Thermo-Fluid Model for High Thermal Conductivity Thermal Ground Planes

2012 ◽  
Author(s):  
Mohammed T. Ababneh ◽  
Frank M. Gerner ◽  
Pramod Chamarthy ◽  
Peter de Bock ◽  
Shakti Chauhan ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Gravitational Field ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Fluid Model ◽  
Ground Plane ◽  
Maximum Heat ◽  
Gravitational Fields ◽  
Capillary Limit ◽  
Heat Transport Capability

The thermal ground plane (TGP) is an advanced planar heat pipe designed for cooling microelectronics in high gravitational fields. A thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). Viscous laminar flow pressure losses are predicted to determine the maximum heat load when the capillary limit is reached. This paper shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that the thermo-fluid model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP. The wick porosity plays an important effect on maximum heat transport capability. A large adverse gravitational field strongly decreases the maximum heat transport capability of the TGP. Axial effective thermal conductivity is mostly unaffected by the gravitational field. The maximum length of the TGP before reaching the capillary limit is inversely proportional to input power.

Experimental Investigation of a Three-Layer Oscillating Heat Pipe

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
C. D. Smoot ◽  
H. B. Ma
Keyword(s):  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Total Power ◽  
Oscillating Heat Pipe ◽  
Layer Effect ◽  
Layering Effect ◽  
Heat Transport Capability

An experimental investigation of a compact, triple-layer oscillating heat pipe (OHP) has been conducted to determine the channel layer effect on the heat transport capability in an OHP. The OHP has dimensions 13 mm thick, 229 mm long, and 76 mm wide embedded with two-independent closed loops forming three layers of channels. The unique design of the investigated OHP can be readily used to explore the channel layering effect on the heat transport capability in the OHP. The experimental results show that the addition of channel layers can increase the total power and at the same time, it can increase the effective thermal conductivity of the OHP. When the OHP switches from one layer of channels to two layers of channels, the highest effective thermal conductivity can be increased from 5760 W/mK to 26,560 W/mK. At the same time, the dryout limit can be increased. With three layers of channels, the OHP investigated herein can transport a power up to 8 kW with a heat flux level of 103 W/cm2 achieving an effective thermal conductivity of 33,170 W/mK.

Thermal Performance of Cooling Enhancement of Miniature Flat Plate Heat Pipe Under Different Angle

2015 ◽  
Vol 32 (1) ◽  
pp. 93-100
Author(s):  
J.-S. Chen ◽  
J.-H. Chou
Keyword(s):  
Thermal Conductivity ◽  
Flat Plate ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Maximum Heat ◽  
Plate Heat ◽  
Tilting Angle ◽  
Cooling Enhancement ◽  
Flat Plate Heat Pipe ◽  
Heat Transport Capability

AbstractThe possibility of cooling enhancement of flat plate heat pipes (FPHPs) by tilting was examined experimentally in this study. All of the FPHPs were made of Al and were partially filled with acetone. They had the same size of 120 mm (length) by 36 mm (width) by 2.5 mm (thickness) and the same liquid filling ratio of 25.1%. The effects of six tilting angles of -30°, -15°, -10°, 0°, 45°, and 90° were explored. The results showed that the thermal resistance decreased and the effective thermal conductivity increased when the tilting angle was increased. By increasing the tilting angle from 0° to 45° and further to 90°, the maximum effective thermal conductivity increased by a factor of 1.205 from 4561 W/mK to 5497 W/mK and of 1.212 to 5530 W/mK, respectively. The corresponding maximum heat transport capability increased by a factor of 2.89 from 39.8 W to 115 W and of 3.27 to 130 W. Hence, by proper tilting into positve angles, cooling enhancement of the FPHPs can be greatly achieved.

Study on a Pulsating Heat Pipe With Self-Rewetting Fluid

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Koji Fumoto ◽  
Masahiro Kawaji ◽  
Tsuyoshi Kawanami
Keyword(s):  
Surface Tension ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heated Surface ◽  
Input Power ◽  
Water Mixture ◽  
Pulsating Heat Pipe ◽  
Maximum Heat ◽  
Dry Spot ◽  
Heat Transport Capability

This paper discusses a pulsating heat pipe (PHP) using a self-rewetting fluid. Unlike other common liquids, self-rewetting fluids have the property that the surface tension increases with temperature. The increasing surface tension at a higher temperature can cause the liquid to be drawn toward a heated surface if a dry spot appears and thus to improve boiling heat transfer. In experiments, 1-butanol and 1-pentanol were added to water at a concentration of less than 1 wt % to make self-rewetting fluid. A pulsating heat pipe made from an extruded multiport tube was partially filled with the self-rewetting fluid water mixture and tested for its heat transport capability at different input power levels. The experiments showed that the maximum heat transport capability was enhanced by a factor of 4 when the maximum heater temperature was limited to 110°C. Thus, the use of a self-rewetting fluid in a PHP was shown to be highly effective in improving the heat transport capability of pulsating heat pipes.

