Heat Transfer During Evaporation on Capillary-Grooved Structures of Heat Pipes

1995 ◽  
Vol 117 (3) ◽  
pp. 740-747 ◽  
Author(s):  
D. Khrustalev ◽  
A. Faghri
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Surface Roughness ◽  
Thermal Resistance ◽  
Heat Pipes ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Interfacial Thermal Resistance ◽  
Interfacial Resistance ◽  
The Heat Transfer Coefficient

A detailed mathematical model is developed that describes heat transfer through thin liquid films in the evaporator of heat pipes with capillary grooves. The model accounts for the effects of interfacial thermal resistance, disjoining pressure, and surface roughness for a given meniscus contact angle. The free surface temperature of the liquid film is determined using the extended Kelvin equation and the expression for interfacial resistance given by the kinetic theory. The numerical results obtained are compared to existing experimental data. The importance of the surface roughness and interfacial thermal resistance in predicting the heat transfer coefficient in the grooved evaporator is demonstrated.

Review of Microscale Heat Transfer

1994 ◽  
Vol 47 (9) ◽  
pp. 397-428 ◽  
Author(s):  
A. B. Duncan ◽  
G. P. Peterson
Keyword(s):  
Heat Transfer ◽  
Final Section ◽  
Radiative Heat ◽  
Heat Pipes ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Review Of The Literature ◽  
Conduction Heat Transfer ◽  
Microscale Heat Transfer ◽  
Micro Heat Pipes

A review of the literature in the area of microscale heat transfer is presented to provide a concise overview of the recent advances in this field of study. The review is divided into three major sections with each subdivided into subsections. The first section deals with the effects of size reductions in conduction heat transfer, and includes subsections on laser induced heating on the microscale and conduction in thin films. The second section addresses microscale forced convection and includes subsections on micro heat pipes, microscale boiling, and thin liquid films near the contact line. The final section examines the effects of small length scales on radiative heat transfer. The three major sections are followed by a summary that identifies, consolidates, and summarizes the most important advances in each of these three areas.

scholarly journals Prediction of the contact thermal resistance of vertical carbon nanotube arrays

2020 ◽  
Vol 24 (2 Part A) ◽  
pp. 745-756
Author(s):  
Bo Shi ◽  
Han Zhang ◽  
Jin Zhang
Keyword(s):  
Experimental Data ◽  
Surface Roughness ◽  
Carbon Nanotube ◽  
Thermal Resistance ◽  
Interfacial Thermal Resistance ◽  
Nanotube Arrays ◽  
Thermal Interface Materials ◽  
Contact Thermal Resistance ◽  
Carbon Nanotube Arrays ◽  
Interface Materials

The vertical carbon nanotube arrays (VACNT), as a result of its flexibility and axial high thermal conductivity, exert a huge potential and play an increasingly important role in thermal interface materials. This paper proposed a model which can predict the contact thermal resistance of VACNT. The contact thermal resistance of VACNT under different pressures is calculated and compared with the experimental data. Also, the effect of variations in the surface roughness and VACNT parameters on the contact thermal resistance is investigated. Results show that the theoretical results are in good agreement with the experimental data. The contact thermal resistance is composed of interfacial thermal resistance, constriction thermal resistance, and VACNT resistance. Among which the interfacial thermal resistance is the major thermal resistance. The variations in VACNT length and diameter can change the bending degree of VACNT under the same pressure, which presents important implications on contact thermal resistance and can be used to optimize the contact thermal resistance of VACNT. The surface roughness exerts little effect on contact thermal resistance.

Boiling Heat Transfer for Freon R21 in Rectangular Minichannel

2006 ◽  
Author(s):  
V. V. Kuznetsov ◽  
A. S. Shamirzaev
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Flow Patterns ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Modified Model ◽  
Wide Range ◽  
Nucleation Boiling ◽  
The Heat Transfer Coefficient ◽  
Transfer Mechanisms

In this paper we study the boiling heat transfer of upward flow of R21 in a vertical mini-channel with size 1.6×6.3 mm. The heat transfer coefficient was measured as a function of heat flux for a wide range of vapor quality and for two levels of mass flow rate, G = 215 kg/m2s and G = 50 kg/m2s. The temperature dispersions over channel perimeter and in time were calculated. Different heat transfer mechanisms were revealed for different flow patterns. We distinguish the dominant nucleation boiling and the joint mode of nucleation boiling and convective evaporation. We also found the modes when the evaporation of thin liquid films makes the main contribution to heat transfer. The modified model of Liu and Winterton describes the experimental data for the flow patterns when the nucleation boiling and convective transfer make the most contribution to the heat transfer.

