Thermo-Hydrodynamic Behavior of Methanol Charged Closed Loop Pulsating Heat Pipe

Abstract

Flow visualization experiment has conducted on the methanol charged vertical Closed Loop Pulsating Heat Pipe (PHP) to investigate the effect of different heat inputs on overall thermal resistance, average evaporator and condenser temperature and corresponding hydrodynamic behavior. A PHP has made from four parallel glass tubes forming adiabatic section, interconnected alternately by copper U tubes, having internal and external diameter 2 mm and 3.06 mm respectively. The length of evaporator, condenser and adiabatic section are 42 mm, 50 mm and 170 mm respectively. For experimentation, filling ratio (FR) 50% and vertical bottom heating mode position was maintained. Electrical heat input to the evaporator varies from 8W to 80W with interval of 8W after steady state was reached. The result shows that, thermal resistance of a PHP rapidly decreases with increasing heating power from 8W to 32W and thereafter reasonably steady for further heating powers. From visualization it is observed that, the thermal performance of a PHP is dependent on the flow patterns in PHP tubes. Continuous unidirectional flow circulation in the tubes of PHP gives best thermal performance than pulsation and dry-out conditions.

Effect of Working Fluid, Filling Ratio and Number of Turns on Pulsating Heat Pipe Thermal Performance

“…In the first part of this paper, Borkar and Pachghare (2014) conclude that, the thermal performance of device increases with increasing heat input. With increasing heat input, the evaporator temperature rises, resulting in a greater density gradient in the tubes, simultaneously the liquid viscosity also drops, that diminishing the wall friction and evaporation rate of working fluid inside the loop.…”

Experimental Investigation of a Large Scale-oscillating Heat Pipe at Different Inclinations

“…However, this benefit does not have much effect on the working fluid movement and heat transfer capability. At start-up, the working fluid regime is generally in the form of slug flow (Borkar & Pachghare, 2014). Thus, the effect of gravitational potential is much more dominant than other patterns, such as annular/semi annular patterns.…”

Temperature Evolution of Large-Scale Oscillating Heat Pipe with Methanol as the Working Fluid

“…One of the methods to evaluate OHP characteristics and performance is by observing the oscillation temperature of the evaporator, adiabatic and condenser. The observations of temperature evolution were analyzed and associated with visualization studies by previous researchers [2,9,12,15,20]. When heat was applied on the evaporator section, the evaporator temperature (T4) and adiabatic (T2 and T8) immediately increased with different degrees of slope (shown in Fig.…”

“…An experimental study by Saha et al [10] showed that methanol and water should be the first consideration when choosing a working fluid for open loop OHP with vertical and horizontal orientation. Several visual studies have been conducted by various researchers that successfully characterized at least five different flow patterns [2,9,[11][12][13][14][15][16]. The results were dispersed bubble, vapor plug, long vapor plug, semi-annular flow and annular flow.…”

“…Higher amplitude and frequency of temperature fluctuation at the condenser also increased, indicating more vapor fully condensed at this stage. According to the visualization study [12], the random movement of working fluid at low heat supply resulted from slug flow of bulk circulation flow. The more active slug flow bulk circulation is, the higher heat transfer coefficient of force convection is and the lower the thermal resistance is.…”