Transient Performance of Heat Pipes Using Nanofluids

2020 ◽  
Author(s):  
Mahboobe Mahdavi ◽  
Amir Faghri
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Response Time ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Volume Concentration ◽  
Heat Pipes ◽  
Operating Conditions ◽  
Vapor Flow ◽  
Transient Performance

Abstract In the present works, a comprehensive transient numerical model was developed to evaluate the effect of nanofluid on the transient performance of heat pipes. The numerical model solves for compressible vapor flow, the liquid flow in the wick region, and the energy equations in the vapor, wick and wall. The distinctive feature of the model is that it can uniquely determine the heat pipe operating pressure based on the physical and operating conditions of the system. Three nanoparticle types were considered: Al2O3, CuO, and TiO2. The effects of the concentration of nanoparticles (5%, 10%, 20% and 40%) were investigated on the heat pipe response time, thermal resistance, and pressure drop under various operating conditions. The results showed that the use of nanofluid decreased the response time of the heat pipe by the maximum of 27%. It was also discovered that the thermal resistance decreased significantly with an increase in the volume concentration. A maximum reduction of 84%, 82% and 78% in thermal resistance was obtained for Al2O3, CuO, and TiO2, respectively. In addition, the effect of nanoparticles on the liquid pressure drop highly depends on the nanoparticle type and volume concentration.

Numerical Analysis of Heat Pipe Turbine Vane Cooling

1998 ◽  
Vol 120 (4) ◽  
pp. 735-743 ◽  
Author(s):  
Z. J. Zuo ◽  
A. Faghri ◽  
L. Langston
Keyword(s):  
Numerical Model ◽  
Heat Pipe ◽  
Solution Method ◽  
Three Dimensional ◽  
Numerical Procedure ◽  
Curvilinear Coordinates ◽  
Vapor Flow ◽  
Transient Performance ◽  
Turbine Engine ◽  
Turbine Vane

A numerical model was developed to simulate transient performance of a heat pipe turbine vane under typical gas turbine engine conditions. Curvilinear coordinates were used to describe the three-dimensional wall and wick heat conduction coupled with the quasi-one-dimensional vapor flow. A unique numerical procedure including two iterative “estimate-correction” processes was proposed to efficiently solve the governing equations along with the boundary conditions. Comparisons with experimental results validated the numerical model and the solution method. A detailed numerical simulation of the heat pipe vane’s transient performance indicated the benefits of incorporating heat pipe vane cooling as well as the areas where precautions should be taken while designing heat pipe vanes.

Investigation of a Heat Pipe Array for Convective Cooling

1995 ◽  
Vol 117 (3) ◽  
pp. 208-214 ◽  
Author(s):  
A. H. Howard ◽  
G. P. Peterson
Keyword(s):  
Pressure Drop ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Base Plate ◽  
Heat Pipes ◽  
Plate Temperature ◽  
Maximum Heat ◽  
Heat Rejection ◽  
Convective Cooling ◽  
Copper Water

A combined experimental and analytical investigation was conducted to evaluate a heat pipe convective cooling device consisting of sixteen small copper/water heat pipes mounted vertically in a 4 × 4 array which was 25.4 mm square. The analytical portion of the investigation focused on determination of the maximum heat transport capacity and the resistance of the individual heat pipes. The resistance of each heat pipe was found to be 2.51 K/Watt, or more than 3 times smaller than the resistance produced by a solid copper rod with the same dimensions. The maximum predicted heat rejection for the module was over 50 Watts, or a power density in excess of 7.75 Watts/cm2. In the experimental portion of the investigation, two different modules were tested. The first module utilized ten circular aluminum fins mounted on the condenser end of each heat pipe to enhance heat rejection, while the second contained only the sixteen copper/water heat pipes. The effects of flow velocity, input power, and base plate temperature on the overall thermal resistance and the heat rejection capacity were determined, as well as the pressure drop resulting from each module. The finned heat pipe array was found to have a lower overall thermal resistance and thus, a higher heat rejection capacity, but also resulted in a significantly larger pressure drop than the array without fins. The results of the heat pipe array experiments were also compared with experimental and empirical results obtained from flow over a flat plate 25.4 mm square.

