真空管直膨式太阳能热泵系统性能分析

该文将真空管集热器与直膨式太阳能热泵结合,提出一种真空管直膨式太阳能热泵系统。实验研究典型工况下太阳辐照度、循环水温度对系统性能的影响,并探讨压缩机变频条件下系统的动态性能。结果表明,提高太阳辐照度、降低循环水温度有利于提高系统性能,在太阳辐照度为850 W/m2,循环水温度为55℃时系统取得最大COP,为5.36。压缩机频率为42 Hz的系统COP为4.08,较45、47、50 Hz分别提高1.23%、8.5%、13.6%。     

直膨式太阳能热泵制热性能的对比研究

直膨式太阳能热泵(direct expansion solar assisted heat pump,DX-SAHP)可直接吸收利用太阳能,进而提高热泵的蒸发温度和性能系数(COP),有利于改善热泵的热性能和结霜。本文在带有太阳模拟发射器的焓差实验室中建立直膨式太阳能热泵和常规直彭热泵的对比实验,对不同条件下的热泵系统参数进行测量并进行性能对比和分析。实验结果显示,直膨式太阳能热泵能够吸收太阳能,在辐照度分别为100和200 W/m~2的工况下,系统制热功率比无辐照时的制热功率分别提高9.8%和21.8%,COP分别提高11.7%和23.7%,且除霜启动延迟23 min;辐照度为200 W/m~2时,直膨式太阳能热泵在环境温度5℃下的制热功率比1℃下的制热功率提高16.92%;在室外温度为1℃,相对湿度为95%的工况下,提高太阳辐照度,可有效减小涂层蒸发器进出口温度的波动,提高蒸发器运行的稳定性。此外,直膨式太阳能热泵在运行过程中吸收的太阳辐射被用来蒸发液态制冷剂工质,导致压缩机进气量增加,系统的制热功率和COP提高。     

R290直膨式太阳能热泵供暖系统实验研究

为分析直膨式太阳能热泵耦合地板辐射供暖系统在北方寒冷地区的实际运行特性,设计并搭建以丙烷(R290)为工质的直膨式太阳能热泵供暖实验平台,分析冬季不同运行工况下环境参数对系统热力性能的影响。实验结果表明：系统可实现室内供暖的稳定性,实验测试期间平均室温保持在16.1～20.8℃之间,热泵系统性能系数(COP)保持在2.57～4.30之间,供暖系统COP保持在2.24～3.98之间。太阳辐照度每增加50 W/m²,热泵系统COP提升4.9%;环境温度每升高1℃,热泵系统COP提升2.4%。太阳辐照度对热泵系统的电子膨胀阀开度和工质质量流量影响较为显著。当终止水温从45℃提升至55℃时,热泵系统COP降低12.2%;而在终止水温为50℃时,供暖系统COP达到最大值3.37。     

小型太阳能热泵地板供暖系统的优化研究

建立了太阳能热泵地板供暖系统的能量分析、可用能分析数学模型,模拟了上海供暖期的气候条件,给出了系统各部件的可用能损失情况。着重从太阳能集热器并联的组数出发对系统进行了优化研究,并给出了系统供暖性能系数和可用能效率,为该系统的设计及应用提供参考。     

并联式太阳热泵热水器中热泵子系统性能研究

对太阳热泵热水器中的热泵子系统建立了相应的数学模型,并对热泵子系统的循环性能进行了研究。研究表明,循环水量对热泵子系统的性能系数、压缩机功耗、加热时间以及保温水箱的实际终了加热温度有较大的影响。     

基于实验数据的复叠式高温热泵系统先进

为了研究复叠式高温热泵系统各部件火用损分布特性及其产生的原因以指明系统优化方向,通过搭建实验台,实现了90 ℃的大温差升温(30~120 ℃)。基于实验数据,分别采用常规火用分析和先进〖HT5”,7〗火用分析（advanced exergy analysis）方法对复叠式热泵系统进行分析。结果显示：高温压缩机和低温压缩机的火用损失最大,系统的内源火用损失占总火用损失的93.73%,可避免火用损失占总火用损失的70.79%,表明火用损失主要来自于部件本身,且部件的改进潜力很大;高温压缩机、低温压缩机和高温冷凝器的内源可避免火用损失最大,在系统优化时应当优先考虑这些部件,可减少系统51.04%的火用损失。     

太阳能热泵供热水系统的实验研究

在青岛地区建立一套太阳能热泵实验系统，此系统可以完成冬季太阳能热泵供暖(启动热泵)和非采暖季太阳能直接供热水实验。进行了太阳能热泵冬季供暖的实验研究，测得热泵机组的平均供热系数COP＝2．71。     

