Synthesis of heat exchanger networks including expansion process is a complex task due to the involvement of both heat and work.A stream that expands through expanders can produce work and cold load,while expansion th...Synthesis of heat exchanger networks including expansion process is a complex task due to the involvement of both heat and work.A stream that expands through expanders can produce work and cold load,while expansion through valves barely affects heat integration.In addition,expansion through expanders at higher temperature produces more work,but consumes more hot utility.Therefore,there is a need to weigh work production and heat consumption.To this end,an enhanced stage-wise superstructure is proposed that involves synchronous optimization of expander/valve placement and heat integration for each pressure-change sub-stream in stages.A mixed-integer nonlinear programming(MINLP)model is established for synthesizing sub and aboveambient heat exchanger networks with multi-stream expansion,which explicitly considers the optimized selection of end-heaters and end-coolers to adjust temperature requirement.Our proposed method can commendably achieve the optimal selection of expanders and valves in a bid for minimizing exergy consumption and total annual cost.Four example studies are conducted with two distinct objective function(minimization of exergy consumption and total annual cost,respectively)to illustrate the feasibility and efficacy of the proposed method.展开更多
This study deals with the high-risk shell-and-tube heat exchangers in the effluent system of hydrogenation reaction of the petrochemical industry.The process of hydroprocessing reactor effluent system is simulated in ...This study deals with the high-risk shell-and-tube heat exchangers in the effluent system of hydrogenation reaction of the petrochemical industry.The process of hydroprocessing reactor effluent system is simulated in Aspen Plus to study the distribution of corrosive medium in the three phases of oil,gas and water.The least-squares method is utilized to calculate the ammonium salt crystallization temperature.Then,the heat exchanger with risk of ammonium salt crystal corrosion is identified.Dynamic mathematical modeling of the heat exchanger is established to determine the transfer function.A temperature control system with proportional integral derivative(PID)control of the heat exchanger outlet is designed,and fuzzy logic is used to implement self-tuning of PID parameters.After MATLAB simulation,the results show the control system can achieve rapid control of the heat exchanger outlet temperature.展开更多
From the viewpoints of environmental conservation and energy efficiency,seawater-source heat pump system(SWHP) to provide district cooling and heating is applied in coastal areas.Based on the system,a heat transfer mo...From the viewpoints of environmental conservation and energy efficiency,seawater-source heat pump system(SWHP) to provide district cooling and heating is applied in coastal areas.Based on the system,a heat transfer model was established for cast heat exchanger(CHE) adopted by SWHP systems.The CHE consists of pipes immersed in the seawater and used for transferring heat between the seawater and the heat exchanger pipes of SWHP system.An experimental study was carried out to test the validity of the model.A program was developed in VB language and the effects of inlet temperature,flow rate of the secondary refrigerant and length of CHE on the results were investigated.The results of the numerical simulation are in consistence with the experiments in both winter and summer conditions.As a result,application of SWHP systems with CHE in coastal areas in China is feasible due to the favorable geographical conditions and environment.展开更多
In a hard chromium electroplating process, a heat exchanger is employed to remove the heat produced from the high current intensity in an electroplating bath.Normally, a conventional U shape heat exchanger is installe...In a hard chromium electroplating process, a heat exchanger is employed to remove the heat produced from the high current intensity in an electroplating bath.Normally, a conventional U shape heat exchanger is installed in the bath, but it provides low heat removal.Thus, this study designs a novel W serpentine shape heat exchanger with identical heat transfer area to the conventional one for increasing heat removal performance.The performance of the heat exchange is tested with various flow velocities in a cross-section in range of 1.6 to 2.4 m·s^(-1).Mathematical models of this process have been formulated in order to simulate and evaluate the heat exchanger performance.The results show that the developed models give a good prediction of the plating solution and cooling water temperature, and the novel heat exchanger provides better results at any flow velocity.In addition, the W serpentine shape heat exchanger has been implemented in a real hard chromium electroplating plant.Actual data collected have shown that the new design gives higher heat removal performance compared with the U shape heat exchanger with identical heat transfer area; it removes more heat out of the process than the conventional one of about 23%.展开更多
A mathematical model has been developed to describe the dynamic heat transfer in the clothing microclimate under transient wear conditions. This model is solved numerically by the implicit finite difference method. If...A mathematical model has been developed to describe the dynamic heat transfer in the clothing microclimate under transient wear conditions. This model is solved numerically by the implicit finite difference method. If the physical activity and ambient conditions are specified, the model can predict the thermoregulatory response of the body. Experimental measurements with garments made of fibers with different levels of hygroscopicity are compared with predictions by the model. There is good agreement between prediction and experiment for the temperature of the clothing microclimate.展开更多
