竖直埋管换热器热响应半径计算方法

随着能源压力的日益增大,世界各国都十分重视可再生能源的利用与开发,地源热泵技术作为一种清洁、高效的可再生能源,近年得到了较快的发展。该文利用无限长线热源传热计算模型,讨论了介质内过余温度场的分布特性。结果表明：介质内温度响应在孔壁处最大,随离孔壁距离的增加呈指数衰减,随时间的增加而增大;热传播区域随时间的增加而增大,随介质的热扩散系数的增加而增大。针对工程中群埋管换热器情况,利用叠加原理计算群埋管的孔壁温度,定义换热器的热响应半径为其他钻孔引起的过余温度影响系数≤5％时相邻钻孔中心线之间的垂直距离。在大量计算分析基础上,提出了竖直埋管换热器热响应半径计算方法。计算结果表明该文方法具有较好的计算精度,竖直埋管换热器的热响应半径随岩土热扩散系数增大而增大,随持续运行时间增加而增大,随钻孔排数增加而增大,随着钻孔孔径增大而增大;钻孔布置方式不同对钻孔热响应半径的影响较明显,相同布置方式下钻孔直径对其热响应半径的影响较小。针对工程中常见的115和135 mm 2种孔径,绘制了不同岩土介质下钻孔单排、双排和三排以上布置时热响应半径-运行时间的关系曲线。工程算例表明该文方法简单方便,为工程设计提供了便利。     

换热器铝基微细通道微纳结构表面制备及其传热特性

在农业工程中,微细通道传热技术在储粮仓温度控制、农产品干燥系统和太阳能热水系统有着广泛的应用。该文使用CuCl2溶液刻蚀铝基微细通道表面并采用超声波清洗的方式得到微纳结构表面,呈现出超亲水性;在微纳结构表面的基础上用氟硅烷溶液修饰后得到超疏水表面,只经过砂纸打磨处理的为普通光滑表面。使用3种不同表面的微细通道进行流动沸腾试验,试验工质为R141b,操作压力为142 kPa,在不同质量流率、热流密度下研究不同润湿性表面对传热特性的影响。试验结果表明,在低热流密度下,超疏水表面有着最佳的传热特性,相对于普通光滑表面传热系数最大提高31.6%;当热流密度升高到一定值后,超亲水表面的传热系数最大,相对于普通光滑表面传热系数最大提高20.6%。继续提高加热功率,超疏水表面的传热系数开始下降,甚至低于普通光滑表面。该文通过改变微通道的表面特性,研究微纳结构表面对微通道流动沸腾传热特性的影响,为制造出更高换热特性的微细通道换热器提供了新的思路,从而实现节能与高效传热。     

逆流式气-气换热器的设计与性能试验

介绍了一种逆流式气-气换热器的结构、设计及工作过程,并利用数值计算与现场试验的方法对该换热器进行了性能测试。该气-气换热器采用聚丙烯（PP）塑料材料作为换热片,流体方向为逆流式换热。数值方法计算结果表明,换热器换热量与风量呈正相关关系,换热效率随热端风量的增大而提高：热端风量为4 475 m3/h时,换热效率为0.55～0.75;热端风量为7 800 m3/h时,换热效率为0.6～0.8。性能测试的结果表明,该换热器的实际换热效率与数值计算的换热效率基本吻合：热端风量为4 475 m3/h时,实测值为0.45～0.7;热端风量为7 800 m3/h时,实测值为0.65～0.9。因此,该PP逆流式气-气换热器具有很好的换热性能。     

Experimental investigation of electrothermal defrost tubes’ arrangement on heat transfer and flow resistance characteristics of evaporator

The paper presents new arrangement types of electrothermal defrost tubes and manufactures four evaporator samples. Through a wind tunnel refrigeration experimental test-bed, relatively experiments for every sample are carried to study heat transfer and flow resistances characteristics of evaporator. The experiment results show that in experimental face velocity range from 1.5 m/s to 4.3 m/s compared with flat-fin evaporator, the unit area of cooling capacity of DK-8 evaporator increased 28.1% to 36.2%, the fin surface coefficient of heat transfer raises 79.2% to 83.5%, the compressor COP (Coefficient of Performance) improves 38.2% to 46.9%, and the air side flow resistance decreases 5.29% to 18.3% in the same experimental condition and geometric size. The increase amplitude of COP is obviously higher than air side flow resistance. The experimental investigation results prove that it is completely feasible optimized combing defrost design with heat transfer enhancement design.     

Comparative Analysis of Heat Exchange Performance ofEnergy Piles and Borehole Heat Exchangers in GSHP System

Due to their enhanced cost-effectiveness and efficiency over traditional borehole exchangers, energy piles are increasingly used in Ground Sourced Heat Pump (GSHP) projects. In this paper, the structural characteristics of these two types of heat exchangers and their heat transfer mechanism were discussed firstly. The thermal response tests (TRT) were performed on two testing energy piles in one GSHP project in Nanjing, China. The TRT results were then used to verify the numerical simulations, which suggests that the heat exchange performance of energy piles is superior to that of the traditional borehole exchangers. Meanwhile, the numerical simulation method used in this paper was considered applicable to the optimization design of ground heat exchangers in GSHP system.     

武汉与重庆典型地质结构下的地埋管换热性能

地埋管地源热泵换热器的换热性能受到不同地质结构的影响。以武汉和重庆地区的典型地质构成为边界条件,建立了三维地埋管的单孔双U管换热模型,通过模型计算,获得了两种地质条件下的地埋管换热性能,以重庆地区的地源热泵热响应测试结果以及工程运行数据出发,对模型的计算结果进行了验证,结果表明,模型吻合度较好,可以应用于工程分析。以模型为条件,进行地质结构对换热性能的影响度分析,预测了两地地埋管地源热泵的换热性能并计算得到换热器的平均换热系数分别为武汉地区K₁=1.65（W/m·K）,重庆地区K₂=1.51（W/m·K）。     

A SYSTBM OF SAVING VENTILATION ENERGY POR MULTI_STORIED HEALTNY BUILDINGS

A sving energy system can get natural ventilation in the storied healthy build-ings with air condition or heating. The principal component of this system is an efficient heat ex-changer made of a set of heat pipes. This system can be operated between two sides of one floor slabto change the energy carried both by the hot air flow and the cold air flow, This svstem can make aspossibly keeping indoor air fresh with a little energy air loss only. It is possible for using this systemto cure a sick building into a healthy building. This system can be put dperation between both thepipes of waste air flow and fresh air flow for an integrated air conditional svstem with fresh air.     

日光温室地下热交换系统的实验和优化设计研究

通过对比观测实验,研究和分析了日光温室采用地下热交换系统,冬季生产喜温蔬菜的可行性和实用性,并且对该设施的节能效果和经济效益作出了客观的初步评价。提出了地下热交换系统的优化设计思想和方法,并编制了优化设计的计算机程序。     

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.