The Effects of Working Fluid on the Heat Transport Capacity of a Microheat Pipe

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
D. Sugumar ◽  
Kek-Kiong Tio
Keyword(s):  
Surface Tension ◽  
Heat Transport ◽  
Cross Section ◽  
Thermophysical Properties ◽  
Dynamic Viscosity ◽  
Working Fluid ◽  
Transport Capacity ◽  
Working Fluids ◽  
Triangular Cross Section ◽  
Operating Temperatures

The effects of the thermophysical properties of the working fluid on the performance of a microheat pipe of triangular cross section are investigated. For this purpose, five different working fluids are selected: water, hepthane, ammonia, methanol, and ethanol. For operating temperatures ranging from 20°Cto100°C, it is found that the behavior of the heat transport capacity is dominated by a property of the working fluid, which is equal to the ratio of the surface tension and dynamic viscosity σ∕μl. This property has the same dimension as velocity and can be interpreted as a measure of the working fluid’s rate of circulation, which can be provided by capillarity after overcoming the effect of viscosity. Of the five working fluids selected, ammonia is preferable for operating temperatures below 50°C since it yields the highest heat transport capacity; however, water is the preferred working fluid for temperatures above 50°C.

The Effect of Type of Working Fluid on the Heat Transport Capacity of a Micro Heat Pipe

2005 ◽  
Author(s):  
Sugumar Dharmalingam ◽  
Kek Kiong Tio
Keyword(s):  
Surface Tension ◽  
Heat Pipe ◽  
Heat Transport ◽  
Operating Temperature ◽  
Working Fluid ◽  
Liquid Viscosity ◽  
Transport Capacity ◽  
Temperature Range ◽  
Controlling Effect ◽  
Micro Heat Pipe

In order to elucidate the effects of working fluid’s properties on the heat transport capacity of a micro heat pipe, 3 commonly used fluids are selected for this study: water, ammonia and methanol. From the results obtained, it shows that for operating temperatures lower than 50°C, ammonia is preferred, but if the operating temperature exceeds 50°C, water is more suitable in transferring heat. Over the temperature range of 20°C∼100°C, the behavior of the heat transport capacity is found to be dominated by a property which is the ratio of the working fluid’s surface tension and liquid viscosity. This property which has the dimension of velocity has a controlling effect on the working fluid’s rate of circulation and therefore, the heat transport capacity.

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.

Experimental Study of Linear and Radial Two-Phase Heat Transport Devices Driven by Electrohydrodynamic Conduction Pumping

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Source ◽  
Capillary Pressure ◽  
Heat Transport ◽  
Radial Direction ◽  
Heat Pipes ◽  
Working Fluid ◽  
Phase Flow ◽  
Transport Capacity ◽  
Two Phase ◽  
Capillary Phenomenon

Heat pipes are well known as simple and effective heat transport devices, utilizing two-phase flow and the capillary phenomenon to remove heat. However, the generation of capillary pressure requires a wicking structure and the overall heat transport capacity of the heat pipe is generally limited by the amount of capillary pressure generation that the wicking structure can achieve. Therefore, to increase the heat transport capacity, the capillary phenomenon must be either augmented or replaced by some other pumping technique. 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. In this study, two two-phase heat transport devices are created. The first device transports the heat in a linear direction. The second device transports the heat in a radial direction from a central heat source. The radial pumping configuration provides several advantages. Most notably, the heat source is wetted with fresh liquid from all directions, thereby reducing the amount of distance that must be travelled by the working fluid. The power required to operate the EHD conduction pumps is a trivial amount relative to the heat that is transported.

Heat Transport Characteristics in Closed Loop Oscillating Heat Pipes

2005 ◽  
Author(s):  
Shuangfeng Wang ◽  
Shigefumi Nishio
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Closed Loop ◽  
Flow Behavior ◽  
Working Fluid ◽  
Liquid Volume ◽  
High Heat Flux ◽  
Two Phase ◽  
Working Fluids ◽  
Inner Diameter

Heat transport rates of micro scale SEMOS (Self-Exciting Mode Oscillating) heat pipe with inner diameter of 1.5mm, 1.2mm and 0.9mm, were investigated by using R141b, ethanol and water as working fluids. The effects of inner diameter, liquid volume faction, and material properties of the working fluids are examined. It shows that the smaller the inner diameter, the higher the thermal transport density is. For removing high heat flux, the water is the most promising working fluid as it has the largest critical heat transfer rate and the widest operating range among the three kinds of working fluids. A one-dimensional numerical simulation is carried out to describe the heat transport characteristics and the two-phase flow behavior in the closed loop SEMOS heat pipe. The numerical prediction agrees with the experimental results fairly well, when the input heat through was not very high and the flow pattern was slug flow.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

Analysis of Microheat Pipes With Axial Conduction in the Solid Wall

2010 ◽  
Vol 132 (7) ◽  
Author(s):  
Yew Mun Hung ◽  
Kek-Kiong Tio
Keyword(s):  
Temperature Distribution ◽  
Heat Transport ◽  
Thermal Effects ◽  
Solid Wall ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Working Fluid ◽  
Transport Capacity ◽  
Axial Temperature ◽  
Energy Equations

