Experimental Study on the Permeability and Thermal Resistance of the Cement Clinker Accumulation

A device was designed for measuring the permeability of cement clinker accumulation in three dimensions. In addition, the equivalent permeability and equivalent thermal resistance coefficient were introduced to evaluate the penetration ability in high temperature. First, the equivalent permeability of the accumulation in three dimensions was measured at a room temperature of 298 K and the order of magnitude was decided to be 10^?6. The difference degree of equivalent permeability was less than 15% in each direction; Then the rule of equivalent permeability in three‐dimensional changed with temperature was obtained by the air‐cooled experiments of the cement clinker accumulation at an initial temperature – 773 K; Finally, the law of equivalent thermal resistance coefficient was obtained through comparing the change of the permeability from high temperature to room temperature. The results showed that the equivalent thermal resistance coefficient change with temperature was nonlinear and the equivalent thermal resistance coefficient changed from 1.0 to 1.3 when the temperature was in the range of 298 K to 773 K.     

Optimization of a vacuum freezing cool‐thermal storage coupled with wastewater treatment process

Purification of wastewater by freezing under vacuum in a cool‐thermal storage process is investigated. Mathematical models of heat transfer and mass transfer in this system are developed to describe the thickness and the solute distribution of ice as the cool‐thermal storage process proceeds. A mathematical treatment for determining the optimum solidification thickness and operating time to remove the maximum amount of solute is presented. For the system of constant volumetric rate of vacuum, the suction rate is an important factor in determining the efficiency of the process. The suction rate should be kept within the range of 10,000 to 20,000 m³/m²hr when the solute distribution coefficient is less than 1. When the coefficient is greater than 1, the suction rate should be run within 5000 to 10,000 m³/m²hr. Over the proper range of operation, the optimal operating time is a weak function of suction rate. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(3): 189–200, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10134     

保温用天然生物质材料的热湿特性

实验分析一些廉价天然材料(椰壳和花生壳)的导热特性。利用同心球稳态测量方法测量确定椰壳和花生壳的导热系数,以及导热系数随温度的变化规律,同时以硅酸铝纤维材料为标准试样,与天然材料的导热性能进行对比分析。还对这些材料的低温吸湿作了初步测试,分析此类材料作为低温绝热材料的吸湿特性。研究结果表明,所有材料的导热系数均随温度的升高而增大,且增大速率都近似相等。影响天然生物质材料导热性质的因素主要有：纤维或多孔固体材料中的导热、孔隙中空气的对流换热,如果温度足够高的话,还有辐射换热。     

The reaction coefficient of an enclosure to the solar energy collection

A dimensionless reaction coefficient R_a is defined which gives a measure of the solar energy collectivity of a room with opaque external walls. This number is defined as the ratio between the absorbed solar energy by the wall and the correspondent thermal gain of the room, and depends on the thermal and structural characteristics of the room and its environment. The reaction coefficient R_a is reduced to a simple expression and provides a simple way of estimating the amount of the net radiation energy gain by the room, when the amount of radiation, which is falling or absorbed by the wall, is given. This analytical relation has been confirmed experimentally especially with respect to the influence of the wall total thermal conductance on the reaction coefficient R_a.     

Nb-doped BaTiO3-(Bi0.5Na0.5)TiO3 ceramics with core-shell structure for high-temperature dielectric applications

Nb-doped 0.90BaTiO₃-0.10(Bi_0.5Na_0.5)TiO₃ temperature-insensitive ceramics with novel core-shell structure were sintered at low temperature by the conventional solid-state reaction method. The beneficial role of Nb in facilitating the formation of core-shell structure because of chemical inhomogeneity is verified, which is responsible for the weak temperature dependence of dielectric properties. Temperature dependence of permittivity measured at different frequencies shows high frequency dispersion at low temperature, while without relaxor characteristic at high temperature. The Vogel–Fulcher model was adopted to study the relaxor behaviour of Nb-doped 0.90BaTiO₃-0.10(Bi_0.5Na_0.5)TiO₃ ceramics at low temperature. The samples with an addition of 1.5?mol% Nb₂O₅ provide a temperature coefficient of capacitance meeting the requirements of the X9R characteristic, and result exhibits an optimum dielectric behaviour of ε_r ～1900, tanδ ～1.8% at room temperature, making the material a promising candidate for high temperature applications.     

