夏热冬冷地区空气源热泵供暖特性实测与分析

以空气源热泵为热源设备,辐射地板为加热末端建立实验系统,基于双气候补偿冬季供暖模式进行监测与分析。在不同的室外环境下,分析出地板辐射系统对室内供热效果、各子系统的温度变化、制热性能的影响规律。为夏热冬冷地区的空气源热泵供暖的发展和提高系统的能效特性提供理论基础和实验依据。结果表明:夏热冬冷地区采用空气源热泵供暖的室内温度为17.0～23.0℃,湿度为25%～45%。采用双气候补偿技术时,室外温度波动会影响主机供水温度、地暖供水温度,并提高室内舒适度。空气源热泵供暖系统的平均小时制热性能比为2.90,双气候补偿对系统能效影响较小。     

空气源热泵直接地板辐射采暖系统实验研究及热力性能分析

针对空气源热泵制冷剂直接地板辐射采暖系统,建立热力分析模型,结合实验实测数据,计算分析了不同室外环境下,系统能效比和各组成部件(火用)损失,并对比分析评价了不同采暖系统综合热力性能,为优化系统能效和各组成部件节能提供理论和实际依据.结果表明:实验条件下,空气源热泵运行供热稳定,地板表面温度达到26℃,室内温度为22℃,完全满足室内供暖要求.空气源热泵机组正常供热运行模式下,室外温度为7.8℃时,系统小时能效比HEER达到3.42,而出现结霜情况下,系统HEER仍在2.4以上.系统(火用)效率在30％以上,系统各部件(火用)损失中,压缩机所占比例最大,地板盘管和蒸发器次之,膨胀阀最小,分别为24％、13％、11％、5％,且系统管路输送系统(火用)损失较大,达到12％.综合比较能量转换率和(火用)效率,空气源直接地板辐射采暖系统具有良好的节能性.     

空气源-地板辐射采暖系统的应用研究

对地板辐射采暖系统在南方采用空气源热泵作为热源的优势进行了分析;并对设计选型及应用中该注意的问题进行了说明.最后,从长远角度探讨了该系统的发展前景.     

基于计算机仿真的低温地板辐射采暖系统的节能性分析

介绍了基于空间热网模型的采暖系统的计算机仿真程序，并运用该程序对低温地板辐射采暖和对流采暖两种系统进行计算机仿真，通过对一个采暖日内两种采暖方式下房间的采暖负荷、室内平均空气温度和维护结构内表面温度的动态分析和比较，证明了在维持房间相同热舒适度的情况下，低温地板辐射采暖系统的采暖负荷比对流采暖系统的采暖负荷小，具有节能性。     

低温热水地板辐射采暖的Yong分析

本文建立了采暖系统的Yong分析模型，利用所建立的模型，对地板辐射采暖和传统的散热器采暖两种采暖方式进行了Yong分析。结果表明，当地板辐射采暖的供回水温度为45℃／35℃时，与传统的散热器采暖相比，其Yong效率大约高18％，地板辐射采暖所需供水温度低，可以充分利用各种低温热源及工业废热等低品位能量，是一种具有发展潜力的节能型采暖方式。     

太阳能地板辐射系统用于夜间采暖时系统性能的实验研究

利用太阳能集热器制得低温热水作为地板辐射采暖系统的热源,是一种清洁、节能、舒适的采暖方式。在南京地区搭建了太阳能地板辐射采暖系统实验台,系统运行策略为白天集热、夜晚采暖,通过实验得到了集热器集热效率、地板进出水温度、室内不同朝向围护结构温度、不同高度的空气温度等参数,最后对系统的性能进行了概括和总结。     

严寒地区太阳能-空气源热泵系统供暖实验研究

针对严寒地区所构建的太阳能-空气源热泵系统供暖实验装置,进行热泵独立运行及蓄热水箱-热泵双热源联合运行的供暖特性研究。结果表明:使用空气源热泵单独供暖时,当室外温度低于-12℃时系统COPs达到最低,无法满足室内采暖需求;当室外温度在-12～-7℃之间时,室内采暖需求虽可得到满足,但系统COPs仅为1.10～1.44,节能效果不明显;当室外温度大于-7℃时,室内平均温度可达到20℃以上,系统节能性较好;蓄热水箱的加入会影响运行初期机组的稳定性,但可使室温得到快速提升并提高系统的制热性能,在相同运行条件下,蓄热水箱-热泵混合供暖期间室内平均温度为24.61℃,系统COPs为2.01,较蓄热水箱与空气源热泵交替供暖及单一空气源热泵供暖模式分别提高6.90%、21.08%,供暖效果最佳。     

太阳能地板辐射采暖系统在连续运行时的系统特性研究

通过实验研究了在一定集热面积和采暖面积比前提下,太阳能地板辐射采暖系统在连续运行时的一些系统特性,主要包括系统的太阳能保证率、地板进出水温度、房间空气温度、地板换热量以及热舒适性指标,用TRNSYS软件对实验系统进行模拟,得出地板层构造对系统性能的影响规律以及服装热阻对热舒适性的影响规律.     