Remote Heat Pipe Based Heat Exchanger Performance in Notebook Cooling

2005 ◽  
Author(s):  
Seyyed Khandani ◽  
Himanshu Pokharna ◽  
Sridhar Machiroutu ◽  
Eric DiStefano
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Cooling System ◽  
Temperature Drop ◽  
Operating Conditions ◽  
Cooling Systems ◽  
Temperature Variations ◽  
Non Linear ◽  
Condenser Temperature

Remote heat pipe based heat exchanger cooling systems are becoming increasingly popular in cooling of notebook computers. In such cooling systems, one or more heat pipes transfer the heat from the more populated area to a location with sufficient space allowing the use of a heat exchanger for removal of the heat from the system. In analsysis of such systems, the temperature drop in the condenser section of the heat pipe is assumed negligible due to the nature of the condensation process. However, in testing of various systems, non linear longitudinal temperature drops in the heat pipe in the range of 2 to 15 °C, for different processor power and heat exchanger airflow, have been measured. Such temperature drops could cause higher condenser thermal resistance and result in lower overall heat exchanger performance. In fact the application of the conventional method of estimating the thermal performance, which does not consider such a nonlinear temperature variations, results in inaccurate design of the cooling system and requires unnecessarily higher safety factors to compensate for this inaccuracy. To address the problem, this paper offers a new analytical approach for modeling the heat pipe based heat exchanger performance under various operating conditions. The method can be used with any arbitrary condenser temperature variations. The results of the model show significant increase in heat exchanger thermal resistance when considering a non linear condenser temperature drop. The experimental data also verifies the result of the model with sufficient accuracy and therefore validates the application of this model in estimating the performance of these systems.   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.

scholarly journals Integration of a Pulsating Heat Pipe in a Flat Plate Heat Sink

2014 ◽  
Author(s):  
Mitchell P. Hoesing ◽  
Gregory J. Michna
Keyword(s):  
Thermal Resistance ◽  
Flat Plate ◽  
Heat Pipe ◽  
Heat Sink ◽  
New Technologies ◽  
Operating Conditions ◽  
Working Fluid ◽  
High Heat Flux ◽  
Pulsating Heat Pipe ◽  
Plate Heat

The ongoing development of faster and smaller electronic components has led to a need for new technologies to effectively dissipate waste thermal energy. The pulsating heat pipe (PHP) shows potential to meet this need, due to its high heat flux capacity, simplicity, and low cost. A 20-turn flat plate PHP was integrated into an aluminum flat plate heat sink with a simulated electronic load. The PHP heat sink used water as the working fluid and had 20 parallel channels with dimensions 2 mm × 2 mm × 119 mm. Experiments were run under various operating conditions, and thermal resistance of the PHP was calculated. The performance enhancement provided by the PHP was assessed by comparing the thermal resistance of the heat sink with no working fluid to that of it charged with water. Uncharged, the PHP was found to have a resistance of 1.97 K/W. Charged to a fill ratio of approximately 75% and oriented vertically, the PHP achieved a resistance of .49 K/W and .53 K/W when the condenser temperature was set to 20°C and 30°C, respectively. When the PHP was tilted to 45° above horizontal the PHP had a resistance of .76 K/W and .59 K/W when the condenser was set 20°C and 30°C, respectively. The PHP greatly improves the heat transfer properties of the heat sink compared to the aluminum plate alone. Additional considerations regarding flat plate PHP design are also presented.

Development and Application of a Thin Flat Heat Pipe Design Optimization Tool for Small Satellite Systems

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Steven A. Isaacs ◽  
Caelan Lapointe ◽  
Peter E. Hamlington
Keyword(s):  
Computational Modeling ◽  
Cost Function ◽  
Heat Pipe ◽  
Heat Pipes ◽  
Operating Conditions ◽  
Small Scale ◽  
Small Satellite ◽  
Modeling And Optimization ◽  
Satellite Systems ◽  
Flat Heat Pipe

