Header Shape Effect on the Inlet Velocity Distribution in Cross-Flow Double-Layered Microchannel Heat Sinks

Counter-flow double-layered microchannel heat sinks are very effective for thermal control of electronic components; however, they require rather complicated headers and flow maldistribution can also play a negative role. The cross-flow configuration allows a much simpler header design and the thermal performance becomes similar to that provided by the counter-flow arrangement if the velocity distribution in the microchannels is not uniform. The aim of this work is to show the possibility of achieving a favorable flow distribution in the microchannels of a cross-flow double-layered heat sink with an adequate header design and the aid of additional elements such as full or partial height baffles made of solid or porous materials. Turbulent RANS numerical simulations of the flow field in headers are carried out with the commercial code ANSYS Fluent. The flow in the microchannel layers is modeled as that in a porous material, whose properties are derived from pressure drop data obtained using an in-house FEM code. It is demonstrated that, with an appropriate baffle selection, inlet headers of cross-flow microchannel heat sinks yield velocity distributions very close to those that would allow optimal hotspot management in electronic devices.

WAYS TO IMPROVE THE QUALITY OF COMBING WHEN HARVESTING SOYBEANS

The use of combing headers for soy harvesting is a promising direction for improving the harvesting process. The method of combing standing crops will reduce the harvest time by increasing working speed, improve the product quality by reducing grain crushing, and minimize the anthropogenic impact of harvesters on the soil because of their reduced number and weight of their working units as compared to harvesters with conventional threshing-and-separating units. This modifi cation will provide livestock industry with cheap feed resulting from grain-soybean heap processing. The purpose of the study was to design and improve technical means for harvesting soybeans with the method of combing. Research was conducted on the “Lazurnaya” soybean variety. The results of soybean weighing and the composition of the grain-soybean heap are presented. The obtained experimental data show a decrease in the loss from the non-combed fraction at increased combing drum speed and reduced ground speed, but this is accompanied by signifi cantly increased loss of soybeans. To improve the quality of soybean harvesting using the combing method, promising solutions for the modernization of the combing headers are considered: installation of an additional beater, which will prevent unwinding of the uncombed parts of the soybean stalks on the drum and their subsequent breaking off ; integration of a sieve into a combing header design to reduce the amount of impurities; the use of hinges to attach the comb to the drum and the stopper, which help prevent accidental contact of the comb with the fi eld surface.

Temperature Uniformity in Cross-Flow Double-Layered Microchannel Heat Sinks

An in-house finite element method (FEM) procedure is used to carry out a numerical study on the thermal behavior of cross-flow double-layered microchannel heat sinks with an unequal number of microchannels in the two layers. The thermal performance is compared with those yielded by other more conventional flow configurations. It is shown that if properly designed, i.e., with several microchannels in the top layer smaller than that in the bottom layer, cross-flow double-layered microchannel heat sinks can provide an acceptable thermal resistance and a reasonably good temperature uniformity of the heated base with a header design that is much simpler than that required by the counter-flow arrangement.

Developing an Optimum Design of the Double Layer Microchannel Heat Sink for High Speed CPUs

High speed CPUs and electronic chips usually dissipate relatively large quantities of energy in the form of heat. The limited available cooling space requires innovative and efficient thermal management techniques. These techniques must accomplish low operation temperatures along with uniform temperature distribution over the chip surface. Recently, several researches focused on developing different microchannel heat sink (MCHS) designs for this purpose. Among these designs is the double layer microchannel heat sink (DL-MCHS), which can be operated in either parallel flow (PF) or counter flow (CF) operation modes. The thermo-hydraulic characteristics of this heat sink was comprehensively investigated in the literature using numerical methods. However, based on the authors literature survey, all the previous numerical investigations considered the computational domain as a straight section with multi-channels in each layer. This approach assumes a uniform velocity for all the flow channels in each layer and neglect the effect of the inlet and outlet headers. In addition, the heat interaction between the coolant in both layers through the header section was not considered. These assumptions cause a considerable discrepancy between the numerical results in the literature and the realistic conditions. Therefore, in this work, a detailed 3D conjugate heat transfer model is developed. In this 3D model, DL-MCHS is designed with and without headers. The designed heat sinks are operated under PF and CF conditions. For a specific electronic chip with dimensions of 13 mm × 40 mm at a heat flux of 5 kW/m2. The model is validated with the experimental results in the literature. It is found that, including the header design in the simulation of the DL-MCHS must be considered in the simulation to predict the accurate thermo-hydraulic performance of the DL-MCHS specially in the CF. Further, using the DL-MCHS in PF operation accomplished a lower average chip temperature compared with the CF. Furthermore, at high coolant flowrate, neglecting the effect of the header in the CFD calculations can be approximated to predict the chip surface temperature. And finally, neglecting the header in the CFD calculations significantly affect the calculated pumping power for both PF and CF operated DL-MCHS.