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.

Hydrodynamic and Thermal Characteristics of Single-Phase and Two-Phase Micro-Pin-Fin Heat Sinks

2007 ◽  
Author(s):  
Abel M. Siu-Ho ◽  
Weilin Qu ◽  
Frank Pfefferkorn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Single Phase ◽  
Thermal Characteristics ◽  
Heat Sinks ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase ◽  
Pin Fin

The pressure drop and heat transfer characteristics of single-phase and two-phase micro-pin-fin heat sinks were investigated experimentally. Fabricated from 110 copper, the heat sink contained an array of 1950 staggered square micro-pin-fins with 200×200 μm2 cross-section by 670 μm height. The ratios of longitudinal pitch and transverse pitch to pin-fin hydraulic diameter are equal to 2. Deionized water was employed as the cooling liquid. A coolant inlet temperature of 30 °C, and six maximum mass velocities, ranging from 183 to 420 kg/m2s, were tested. The corresponding inlet Reynolds number ranged from 45.9 to 105.9. General hydrodynamic and thermal characteristics of the two flow regimes of single-phase flow and flow boiling were described. The measured temperature distribution was used to evaluate single-phase heat transfer coefficient and Nusselt number. Predictions of the previous friction factor and heat transfer correlations that were developed for low Reynolds number (Re<1000) single-phase flow in short pin-fin arrays were compared to the present micro-pin-fin single-phase pressure drop and Nusselt number data, respectively. The Short et al friction factor correlation and the Kos¸ar et al. heat transfer correlation provided acceptable predictions.

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

Flow Patterns During Flow Boiling Instability in Silicon-Based Pin-Fin Microchannels

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Fayao Xu ◽  
Huiying Wu ◽  
Zhenyu Liu
Keyword(s):  
Single Phase ◽  
Flow Instability ◽  
Flow Boiling ◽  
Flow Patterns ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Pin Fin ◽  
Short Period ◽  
Pin Fins ◽  
Amplitude Mode

In this paper, the flow patterns during water flow boiling instability in pin-fin microchannels were experimentally studied. Three types of pin-fin arrays (in-line/circular pin-fins, staggered/circular pin-fins, and staggered/square pin-fins) were used in the study. The flow instability started to occur as the outlet water reached the saturation temperature. Before the unstable boiling, a wider range of stable boiling existed in the pin-fin microchannels compared to that in the plain microchannels. Two flow instability modes for the temperature and pressure oscillations, which were long-period/large-amplitude mode and short-period/small-amplitude mode, were identified. The temperature variation during the oscillation period of the long-period/large-amplitude mode can be divided into two stages: increasing stage and decreasing stage. In the increasing stage, bubbly flow, vapor-slug flow, stratified flow, and wispy flow occurred sequentially with time for the in-line pin-fin microchannels; liquid single-phase flow, aforementioned four kinds of two-phase flow patterns, and vapor single-phase flow occurred sequentially with time for the staggered pin-fin microchannel. The flow pattern transitions in the decreasing stage were the inverse of those in the increasing stage for both in-line and staggered pin-fin microchannels. For the short-period/small-amplitude oscillation mode, only the wispy flow occurred. With the increase of heat flux, the wispy flow and the vapor single-phase flow occupied more and more time ratio during an oscillation period in the in-line and staggered pin-fin microchannels.

Heat Transfer and Pressure Loss Characteristics of Pin-Fins With Different Shapes in a Wide Channel

2017 ◽  
Author(s):  
Jin Xu ◽  
Jiaxu Yao ◽  
Pengfei Su ◽  
Jiang Lei ◽  
Junmei Wu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Bottom Surface ◽  
Number Range ◽  
Pin Fin ◽  
Nominal Diameter ◽  
Pin Fins