Energy performance of a hybrid space-cooling system in an office building using SSPCM thermal storage and night ventilation

Thermal performance of a hybrid space-cooling system with night ventilation and thermal storage using shape-stabilized phase change material (SSPCM) is investigated numerically. A south-facing room of an office building in Beijing is analyzed, which includes SSPCM plates as the inner linings of walls and the ceiling. Natural cool energy is charged to SSPCM plates by night ventilation with air change per hour (ACH) of 40 h⁻¹ and is discharged to room environment during daytime. Additional cool-supply is provided by an active system during office hours (8:00-18:00) necessary to keep the maximum indoor air temperature below 28 °C. Unsteady simulation is carried out using a verified enthalpy model, with a time period covering the whole summer season. The results indicate that the thermal-storage effect of SSPCM plates combined with night ventilation could improve the indoor thermal-comfort level and save 76% of daytime cooling energy consumption (compared with the case without SSPCM and night ventilation) in summer in Beijing. The electrical COPs of night ventilation (the reduced cooling energy divided by fan power) are 7.5 and 6.5 for cases with and without SSPCM, respectively.     

窗总热阻和遮阳系数的动态测试

针对夏季室外热扰变化剧烈，室内外热传递为非稳定传热的情况，提出了测量窗总热阻R0值和遮阳系数SC值的动态防护热箱方法，并用这个方法实际测试了广州地区某住宅西向外窗，介绍了测试过程和数据处理过程。本实验方法是对现场动态测定窗节能参数的探索，为研究南方夏季窗口节能的动态测试工作提供了参考。     

A new apparatus for measuring total hemispherical emittance of surfaces at room temperature

Radiation heat transfer is an important mode of heat transfer even in our life space at room temperature. Such radiation heat transfer is evaluated mostly by calculating the radiation energy exchange among surfaces in an enclosure. For this evaluation, knowledge of the hemispherical emittances of the constituent life surfaces is needed. However, there has not been a suitable technique for measuring the emittance of each surface in the life space at room temperature. In the present work we develop a new apparatus for measuring total hemispherical emittances of real surfaces at room temperature. The apparatus consists of a total radiation flux meter and a Peltier element cooler to cool the flux meter surface from the back, and measure the net total radiation flux from the specimen surface to the surrounding surfaces to determine the total hemispherical emittance of the specimen surface. This apparatus is effective to measure total hemispherical emittances of surfaces at room temperature on site. We apply the developed apparatus to measure the total hemispherical emittances of various surfaces in the life space, such as metals, human skin, cloth, floor mat, wood, glass, brick tile, stone, cement, plant leaves, etc., and demonstrate the feasibility of the apparatus. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20349     

Monitoring of transient 3D temperature distribution and thermal stress in pressure elements based on the wall temperature measurement

Abstract

Two methods for monitoring the thermal stresses in pressure components of thermal power plants are presented. In the first method, the transient temperature distribution in the pressure component is determined by measuring the transient wall temperature at several points located on the outer insulated surface of the component. The transient temperature distribution in the pressure component, including the temperature of the inner surface is determined from the solution of the inverse heat conduction problem (IHCP). In the first method, there is no need to know the temperature of the fluid and the heat transfer coefficient. In the second method, thermal stresses in a pressure component with a complicated shape are computed using the finite element method (FEM) based on experimentally estimated fluid temperature and known heat transfer coefficient. A new thermometer with good dynamic properties has been developed and applied in practice, providing a much more accurate measurement of the temperature of the flowing fluid in comparison with standard thermometers. The heat transfer coefficient on the inner surface of a pressure element can be determined from the empirical relationships available in the literature. A numerical-experimental method of determination of the transient heat transfer coefficient based on the solution of the 3D-inverse heat conduction problem has also been proposed. The heat transfer coefficient on the internal surface of a pressure element is determined based on an experimentally determined local transient temperature distribution on the external surface of the element or the basis of wall temperature measurement at six points located near the internal surface if fluid temperature changes are fast. Examples of determining thermal and pressure stresses in the thick-walled horizontal superheater header and the horizontal header of the steam cooler in a power boiler with the use of real measurement data are presented.     

THERMAL STRESSES IN PARTIALLY ABSORBING FLAT PLATE DUE TO SUDDEN INTERRUPTION OF STEADY-STATE ASYMMETRIC RADIATION,II: CONVECTIVE COOLING AT FRONT SURFACE

In Part II of this study the thermal stresses are analyzed in a partially absorbing flat plate, due to a sudden interruption of steady-state asymmetric radiation on the convectively cooled front face. As in the case of Part I, the maximum tensile stresses occur in the rear face. For the optical thickness μa ≥ 0.5, the maximum tensile stress initially rises to a peak and then decreases with time. On the other hand, for μa ≤ 0.5, the stresses decrease monotonically with time.

