Effect of Thin Film Condensation on Thermal Performance of Oscillating Heat Pipes

2006 ◽  
Author(s):  
S. B. Liang ◽  
G. P. Xu
Keyword(s):  
Thin Film ◽  
Liquid Film ◽  
Heat Pipe ◽  
Heat Transport ◽  
Slug Flow ◽  
Thin Liquid Film ◽  
Experimental Studies ◽  
Heat Pipes ◽  
Film Condensation ◽  
Working Fluid

Self-sustainable motions of the slug flow in oscillating heat pipes have been investigated in the paper. Thin film condensation in the capillary channels of the condenser of the oscillating heat pipes was studied. Instability of the thin liquid film on the characteristics of heat pipes was analysed. The extra thermal resistance caused by the thickness of the thin liquid film was taken into account for the numerical simulation of the oscillatory motions of the slug flow in the heat pipes. Saturated temperatures and pressures of the working fluid in the condenser were obtained. Thermoacoustic theory was applied to calculate heat transport through the adiabatic section of the heat pipes. Experimental studies were carried out to understand the heat transfer behaviours of heat pipes. One heat pipe with the working fluid of HFC-134a was evaluated. The heat pipe is made of aluminium plate and has the width of 50 mm and thickness of 1.9 mm. Numerical and experimental results relevant to the heat transport capability of the heat pipe were analysed and compared.

Radial, Two-Phase Heat Transport Device Driven by Electrohydrodynamic Conduction Pumping

2011 ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Thin Film ◽  
Heat Flux ◽  
Heat Source ◽  
Liquid Film ◽  
Heat Pipe ◽  
Heat Transport ◽  
Working Fluid ◽  
Bottom Surface ◽  
Two Phase ◽  
Transport Device

Electrohydrodynamic (EHD) conduction pumping can be readily used to pump a thin film of a dielectric liquid along a surface, using electrodes that are embedded into the surface. This effect has been demonstrated under adiabatic conditions and has also been used to create a two-phase heat transport device that is similar to a heat pipe, but with the wicking structure replaced by an EHD conduction pump. In this study, a circular two-phase heat transport device is created. The device features circular electrodes that are arranged concentrically on the bottom surface and that pump a liquid film towards a heat source located at the center of the device. This heat source evaporates the liquid, and a large annular condenser at the periphery of the bottom surface provides a continuous supply of fresh liquid. This radial pumping configuration provides several advantages. Most notably, the heat source is wetted with fresh liquid from all 360 degrees, thereby reducing the amount of distance that must be travelled compared to a linear device. Consequently, the heat flux that can be removed from the central heat source far exceeds the normal critical heat flux of the working fluid. Electrodes are embedded in the condenser, adiabatic, and evaporator sections to maximize the amount of pumping head that can be generated and thereby maximize the heat flux removal.

Effect of Fluid Loading on the Performance of Wicked Heat Pipes

Volume 3 ◽  
2004 ◽  
Author(s):  
R. Kempers ◽  
A. Robinson ◽  
C. Ching ◽  
D. Ewing
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heat Pipes ◽  
Working Fluid ◽  
Fluid Loading ◽  
Maximum Heat ◽  
Horizontal Orientation ◽  
Maximum Heat Flux ◽  
Dry Out

A study was performed to experimentally characterize the effect of fluid loading on the heat transport performance of wicked heat pipes. In particular, experiments were performed to characterize the performance of heat pipes with insufficient fluid to saturate the wick and excess fluid for a variety of orientations. It was found that excess working fluid in the heat pipe increased the thermal resistance of the heat pipe, but increased maximum heat flux through the pipe in a horizontal orientation. The thermal performance of the heat pipe was reduced when the amount of working fluid was less than required to saturate the wick, but the maximum heat flux through the heat pipe was significantly reduced at all orientations. It was also found in this case the performance of this heat pipe deteriorated once dry-out occurred.

scholarly journals Thermal analysis of heat pipe using self rewetting fluids

2011 ◽  
Vol 15 (3) ◽  
pp. 879-888 ◽  
Author(s):  
Rathinasamy Senthilkumar ◽  
Subaiah Vaidyanathan ◽  
Sivaramanb Balasubramanian
Keyword(s):  
Surface Tension ◽  
Heat Pipe ◽  
Heat Transport ◽  
Pure Water ◽  
Heat Pipes ◽  
The Self ◽  
Working Fluid ◽  
Surface Tension Gradient ◽  
Condenser Section ◽  
Maximum Heat

This paper discuses the use of self rewetting fluids in the heat pipe. In conventional heat pipes, the working fluid used has a negative surface-tension gradient with temperature. It is an unfavourable one and it decreases the heat transport between the evaporator section and the condenser section. Self rewetting fluids are dilute aqueous alcoholic solutions which have the number of carbon atoms more than four. Unlike other common liquids, self-rewetting fluids have the property that the surface tension increases with temperature up to a certain limit. The experiments are conducted to improve the heat-transport capability and thermal efficiency of capillary assisted heat pipes with the self rewetting fluids like aqueous solutions of n-Butanol and n-Pentanol and its performance is compared with that of pure water. The n-Butanol and n-Pentanol are added to the pure water at a concentration of 0.001moles/lit to prepare the self rewetting fluids. The heat pipes are made up of copper container with a two-layered stainless steel wick consisting of mesh wrapped screen. The experimental results show that the maximum heat transport of the heat pipe is enhanced and the thermal resistances are considerably decreased than the traditional heat pipes filled with water. The fluids used exhibit an anomalous increase in the surface tension with increasing temperature.