Convective heat transfer enhancement and pressure loss characteristics in a wide rectangular channel (AR = 4) with staggered pin fin arrays are investigated experimentally. Six sets of pin fins with the same nominal diameter (Dn = 8mm) are tested, including: Circular, Elliptic, Oblong, Dropform, NACA and Lancet. The relative spanwise pitch (S/Dn = 2) and streamwise pitch (X/Dn = 4.5) are kept the same for all six sets. Same nominal diameter and arrangement guarantee the same blockage area in the channel for each set. Reynolds number based on channel hydraulic diameter is from 10000 to 70000 with an increment of 10000. Using thermochromic liquid crystal (R40C20W), heat transfer coefficients on bottom surface of the channel are achieved. The obtained friction factor, Nusselt number and overall thermal performance are compared with the previously published data from other groups. The averaged Nusselt number of Circular pin fins is the largest in these six pin fins under different Re. Though Elliptic has a moderate level of Nusselt number, its pressure loss is next to the lowest. Elliptic pin fins have pretty good overall thermal performance in the tested Reynolds number range. When Re>40000, Lancet has a same level of performance as Circular, but its pressure loss is much lower than Circular. These two types are both promising alternative configuration to Circular pin fin used in gas turbine blade.

Effect of Variation of Pin-fin Height on Jet Impingement Heat Transfer on a Rotating Surface

2021 ◽  
Author(s):  
Pratik S. Bhansali ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Gas Turbine ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Impinging Jet ◽  
Rotating Disc ◽  
Disc Surface ◽  
Pin Fins

Abstract Heat transfer over rotating surfaces is of particular interest in rotating machinery such as gas turbine engines. The rotation of the gas turbine disc creates a radially outward flow on the disc surface, which may lead to ingress of hot gases into the narrow cavity between the disc and the stator. Impingement of cooling jet is an effective way of cooling the disc and countering the ingress of the hot gases. Present study focusses on investigating the effect of introducing pin-fins over the rotating disc on the heat transfer. The jet Reynolds number has been varied from 5000 to 18000, and the rotating Reynolds number has been varied from 5487 to 12803 for an aluminum disc of thickness 6.35mm and diameter 10.16 cm, over which square pins have been arranged in an inline fashion. Steady state temperature measurements have been taken using thermocouples embedded in the disc close to the target surface, and area average Nusselt number has been calculated. The effects of varying the height of the pin-fins, distance between nozzle and the disc surface and the inclination of the impinging jet with the axis of rotation have also been studied. The results have been compared with those for a smooth aluminum disc of equal dimensions and without any pin-fins. The average Nusselt number is significantly enhanced by the presence of pin fins. In the impingement dominant regime, where the effect of disc rotation is minimal for a smooth disc, the heat transfer increases with rotational speed in case of pin fins. The effect of inclination angle of the impinging jet is insignificant in the range explored in this paper (0° to 20°).

Single-Phase Heat Transfer in Mems-Based Pin Fin Heat Sink

2005 ◽  
Author(s):  
Ali Kosar ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Single Phase ◽  
Reynolds Numbers ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Pin Fins ◽  
Micro Pin Fins

An experimental study has been performed on single-phase heat transfer of de-ionized water over a bank of shrouded micro pin fins 243-μm long with hydraulic diameter of 99.5-μm. Heat transfer coefficients and Nusselt numbers have been obtained over effective heat fluxes ranging from 3.8 to 167 W/cm2 and Reynolds numbers from 14 to 112. The results were used to derive the Nusselt numbers and total thermal resistances. It has been found that endwalls effects are significant at low Reynolds numbers and diminish at higher Reynolds numbers.

Numerical Investigation on the Flow and Heat Transfer Characteristics of the Superheated Steam in the Wedge Duct With Pin-Fins

2013 ◽  
Author(s):  
Gaoliang Liao ◽  
Xinjun Wang ◽  
Xiaowei Bai ◽  
Ding Zhu ◽  
Jinling Yao
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Three Dimensional ◽  
Heat Transfer Characteristics ◽  
Pin Fin ◽  
Transfer Characteristics ◽  
Flow And Heat Transfer ◽  
Pin Fins ◽  
Steam Superheat

By using the CFX software, the three-dimensional flow and heat transfer characteristics in the cooling duct with pin-fin in the blade trailing edge were numerically simulated. The effects of pin-fin arrangements, Reynolds number, steam superheat degrees, streamwise pin density and convergence angle of the wedge duct on the flow and heat transfer characteristics were analysed. The results show that the Nusselt number on the endwall and pin-fin surfaces as well as the pin-fin row averaged Nusselt number increase with the increasing of Reynolds number, while it decreased with the with the increasing of X/D. The pressure drop increases with the increasing of Reynolds number while decreases with the increasing of X/D in the wedge duct. The degree of superheat has little effect on the pressure loss in the wedge duct. A comprehensive analysis and comparison show that the highest thermal performance is reached in the wedge duct when the value of X/D is 1.5.

