两种新型太阳能空气集热器热性能研究

研究两种采用冲缝吸热板的渗透式太阳能空气集热器,对Ⅱ型集热器建立传热数学模型,模拟结果与实测结果吻合较好,验证数学模型可以作为理论研究的基础。分别模拟研究结构参数、运行参数对两种集热器热性能的影响。当集热器空腔内空气来源于室外环境时,两种集热器的集热效率均随太阳辐射照度的增大而增加,均随室外风速和环境温度的增大而减小;Ⅰ型集热器的集热效率随太阳辐射照度、室外风速和环境温度的变化率高于Ⅱ型集热器;当玻璃盖板透过率大于0.69时,Π型集热器的集热效率高于Ⅰ型集热器。     

椭球面冲孔吸热板太阳能空气集热器性能模拟

提出采用椭球面冲孔吸热板的渗透型空气集热器,模拟分析进风量、太阳辐照度、进口空气温度、环境温度、冲孔尺寸对空气集热器出口空气温升、集热效率的影响。冲孔尺寸一定时,在进风量、太阳辐照度、进口空气温度、环境温度变化范围内,集热效率均可达到50%以上。进风量、太阳辐照度、进口空气温度、环境温度、冲孔进口半径一定时,存在最佳冲孔出口半径,使出口空气温升、集热效率达到最大。较小的冲孔进口半径可获得较高出口空气温升、集热效率,但也增大了空气阻力,提高了加工难度,因此应选取适当的冲孔进口半径。     

半圆形波纹吸热板太阳能空气集热器数值模拟

以采用半圆形波纹吸热板的平板型太阳能空气集热器(以下简称集热器)作为研究对象,在风道进口空气温度为276 K、外界空气温度为273 K条件下,采用Fluent软件,模拟分析半圆形波纹吸热板的半圆半径(变化范围为5～30 mm)、风道进口空气流速(变化范围为1. 0～3. 0m/s)对风道内空气温度分布(包括风道出口空气温度)、集热器集热效率、空气压力损失的影响。集热器由半圆形波纹吸热板平均分为上下风道(分设空气进出口)。总体上,上下风道内空气温度均沿着流动方向逐渐升高,下风道的空气温度高于上风道。风道进口空气流速为2. 0 m/s时,随着半圆半径的增大,上下风道空气出口温度均呈增大趋势,集热效率也随之增大,说明增大半圆半径对增强空气扰动的效果明显。半圆半径为30 mm时,随着风道进口空气流速的增大,上下风道出口温度均呈下降趋势,集热效率与空气压力损失均呈增大趋势。在选取风道进口空气流速时,除考虑集热效率外,空气压力损失也是需要考虑的因素,这关系到送风机的耗电与集热器的承压能力。     

真空管太阳能空气集热系统阻力影响因素研究

通过对真空管太阳能空气集热系统内部流动过程的分析,建立了集热系统阻力计算模型,分析了不同设计参数下真空管太阳能空气集热器、串联集热系统阻力变化规律。结果表明:随着集热工质温度升高,集热器阻抗呈指数减小趋势;各影响因素中,串联集热器数量和工质流量对系统阻力影响最大,集热系统各组集热器阻力随串联集热器数量增加呈增长率减小的增大趋势,随质量流量增大呈指数增大趋势,最大值为最小值的3.6倍。此外,系统阻力随环境温度、太阳辐照度、进口温度升高呈线性增大趋势,其中环境温度对系统阻力的影响可忽略不计。通过该研究建立的真空管太阳能空气集热系统阻力计算模型及总结得到的单位面积集热器阻力计算表,可为该集热器、集热系统阻力理论计算提供便捷可靠的依据。     

新型渗透式太阳能空气集热器性能影响参数

对采用冲缝吸热板的渗透式太阳能空气集热器,以集热效率为目标函数,模拟研究结构参数、运行参数对其热性能的影响。集热效率随送风量增大而增长,但增长趋势是逐渐减缓的;集热效率随室外风速、冲缝当量直径和集热器长度增大而下降,其中,集热效率随室外风速和集热器长度下降的趋势逐渐增强,随冲缝当量直径下降的趋势逐渐变缓。     

闭式热源塔换热性能实验研究

建立了闭式热源塔热泵实验系统,实验研究了不同空气温度和相对湿度、溶液流量、风量下闭式热源塔换热性能的变化规律。结果表明:闭式热源塔的总吸热量在7 kW以上,总吸热量随空气温度、相对湿度和溶液流量增大而增大,注重潜热能的利用能有效地增加总换热量;热源塔能效比随空气温度和相对湿度的升高而增大,随溶液流量增大而减小,在满足吸热量的前提下应减小风机转速以降低能耗。     

