Numerical and experimental analysis of a horizontal ground-coupled heat pump system

The main objective of this work is to evaluate a heat pump system using the ground as a source of heat. A ground-coupled heat pump (GCHP) system has been installed and tested at the test room, University of Firat, Elazig, Turkey. Results obtained during experimental testing are presented and discussed here. The coefficient of performance (COP_sys) of the GCHP system is determined from the measured data. A numerical model of heat transfer in the ground was developed for determining the temperature distribution in the vicinity of the pipe. The finite difference approximation is used for numerical analysis. It is observed that the numerical results agree with the experimental results.     

热电制冷器多通道内空气混合对流及耦合换热

建立了热电制冷器通风及耦合换热数学和物理模型,模拟计算了不同雷诺数、材料有效导热系数比率、几何参数时各通道的流体流动及温度场分布情况,分析了冷风侧排风、几何参数对通道换热能力的影响,以优化制冷器通风换热风道的设计参数。     

被动式太阳能温室中传热与气流分布的数值分析

建立了被动式太阳能温室系统的热平衡方程和土壤热、湿迁移过程的理论模型,针对武汉市11月份的典型气候条件,采用数值模拟和实验研究了温室中土温、气温的变化规律;分析了温室北墙内表面采用不同材料或涂层时,对温室中气流和温度分布的影响。     

Numerical analysis and experimental validation of heat transfer in ground heat exchangers in alternative operation modes

A finite element numerical model has been developed for the simulation of the ground heat exchangers (GHEs) in alternative operation modes over a short time period for ground-coupled heat pump applications. Comparisons between the numerical and analytical results show that the finite line-source model is not capable of modeling the GHEs within a few hours because of the line-source assumption. On the other hand, the experiments with respect to the alternative cooling and heating modes have been undertaken during a short-time period. The comparisons show a reasonable agreement between the numerical and the measured data. The results illustrate that the finite element numerical model can be used to simulate the heat transfer behavior of the GHEs in short time scales instead of the typical finite line-source model. Finally, the variation of the U-tube pipe wall temperatures demonstrates that the discontinuous operation mode and the alternative cooling/heating modes can effectively alleviate the heat buildup in the surrounding soil.     

电流体力学强化水平管内凝结传热试验研究

在电流体力学(EHD)强化传热试验台上进行了水平管内凝结传热的强化试验研究,结果表明,EHD技术对水平管内的凝结传热有明显的强化效果;低热流密度时,强化效果较好,增大热流密度时,强化效果减弱;热流密度维持不变时,强化系数随强化电压的升高而增大;在本试验条件下,对凝结传热的最大强化系数为156％。     

微通道换热器空气侧换热性能影响实验研究

针对微通道蒸发器的换热性能,在结露条件下,分析了冷冻水进口温度、空气进口温度、空气流速大小等参数对空气出口温度、换热器换热系数、空气侧压降等实验结果的影响程度,研究发现:提高冷冻水进口温度,空气侧换热系数和压降有不同程度降低,而空气出口温度有所升高。     

铁路空调客车内流场、温度场的数值模拟和实验研究

采用K-ε湍流模型对空调客车内三维空气流场和温度场进行了数值模拟,并进行了相应的实验研究。研究结果表明,车厢内下部乘客区空气温度高于上部区域,对热舒适性不利;上部区域存在新风短路现象,建议采用下送风方式。     

多联式空调机组室外机与环境换热的数值模拟研究

将肋片盘管结构近似为多孔介质,应用CFD模拟方法分析了室外机与环境空气的换热过程,实验测试获得的速度和温度分布结果验证了CFD模拟方法的准确性.应用CFD模拟方法分析了不同布置方案下室外机的进风温度,得出3台室外机呈直线布置时的优化方案:相邻2台机组之间的最小距离为0.2 m,机组主要进风侧与其周围高于机组的竖直壁面的极限间距为0.8 m.     

Numerical analysis on heat transfer characteristics of ionic liquids in a tubular heat exchanger

ABSTRACT

The efficiency of the solar thermal system depends on the performance of the solar collectors. There is a need to operate solar collector at higher possible temperature to attain maximum efficiency limits. However, the performance of the collector system is limited by the heat transfer characteristics of the working fluid called as the heat transfer fluid (HTF). Water is widely used as the HTF in the solar collector, but the major problem of using water as the HTF is its limited operating temperature. The objective of the work is to investigate the heat transfer characteristics of ionic liquids in tubular heat exchanger (HE) suitable for the solar thermal application. The HE was designed for a heat duty of 1?kW based on the thermal transport property of available ionic liquids and the computational fluid dynamics (CFD) analysis was performed. The results indicate that there is only minimal deviation between the assumed and CFD data.     

数值模拟技术在多孔砖墙传热性能研究中应用

本文总结了多孔砖的数值设计优化步骤。通过例子介绍了多孔砖墙传热数值模拟过程,以及砖孔可视表面辐射的模拟和墙体表面温度、热流密度的计算方法,并给出了有关结果。     

地表水换热盘管换热特性的理论与试验研究

建立了地表水换热盘管的换热模型.对换热盘管在不同换热工况下的换热性能进行了测试,分析了管内外流速、管径及放热或吸热工况对换热性能的影响,分析了换热盘管换热量与盘管长度的关系,给出了不同接近温差时吸热量与盘管长度的关系曲线图.     

