Experimental investigation on the photovoltaic–thermal solar heat pump air-conditioning system on water-heating mode

An experimental study on operation performance of photovoltaic–thermal solar heat pump air-conditioning system was conducted in this paper. The experimental system of photovoltaic–thermal solar heat pump air-conditioning system was set up. The performance parameters such as the evaporation pressure, the condensation pressure and the coefficient of performance (COP) of heat pump air-conditioning system, the water temperature and receiving heat capacity in water heater, the photovoltaic (PV) module temperature and the photovoltaic efficiency were investigated. The experimental results show that the mean photovoltaic efficiency of photovoltaic–thermal (PV/T) solar heat pump air-conditioning system reaches 10.4%, and can improve 23.8% in comparison with that of the conventional photovoltaic module, the mean COP of heat pump air-conditioning system may attain 2.88 and the water temperature in water heater can increase to 42 °C. These results indicate that the photovoltaic–thermal solar heat pump air-conditioning system has better performances and can stably work.     

拓扑优化与仿生设计在空间太阳能电站热设计中的应用

高效热设计与热控制是高功率连续微波无线传能与空间太阳电站(SSPS)领域的研究热点之一,引起了国内外同行专家的高度关注与浓厚兴趣.本文针对欧米伽空间太阳能电站(SSPS-OM EGA)的结构特点及其对热设计与热控提出的巨大挑战,基于拓扑优化与仿生的思想,提出了一种新的热设计策略与方法.首先,联合流体出口边界与流道构型,...     

Study on the thermal protection performance of superalloy honeycomb panels in high-speed thermal shock environments

The thermal protection performance of superalloy honeycomb structure in high-temperature environments are important for thermal protection design of high-speed aircrafts. By using a self-developed transient aerodynamic thermal simulation system, the thermal protection performance of superalloy honeycomb panel was tested in this paper at different transient heating rates ranging from 5°C/s to 30°C/s, with the maximum instantaneous temperature reaching 950°C. Furthermore, the thermal protection performance of superalloy honeycomb structure under simulated thermal environments was computed for different high heating rates by using 3D finite element method, and a comparison between calculational and experimental results was carried out. The results of this research provide an important reference for the design of thermal protection systems comprising superalloy honeycomb panel.     

基于相敏瞬态热反射系统的多层热界面材料的拟合研究

厚度微米级热界面材料的热物性参数,可通过相敏瞬态热反射测量法拟合得出。本文对该方法的原理进行了发展研究:基于数据测量过程中,不同调制频率区间对应在样品中的热穿透深度不同(高频区间内热穿透深度小,低频区间内热穿透深度大),提出针对多层材料,分频率段依次对各层热参数拟合的方法。本方法的途径是通过不同频率区间的选择,沿着热穿透方向依次对各层参数进行拟合,从而减少后层材料未知参数对当前层参数拟合的影响,同时减少对已知参数条件的要求,提高了拟合结果的质量。用本文方法对四层材料样品做了测量及拟合数据对比,结果表明拟合结果相对误差保持在±8%之内,同时对界面热导的信号敏感度进行了分析,发现拟合参数的信号敏感度依赖于频率的选择。     

Measuring the thermal conducitivity of uranin

A convenient experimental method for measuring the thermal conductivity of uranin (fluorecein sodium, C₂₀H₁₀O₅Na₂) is described. Two similar blocks of uranin, produced from a strong uranin/water solution, were exposed to one-dimensional steady-state conduction. It was found that, for a mean bulk temperature ranging from ambient up to 55°C, the uranin has a constant thermal conductivity of 0.43 W/mK. Above these temperatures, the material begins to soften and the thermal conductivity is seen to decrease     

Convective cooling/heating induced thermal stresses in a fluid saturated porous medium undergoing local thermal non-equilibrium

Local thermal non-equilibrium (LTNE) may have profound effects on the pore pressure and thermal stresses in fluid saturated porous media under transient thermal loads. This work investigates the temperature, pore pressure, and thermal stress distributions in a porous medium subjected to convective cooling/heating on its boundary. The LTNE thermo-poroelasticity equations are solved by means of Laplace transform for two fundamental problems in petroleum engineering and nuclear waste storage applications, i.e., an infinite porous medium containing a cylindrical hole or a spherical cavity subjected to symmetrical thermo-mechanical loads on the cavity boundary. Numerical examples are presented to examine the effects of LTNE under convective cooling/heating conditions on the temperature, pore pressure and thermal stresses around the cavities. The results show that the LTNE effects become more pronounced when the convective heat transfer boundary conditions are employed. For the cylindrical hole problem of a sandstone formation, the thermally induced pore pressure and the magnitude of thermal stresses are significantly higher than the corresponding values in the classical poroelasticity, which is particularly true under convective cooling with moderate Biot numbers. For the spherical cavity problem of a clay medium, the LTNE effect may become significant depending on the boundary conditions employed in the classical theory.     