四种交叉V型吸热板-底板太阳能空气集热器热性能的数值模拟对比分析

作为最常用的一类平板型空气集热器,V型波纹吸热板空气集热器近年来被广泛应用和研究.采用相同几何尺寸(长2m,宽1m)的波形板,构成四种不同流道的交叉V型吸热板-底板太阳能空气集热器,应用太阳载荷模型,利用FLUENT软件,对集热器在倾角为30°,入口空气流量为60m3/h的工况进行了三维数值模拟,得到集热器不同位置的温度场、吸热板中心宽度0.5m处的平均努赛尔数和瞬时效率,并对其进行了对比分析,得出空气集热器的V型吸热板横向放置、底板纵向放置结构的瞬时效率最高.     

双风道回风式太阳能空气集热器的数值模拟

提出一种带半圆形吸热板的双风道回风式太阳能集热器,上层风道是由PC盖板与半圆形吸热板组成的空间,室外空气进入上层风道后,在上层的10个独立小风道中流动;下层风道是由半圆形吸热板和隔热层组成的空间。PC盖板为半透明介质,太阳辐射热量主要由吸热板吸收后,通过对流换热将热量传递给上、下层风道内的空气。上层风道内的空气通过与吸热板进行对流换热以及吸收太阳辐射热量获得热量,其中与吸热板的对流换热占主导。半圆形吸热板增加了空气的扰流,使换热更加充分。对该集热器建立物理模型,利用Fluent软件进行数值模拟。结果表明,对上下层风道进风速度相同工况:太阳能空气集热器的出风温度与进风速度有关,进风速度越大,出风温度越低。当进风速度为0. 5～2. 0 m/s,上层风道的进风温度设定为273 K,下层风道的进风温度设定为291 K时,上层风道的最高出风温度可达374. 47 K,下层风道的最高出风温度可达343. 38 K。上下层风道进风速度相同时,进风速度由0. 5m/s增大到2.0m/s时,集热器的瞬时集热效率随之增大,但增大的幅度逐渐降低。对上下层风道不同进风速度工况:当下层风道的进风速度不变时,上层风道的进风速度越大,集热器的瞬时集热效率越高。当上层风道的进风速度一定时,集热器的瞬时集热效率随着下层风道进风速度的增大先增大后减小。当上层风道的进风速度为2. 0m/s,下层风道的进风速度为1. 0 m/s时,集热效率最高,达63. 08%。当上层风道的进风速度为0. 5 m/s,下层风道的进风速度为2. 0 m/s时,集热效率最低,为41. 87%。     

冬季喷淋工况下闭式热源塔换热性能实验

建立了闭式热源塔热泵实验台。研究了管内溶液进口温度分别对管内溶液出口温度、吸热量和能效比的影响规律,以及水汽比对吸热效率的影响规律,分析了5种因素对闭式热源塔吸热效率和能效比影响的显著性。结果表明:管内溶液出口温度随管内溶液进口温度的升高而升高,吸热量和能效比均随管内溶液进口温度的升高而降低,吸热效率随水汽比的增大而减小;各因素中,风量对吸热效率和能效比的影响最大。     

微通道换热器换热性能的数值模拟及试验

采用数值模拟、试验方法,对微通道换热器的换热性能进行探究(主要考核空气出口温度、换热量、空气压力降、空气侧表面传热系数等)。将空气作为微通道换热器外部高温换热介质,将冷水作为微通道内部低温换热介质,不考虑冷水分配的不均匀性,对比分析在不同迎面风速、冷水进口温度条件下微通道换热器的换热性能。空气进口温度设定为35℃,相对湿度设定为60%(模拟时不考虑空气相对湿度对微通道换热器结露的影响),微通道换热器的迎面风速变化范围为1. 00～1. 75 m/s。冷水流量设定为1 m~3/h,冷水进口温度变化范围为5～8℃。空气出口温度、换热量、空气压力降、空气侧表面传热系数随迎面风速、冷水进口温度的变化趋势模拟与试验基本一致,由于试验条件下微通道换热器翅片易出现结露,使得试验条件下的空气压力降大于模拟结果。冷水进口温度为5℃时,空气出口温度、换热量、空气压力降、空气侧表面传热系数均随迎面风速的增大而增大。迎面风速为1. 5 m/s时,空气出口温度随冷水进口温度的增大而增大,换热量、空气压力降、空气侧表面传热系数均随冷水进口温度的增大而减小。     

