2.3℃,5.4℃,0.8℃,and 31.7℃,respectively.Reflective super cool broadband materials achieve sub-ambient temperatures up to 11.7℃during peak hours,reduce surface wind speed by 2.5 m s−1,and lower the planetary boundary layer by 1475 m.The average daytime drop is approximately 7.3℃,and at night,it is close to 2.4℃.Deployment induces a“regional high”over urban areas,disrupting sea breeze onset and lowering the planetary boundary layer.Finally,an optimal cooling performance for super cool broadband radiative coolers can be achieved in lower humidity conditions,as their efficiency decreases with increased humidity.Though needing further investigation,these findings of nano-science-based super cool broadband materials offer valuable insights for policymakers and urban planners addressing thermal management in densely packed tropical urban environments.展开更多
A detailed model of three-dimensional computational fluid dynamics(CFD)on a finned-tube CO_(2)gas cooler has been developed and validated.The model is then applied to investigate the effect of uniform and mal-distribu...A detailed model of three-dimensional computational fluid dynamics(CFD)on a finned-tube CO_(2)gas cooler has been developed and validated.The model is then applied to investigate the effect of uniform and mal-distribution inlet airflow profiles on the coil performance.The airflow mal-distribution velocity profiles include linear-up,linear-down and parabolic while the effected coil performance parameters contain airside pressure drop,average airside heat transfer coefficient,approach temperature and coil heating capacity.The model also enables to predict the CO_(2)refrigerant temperature profile along the coil pipes from refrigerant inlet to outlet at different operation conditions.The simulation results reveal that different types of inlet airflow velocity profiles have significant effects on the gas cooler performance.The uniform airflow velocity profile case shows the best thermal performance of gas cooler.Compared with the cases of linear-up and parabolic air velocity profiles,the linear-down airflow profile can influence more on the coil heat transfer performance.Due to the thermal conduction between neighbour tubes through coil fins,reversed heat transfer phenomenon exists which can be detected and simulated by the CFD model.It is predicted that the linear-down airflow profile can increase greatly the reversed heat transfer phenomenon and thus lead to the highest approach temperature and the lowest heating capacity amongst these four types of airflow profiles.The research method and outcomes presented in this paper can have great potentials to optimize the performance of a CO_(2)gas cooler and its associated refrigeration system.展开更多
Oxy-combustion is a promising carbon-capture technology,but atmospheric-pressure oxy-combustion has a relatively low net efficiency,limiting its application in power plants.In pressurized oxycombustion(POC),the boiler...Oxy-combustion is a promising carbon-capture technology,but atmospheric-pressure oxy-combustion has a relatively low net efficiency,limiting its application in power plants.In pressurized oxycombustion(POC),the boiler,air separation unit,flue gas recirculation unit,and CO_(2)purification and compression unit are all operated at elevated pressure;this makes the process more efficient,with many advantages over atmospheric pressure,such as low NO_(x)emissions,a smaller boiler size,and more.POC is also more promising for industrial application and has attracted widespread research interest in recent years.It can produce high-pressure CO_(2)with a purity of approximately 95%,which can be used directly for enhanced oil recovery or geo-sequestration.However,the pollutant emissions must meet the standards for carbon capture,storage,and utilization.Because of the high oxygen and moisture concentrations in POC,the formation of acids via the oxidation and solution of SO_(x)and NO_(x)can be increased,causing the corrosion of pipelines and equipment.Furthermore,particulate matter(PM)and mercury emissions can harm the environment and human health.The main distinction between pressurized and atmospheric-pressure oxy-combustion is the former’s elevated pressure;thus,the effect of this pressure on the pollutants emitted from POC—including SO_(x),NO_(x),PM,and mercury—must be understood,and effective control methodologies must be incorporated to control the formation of these pollutants.This paper reviews recent advances in research on SO_(x),NO_(x),PM,and mercury formation and control in POC systems that can aid in pollutant control in such systems.展开更多
Radiant syngas cooler(RSC)is widely used as a waste heat recovery equipment in industrial gasification.In this work,an RSC with radiation screens is established and the impact of gaseous radiative property models,gas ...Radiant syngas cooler(RSC)is widely used as a waste heat recovery equipment in industrial gasification.In this work,an RSC with radiation screens is established and the impact of gaseous radiative property models,gas components,and ash particles on heat transfer is investigated by the numerical simulation method.Considering the syngas components and the pressure environment of the RSC,a modified weighted-sum-of-gray-gases model was developed.The modified model shows high accuracy in validation.In computational fluid dynamics simulation,the calculated steam production is only 0.63%in error with the industrial data.Compared with Smith's model,the temperature decay along the axial direction calculated by the modified model is faster.Syngas components are of great significance to heat recovery capacity,especially when the absorbing gas fraction is less than 10%.After considering the influence of particles,the outlet temperature and the proportion of radiative heat transfer are less affected,but the difference in steam output reaches 2.7 t·h^(-1).The particle deposition on the wall greatly reduces the heat recovery performance of an RSC.展开更多
Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirm...Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirmed that the damage was caused by erosion-corrosion(E-C).Numerical and experimental methods were applied to investigate the E-C mechanism in the air cooler.Computational fluid dynamics(CFD)was used to calculate the hydrodynamic parameters of the air cooler.The results showed that there was a biased flow in the air cooler,which led to a significant increase in velocity,turbulent kinetic energy and wall shear within 0.2 m of the tube entrance.A visualization experiment was then performed to determine the principles of migration and transformation of multiphase flow in the air cooler tubes.Various flow patterns(pure droplet flow,mist flow,and annular flow)and their evolutionary processes were clearly depicted experimentally.The initiation mechanism and processes leading to the development of E-C in the air cooler were also determined.This study provided a comprehensive explanation for the E-C failures that occur in air coolers during operation.展开更多
To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooli...To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooling technique.The design calculation of the porous ceramics tube type dew point indirect evaporative cooler are carried out from such aspects as the volumes and status parameters of the primary and secondary air,the cooler structure,the heat transfer of the solid porous ceramic tubes and the resistance of the cooler.The calculation results show that the design is reasonable.Finally,based on the design calculation,the porous ceramics tube type dew point indirect evaporative cooler is successfully manufactured.展开更多
The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the...The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the two or three stage pressure ratio is analyzed in two cases of constant heat transfer rate for the inter cooler or constant inter stage inlet temperature, based on the minimum of the sum of theoretical compression power at each stage about a multi stage reciprocating compressor. Furthermore, with an example of two stage compressor the influence on the sum of the power of each stage is analyzed when practical pressure ratio deviates from the optimum value. It is obtained that under different cooling conditions the optimum pressure ratio distribution of the multi stage compression is various, and the change of the optimum pressure ratio within a small range has little influence on the sum of the power each stage. For the two stage compression, this range can be represented as ε 1=(0 96~1 06)ε 1j .展开更多
Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current (DC) flow induced by the introduction of a double-inlet in a pulse tube cooler is investigate...Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current (DC) flow induced by the introduction of a double-inlet in a pulse tube cooler is investigated theoretically. The calculation results show that increasing regenerator flow resistance can lead to a smaller extent of DC flow.Therefore,a better stability performance of the cooler can be realized.On this basis,the stability characteristics of the cooler with various regenerator matrix arrangements are studied by experiments.By replacing 30% space of 247 screens of stainless steel mesh at the cold part of the regenerator by lead balls of 0.25 mm diameter,a long-time stable temperature output at 80 K region is achieved. This achievement provides a new way to obtain stable performance for pulse tube coolers at high temperature and is helpful for its application.展开更多
980 nm InGaAs/GaAs separate confinement heterostructure (SCH) strained quantum well (QW) laser with non-absorbing facets was fabricated by using thermal treatment. Microchannel coolers with a five-layer thin oxyge...980 nm InGaAs/GaAs separate confinement heterostructure (SCH) strained quantum well (QW) laser with non-absorbing facets was fabricated by using thermal treatment. Microchannel coolers with a five-layer thin oxygen-free copper plate structure were designed and fabricated through thermal bonding in hydrogen ambient. The highest CW (continuous wave) output power of 200 W for 5-bar arrays packaged by microchannel coolers was presented.展开更多
When sinters are filled into the sinter cooler from the sintering machine, it is commonly seen that, due to segregation effects, sinters of larger size usually accumulate closer to the inner wall of the sinter cooler,...When sinters are filled into the sinter cooler from the sintering machine, it is commonly seen that, due to segregation effects, sinters of larger size usually accumulate closer to the inner wall of the sinter cooler, whereas those of smaller size are to the outer wall. This nonuniform distribution of sinters has led to uneven cooling effect throughout the cooler. This causes the sinters leaving the cooler at a large temperature difference. This undesired temperature difference leads to the deformation and even the destruction of the conveyors. The computational fluid dynamics (CFD) technique was used in the present work to investigate the heat and fluid flow phenomena within the sinter cooler corresponding to the different distribution of sinter layer porosity, which was highly dependent on the arrangement and orientation of sinters within the sinter cooler. It is confirmed that a high mass flow rate within the sinter layer causes a low temperature region and vice versa. The flow fields for vertically reducing porosity distribution and random distribution are almost identical indicating the relative insignificance of convective heat transfer mechanism.展开更多
