Visualization Experiment on the Steady Operating Process of the close Loop Pulsating Heat Pipe

2013 ◽  
Vol 732-733 ◽  
pp. 318-321 ◽  
Author(s):  
Xun Wang ◽  
Yun Zhao Li ◽  
Cheng Si Yang ◽  
Xiao Wen Zhang
Keyword(s):  
Heat Pipe ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Heating Power ◽  
Pulsating Heat Pipe ◽  
Heating Section ◽  
Operating Process ◽  
Visualization Experiment ◽  
Long Time ◽  
Churn Flow

A visualization experimental investigation for the pulsating heat pipe (PHP) was carried out to obtain the flow characteristics in the PHP steady operating process with controlling the input heat flux and condensing temperature. The experimental results show that the flow patterns are mainly slug flow with the intermittent pulsation at low heating power, churn flow, and annular flow with steady unidirectional circulation at high heating power. The flow direction switch phenomenon was also observed and analyzed. When the PHP heating section is occupied by vapor slugs for a long time, the backflow phenomenon provides liquid to the bottom of the heating section and reforms a new liquid slug.

Visualization Experiment on the Start-up Performance of the Close Loop Pulsating Heat Pipe

2012 ◽  
Vol 550-553 ◽  
pp. 3150-3154 ◽  
Author(s):  
Xun Wang ◽  
Cheng Si Yang ◽  
Xin Xin Mao ◽  
Tong Han
Keyword(s):  
Heat Pipe ◽  
Heat Load ◽  
Early Stage ◽  
Flow Direction ◽  
High Heat ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Optical Visualization ◽  
Start Up ◽  
Visualization Experiment

Through the visualization experiment, the behavior evolution of the vapor and liquid slugs in the pulsating heat pipe (PHP) was investigated in the start-up process. Optical visualization results indicate that the flow pattern mainly is slug flow in the start-up process. In the early stage of the start-up process, the distribution of vapor and liquid slugs was random at the beginning, and then gradually develops to the other form which can easily pulsate in the PHP. In the later stage, pulsation stagnation in short time and reversing of the flow direction of the working fluid could be found at low heat load, when there exists the circulation flow in the PHP. Circulation was formed along a certain direction at high heat load. In addition, the PHP can be started up with less time and lower minimum start load by using working fluid which has lower latent heat.

Experimental and numerical analysis of heat transfer and fluid flow characteristics inside pulsating heat pipe

2021 ◽  
pp. 1-17
Author(s):  
Chandrakant R. Sonawane ◽  
Kuldeep Tolia ◽  
Anand Pandey ◽  
Atul Kulkarni ◽  
Hitesh Punchal ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Numerical Analysis ◽  
Heat Pipe ◽  
Flow Characteristics ◽  
Pulsating Heat Pipe ◽  
Fluid Flow Characteristics

Mechanisms of Coupled Heat Transfer and Flow of High Heat Flux Pulsating Heat Pipe

2004 ◽  
Author(s):  
Wei Qu ◽  
Yantao Qu ◽  
Tongze Ma
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Pipe ◽  
Latent Heat ◽  
High Heat ◽  
High Heat Flux ◽  
Sensible Heat ◽  
Pulsating Heat Pipe ◽  
Coupled Heat Transfer ◽  
Heating Section

The mechanisms of coupled heat transfer and flow are modeled to describe the looped pulsating heat pipe of high heat flux. The latent heat transfer produces the pressure difference between the heating section and cooling section. This can provide the operational driving force to overcome the total flow resistances. While the sensible heat transfer contributes more to the transferred power. The results demonstrate that the circulation flow velocity can balance the heat and mass transfers automatically. And the ratio of latent heat transfer to sensible heat transfer is within 30 percent.

scholarly journals Experimental Study on the Starting-Up and Heat Transfer Characteristics of Pulsating Heat Pipe Under Local Low-Frequency Vibrations

2021 ◽  
Author(s):  
Jing Chen ◽  
Junbiao Dong ◽  
Ye Yao
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Low Frequency ◽  
Heating Power ◽  
Pulsating Heat Pipe ◽  
Heat Transfer Characteristics ◽  
Condensation Section ◽  
Adiabatic Section

This study mainly experimentally investigates and explores the effects of local low-frequency vibrations on the starting-up and heat transfer characteristics of the pulsating heat pipe. A micro motors with the vibration frequency of 200 Hz were imposed on the external surface of evaporation, condensation and adiabatic section of the pulsating heat pipe, respectively, and the starting-up temperature and the average temperatures along the evaporation section as well as the thermal performances of the vibrating heat pipe were experimentally scrutinized under the local vibrations of different positions. The following important conclusions can be achieved by the experimental study: 1) The effect of vibrations at the evaporation section and at the adiabatic section on the starting-up time of pulsating heat pipe is more significant than that at the condensation section. 2) The vibrations at different positions can reduce the starting-up temperature of the pulsating heat pipe. The effect of the vibrations at the evaporation section is the best as the heating power is lower, and the effect of the vibration at the adiabatic section is the best as the heating power is higher. 3) The vibrations at the evaporation section and at the adiabatic section can reduce the thermal resistance of the pulsating heat pipe. However, the vibrations at the condensation section have little effect on the thermal resistance of the pulsating heat pipe. 4) The vibrations at the evaporation section and at the adiabatic section can effectively reduce the temperature of evaporation section of the pulsating heat pipe, but the vibrations at the condensation section have no effect on the temperature of evaporation section of the pulsating heat pipe.

