直热式空气源CO2热泵热水器系统运行特性试验研究

设计了一种直热式空气源CO₂热泵热水器系统,利用试验研究的方法研究了环境温度、气冷器冷却水入水温度及流量对系统性能的影响。试验结果表明:设计的空气源CO₂热泵热水器系统,其系统能效系数(COP_h)基本达到了国家标准;环境温度、气冷器冷却水入水温度以及流量对系统COP_h、系统制热量以及气冷器出水温度的影响显著。通过调节热泵热水器系统低温热源温度、气冷器冷却水入水温度及流量,可改善系统COP_h,提高系统制热量以及气冷器出水温度。     

Cooling of a heated surface with an impinging water spray

Several important parameters, such as liquid mass flux, droplet size distribution, droplet velocity, and heating target conditions (roughness and surface temperature) are involved in the industrial spray cooling heat transfer process. In this study, we investigated the effect of liquid mass flux, heating target roughness, and the droplet size on the droplet wall direct contact heat transfer in spray cooling phenomena. Three different conditions of surface roughness were investigated. The measurement of test surface temperature was performed using a non-intrusive method, i. e., using an infrared thermometer. The droplet size distribution of water spray was measured with Malvern 2600. The results indicated that the most influential parameters were the liquid mass flux and the surface roughness. The droplet size and the velocity played a less important role in the direct contact heat transfer because the interactions between droplets were very strong in a dense spray. The smooth surface showed the highest heat transfer among the surfaces tested. At high air pressure ([7] kPa), however, the degree of roughness did not affect much the heat transfer rate.     

A study on the effects of system pressure on heat and mass transfer rates of an air cooler

In the present paper, the effects of inlet pressure on the heat and mass transfer rates of an air cooler are numerically predicted by a local analysis method. The pressures of the moist air vary from 2 to 4 bars. The psychrometric properties such as dew point temperature, relative humidity and humidity ratio are employed to treat the condensing water vapor in the moist air when the surface temperatures are dropped below the dew point. The effects of the inlet pressures on the heat transfer rate, the dew point temperature, the rate of condensed water, the outlet temperature of air and cooling water are calculated. The condensation process of water vapor is discussed in detail. The results of present calculations are compared with the test data and shows good agreements.     

基于毛细管空调系统的试验研究

以能源与动力工程实验中心节能减排实验室为背景,对毛细管空调系统进行制冷及除湿实验。监测室内温湿度在水平和垂直方向上的温湿度分布情况;并且通过实验确定毛细管重力循环空调柜除湿和换热性能的影响因素及其最佳运行工况。结果表明:在人体的高度范围1.6².0m之间,室内温度维持在26.5℃左右,对人体非常适宜;供水流量在6002.0m之间,室内温度维持在26.5℃左右,对人体非常适宜;供水流量在600⁷00L/h,供水温度在17.5700L/h,供水温度在17.5¹8℃时,进出口空气温差增长的速度最快,重力循环空调柜换热经济性最佳;供水流量在50018℃时,进出口空气温差增长的速度最快,重力循环空调柜换热经济性最佳;供水流量在500⁶00L/h,供水温度在15.5600L/h,供水温度在15.5¹6℃时,出口空气流速增长的速度最快,重力循环空调柜除湿经济性最佳。     

干盘管系统冷冻水流量调节试验研究

通过对独立新风加干式风机盘管空调系统在不同室外工况下的试验研究,分析了冷冻水流量调节对空调系统性能及室内温湿度影响。结果表明,随冷冻水流量增加,系统提供的显热制冷量及潜热制冷量增加,而提供的冷量显热比减少;当冷冻水不能满足新风机组制冷要求时,增加水流量可以明显降低室内冷量显热比,在冷冻水流量满足新风机组制冷要求的基础上增加水流量,对新风机组的制冷量及室内显热比的影响不大;增加冷冻水流量对室内温度影响较大,而对室内相对湿度影响较小。     

小型热泵型蓄能空调水蓄热特性的试验研究

结合蓄能空调系统自身的特点,设计了小型热泵型水蓄能空调装置并进行试验研究。试验结果表明,采用蓄能桶蓄热装置,在热泵机组进行制热性能运行时能有效提高压缩机吸气温度,排气温度也相对较高;在低温制热工况下,系统的最大制热量可以达到额定制热量以上,除霜性能也较优;水蓄热时不同工况下的压缩机吸排气温度以及压缩机功率会有变化,并且在释热状态下运行时,机组的COP有显著提高。由于该系统使用水作为蓄热材料,蓄热量有限。     

Air to air fixed plate enthalpy heat exchanger, performance variation and energy analysis

The thermal performance of a Z shape enthalpy heat exchanger utilising 70 gsm Kraft paper as the heat and moisture transfer surface has been investigated. Effects of different inlet air humidity ratio conditions on the heat exchanger effectiveness and on the energy recovered by the heat exchanger have been the main focus of this investigation. A typical air conditioning cooling coil which incorporates an enthalpy heat exchanger has been modelled for tropical climate. Under test conditions, results have shown that latent effectiveness and the moisture resistance coefficient have strong dependency on the inlet air humidity ratio. Moreover, the latent effectiveness has been found to be strongly dependent on the moisture resistance coefficient rather than the convective mass transfer coefficient. Finally, annual energy analysis for Singapore weather conditions have also shown that energy recovered under variable inlet air conditions is 15% less than that recovered under constant inlet air conditions for the same heat exchanger.     

