Experimental investigation on the thermal characteristics of ultra-thin flattened heat pipes with bending angles

摘要

Although many works have been published with regard to devising ultra-thin flattened heat pipes (UTFHPs) and flexible heat pipes, none conceives the idea of combining flexibility with UTFHPs. This work makes great efforts to experimentally ascertaining the effects of bending on the thermal performance of UTFHPs with thickness below 1.5 mm in order to bridge the gap between flexibility and UTFHPs. The samples were tested under the bending angle from 0 degrees to 180 degrees with three different curvature diameters: 1.5 cm, 2 cm, and 2.5 cm. The testing results demonstrate that at constant input power, larger bending angle or smaller curvature diameter cause the thermal resistance and evaporator temperature climb up. Besides, uniformity of axial temperature was upset by bending due to continuously expanded temperature differences in adiabatic section. Maximum heat transfer capacity declined for more than 90% when the bending angle changes from 0 degrees to 180 degrees. The most severe degradation of it sits within the bending angle of 0 degrees to 30 degrees for more than 50%. But even at the largest bending deformation, the UTFHPs could still efficiently operate with low thermal resistance and low evaporator temperature within allowable input power. Finally, an empirical equation to predict the evaporator temperature at given input power, bending angle, and curvature diameter was proposed on the basis of experimental data.

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