THERMODYNAMIC ANALYSIS AND PERFORMANCE EVALUATION OF CONVECTIVE HEAT TRANSFER THROUGH DUCTS

A second law analysis is carried out on convective heat transfer in fully developed region with constant wall temperature through circular, trianglar and rectangular ducts. Besides, the entropy generation rate expression is obtained and the loss rate of available energy in convective heat transfer processes is defined as well. At the same time, the influence of initial temperature difference between fluid and wall as well as the influence of fluid friction on the loss rate of available energy is discussed. Then, the thermodynamic performances of several typical ducts are compared. Finally , the optimum initial temperature difference with the minimum loss rate of available energy is also obtained.     

Spray Characteristics of a Two Phase Air water Nozzle for Indirect Evaporative Cooling

We present a two phase air water nozzle that can be applied to indirect evaporative cooling to improve the heat transfer efficiency of indirect evaporative coolers by improving the uniformity of the water film on the surface of the heat exchanger. The spray characteristics of a nozzle with a fan shaped orifice at various air and water pressure conditions was studied. The spray cone angle, the air water mass flow rate, and the relationship between the mass flow rate and the air water pressure ratio were obtained. The best air water pressure ratio and spray cone angle were also found.     

Energy efficiency analysis on intermittent operation based on life cycle cost in the vertical ground source heat pump system

Intermittent operation can affect the heat exchange performance of the vertical ground source heat pump system, thereby affecting life cycle cost (LCC) of the ground source heat pump system. The simulation analysis on the hourly load of an office building is implemented by using the DeST software.The heat exchange model of vertical ground heat exchanger pipe-group and energy consumption model of per part of heat pump system are established. Through the comparison between calculation results of continuous operation for 15 years and calculation results of intermittent operation 15 years of the heat pump system, it can be concluded that the LCC value of intermittent operation decreased by 13.45%,relative to the LCC value of continuous operation, and the average energy saving rate of intermittent operation mode is 17.20% in the entire life cycle. Intermittent operation mode can effectively improve energy efficiency of the ground source heat pump system and reduce the LCC value.     

冰蓄冷低温送风空调系统㶲损因素分析

低温送风空调系统引进新型冰蓄冷设备,采用正丁烷作为制冷剂,制冷剂与水直接接触,换热更强烈且稳定。为了研究该系统相应㶲损因素条件下的节能薄弱环节,实现系统性能优化,基于该系统及各表冷器㶲分析模型,分析了热湿比、新风比、送风温差等㶲损因素对系统㶲效率和各表冷器㶲损率的影响。结果表明:当热湿比变化时,处理二次混风的表冷器㶲损率随之呈正比变化,其他表冷器㶲损率及系统㶲效率随之呈反比变化;当新风比变化时,处理新风的两级表冷器㶲损率随之呈正比变化,其他表冷器㶲损率及系统㶲效率随之呈反比变化;当送风温差变化时,处理一次回风的表冷器㶲损率随之呈正比变化,其他表冷器㶲损率及系统㶲效率随之呈反比变化。     

GGH heat transfer enhancement and a new type heat exchangerin the desulphurization system of wet flue gas

This paper conducts in-tube heat transfer experiments in a three dimensional fin tube with 102 mm outer diameter.Compared with the smooth tube,the heat transfer enhancement ratio is between 1.65 and 1.7,and the pressure drop ratio is between 1.65 and 1.7.Based on the analysis of the heat transfer and tube surface temperature,a new type heat exchanger is put forward.Moreover,the design and calculation method is explored.The engineering example indicate that not only the tube surface temperature is higher than the smooth tube,but also the quantity of heat is increased by about 20% than the smooth tube.Compared with other types,the new type heat exchanger has a overall better performance.     

主动式冷梁热工性能仿真模型及实验验证

以无限空间射流理论和表冷器换热理论为基础,对主动式冷梁的工作原理进行了分析。在假设条件下,建立了诱导送风模型和干工况表冷器换热模型。结合这两种模型,最终建立了主动式冷梁工作模型。在设定的5种静压箱静压值下,对主动式冷梁样品的一次风量、二次风量、水侧换热量等热工参数进行测试。选取诱导比和制冷量两个表征冷梁性能的参数作为标准,对模型理论值与样品实际值进行了一致性与差异性分析,验证了所构建的主动式冷梁模型。     

Analysis of the Temperature Limit of Dynamic Water Intake of Open loop Surface Water Source Heat Pump Systems

Energy consumption of water intake is one of the key factors for energy saving in the application of the open loop surface water heat pump system. An energy efficiency ratio coupling model for open loop surface water source heat pump systems was established on the basis of the energy consumption model for the water intake and the heat pump units. According to energy saving rate and regulation of energy consumption of water intake, dynamic temperature limits of water intake in different water supply temperature of cooling tower and different pump head were proposed so as to find a calculation method of temperature limits of water intake of open loop surface water heat pumps. Moreover, the energy saving rate of surface water source heat pump systems compared with traditional air conditioning systems under various condition was also calculated.     