Transient Analysis of a Cylindrical Heat Pipe Considering Different Wick Structures

2016 ◽  
Author(s):  
Mehdi Famouri ◽  
M. Mahdi Abdollahzadeh ◽  
Ahmed Abdulshaheed ◽  
GuangHan Huang ◽  
Gerardo Carbajal ◽  
...  
Keyword(s):  
Heat Pipe ◽  
Experimental Studies ◽  
Simple Algorithm ◽  
Heat Pipes ◽  
Working Fluid ◽  
Time Step ◽  
Base Scheme ◽  
The Stability ◽  
Stability And Accuracy ◽  
Energy Equations

Heat pipes have been shown to be one of the most efficient passive cooling devices for electronic cooling. Only a handful of studies were capable of solving transient performances of heat pipes based on realistic assumptions. A segregated finite volume base scheme using SIMPLE algorithm is used along with system pressurization and overall mass balance to solve mass transfer at the interface, continuity, momentum and energy equations. The fluid flow and heat transfer are solved throughout the wick and vapor core and no assumptions are made at the locations where evaporation and condensations occur. Water is the working fluid and variable densities are used for both liquid and vapor phases to account for continuity at the interface as well as inside of wick and vapor core. The wick is modeled as a non-homogeneous porous media and the effective thermal conductivities and viscous properties are calculated for each type of structure separately using the available relations from the literature. In this study, an axisymmetric two-dimensional solver for cylindrical heat pipe is developed using FLUENT package with the help of User Defined Functions (UDFs) and User Defined Scalar (UDS). The model is tested for grid and time step independency and the results show the stability and accuracy of the proposed method. The numerical results of the present study were in good agreement with the data from previous numerical and experimental studies available in the literature. Additionally, two different wick structures were studied to determine its effect on the thermal performance of heat pipes.

scholarly journals Visualization of heat transport in heat pipes using thermocamera

2010 ◽  
Vol 31 (4) ◽  
pp. 125-132 ◽  
Author(s):  
Patrik Nemec ◽  
Alexander Čaja ◽  
Richard Lenhard
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Fluid Transport ◽  
Heat Pipes ◽  
Working Fluid ◽  
Vertical Position ◽  
Change Of State ◽  
Heat Processes ◽  
High Level ◽  
The Impact

Visualization of heat transport in heat pipes using thermocamera Heat pipes, as passive elements show a high level of reliability when taking heat away and they can take away heat flows having a significantly higher density than systems with forced convection. A heat pipe is a hermetically closed duct, filled with working fluid. Transport of heat in heat pipes is procured by the change of state of the working fluid from liquid state to steam and vice versa and depends on the hydrodynamic and heat processes in the pipe. This study have been focused on observing the impact these processes have on the heat process, the transport of heat within the heat pipe with the help of thermovision. The experiment is oriented at scanning the changes in the surface temperatures of the basic structural types of capillary heat pipes in vertical position.

The Performance of Methanol and Water Heat Pipes for Electronics Cooling Applications in Spacecraft Instrumentation

2005 ◽  
Author(s):  
John D. Bernardin
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Thermal Performance ◽  
Electronics Cooling ◽  
Heat Pipes ◽  
Electronic Cooling ◽  
Working Fluid ◽  
Cooling Systems ◽  
Experimental Apparatus ◽  
Moving Parts

Increases in the power density of electronics and the corresponding decreases in packaging space have driven the development and enhancement of numerous electronics cooling strategies. The design of cooling systems for electronics are particularly challenging in spacecraft environments where there exists the additional requirements of minimal mass and volume, high reliability, reduced complexity and number of moving parts, and ability to operate in a reduced or gravity-free environment. One cooling technique that has proven to satisfy these demanding and integrated requirements for spacecraft electronics cooling applications, involves the use of heat pipes. The heat pipe is a passive heat transport device that requires no moving parts, is highly compact and reliable, and is an efficient mover of thermal energy in reduced gravity environments. Despite all of these positive features, heat pipes do have limitations and functional characteristics that designers must be keenly aware of when incorporating them into the development of electronic cooling systems. These include, in part, limits on the heat transport capacity and operational temperature, as well as performance variations between seemingly identical heat pipes due to contamination or manufacturing flaws. This paper discusses thermal analyses and performance testing of commercial copper heat pipes that utilize a sintered copper wick with either methanol or water as the working fluid. First, the electronic cooling application, thermal operating requirements, and commercial heat pipe designs are introduced. Next, the models and analyses used to predict the heat transport limits for the heat pipes are discussed. Following this, the experimental apparatus and procedures used to characterize the thermal performance of the heat pipes are presented. Finally, with the aid of empirical data, assessments of the thermal performance of each heat pipe, the range of performance variation between heat pipes, as well as the applicability and accuracy of the analytical performance models are provided.