Design Formulas for Oscillatory Heat Transport in Open-Ended Tubes

2003 ◽  
Vol 125 (6) ◽  
pp. 1183-1186 ◽  
Author(s):  
Masao Furukawa
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Pipe Flow ◽  
Tube Bundle ◽  
Womersley Number ◽  
Algebraic Expressions ◽  
Conductivity Increase ◽  
Bundle Size ◽  
Relative Conductivity

Modified Watson’s functions dependent on the Womersley Number, concerning a forced oscillatory pipe flow, are introduced to mathematically simply express the effective thermal conductivity, the tidal displacement, and the tidal work of fluid. Those three are developed into algebraic expressions giving the required electrical oscillating power and the necessary number of capillary tubes. The relative conductivity increase, the specific shaker driving power, and the specific tube bundle size are graphically shown in the figures for several fluids of interest to contribute to designing a heaterless liquid warmer.

Influence of Transverse Fins Attached to the Heated Wall of a Rayleigh-Be´nard Cavity

2004 ◽  
Author(s):  
Darren L. Hitt ◽  
Antonio Campo
Keyword(s):  
Thermal Conductivity ◽  
Nusselt Number ◽  
Numerical Simulations ◽  
Heat Transport ◽  
Local Heat ◽  
Heated Wall ◽  
Lower Plate ◽  
Maximum Heat ◽  
Rayleigh Numbers ◽  
Fin Spacing

In this article we examine the augmentation of classic Rayleigh-Be´nard convection by the addition of periodically-spaced tranverse fins attached to the heated, lower plate. The respective impacts of the fin size, the fin spacing and the thermal conductivity of the fin material are examined through numerical simulations for different laminar Rayleigh numbers and reported it terms of the Nusselt number. With the exception of very closely spaced fins, the heat transport is observed to exceed that of the idealized Rayleigh-Be´nard case. It is found that local heat transport maxima and minima do exist for specific fin spacings and that the maxima become more pronounced at higher Rayleigh numbers. For ‘small fins’ the fin spacing corresponding to maximum heat transport is such that the fin spacing is approximately equal to the enclosure height.

An Experimental Study of a Bubble-Driven Heat-Transport Device

2007 ◽  
Author(s):  
Osamu Suzuki
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Tube Bundle ◽  
Temperature Fluctuations ◽  
Temperature Gradients ◽  
Heating And Cooling ◽  
Tube Bundles ◽  
Steady State Time ◽  
Transport Device

We experimentally measured the heat-transport characteristics of a bubble-driven heat-transport device. The device consisted of a non-looped copper tube containing water. The tube was either meandered or spiraled to form tube bundles. The inner surface of the tube was smooth and its diameter small enough to enable the formation of vapor and liquid plugs in it. Two copper blocks were attached to the tube bundles, one as a heating block and the other as a cooling block. In the experiment, most of the wall temperatures measured on the tube fluctuated periodically at a quasi-steady state. Time-averaged temperature gradients between the heating and cooling sections of the device were constant. By increasing heater input from 300W to 350W, the amplitude of the temperature fluctuations decreased and the temperature gradients increased significantly. This behavior was regarded as a transition to critical heat transport condition. The effective thermal conductivity of the device was proportional to the heat-transport rate but did not depend on the formation of the tube bundle and the gravity effect. The temperature fluctuations had specific peak frequencies and a positive correlation was found between the frequency and effective thermal conductivity. These experimental results strongly suggest that the main heat-transport mechanism of the investigated device is based on the oscillation-induced transport of sensible heat.

