The effects induced by streamwise conduction on the thermal characteristics of forced convection for single-phase liquid flow in rectangular microchannel heat sinks under imposed constant wall temperature have been st...The effects induced by streamwise conduction on the thermal characteristics of forced convection for single-phase liquid flow in rectangular microchannel heat sinks under imposed constant wall temperature have been studied. By employing the fin approach in the first law of analysis, models with and without streamwise conduction term in the energy equation were developed for hydrodynamically and thermally fully-developed flow under local thermal non-equilibrium for the solid and fluid phases. These two models were solved to obtain closed form analytical solutions for the fluid and solid temperature distributions and the analysis emphasized details of the variations induced by the streamwise conduction on the fluid temperature distributions. The effects of the Peclet number, aspect ratio, and thermal conductivity ratio on the thermal characteristics of forced convection in microchannel heat sinks were analyzed and discussed. This study reveals the conditions under which the effect of streamwise conduction is significant and should not be neglected in the forced convective heat transfer analysis of microchannel heat sinks.展开更多
针对翅片管规格与汽源参数对蒸汽空气预热器的传热特性、材料重量以及垃圾焚烧发电锅炉运行效益的影响,提出基于逼近理想解排序法(techniquefororderpreferenceby similarity to an ideal solution,TOPSIS)的综合评价方法。首先,以翅片...针对翅片管规格与汽源参数对蒸汽空气预热器的传热特性、材料重量以及垃圾焚烧发电锅炉运行效益的影响,提出基于逼近理想解排序法(techniquefororderpreferenceby similarity to an ideal solution,TOPSIS)的综合评价方法。首先,以翅片管重量、空气阻力、换热面积、加权平均传热系数、饱和蒸汽量、汽机抽汽量、锅炉出力变化、有效输出热量增加和热效率构建评估指标体系,并利用信息熵确定指标权重。其次,采用改进的相对接近度法计算各方案与正负理想解的接近程度,然后确定20个设计方案完全序的偏好排序。最后通过测试分析,验证了TOPSIS评价方法的有效性,实现对蒸汽空气预热器设计方案的优化。展开更多
Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cr...Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.展开更多
文摘The effects induced by streamwise conduction on the thermal characteristics of forced convection for single-phase liquid flow in rectangular microchannel heat sinks under imposed constant wall temperature have been studied. By employing the fin approach in the first law of analysis, models with and without streamwise conduction term in the energy equation were developed for hydrodynamically and thermally fully-developed flow under local thermal non-equilibrium for the solid and fluid phases. These two models were solved to obtain closed form analytical solutions for the fluid and solid temperature distributions and the analysis emphasized details of the variations induced by the streamwise conduction on the fluid temperature distributions. The effects of the Peclet number, aspect ratio, and thermal conductivity ratio on the thermal characteristics of forced convection in microchannel heat sinks were analyzed and discussed. This study reveals the conditions under which the effect of streamwise conduction is significant and should not be neglected in the forced convective heat transfer analysis of microchannel heat sinks.
文摘针对翅片管规格与汽源参数对蒸汽空气预热器的传热特性、材料重量以及垃圾焚烧发电锅炉运行效益的影响,提出基于逼近理想解排序法(techniquefororderpreferenceby similarity to an ideal solution,TOPSIS)的综合评价方法。首先,以翅片管重量、空气阻力、换热面积、加权平均传热系数、饱和蒸汽量、汽机抽汽量、锅炉出力变化、有效输出热量增加和热效率构建评估指标体系,并利用信息熵确定指标权重。其次,采用改进的相对接近度法计算各方案与正负理想解的接近程度,然后确定20个设计方案完全序的偏好排序。最后通过测试分析,验证了TOPSIS评价方法的有效性,实现对蒸汽空气预热器设计方案的优化。
文摘Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.
