Heat transfer and pressure drop performance of printed circuit heat exchanger with different fin structures

Abstract

With the development of compact electronic system, the cooling problem with high heat flux in the electronic system has attached much more attention. The high-efficiency cooling devices with micro-channels are investigated and widely used in order to stabilize the surface of the component under the safe temperature. In recent years, a new type of cooler called printed circuit heat exchanger (PCHE), which has characteristics of high heat transfer ability and high compactness, is applied to act the heat sink of devices with high heat flux. The plates of the PCHE are fabricated by photochemical etching method, which can easily process the complex flow channels at low cost. Then, the plates can be stacked and brazed with the diffusion bonding technique in the vacuum circumstance. In this paper, the electronic device with the heat flux of 6.05×105 W/m2 is cooling by water at 25°C and 0.2 MPa. The geometric dimension is 143.2 mm×30 mm and the material is copper. Meanwhile, the heat is original generated from the bottom of the device and the PCHE is fixed on the top of the model to transfer heat. The hydrodynamic and heat transfer performances of PCHEs with different structures of fins are analyzed by numerical method. The models of PCHE with continuous straight fins and discontinuous fins, including the circle fins, ellipse fins, airfoil fins and modified airfoil fins, are constructed. It is worth to point out that the straight model and the circle model are compared in the same cross section area and the other three discontinuous models are compared in the same fin perimeters. Furthermore, the symmetry boundary condition is used in the width direction and the edge effect is neglected according to previous research. The SST k - ω turbulence model assembled in the commercial CFX 12.1 software is validated reasonably to solve the problem in our cases. The result shows that the discontinuous circle fins have better heat transfer performance than the continuous straight fins, which because the fluid can break the boundary layer more effectively with the velocity variation in flow direction. However, the pressure drop also increases in the discontinuous model due to the separated blocks. On the other hand, it can be seen that the Nusselt number increases with the increase of Reynolds number and the gradient become slow, which indicated that it is limited to enhance the heat transfer by increasing the mass flow rate. However, the pressure drop increase exponentially at high Reynolds number. The average Nusselt number of the PCHE with circle fins, ellipse fins, airfoil fins increases 70.2%, 45.5% and 29.1% and the pressure drop also increases 340%, 114% and 40.9%, respectively, comparing with the continuous straight fins. Furthermore, it is found that the PCHE cooler with modified airfoil fins has better comprehensive heat transfer performance, which is based on the heat transfer rate and pressure loss per unit length, especially under the high mass flow rate condition. Comparing with the continuous straight fins, it can be seen that the average Nusselt number increases by 20.2%, and the pump power only increase by 5.6%. It can be concluded that the reduction of pressure loss is the major point for the optimization of the PCHE with discontinuous fins.