直膨式太阳能热泵热水器的仿真分析

基于直膨式太阳能热泵热水器的热力循环,在建立太阳集热器/蒸发器和冷凝器的分布参数数学模型、压缩机和热力膨胀阀的集总参数数学模型的基础上,用能量平衡和质量平衡等约束条件将四大部件结合起来并进行求解。理论计算结果与若干典型工况下的实验数据对比表明:集热器平均集热效率的平均相对误差为4.6%,热水得热量、压缩机功耗、COP等指标的平均相对误差都在1%以内;热水温度、COP和集热器集热效率的理论和实验值的瞬时变化规律吻合良好,从而验证了此仿真数学模型的准确性。     

厨房余热回收热电热泵储水式热水器的研究

在热电热泵热力学分析的基础上,设计研制了一台用于回收公共厨房排气余热、容积为36L的热电热泵储水式热水器,该装置采用热管散热器对热电热泵冷、热端散热,在回收厨房余热的同时制取生活热水.针对该热电热泵储水式热水器,对其制热性能进行实验研究,结果表明:热电热泵冷、热端温差是影响热电热泵制热性能的重要因素:排气温度越高,热水温度越低,则冷、热端温差越小,制热系数越大.在此基础上,对热电热泵储水式热水器进行优化,并对样机的性能进行测试,结果表明:工作电压对热水加热时间影响较大,工作电压越大,加热时间越短;在电压20V时将热水从28℃加热到46℃,样机相比普通电热水器节省电耗30%以上.     

提高水源热泵机组效率的技术条件分析

以热力学完善度为评价指标,分析水源热泵在标准工况下各部件的不可逆损失程度,其中由压缩机和换热器引起的不可逆损失占总不可逆损失的80%以上。在此基础上,针对水源热泵的特点,对几种能提高其能效水平的技术进行定性和定量分析,结果表明均能有效提高机组的热力学完善度。对采用这些技术的水源热泵机组进行的测试中,制冷,45℃、55℃制热工况下,性能系数分别达到6.64、4.79和3.99。对市场上的部分水源热泵产品样本进行统计分析,结果表明制冷和制热工况的性能水平较低,热力学完善度平均值分别为0.270和0.423,绝大部分产品的性能提升空间超过20%。     

不同朝向玻璃窗太阳辐射得热系数模拟与实验研究

建立了太阳辐射得热系数的计算模型,并搭建了测量窗户太阳辐射得热系数的实验台,得到了玻璃窗的太阳辐射得热系数的实验值和模拟值,两者吻合度很好.结果表明:太阳辐射得热系数与太阳入射角密切相关,不同朝向玻璃窗的太阳辐射得热系数随着太阳入射角有规律地变化.当玻璃窗朝南时,一天之内太阳辐射得热系数先增大,中午时达到最大值而后减少;当玻璃窗朝西时,太阳辐射得热系数上午基本保持不变,而后减少(大概中午时分达到最小值),然后逐渐增大;玻璃窗朝东时太阳辐射得热系数变化情况与西向相反;当玻璃窗表面没有太阳直射辐射时,太阳辐射得热系数基本保持不变.     

Self-consistent optical parameters of intrinsic silicon at 300 K including temperature coefficients

An updated tabulation is presented of the optical properties of intrinsic silicon, of particular interest in solar cell calculations. Improved values of absorption coefficient, refractive index and extinction coefficient at 300 K are tabulated over the 0.25-1.45 μm wavelength range at 0.01 μm intervals. The self-consistent tabulation was derived from Kramers-Kronig analysis of updated reflectance data deduced from the literature. The inclusion of normalised temperature coefficients allows extrapolation over a wide temperature range, with accuracy similar to that of available experimental data demonstrated over the −24 °C to 200 °C range.     

An analysis of geometrical shapes for PV module glass encapsulation

In this work we simulate structured-surface covers of photovoltaic modules with different patterns in order to compare the optical performance (light trapping) of these patterns at different conditions. To achieve this, we use a new software application with an optical calculus engine. Although the primarily reflected light represents a small percentage of the total incoming energy at normal incidence and some part of that fraction will be lost due to Fresnel and absorption losses, there is a substantial increase of the final energy reaching the photocell, specially for large angles of light incidence. In particular, we analyze two different covers: an abrupt-shaped pattern of triangular form and a smoothed-shaped pattern of sinusoidal form in order to evaluate and compare their light transmission properties. We study both structures by varying their geometrical parameters, and also by considering different angles of the incoming light, and different absorption coefficients of the materials. We conclude that the use of these types of covers can improve the performance of regular photocells molding these structures in their encapsulation.     

