共查询到18条相似文献,搜索用时 171 毫秒
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随着高效预冷器在航天航空领域发挥越来越重要的作用,紧凑高效换热器的研究成为了人们关注的热点。本文基于紧凑微通道换热器的几何特征,针对矩形截面平行流道换热器内超临界压力低温流体(氢和氦)在大温差条件下的流动换热现象进行数值模拟研究。通道截面边长小于1 mm,热流体氦和冷流体氢的进出口温差均大于600 K。通道内流体换热系数在顺流和逆流条件下有不同的变化趋势,并出现峰值。换热量随着通道宽度的增大而增大,流动压降随着通道宽度的增大而减小。冷热流体逆流时换热量大,压降较小,但对换热器材料要求较高。 相似文献
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针对聚光光伏(CPV) 电池高热流密度散热问题, 本文提出了射流冲击与分形微通道散热相结合的解决方案, 对其流动和换热进行了模拟. 首先对分形微通道的分形级数进行分析, 四级相比三级分形微通道换热系数只增加了4.62% , 压降却升高了54.37% ; 接着对管道截面形状进行优化, 对圆形截面, 方形渐缩截面和扁管截面内流体的流动进行了模拟, 结果表明在换热量相近的情况下, 扁管拥有最低的压降; 随后对比分叉处倒圆角、 倒角和 Y形三种布置形状, 结果表明 Y 形布置有效地减少了内部流体的涡旋区, 能够在牺牲较少的换热面积的条件下, 将压降降低85 .51 % . 最后在相同水力直径条件下研究单个喷嘴、 均匀喷嘴阵列、 非均匀喷嘴阵列射流冲击分形微通道的换热性能, 模拟结果表明, 非均匀喷嘴阵列分形微通道拥有最佳的换热性能, 且压降降低了25 .99 % . 相似文献
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为探究磁场强度和肋片高度对微通道内Fe3O4-H2O纳米磁流体流动换热性能的影响,采用数值模拟的方法,以开放式间断微通道热沉为研究对象,在雷诺数为200到500之间展开数值模拟研究,模拟微通道内流体工质流动换热过程。结果表明:进出口压降随雷诺数的增大而增大,且随着磁场强度的增大,压降的增大趋势愈显著;微通道的换热性能随着磁场强度的增大,呈现出先增大后减小的趋势;通过增加肋片高度,可以有效的提高热沉的传热性能。研究发现,开放型微通道综合换热性能优于封闭型,在所研究的参数范围内,微通道肋片高度达到0.9 mm时,综合换热性能和均温性最佳。 相似文献
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基于换热器几何结构参数以及流路布置等相同的3HP商用空调,在空调工况下,研究了相对湿度对R22替代制冷剂R407C、R410A、R32以及R290在蒸发器内的流动和传热性能的影响规律。研究表明:在一定的条件下,增加环境相对湿度,这五种制冷剂对应蒸发器换热量、压降和质量流量均增加,其中R407C蒸发器换热量最大,R290和R32蒸发器压降和制冷剂质量流量均小于R22蒸发器。在低湿度环境下(约20—30%相对湿度),显热换热占主导因素。随着相对湿度的增加,显然换热减少,潜热换热增强且起主导因素。在满足换热量的要求下,R290在协调压降与质量流量具有一定的优势且满足现行工质替代理念,可以作为现有商用空调的环保型替代工质。 相似文献
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In this work, a double-layered microchannel heat exchanger is designed for investigation on gas-to-gas heat transfer. The micro-device contains 133 parallel microchannels machined into a polished polyether ether ketone plate for both the hot side and cold side. The microchannels are 200 μm high, 200 μm wide, and 39.8 mm long. The design of the micro-device allows tests with partition foils in different materials and of flexible thickness. A test rig is developed with the integration of customized pressure and temperature sensors for in situ measurements. Experimental tests on the counter-flow micro heat exchanger have been carried out for five different partition foils and various mass flow rates. The experimental results, in terms of pressure drop, heat transfer coefficients, and heat exchanger effectiveness are discussed and compared with the predictions of the classic theory for conventionally sized heat exchangers. 相似文献
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A. G. Agwu Nnanna 《实验传热》2013,26(2):157-173
This article presents an experimental study of thermo-hydrodynamic phenomena in a microchannel heat exchanger system. The aim of this investigation is to develop correlations between flow/thermal characteristics in the manifolds and the heat transfer performance of the microchannel. A rectangular microchannel fabricated by a laser-machining technique with channel width and hydraulic diameter of 87 μm and 0.17 mm, respectively, and a trapezoidal-shaped manifold are used in this study. The heat sink is subjected to iso-flux heating condition with liquid convective cooling through the channels. The temporal and spatial evolutions of temperature as well as total pressure drop across the system are monitored using appropriate sensors. Data obtained from this study were used to establish relationships between parameters