Experimental study on a large scale pulsating heat pipe operating at high heat loads, different adiabatic lengths and various filling ratios of acetone, ethanol, and water

The paper presents the experimental investigation of a large scale Pulsating Heat Pipe (PHP) operating under high heating power load of up to 2 kW (56 kW/m(2)). Different Filling Ratios (FR) equal to 25, 50 and 75%, the lengths of the adiabatic Section 500, 750 and 1000 mm, respectively, and types of working fluid such as: acetone, ethanol and water were incorporated. The unique test stand consists of a meandrically arranged capillary tube with 14 bends, and a 2.5 nun internal diameter. The geometry of the PHP's tube was determined using the Bond criterion and matched to maintain capillary diameter with a wide range of used working fluid properties. For FR values of 50% and 75%, two different flow regimes were observed. It was noticed that at FR = 25% even a minimum heat load often causes dry-out phenomena. For the large PHP's scale, the maximum thermal performances were observed for FR equal to 75%. Further, water was characterized by the lowest value of thermal resistance. For acetone, at the same operational parameters, faster initiation of the pulse process and a lower value of thermal resistance was observed. The experiment indicated that for a specific liquid, the tested length of the adiabatic section does not have a significant influence on the performances. However, the impact of the adiabatic section length differed for different working fluids was recorded.