Experimental Investigation and Numerical Simulation of Loop Thermosyphons

A Non-phase change heat pipe (NPCHP) with no wick was proposed recently as a new heat pipe which is not dependent on a wick or phase change at steady state operation and where the heat transfer is driven by the pressure response to a heat input, rather than phase change. The NPCHP is not a new device as suggested but is a loop thermosyphon with very high fill ratio. This effort focuses on proving the NPCHP, as an overfilled loop thermosyphon, is an effective heat transfer device through experiments and numerical simulations. An analysis of the operation and effectiveness of the thermosyphon is performed through both experimentation and numerical simulation. The loop thermosyphon is shown to have a high effective thermal conductivity when tested with water and R134a as working fluids in several fill ratios and heat inputs greater than 200W, a fast thermal response time, and a high heat flux on the order of 105 W/m2. NPCHP exhibits characteristics of a loop thermosyphon and can be classified as such. This effort also focuses on understanding how changing different system parameters, including heat inputs of 100-350W, fill ratios of 25-100% for water and R314a as working fluids, and inclination angles of with the evaporator vertically below the condenser, at a 45o angle with the evaporator below the condenser, horizontal, and vertical with the evaporator above the condenser, affect the overall system performance of the loop thermosyphon. A detailed experimental investigation including flow visualization is performed. Depending on the initial fill ratio and working fluid, the loop thermosyphon is shown to either operate as a two-phase loop thermosyphon (TPLTS) or a single-phase loop thermosyphon (SPLTS). Finally, a detailed 2D computational fluid dynamics (CFD) model simulating two-phase flow and heat transfer in a TPLTS is presented. The CFD simulation was built to represent two-phase flow and heat transfer phenomena during the transient analysis of a TPLTS under various operating conditions. The two-phase flow was modeled using the volume of fluid (VOF) model, and the Lee model was utilized for evaporation and condensation. Simulation results were compared with experimental temperature, pressure, and flow visualization data