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

Abstract

Pulsating heat pipe's (PHP) are one of the alternatives to conventional heat transfer technologies. First part of this paper, titled: thermohydrodynamic behavior of methanol charged closed loop pulsating heat pipe has given information about thermo-hydrodynamic operational characteristics such as; bubble nucleation and collapse, bubble agglomeration and pumping action, flow regime changes, pressure/temperature perturbations, dynamic instabilities, meta-stable non-equilibrium conditions etc. in the PHP. Present paper, which is an extension of the previous work, it presents some more thermal results to highlight the effect of; thermo-physical properties of working fluid, filling ratio and number of turns on thermal performance of PHP. Three different PHP loop has been made from six, four and two parallel glass tubes (i.e. three turns, two turns and one turn at evaporator section) 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. The experimentation conducted for different working fluids (water, ethanol, methanol and acetone), different filling ratio's (30%FR, 50%FR and 70%FR) and different number of turns (one, two and three turns). The motto of present research is to understand the thermal performance in terms of thermal resistance of PHP in details. The result shows that, thermal resistance for all working fluid PHP's rapidly decreases with increasing heating power up to 32W. For low heating power, working fluid (acetone) which has lower boiling temperature is best, but it cannot give the service for higher heating power. Two turn PHP loop with methanol 50% volumetric filling ratio at more than 32W heating power with one directional flow circulation is the optimum operating condition of present research.

Small-Sized Pulsating Heat Pipes/Oscillating Heat Pipes with Low Thermal Resistance and High Heat Transport Capability

“…In contrast to this, as shown above, no dryout phenomena were observed on the PHP with 1 × 1 mm 2 channels. The higher stability of PHP activity in the small-channel PHP for high heat powers is in good agreement with previous reports in the literature [10,14], as outlined in Section 2.1. For horizontal orientation, taking care to ensure a high PHP activity (bubble growth, collapse, fluid exchange between evaporator and condenser, etc.)…”

“…The reason is that as the number of channels increases, so does the internal pertubation in terms of bubble growth and collapse [10], which is one of the basic processes governing PHP activity and performance. Additionally, the higher level of local perturbations helps to avoid vapor phase recoiling in the evaporator and liquid merging in the condenser [14]. From this, it can be concluded that PHPs with a larger number of channels are likely to work in a more "stable" way, as the pulsating motion can be sustained for a larger range of input powers.…”

Thermal performance prediction models for a pulsating heat pipe using Artificial Neural Network (ANN) and Regression/Correlation Analysis (RCA)

“…The dimensionless numbers depend on thermophysical properties of the WFs, which in turn depend on temperature. Temperature data reported in the literature are very limited [41][42][43][44][45][46][47][48]. Hence, the subsequent development of correlation is carried out with a total of 920 data.…”

Flat-Plate PHP with Gravity-Independent Performance and High Maximum Thermal Load

“…As the number of channels increases, so does the internal perturbation in terms of bubble growth and collapse [10], which is one of the basic processes governing PHP activity and performance. Additionally, the higher level of local perturbations helps to avoid vapor phase recoiling in the evaporator and liquid merging in the condenser [12]. From this, it can be concluded that PHPs with a large number of channels are likely to work more "stable" as the pulsating motion can be sustained for a larger range of input powers.…”