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The IUP Journal of Mechanical Engineering
Experimental Investigation of Thermal Performance Characteristics
of Different Fluids in a Closed Loop Pulsating Heat Pipe
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In the present paper, a simplified geometry of Closed Loop Pulsating Heat Pipe (CLPHP), made of Copper (Cu) tube of internal diameter 2 mm and outer diameter 4 mm having 9 number of turns charged with three different fluids, namely, methanol, acetone and ethyl acetate, is used. The various input parameters such as heating power and evaporator temperature are varied to evaluate the thermal performance in terms of thermal resistance, heat transfer rate and heat transfer coefficient and their thermodynamical properties. Acetone shows the best performance among the three fluids in heat transfer performance due to least value of dynamic viscosity. The heat transfer rate clearly shows the increase of amplitude with increase in evaporator temperature. Acetone and ethyl acetate show less start-up period due to higher value of surface tension. Due to higher value of specific heat, ethyl acetate shows high frequency and least amplitude of heat transfer rate in CLPHP. The value of latent heat of vaporization influences the timings of phenomenon of dry out and affects the heat transfer coefficient and thermal resistance.

 
 

Energy management is an important factor in designing electronic components. Pulsating Heat Pipe (PHP) is an emerging solution to heat transfer in micro, mini and macro components. PHP is basically a capillary tube filled with two-phase of fluid inside it. The tube can be of any conducting material and has three fragments. Evaporator section helps to increase temperature difference between sections. Adiabatic section is middle of both sections and is set at atmosphere temperature. Condenser section, also called cold region, helps to create oscillation of fluid inside the PHP by creating the pressure difference. PHP as a passive device of heat transfer emerges as major source of heat transfer in micro, mini and macro components of electronic and other applications. Zhihu and Wie (2014) studied the performance of Closed Loop Pulsating Heat Pipe (CLPHP) using ammonia as working fluid, consisting of six turns, fully made of quartz glass tubes with 6 mm outer diameter and 2 mm inner diameter for filling ratio 50%. The thermal resistance decreases with the increase in inclination angle (Zhu et al., 2014).

Xu et al. (2005) studied the high speed flow visualization results for the CLPHPs and concluded that the intricate collective effects of bubble nucleation, condensation and coalescence were responsible for the oscillation flow in PHP. Han et al. (2014) investigated by taking CLPHP (i.d 2.0 mm) filled with deionized water, acetone, methanol, ethanol for heat transfer performance and oscillating characteristics so as to check the influence of thermophysics properties over PHP’s performance under different conditions such as different filling ratios (20-95%) and different heat inputs (5-100 w). Oscillation characteristics and the heat transfer performance of a CLPHP (inner diameter 2 mm) charged with deionised water, methanol, ethanol and acetone were investigated. The results explained that at higher heat input, higher latent heat of vaporization was not favorable. Fluid with less latent heat of vaporization has low boiling point so easy to dry out at low filling ratio.