Generally, the cooler life can determine the blast furnace life. Theslag-metal skull frozen on the cooler can separate the cooler from the hot gas flow in blastfurnace. The key problem is how to freeze liquid slag-met...Generally, the cooler life can determine the blast furnace life. Theslag-metal skull frozen on the cooler can separate the cooler from the hot gas flow in blastfurnace. The key problem is how to freeze liquid slag-metal on the cooler, and the main measure isto decrease the hot surface temperature of the cooler. The computational technology of heat transferwas practically used for long campaign blast furnace design. The optimum design of the cast ironstave, copper stave, plate-stave combined system and flange stave was given by the computingresults. According to the results, the optimum arrangement of different coolers (cast iron or copperstave, flange stave and plate-stave combined system) on different height of blast furnace wall canbe found through all these temperature fields.展开更多
The physical and mathematical model of temperature field for blast furnace stave coolers was established. The computation results show that the heat resistance of 2-6 mm water scale within the cooling pipe is about 7...The physical and mathematical model of temperature field for blast furnace stave coolers was established. The computation results show that the heat resistance of 2-6 mm water scale within the cooling pipe is about 7%-20% of the total heat resistance of cooling stave body, as for drilling duct type, the heat resistance of 2-6 mm water scale is about 88%-98% of the total heat resistance. Using drilling duct or full cast pipe can eliminate gas clearance and coating layer between pipes and cast iron body and reduce the heat resistance of the cooler sharply and improve the coefficient of heat transfer to a great extent. The water velocity within coolers can be kept at the 1evel of 0.5- 1 .5 m/s, the higher water velocity can not decrease the hot surface temperature, but can increase energy consumption for cooling water.展开更多
A collector with high perveance,efficient recu-peration,and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex.To optimize the collection efficiency of the collector,a ...A collector with high perveance,efficient recu-peration,and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex.To optimize the collection efficiency of the collector,a simulation program,based on the Monte Carlo simulations,was developed in the world’s first attempt to calculate the electron collection efficiency.In this program,the backscattering electrons and secondary electrons generated on the collector surface are calculated using a Monte Carlo approach,and all electron trajectories in the collector region are tracked by the Runge–Kutta method.In this paper,the features and structure of our program are described.The backscattering electron yields,with various collector surface materials,are calculated using our pro-gram.Moreover,the collector efficiencies for various col-lector structures and electromagnetic fields are simulated and optimized.The measurement results of the collection efficiency of the HIAF collector prototype and the CSRm synchrotron are also reported.These experimental results were in good agreement with the simulation results of our program.展开更多
The ammonium salt corrosion is a typical failure mode for the hydrogenation reaction effluent air cooler(REAC) system. In order to investigate the corrosion characteristics in the REAC system, numerical simulations we...The ammonium salt corrosion is a typical failure mode for the hydrogenation reaction effluent air cooler(REAC) system. In order to investigate the corrosion characteristics in the REAC system, numerical simulations were performed by using the mixture model, the heating transfer model, and the particles tracking model. The results show that the differences between the temperature and the velocity at each cross section of the first-row and second-row tubes are small. The inertia of the particles plays an important role in the particle’s deposition, and the smaller particles distribute more uniformly in the air cooler. However, for larger particles, they prefer falling from the inner side of the vertical elbow, and preferentially depositing at the inlet header and pipes before saturation. In the heat exchanger tubes, the particle deposition number is larger in the second-row tubes than that in the first-row tubes, and the high-risk tubes mainly concentrate on the middle and right side of the air cooler. The kinetic parameters of the particles are in accordance with the blocking-prone position in many real operating conditions.展开更多
