室外气候对空气全热交换器运行效率的影响

在对空气全热交换器在上海市冬季和夏季运行效率进行连续实测的基础上,利用湿度势理论,得到了全热交换器运行效率随室外温湿度变化的规律.     

Experimental and numerical analysis of an earth-air heat exchanger

The need to develop new technologies that allow the use of sustainable alternative sources of energy is increasingly evident. Thus, this work presents an experimental and numerical study of earth-air heat exchangers, which are used to reduce consumption of conventional energy for heating and cooling of built environments through the use of thermal energy contained in the soil. The experiment was conducted in southern Brazil in the city of Viamão, and its results were used to validate the computational modeling of heat exchangers. In the present work, the variation of air temperature inside the ducts, to an annual cycle, was investigated. The numerical solution of the conservation equations of the problem is performed with a commercial code (FLUENT) which is based on the Finite Volume Method (FVM). Turbulence is tackled with the Reynolds Stress Model (RSM). The transient temperature fields predicted numerically was compared with the experimental ones, the highest difference found was lower than 15%. The results showed the validity and effectiveness of the employed computational model, enabling its use for future researches and projects developments about earth-air heat exchangers.     

制冷工况下水平埋管换热器运行试验研究

通过夏季工况的地源热泵运行试验,对运行过程中水平埋管的换热性能参数、试验场地周围气象因素和换热过程中土体的温湿度变化等因素进行实时监测,探讨了地源热泵运行过程中水平埋管换热器热交换性能及其周围土壤的温、湿度场变化规律。研究结果表明,地源热泵间隙运行有利于土壤温度场的恢复,随着停机时间的增加,水平埋管与周围土壤的热交换能力明显提高;气候变化对水平埋管周围土壤的温度场分布具有显著影响,随着埋深的递减,土壤温度受气候变化的影响越明显;水平埋管周围土壤温度的变化幅度随着与埋管距离的增加呈递减趋势,其影响半径为1.0m左右;热交换对水平埋管周围土壤湿度场的影响不明显,但大气降雨引起的地表水入渗对土壤湿度场的分布具有显著影响。     

Experimental investigation on heat transfer characteristics of heat exchanger with bubble fin assistance

ABSTRACT

Heat transfer area per unit volume (m²/m³) of heat exchangers decides the size of the heat exchangers, over the period of years heat exchangers have undergone numerous development in this aspect. One such attractive design is plate heat exchanger which is very compact and has high thermal effectiveness, whereas the flow nature of fluid through this type of heat exchangers is complex. The most common type of plate heat exchanger is chevron type which suffers from large pressure drop (Δp) at higher heat transfer rates, to overcome this problem bubble finned heat exchangers are designed. In this paper the performance of bubble finned heat exchanger is studied with single phase fluid flow condition. The comparative study of finned and no fin configuration shows that the former has 1.8 times higher rate of heat transfer at lower value of Reynold’s number, further the flow remains laminar hence the Δp is minimum.     

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.     

热管换热器在空调系统应用中的节能经济性分析

简要介绍了热管换热器的特点,通过对热管换热器与其他换热器的对比分析,明确了热管换热器在空调热回收领域的优势,并结合工程实例,以实际数据证明了热管换热器在空调节能方面的经济性。     

适用于湿工况的风机盘管简化换热模型

针对半集中式空调系统风机盘管的换热计算问题,通过干湿工况转换方法,设计了一种适用于湿工况的风机盘管换热模型.根据能量平衡和热传递原理,简化了该换热模型,使换热量仅由冷水流量、进水温度、盘管风量和进风温度等独立控制变量确定.在实际风机盘管上进行了仿真验证,得到了不同工作条件下的换热曲线.实验结果表明,该简化换热模型计算精度较高.     

New counter flow heat exchanger designed for ventilation systems in cold climates

In cold climates, mechanical ventilation systems with highly efficient heat recovery will experience problems with condensing water from the extracted humid indoor air. If the condensed water changes to ice in the heat exchanger, the airflow rate will quickly fall due to the increasing pressure drop.     