低温地板辐射采暖传热特性研究

为了揭示低温地板辐射供暖的传热特性,利用Fluent软件和k-ε湍流模型对低温地板辐射采暖系统的温度场进行数值模拟.搭建电热地板辐射采暖实验系统,进行室内温度场的测量和数值模拟,通过实验测试值及模拟值的对比分析,验证数值模拟的正确性.建立低温热水地板辐射采暖物理模型,对不同供水流速和供水温度进行地面温度分布、地板层温度...     

采用散热器和低温地板辐射供暖的室内热环境与能耗研究

建立了供暖房间室内空气自然对流二维空气湍流流动与传热数学模型，利用PHOE—NICS3．3计算软件对低温地板辐射供暖房间和散热器供暖房间的温度场进行了仿真模拟。建立了供暖房间热过程数学模型，对两种房间进行了编程计算。两个模型计算结果反映了低温地板辐射供暖房间的室内热环境优于散热器供暖房间。根据各自热环境特点，计算了两种房间的能耗。发现低温地板辐射供暖房间比散热器供暖房间节能109／6～129／6，其节能的主要原因是消除了空气局部高温区，避免了外围护上的附加传热量。     

A review of the applications of heat pipe heat exchangers for heat recovery

The waste heat recovery by heat pipes is accepted as an excellent way of saving energy and preventing global warming. This paper is a literature review of the application of heat pipes heat exchangers for the heat recovery that is focused on the energy saving and the enhanced effectiveness of the conventional heat pipe (CHP), two-phase closed thermosyphon (TPCT) and oscillating heat pipe (OHP) heat exchangers. The relevant papers were allocated into three main categories, and the experimental studies were summarized. These research papers were analyzed to support future works. Finally, the parameters of effectiveness of the CHP, TPCT and OHP heat exchangers were described. This review article provides additional information for the design of heat pipe heat exchangers with optimum conditions in the heat recovery system.     

地源热泵的套管式地下换热器传热研究

地源热泵是一种节能、对环境无害的绿色空调设备,可成为下个世纪冷暖技术的核心,采用能量平衡,建立了地下浅埋套管式换热器传热平衡式,进行求解,并分析了影响传热的各关联因子,提出了需研究的强化地下换热的措施,根据求解结果,给出了相应的函数关系图。对实验设计和工程实践有一定的指导作用。     

Frosting of heat pump with heat recovery facility

This paper aims to prolong the heat pump frost time and reduce its growth with heat recovery facility, which should mix the exhausted indoor and outdoor air before entering the evaporator. An ideal mathematic model is developed for heat transfer, frost generation and airside pressure drop. The properties of the mixture would be obtained by solving the mass and energy conservation equations. A parametric analysis is performed to investigate the effects of air inlet temperature, relative humidity and air mass flow rate on total heat transfer coefficient, frost thickness and airside pressure drop, respectively. The results show that rationalizing the ratio of indoor and outdoor air could prolong frosting time and reduce the frost thickness greatly. The total heat transfer coefficient, frost thickness and airside pressure drop increase monotonically with time going, but are not proportional. Decreasing the mixture inlet air temperature and relative humidity could essentially reduce frost growth on the tube surfaces. This can also be observed when increasing the air mass flow rate.     

Analysis of three-dimensional heat transfer in micro-channel heat sinks

In this study, the three-dimensional fluid flow and heat transfer in a rectangular micro-channel heat sink are analyzed numerically using water as the cooling fluid. The heat sink consists of a 1-cm² silicon wafer. The micro-channels have a width of 57 μm and a depth of 180 μm, and are separated by a 43 μm wall. A numerical code based on the finite difference method and the SIMPLE algorithm is developed to solve the governing equations. The code is carefully validated by comparing the predictions with analytical solutions and available experimental data. For the micro-channel heat sink investigated, it is found that the temperature rise along the flow direction in the solid and fluid regions can be approximated as linear. The highest temperature is encountered at the heated base surface of the heat sink immediately above the channel outlet. The heat flux and Nusselt number have much higher values near the channel inlet and vary around the channel periphery, approaching zero in the corners. Flow Reynolds number affects the length of the flow developing region. For a relatively high Reynolds number of 1400, fully developed flow may not be achieved inside the heat sink. Increasing the thermal conductivity of the solid substrate reduces the temperature at the heated base surface of the heat sink, especially near the channel outlet. Although the classical fin analysis method provides a simplified means to modeling heat transfer in micro-channel heat sinks, some key assumptions introduced in the fin method deviate significantly from the real situation, which may compromise the accuracy of this method.     