Corrosion leakage occurred in the 14th tube bundle in the first row of a residual oil hydrotreating air cooler after operating for two years.The failure location was 0.5 m from the outlet header box.In this paper,the ...Corrosion leakage occurred in the 14th tube bundle in the first row of a residual oil hydrotreating air cooler after operating for two years.The failure location was 0.5 m from the outlet header box.In this paper,the erosion corrosion of the air cooler tube bundle was investigated by experimental and numerical methods.Visual inspection,scanning electron microscopy(SEM),and X-ray diffraction(XRD)experiments were performed,and the failure morphology and material composition confirmed that the damage was caused by erosion corrosion.The shear stress transport k–ωturbulence model(SST-k–ω)was then used to investigate the flow and erosion corrosion characteristics,combined with mass transfer,corrosion rate,and ionization equilibrium models.The numerical simulation results revealed that the water phase volume fraction increased with flow and heat transfer in the fluid,which increased the mass flow rate and concentration of hydrogen sulfide.The mass transfer coefficient and corrosion rate were proposed as important parameters to characterize erosion corrosion.Moreover,the local concentration of wall shear stress was found to increase the risk of erosion corrosion.The predicted high-risk area was consistent with the actual failure area,which verified that this failure incident was attributable to erosion corrosion by the water phase.展开更多
Through the numerical modeling of temperature field for Blast Furnace (BF) lining and stave coolers, it can tell designers how to design a cooler which the hot surface temperature is less than its critical temperature...Through the numerical modeling of temperature field for Blast Furnace (BF) lining and stave coolers, it can tell designers how to design a cooler which the hot surface temperature is less than its critical temperature under very high heat flux. Applying low heat re- sistance lining and staves cooler to BF is good for a layer of slag skull frozen on the hot surface of cooling stave. As long as the slag skull can stand, the furnace wall is stable and the heat loss of furnace does not increase. This is the basic principle for designing long campa- ignship BF.展开更多
The EGR (exhaust gas recirculation) technique can greatly reduce the NOx emission of diesel engines, especially when an EGR cooler is employed. Numerical simulations are applied to study the flow field and temperature...The EGR (exhaust gas recirculation) technique can greatly reduce the NOx emission of diesel engines, especially when an EGR cooler is employed. Numerical simulations are applied to study the flow field and temperature distributions inside the EGR cooler. Three different models of EGR cooler are investigated, among which model A is a traditional one, and models B and C are improved by adding a helical baffle in the cooling area. In models B and C the entry directions of cooling water are different, which mostly influences the flow resistance. The results show that the improved structures not only lengthen the flow path of the cooling water, but also enhance the heat exchange rate between the cool and hot media. In conclusion we suggest that the improved structures are more powerful than the traditional one.展开更多
The air cooler is an important equipment in the petroleum refining industry.Ammonium chloride(NH4 Cl)deposition-induced corrosion is one of its main failure forms.In this study,the ammonium salt crystallization temper...The air cooler is an important equipment in the petroleum refining industry.Ammonium chloride(NH4 Cl)deposition-induced corrosion is one of its main failure forms.In this study,the ammonium salt crystallization temperature is chosen as the key decision variable of NH4 Cl deposition-induced corrosion through in-depth mechanism research and experimental analysis.The functional link neural network(FLNN)is adopted as the basic algorithm for modeling because of its advantages in dealing with non-linear problems and its fast-computational ability.A hybrid FLNN attached to a small norm is built to improve the generalization performance of the model.Then,the trained model is used to predict the NH4 Cl salt crystallization temperature in the air cooler of a sour water stripper plant.Experimental results show the proposed improved FLNN algorithm can achieve better generalization performance than the PLS,the back propagation neural network,and the conventional FLNN models.展开更多
基金supported by Science Council of Taiwan, China (Grant No. NSC 98-2622-E-167-029-CC3)Industrial Technology Research Institute of Taiwan, China
文摘The machine tool coolers are the best managers of coolant temperature in avoiding the deviation of spindle centerline for machine tools. However, the machine coolers are facing the compressed schedule to phase out the HCFC (hydro-chloro-floro-carbon) refrigerant and little attention has been paid to comparative study on sizing capillary tube for retrofitted HFC (hydro-floro-carbon) refrigerant. In this paper, the adiabatic flow in capillary tube is analyzed and modeled for retrofitting of HFC-407C refrigerant in a machine tool cooler system. A computer code including determining the length of sub-cooled flow region and the two phase region of capillary tube is developed. Comparative study of HCFC-22 and HFC-407C in a capillary tube is derived and conducted to simplify the traditional trial-and-error method of predicting the length of capillary tubes. Besides, experimental investigation is carried out by field tests to verify the simulation model and cooling performance of the machine tool cooler system. The results from the experiments reveal that the numerical model provides an effective approach to determine the performance data of capillary tube specific for retrofitting a HFC-407C machine tool cooler. The developed machine tool cooler system is not only directly compatible with new HFC-407C refrigerant, but can also perform a cost-effective temperature control specific for industrial machines.
