Experimental Investigation of a Flat-Plate Oscillating Heat Pipe With Modified Evaporator and Condenser

Abstract

The thermal performance of a flat-plate oscillating heat pipe (FP-OHP) - with modified evaporator and condenser was experimentally investigated during high heat flux conditions. The copper FP-OHP (101.6 × 101.6 × 3.18 mm3) possessed two inter-connected layers of 1.02 mm2 square channels with the evaporator and condenser possessing two parallel, 0.25 × 0.51 mm2 square microchannels. The microchannels were integrated to enhance evaporation and condensation heat transfer to improve the FP-OHP’s ability to transport high heat flux. The FP-OHP was oriented vertically and locally heated with a 14.52 cm2 heating block at its base and cooled with a water block that provided either: 20 °C, 40 °C, or 60 °C operating temperatures. A FP-OHP without embedded microchannels was also investigated for baseline performance comparison. Both FP-OHPs were filled with Novec HFE-7200 (3M) working fluid at a filling ratio of approximately 80% by volume. The maximum temperature of each FP-OHP was recorded versus time for various heat inputs for the investigated operating temperatures. The results indicate that the integrated microchannels enhance the FP-OHP’s thermal performance for all operating temperatures. At 20 °C, 40 °C, and 60 °C, the microchannel-embedded evaporator and condenser dissipated 80 W, 65 W, and 55 W more than the baseline control with a minimum thermal resistance of 0.219 °C/W, 0.205 °C/W, and 0.170 °C/W, respectively — corresponding to a percent enhancement on-the-order of 25%. This percent enhancement increased with operating temperature. It has also been shown that Novec HFE-7200 allows the FP-OHP to start at relatively lower heat inputs — as low as 35 W, demonstrating that this working fluid can enhance heat transfer even at lower heat flux applications.

High-Speed Visual Analysis of Fluid Flow and Heat Transfer in Oscillating Heat Pipes with Different Diameters

“…In addition, some researchers made efforts to enhance the thermal performance of the OHP by using the nanofluids [23,24] and mixed working fluid [25]. The optimal design of capillary channel geometry has also been conducted to successfully improve the operation stability and heat transfer of the flat-plate OHP [26][27][28]. Note that the previous studies indicated that the thermal performance of OHP is affected by many parameters such as geometric parameters, working fluid properties, heating load and heating modes, inclination angle, filling ratio, number of turns, and gravity load, etc.…”