HEAT TRANSFER IN THIN LIQUID FILMS FLOWING DOWN HEATED INCLINED GROOVED PLATES

2010 ◽  
Vol 2 (5) ◽  
pp. 455-468 ◽  
Author(s):  
Hongyi Yu ◽  
Karsten Loffler ◽  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Heat Transfer ◽  
Liquid Films ◽  
Thin Liquid Films

Study of the Fluid Dynamics of Thin Liquid Films Flowing Down a Vertical String With Counterflow of Gas

2015 ◽  
Author(s):  
Zezhi Zeng ◽  
Gopinath Warrier ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Film Thickness ◽  
Liquid Film ◽  
Direct Contact ◽  
High Speed ◽  
Small Diameter ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Liquid Coolant

Direct-contact heat transfer between a falling liquid film and a gas stream yield high heat transfer rates and as such it is routinely used in several industrial applications. This concept has been incorporated by us into the proposed design of a novel heat exchanger for indirect cooling of steam in power plants. The DILSHE (Direct-contact Liquid-on-String Heat Exchangers) module consists of an array of small diameter (∼ 1 mm) vertical strings with hot liquid coolant flowing down them due to gravity. A low- or near-zero vapor pressure liquid coolant is essential to minimize/eliminate coolant loss. Consequently, liquids such as Ionic Liquids and Silicone oils are ideal candidates for the coolant. The liquid film thickness is of the order of 1 mm. Gas (ambient air) flowing upwards cools the hot liquid coolant. Onset of fluid instabilities (Rayleigh-Plateau and/or Kapitza instabilities) result in the formation of a liquid beads, which enhance heat transfer due to additional mixing. The key to successfully designing and operating DILSHE is understanding the fundamentals of the liquid film fluid dynamics and heat transfer and developing an operational performance map. As a first step towards achieving these goals, we have undertaken a parametric experimental and numerical study to investigate the fluid dynamics of thin liquid films flowing down small diameter strings. Silicone oil and air are the working fluids in the experiments. The experiments were performed with a single nylon sting (fishing line) of diameter = 0.61 mm and height = 1.6 m. The inlet temperature of both liquid and air were constant (∼ 20 °C). In the present set of experiments the variables that were parametrically varied were: (i) liquid mass flow rate (0.05 to 0.23 g/s) and (ii) average air velocity (0 to 2.7 m/s). Visualization of the liquid flow was performed using a high-speed camera. Parameters such as base liquid film thickness, liquid bead shape and size, velocity (and hence frequency) of beads were measured from the high-speed video recordings. The effect of gas velocity on the dynamics of the liquid beads was compared to data available in the open literature. Within the range of gas velocities used in the experiments, the occurrence of liquid hold up and/or liquid blow over, if any, were also identified. Numerical simulations of the two-phase flow are currently being performed. The experimental results will be invaluable in validation/refinement of the numerical simulations and development of the operational map.

Experimental and theoretical investigation of heat transfer characteristics of cylindrical heat pipe using Al2O3–SiO2/W-EG hybrid nanofluids by RSM modeling approach

2021 ◽  
Vol 68 (1) ◽  
Author(s):  
R. Vidhya ◽  
T. Balakrishnan ◽  
B. Suresh Kumar
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Transfer Coefficient ◽  
Thermal Resistance ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Diffraction Spectrum ◽  
Step Method ◽  
Ceramic Nanoparticles ◽  
Transfer Mechanisms

AbstractNanofluids are emerging two-phase thermal fluids that play a vital part in heat exchangers owing to its heat transfer features. Ceramic nanoparticles aluminium oxide (Al2O3) and silicon dioxide (SiO2) were produced by the sol-gel technique. Characterizations have been done through powder X-ray diffraction spectrum and scanning electron microscopy analysis. Subsequently, few volume concentrations (0.0125–0.1%) of hybrid Al2O3–SiO2 nanofluids were formulated via dispersing both ceramic nanoparticles considered at 50:50 ratio into base fluid combination of 60% distilled water (W) with 40% ethylene glycol (EG) using an ultrasonic-assisted two-step method. Thermal resistance besides heat transfer coefficient have been examined with cylindrical mesh heat pipe reveals that the rise of power input decreases the thermal resistance and inversely increases heat transfer coefficient about 5.54% and 43.16% respectively. Response surface methodology (RSM) has been employed for the investigation of heat pipe experimental data. The significant factors on the various convective heat transfer mechanisms have been identified using the analysis of variance (ANOVA) tool. Finally, the empirical models were developed to forecast the heat transfer mechanisms by regression analysis and validated with experimental data which exposed the models have the best agreement with experimental results.

