scholarly journals INVESTIGATION OF SINGLE-PHASE FLOW CHARACTERISTICS IN A STAGGER PIN-FINS COMPLEX GEOMETRY

2021 ◽  
Vol 25 (6) ◽  
pp. 74-81
Author(s):  
R. Shakir ◽  
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Complex Geometry ◽  
Flow Characteristics ◽  
Inlet Temperature ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Single Phase Flow ◽  
Pin Fins ◽  
Micro Pin Fins

The cooling equipment project must use electrical and electronic equipment because of the need to remove the heat generated by this equipment. Investigation; R-113 single-phase flow heat transfer; (50 x 50 mm2) cross-section and (5 mm) height; used in a series of stagger-square micro-pin fins. Inlet temperature of (25 °C); (6) Mass flow rate at this temperature, the recommended range is (0. 0025 -0.01 kg/sec) the inlet and outlet pressures are approximately (1-1.10 bar), and through (25- 225 watts) applied heat. The iterative process is used to obtain the heat flow characteristics, for example; the single-phase heat transfer coefficient is completely laminar flow developing, in this flow, guesses the wall temperature, guess the fluid temperature. The possible mechanism of heat transfer has been discussed

Liquid Single-Phase Flow in an Array of Micro-Pin-Fins—Part I: Heat Transfer Characteristics

2008 ◽  
Vol 130 (12) ◽  
Author(s):  
Weilin Qu ◽  
Abel Siu-Ho
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Average Nusselt Number ◽  
Single Phase ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pin Fin ◽  
Pin Fins ◽  
Micro Pin Fins

This is Paper I of a two-part study concerning thermal and hydrodynamic characteristics of liquid single-phase flow in an array of micro-pin-fins. This paper reports the heat transfer results of the study. An array of 1950 staggered square micro-pin-fins with 200×200 μm2 cross-section by 670 μm height were fabricated into a copper test section. De-ionized water was used as the cooling liquid. Two coolant inlet temperatures of 30°C and 60°C and six maximum mass velocities for each inlet temperature ranging from 183 to 420 kg/m2 s were tested. The corresponding inlet Reynolds number ranged from 45.9 to 179.6. General characteristics of average and local heat transfer were described. Six previous conventional long and intermediate pin-fin correlations and two micro-pin-fin correlations were examined and were found to overpredict the average Nusselt number data. Two new heat transfer correlations were proposed for the average heat transfer based on the present data, in which the average Nusselt number is correlated with the average Reynolds number by power law. Values of the exponent m of the Reynolds number for the two new correlations are fairly close to those for the two previous micro-pin-fin correlations but substantially higher than those for the previous conventional pin-fin correlations, indicating a stronger dependence of the Nusselt number on the Reynolds number in micro-pin-fin arrays. The correlations developed for the average Nusselt number can adequately predict the local Nusselt number data.

An Experimental Investigation of Gas-Liquid Heat Transfer in Rectangular Micro-Channels

2013 ◽  
Author(s):  
Sira Saisorn ◽  
Somchai Wongwises ◽  
Piyawat Kuaseng ◽  
Chompunut Nuibutr ◽  
Wattana Chanphan
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Camera System ◽  
Micro Channels ◽  
Flow Mechanisms

The investigations of heat transfer and fluid flow characteristics of non-boiling air-water flow in micro-channels are experimentally studied. The gas-liquid mixture from y-shape mixer is forced to flow in the 21 parallel rectangular microchannels with 40 mm long in the flow direction. Each channel has a width and a depth of 0.45 and 0.41 mm, respectively. Flow visualization is feasible by incorporating the stereozoom microscope into the camera system and different flow patterns are recorded. The experiments are performed under low superficial velocities. Two-phase heat transfer gives better results when compared with the single-phase flow. It is found from the experiment that heat transfer enhancement up to 53% is obtained over the single-phase flow. Also, the change in the configuration of the inlet plenum can result in the different two-phase flow mechanisms.

Thermal and Flow Characteristics of Water–Nitrogen Taylor Flow Inside Vertical Circular Tubes

2018 ◽  
Vol 140 (8) ◽  
Author(s):  
Jingzhi Zhang ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Characteristics ◽  
Numerical Data ◽  
Bond Number ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pressure Drops ◽  
Taylor Flow ◽  
Bubble Rising Velocity

Heat transfer and flow characteristics of Taylor flows in vertical capillaries with tube diameters ranging from 0.5 mm to 2 mm were studied numerically with the volume of fluid (VOF) method. Streamlines, bubble shapes, pressure drops, and heat transfer characteristics of the fully developed gas–liquid Taylor flow were investigated in detail. The numerical data fitted well with experimental results and with the predicted values of empirical correlations. The results indicate that the dimensionless liquid film thickness and bubble rising velocity increase with increasing capillary number. Pressure drops in liquid slug region are higher than the single-phase flow because of the Laplace pressure drop. The flow pattern dependent model and modified flow separation model which takes Bond number and Reynolds number into account can predict the numerical pressure drops well. Compared with the single-phase flow, less time is needed for the Taylor flow to reach a thermal fully developed status. The Nusselt number of Taylor flow is about 1.16–3.5 times of the fully developed single-phase flow with a constant wall heat flux. The recirculation regions in the liquid and gas slugs can enhance the heat transfer coefficient and accelerate the development of the thermal boundary layer.

