An analytical and experimental study of heat pipe performance with a working fluid exhibiting strong concentration Marangoni effects

An original performance study of an inclined gravity-assisted heat pipe with a 0.05 M 2-propanol/water binary mixture, exhibiting strong concentration Marangoni effects, was experimentally investigated. Initial experiments were carried out for varying liquid charge levels between 30% and 70%, to determine an optimal value that would enhance heat transport performance by maximizing the critical heat flux (CHF) condition, while reducing the evaporator wall superheat. A 45% liquid charge ratio was found to have the lowest overall superheat, and highest CHF condition attained, as high as 114.8 W/cm2. Nucleate pool boiling contributions were found to have a greater impact on heat pipe thermal conductance, constituting 65% and 71% of the total heat transport for water and 0.05 M 2-propanol/water mixture respectively. Additionally, a 49% thermal conductance and 53% CHF improvement was found with 0.05 M 2-propanol/water as the working fluid over that of pure water. This investigation also introduces a novel binary mixture model for the inclined, gravity-assisted heat pipe. Modeling results of the system with a 45% fill ratio were found to provide good prediction of the experimental results with an average thermal conductance deviation of 0.5 W/K, and an evaporator-section pool boiling rms deviation of 14.3%. This model employs an average pseudo single-component (PSC) coefficient in place of an ideal heat transfer coefficient (HTC), and an empirically-determined binary mixture surface tension correlation, due to the non-ideal nature of the low concentration 2-propanol/water mixture.