Effect of the storage tank thermal insulation on the thermal performance of an integrated collector storage solar water heater (ICSSWH)

The thermal behavior of an integrated collector storage solar water heater (ICSSWH) is numerically studied using CFD simulations. Based on the good agreement between the numerical results and the experimental data from literature, we propose a geometrical change allowing limiting the main disadvantage of this solar system which is its high night losses due to the non-insulated storage tank surface. A second 3D CFD model of an ICSSWH in which the storage tank is partially insulated is developed and three values of this tank thermal insulated fraction are studied. Numerical results show that the partially insulated tank based ICSSWH presents lower thermal losses during the night and this night thermal losses coefficient is reduced from 14.6 to 11.64 W K^?1 for the tank thermal insulation fraction τ = 1/4. Similarly, the modified system presents the advantage of its lower thermal losses even during the day. Regarding the thermal production, it is seen that the modified system presents higher water temperature at night and that for all the tank thermal insulation fractions. Concerning the operation of this modified system during the day, the water temperature is lower during the day and that up to 16 h but the water temperature which achieves 324 K for the storage tank thermal insulation fraction τ = 1/8 still sufficiently high to satisfy a family hot water needs.     

线圈隔热层对光纤陀螺温度误差的影响分析

针对温度变化所引起的光纤陀螺非互易相移误差,详细研究了隔热材料对减小热漂移误差的作用,并详细比较了使用不同厚度隔热层的光纤陀螺在相同变温历程下的热漂移误差大小以及达到热平衡状态所需的时间。仿真结果表明,当隔热层的厚度由0mm变化到4mm的过程中,热漂移误差的峰值由0.12(°)/h降低到了0.08(°)/h,同时达到热平衡的时间从2 520 s增加到了3 600 s。利用该仿真结果,可以在保证热启动时间满足条件的前提下找到一个最优的隔热层厚度,从而使热漂移误差的峰值最小。     

Laboratory techniques to evaluate thermal conductivity for some soils

The thermal conductivity of two soils was investigated through laboratory studies. These laboratory experiments used the single probe and dual probe methods to measure and compare thermal conductivities. The soils used were classified as sand and loam. Thermal conductivity measured using single probe method ranged from 0.95 to 2.11 for sand and from 0.49 to 0.76 W/m K for loam. Thermal conductivity measured using dual probe method ranged from 0.98 to 2.17 for sand and from 0.51 to 0.78 W/m K for loam. Finally, it was found that sand had higher values of thermal conductivity than loam for all soil conditions studied.     

The phase-lag concept in the thermal behavior of lumped systems

The phase-lag concept in the wave theory of heat conduction is extended to describe the thermal behavior of lumped systems. It is assumed that a phase-lag exists between the convection heat flux from the lumped system and the temperature difference between the lumped system and its surroundings. It is found that the dimensionless delay time τ is an important parameter in specifying the qualitative behavior of the lumped system. The phase-lag concept has no significant effects on the thermal behavior of lumped systems having τ < 1/4. In this case, the classical theory without delay can give an accurate prediction for the system thermal behavior. On the other hand, the phase-lag concept changes the quantitative and qualitative behavior of systems having τ > 1/4 and these changes are enhanced as τ increases. However, it is shown that the thermal behavior of systems having τ > 1/4 violates the second law of thermodynamics. The physical reasoning for this violation is explained. Also, the phase-lag concept is extended to describe the thermal behavior of composite system which consists of two domains each is lumped at different temperature.     

A generalized thermal boundary condition

 A generalized thermal boundary condition is derived to include all thermal effects of a thin layer which is in thermal contact with an adjacent domain. The thin layer may be a stationary or moving solid-skin or fluid-film. The included thermal effects of the thin layer are the thermal capacity of the layer, thermal diffusion, enthalpy flow, viscous dissipation within the layer, convective losses from the layer, and other effects. Six different kinds of thermal boundary conditions can be obtained as special cases of the generalized boundary condition. The generalized boundary condition is given for perfect and imperfect thermal contact between the thin layer and its adjacent domain. The importance of the generalized boundary condition is demonstrated in an example. Received on 23 December 1996     

Efficiency of a radiative-evaporative aircraft thermal protection system

The coupled boundary-value problem of nonstationary heat and mass transfer within the outer thermal insulation layer and the vapor outlet channel of a combined radiative-evaporative thermal protection system is formulated. The overall dimensional and weight characteristics of the system are calculated for a set of its parameters and two specified modes of the external heat flux and pressure variation, schematically modeling hypersonic aircraft flights 30 min and 60 min long with a maximum heat flux of 10⁵ W/m². Combined and passive radiative thermal protection systems are compared under the above-mentioned external conditions. It is shown that both the thickness of the outer thermal insulation layer and the total weight of the combined thermal protection system may be considerably less than the passive equivalents.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 1, pp. 24–36, January–February, 1995.     