Experimental Investigation of Heat Transfer in Impingement Air Cooled Plate Fin Heat Sinks

2005 ◽  
Vol 128 (4) ◽  
pp. 412-418 ◽  
Author(s):  
Zhipeng Duan ◽  
Y. S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Transfer Model ◽  
Heat Sinks ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Developing Flow ◽  
Rectangular Channels

Impingement cooling of plate fin heat sinks is examined. Experimental measurements of thermal performance were performed with four heat sinks of various impingement inlet widths, fin spacings, fin heights, and airflow velocities. The percent uncertainty in the measured thermal resistance was a maximum of 2.6% in the validation tests. Using a simple thermal resistance model based on developing laminar flow in rectangular channels, the actual mean heat transfer coefficients are obtained in order to develop a simple heat transfer model for the impingement plate fin heat sink system. The experimental results are combined into a dimensionless correlation for channel average Nusselt number Nu∼f(L*,Pr). We use a dimensionless thermal developing flow length, L*=(L∕2)∕(DhRePr), as the independent parameter. Results show that Nu∼1∕L*, similar to developing flow in parallel channels. The heat transfer model covers the practical operating range of most heat sinks, 0.01<L*<0.18. The accuracy of the heat transfer model was found to be within 11% of the experimental data taken on four heat sinks and other experimental data from the published literature at channel Reynolds numbers less than 1200. The proposed heat transfer model may be used to predict the thermal performance of impingement air cooled plate fin heat sinks for design purposes.

Experimental Investigation on Thermal Performance of Heat Sink With Two Pairs of Embedded Heat Pipes

2007 ◽  
Author(s):  
Hsiang-Sheng Huang ◽  
Jung-Chang Wang ◽  
Sih-Li Chen
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Heat Transfer Rate ◽  
Thermal Performance ◽  
Heat Sink ◽  
Transfer Rate ◽  
Heat Pipes ◽  
Total Heat ◽  
Heating Power ◽  
Total Heat Transfer

This article provides an experimental method to study the thermal performance of a heat sink with two pairs (outer and inner pair) of embedded heat pipes. The proposed method can determine the heat transfer rate of the heat pipes under various heating power of the heat source. A comprehensive thermal resistance network of the heat sink is also developed. The network estimates the thermal resistances of the heat sink by applying the thermal performance test result. The results show that the outer and inner pairs of heat pipes carries 21% and 27% of the total heat transfer rate respectively, while 52% of the heating power is dissipated from the base plate to the fins. The dominated thermal resistance of the heat sink is the base to heat pipes resistance which is strongly affected by the thermal performance of the heat pipes. The total thermal resistance of the heat sink shows the lowest value, 0.23°C/W, while the total heat transfer rate of the heat sink is 140W and the heat transfer rate of the outer and inner pairs of heat pipes is 30W and 38 W, respectively.

Effects of process conditions on the heat transfer coefficient at the polymer-mold interface and tensile strength of thin-wall injection molding parts

2019 ◽  
Vol 39 (5) ◽  
pp. 493-500
Author(s):  
Laiyu Zhu ◽  
Liping Min ◽  
Xianglin Li ◽  
Zhanyu Zhai ◽  
Dietmar Drummer ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Tensile Strength ◽  
Weld Line ◽  
Polymer Melt ◽  
Mold Cavity ◽  
Cavity Surface ◽  
Thin Wall ◽  
Wall Injection ◽  
The Heat Transfer Coefficient

Abstract Generally, the strength at the weld line of the injection molded part is very weak. The heat transfer coefficient (HTC) between the polymer melt and the mold cavity surface was analyzed to solve this problem. The surface roughness of the mold cavity and the material of the mold insert were changed to adjust the interface environment between the polymer melt and the mold cavity surface. HTC was obtained by combing the experimental measurement with the theoretical calculation. In the current study, the influence of HTC on the tensile strength of the weld line of the molded specimen was investigated. The results show that the weld line strength of the molded specimen increases with the decrease in HTC between the polymer and the mold cavity surface. Meanwhile, the decrease in the surface roughness of the mold cavity or replacing the mold material with lower thermal conductivity can reduce the value of the HTC between the polymer and the mold effectively and can delay the cooling rate of the hot polymer melt. This provides a new idea to solve thin-wall injection molding weld line defects.

Investigation of Interfacial Thermal Resistance on Nano-Structures Using Molecular Dynamics Simulations

2010 ◽  
Author(s):  
Navdeep Singh ◽  
Debjyoti Banerjee
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Thermal Resistance ◽  
Md Simulations ◽  
Interfacial Thermal Resistance ◽  
Filler Materials ◽  
Nano Structures ◽  
Dynamics Simulations ◽  
Very High

Due to their very high thermal conductivity carbon nanotubes have been found to be an excellent material for thermal management. Experiments have shown that the heaters coated with carbon nanotubes increase the heat transfer by as much as 60%. Also when nanotubes are used as filler materials in composites, they tend to increase the thermal conductivity of the composites. But the increase in the heat transfer and the thermal conductivity has been found to be much less than the calculated values. This decrease has been attributed to the interfacial thermal resistance between the carbon nanotubes and the surrounding material. MD simulations were performed to study the interfacial thermal resistance between the carbon nanotubes and the liquid molecules. In the simulations, the nanotube is placed at the center of the simulation box and a temperature of 300K is imposed on the system. Then the temperature of the nanotube is raised instantaneously and the system is allowed to relax. From the temperature decay, the interfacial thermal resistance between the carbon nanotube and the liquid molecules is calculated. In this study the liquid molecules under investigation are n-heptane, n-tridecane and n-nonadecane.

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