Testing the Thermal Resistance and Power Capacity of Production Heat Pipes

2005 ◽  
Author(s):  
Sukhvinder Kang ◽  
Randy Cook ◽  
Dave Gailus
Keyword(s):  
Thermal Resistance ◽  
Specific Heat ◽  
Heat Pipe ◽  
Heat Transport ◽  
Manufacturing Process ◽  
Heat Pipes ◽  
Test Method ◽  
Heat Sinks ◽  
Working Fluid ◽  
Transport Capacity

In recent years heat pipes have become widely use in high performance air-cooled heat sinks for cooling electronics equipment. Such heat sinks rely on the heat pipes to collect heat from small high heat flux sources, transport it over some distance, and spread the heat efficiently to a volume of fins where the heat is transferred to an air flow stream by convection. When used effectively, heat pipes enable heat sinks that have low thermal resistance and low mass. For the heat sink to be successful, the heat pipes must also have sufficient heat transport capacity. To deliver their design thermal resistance and heat transport capacity, heat pipes need to be manufactured with well-controlled wick characteristics, working fluid fill volume and minimal residual non-condensable gases. It is standard procedure for heat pipe manufacturing companies to test 100 percent of the heat pipes they manufacture. The most commonly used production test is designed to rapidly show whether or not a heat pipe functions as a heat pipe. On a sampling basis, manufacturers also test the heat transport capacity of their heat pipes. There is no rapid test that can verify that any specific heat pipe will achieve the desired operational life — this is achieved by validation of the manufacturing process and adequate manufacturing process controls. In this paper we describe a test method and apparatus that can be used to rapidly test whether a heat pipe has the required thermal resistance at the specified heat transport capacity. The apparatus is capable of testing heat pipes over a wide range of diameters and lengths in their end use configuration (with bends and flattened regions). The key design criteria for the test apparatus is described and test data for several application specific heat pipes is presented.

Investigation of Heat Pipe Drilling Application

2004 ◽  
Author(s):  
Tien-Chien Jen ◽  
Yau Min Chen ◽  
Fern Tuchowski
Keyword(s):  
Heat Pipe ◽  
Experimental Studies ◽  
Heat Pipes ◽  
Cutting Fluid ◽  
Working Fluid ◽  
Federal State ◽  
Hole Making ◽  
Wick Structure ◽  
The Operating Mechanism ◽  
State And Local

It’s widely known that hole making is, by a significant margin, the most frequently performed process among metalworking operations. It’s also among the most difficult operations to control from a thermal perspective. The most common cooling method is the use of cutting fluids flooding through the cutting zone. However, disposal of the used fluids is subject to federal, state and local laws and regulations. More stringent regulations in environmental pollution are expected in the future, we can expect the cost associated with coolants to continue to rise. Experimental studies implementing the use of a heat pipe to cool the drill and thus reduce the amount of cutting fluid required have been recently conducted. The heat pipe works with no moving parts or electronics and it also offers an effective alternative to removing heat without significant increases in operating temperatures. The operating mechanism of heat pipes have been extensively studied, however, rotating heat pipes with a wick structure has not received adequate attention in the past. In this study, a numerical analysis has been conducted to model the flow in an axially rotating heat pipe. The result shows the transport capacity is strongly affected by changes in the thermal physical properties of the working fluid with the temperature. The rotating speeds have strong effect in the vapor core but this effect is weak in the liquid flow of the wick structure.

Thin Film Condensation Supported on Ambiphilic Microstructures

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Emre Ölçeroğlu ◽  
Chia-Yun Hsieh ◽  
Kenneth K. S. Lau ◽  
Matthew McCarthy
Keyword(s):  
Thin Film ◽  
Thermal Resistance ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Environmental Scanning Electron Microscopy ◽  
Hierarchical Structures ◽  
Liquid Films ◽  
Film Condensation ◽  
Environmental Scanning ◽  
C 50

Ambiphilic surfaces have been used to support thin liquid films during condensation and imaged using environmental scanning electron microscopy (ESEM). Ambiphilic microstructures (a) are comprised of hydrophilic deep etched silicon micropillars with hydrophobic post tops made of PTFE deposited using iCVD. By restraining the growth of the liquid film using hydrophobic post tops (b), thermal resistance is reduced and heat transfer is increased. During condensation on ambiphilic microstructures the condensate initially fills the post array (b), but then bursts outward to accommodate continued production of liquid (c). This creates a low contact angle droplet on the surface (c), and could lead to complete flooding and decreased performance. With the addition of hydrophilic nanostructures to the micropost array (d), ambiphilic hierarchical structures have been fabricated with dedicated burst sites (e). During condensation the structures maintain a thin liquid film and excess liquid emerges from the burst sites as highly mobile spherical droplets (e). This maximizes the thin film area available for vapor-to-liquid phase change while minimizing thermal resistance across the condensate layer. Scale bars: (a) 5 µm, (b,c) 50 µm, (d) 2 µm, and (e) 25 µm.

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