Numerical Analysis of Oscillating Heat Pipes for High Heat Flux Applications

Abstract

This research investigates oscillating heat pipes (OHPs) through numerical models. The goal is to numerically simulate OHPs and study their application for the thermal management of high heat fluxes in aerospace applications. OHPs have complex physics and are difficult to model numerically. This work first analyzes the OHPs with water as a working fluid. Learnings from the investigation are used to explore OHPs with liquid metals as working fluids. ANSYS Fluent is used with the Volume of Fluid method for the two-phase model, and the Lee Model is chosen for modeling phase change between liquid and vapor. The initial geometry of the OHP considered for the simulations is a 2D single loop, including solid walls and water as a working fluid. The boundary conditions are constant heat flux into the evaporator end, adiabatic conditions in the middle, and constant temperature at the condenser end. After exploration of the model with water as fluid, liquid metals are chosen as working fluids due to their demonstrated ability to dissipate high heat fluxes. The boundary conditions for the liquid metal OHP are similar to water-based OHPs, but high heat fluxes relevant to the leading edges of high Mach number vehicles are applied in the evaporator region. The results from the study are depicted in the form of visual vapor-slug volume fraction contours, effective thermal resistances (effective conductivities), and temperature contours.