A comparison of the results for the front (Part II) and rear (Part I) cooling indicates that values of the maximum stress are numerically indentical for small values of heat transfer coefficient h, and plate thickness a. Increasing difference in the magnitude of the stresses for the two cases is found with increasing h and a.     

板式相变贮能换热器传热模型和热性能分析

建立了板式相变贮能换热器的无量纲传热模型。它对流体入口流量、入口温度随时间变化情况和需考虑入口效应及添加肋片的情况均适用。模型解和文献准稳态解吻合。作为算例,藉此模型从各时刻的流体温度、相变界面随空间的分布情况和相变蓄热比、相变传热效率、传热系数、完全相变截面位置随时间的变化情况六个角度分析了一板式相变贮能换热器的相变传热性能。该模型可为板式相变贮能换热器的结构优化设计和热性能分析提供帮助。     

Thermal management performance of a fin-enhanced phase change material system for the lithium-ion battery

A fin-enhanced phase change material (PCM) system was introduced for cylindrical lithium-ion batteries. Experiments were performed to explore the performance of the systems during discharging. The working time of the PCM-Fin system is improved by 75%, 68%, and 61% compared to that of the system without fins under the heat production rate of 10, 12.5, and 15 W, accordingly. Simulations were performed by ANSYS Fluent to explore the influence of the geometric parameters (thickness, length, and number) and materials (nylon, titanium, steel, Al alloy, and copper) of the fins on the thermal performance. A function considering both the improvement in thermal performance and the increase in system weight was defined to assess the overall performance. Results indicate that fins made of Al alloy with the number of 8, a length of 7.5 mm, and a thickness of 0.5 mm give the best performance. Besides, the working time of the PCM-Fin system is 2150, 2490, 2940, and 3570 seconds for the coefficient of heat transfer of 5, 10, 15, and 20 W m⁻² K⁻¹, respectively, which is increased by 14%, 32%, 56%, and 90%, compared to that of the adiabatic condition, demonstrating the effectiveness of the PCM-Fin system.     

Passive room conditioning using phase change materials—Demonstration of a long-term real size experiment

The thermal properties of lightweight buildings can be efficiently improved by using phase change materials (PCMs). The heat storage capacity of the building can be extended exactly at the desired temperature level, which leads to an enormous increase in residential comfort. This is shown in the present paper using the example of a prefabricated wooden house. The house was divided into two identical rooms. One of them was equipped with almost one ton of phase change material based on salt hydrates with a melting temperature of approx. 21°C. The material was encapsulated in 1-l Polyethylene containers and installed in two back-ventilated layers inside of the walls. The house was monitored for a period of 87 days in terms of temperatures, solar radiation and air velocity inside the PCM wall system. A considerable temperature buffering could be observed in the PCM room compared to the reference room. An overall reduction of the temperature fluctuations of 57% and a reduction of the day/night fluctuations of 62% compared to the reference room could be obtained. In addition, a prediction regarding the energy demand of such buildings is discussed on the basis of a simulation program. Thus, the annual cooling capacity can be reduced by 36.5% compared to the regular timber construction technique by introducing PCM. Furthermore, the good correlation of the simulation results with the experimental ones allows using the simulation as a tool to design a house with additional thermal storages.     

Solid-state oligomer electrolyte with amine–acid interaction for dye-sensitized solar cells

A pair of poly(ethylene glycol) oligomers with terminal groups capable of providing amine–acid interactions are used in dye-sensitized solar cells (DSSCs) as an electrolyte that can be easily solidified at room temperature. In spite of its solidity, the oligomer electrolyte has high ionic diffusion and good permeability into the nanopores of a TiO₂ electrode. The electron diffusion coefficient and lifetime in a photoelectrode are largely affected by the adsorptive interaction between cations and the TiO₂ surface. The energy-conversion efficiency of DSSCs using the oligomer electrolyte is greater than 4.5%. Long-term storage at room temperature demonstrates that the stability of the oligomer electrolyte system is superior to that of a volatile solvent electrolyte.     

