On Studying Fluidic Motions in an Oscillating Heat Pipe

2013 ◽  
Vol 284-287 ◽  
pp. 513-517
Author(s):  
Han Ming Chen ◽  
Ching Ming Chiang ◽  
Kuo Hsiang Chien ◽  
Chi Chuan Wang
Keyword(s):  
Heat Pipe ◽  
Temperature Difference ◽  
Closed Loop ◽  
Operating Temperature ◽  
Lower Number ◽  
Liquid Ratio ◽  
Oscillating Heat Pipe ◽  
Thermally Driven ◽  
Higher Temperature ◽  
Channel Configuration

This study develops an analytical model applicable for predicting the fluidic motion of an oscillating heat pipe (OHP) with asymmetric arrayed channel configuration. The analytic model considers the temperature difference between the average evaporating region and the average condensing region as the thermally driven force for the fluidic motion. The calculated results show that the closed-loop OHP with asymmetric arrayed channel under lower number of turns, lower filled liquid ratio, higher operating temperature and higher temperature difference between the average evaporating region and the average condensing region for the frequency ratio of unity could attain a better performance of the fluidic motions.

Heat Transport Limitation of a Triangular Micro Heat Pipe

2003 ◽  
Author(s):  
D. Sugumar ◽  
Kek Kiong Tio
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Operating Temperature ◽  
Working Fluid ◽  
Transport Capacity ◽  
Condenser Section ◽  
Micro Heat Pipe ◽  
Evaporator Section ◽  
Higher Temperature ◽  
Specific Temperature

A micro heat pipe will operate effectively by achieving its maximum possible heat transport capacity only if it is to operate at a specific temperature, i.e., design temperature. In reality, micro heat pipe’s may be required to operate at temperatures different from the design temperature. In this study, the heat transport capacity of an equilateral triangle micro heat pipe is investigated. The micro heat pipe is filled optimally with working fluid for a specific design temperature and operated at different operating temperatures. For this purpose, water, pentane and acetone was selected as the working fluids. From the numerical results obtained, it shows that the optimal charge level of the micro heat pipe is dependent on the operating temperature. Furthermore, the results also shows that if the micro heat pipe is to be operated at temperatures other than its design temperature, its heat transport capacity is limited by the occurrence of flooding at the condenser section or dryout at the evaporator section, depending on the operating temperature and type of working fluid. It is observed that when the micro heat pipe is operated at a higher temperature than its design temperature, the heat transport capacity increases but limited by the onset of dryout at the evaporator section. However, the heat transport capacity decreases if it is to be operated at lower temperatures than its design temperature due to the occurrence of flooding at condenser end. From the results obtained, we can conclude that the performance of a micro heat pipe is decreased if it is to be operated at temperatures other than its design temperature.

Acoustic Radiation, Cavitation Collapses, and Dryout in a Capillary Oscillating Heat Pipe

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Steve Q. Cai
Keyword(s):  
Heat Pipe ◽  
Temperature Difference ◽  
Two Phase Flow ◽  
Acoustic Radiation ◽  
Operating Temperature ◽  
Critical Diameter ◽  
Phase Flow ◽  
Vapor Bubbles ◽  
Temperature Zone ◽  
Two Phase

Abstract In an oscillation heat pipe (OHP), when two-phase flow oscillates to the condensation region, saturated vapor bubbles/slugs are subjected to a sudden temperature reduction or immediate subcooling. Rapid condensation ruptures vapor bubbles and generates cavitation erosions on the tube interior surface. In this article, a thorough study is performed to understand discrepancy of variation tendency between acoustic radiation and OHP temperature difference that both are operating temperature-dependent. On this basis, three temperature zones were identified: (1) low operating temperature zone with strong cavitation collapse and acoustic radiations, (2) optimal temperature zone with the minimum temperature difference and weakening cavitation collapses, and, (3) high-temperature zone where dryout and oscillation failures develop. At the optimal operating temperature, high-frequent oscillations reduce subcooling of two-phase flow, alleviating the impact of cavitation collapses and ceasing acoustic radiations. At high operating temperature, liquid surface tension dramatically reduces and dynamic contact angle significantly increases. Both the factors tend to lower the critical diameter necessary to maintain pressure difference and oscillating two-phase slug flow. When the critical diameter reduces to be less than the OHP tube diameter, liquid slugs are not able to seal the OHP capillary tubes, leading to dryout or insufficient heat and mass transfer.

Heat Transport Capability in an Oscillating Heat Pipe

2008 ◽  
Vol 130 (8) ◽  
Author(s):  
H. B. Ma ◽  
B. Borgmeyer ◽  
P. Cheng ◽  
Y. Zhang
Keyword(s):  
Heat Transfer ◽  
Mathematical Model ◽  
Experimental Investigation ◽  
Heat Pipe ◽  
Temperature Difference ◽  
Convection Heat Transfer ◽  
Power Input ◽  
Film Condensation ◽  
Oscillating Heat Pipe ◽  
Oscillating Motion

A mathematical model predicting the oscillating motion in an oscillating heat pipe is developed. The model considers the vapor bubble as the gas spring for the oscillating motions including effects of operating temperature, nonlinear vapor bulk modulus, and temperature difference between the evaporator and the condenser. Combining the oscillating motion predicted by the model, a mathematical model predicting the temperature difference between the evaporator and the condenser is developed including the effects of the forced convection heat transfer due to the oscillating motion, the confined evaporating heat transfer in the evaporating section, and the thin film condensation in the condensing section. In order to verify the mathematical model, an experimental investigation was conducted on a copper oscillating heat pipe with eight turns. Experimental results indicate that there exists an onset power input for the excitation of oscillating motions in an oscillating heat pipe, i.e., when the input power or the temperature difference from the evaporating section to the condensing section was higher than this onset value the oscillating motion started, resulting in an enhancement of the heat transfer in the oscillating heat pipe. Results of the combined theoretical and experimental investigation will assist in optimizing the heat transfer performance and provide a better understanding of heat transfer mechanisms occurring in the oscillating heat pipe.

Sign in / Sign up

Export Citation Format

Share Document