Thermal fluid characteristics of pulsating heat pipe in radially rotating thin pad

Abstract

The thermal performances of a radially rotating pulsating heat pipe (RPHP) formulated by the interconnected 1 × 4 mm2 channels in the thin pad were investigated. With the 50% filling ratio of water and the specific geometric configurations, the selected parameters controlling the thermal-fluid phenomena by the present study were boiling number (Bn), dimensionless centrifugal acceleration (Ω) and thermal resistance of condenser (Rth,cond). The vapor-liquid flow images, heat transfer rates and thermal resistances of the pad-type RPHP were detected at the rotor speeds of 0, 100, 300 and 500 rev/min. The matrix of test conditions was formulated by four Bn, four Rth,cond and four Ω for both sets of flow visualization and heat transfer tests. As Ω increased from 0 to 27.8, the intermittent vapor slugs gradually deformed toward the tiny bubbles to incur the respective Nusselt number reductions and elevations over the evaporator and condenser of the RPHP. As the dominance of condenser heat transfer rate in constructing the overall thermal resistance (Rth) took precedence to its evaporator counterpart, the increases of Ω led to the Rth reductions for the present RPHP. The empirical correlations using Bn, Ω and Rth,con as the controlling parameters were devised to evaluate Rth and the regionally averaged Nusselt numbers over the evaporator and condenser of the present RPHP for relevant applications.