Study on transient heat transfer through multilayer thermal insulation: Numerical analysis and experimental investigation

This paper reports on a numerical and experimental study of heat transfer phenomena through two different multilayer fibrous insulations for building applications. The investigated samples were composed of different layers of fibrous materials and aluminium foils, placed between one or two air gaps in the vertical dimension. An experimental apparatus (a guarded hot box) has been used to measure heat transfer through the samples, while a finite volume numerical model combined radiation/conduction heat transfer was developed to predict the temperature distribution and heat transfer in such insulation systems comprised of the materials separated by multiple reflective foils. The model takes into account the coupling between the solid conduction of the fibrous system and the gaseous conduction and radiation. The radiation heat transfer through the insulation system has been modelled via the two flux approximation. The numerical results were compared with the experimental data from the guarded hot box for model validation, as well as to assess the effectiveness of the reflective foils in changing the resistance of the insulations. The comparative verification of the model showed that the numerical results were consistent with the experimental data through the environmental conditions under examination.     

低温地板辐射供暖的传热模拟

建立了低温地板辐射供暖系统的传热数学模型,应用有限差分法对数学模型进行了求解;通过实测及理论计算,得出地板内及室内温度分布特点;计算值与实,测值相对误差小于5％。     

Numerical investigation on thermophoretic deposition of particles in turbulent duct flow with conjugate heat transfer: Analysis of influencing factors

Building Simulation - Thermophoretic deposition of particles in turbulent duct flow is of significant relevance in energy and thermal engineering applications. However, conjugate heat transfer...     

Numerical study on the heat storing capacity of concrete walls with air cavities

Finite element analyses using COMSOL have been carried out to study the heat transfer behavior and storing capacity of concrete walls with air cavities, and to explore the possibility of using one-layer and two-layer one-dimensional models with equivalent thermal conductivity and mass density to represent the effect of concrete walls with air cavities in a building energy simulation. Three typical wall geometries were chosen and both stationary and transient analyses have been carried out. The stationary analyses were performed first to find the equivalent thermal conductivity which was further used in the transient analyses to fit the equivalent mass density. Because of the presence of air cavities the equivalent thermal conductivities are always smaller than the bulk thermal conductivity. However, for the one-layer model an exaggerated equivalent mass density as high as two times the bulk density should be used in order to simulate the heat storing capacity of the concrete walls with air cavities. The values of the fitted equivalent mass density are strongly dependent on the wall thickness.     

节能空心墙体传热引起的夏季空调负荷的数值计算

介绍了夏季空调室外气象参数和太阳辐射照度的计算及气象参数的数值离散,采用有限容积法,计算了夏季标准设计日多种空心墙体由传热引起的空调冷负荷及冷负荷温度,并与标准Ⅱ~Ⅳ型墙体的相应数值进行了比较。     

热泵热回收新风机在寒冷地区的实验研究

为解决寒冷地区冬季空气源热泵运行效率、新风机冻损等运行问题,保证冬季室内良好的空气品质,设计了在冬季将排风引入热泵蒸发器,通过热交换回收排风的能量,并利用热泵冷凝器加热引入室内新风的热泵热回收新风机。采用空气焓差法对该机组在利用排风及排风混室外空气2种运行工况下的制热量、输入功率、热泵能效比(COP)、热回收效率的对比实验。用热泵热回收新风机引进新风后基本没有改变机组输入功率,相同环境条件下的制热量增加,COP值增大,焓差热回收效率最高可达到51.4%。新风机和热泵相结合,利用排风余热提高热泵蒸发器工作温度,改善了热泵和新风机在北方寒冷地区冬季的运行性能。     

Numerical modeling of radiative heat transfer in water sprays

A numerical method is developed for the transport of polychromatic radiation in polydisperse sprays. The method is implemented within a wide-band radiation solver using the Finite Volume Method. Mie theory is used to compute the absorption and scattering characteristics of the water droplets. The solver is designed to be computationally effective because the simulations of fire scenarios are inherently time-dependent and the radiative transport equation must be solved many times. The model is compared with two sets of experimental data, and a discussion of the results is presented.     

室内空气自然对流换热的数值模拟研究

应用PHOENICS软件对自然对流换热条件下室内空气温度场和速度场进行了数值模拟,并对温度场的模拟结果进行了实验验证。结果表明,模拟计算值与实验值吻合得较好。     

Numerical and experimental study on heat pump water heater with PCM for thermal storage

An air source heat pump water heater with phase change material (PCM) for thermal storage was designed to take advantage of off-peak electrical energy. The heat transfer model of PCM was based upon a pure conduction formulation. Quasi-steady state method was used to calculate the temperature distribution and phase front location of PCM during thermal storage process. Temperature and thermal resistance iteration approach has been developed for the analysis of temperature variation of heat transfer fluid (HTF) and phase front location of PCM during thermal release process. To test the physical validity of the calculational results, experimental studies about storing heat and releasing heat of PCM were carried. Comparison between the calculational results and the experimental data shows good agreement. Graphical results including system pressure and input power of heat pump, time-wise variation of stored and released thermal energy of PCM were presented and discussed.