文摘The tests on the thermoelectric shock of semiconductor coolers show that the life of semiconductor coolers follows the Weibull distribution. After the early failed devices are removed, the failure rule of the devices can be described as an exponential distribution. The main failure mode is tile crack between electric couple material and welding pad. The failure mechanism is the orientated incline and easy splitting of the thermoelectric materials and the stress of substrate deformation due to the temperature difference between the two sides of the cooler. The reliability of the devices can be improved by using multi-layer metalization in electric couple welding.
基金Dev Niyogi acknowledges the William Stamps Farish Chair through the Jackson School of Geosciences at University of Texasfunding from NOAA NIHHIS NA21OAR4310146,NASA Interdisciplinary Sciences(IDS)Program(NNH19ZDA001N-IDS and 80NSSC20K1268),and DOE Urban Integrated Field Labs(IFL).
文摘The presence of water molecules in the air can impact how super cool broadband radiative coolers behave.Higher humidity in the lower atmosphere traps infrared radiation,reducing heat sent back to outer space.In this study,a mesoscale urban climate model is used to evaluate the newly developed super cool materials with broadband emissivity not selective in atmospheric window as an arsenal for urban heat management of tropical wet and dry cities like Kolkata.The results suggest that the energy balance over urban domain has substantially been altered by the city scale deployment of super cool broadband radiative cooling materials on the building rooftop.Bowen ratio and evaporative fraction values were found decreasing and increasing,respectively with a positive directional polynomial(R2=0.968)relationship,after the implementation of super cool broadband radiative cooling materials and in comparison,to the unmitigated scenario.At high solar hour(14:00 LT),additional thermal variables of urban domain such as 2 m air temperature,surface skin temperature,urban canopy temperature,and roof surface temperature decrease by 2.3℃,5.4℃,0.8℃,and 31.7℃,respectively.Reflective super cool broadband materials achieve sub-ambient temperatures up to 11.7℃during peak hours,reduce surface wind speed by 2.5 m s−1,and lower the planetary boundary layer by 1475 m.The average daytime drop is approximately 7.3℃,and at night,it is close to 2.4℃.Deployment induces a“regional high”over urban areas,disrupting sea breeze onset and lowering the planetary boundary layer.Finally,an optimal cooling performance for super cool broadband radiative coolers can be achieved in lower humidity conditions,as their efficiency decreases with increased humidity.Though needing further investigation,these findings of nano-science-based super cool broadband materials offer valuable insights for policymakers and urban planners addressing thermal management in densely packed tropical urban environments.
基金the support received from GEA Searle and Research Councils UK(RCUK)for this project.
文摘A detailed model of three-dimensional computational fluid dynamics(CFD)on a finned-tube CO_(2)gas cooler has been developed and validated.The model is then applied to investigate the effect of uniform and mal-distribution inlet airflow profiles on the coil performance.The airflow mal-distribution velocity profiles include linear-up,linear-down and parabolic while the effected coil performance parameters contain airside pressure drop,average airside heat transfer coefficient,approach temperature and coil heating capacity.The model also enables to predict the CO_(2)refrigerant temperature profile along the coil pipes from refrigerant inlet to outlet at different operation conditions.The simulation results reveal that different types of inlet airflow velocity profiles have significant effects on the gas cooler performance.The uniform airflow velocity profile case shows the best thermal performance of gas cooler.Compared with the cases of linear-up and parabolic air velocity profiles,the linear-down airflow profile can influence more on the coil heat transfer performance.Due to the thermal conduction between neighbour tubes through coil fins,reversed heat transfer phenomenon exists which can be detected and simulated by the CFD model.It is predicted that the linear-down airflow profile can increase greatly the reversed heat transfer phenomenon and thus lead to the highest approach temperature and the lowest heating capacity amongst these four types of airflow profiles.The research method and outcomes presented in this paper can have great potentials to optimize the performance of a CO_(2)gas cooler and its associated refrigeration system.
基金support of the National Key Research and Development Program of China(2022YFE0206600)the National Natural Science Foundation of China(52376125)Fundamental Research Funds for the Central Universities.