Experimental Study on Flat Plate Pulsating Heat Pipe

2010 ◽  
Author(s):  
Chaofa Hu ◽  
Li Jia
Keyword(s):  
Flat Plate ◽  
Heat Pipe ◽  
Great Influence ◽  
Experimental System ◽  
Heating Power ◽  
Pulsating Heat Pipe ◽  
Operating Characteristics ◽  
Filling Rate ◽  
Start Up ◽  
Better Than

An experimental system of flat plate pulsating heat pipe was established and experimental research was carried out in this system to know the mechanism of heat transfer, start-up and operating characteristics. The factors, such as filling rate, heating power, heating method etc, which have great influence on the thermal performance of the plate pulsating heat pipe were discussed. The results indicate that heating power and filling rate are the important factors for the start-up of the plate pulsating heat pipe. Different filling rate needs different start-up power, and the start-up of the heat pipe in case of bottom heated is much easier than that of top heated. Increasing the heating power and enlarging the heating area can make the start-up easier. Heating power can also affect the start-up time of heat pipe under the condition of bottom heated, while it does not have some influence to the heat pipe of top heated. The thermal resistances of plate pulsating heat pipe are related with the heating power, and the higher the heating power is, the smaller the thermal resistances are. But the best filling rate which the heat pipe needs is different with different heating methods, and the performance of the heat pipe in the case of the bottom heated is better than the other.

Experimental Study on Start-up Characteristics of Pulsating Heat Pipe

2011 ◽  
Vol 354-355 ◽  
pp. 87-91 ◽  
Author(s):  
Xun Wang ◽  
Tong Han ◽  
Lei Wang ◽  
Xin Xin Mao ◽  
Cheng Si Yang
Keyword(s):  
Experimental Study ◽  
Heat Pipe ◽  
Filling Ratio ◽  
Heating Power ◽  
Working Fluid ◽  
Incline Angle ◽  
Distilled Water ◽  
Pulsating Heat Pipe ◽  
Start Up ◽  
Time Required

Pulsating heat pipe (PHP) with distilled water and acetone as working fluids was experimentally investigated. It is found that the PHP required a certain range of heating power to be started, within which the time required to start the PHP became shorter when the heating power was higher. There was a certain incline angle which is 45°in this experiment to start the PHP more quickly than other angles performed. The minimum power to start the PHP became higher when the filling ratio was higher. Compared with distilled water, the PHP was more readily to be started with acetone as working fluid.

Experimental Performance of a Nanofluid Pulsating Heat Pipe

2008 ◽  
Author(s):  
Wei Qu ◽  
Chong Qu ◽  
Jianchao Feng
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Operating Temperature ◽  
Nano Particles ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Operation Temperature ◽  
Heating Section ◽  
Inclination Angles

The startup and operating performances of a nanofluid pulsating heat pipe are experimented. When the working fluid is selected as nanofluid instead of the base working fluid, the pulsating heat pipe can work at lower heating loads and start up more quickly and the thermal resistance between the heating section and the cooling section significantly decreases. For the nanofluid and base working fluid, the operating temperature increases with the heating load, the thermal resistance of pulsating heat pipe decreases with the operating temperature. The inclination angles of pulsating heat pipe as 30°, 60°, or 90°, have little effects on heat transfer performance. Under a vertical bottom heating mode of 100 watts and at the operation temperature of 110 °C, the thermal resistance of TiO2/H2O nanofluid pulsating heat pipe can be 0.11 °C/W, while it is 0.23 °C/W for the base working fluid. The mechanisms that the nanofluid pulsating heat pipe has better performance are tentatively explained as, the nano particles can form many micro nuclear centers for the boiling, and can lead to several heat transfer enhancement.

scholarly journals Boiling-condensation heat transfer and flow characteristics in ultrathin limited enclosed space based on numerical simulation and visualization experiment

2021 ◽  
pp. 348-348
Author(s):  
Li Cong ◽  
Huang Ying ◽  
Tan Jianping
Keyword(s):  
Heat Transfer ◽  
Flow Characteristics ◽  
Condensation Heat Transfer ◽  
Anhydrous Ethanol ◽  
Upward Movement ◽  
Heating Section ◽  
Working Medium ◽  
Evaporation Heat ◽  
Visualization Experiment ◽  
Enclosed Space

Boiling-condensation heat transfer in ultrathin flat heat pipes are complicated and difficult to observe. In this study, a visualization experiment and simulation analysis in an ultrathin limited enclosed space were carried out. Width of the ultrathin enclosed space was 1 mm, with anhydrous ethanol as the working medium. The enclosed space was oriented vertically with the heating section on the bottom and the cooling section on the top. Flow characteristics of the anhydrous ethanol were photographed using a high-speed camera through the quartz cover. The boiling-condensation heat transfer and fluid flow in the limited enclosed space were simulated. Effective heat transfer coefficient calculated based on the experimental data varied from 1.0 to 1.1 W/?C, while that of the inner wall obtained by the simulation varied within the range of 1.068-1.076 W/?C. The maximum error was 2.9%, which verified the reliability of the simulation results. By analyzing the pressure change in condensation section, it was found that the boiling-condensation heat released in the enclosed space changed periodically, because of the growth and bursting of bubbles and falling of the working medium due to gravity. Restricted by the thickness, the bubbles produced by boiling of the working medium grew in flat and irregular shapes, promoting the upward movement of the rest of the liquid working medium, and a liquid film was formed at the heated inner surface for evaporation heat transfer, which enhanced the heat transfer capacity of the heating section.

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