Thermal performance analysis of the glass evacuated tube solar collector with U-tube

In this paper, based on the energy balance for the glass evacuated tube solar collector with U-tube, the thermal performance of the individual glass evacuated tube solar collector is investigated by analytical method. The solar collector considered in this study is a two-layered glass evacuated tube, and the absorber film is deposited in the outer surface of the absorber tube. The heat loss coefficient and heat efficiency factor are analyzed using one-dimensional analytical solution. And the influence of air layer between the absorber tube and the copper fin on the heat efficiency is also studied. The results show that the function relation of the heat loss coefficient of the glass evacuated tube solar collector with temperature difference between the absorbing coating surface and the ambient air is nonlinear. In the different ambient temperatures, the heat loss coefficient of the solar collector should be calculated by different expressions. The heat efficiency factor will be subject to influence of air layer between absorber tube and the copper fin. Specially, the influence is remarkable when the heat loss coefficient of the collector is large. When the synthetical conductance amounts to 5 W/m K, the solar collector efficiency decreases 10%, and the outlet fluid temperature decreases 16% compared with the case which the air thermal resistance is neglected. And the surface temperature of the absorbing coating increases 30 °C due to the effect of air thermal resistance. So the surface temperature of the absorbing coating is an important parameter to evaluate the thermal performance of the glass evacuated tube solar collector.     

U型管式全玻璃真空管太阳集热器的热性能

在U型管式全玻璃真空管集热器能量平衡分析的基础上，推导了集热器热损系数、效率因子等性能参数计算公式，其理论计算结果与实验数据吻合良好。计算分析表明：真空管热损系数与吸热管温和环境温度之差是非线性关系，将两者的计算关系式按环境温度分段整理将使计算结果更接近实际;涂层发射比对集热器效率影响较大，降低涂层发射比是提高集热器效率的有效途径;采取适当的措施降低吸热管与肋片接触热阻后，采用U型管连接方式不会对热水系统集热器效率造成太大影响。     

太阳能辅助地源热泵供热运行特性研究

介绍了太阳能辅助地源热泵,对其各装置性能进行了研究。分析了地下埋管换热器进出口水温及有、无蓄热水箱对太阳能辅助地源热泵性能的影响。太阳能辅助地源热泵制热性能系数随地下埋管换热器进口水温的升高呈下降趋势,随其出口水温的升高呈上升趋势。随地下埋管换热器出口水温升高,蒸发器传热量增大。当太阳能辅助地源热泵中无蓄热水箱时太阳能集热器的瞬时集热效率高于有蓄热水箱时的瞬时集热效率。就总体效果而言,有蓄热水箱要优于无蓄热水箱,这样可使地源热泵运行更加稳定。     

Numerical model of natural convective heat transfer within a solar dryer using an indirect double pass collector

The double pass collector is one of the most efficient means of drying crops because heating of air takes place from both sides of the absorber plate. To investigate the performance, a double pass natural convection solar dryer was fabricated for experimentation; the results were collected and used to develop a validated numerical model using MATLAB. The experiments were undertaken during February–March 2016 in Salem Tamil Nadu, India over 10 sunshine days. The simulation was carried using the developed model under the measured ambient conditions. The results showed that the mathematical model could predict the performance of the double pass collector for a particular ambient condition to an uncertainty of ±5%. This model could be used to optimise the performance of the collector so that we can predict and investigate the actual performance of the collector with the various optimised designs before fabricating the dryer.     

Collector characterisation and heat loss tests on a novel batch solar water heater with CPC reflector for households

ABSTRACT

This solar water-heating unit is an integration of the older concept of batch water heating with the modern trends in solar water-heating technologies i.e. incorporating a concentrator in the design. The concentrator used is the compound parabolic type (CPC) which is a non-imaging device having wider acceptance angle (64°) and supported on a wooden cradle, which comprises the two arms of the parabola. To suppress the heat loss, an air gap has been introduced in the arms of the CPC. The collector is a single larger diameter drum which serves both as an absorber and storage unit positioned at the focus of CPC. The parametric study of the model showed the thermal efficiency of the collector as high as 38% and maximum water temperature attained was 53°C. Heat loss tests performed on the collector on a 24-hr cycle period showed good long time performance estimates. The response time of collector computed and performance characteristic curve plotted to predict system response under any given conditions of solar insolation and ambient temperature.     