The effect of vegetation on the water-heat exchange in the freezing-thawing processes of active layer is one of the key issues in the study of land surface processes and in predicting the response of alpine ecosystems...The effect of vegetation on the water-heat exchange in the freezing-thawing processes of active layer is one of the key issues in the study of land surface processes and in predicting the response of alpine ecosystems to climate change in permafrost regions. In this study, we used the simultaneous heat and water model to investigate the effects of plant canopy on surface and subsurface hydrothermal dynamics in the Fenghuoshan area of the QinghaiTibet Plateau by changing the leaf area index(LAI) and keeping other variables constant. Results showed that the sensible heat, latent heat and net radiation are increased with an increase in the LAI. However, the ground heat flux decreased with an increasing LAI. The annual total evapotranspiration and vegetation transpiration ranged from-16% to 9% and-100% to 15%, respectively, in response to extremes of doubled and zero LAI, respectively. There was a negative feedback between vegetation and the volumetric unfrozen water content at 0.2 m through changing evapotranspiration. The simulation results of soil temperature and moisture suggest that better vegetation conditions are conducive to maintaining the thermal stability of the underlying permafrost, and the advanced initial thawing time and increasing thawing rate of soil ice with the increase in the LAI may have a great influence on the timing and magnitude of supra-permafrost groundwater. This study quantifies the impact of vegetation change on surface and subsurface hydrothermal processes and provides a basic understanding for evaluating the impact of vegetation degradation on the water-heat exchange in permafrost regions under climate change.展开更多
A mathematical model is established on the basis of the physical characteristic of the negative resistance arc when a low current of 0—50 A is applied in pulsed TIG welding. The simulation model converted from the ma...A mathematical model is established on the basis of the physical characteristic of the negative resistance arc when a low current of 0—50 A is applied in pulsed TIG welding. The simulation model converted from the mathematical model is run in MATLAB environment, and the discussion is focused on the way the peak current ranging from 29 A to 50 A and the time constant of arc in the span of 0.003—0.006 s influence the simulating results and the dynamic characteristic. The simulating data are close to that of welding experiments and correspond to the theoretical conclusion.展开更多
In the paper, a dynamical model of gas-liquid mixture motion through a pipeline with regard to change of rheological properties that occur as a result of heat-exchange process, is constructed, and the solutions of the...In the paper, a dynamical model of gas-liquid mixture motion through a pipeline with regard to change of rheological properties that occur as a result of heat-exchange process, is constructed, and the solutions of the obtained connected differential equations are given. Analytic expression allowing to determine pressure change along the length of a pipeline, is obtained.展开更多
基金the financial support provided by the National Natural Science Foundation of China(No.21776035)China Postdoctoral Science Foundation(No.2019TQ0045)。
文摘Synthesis of heat exchanger networks including expansion process is a complex task due to the involvement of both heat and work.A stream that expands through expanders can produce work and cold load,while expansion through valves barely affects heat integration.In addition,expansion through expanders at higher temperature produces more work,but consumes more hot utility.Therefore,there is a need to weigh work production and heat consumption.To this end,an enhanced stage-wise superstructure is proposed that involves synchronous optimization of expander/valve placement and heat integration for each pressure-change sub-stream in stages.A mixed-integer nonlinear programming(MINLP)model is established for synthesizing sub and aboveambient heat exchanger networks with multi-stream expansion,which explicitly considers the optimized selection of end-heaters and end-coolers to adjust temperature requirement.Our proposed method can commendably achieve the optimal selection of expanders and valves in a bid for minimizing exergy consumption and total annual cost.Four example studies are conducted with two distinct objective function(minimization of exergy consumption and total annual cost,respectively)to illustrate the feasibility and efficacy of the proposed method.
基金supported by the National Natural Science Foundation of China(Grant No.51876194U1909216)General Research Project of Zhejiang Provincial Department of Education(Y201942785)。
文摘This study deals with the high-risk shell-and-tube heat exchangers in the effluent system of hydrogenation reaction of the petrochemical industry.The process of hydroprocessing reactor effluent system is simulated in Aspen Plus to study the distribution of corrosive medium in the three phases of oil,gas and water.The least-squares method is utilized to calculate the ammonium salt crystallization temperature.Then,the heat exchanger with risk of ammonium salt crystal corrosion is identified.Dynamic mathematical modeling of the heat exchanger is established to determine the transfer function.A temperature control system with proportional integral derivative(PID)control of the heat exchanger outlet is designed,and fuzzy logic is used to implement self-tuning of PID parameters.After MATLAB simulation,the results show the control system can achieve rapid control of the heat exchanger outlet temperature.
