Heat transfer performance of a flexible looped heat pipe using R134a as a working fluid: Proposal for a method to predict the maximum heat transfer rate of FLHP

2003 ◽  
Vol 32 (4) ◽  
pp. 306-318 ◽  
Author(s):  
Takashi Kobayashi ◽  
Tetsurou Ogushi ◽  
Seiji Haga ◽  
Eiichi Ozaki ◽  
Masao Fujii
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Experimental Investigation of the Heat Transfer Performance of a Hybrid Cooling Fin Thermosyphon

2014 ◽  
Vol 136 (10) ◽  
Author(s):  
Christina A. Pappas ◽  
Donald A. Jordan ◽  
Pamela M. Norris
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Working Fluid ◽  
Transfer Performance ◽  
Maximum Heat ◽  
Hybrid Cooling ◽  
Evaporator Section ◽  
Fill Volume

The effect of fill volume on the heat transfer performance of a hybrid cooling fin thermosyphon, characterized by an airfoil cross-sectional shape and a slot-shaped cavity, is investigated. The performance was examined at three fill volumes, expressed as a percentage of the evaporator section: 0%, 60%, and 240%. These were chosen to represent three distinct regimes: unfilled, filled, and overfilled evaporator sections, respectively. The cross section of this copper–water thermosyphon has a NACA0010 shape with a chord length of 63.5 mm and an aspect ratio (ratio of the length of the evaporator section to the cavity width) of 1.109. The evaporator length comprises 8.3% of the total thermosyphon length. The air-cooled condenser section was placed in a uniform air flow in the test section of an open return wind tunnel. The rate of heat transfer, or performance, was measured as a function of fill volume and evaporator temperature. The heat transfer performance increased by 100–170% by adding 0.86 ml of working fluid (de-ionized water), i.e., when the fill volume increased from 0% to 60%, which illustrates the improvement of a cooling fin's heat transfer rate by converting it to a hybrid cooling fin thermosyphon. Of the fill volumes investigated, the thermosyphon achieves a maximum heat transfer rate and highest average surface temperature at the 60% fill volume. Overfilling the evaporator section at 240% fill results in a slight decrease in performance from the 60% fill volume. The results of this study demonstrate the feasibility of hybridizing a cooling fin to act both as a cooling fin and a thermosyphon.

Reducing Crossflow Effects in Arrays of Impinging Jets

2017 ◽  
Author(s):  
Nicholas R. Arens ◽  
Mitchell P. Morem ◽  
Jeffrey Doom ◽  
Gregory J. Michna
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Cfd Modeling ◽  
Working Fluid ◽  
Transfer Performance ◽  
Simulation Data ◽  
Jet Array

With increasing heat fluxes in microelectronics, thermal management of these devices will soon no longer be attainable through current methods. One thermal management technology that could be integrated into the design of microelectronics is jet impingement cooling. Past research has primarily focused on evenly spaced, equal-sized, circular or slot jets perpendicular to the surface. A significant problem associated with this technology, especially as the surface to be cooled increases in size, is crossflow. This is the interaction of the transverse flow from the spent inner jet fluid with the jets closer to the outer edge of the surface. In an attempt to attenuate the crossflow effects, the heat transfer performance of jet arrays with non-uniform jet diameter and jet spacing were investigated. The testing apparatus housed a 3D-printed jet array nozzle that could be easily exchanged to accommodate many tests. The use of advanced manufacturing techniques allows for array geometries that may have previously been difficult to create. The impingement surface was a circular, polished, oxygen-free copper surface with a diameter of 25.4 mm. Heat transfer rates nearing 400 W could be delivered to the surface, for a heat flux of more than 75 W/cm2. The working fluid was single phase water, and the heat transfer rate was measured for each jet array over a range of flow rates. Experimental data was compared to simulation data obtained through CFD analysis. CFD modeling was used to predict the most promising geometries, which were then validated through experiment. Out of the nozzles tested, it was determined that the nozzle with larger diameters toward the edge of the surface attained the highest heat transfer rate of h = 38,822 W/m2-K. The nozzle with closer jet spacing at the outside of the array was found to have the highest experimental Nusselt number with NuD = 88.8. It was determined that angled confining walls do not have a definitive association with improved heat transfer. The simulation data was found to predict the heat transfer performance of the various geometries with an average percent difference in heat transfer coefficient of 11%.

Heat Transfer Characteristic of Flat Trapezoid Grooved Micro Heat Pipes

2014 ◽  
Vol 609-610 ◽  
pp. 1526-1531 ◽  
Author(s):  
Yan Xia Yang ◽  
Xiao Dong Wang ◽  
Yi Luo ◽  
Liang Liang Zou
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Performance ◽  
Capillary Flow ◽  
Transfer Characteristic ◽  
Fluid Distribution ◽  
Working Fluid ◽  
Transfer Performance ◽  
Maximum Heat ◽  
Micro Heat Pipe

To study the heat transfer performance of micro heat pipe, theoretical analysis of flat plate micro heat pipe with trapezoid cross section are presented in this paper. A one-dimensional stationary mathematical model for micro heat pipe grooved capillary flow using finite volume method (FVM) was established. The micro heat pipe had vapor space connect with each other and the influences of shear stress between vapor and fluid in the working process were described in the model which made the model more precisely. The axial variation of working fluid distribution in the heat pipe, pressure difference between vapor and liquid, and velocity of vapor and liquid were analyzed. In addition, the maximum heat transport capacity of micro heat pipe was calculated. The simulation results showed good agreement with the experiment results, and it could predict the heat transfer performance accurately, which was useful to micro heat pipe structural design.

