MicroChannel heat sink

Kim SJ (2004) Methods for thermal optimization of microchannel heat sinks. Heat Transfer Eng 25(l) 37-49... 

Ng EYK, Poh ST (1999) Investigative study of manifold microchannel heat sinks for electronic cooling design. J Electron Manuf 9(2) 155-166... 

Taking into account typical numbers for a and D, this underlines that the channel width should be considerably smaller than 1 mm (1000 pm) in order to achieve short residence times. Actually, heat exchangers of such small dimensions are not completely new, because liquid cooled microchannel heat sinks for electronic applications allowing heat fluxes of 790 watts/cm2 were already known in 1981 [46]. About 9 years later a 1 cm3 cross flow heat exchanger with a high aspect ratio and channel widths between 80 and 100 pm was fabricated by KFK [10, 47]. The overall heat transport for this system was reported to be 20 kW. This concept of multiple, parallel channels of short length to obtain small pressure drops has also been realized by other workers, e.g. by PNNL and IMM. IMM has reported a counter-current flow heat exchanger with heat transfer coefficients of up to 2.4 kW/m2 K [45] (see Fig. 3). 

Research topics on gas-liquid two-phase flows in microchannels are receiving increasing notice recently due to its importance in such areas as two-phase microchannel heat sinks, identification of micro-scaled... 

Choquette et al. [10] performed analyses to obtain momentum and thermal characteristics in microchannel heat sinks. A computer code was developed to evaluate the performance capabilities, power requirements, efficiencies of heat sinks, and for heat sink optimization. Significant reductions in the total thermal resistance were found not to be achieved by designing for turbulent flows, mainly due to the significantly higher pumping power requirements realized, which offset the slight increase in the thermal performance. 

Kim et al. [22] modeled microchannel heat sinks as porous structures, while stud3ung the forced convective heat transfer through the microchannels. From the analytical solution, the Darcy number and the effective thermal conductivity ratio were identified as variables of engineering importance. 

Choquette, S.F., Faghri, M., Channchi, M. and Asako, Y., Optimum Design of MicroChannel Heat Sinks, ASME Microelectromechanical Systems, 1996, DSC-59, 115-126. 

Ryu, J.H., Choi, D.H. and Kim, S.J., Three-Dimensional Numerical Optimization of a Manifold MicroChannel Heat Sink, Int. J. Heat Mass Transfer, 2003, 46, 1553-1562. 

For the effective and economical design of microchannel heat sinks, some key design parameters should be considered and optimized. These are, the pressure required for pumping the cooling fluid, the mass flow rate of the cooling fluid, the hydraulic diameter of the channels, the temperature of the fluid and the channel wall, and the number of channels. In order to imderstand the effect of these parameters on the system, the dynamic behavior and heat transfer characteristics of fluids at the microscale must be well-understood. 

Zhang L, Goodson KE, Kenny TW (2004) Silicon microchannel heat sinks. Springer, Berlin/Heidelberg... 

Flow of coolants in micro-cOTiduits MicroChannel heat sinks (MCHS) Micro-heat exchangers Miniature heat-removal devices Nanofluid flow in microchannels... 

Microscale Cooling Devices, Fig. 1 Typical microchannel heat sink elements and the current computational trapezoidal microchannel unit... 

In order to provide some physical insight into the dynamics of microchannel heat sinks (MCHS), steady laminar water flow in a smooth single trapezoidal microchannel is discussed and compared with measured data sets. Then the effects of nanofluids on augmented MCHS heat transfer are introduced, employing very simple correlations for the enhanced thermal conductivities of the mixtures. The fluid flow and heat transfer simulations have been carried out with the commercial... 

Heat removal and control has become a challenging task with the application of various high-power, high-speed microelectromechanical systems (MEMS) in electronics or mechanical equipment. As discussed, most solutions are based mi microchannel heat sinks which commonly consist of an array of microchannels. 

Qu and Mudawar [19] discussed a comprehensive methodology for optimizing the design of a two-phase microchannel heat sink. In their study, flow rate and pressure drop were key constraints in the design of microchannel heat sinks which often demanded specialized micro-pumps with performances dictated by either flow rate or pressure drop. For a fixed flow rate of Q = 60 ml/min and a device heat flux of qeft" = 500 W/cm, the acceptable range of two-phase operation was confined so that the dissipative heat flux will not exceed the maximum dissipative heat flux of the microchannel heat sink. For two-phase microchannel heat sinks, the minimum dissipative heat and maximum dissipative heat are defined as ... 

Here, and Tjn are the fluid saturation temperature and inlet temperature, respectively W and L are the width and length of the microchannel heat sink, respectively and h is the latent heat of vaporization. Finally, they provided the numerical procedure for the optimal design of two-phase microchannel heat sink either... 

Jang and Kim [20] investigated experimentally fluid flow and heat transfer characteristics of a microchannel heat sink, again subject to an impinging jet. This type of heat sink retains the high heat transfer coefficient associated with a typical microchannel heat sink and experiences a low pressure drop compared to the microchannel heat sink with parallel flow. 

The authors modeled the microchannel heat sink, subject to an impinging jet, as a porous medium. Based on their experimental results, they suggested correlatiOTis for the pressure drop across a microchannel heat sink subject to an impinging jet as well as its thermal resistance as follows ... 

Microscale Cooling Devices, Fig. 6 Map of general performance trends for a typical two-phase microchannel heat sink (a) fixed total volume flow rate and (b) fixed pressure drop [19]... 

Li and Peterson [9] investigated numerically the thermal performance of silicon-based microchannel heat sinks using a simplified heat transfer model, i.e., 2D fluid flow and 3D heat transfer analysis. The tested rectangular microchannels had widths ranging from 20 to 220 pm and depths ranging from 100 to 400 pm. The effect of microchannel geometry... 

Microscale Cooling Devices, Fig. 8 Thermal resistances forFHS of both 60 and 100 PPI and the microchannel heat sink with respect to (a) the pressure drop and (b) the pumping power [21]... 

Chein and Huang [15] analyzed the silicon microchannel heat sink performance using Cu — H2O nanofluid. Two specific geometries, one with Vkch = fin = 100 fiin and Lch = 300 pm and the other with Wch = = 57 pm and... 

Jang and Choi [26] numerically investigated the cooling performance of a microchannel heat sink with nanofluids. Two kinds of nanofluids were investigated in this study, i.e., d = 6 nm nanoparticles in a copper-water mixture and dp = 2 nm diamond-in-water nanofluid. A theoretical model was employed for the thermal conductivity of nanofluids that accounts for four modes of energy transport the thermal diffusion in the base fluid, the thermal diffusion of nanoparticles, the collision between the nanoparticles, and the nanoconvection due to Brownian motion. Specifically,... 

Figure 10a compares the previous experimental findings [27] with the results of the new model. With the new effective thermal conductivity model, the cooling performance of the microchannel heat sink with nanofluids was considered. The cooling performance of a microchannel heat sink with nanofluids was evaluated in terms of the thermal resistance 0, which is defined as... 

Fig. 10 Nanofluid flow applications in microchannel heat sinks ...

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