文摘Oxy-combustion is a promising carbon-capture technology,but atmospheric-pressure oxy-combustion has a relatively low net efficiency,limiting its application in power plants.In pressurized oxycombustion(POC),the boiler,air separation unit,flue gas recirculation unit,and CO_(2)purification and compression unit are all operated at elevated pressure;this makes the process more efficient,with many advantages over atmospheric pressure,such as low NO_(x)emissions,a smaller boiler size,and more.POC is also more promising for industrial application and has attracted widespread research interest in recent years.It can produce high-pressure CO_(2)with a purity of approximately 95%,which can be used directly for enhanced oil recovery or geo-sequestration.However,the pollutant emissions must meet the standards for carbon capture,storage,and utilization.Because of the high oxygen and moisture concentrations in POC,the formation of acids via the oxidation and solution of SO_(x)and NO_(x)can be increased,causing the corrosion of pipelines and equipment.Furthermore,particulate matter(PM)and mercury emissions can harm the environment and human health.The main distinction between pressurized and atmospheric-pressure oxy-combustion is the former’s elevated pressure;thus,the effect of this pressure on the pollutants emitted from POC—including SO_(x),NO_(x),PM,and mercury—must be understood,and effective control methodologies must be incorporated to control the formation of these pollutants.This paper reviews recent advances in research on SO_(x),NO_(x),PM,and mercury formation and control in POC systems that can aid in pollutant control in such systems.
基金supported by the National Natural Science Foundation of China(21878082).
文摘Radiant syngas cooler(RSC)is widely used as a waste heat recovery equipment in industrial gasification.In this work,an RSC with radiation screens is established and the impact of gaseous radiative property models,gas components,and ash particles on heat transfer is investigated by the numerical simulation method.Considering the syngas components and the pressure environment of the RSC,a modified weighted-sum-of-gray-gases model was developed.The modified model shows high accuracy in validation.In computational fluid dynamics simulation,the calculated steam production is only 0.63%in error with the industrial data.Compared with Smith's model,the temperature decay along the axial direction calculated by the modified model is faster.Syngas components are of great significance to heat recovery capacity,especially when the absorbing gas fraction is less than 10%.After considering the influence of particles,the outlet temperature and the proportion of radiative heat transfer are less affected,but the difference in steam output reaches 2.7 t·h^(-1).The particle deposition on the wall greatly reduces the heat recovery performance of an RSC.
基金supported by the National Key R&D Program of China(2021YFB3301100)Beijing University of Chemical Technology Interdisciplinary Program(XK2023-07).
文摘Corrosion leakages often occur in the air cooler of a hydrocracking unit,with the failure sites mainly located in the entrance area of the tubes.An analysis of the macroscopic morphology and corrosion products confirmed that the damage was caused by erosion-corrosion(E-C).Numerical and experimental methods were applied to investigate the E-C mechanism in the air cooler.Computational fluid dynamics(CFD)was used to calculate the hydrodynamic parameters of the air cooler.The results showed that there was a biased flow in the air cooler,which led to a significant increase in velocity,turbulent kinetic energy and wall shear within 0.2 m of the tube entrance.A visualization experiment was then performed to determine the principles of migration and transformation of multiphase flow in the air cooler tubes.Various flow patterns(pure droplet flow,mist flow,and annular flow)and their evolutionary processes were clearly depicted experimentally.The initiation mechanism and processes leading to the development of E-C in the air cooler were also determined.This study provided a comprehensive explanation for the E-C failures that occur in air coolers during operation.
基金The National Natural Science Foundation of China(No.50846056)
文摘To improve the wall surface hydrophilicity of a tube type indirect evaporative cooler,a new method adopting porous ceramics is proposed.This method realizes the combination of porous ceramics and the evaporative cooling technique.The design calculation of the porous ceramics tube type dew point indirect evaporative cooler are carried out from such aspects as the volumes and status parameters of the primary and secondary air,the cooler structure,the heat transfer of the solid porous ceramic tubes and the resistance of the cooler.The calculation results show that the design is reasonable.Finally,based on the design calculation,the porous ceramics tube type dew point indirect evaporative cooler is successfully manufactured.
文摘The optimum pressure ratio distribution of a multistage reciprocating compressor is presented based on the assumption, i.e. the inter stage cooling is perfect and there are no pressure losses. The optimization of the two or three stage pressure ratio is analyzed in two cases of constant heat transfer rate for the inter cooler or constant inter stage inlet temperature, based on the minimum of the sum of theoretical compression power at each stage about a multi stage reciprocating compressor. Furthermore, with an example of two stage compressor the influence on the sum of the power of each stage is analyzed when practical pressure ratio deviates from the optimum value. It is obtained that under different cooling conditions the optimum pressure ratio distribution of the multi stage compression is various, and the change of the optimum pressure ratio within a small range has little influence on the sum of the power each stage. For the two stage compression, this range can be represented as ε 1=(0 96~1 06)ε 1j .