Subamorphous Thermal Conductivity of Crystalline Half-Heusler Superlattices

The quest to improve the thermoelectric figure of merit has mainly followed the roadmap of lowering the thermal conductivity while keeping unaltered the power factor of the material. Ideally an electron-crystal phonon-glass system is desired. In this work, we report an extraordinary reduction of the cross-plane thermal conductivity in crystalline (TiNiSn):(HfNiSn) half-Heusler superlattices (SLs). We create SLs with thermal conductivities below the effective amorphous limit, which is kept in a large temperature range (120–300 K). We measured thermal conductivity at room temperature values as low as 0.75 W m^?1 K^?1, the lowest thermal conductivity value reported so far for half-Heusler compounds. By changing the deposition conditions, we also demonstrate that the thermal conductivity is highly impacted by the way the single segments of the SL grow. These findings show a huge potential for thermoelectric generators where an extraordinary reduction of the thermal conductivity is required but without losing the crystal quality of the system     

多孔太阳墙式太阳能房间与普通房间热舒适性分析

通过对某多孔太阳墙式太阳能房间和普通房间的数值模拟,分析太阳墙板内空气的受热过程及流动情况,同时系统地比较两种建筑在工作区范围内的热舒适性。与普通采暖房间相比,在有多孔太阳墙送风的情况下,可将室外空气由-3℃加热到21℃,空气流动速度由0.1m/s提高到0.31m/s,提供44.6m3/h的新风量,一定程度上解决了冬季开窗换气所引起的室内热负荷及采暖负荷,论证了多孔太阳墙可使室内热舒适性明显增强的结论。     

Aquifer thermal storage (ATES) for air-conditioning of a supermarket in Turkey

A heating, ventilation and air-conditioning (HVAC) system with integrated aquifer thermal energy storage (ATES) was designed for a supermarket building in Mersin, a city near the Mediterranean coast in Turkey (36° 49′ N and 34° 36′ E). This is the first ATES application carried out in Turkey. The peak cooling and heating loads of the building are 195 and 74 kW, respectively. The general objective of the system is to use the groundwater from the aquifer to cool down the condenser of the HVAC system and at the same time storing this waste heat in the aquifer. Cooling with groundwater at around 18 °C instead of utilizing outside summer air at 30–35 °C decreases consumption of electrical energy significantly. In addition, stored heat can be recovered when it is needed in winter. The HVAC system with ATES started operation in August 2001 in cooling mode with an average coefficient of performance (COP) of 4.18, which is almost 60% higher than a conventional system.     

Numerical analysis of effect of shape-stabilized phase change material plates in a building combined with night ventilation

Effect of shape-stabilized phase change material (SSPCM) plates combined with night ventilation in summer is investigated numerically. A building in Beijing without active air-conditioning is considered for analysis, which includes SSPCM plates as inner linings of walls and the ceiling. Unsteady simulation is performed using a verified enthalpy model, with time period covering the summer season. Effects of the following factors on room air temperature are investigated: the thermophysical properties of the SSPCM, the thickness of SSPCM plate and air change per hour (ACH) at both nighttime and daytime. The results show that the SSPCM plates could decrease the daily maximum temperature by up to 2 °C due to the cool storage at night. The appropriate values for melting temperature, heat of fusion, thermal conductivity and thickness of SSPCM plates need to be considered and calculated according to the climate conditions and building structure. The ACH at night needs to be as high as possible but the ACH at daytime should be controlled.     

Numerical simulation of a building with one transparently insulated wall

A numerical simulation model is developed to study the thermal performance of an outdoor test-room with one Transparently Insulated (TI) wall. The thermal behavior of the room is examined under different control strategies for the shading device. Simulation results indicate significant energy savings. However, appropriate control strategies are required to prevent overheating of the room and discomfort.     

Modelling airflow,heat transfer and moisture transport around a standing human body by computational fluid dynamics

In this study a combined computational model of a room with virtual thermal manikin with real dimensions and physiological shape was used to determine heat and mass transfer between human body and environment. Three dimensional fluid flow, temperature and moisture distribution, heat transfer (sensible and latent) between human body and ambient, radiation and convection heat transfer rates on human body surfaces, local and average convection coefficients and skin temperatures were calculated. The radiative heat transfer coefficient predicted for the whole-body was 4.6 W m^− 2 K^− 1, closely matching the generally accepted whole-body value of 4.7 W m^− 2 K^− 1. Similarly, the whole-body natural convection coefficient for the manikin fell within the mid-range of previously published values at 3.8 W m^− 2 K^− 1. Results of calculations were in agreement with available experimental and theoretical data in literature.