A one-dimensional, steady-state model of a triangular microheat pipe (MHP) is developed, with the main purpose of investigating the thermal effects of the solid wall on the heat transport capacity of an MHP. The energy equation of the solid wall is solved analytically to obtain the axial temperature distribution, the average of which over the entire length of the MHP is simply its operating temperature. Next, the liquid phase is coupled with the solid wall by a heat transfer coefficient. Then, the continuity, momentum, and energy equations of the liquid and vapor phases are, together with the Young–Laplace equation, solved numerically to yield the heat and fluid flow characteristics of the MHP. The heat transport capacity and the associated optimal charge level of the working fluid are predicted for different operating conditions. Comparison between the models with and without a solid wall reveals that the presence of the solid wall induces a change in the phase change heat transport by the working fluid, besides facilitating axial heat conduction in the solid wall. The analysis also highlights the effects of the thickness and thermal conductivity of the solid wall on its axial temperature distribution. Finally, while the contribution of the thermal effects of the solid wall on the heat transport capacity of the MHP is usually not dominant, it is, nevertheless, not negligible either.

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.

Investigation of a Novel Flat Heat Pipe

2005 ◽  
Vol 127 (2) ◽  
pp. 165-170 ◽  
Author(s):  
Yaxiong Wang ◽  
G. P. Peterson
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Thermal Design ◽  
Experimental Results ◽  
Design Parameters ◽  
Working Fluid ◽  
Transport Capacity ◽  
Maximum Heat ◽  
Mesh Screen ◽  
Flat Heat Pipe

A novel flat heat pipe has been developed to assist in meeting the high thermal design requirements in high power microelectronics, power converting systems, laptop computers and spacecraft thermal control systems. Two different prototypes, each measuring 152.4 mm by 25.4 mm were constructed and evaluated experimentally. Sintered copper screen mesh was used as the primary wicking structure, in conjunction with a series of parallel wires, which formed liquid arteries. Water was selected as the working fluid. Both experimental and analytical investigations were conducted to examine the maximum heat transport capacity and optimize the design parameters of this particular design. The experimental results indicated that the maximum heat transport capacity and heat flux for Prototype 1, which utilized four layers of 100 mesh screen were 112 W and 17.4W/cm2, respectively, in the horizontal position. For Prototype 2, which utilized six layers of 150 mesh screen, these values were 123 W and 19.1W/cm2, respectively. The experimental results were in good agreement with the theoretical predictions for a mesh compact coefficient of C=1.15.

Performance Analysis of Near-Critical and Subcritical Organic Rankine Cycle

2013 ◽  
Vol 448-453 ◽  
pp. 3270-3276
Author(s):  
Yu Ping Wang ◽  
Yi Wu Weng ◽  
Ping Yang ◽  
Lei Tang
Keyword(s):  
Performance Analysis ◽  
Thermophysical Properties ◽  
Thermodynamic Model ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Vapor Generation ◽  
Working Fluids ◽  
The Difference ◽  
Better Than

In this paper, three typical working fluids were selected for the near-critical ORC and subcritical ORC. The difference of performance between the near-critical ORC and subcritical ORC was analyzed by establishing the thermodynamic model. The reason for difference was analyzed in terms of the thermophysical properties. The results indicate that the performance of the near-critical ORC is better than the subcritical ORC. The net absorbed heat, net power and efficiency of the near-critical ORC vary slowly with the vapor generation temperature, which means that the near-critical ORC has good off-design performance. The dry working fluid R236fa is best adapted for the near-critical ORC among the three working fluids. The singular performance of the near-critical ORC depends on the properties of latent heat and type of working fluid in near-critical region.

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.

Experimental Study of a Two-Phase Heat Transport Device Driven by Electrohydrodynamic Conduction Pumping

2008 ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Experimental Study ◽  
Electric Field ◽  
Capillary Pressure ◽  
Heat Transport ◽  
Working Fluid ◽  
Transport Capacity ◽  
Two Phase ◽  
Macro Scale ◽  
Transport Device ◽  
Capillary Phenomenon

Heat pipes are well-known as simple and effective heat transport devices, utilizing two-phase flow and the capillary phenomenon to remove heat. However, the generation of capillary pressure requires a wicking structure and the overall heat transport capacity of the heat pipe is generally limited by the amount of capillary pressure generation that the wicking structure can achieve. Therefore, to increase the heat transport capacity, the capillary phenomenon must be either augmented or replaced by some other pumping technique. Electro-hydrodynamic (EHD) conduction pumping has been demonstrated as an effective method for pumping liquid films by using DC electric fields and a dielectric working fluid. Beyond increased pumping capacity, EHD conduction pumping offers other advantages over capillary pumping, such as active control of the pumping capacity via the intensity of the applied electric field. This experimental study demonstrates the prospects of a macro-scale two-phase heat transport device that is driven by EHD conduction pumping. Various liquid film thicknesses are considered. In each case, the performance of the EHD-driven heat transport device at various electric field intensities is compared to the capabilities of the same device under gravity alone. The effect of tilt on the device is also considered.

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