A study on energy saving of cooling/reheating system using compact heat exchanger

When circulated air passes through the cooling coil in an air-conditioning system, the air is over-cooled to eliminate the moisture and decrease the temperature. The cooled air is then reheated to recover the temperature. The purpose of the present study was to evaluate the performance of a cooling/reheating system with regard to both cooling and reheating energy savings affected by exchanging heat between the cooled air and the reheated air with a compact heat exchanger. The thermal and dehumidification behaviors of the system were evaluated experimentally and then compared with simulation data. The results show that the energy saving rate was as high as 50% under the present experimental conditions and was affected by the face velocity of the heat exchanger, the inlet temperature, the inlet humidity ratio, and the effectiveness of heat exchanger. Furthermore, the experimental data were found to be in fairly good agreement with the simulation data.     

空调-海水淡化复合装置除湿特性研究

对采用氯化锂作为除湿剂的空调-海水淡化复合装置的除湿特性进行了研究。在实验过程中用热泵蒸发器产生的冷量来冷却除湿过程,同时用冷凝器产生的废热来再生稀溶液。分析了各个操作参数对除湿量的影响,得出了当前研究的经验公式。结果表明：除湿量随着空气湿度、除湿溶液的浓度和除湿溶液的流量的增加而增大,而空气温度和溶液温度对除湿量的影响非常小。本文取得的实验数据和经验公式为进一步完善和分析除湿系统的性能提供了可靠依据。     

CO2跨临界水-水热泵系统模拟与试验研究

主要对带节流阀的CO2跨临界水-水热泵系统建立了数学模型,对系统的制热性能进行了模拟计算,并与试验数据做了对比。主要分析了高压侧压力、冷却水和冷冻水的进口温度和流量分别对系统制热系数和制热量的影响。结果表明,模拟计算结果与试验测试值的一致性较好,从而验证了模型的可信度。模拟所得对应最大制热系数的最佳高压侧压力与实验结果存在一定的偏差。系统的制热性能系数和制热量随着冷却水进口温度的升高而降低,随冷冻水进口温度的升高而增大;而且都随着冷却水和冷冻水流量的增加呈现出升高趋势。     

Measurements of air temperature distribution and optimum cooling condition inside the computer system

Measurements of the temperature distributions of the cooling air flow inside a computer system have been made. An investigation of the optimum cooling condition for the computer system has also been made. Seventy-one K-type (Chromega-Alumega) thermocouples were used to measure distributions of the air flow temperature inside the computer system. They were calibrated against the standard platinum resistance thermometer (PRT) in a constant water circulating bath within an accuracy of ± 0.15 °C. It was found that the number and position of cooling fans as well as their operating condition, whether air intake or air discharge, can greatly influence the cooling effectiveness in the computer system. The results show that the flow rate of intake air should not be higher than that of the discharge air for the most effective cooling. It follows that the optimum cooling has been achieved inside the computer when the three fans are positioned in the inlet front, outlet back, and outlet top in the computer, respectively. Under these conditions, not only is the average temperature inside the computer system maintained at an appropriate level, but the most effective cooling around the central processor (CPU) and graphic card which are responsible for the largest amount of heat dissipation can be accomplished. This paper was recommended for publication in revised form by Associate Editor Man-Yeong Ha Dae Hee Lee received a B.S. degree in Mechanical Engineering from Hanyang University in 1984. He then went on to receive his M.S. and Ph.D. degrees from University of California at Davis in 1984 and 1987, respectively. Dr. Lee is currently a Professor at the School of Mechanical Engineering and a Dean of Academic Affairs at Inje University in Korea. Dr. Lee’s research interests are in the area of Convection Heat Transfer, Liquid Crystal Thermography, Co-generation, and Renewable Energy.     

毛细管平面辐射空调系统的优化控制

针对传统空调系统中主要通过对流换热的方式来消除室内的热湿负荷造成能源品味上的浪费问题,将毛细管辐射换热技术应用于空调系统中,开展了由毛细管承担室内显热负荷而由新风系统承担全部的室内潜热负荷空调处理方案的分析,建立了空调房间温度与湿度之间相互独立的控制方法,并提出了采用冷冻水变流量优化控制法解决毛细管换热中的结露问题.在新风系统运行时,毛细管辐射供冷系统停止供水;新风系统除湿结束后,毛细管辐射供冷系统开始供水,在此基础上对毛细管辐射供冷系统采用间歇性流量控制方案进行了评价.研究结果表明,该控制方案不仅简单易行,而且节约能源.     