太阳能热利用系统能势匹配程度的对比分析

基于太阳能热利用系统,建立能势分析模型,对太阳能聚光过程、光热发电、光热化学等主要环节进行能量分析和能势分析,并对光热发电、光热化学2种技术路线进行对比。结果表明太阳能与吸热工质能势不匹配是太阳能热利用系统效率的关键限制因素,热功转化、热化学过程的不可逆性相对较小。现有太阳能光热、光热化学热利用系统的效率均较低,有较大的提升潜力。     

A TRANSPARENT INSULATION MATERIAL FOR SOLAR COOKERS AND COLLECTORS

A Transparent Insulation Material (TIM) was manufactured from plastic film and shown to reduce the cover normalised heat loss coefficient, U/η₀ by over 50% relative to a double-glazed cover system. Such a TIM could be made from polyester film to produce a stagnation-proof and cost-effective cooker which would have greater chance of adoption than less efficient cookers currently made. A cover produced in this fashion would have a normalised loss coefficient, U/η₀, of approximately 3 W/m²K.     

Natural convective heat transfer in trapezoidal enclosure of box-type solar cooker

This paper presents simple thermal analysis to evaluate the natural convective heat transfer coefficient, h_c12 for a trapezoidal absorber plate-inner glass cover enclosure of a double-glazed box-type solar cooker. Several indoor simulation experiments in steady state conditions have been performed to measure the temperatures of absorber plate, inner and outer glass covers, ambient air, electrical input supply and wind speed. The experimental data has been correlated by an equation of the form, Nu = CRaⁿ. The values of the constants C and n, obtained by linear regression analysis are used to calculate the convective heat transfer coefficient. The heat transfer analysis predicts that h_c12 varies from 4.84 to 6.23 W m^{−2 o}C⁻¹ for the absorber plate temperature from 54 to 141 ^oC. The results of h_c12 are compared with those of rectangular enclosure for the same absorber-inner glass cover temperatures and gap spacing. The study reveals that the values of convective heat transfer coefficient and top heat loss coefficient for rectangular enclosure are lower by 31–35% and 7% respectively.     

Evaluation of temperature characteristics of high-efficiency InGaP/InGaAs/Ge triple-junction solar cells under concentration

Temperature characteristics of the open-circuit voltage (V_oc) were investigated in the temperature range from 30°C to 240°C for the InGaP/InGaAs/Ge triple-junction cells. Also, single-junction cells that had the similar structure to the subcells in the triple-junction cells were studied. In the high-temperature range (from 170°C to 240°C), the temperature coefficients of V_oc of the InGaP/InGaAs/Ge triple-junction solar cell (dV_oc/dT) were different from those in the low-temperature range (from 30°C to 100°C). This is because photo-voltage from the Ge subcell becomes almost 0 V in the high-temperature range. It was found that the open-circuit voltage of a Ge single-junction cell reduced to almost 0 V temperatures over 120°C under 1 sun condition.     

Annual output estimation of concentrator photovoltaic systems using high-efficiency InGaP/InGaAs/Ge triple-junction solar cells based on experimental solar cell's characteristics and field-test meteorological data

The temperature dependences of the electrical characteristics of InGaP/InGaAs/Ge triple-junction solar cells under concentration were evaluated. For these solar cells, conversion efficiency (η) decreased with increasing temperature, and increased with increasing concentration ratio owing to an increase in open-circuit voltage. The decrease in η with increasing temperature decreases with increasing concentration ratio. Moreover, the annual output of a concentrator system with a high-efficiency triple-junction cell was estimated utilizing the experimental solar cell's characteristics obtained in this study and field-test meteorological data collected for 1 year at the Nara Institute of Science and Technology, and compared with that of a nonconcentration flat-plate system.     

整体式太阳热水器在寒冷气候条件下的冻结厚度与热损系数U值及水层深度的关系

利用一维焓法建立了第三类边界条件下有限厚度的水存在自然对流时的冻结过程的理论模型，并利用类似于反问题的方法。结合计算和实验的手段确定了热损系数U值，所建模型和计算结果通过不同的实验条件得到了验证。该模型可用来确定在寒冷气候条件下整体式（ICS）太阳热水器的冻结厚度与热损系数U值及水层深度的关系，并根据国内一些城市冬季的气象参数，给出了典型的计算结果，所得结果可对ICS太阳热水器的设计及对透明盖板材料和选择性涂层的选用提供参考。     

Thin layer solar drying and mathematical modeling of mulberry

In this study, drying parameters of mulberry grown in Elaz?? were investigated as experimental and theoretical using solar dryer system. The drying experiments were conducted at seven different drying mass flow rates varied between 0.0015 and 0.036 kg s^?1. As results of the drying experiments were conducted at different drying mass flow rates, it was shown that the drying time was decreased with the drying mass flow rate. This paper also presents a new mathematical modeling of thin layer solar drying of mulberry samples. In order to estimate the suitable form of solar drying curves, 10 different mathematical models to be in the literature and new model were applied to the experimental data and compared according to their correlation coefficients (R) and chi‐squared (χ²), which were predicted by non‐linear regression analysis using the Statistica Computer Program. It was concluded that the Midilli model and the newly developed model represent drying characteristics better than the other models. The effective moisture diffusivity values were in the range 3.47×10^?12–1.46×10^?9 m² s^?1. Copyright © 2009 John Wiley & Sons, Ltd.