共查询到19条相似文献,搜索用时 218 毫秒
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动态性是围护结构传热的本质属性,动态热响应机理是其动态运行规律的体现。围护结构在夏季的动态性比在冬季表现更为典型,因此该文开展隔热建筑的围护结构动态性机理及应用研究。通过研究围护结构的动态热响应机理提出围护结构最大防热量Gmax,该指标兼顾多种工况下围护结构热性能的评价。以夏热冬冷地区的重庆为例进行模拟分析。研究发现:Gmax<60 W/m2时,提升墙体最大防热量可有效提升其动态热响应性能;Gmax在60~90 W/m2之间时,提升墙体最大防热量可较少提升其动态热响应性能;Gmax>90 W/m2时,提升墙体最大防热量反而会降低其动态热响应性能。 相似文献
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燃烧室部件耦合系统过渡工况传热全仿真模拟研究 总被引:9,自引:1,他引:8
内燃机的起动、停车、加载等运行工况发生急剧变化(过渡工况)过程中,其燃烧室部位外于强烈地被加热或被冷却状态。这种热冲击增加了部件的动态疲劳热应力,给内燃机的可靠性带来严重恶果,是导致燃烧室部位破裂的主要原因之一。燃烧室部件的传热研究是热负荷计算和评定的基础,对内燃机的可靠性设计具有重要意义。作对燃烧室部件活塞组气缸套耦合系统在过渡工况下的耦合传热关系进行了较深入的研究,建立了描述这一传热过程的数学模型;并利用该模型,模拟了125风冷柴油机在各种过渡工况下的传热情况。 相似文献
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对于节能建筑,围护结构保温性能优劣是影响其能耗的重要标准.以哈尔滨地区为例,通过对新建建筑围护结构热质耦合传递的模拟结果,对比分析了严寒地区典型新建建筑不同设置的多层围护结构在最初四年内热质耦合传递对围护结构墙体热负荷的影响.分析结果表明:围护结构保温层内表面安装隔汽层能有效缓解保温层受潮,对降低能耗较为有利,围护结构外表面粘贴釉面砖时对能耗影响最大,但若降低保温层初始含湿量会降低其影响. 相似文献
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相变材料具有高效的能量储存功能。相变材料与建材基体结合,制成一种具有储热功能的围护结构。该围护结构可发挥相变储热功能,降低建筑室内温度波动,增强建筑热舒适度,能够更加有效地减少建筑物运行能耗,从而实现建筑节能。本文对当前现有相变材料的优缺点、相变材料在不同围护结构中的应用、相变储能围护结构对室内热环境的影响及对建筑运行能耗的影响、相变储能围护结构应用的经济性等方面进行了分析,提出相变储能围护结构在工程应用中所存在的不足及其发展前景。 相似文献
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An in situ thermal response test for borehole heat exchangers of the ground-coupled heat pump system
Thermal response tests (TRTs) are crucial for the estimation of the ground thermal properties and thermal performance of the borehole heat exchanger (BHE) of the ground-coupled heat pump (GCHP) system. In this article, a TRT apparatus was designed and built to measure the temperature response of inlet and outlet sections of BHE in the test borehole, the apparatus can effectively operate under both constant heating flux modes and heat injection and extraction modes with a constant inlet temperature. A TRT for a project of GCHP located in the Jiangsu province of China was carried out by the experimental apparatus. Based on the experimental data, the heat transfer performances of BHE under heating and cooling modes were evaluated, and the ground thermal properties, which include the ground thermal conductivity, ground volumetric specific heat, borehole thermal resistance and effective soil thermal resistance, were determined by the line source model. The results indicate that the experimental device and analysis model proposed in this article can be effectively applied to estimate the ground thermal properties and thermal performance of BHE. During the process of thermal response of ground, the fluid temperatures vary acutely at the start-stage of 8 h, and then tend to be a steady state after 40 h. The test data during the start-stage should be discarded for improving the estimation accuracy of ground thermal properties. At the same time, the effective soil thermal resistance increases continuously with time and a steady-state value would be reached after the start-time, and this steady-state thermal resistance can be used to evaluate the required length of BHE. In addition, the heat transfer rate of the BHE under different operating conditions can be used for the further evaluation on long-term operation performance of GCHPs. 相似文献
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A mathematical model of evaporation and condensation heat transfer in a copper-water wicked heat pipe with a sintered-grooved composite wick is developed and compared with experiments. The wall temperatures are measured under different input power levels and working temperature conditions. The results show that the heat transfer in the condenser section was found to be only by conduction. In the evaporator, however, either conduction or boiling heat transfer can occur. The experimental data for the boiling heat transfer are well correlated by the theory of Stralen and Cole. Higher heat load drives the heat pipe to spend more time achieving the equilibrium state during the transient start-up process. The response curves of the evaporator thermal resistance are overlapped, and the condenser thermal resistance increases more sharply at the beginning. The total thermal resistance of the heat pipe ranges from 0.02 to 0.56 K/W. 相似文献
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附加阳光间型被动房传热量受室外空气温度和太阳辐射双波动扰动影响,导致其热负荷具有显著波动特征,传统稳态计算方法难以适用,而动态方法过于复杂,不适用于工程设计使用。基于此,该文采用周期反应系数法研究结构参数和被动房传热量之间的定量关系,并结合结构参数,提出附加阳光间型被动房热负荷简化计算新方法。结果表明阳光间总传热量受公用墙体构造变化影响较大,内门传热量与公用墙体热阻呈正相关,墙体传热量与墙体热阻呈负相关;同类围护结构下,不同参数组合下公用墙导热量与阳光间空气温度变化规律趋势一致,进而提出附加阳光间导热变化系数和温度变化系数,以该参数为基础建立了关键结构参数与传热量之间的多元回归模型,该简化计算方法与实测值对比结果表明吻合度较大,简化计算方法精度较高,可供实际工程设计使用。 相似文献