Abstract With easier access to space and the growing integration of power-dense components, small-scale thermal management solutions are increasingly in demand for small satellite systems. Due to the strict mass and volume requirements commanded by such power-dense small spacecraft, heat pipes with thin and flat architectures provide nearly ideal solutions for the efficient transfer and dissipation of heat. Unlike traditional heat pipes, however, the performance of thin heat pipes is heavily dependent on details of the internal heat pipe structure, including the vapor core geometry and structural mechanical characteristics. In this study, the development and testing of a new computational modeling and optimization tool are presented for the design of thin flat heat pipes. The computational model is described in detail and includes parameters that define properties of the liquid wick, vapor core, and structural case. The model is coupled to a gradient-based optimization procedure that minimizes a multi-objective cost function for a range of operating conditions. The cost function is expressed as the weighted sum of the total temperature drop, the liquid/vapor pressure ratio, the total mass of the heat pipe, and the structural deflection of the heat pipe during operation. The combined computational modeling and optimization tool is then used to design a copper-methanol flat heat pipe for a small satellite mission, where the optimization is performed with respect to both cold and hot orbital conditions. Validation of the optimized heat pipe is performed using computational fluid dynamics (CFD) simulations of the initial and final designs.

Advanced Cooling With Embedded Heat Pipes for High Power Microelectronics

2009 ◽  
Author(s):  
Victor Adrian Chiriac
Keyword(s):  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Sink ◽  
Heat Pipes ◽  
Optimal Operation ◽  
Operating Conditions ◽  
Peak Temperature ◽  
Transient Temperature ◽  
Efficient Operation ◽  
The Impact

The transient thermal behavior of a complex testing system including multiple fans, a mixing enclosure, Cu inserts and a leaded package dissipating large amounts of power over short time durations is evaluated via numerical simulations. The system performance is optimized with heat sink/fan structure for device efficient operation under constant powering. The study provides meaningful understanding and prediction of a transient powering scenario at high powering levels, evaluating the impact of alternative cooling fan/heat pipe configurations on the thermal performance of the system. One design is chosen due to its effective thermal performance and assembly simplicity, with the package embedded in heat sink base with multiple (5) heat pipes. The peak temperature reached by the modified design with 4 cooling fans is ∼95°C, with the corresponding Rja thermal resistance ∼0.58°C/W. For the transient study (with embedded heat pipes and 4 fans), after one cycle, both peak temperature (at 45 s) and the end temperature (at 49 s) decrease as compared to the previous no heat pipe/single fan case (especially the end temperature reduces by ∼16%). The temperature drop between peak and end for each cycle is ∼80.2°C, while the average power per transient cycle is ∼31.27W. With this power, the design with 5 perpendicular heat pipes, 4 fans and insert reaches a steady state peak temperature of ∼98°C. Applying the superposition principle, the maximum transient temperature after a large number of operating cycles will not exceed ∼138.1°C, satisfying the thermal budget under the current operating conditions. The benefit of the study is related to the possibility to extract the maximum/minimum temperatures for a real test involving a large number of heating-cooling cycles, yet maintaining the initial and peak temperatures within a certain range for the optimal operation of the device. The flow and heat transfer fields are thoroughly investigated: using a combination of numerical and analytical study, the thermal performance of the device undergoing large number of periodic thermal cycles is predicted. Further comparison between measurement and simulation results reveals good agreement.

Modeling of the Flow and Heat Transfer in Micro Heat Pipes

2004 ◽  
Author(s):  
C. B. Sobhan ◽  
G. P. (Bud) Peterson
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Pipes ◽  
Radius Of Curvature ◽  
Vapor Flow ◽  
Axial Distribution ◽  
Cross Sectional ◽  
Flow And Heat Transfer ◽  
Physical Phenomena ◽  
Micro Heat Pipes

The fluid flow and heat transfer characteristics of micro heat pipes are analyzed theoretically, in order to understand the physical phenomena and quantify the influence of various parameters on overall thermal performance of these devices. A one-dimensional model is utilized to solve the governing equations for the liquid/vapor flow and the heat transfer in the heat pipe channel. Variations in the liquid and vapor cross-sectional areas along the axial length of the heat pipe are included and the equations are solved using an implicit finite difference scheme. Appropriate models for fluid friction in small passages with varying cross-sectional areas have been incorporated to yield the axial distribution of the meniscus radius of curvature and the velocity, temperature and pressure in both the liquid and the vapor phases. Using this information, the effective thermal conductivity of the micro heat pipe is modeled, and parametric studies are performed by changing the heat load and cooling rate. The results of the analysis are discussed and compared with other theoretical models and experimental results found in the literature. By so doing, this analysis provides greater insight into the physical phenomena of flow and heat transfer in micro heat pipes and identifies a methodology for optimizing the design of these devices.