Single Phase Flow in the Randomly Packed Bed With Spheres: Simulation and Experimental Validation

2016 ◽  
Author(s):  
Nan Zhang ◽  
Zhongning Sun ◽  
Ming Ding
Keyword(s):  
Single Phase ◽  
Complex Geometry ◽  
Three Dimensional ◽  
Particle Diameter ◽  
Flow Characteristics ◽  
Packed Bed ◽  
Spherical Particles ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Local Flow

A computational fluid dynamic (CFD) model for single phase flow in the three dimensional randomly packed bed with spherical particles has been developed and validated with experimental results. The flow characteristics within this complex geometry are very complicated. In order to obtain insight into the interior and local flow characteristics, Three-dimensional simulation is required. First, we constructed the randomly packed bed with spherical particle, using Discrete Element Method (DEM) based on the integration of Newton’s laws of motion. To validate the DEM simulations the global bed porosity and the radial porosity distribution were compared with empirical correlation from literature. Second, the complex geometrical properties of random packed bed make it difficult to produce a fine mesh. Herein, the bridge method for meshing the particle-particle and particle-wall contact points in the packed bed was applied. The contact zones are modified and then partitioned into several regular parts, so the structure gird was meshed. Finally, the simulation of water flow in the randomly packed bed with a tube-to-particle diameter ratio of 6.325 has been carried out by the commercial CFD code. A comparison with previously published correlations and experimental data shows that the relationship proposed by KTA agree well with the measured pressure drop. Furthermore the results of simulation for distribution of velocity in the bed were analyzed and discussed.

Thermal and Hydrodynamic Characteristics of Single-Phase Flow and Flow Boiling in a Staggered Micro-Pin-Fin Array

2008 ◽  
Author(s):  
Weilin Qu
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Single Phase ◽  
Flow Boiling ◽  
Hydrodynamic Characteristics ◽  
Inlet Temperature ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pin Fin ◽  
Pin Fin Array

This study concerns thermal and hydrodynamic characteristics of water single-phase flow and flow boiling in a micro-pin-fin array. An array of 1950 staggered square micro-pin-fins with a 200×200 μm2 cross-section by a 670 μm height were fabricated into a copper heat sink test section. Two inlet temperatures of 30 °C and 60 °C, and six maximum mass velocities for each inlet temperature, ranging from 183 to 420 kg/m2s, were tested. The corresponding inlet Reynolds number ranged from 45.9 to 179.6. General characteristics of single-phase flow and flow boiling were described. Predictive tools were proposed for single-phase heat transfer coefficient and pressure drop. Unique features of flow boiling heat transfer in the micro-pin-fin array were identified. The classic Lockhart-Martinelli correlation incorporating a single-phase micro-pin-fin friction factor correlation and the laminar liquid–laminar vapor combination assumption was used to predict two-phase pressure drop in the micro-pin-fin array. The predictions agreed well with the experimental data.

Thermal and Flow Characteristics of Water-Nitrogen Taylor Flow Inside Vertical Circular Tubes

2016 ◽  
Author(s):  
Jingzhi Zhang ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Flow Characteristics ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Liquid Slug ◽  
Pressure Drops ◽  
Taylor Flow ◽  
Separate Model ◽  
Bubble Length

Heat transfer and flow characteristics of Taylor flow in vertical capillaries with tube diameters ranging from 0.5 mm to 2 mm have been investigated numerically with the Volume of Fluid (VOF) method. Streamlines, bubble shapes, pressure drops, and heat transfer characteristics of Taylor flow were investigated in detail. The results indicate that the dimensionless bubble length increases with increasing Re, while the variation of diameters have slight influence on it. A flat tail and sharper nose bubble with longer bubble length and thicker film thickness are obtained at higher Re for the increasing inertia force. Pressure drops in liquid slug region are higher than single phase flow because of the Laplace pressure drop. The flow pattern dependent model and modified separate model in this work can predict the simulation data well with a MAE of 2.416% and 2.289%, respectively. Bo and Re are adopted in the modified separate model to taking surface tension, gravity, inertia, and viscous force into account. The wall temperature Tw increases along X axis in liquid region, and gets its peak at the tail of Taylor bubble region. Nutp, which is about 1.2∼3 times of fully developed single phase flow with constant wall heat flux, is negatively proportional to the dimensionless liquid slug length (Ls*). Taylor flow can enhance the heat transfer efficiently.

A Theoretical Model for Axial Heat Conduction Effects During Single-Phase Flow in Microchannels

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Ting-Yu Lin ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Single Phase ◽  
Inlet Section ◽  
Phase Flow ◽  
Fluid Temperature ◽  
Single Phase Flow ◽  
Axial Conduction ◽  
Axial Heat ◽  
Axial Heat Conduction

A model is developed to analyze the effect of axial conduction on heat transfer during single-phase flow in microchannels. The axial heat conduction in the wall introduces heat flow toward the inlet section resulting in an increase in the local fluid temperature and a corresponding increase in the wall temperature. Neglecting this effect while reducing the experimental data results in a lower value of the experimental Nusselt number. The model derived in this work takes into account this effect and offers a parameter to estimate the effect introduced by the axial heat conduction effect in the wall.

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