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Impact of the Relationship between Phase Change Temperature and Boundary Temperature on the Thermal Performance of a PCM Wall and the Presentation of PCM Thermal Performance Indexes
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In the composite phase change material (PCM) building envelope, the matching relationship between the phase change temperature of the PCM and the wall's boundary temperature significantly affects the energy storage performance of the PCM building envelope. In this paper, a type of concrete hollow block with a typical structure and a common PCM were adopted to produce multiform composite PCM hollow blocks, and the temperature changing hot chamber method was performed to test the thermal performance of the hollow block walls under different temperature conditions. New indexes were proposed for the thermal performance evaluation of the PCM wall. Meanwhile, combined with experimental data, the effective heat capacity model and the enthalpy model were used to analyze the effect of correlations concerning how the relationship between phase change temperature and wall's boundary temperature influenced the thermal performance of PCM wall. Three main impact factors related to temperature were obtained through the analysis. In addition, approaches for improving the thermal performance of a composite PCM wall were put forward. This paper provides the theoretical basis, data reference and practical instruction for the proper use of a PCM wall and ways for improving the thermal performance of a composite PCM wall. 相似文献
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In this paper a detailed one dimensional nonuniform thermal model of a parabolic trough solar collector/receiver is presented. The entire receiver is divided into two linear halves and two inactive ends for the nonuniform solar radiation, heat transfers and fluid dynamics. Different solar radiation and heat transfer modes can be taken into consideration for these four different regions respectively. This enables the study of different design parameters, material properties, operating conditions, fluid flow and heat transfer performance for the corresponding regions or the whole receiver. Then the nonuniform model and the corresponding uniform thermal model are validated with known performance of an existing parabolic trough solar collector/receiver. For applications, the uniform thermal model can be used to quickly compute the integral heat transfer performance of the whole PTC system while the nonuniform thermal model can be used to analyze the local nonuniform solar radiation and heat transfer performance characteristics and nonuniform heat transfer enhancements or optimizations. Later, it could also be effectively used with an intelligent optimization, such as the genetic algorithm or the particle swarm optimization, to quickly evaluate and optimize the characteristics and performance of PTCs under series of nonuniform conditions in detail. 相似文献
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Theoretical and experimental studies are conducted to evaluate the overall thermal performance of single-component and gas-loaded heat pipes. In the analysis, the simple conduction model developed recently for the single-component heat pipes has been extended to predict the wall temperature profiles of gas-loaded heat pipes with phase change occurring in the evaporator wick. Experimental evaluation of the thermal performance is made with two working fluids (water and acetone) under two corresponding sink environments (boiling water and boiling alcohol). The heat pipe system is designed with variable-length heat input and output sections under a wide range of heat input conditions. Measured results agree well with theoretical predictions. 相似文献
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为充分挖掘吸收式热泵的动态运行特性,考虑各部件存量工质的储热特性建立考虑传质和分布参数的溴化锂吸收式热泵动态仿真模型。在机组各设备存量工质质量不同的情况下,分析了热源工质进口温度的提升对冷却水和冷媒水出口温度的动态影响及系统的热惯性特征,同时在热源工质进口、冷却水进口和冷媒水进口温度变化的情况下,分析了系统的性能系数(Coefficient of Performance, COP)变化特性及结晶风险变化特性。结果表明:该模型能准确地模拟吸收式热泵的稳态特性和动态特性;机组的热惯性主要与机组内各设备中的存量溶液质量有关;热源工质入口温度的上限受到系统COP及结晶风险的双重影响;冷却水入口温度的下降可增大系统COP,其下限受到结晶风险的限制;冷媒水入口温度的上限不受结晶特性限制;主要受用户侧的用能需求限制。 相似文献