Amplification of the Thermocapillary Convection during Evapo-Condensation Cycle in Heat Pipes

2007 ◽  
Vol 553 ◽  
pp. 209-214
Author(s):  
Rachid Bennacer ◽  
Mohammed El Ganaoui
Keyword(s):  
Thermal Analysis ◽  
Numerical Model ◽  
Heat Pipe ◽  
Thermocapillary Convection ◽  
Thermal Conditions ◽  
Heat Pipes ◽  
External Conditions ◽  
Local Coupling

The control of a process dealing with heat pipe exploitation needs the thermal analysis of the evaporation-condensation cycle and noticeably the imposed external conditions (in instance modeling the heating). In this work a numerical model has been developed to describe the local coupling near the liquid/vapour interface. Simulations exhibits and quantify the response of the capillary motion to the thermal conditions.

An Experimental Study of Mesh Type Flat Heat Pipes

2011 ◽  
Vol 27 (2) ◽  
pp. 167-176 ◽  
Author(s):  
L.-H. Chien ◽  
Y.-C. Shih
Keyword(s):  
Thermal Resistance ◽  
Heat Pipe ◽  
Inclination Angle ◽  
Volume Fraction ◽  
Mesh Size ◽  
Heat Pipes ◽  
Working Fluid ◽  
Internal Space ◽  
Horizontal Orientation ◽  
Semi Empirical

ABSTRACTFlat heat pipes having mesh capillaries were investigated experimentally in this study. An apparatus was designed to test thermal performance of plate type copper water heat pipe having one or two layers of #50 or #80 mesh capillary structures with 5 to 50 W heat input. The working fluid, water, is charged in volumes equivalent to 25%, 33%, or 50% of the internal space. In addition to horizontal orientation, heat pipes were tested with the evaporator section elevated up to 40 degree inclination angle. Temperature distribution of the heat pipe was measured, and the evaporator, adiabatic and condensation resistances were calculated separately. The effects of mesh size, charge volume fraction, and inclination angle on thermal resistance were discussed. In general, the #80 mesh yielded lower thermal resistance than the #50 mesh. Inclination angle has a more significant effect on condenser than evaporator. Analysis of evaporation and condensation in flat heat pipes was conducted and semi-empirical correlations were derived. The present evaporation correlation predicts evaporation resistance between −20% and +30%, and the condensation correlation predicts most condensation resistance data within ±30% for 25% and 33% charge volume fraction.

Investigation on the Use of Nanofluids to Enhance Heat Pipe Performance

Solar Energy ◽  
2005 ◽  
Author(s):  
Tomer Israeli ◽  
T. Agami Reddy ◽  
Young I. Cho
Keyword(s):  
Thermal Conductivity ◽  
Surface Tension ◽  
Thermal Resistance ◽  
Copper Oxide ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Experimental Studies ◽  
Heat Pipes ◽  
Thermal Network ◽  
Overall Resistance

This paper reports on preliminary experimental results on using nanofluids to enhance the thermal performance of heat pipes. Our experience with preparing copper oxide (CuO) nanofluids is described. Contrary to earlier studies which report infinite shelf life, we found that nanofluid stability lasted for about three weeks only; an issue which merits further study. We have also conducted various experiments to measure the variation of thermal conductivity and surface tension with CuO nanofluid concentration. Actual experiments on nanofluid heat pipes were also performed which indicated an average 12.5% decrease in the overall thermal resistance of the heat pipe using nanofluid of 3% vol concentration. This observed improvement is fairly consistent with our predictions using a simple analytical thermal network model for heat pipe overall resistance and the measured nanofluid conductivity. The results, though encouraging, need more careful and elaborate experimental studies before the evidence can be deemed conclusive.

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