Performance of heat pipes as capillary pumps: modelling and comparison with experimental results

Abstract

The objective of this paper is to present a theoretical investigation of the operational characteristics on a small-scale Capillary Pump Loop (CPL), focused on the CPL capacity to create flow in addition to its heat transfer capacity. A typical design of a CPL is composed of a capillary evaporator, a condenser, a two-phase reservoir, liquid and vapour lines. The capillary evaporator generates the required pressure pumping for moving the working fluid from the condenser to the evaporator section. The fundamental principles of the proposed modelling are: The overall pressure drop in the loop must be less than the maximum capillary pressure in order to ensure that the system will operate continuously. The major components of the CPL pressure drop are related to the flow in the wick structure, condenser, vapour and liquid lines. The wick structure present in the evaporator causes a flow restriction that affects the CPL performance, which is dependent on the wick permeability, a property of the porous material that describes its ability to transport the liquid under an applied pressure gradient. An experimental lab-scale installation is used for the validation of the theoretical analysis. The results showed that the proposed CPL modelling is able to describe the CPL performance very well.