Heat transfer and pressure drop amidst frost layer presence for the full geometry of fin-tube heat exchanger

The present study numerically solves the flow and thermal fields in the full geometry of heat exchanger modeling with frost layer presence on the heat exchanger surface. The effects of air inlet velocity, air inlet temperature, frost layer thickness, fin pitch, fin thickness, and heat exchanger shape on the thermo-hydraulic performance of a fin-tube heat exchanger are investigated. Heat transfer rate rises with increasing air inlet velocity and temperature, and decreasing frost layer thickness and fin pitch. Pressure drop rises with increasing air inlet velocity and frost layer thickness, and decreasing fin pitch. The effect of fin thickness on heat transfer and pressure drop is negligible. Based on the present results, we derived the correlations, which express pressure drop and temperature difference between air inlet and outlet as a function of air inlet velocity and temperature, as well as frost layer thickness.     

空气处理设备动态换热特性分析

为分析动态变化过程中空气处理设备参数变化对其换热特性的影响,通过建立表冷器的湿工况数学模型,进行了不同进风参数、送风参数下的空气处理设备换热动特性仿真分析,得出了不同的进风干球温度、进风相对湿度、送风干球温度、送风相对湿度和送风量下空气处理设备的动态换热特性曲线,为制定设备节能运行的控制策略提供参考。     

煤矿井下空调蒸发器对流传热特性试验

对恒定控制制冷剂R407C工作温度为9℃、额定制冷量为45k W条件下的蒸发器进行了模拟矿井条件湿空气的对流传热试验。研究结果表明:蒸发器的制冷量随进口空气温度的升高而增加,随进口空气相对湿度的增加而增加;出口空气温降随进口空气温度的升高而增加,随进口空气相对湿度的增加而缓慢降低;对流传热的Nu数随Re数的增加而增加,随进口空气相对湿度的增加而降低。     

板式蒸发式冷凝器传热性能试验研究

搭建了板式蒸发式冷凝器传热性能试验平台,对影响板式蒸发式冷凝器传热性能的主要因素———喷淋水流量、风速、汽液流向以及工艺流体进出口位置进行试验研究。结果表明:空气与水并流时传热效果最好、逆流次之、错流最差;板内冷凝压力随冷却循环水喷淋密度、风速的增大而减小;在各自最佳风速,不同汽液流向操作下,蒸汽对角进出时的热流密度均比蒸汽同侧进出时大。     

空调水系统等效模型的水力特性理论研究

首先对现有采暖空调系统的输送能耗状况及其存在的问题做了深入分析,采暖空调系统的输送系统可等效为异程或者同程式水力模型.然后分别对异程或者同程式水力模型的能量模型、温度模型及压力模型做了深入研究,发现采暖空调系统的设计模型是导致输送系统"大流量、小温差、高功耗"的根本原因.最后提出一种新型空调输送系统的解决方案 ——双冷...     

中央空调水系统中变频控制技术的应用

针对当前中央空调系统中水泵能耗大的问题,阐述了中央空调系统的工作原理和水泵的工作特性,分析了水泵在不同调节方法下的性能变化情况,结果表明,采用变频控制的调速方法更适合于水泵的节能运行和延长使用寿命,同时提出了在冷冻水系统和冷却水系统中分别以回水温度和冷凝器出水温度为控制对象的闭环控制方式,并针对不同的冷凝器出水温度提出了水泵调速的分段控制方法,不仅方法简单、可靠,而且节能效果好。     

管内流体换热性能测试系统

设计了一种测试流体(煤油)管内换热性能的实验系统.该实验系统包括了循环系统、加热系统、冷却系统、增压系统、测量系统(流量测量、压力测量、温度测量)和数据采集系统,各部分做了详细的说明,对其测试原理也作了说明.流体进、出口温度以及预热段流体进口温度都用铠装热偶测量.预热段和实验段都采用电加热方法加热(采用低电压、大电流加热).预热段和实验段都均匀布置20个热电偶测量管外壁温度,电加热管内壁温可通过龙格一库塔方法由外壁温和加热功率求得.该系统也可以用来测量其它流体管内换热性能,还可以用来测量流体的比热;还可以测量流动压降和摩擦阻力系数.     

A new method for field test of the heating capacity of air source heat pumps

The operation performance measurement of the air source heat pumps in the field, in which conditions are complicated and the accuracy could not be ensured, is very crucial for its performance evaluation and improvement. In this investigation, a novel method for measuring the heating capacity of the air source heat pump is established. An auxiliary electric heater is installed along the pipeline between the compressor and the condenser, and the refrigerant temperature difference caused by the heater is gathered to calculate the refrigerant mass flow rate based on the energy conservation. The heating capacity is calculated with the measured data of the refrigerant enthalpy at the inlet and outlet of the condenser and the refrigerant mass flow rate of the compressor discharge pipe. The validation results in laboratory tests show that the measured heating capacity accuracy is within 9.2%. It is also found that the impact of the novel test method on the heating capacity of the air source heat pumps is below 1.7%, and the power consumption of the tested units is increasing of within 1.8% compared with it when the electric heater is off. The refrigerant enthalpy difference method with an electric heater presented in this research can be applied to measure the heating capacity of different air source heat pump air heaters accurately in the field, which will be much helpful to improve the performance for cleaning heating in northern China.