基金The National Natural Science Foundation of China(No.50406009).
文摘Based on the fluid network theory,the possibility of utilizing regenerator flow resistance to suppress the direct current (DC) flow induced by the introduction of a double-inlet in a pulse tube cooler is investigated theoretically. The calculation results show that increasing regenerator flow resistance can lead to a smaller extent of DC flow.Therefore,a better stability performance of the cooler can be realized.On this basis,the stability characteristics of the cooler with various regenerator matrix arrangements are studied by experiments.By replacing 30% space of 247 screens of stainless steel mesh at the cold part of the regenerator by lead balls of 0.25 mm diameter,a long-time stable temperature output at 80 K region is achieved. This achievement provides a new way to obtain stable performance for pulse tube coolers at high temperature and is helpful for its application.
文摘980 nm InGaAs/GaAs separate confinement heterostructure (SCH) strained quantum well (QW) laser with non-absorbing facets was fabricated by using thermal treatment. Microchannel coolers with a five-layer thin oxygen-free copper plate structure were designed and fabricated through thermal bonding in hydrogen ambient. The highest CW (continuous wave) output power of 200 W for 5-bar arrays packaged by microchannel coolers was presented.
文摘When sinters are filled into the sinter cooler from the sintering machine, it is commonly seen that, due to segregation effects, sinters of larger size usually accumulate closer to the inner wall of the sinter cooler, whereas those of smaller size are to the outer wall. This nonuniform distribution of sinters has led to uneven cooling effect throughout the cooler. This causes the sinters leaving the cooler at a large temperature difference. This undesired temperature difference leads to the deformation and even the destruction of the conveyors. The computational fluid dynamics (CFD) technique was used in the present work to investigate the heat and fluid flow phenomena within the sinter cooler corresponding to the different distribution of sinter layer porosity, which was highly dependent on the arrangement and orientation of sinters within the sinter cooler. It is confirmed that a high mass flow rate within the sinter layer causes a low temperature region and vice versa. The flow fields for vertically reducing porosity distribution and random distribution are almost identical indicating the relative insignificance of convective heat transfer mechanism.
文摘Generally, the cooler life can determine the blast furnace life. Theslag-metal skull frozen on the cooler can separate the cooler from the hot gas flow in blastfurnace. The key problem is how to freeze liquid slag-metal on the cooler, and the main measure isto decrease the hot surface temperature of the cooler. The computational technology of heat transferwas practically used for long campaign blast furnace design. The optimum design of the cast ironstave, copper stave, plate-stave combined system and flange stave was given by the computingresults. According to the results, the optimum arrangement of different coolers (cast iron or copperstave, flange stave and plate-stave combined system) on different height of blast furnace wall canbe found through all these temperature fields.
文摘The physical and mathematical model of temperature field for blast furnace stave coolers was established. The computation results show that the heat resistance of 2-6 mm water scale within the cooling pipe is about 7%-20% of the total heat resistance of cooling stave body, as for drilling duct type, the heat resistance of 2-6 mm water scale is about 88%-98% of the total heat resistance. Using drilling duct or full cast pipe can eliminate gas clearance and coating layer between pipes and cast iron body and reduce the heat resistance of the cooler sharply and improve the coefficient of heat transfer to a great extent. The water velocity within coolers can be kept at the 1evel of 0.5- 1 .5 m/s, the higher water velocity can not decrease the hot surface temperature, but can increase energy consumption for cooling water.
基金This work was supported by the International Partnership Program of the Chinese Academy of Sciences(No.113462KYSB20170051)the National Natural Science Foundation of China(No.11575264)the National Key R&D Program of China(No.2019YFA0405400).
文摘A collector with high perveance,efficient recu-peration,and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex.To optimize the collection efficiency of the collector,a simulation program,based on the Monte Carlo simulations,was developed in the world’s first attempt to calculate the electron collection efficiency.In this program,the backscattering electrons and secondary electrons generated on the collector surface are calculated using a Monte Carlo approach,and all electron trajectories in the collector region are tracked by the Runge–Kutta method.In this paper,the features and structure of our program are described.The backscattering electron yields,with various collector surface materials,are calculated using our pro-gram.Moreover,the collector efficiencies for various col-lector structures and electromagnetic fields are simulated and optimized.The measurement results of the collection efficiency of the HIAF collector prototype and the CSRm synchrotron are also reported.These experimental results were in good agreement with the simulation results of our program.