Convective Heat Transfer Analysis of Open Cell Metal Foam for Solar Air Heaters

Solar Energy ◽  
2003 ◽  
Author(s):  
Nihad Dukhan ◽  
Pablo D. Quinones
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Metal Foam ◽  
Heat Transfer Analysis ◽  
Transfer Model ◽  
Aluminum Foams ◽  
Maximum Heat ◽  
Open Cell ◽  
Maximum Heat Transfer

A one-dimensional heat transfer model for open-cell metal foam is presented. Three aluminum foams having different areas, relative densities, ligament diameters, and number of pores per inch were analyzed. The effective thermal conductivity and the heat transfer increased with the number of pores per inch. The effective thermal conductivity of the foams can be up to four times higher than that of solid aluminum. The resulting improvement in heat transfer can be as high as 50 percent. The maximum heat transfer for the aluminum foams occurs at a pore Reynolds number of 52. The heat transfer, in addition, becomes insensitive to the flow regime for pore Reynolds numbers beyond 200.

scholarly journals Hyperthermia Treatment Planning Including Convective Flow in Cerebrospinal Fluid for Brain Tumour Hyperthermia Treatment Using a Novel Dedicated Paediatric Brain Applicator

Cancers ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1183 ◽  
Author(s):  
Gerben Schooneveldt ◽  
Hana Dobšíček Trefná ◽  
Mikael Persson ◽  
Theo M. de Reijke ◽  
Klas Blomgren ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Cerebrospinal Fluid ◽  
Effective Thermal Conductivity ◽  
Treatment Planning ◽  
Brain Tumours ◽  
Fluid Model ◽  
Hyperthermia Treatment ◽  
Operative Case ◽  
High K ◽  
Convective Fluid

Hyperthermia therapy (40–44 °C) is a promising option to increase efficacy of radiotherapy/chemotherapy for brain tumours, in particular paediatric brain tumours. The Chalmers Hyperthermia Helmet is developed for this purpose. Hyperthermia treatment planning is required for treatment optimisation, but current planning systems do not involve a physically correct model of cerebrospinal fluid (CSF). This study investigates the necessity of fluid modelling for treatment planning. We made treatments plans using the Helmet for both pre-operative and post-operative cases, comparing temperature distributions predicted with three CSF models: a convective “fluid” model, a non-convective “solid” CSF model, and CSF models with increased effective thermal conductivity (“high-k”). Treatment plans were evaluated by T90, T50 and T10 target temperatures and treatment-limiting hot spots. Adequate heating is possible with the helmet. In the pre-operative case, treatment plan quality was comparable for all three models. In the post-operative case, the high-k models were more accurate than the solid model. Predictions to within ±1 °C were obtained by a 10–20-fold increased effective thermal conductivity. Accurate modelling of the temperature in CSF requires fluid dynamics, but modelling CSF as a solid with enhanced effective thermal conductivity might be a practical alternative for a convective fluid model for many applications.

Heat Transfer Limitation of a Micro Heat Pipe

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
K. N. Shukla
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transport ◽  
Analytical Expression ◽  
Micro Heat Pipe ◽  
Capillary Limit ◽  
Heat Transport Capability

An analytical expression for the heat transport capability of micro heat pipe is derived. The vapor continuum limitation has been considered in deriving the heat transport capability of a micro heat pipe. As the micro heat pipe uses sharp-cornered square, triangular, or other polygonal channels that can serve as capillary arteries, its transport capability depends on the capillary limit. It has been shown that the operating limit of the micro heat pipe depends on the vapor continuum limitation, capillary limit, and the gravity.

scholarly journals Ballistic-Diffusive Model for Heat Transport in Superlattices and the Minimum Effective Heat Conductivity

Entropy ◽  
2020 ◽  
Vol 22 (2) ◽  
pp. 167 ◽  
Author(s):  
Federico Vázquez ◽  
Péter Ván ◽  
Róbert Kovács
Keyword(s):  
Thermal Conductivity ◽  
Effective Thermal Conductivity ◽  
Heat Transport ◽  
Heat Conductivity ◽  
Room Temperature ◽  
Heat Fluxes ◽  
Multilayer Systems ◽  
Effective Heat Conductivity ◽  
Effective Heat ◽  
Kinetic Calculations

There has been much interest in semiconductor superlattices because of their low thermal conductivities. This makes them especially suitable for applications in a variety of devices for the thermoelectric generation of energy, heat control at the nanometric length scale, etc. Recent experiments have confirmed that the effective thermal conductivity of superlattices at room temperature have a minimum for very short periods (in the order of nanometers) as some kinetic calculations had anticipated previously. This work will show advances on a thermodynamic theory of heat transport in nanometric 1D multilayer systems by considering the separation of ballistic and diffusive heat fluxes, which are both described by Guyer-Krumhansl constitutive equations. The dispersion relations, as derived from the ballistic and diffusive heat transport equations, are used to derive an effective heat conductivity of the superlattice and to explain the minimum of the effective thermal conductivity.

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