Experimental and numerical investigation of flattened and bent miniature heat pipes with two heat sources for laptop computers

Abstract

In this study, the combined effects of bending and flattening heat pipes with two heat sources on thermal resistance were numerically and experimentally studied. A composite wick of grooves and fibers was used in the heat pipe to prevent wick damage from the deformation of the heat pipe. The heat pipes were bent up to 90° and flattened to three final thicknesses of 2.5, 3.0 and 4.0 mm. Two discrete heat sources were supplied to the heat pipe, with a total heat load of 40 W. It was observed that not only damage to the composite wick was prevented but also the thermal performance of the heat pipe was slightly enhanced, particularly when a higher heat load was placed farther from the condenser. Bending the 3 mm final thickness heat pipe from 0° to 90° led to a 40.8% reduction in thermal resistance when supplying evaporator section 1 (located farthest from the condenser) at 30 W and a 25% reduction for another case when supplying 10 W at evaporator section 1. The mathematical models, generally used in previous studies, predicted the thermal resistance unsatisfactorily with a relative root mean square error of up to 70.74% compared with the experimental results. In this study, a novel mathematical model was developed to include the existence of liquid receding in the wick, a new concept of the contact factor at the heating surface, and the extension of an absorbable length in the fibrous wick. The proposed model provided a much better agreement with a relative root-mean-square error as low as 23.68%. Thus, the proposed mathematical model can provide better predictions of the thermal performance of the groove–fiber wick heat pipe.