Analysis of Sewage-water Heat Exchanger withthe Function of Auto-de-fouling

A sewage-water shell-tube heat exchanger with the function of de-fouling was proposed and designed for sewage-source heat pump. Its new simulation program which relies on a distribution parameter computational method was set up. Then the model was solved with the method of Matrix Control. Based on the model, the distribution of bilateral fluid temperature were studied, under the conditions of different flow rates and heat exchange area before and after the de-fouling. Results showed that there will be heat anti-transfer phenomenon if the heat exchanger area is bigger than need and the region of this phenomenon was point out. Setting the function of auto-de-fouling in shell-tube heat exchanger and reducing the equipment's volume accordingly can make the sewage-water heat exchanger run in the best conditions.     

Numerical Analysis and Optimization of a Small Vehicle Heat Exchanger

This paper analyzes the fluid flow and heat transfer of the heat exchanger, and obtainsd the distribution of fluid field, heat field and pressure field in heat exchanger. According the analysis result, some modify measure is adopted, such as decreasing the number of tube bundle, the size of baffle plate and increasing the diameter of exchange heat tube. In the new heat exchanger, the resistance decreased 32.3%, is 103.2 Pa and the temperature of the exit is 130 K. The new heat exchanger satisfies the requirement of exchanging heat. The study indicates that adopting the numerical simulation method could get temperature, pressure and fluid - velocity of anywhere of the heat exchanger, and understand effecfing of structure parameter on fluid flied and heat flied of the heat exchanger. Therefore, it provides a new method for optimization design of heat exchanger.     

Influence of Backfill on Performance of Ground Heat Exchanger

The physical and mathematical model of three dimensional unsteady coupled heat transfer in the ground heat exchanger is proposed, and corresponding numerical simulations for actual ground heat exchanger and operation condition are carried out. The computed results are compared with those of the thermal resistance test of the ground heat exchanger, which proves the correctness of the model and corresponding numerical methods. Then, the effects of thermal conductivity and specific heat of the ground backfill material on the ground heat exchanger are investigated, which provides theoretical guidance for the thermal response test and the engineering design of the ground heat exchanger.     

The determination method of limit energy consumption of water supply in open-loop surface water source heatpump systems

For the open-loop surface water source heat pump systems, energy consumption of water supply is the key factor for energy saving of system. On the basis of energy consumption model of heat pump unit and energy consumption model of water supply etc., open-loop surface water source heat pump system energy efficiency ratio coupling model is established. Based on energy efficiency ratio,the coupling limit value of surface water source heat pump system in different temperature of water supply and different energy consumption of water supply is obtained.Through the actual case, energy saving rate of the system is calculated in different temperatures of water supply and different system modes. And the determination method of the limit energy consumption of water supply of open-loop surface water source heatpump systems is established.     

亚热带稻田能量平衡闭合状况分析

通过采用线性回归,能量平衡比率和相对残差频率分布3种统计方法对涡度相关法通量观测的稻田能量平衡闭合状况进行了评价,并分析了能量平衡闭合程度的季节变化趋势。结果表明,在稻田生态系统中存在能量不闭合现象,年能量平衡比率为0.87,年平均不闭合程度为13%;能量平衡比率在5—8月份平均为0.85,能量不闭合程度较高;1—4月份和9—12月份平均为0.92,不闭合程度较低。在假定常规的有效能量测定正确的前提下,可以认为涡度相关测定的湍流通量可能被低估了     

Experimental Study of Ground-source Heat Pump Systems with Horizontal Heat Exchanger

This paper describes the double layer horizontal ground source heat pump systems constructed in 1998 with the buried depth of 0.9 m and 1.8 m. The program of study includes experimental equipments, heat exchanger size, testing meter and methods for data analysis. In addition, the heating and cooling performance at typical days are also illustrated. Among the influencing factors on the performance of the ground source heat pump systems, the parameter of heat exchanger and operation patterns of heat pump systems are analyzed.A heat transfer model has been set up for horizontal heat exchanger.     