Second-law performance of heat exchangers for waste heat recovery

Exergy change rate in an ideal gas flow or an incompressible flow can be divided into a thermal exergy change rate and a mechanical exergy loss rate. The mechanical exergy loss rates in the two flows were generalized using a pressure-drop factor. For heat exchangers using in waste heat recovery, the consumed mechanical exergy is usually more valuable than the recovered thermal exergy. A weighing factor was proposed to modify the pressure-drop factor. An exergy recovery index (η_II) was defined and it was expressed as a function of effectiveness (?), ratio of modified heat capacity rates (C^∗), hot stream-to-dead-state temperature ratio, cold stream-to-dead-state temperature ratio and modified overall pressure-drop factor. This η_II–? relation can be used to find the η_II value of a heat exchanger with any flow arrangement. The η_II−Ntu and η_II−Ntu_h relations of cross-flow heat exchanger with both fluids unmixed were established respectively. The former provides a minimum Ntu design principle and the latter provides a minimum Ntu_h design principle. A numerical example showed that, at a fixed heat capacity rate of the hot stream, the heat exchanger size yielded by the minimum Ntu_h principle is smaller than that yielded by the minimum Ntu principle.     

Investigation of heat transfer characteristics in plate-fin heat sink

The present study applies the inverse method in conjunction with the experimental temperature data to investigate the accuracy of the heat transfer coefficient on the fin in the plate-fin heat sink for various fin spacings. The commercial software is applied to solve the governing differential equations with the RNG k–? model in order to obtain the heat transfer and fluid flow characteristics. Under the assumption of the non-uniform heat transfer coefficient, the entire fin is divided into several sub-fin regions before performing the inverse scheme. The average heat transfer coefficient in each sub-fin region is assumed to be unknown. Later, the present inverse scheme in conjunction with the experimental temperature data is applied to determine the heat transfer coefficient and fin efficiency. In order to determine a more reliable heat transfer coefficient, a comparison between the present inverse and numerical results and those obtained from the existing correlations will be made. The numerical fin temperatures will also be compared with the experimental data.     

Mass and heat transfer enhancement of chemical heat pumps

An inert additive, expanded graphite (EG), has been prepared and used to enhance the heat and mass transfer process of chemical heat pumps. The effects of mixing ratio and mixing method on the chemical reaction time are investigated.     

Hierarchic modeling of heat transfer processes in heat exchangers

An alternate approach based on hierarchic modeling is proposed to simulate fluid and heat flow in heat exchangers. On the first level, the direct simulations have been performed for the geometry that is similar to a segment of the examined heat sink. Based on the obtained results, the Reynolds number dependencies of the scaling factors f and StPr^2/3 have been established. On the second level, the integral model of the whole heat sink has been built using the volume averaging technique (VAT). The averaging of the transport equations leads to a closure problem. The direct model Reynolds number dependencies f and StPr^2/3 have been used to calculate the local values of the drag coefficient and the heat transfer coefficient , which are needed in the integral model. The example calculations have been performed for 14 different pressure drops across the aluminum heat sink. The whole-section drag coefficient and Nusselt number have been calculated and compared with the experimental data [M. Rizzi, M. Canino, K. Hu, S. Jones, V. Travkin, I. Catton, Experimental investigation of pin fin heat sink effectiveness, in: Proc. of the 35th National Heat Transfer Conference Anaheim, California, 2001]. A good agreement between the modeling results and the experiment data has been reached with same discrepancies in the transitional regime. The constructed computational algorithm offers possibilities for geometry improvements and optimization, to achieve higher thermal effectiveness.     

Experimental research on heat transfer of pulsating heat pipe

Experimental research was conducted to understand heat transfer characteristic of pulsating heat pipe in this paper, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appears in top heating condition. Under different fall ratios and heat transfer rate, the flow pattern in PHP is transferred from bulk flow to semi-annular flow and annular flow, and the performance of heat transfer is improved for down heating case. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.     

螺旋管传热系数的研究

螺旋管传热器优越的结构和传热特性,使其在传热领域得到了广泛应用.采用实验方法对其对流传热系数进行了测定,并利用Fluent软件对螺旋管传热情况进行了模拟.结果表明,在设定的实验条件下,水-水螺旋管传热系数,自然对流情况下为350~550 W/(m2·K),强制对流(搅拌状态)下为400~650 W/(m2·K),所建立的Fluent软件模型能基本反映流场的实际情况,其计算结果与实验情况基本吻合.