Thermal performance of a cylindrical shell-like thin networked pulsating heat pipe

Abstract

The cylindrical vapor chamber with its interior vapor–liquid circulation facilitated by the pulsating heat pipe network at the 50% filling ratio of distilled water was proposed. The total heating area of the two annular evaporators at both axial ends is identical with the middle condenser cooling area. With the equal heat flux emitted from each evaporator, the measurements of the overall thermal resistance, the Nusselt numbers of evaporator and condenser, the temporal pressure variation and the skin temperature uniformity over the condenser were carried out with the total heating power in the range of 30–90 W at the inclination angles of 0 (horizontal), π/6, π/3, π/2 (vertical) and six cooling airflow rates for each heating power tested. The thermal resistances of the two evaporators were both decreased as the heater power increased but their difference was systematically enlarged by tilting the vapor chamber from horizontal to vertical orientations. The power spectrum of the time-domain pressure signal revealed two dominant frequencies in association with the vapor bubble agitations in the pulsating heat pipe network at all the test conditions. These frequencies and the heating power dominated the thermal performances of the vapor chamber after demonstrating that the responses of the dominant frequencies to the changes in heating and cooling conditions correlated well with the corresponding variations in the overall thermal resistance and the temperature uniformity of the condenser. Referring to the results measured from the planar vapor chambers in the literature, the comparative thermal performances of the cylindrical thin vapor chamber were disclosed. A set of empirical correlation was developed to permit the evaluation of the overall thermal resistances of the two evaporators for relevant applications.