Modeling Laminar Fluid Flows in Rectangular Vapor Grooves of Evaporators Used in Loop Heat Pipes

Loop heat pipes (LHPs) are devices in which capillary forces in a wick and liquid-vapor phase-change phenomena are used to achieve continuous and relatively high rates of transfer of thermal energy from a heat source to a heat sink. Quasi one-dimensional models of the fluid flow and heat transfer within LHPs, with empirical correlations as inputs, are commonly used as the basis of cost-effective computer simulations for the design and optimization of these devices for specific applications. The focus in this work is on laminar fluid flows in straight rectangular vapor grooves of flat evaporators used in LHPs. The pressure drops for such fluid flows are computed in available quasi one-dimensional models of LHPs using correlations for a friction factor that applies strictly only in the fully-developed region of flows in straight rectangular ducts with impermeable walls. The resulting errors can become serious if the pressure drop in the vapor grooves is a significant contributor to the overall pressure drop in the LHP. Thus, to enhance the capabilities of current quasi one-dimensional models of LHPs, more accurate correlations for predicting the aforementioned pressure drop are needed. In this work, a three-dimensional parabolic finite volume method is used to simulate laminar Newtonian fluid flows in straight rectangular vapor grooves of flat evaporators, for a representative range of LHP operating conditions. The mathematical model, computational methodology, results, and suitable correlations for the pressure drops are presented and discussed in this paper.