基金supported by the National Key R&D Program of China(Grant No.2017YFF0210403)the Zhejiang Provincial Natural Science Foundation of China(Grant No.LY17E060008)the Talent Project of Zhejiang Association for Science and Development Project of SINOPEC(No.318023-2)
文摘The ammonium salt corrosion is a typical failure mode for the hydrogenation reaction effluent air cooler(REAC) system. In order to investigate the corrosion characteristics in the REAC system, numerical simulations were performed by using the mixture model, the heating transfer model, and the particles tracking model. The results show that the differences between the temperature and the velocity at each cross section of the first-row and second-row tubes are small. The inertia of the particles plays an important role in the particle’s deposition, and the smaller particles distribute more uniformly in the air cooler. However, for larger particles, they prefer falling from the inner side of the vertical elbow, and preferentially depositing at the inlet header and pipes before saturation. In the heat exchanger tubes, the particle deposition number is larger in the second-row tubes than that in the first-row tubes, and the high-risk tubes mainly concentrate on the middle and right side of the air cooler. The kinetic parameters of the particles are in accordance with the blocking-prone position in many real operating conditions.
基金supported by the National Natural Science Foundation of China(Grant Nos.51876194,U1909216,and 52176048)the Fundamental Research Funds of Zhejiang Sci-Tech University(Grant No.2021Q020).
文摘Corrosion leakage occurred in the 14th tube bundle in the first row of a residual oil hydrotreating air cooler after operating for two years.The failure location was 0.5 m from the outlet header box.In this paper,the erosion corrosion of the air cooler tube bundle was investigated by experimental and numerical methods.Visual inspection,scanning electron microscopy(SEM),and X-ray diffraction(XRD)experiments were performed,and the failure morphology and material composition confirmed that the damage was caused by erosion corrosion.The shear stress transport k–ωturbulence model(SST-k–ω)was then used to investigate the flow and erosion corrosion characteristics,combined with mass transfer,corrosion rate,and ionization equilibrium models.The numerical simulation results revealed that the water phase volume fraction increased with flow and heat transfer in the fluid,which increased the mass flow rate and concentration of hydrogen sulfide.The mass transfer coefficient and corrosion rate were proposed as important parameters to characterize erosion corrosion.Moreover,the local concentration of wall shear stress was found to increase the risk of erosion corrosion.The predicted high-risk area was consistent with the actual failure area,which verified that this failure incident was attributable to erosion corrosion by the water phase.
文摘Through the numerical modeling of temperature field for Blast Furnace (BF) lining and stave coolers, it can tell designers how to design a cooler which the hot surface temperature is less than its critical temperature under very high heat flux. Applying low heat re- sistance lining and staves cooler to BF is good for a layer of slag skull frozen on the hot surface of cooling stave. As long as the slag skull can stand, the furnace wall is stable and the heat loss of furnace does not increase. This is the basic principle for designing long campa- ignship BF.
文摘The EGR (exhaust gas recirculation) technique can greatly reduce the NOx emission of diesel engines, especially when an EGR cooler is employed. Numerical simulations are applied to study the flow field and temperature distributions inside the EGR cooler. Three different models of EGR cooler are investigated, among which model A is a traditional one, and models B and C are improved by adding a helical baffle in the cooling area. In models B and C the entry directions of cooling water are different, which mostly influences the flow resistance. The results show that the improved structures not only lengthen the flow path of the cooling water, but also enhance the heat exchange rate between the cool and hot media. In conclusion we suggest that the improved structures are more powerful than the traditional one.
基金supported by the National Natural Science Foundation of China(Grant No.51876194,U1909216)the China Petrochemical Corporation Research Project(318023-2)the Zhejiang Public Welfare Technology Research Project(LGG20F030007)。
文摘The air cooler is an important equipment in the petroleum refining industry.Ammonium chloride(NH4 Cl)deposition-induced corrosion is one of its main failure forms.In this study,the ammonium salt crystallization temperature is chosen as the key decision variable of NH4 Cl deposition-induced corrosion through in-depth mechanism research and experimental analysis.The functional link neural network(FLNN)is adopted as the basic algorithm for modeling because of its advantages in dealing with non-linear problems and its fast-computational ability.A hybrid FLNN attached to a small norm is built to improve the generalization performance of the model.Then,the trained model is used to predict the NH4 Cl salt crystallization temperature in the air cooler of a sour water stripper plant.Experimental results show the proposed improved FLNN algorithm can achieve better generalization performance than the PLS,the back propagation neural network,and the conventional FLNN models.