Modeling Ultra-Thin Flat Loop Heat Pipes using a 1-D Lumped Parameter Approach

In the present study, the transient behavior of a diffusion-bonded ultra-thin LHP, specifically designed for the thermal management of smartphones, is predicted by means of a 1-D Lumped Parameter Model (LPM). The LPM approach was previously validated for larger LHPs with different working fluids and is one of the few highly reliable transient models available in literature. The main novelty of this work is the extension of the application range of the LPM model to ultra-thin LHPs, where various parameters may affect the operation of these devices, such as heat leakage by conduction through the case material. The proposed LPM consists of a thermal network describing the thermo-fluidic behavior of the evaporator, connected to a series of mass, momentum, and energy conservation, solved iteratively to predict the device temperatures, heat transfer rates, and thermal resistances. The LPM model successfully predicted the transient temperature of the LHP with the highest and lowest average difference of 0.99 °C and 1.65 °C, respectively. Also, this approach estimated the steady-state thermal resistance with an average discrepancy of 28%. Therefore, the LPM showed to be a powerful design tool to predict and simulate the operation conditions of heat pipes, from ultra-thin to larger ones.