热风炉换热系统的热工特性

介绍了干燥热风炉的概念,分析了热风炉的设计现状。通过与加热炉的对比,阐述了热风炉操作参数的特点;基于换热器在热风炉上不可替代的地位,从热工理论出发,分析指出了热风炉用换热器与余热利用换热器的主要区别。     

A Three-Dimensional Numerical Model and Experimental Research for U-Tube Ground Heat Exchanger in Heating Operation

In terms of the theory of a transient energy balance on the finite controlled volume, in this paper, a transient three-dimensional heat transfer model for the simulation of a single vertical U-tube ground heat exchanger based on finite-difference methods is systematically proposed. The model is also compared with experimental results during the heating operation in winter. What's more,based on test data and domestic and foreign literature, the equations to determine the undisturbed ground temperature for wet and heavy soil in Chongqing are presented. These formulae are essential conditions to calculate the heat transfer model.     

Study on Heat Transfer Characteristics in Waste Gas of the Exchanger

By the calculation and experiment,analysed the heat transfer characteristies in waste gas of the high temperature exchanger.The results which the reasonable vertical and horizontal distances were obtained,these turned out that the metallic rediation net was the effectve method intensified heat transfer in hot waste gas.The infulence of the velcity and temperature of waste gas on the multiple heat transfer caefficrent of the exchanger was studied by the experiment data.     

Analysis of the Ground Adjustment Ability of the Ground Source Heat Pump Systems in Winter

Based on an actual ground source heat pump system in hot summer and cold winter area, the system operation parameters were tested for 6 years under the state of using cooling tower for cooling in summer but the ground heat exchanger and fire pool for heating in winter. A three dimensional (3D) tube group model was established, and the thermal balance analysis and calculation of the ground temperature distribution around the ground heat exchanger were conducted by the numerical calculation. According to the comparison between the test data and the theoretical results, the influencing factors of the ground adjustment ability were obtained.     

The Key Parameters Method of Calculating Geothermal Heat Exchanger Length

The geothermal heat exchanger is the key component of ground coupled heat pump systems. We discuss the key parameters method of calculating geothermal heat exchanger length based on line source theory. Typical meteorological year data is used to determine the hottest month, the coldest month and annual average surface temperature. The building hourly load can be obtained by introducing the concept of equilibrium temperature. The cooling fraction and the heating fraction then can be calculated using building hourly load and performance parameters curve fit of a water source heat pump unit. The method for selecting the hottest and lowest entering fluid temperature and calculating the borehole and ground thermal resistance is given. A vertical U tube heat exchanger length calculation procedure is proposed.     

Experimental Study of Flow and Heat Transfer in Heat Exchanger with Small Channels

The experimental study of the flow resistance and heat transfer characteristics are conducted for water and ethylene glycol solution (66% Wt) flowing in the heat exchanger with small rectangular microchannels . The heat exchanger having the channels of 0.4 mm in width, 2.0 mm in height, and 20 mm in length is heated by a hearing rod at the bottom surface, the upper and two side surfaces are adiabatic. During experiments, the Reynolds number are ranged from 2 to 2 500. The experimental results show that the flow friction factor decreases and Nusselt number increases with increasing Reynolds number for water and ethylene glycol solution. At a fixed Reynolds number, the Nusselt number for ethylene glycol solution with larger Prandtl number is greater than that for water. Meanwhile, the correlations of flow resistance and heat transfer in the heat exchanger with small channels are obtained for engineering application.     

Thermodynamic Analysis of River Water Fouling on Constant Wall Temperature Tube of Small Diameter

In order to improve utilization of cold and heat source from river, turbulence theory and entropy generation theory were adopted to analyze the effect of fouling on convective heat transfer performance in small diameter tube of constant wall temperature.It is found that the entropy generation caused by conduction of fouling plays a more important role in total entropy generation of heat transfer process through a duct than that in cveast rate of caused by temperature difference.The entropy generation caused by viscous flow is more than the entropy generation caused by temperature difference in flow with bigger Reynolds and small radius.The increase rate of entropy generation monotonically increase with Reynolds and the generation process of fouling resistance.Thereafter, the effect of fouling resistance on the heat transfer performance of water source heat pump heat exchanger should be paid more attention, when river water are used as the cold and heat source of heat pump.