such as longitudinal wall conduction factor, residence and switching time, and thermal spreading resistance with Reynolds number. Result shows that there exist an optimum Reynolds number and conditions for the microchannel heat exchanger system to result in maximum heat transfer performance. The condition in which the inlet manifold temperature surpasses the exit fluid temperature results in lower junction temperature. It further shows that for a high Reynolds number, the longitudinal wall conduction parameter is greater than unity and that the fluid has sufficient dwelling time to absorb heat from the wall of the manifold, leading to high thermal performance. 相似文献
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Influences of simultaneous utilization of pin channel and copper–water nanofluid on performance of plate-fin heat exchangers were experimentally explored and compared with results obtained for the base fluid flow inside a plain channel. Experimental results clearly indicate that compared with the plain channel, the pin channel significantly improves the thermal-hydraulic performance of the plate-fin heat exchanger, about 38%. In addition, the heat transfer coefficient as well as pressure drop are increased by using the nanofluids instead of the base fluid. Noticeable average performance factor of 1.65 is obtained for the simultaneous utilization of pin channel and nanofluid inside the plate-fin heat exchanger. 相似文献
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随着系统级封装(SIP)所容纳的电子元器件和集成密度迅速增加,传统的散热方法(热通孔、风冷散热等)越来越难以满足系统级封装的热管理需求。低温共烧陶瓷(LTCC)作为常见的封装基板材料之一,设计并研制了三种内嵌于LTCC基板的微流道,其中包括直排型、蛇型和螺旋型微流道(高度为0.3 mm,宽度分别为0.4, 0.5和0.8 mm)。通过数值仿真和红外热像仪测试相结合的方式分析了微流道网络结构、流体质量流量、雷诺数、材料热导率对内嵌微流道LTCC基板换热性能的影响,实验结果表明:当去离子水的流量为10 mL/min,热源等效功率为2 W/cm2时,直排型微流道的LTCC基板最高温度在3.1 kPa输入泵压差下能降低75.4 ℃,蛇型微流道的LTCC基板最高温度在85.8 kPa输入泵压差下能降低80.2 ℃,螺旋型微流道的LTCC基板最高温度在103.1 kPa输入泵压差下能降低86.7 ℃。在三种微流道中,直排型微流道具有最小的雷诺数,在相同的输入泵压差下有最好的散热性能。窄的直排型微流道(0.4 mm)在相同的流道排布密度和流体流量时比宽的微流道(0.8 mm)能多降低基板温度10 ℃。此外,提高封装材料的热导率有助于提高微流道的换热性能。 相似文献
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H.A. Mohammed G. BhaskaranN.H. Shuaib R. Saidur 《Superlattices and Microstructures》2011,50(3):215-233
This paper reports a numerical analysis of the performance of a counter-flow rectangular shaped microchannel heat exchanger (MCHE) using nanofluids as the working fluids. Finite volume method was used to solve the three-dimensional steady, laminar developing flow and conjugate heat transfer in aluminum MCHE. The nanofluids used were Ag, Al2O3, CuO, SiO2, and TiO2 and the performance was compared with water. The thermal, flow fields and performance of the MCHE were analyzed using different nanofluids, different Reynolds numbers and different nanoparticle concentrations. Temperature profile, heat transfer coefficient, pressure profile, and wall shear stress were obtained from the simulations and the performance was discussed in terms of heat transfer rate, pumping power, effectiveness, and performance index. Results indicated enhanced performance with the usage of nanofluids, and slight penalty in pressure drop. The increase in Reynolds number caused an increase in the heat transfer rate and a decrease in the overall bulk temperature of the cold fluid. The increase in nanoparticle concentration also yielded better performance at the expense of increased pressure drop. 相似文献