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Abstract: In this study, thermal performance of the cooling modules applicable for Par 38 light bulb is investigated. A total of six heat sink modules, including the basic reference design, metal foam, and carbon foam are tested and compared. Tests are performed and analyzed using the transient test method based on JESD51-1 standard. It is found that the thermal resistance from junction to die attach is quite small. By contrast, the thermal resistance of the heat sink dominates the total resistance, and it comprises 55% of the total resistance for the standard heat sink module. With some slight opening on the base plate, the thermal resistance can be improved by approximately 12%. The thermal resistance for the carbon foam having an embedded metal plate shows the least thermal resistance of 1.14K/W, followed by the carbon foam, and then the metal foam. The lower thermal resistance of carbon foam in association with copper metal foam is due to its higher emissivity. In addition to better heat transfer performance as compared to the standard plate heat sink, the utilization of carbon foam and metal foam can also significantly reduce the weight of the heat sink. In this study, the weight of the heat sink can be reduced as much as 33%. [Copyright &y& Elsevier]

In this study experiments were conducted to study the porous thin plate drying process. An analysis was also carried out to determine the moisture transfer coefficients that vary with the moisture content of the plate during drying. The study is useful for analyzing the transient drying process of porous thin plates. Furthermore, energy and exergetic analyses based on the measured results were carried out to determine the dryer performance. It is found that, although the drying rate increases, the energy utilization ratio of the drying process decreases with either an increase in the rate of air flow or an increase in the size of the drying air inlet. The results indicate that a significant amount of the energy provided to the system was lost and not utilized for drying, especially for high drying rate dryers. An exergetic analysis showed that by adjusting the configuration of the air inlet and flow rate, the exergetic efficiency of the dryer can be significantly increased (from 0.5% to 10%). An overall transport phenomena analysis and performance evaluation including the transient moisture transfer coefficients, drying rate, energy utilization ratio, and exergetic efficiency in the current study provide comprehensive and important insights to the thermal physics of porous thin plate drying processes and the design of efficient dryer systems. [ABSTRACT FROM AUTHOR]

Abstract: Based on our previous study, experiments were conducted to explore frictional pressure drop and heat transfer performance of de-ionized water flowing through rectangular microchannels having longitudinal vortex generators (LVGs). The experimental investigation was conducted under three-sided constant wall temperature boundary condition for the Reynolds numbers ranging from 350 to 1500 for LVGs with different number of pairs and dimensions. The aspect ratios of rectangular microchannels were 0.25 and 0.0667, and the corresponding hydraulic diameters were 160μm and 187.5μm, respectively. The heights of associated LVGs were 1/4H, 3/4H and H, respectively, where H was the height of microchannel. It was found that heat transfer performance was enhanced by 12.3–73.8% and 3.4–45.4% for microchannels with aspect ratios of 0.0667 and 0.25, respectively, while the pressure losses were increased by 40.3–158.6% and 6.5–47.7%, respectively; and the overall heat transfer performances of some specific microchannels were more than 1 in our study. With the help of LVGs, the critical Reynolds numbers were lower than 1000, which were smaller than the generally accepted value of 2300 for regular channel flow. [Copyright &y& Elsevier]

The selective laser melting (SLM) process is an additive manufacturing technique that can fabricate three-dimensional workpiece by laser scanning and sintering of designated material in powder form on a preset scanning route along a bed of powders. This process involves a moving laser heating source which causes local transient mass and heat transfer with phase change, i.e., melting and solidifying, in a pool of melted powders. To fully investigate such a complicated transport process with reasonable computation cost, a novel quasi-transient numerical model (hopping model) was proposed and validated experimentally in this study. This approach includes a volumetric heat source defined as an elliptical Gaussian laser spot which hops along the scan path. Inconel 718 (IN718) superalloy powder is selected as the material for demonstration. Thermal analysis was carried out using a number of laser power and scan speeds in the range from 80 W to 120 W and from 80 mm/s to 140 mm/s, respectively. The comparison of molding appearance of the work pieces from the developed hopping model, full transient model, effective-transient model, and experiments illustrates the accuracy and the efficiency of the proposed hopping model. Molding appearance obtained from the quasi-transient model was consistent with experimental results with a relative error of less than 1.71% on the width of the IN718 stripes fabricated by SLM. For the cases analyzed in the current study, the quasi-transient model showed a 99% and a 60% reduction in both the computation time and the amount of computer memory needed compared to the full transient model and the effective-transient model, respectively. This novel quasi-transient simulation technique can be used to rapidly and effectively optimize process parameters for intelligent additive manufacturing. [ABSTRACT FROM AUTHOR]