Dynamic performance analysis on start-up of closed-loop pulsating heat pipes (CLPHPs)

The control theory (system identification theory) is introduced to quantitatively analyze the start-up performance of the closed-loop pulsating heat pipes (CLPHPs) based on an experimental investigation with various working fluids under different working conditions. A preliminary dynamic relationship between the 'input' (heat load) and 'output' (evaporator temperature) and corresponding six evaluation criteria are proposed to realize the quantitative characterization of the dynamic performance of two most common types of start-up, respectively, which provide a prerequisite for the further simulation and control design of the CLPHPs' start-up. Based on such analysis, it is indicated that the optimal liquid filling ratio for start-up is about 41% for water, 52% for ethanol, and falls within the range from 35% to 41% for methanol. The start-up performance is improved with increasing inclination angle from 0 degrees to 90 degrees. With the increasing heat load, a faster start-up speed and a better relative stability are observed while the start-up temperature is increased. Moreover, the working fluid with small dynamic viscosity, small specific heat, and especially large saturation pressure gradient versus temperature is beneficial to the start-up performance of the CLPHPs. (C) 2012 Elsevier Masson SAS. All rights reserved.