scholarly journals Effects of Coil Pitch Spacing on Heat Transfer Performance of Nanofluid Turbulent Flow through Helical Microtube Heat Exchanger

2019 ◽  
Vol 7 (4.14) ◽  
pp. 356
Author(s):  
A. H. Rasheed ◽  
H. Alias ◽  
S. D. Salman
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Volume Concentration ◽  
Transfer Performance ◽  
Ansys Fluent ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Momentum And Heat Transfer

This article provides Numerical simulation on forced convective heat transfer performance of Nanofluid flowing through copper helical microtube of inner diameter of 1.5 mm with different pitch using ANSYS-FLUENT 18.0. The simulation was performed for water, CuO/water, Al2O3/water Nanofluid with 1-2% volume concentration and different pitch of microtube (10, 14 and 18 mm) for turbulent flow regime of Reynolds number varied 5000 to 20000 and governing equations of mass, momentum and heat transfer were solved simultaneously, using the k-e two equations turbulence model. Based on the obtained results, regardless of the concentrations used, the nanofluids exhibited a higher transfer rate than water. This is mainly attributed to the nanoparticles that are in the used nanofluids. The friction factor and the heat transfer rate were enhanced considerably due to the shape and size of the tube, which in this case is a helical microtube. Moreover, the maximum heat transfer performance has been conducted by Al2O3/water Nanofluid with 2% volume concentration and microtube pitch of 18 mm.    

scholarly journals Significance of Shape Factor in Heat Transfer Performance of Molybdenum-Disulfide Nanofluid in Multiple Flow Situations; A Comparative Fractional Study

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3711
Author(s):  
Asifa ◽  
Talha Anwar ◽  
Poom Kumam ◽  
Zahir Shah ◽  
Kanokwan Sitthithakerngkiet
Keyword(s):  
Heat Transfer ◽  
Skin Friction ◽  
Molybdenum Disulfide ◽  
Heat Transfer Rate ◽  
Shape Factor ◽  
Transfer Rate ◽  
Maximum Heat ◽  
Left Wall ◽  
Maximum Heat Transfer ◽  
Mos2 Nanoparticles

In this modern era, nanofluids are considered one of the advanced kinds of heat transferring fluids due to their enhanced thermal features. The present study is conducted to investigate that how the suspension of molybdenum-disulfide (MoS2) nanoparticles boosts the thermal performance of a Casson-type fluid. Sodium alginate (NaAlg) based nanofluid is contained inside a vertical channel of width d and it exhibits a flow due to the movement of the left wall. The walls are nested in a permeable medium, and a uniform magnetic field and radiation flux are also involved in determining flow patterns and thermal behavior of the nanofluid. Depending on velocity boundary conditions, the flow phenomenon is examined for three different situations. To evaluate the influence of shape factor, MoS2 nanoparticles of blade, cylinder, platelet, and brick shapes are considered. The mathematical modeling is performed in the form of non-integer order operators, and a double fractional analysis is carried out by separately solving Caputo-Fabrizio and Atangana-Baleanu operators based fractional models. The system of coupled PDEs is converted to ODEs by operating the Laplace transformation, and Zakian’s algorithm is applied to approximate the Laplace inversion numerically. The solutions of flow and energy equations are presented in terms of graphical illustrations and tables to discuss important physical aspects of the observed problem. Moreover, a detailed inspection on shear stress and Nusselt number is carried out to get a deep insight into skin friction and heat transfer mechanisms. It is analyzed that the suspension of MoS2 nanoparticles leads to ameliorating the heat transfer rate up to 9.5%. To serve the purpose of achieving maximum heat transfer rate and reduced skin friction, the Atangana-Baleanu operator based fractional model is more effective. Furthermore, it is perceived that velocity and energy functions of the nanofluid exhibit significant variations because of the different shapes of nanoparticles.

Heat Transfer in Serpentine Flow Passages With Rotation

1994 ◽  
Vol 116 (1) ◽  
pp. 133-140 ◽  
Author(s):  
S. Mochizuki ◽  
J. Takamura ◽  
S. Yamawaki ◽  
Wen-Jei Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Flow Passage ◽  
Rotation Numbers ◽  
Straight Flow

Heat transfer characteristics of a three-pass serpentine flow passage with rotation are experimentally studied. The walls of the square flow passage are plated with thin stainless-steel foils through which electrical current is applied to generate heat. The local heat transfer performance on the four side walls of the three straight flow passages and two turning elbows are determined for both stationary and rotating cases. The throughflow Reynolds, Rayleigh (centrifugal type), and rotation numbers are varied. It is revealed that three-dimensional flow structures cause the heat transfer rate at the bends to be substantially higher than at the straight flow passages. This mechanism is revealed by means of a flow visualization experiment for a nonrotating case. Along the first straight flow passage, the heat transfer rate is increased on the trailing surface but is reduced on the leading surface, due to the action of secondary streams induced by the Coriolis force. At low Reynolds numbers, the local heat transfer performance is primarily a function of buoyancy force. In the higher Reynolds number range, however, the circumferentially averaged Nusselt number is only a weak function of the Rayleigh and rotation numbers.

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