A generalized thermal boundary condition for the hyperbolic heat conduction model

 A generalized thermal boundary condition is derived for the hyperbolic heat conduction equation to include all thermal effects of a thin layer, whether solid-skin or fluid film, moving or stationary, in perfect or imperfect thermal contact with an adjacent domain. The thin layer thermal effects include, among others, thermal capacity of the layer, thermal diffusion, enthalpy flow, viscous dissipation within the layer and convective losses from the layer. Six different kinds of thermal boundary conditions can be obtained as special cases of the generalized boundary condition. The importance of the generalized boundary condition is demonstrated comprehensively in an example. The effects of different geometrical and thermophysical properties on the validity of the generalized thermal boundary condition are investigated. Received on 23 May 2001 / Published online: 29 November 2001     

Thermoelastic coupled modeling for a thermal bimorph actuator

This paper presents a theoretical thermoelastic coupled model for a thermal bimorph actuator driven by a harmonically varying thermal load in micro-electro-mechanical systems. The thermoelastic coupling, which arises from the coupling of the strain rate to the temperature field of the heat transport, is considered in this model. The frequency responses are simulated using the theorem of eigenmode expansion. The effects of thermoelastic coupling on the resonant frequency and the quality factor Q for each eigenmode resonance of the deflection are calculated and compared with the same effects resulted from air damping. It shows that for the example of an aluminum–polysilicon thermal bimorph actuator, the resonant frequencies are generally shifted downward with the order larger than that of air damping, whereas the influence of thermoelastic coupling on the Q is more significant than that of air damping under high vacuum level.     

Residual stress evolution regularity in thermal barrier coatings under thermal shock loading

Residual stress evolution regularity in thermal barrier ceramic coatings (TBCs) under different cycles of thermal shock loading of 1100°C was investigated by the microscopic digital image correlation (DIC) and micro-Raman spectroscopy, respectively. The obtained results showed that, as the cycle number of the thermal shock loading increases, the evolution of the residual stress undergoes three distinct stages: a sharp increase, a gradual change, and a reduction. The extension stress near the TBC surface is fast transformed to compressive one through just one thermal cycle. After different thermal shock cycles with peak temperature of 1100°C, phase transformation in TBC does not happen, whereas the generation, development, evolution of the thermally grown oxide (TGO) layer and micro-cracks are the main reasons causing the evolution regularity of the residual stress.     

On the thermal boundary layer on an electrode

In the present paper we consider the approximate calculation of the temperature distribution in a MHD channel operating in the accelerator regime with account for the dependence of the electrical conductance and thermal conductance coefficients on the temperature and with account for Joule dissipation. If the plasma temperature in the channel is about 10⁴ K, then the Prandtl number is much less than unity. Therefore the length of the inlet dynamic segment is much greater than the inlet thermal segment, and we can neglect the transverse velocity component. This permits solving the problem without imposing any constraint on the longitudinal velocity and density. Moreover, under certain conditions we can neglect the term with the pressure gradient in comparison with the Joulean dissipation in the heat transport equation, which permits separation of the thermal problem from the dynamic. In the study we investigate the length of the inlet thermal segment, the heat exchange at the channel wall as a function of the wall temperature, and we also analyze the applicability of the suggested method of calculation.     

Observing real-time thermal deformations in electronic packaging

Experimental Techniques - A robust scheme of moiré interferometry for real-time observation of thermal deformations was developed. It was implemented with a convection-type heating/cooling...     

Research on thermal protection mechanism of forward-facing cavity and opposing jet combinatorial thermal protection system

Validated by the correlated experiments, a nose-tip with forward-facing cavity/opposing jet/the combinatorial configuration of forward-facing cavity and opposing jet thermal protection system (TPS) are investigated numerically. The physical mechanism of these TPS is discussed, and the cooling efficiency of them is compared. The combinatorial system is more suitable to be the TPS for the high speed vehicles which need fly under various flow conditions with long-range and long time.     

Photoelastic-coating analysis in thermal fields

If photoelastic-coating materials exhibited thermal conductivity and thermal expansion equal to that of structural materials, and if strain-optical sensitivity did not vary with temperature, photoelasticcoating analyses could be conducted in thermal fields exactly as in room-temperature test. Methods for circumventing problems associated with these material properties are presented. Corrections are introduced as analytically and empirically derived factors to account for birefringence resulting from differential thermal expansion of coating and workpiece. Surface strains induced by external loading and by thermal stresses can be performed in the temperature range of ?60° F to +350° F for tests of extended duration and to +500° F for brief periods.