空调热回收热虹吸管换热器工质的试验研究

针对热虹吸管挟热器样机R22和R32两种工质,做了对比试验研究,得到了不同工况下热虹吸管换热器的温度效率,比较分析表明,模拟计算的模型能够较好地反映热虹吸管换热器的能量回收性能,同时试验分析也验证热虹吸管换热器新型工质R32的性能。     

地源热泵U型竖直埋管换热器性能实验分析

利用已经搭建好的地源热泵实验系统对系统的U型竖直埋管换热器进行实验研究。分析了系统进入非稳态导热的"正规热状况阶段"的特性,对比了夏季连续运行工况下埋管间距为4 m时,单、双U型埋管换热器的换热性能及不同运行方式下埋管换热器的换热性能,探讨了冬、夏两季地源热泵系统的运行性能差异。     

Experimental investigation of solar heating and humidification system based on desiccant bed heat exchanger

In this article, an experimental investigation has been made on a solar heating and humidification system. In this system, an evacuated tube solar water heater is connected to the desiccant bed heat exchanger (DBHE) by connecting pipes. The evacuated tube solar water heater supplies required heat to the DBHE for the regeneration of desiccant material. Various types of solid and composite desiccant materials have been used in the DBHE to investigate their effect on the system performance. It has been found that the system obtained its best performance with silica gel with average humidification rate of 0.63?kg/h. The maximum temperature difference of process air has been found as 16°C at the flow rate of 295.2?kg/h.     

The use of a double heat pipe heat exchanger system for reducing energy consumption of treating ventilation air in an operating theatre—A full year energy consumption model simulation

In two earlier papers [Y.H. Yau, Application of a heat pipe heat exchanger to dehumidification enhancement in tropical HVAC systems—a baseline performance characteristics study, International Journal of Thermal Sciences 46 (2) (2007) 164–171; Y.H. Yau, The analysis of enthalpy change with and without a heat pipe heat exchanger in a tropical air conditioning system, International Journal of Energy Research 30 (15) (2006) 1251–1263], two series of experiments were conducted under controlled conditions to establish the baseline performance characteristics of the heat pipe heat exchanger (HPHX). In the present paper, a complete empirical transient systems simulation program model is assembled to estimate the air states as well as the entire typical meteorological year energy consumption of an operating theatre located in Kuala Lumpur, Malaysia.     

Experimental investigation of two-stage indirect/direct evaporative cooling system in various climatic conditions

Cooling performance of two-stage indirect/direct evaporative cooling system is experimentally investigated in the various simulated climatic conditions. For this purpose, a two-stage evaporative cooling experimental setup consisting of an indirect evaporative cooling stage (IEC) followed by a direct evaporative cooling stage (DEC) was designed, constructed and tested. Due to the wide variety of climatic conditions in Iran, two air simulators were provided to simulate outdoor design condition of different cities in primary and secondary air streams. Results show that under various outdoor conditions, the effectiveness of IEC stage varies over a range of 55–61% and the effectiveness of IEC/DEC unit varies over a range of 108–111%. Aspects of achieving comfort conditions and power saving have been investigated with related excess water consumption. Considering the evaporative comfort zone, this system can provide comfort condition in a vast region in Iran where direct evaporative alone is not able to provide summer comfort condition. More than 60% power saving could be obtained by this system in comparison with mechanical vapor compression systems with just 55% increase in water consumption with respect to direct evaporative cooling systems. This system can fill the gap between direct evaporative cooling systems and mechanical vapor compression systems as an energy efficient and environmentally clean alternate.     

Experimental study of a ground sink direct cooling system in cold areas

A conception with ground as a heat sink directly for cooling of the buildings in cold areas is presented. A corresponding experimental system was constructed in Harbin area and operated in summer in 2006. Some important performance parameters, such as the cooling seasonal performance factor (CSPF) and the average heat rejection rate unit depth of borehole, were obtained and some analyses for the system characteristics are made. The experimental results show that the ground sink direct cooling system (GSDCS) presented has great potentialities in energy saving within a specified region.     

上海地区别墅建筑地源热泵空调系统设计

指出上海别墅建筑常用空调系统存在的问题，分析了在该类建筑中使用地源热泵空调系统的可行性，结合工程设计实例，着重介绍了U型竖埋管地下换热器的设计方法。     

Experimental investigation of the influence of the air jet trajectory on convective heat transfer in buildings equipped with air-based and radiant cooling systems

The complexity and diversity of airflow in buildings make the accurate definition of convective heat transfer coefficients (CHTCs) difficult. In a full-scale test facility, the convective heat transfer of two cooling systems (active chilled beam and radiant wall) has been investigated under steady-state and dynamic conditions. With the air-based cooling system, a dependency of the convective heat transfer on the air jet trajectory has been observed. New correlations have been developed, introducing a modified Archimedes number to account for the air flow pattern. The accuracy of the new correlations has been evaluated to±15%. Besides the study with an air-based cooling system, the convective heat transfer with a radiant cooling system has also been investigated. The convective flow at the activated surface is mainly driven by natural convection. For other surfaces, the complexity of the flow and the large uncertainty on the CHTCs make the validation of existing correlations difficult.