Heat Transfer Augmentation in 3D Inner Finned Helical Tube

Volume 3 ◽  
2004 ◽  
Author(s):  
Longjian Li ◽  
Wenzhi Cui ◽  
Quan Liao ◽  
Mingdao Xin ◽  
Tien-Chien Jen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boiling Heat Transfer ◽  
Flow Resistance ◽  
Single Phase ◽  
Flow Boiling ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Helical Tube ◽  
Helical Tubes

Experiments were performed to investigate the performance enhancement of single-phase flow and boiling heat transfer in the 3D inner finned helical tubes. The tests for single-phase flow and heat transfer were carried out in the helical tubes with a curvature of 0.0663 and a length of 1.15m, the range of the Reynolds number examined varies from 1000 to 8500. In comparison to the smooth helical tube, the experimental results of two finned helical tubes with different inner fin geometry showed that the heat transfer and flow resistance in the 3D inner finned helical tube gains greater augmentation. Within the measured range of Reynolds number, the average augmentation ratio of heat transfer of the two finned tubes are 71% and 103%, compared with the smooth helical tube, and 90% and 140% for flow resistance, respectively. The tests for flow boiling heat transfer was carried out in the 3D inner finned helical tube with a curvature of 0.0605 and a length of 0.668m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D inner finned helical tube is increased by 40%∼120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance coefficient increased by 18%∼119%.

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.

scholarly journals  A Simplified Model of Low Reynolds Number, immiscible, Gas-Liquid Flow and Heat Transfer in Porous Media (Numerical Solution with Experimental Validation)

2021 ◽  
Author(s):  
Gamal B. Abdelaziz ◽  
M. Abdelgaleel ◽  
Z.M. Omara ◽  
A. S. Abdullah ◽  
Emad M.S. El-Said ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Porous Media ◽  
Numerical Solution ◽  
Single Phase ◽  
Energy Equation ◽  
Numerical Results ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Two Phase

Abstract This study investigates the thermal-hydraulic characteristics of immiscible two-phase flow (gas/liquid) and heat transfer through porous media. This research topic is interested among others in trickle bed reactors, the reservoirs production of oil, and the science of the earth. Characteristics of two-phase concurrent flow with heat transfer through a vertical, cylindrical, and homogeneous porous medium were investigated both numerically and experimentally. A generalized Darcy model for each phase is applied to derive the momentum equations of a two-phase mixture by appending some constitutive relations. Gravity force is considered through investigation. To promote the system energy equation, the energy equation of solid matrix for each phase are deemed. The test section is exposed to a constant wall temperature after filled with spherical beads. Numerical solution of the model is achieved by the finite volume method. The numerical procedure is generalized such that it can be reduced and applied to single phase flow model. The numerical results are acquired according to, air/water downward flow, spherical beads, ratio of particle diameter to pipe radius D=0.412, porosity φ=0.396, 0.01≤Re≤500, water to air volume ratio 0≤W/A≤∞, and saturation ratio 0≤S1≤1. To validate this model an experimental test rig is designed and constructed, and the corresponding numerical results are compared with its results. Also, the numerical results were compared with other available numerical results. The comparisons show good agreement and validate the numerical model. One of the important results reveals that the heat transfer is influenced by two main parameters; saturation ratios of the two fluids; S1 and S2, and the mixture Reynolds number Re. The thermal entry length is directly dependent on Re, S1, and the thermofluid properties of the fluids. A modified empirical correlation for the entrance length; Xe =0.1 Re.Pr.Rm is predicted, where Rm =Rm(S1, S2, ρ1, ρ2, c1, c2). The predicted correlation is verified by comparing with the supposed correlation of Poulikakos and Ranken (1987) and El-Kady (1997) for a single-phase flow; Xe/Pr=0.1 Re.

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