基金Project(2006BAJ04A15-03) supported by the National Science and Technology Pillar Program during the Eleventh Five-year Plan Period
文摘From the viewpoints of environmental conservation and energy efficiency,seawater-source heat pump system(SWHP) to provide district cooling and heating is applied in coastal areas.Based on the system,a heat transfer model was established for cast heat exchanger(CHE) adopted by SWHP systems.The CHE consists of pipes immersed in the seawater and used for transferring heat between the seawater and the heat exchanger pipes of SWHP system.An experimental study was carried out to test the validity of the model.A program was developed in VB language and the effects of inlet temperature,flow rate of the secondary refrigerant and length of CHE on the results were investigated.The results of the numerical simulation are in consistence with the experiments in both winter and summer conditions.As a result,application of SWHP systems with CHE in coastal areas in China is feasible due to the favorable geographical conditions and environment.
基金Supported by Thailand Research Fund(TRF)under The Royal Golden Jubilee Ph.D.Program(PHD/0158/2550)Chulalongkorn University(Contract No.RES_57_411_21_076)Chulalongkorn Academic Advancement into its 2nd Century Project
文摘In a hard chromium electroplating process, a heat exchanger is employed to remove the heat produced from the high current intensity in an electroplating bath.Normally, a conventional U shape heat exchanger is installed in the bath, but it provides low heat removal.Thus, this study designs a novel W serpentine shape heat exchanger with identical heat transfer area to the conventional one for increasing heat removal performance.The performance of the heat exchange is tested with various flow velocities in a cross-section in range of 1.6 to 2.4 m·s^(-1).Mathematical models of this process have been formulated in order to simulate and evaluate the heat exchanger performance.The results show that the developed models give a good prediction of the plating solution and cooling water temperature, and the novel heat exchanger provides better results at any flow velocity.In addition, the W serpentine shape heat exchanger has been implemented in a real hard chromium electroplating plant.Actual data collected have shown that the new design gives higher heat removal performance compared with the U shape heat exchanger with identical heat transfer area; it removes more heat out of the process than the conventional one of about 23%.
文摘A mathematical model has been developed to describe the dynamic heat transfer in the clothing microclimate under transient wear conditions. This model is solved numerically by the implicit finite difference method. If the physical activity and ambient conditions are specified, the model can predict the thermoregulatory response of the body. Experimental measurements with garments made of fibers with different levels of hygroscopicity are compared with predictions by the model. There is good agreement between prediction and experiment for the temperature of the clothing microclimate.
基金This study was supported by the National Nature Science Foundation of China(No.41671015,No.42071027,No.41890821)。
文摘The effect of vegetation on the water-heat exchange in the freezing-thawing processes of active layer is one of the key issues in the study of land surface processes and in predicting the response of alpine ecosystems to climate change in permafrost regions. In this study, we used the simultaneous heat and water model to investigate the effects of plant canopy on surface and subsurface hydrothermal dynamics in the Fenghuoshan area of the QinghaiTibet Plateau by changing the leaf area index(LAI) and keeping other variables constant. Results showed that the sensible heat, latent heat and net radiation are increased with an increase in the LAI. However, the ground heat flux decreased with an increasing LAI. The annual total evapotranspiration and vegetation transpiration ranged from-16% to 9% and-100% to 15%, respectively, in response to extremes of doubled and zero LAI, respectively. There was a negative feedback between vegetation and the volumetric unfrozen water content at 0.2 m through changing evapotranspiration. The simulation results of soil temperature and moisture suggest that better vegetation conditions are conducive to maintaining the thermal stability of the underlying permafrost, and the advanced initial thawing time and increasing thawing rate of soil ice with the increase in the LAI may have a great influence on the timing and magnitude of supra-permafrost groundwater. This study quantifies the impact of vegetation change on surface and subsurface hydrothermal processes and provides a basic understanding for evaluating the impact of vegetation degradation on the water-heat exchange in permafrost regions under climate change.
基金National Natural Science Foundation of China (No 59975068) Natural Science Foundation of Tianjin (No993602911)
文摘A mathematical model is established on the basis of the physical characteristic of the negative resistance arc when a low current of 0—50 A is applied in pulsed TIG welding. The simulation model converted from the mathematical model is run in MATLAB environment, and the discussion is focused on the way the peak current ranging from 29 A to 50 A and the time constant of arc in the span of 0.003—0.006 s influence the simulating results and the dynamic characteristic. The simulating data are close to that of welding experiments and correspond to the theoretical conclusion.
文摘In the paper, a dynamical model of gas-liquid mixture motion through a pipeline with regard to change of rheological properties that occur as a result of heat-exchange process, is constructed, and the solutions of the obtained connected differential equations are given. Analytic expression allowing to determine pressure change along the length of a pipeline, is obtained.