Experimental energy and exergy analysis of a double-flow solar air heater having different obstacles on absorber plates

This paper presents an experimental energy and exergy analysis for a novel flat plate solar air heater (SAH) with several obstacles and without obstacles. For increasing the available heat-transfer area may be achieved if air is flowing simultaneously and separately over and under the different obstacle absorbing plates, instead of only flowing either over or under the different obstacle absorbing plates, leading to improved collector efficiency. The measured parameters were the inlet and outlet temperatures, the absorbing plate temperatures, the ambient temperature, and the solar radiation. Further, the measurements were performed at different values of mass flow rate of air and different levels of absorbing plates in flow channel duct. After the analysis of the results, the optimal value of efficiency is middle level of absorbing plate in flow channel duct for all operating conditions and the double-flow collector supplied with obstacles appears significantly better than that without obstacles. At the end of this study, the exergy relations are delivered for different SAHs. The results show that the largest irreversibility is occurring at the flat plate (without obstacles) collector in which collector efficiency is smallest.     

两种手段提升太阳能新风热利用效率的研究

严寒地区居住建筑面临较为严重的冬季新风不足问题,太阳能新风系统是改善室内空气品质的一种重要手段。研究目的:了解空气流道厚度降低和使用双层玻璃盖板对于提升基础型太阳能新风集热器效率的实际效果。方法:通过搭建太阳能新风集热器实验平台,自制单层、双层玻璃盖板太阳能新风集热器,对比研究空气流道厚度(10mm和30mm)以及不同玻璃盖板层数对集热器效率的影响,并对不同工况下的出口温度和逐时效率进行监测和分析。结果表明:改小集热器空气流道厚度之后平均集热效率上升了10.8%,使用双层玻璃盖板之后平均集热效率上升了7.5%。双层玻璃盖板在低温下能够进一步发挥保温优势,减少了玻璃盖板表面的热损失。结论:减小空气流道厚度,采用双层玻璃盖板具有明显的实际效果,太阳能新风系统具有很好的推广应用潜力。     

A theoretical study of Cu-H2O nano-fluid effect on heat transfer enhancement of a solar water heater

In the present work, an attempt has been made to enhance the heat transfer in a solar water heater by using Cu nano-particles dispersed in water for various concentrations ranging from 0% to 5%. Considerable improvement in the solar collector efficiency is obtained by increasing the nano-particle concentration up to 17.5 for a concentration of 5% and for a mass flow rate ratio of 10. The outlet water temperature increases by increasing the nano-particle concentration up to 8.35% for a concentration of 5% and for a mass flow rate ratio of 5. The study showed that the solar heater collecting area takes into account significant factors for increasing the outlet temperature. An increase in the collecting area of the solar water heater by 6 times could increase the water temperature by 39% for a 5% nano-particle volume fraction. The helical heat exchanger effectiveness is increased up to 65.71 for a concentration of 5% for a mass flow rate ratio of 10.     

直膨式太阳能热泵系统仿真

随着太阳能热利用和热泵技术的成熟及商品化,直膨式太阳能热泵技术将太阳能资源的清洁性、可再生性等特点和热泵系统的节能、高效的优点相结合,极具研究价值。但是目前直膨式太阳能热泵不能产品化推广的主要限制因素是系统设计不合理、运行不稳定、整体性能不佳等问题。现以直膨式太阳能热泵系统的优化和设计匹配为研究目标,同时,建立压缩机、集热器/蒸发器、热力膨胀阀、冷凝器及储热水箱的数学模型。从理论上分析集热器中集热面积、太阳能辐照度、环境温度、压缩机容积及冷凝温度等因素对直膨式太阳能热泵系统热工性能的影响,通过系统仿真及实验研究系统的整体热力性能,并在此基础上给出改善系统性能的建议。     

Numerical and experimental analysis of heat and moisture content transfer in a lean-to greenhouse

In this paper, heat transfer and moisture content in a lean-to passive solar greenhouse has been studied. A mathematical model based on energy equilibrium and a one-dimensional mathematical model for the unsaturated porous medium have been founded and developed to predict the temperature and moisture content in soil and the enclosed air temperature in the greenhouse. On the condition that plant and massive wall is neglected, the air is mainly heated by the soil surface in the greenhouse, which absorbs the incident solar radiation. With increase in depth, the variation of the temperature and moisture content in soil decreases on account of ambient, and the appearance of the peak temperature in soil postpones. All results should be taken into account for a better design and run of a greenhouse.