Measurement of Heat Transfer Enhancement and Pressure Drop Across Eddy Promoter Air Screens in a Liquid-to-Air-Membrane Energy Exchanger (LAMEE)

2013 ◽  
Author(s):  
Ashkan Oghabi ◽  
Davood Ghadiri Moghaddam ◽  
Carey Simonson ◽  
Robert W. Besant
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat Transfer Coefficient ◽  
Transfer Enhancement ◽  
Membrane Energy ◽  
Air Channel

In liquid-to-air membrane energy exchangers (LAMEEs), the heat and mass transfer resistances in the air channel are dominant. An eddy promoter air screen can effectively enhance the heat and mass transfers in the air channel. In this study, the heat transfer enhancement and pressure drop across three different eddy promoter air screens in an air channel are experimentally investigated. Eddy promoter air screens are comprised of plastic ribs in the stream-wise direction and aluminum cross-bars normal to the air flow direction. A low speed wind tunnel test facility, which simulates the air channel of a LAMEE is designed to measure the friction factor and enhanced convective heat transfer coefficient in the air channel with an eddy promoter air screen. Tests were conducted at Reynolds numbers of 920, 1550, and 2160. In this paper, the effects of the spacing of the cylindrical bars and plastic ribs on the heat transfer performance are studied experimentally. Also, the performance of eddy promoter air screens as a function of enhanced heat transfer coefficient and increased pressure drop is investigated. Results show that the eddy promoter air screens have the highest efficiencies at Reynolds of 1550 and double the convective heat transfer coefficient of the air with respect to a smooth channel.

Heat Transfer Enhancement in Split and Recombine Flow Configurations: A Numerical and Experimental Study

2016 ◽  
Author(s):  
Mojtaba Jarrahi ◽  
Jean-Pierre Thermeau ◽  
Hassan Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Working Fluid ◽  
Transfer Enhancement

Heat transfer enhancement in laminar regime by split and recombine (SAR) mechanism, based on the baker’s transformation, is investigated. Two different heat exchangers, called SAR1 and SAR2, are studied. Their geometries are inspired from the previous studies reported in the literature. The working fluid on both, shell and tube side, is water and the temperature on the shell side is kept constant. Experiments are carried out for the Reynolds number range 100<Re<3000 when the Prandtl number is between 4.5 and 7.5. The results show that the convective heat transfer coefficient in the first element of heat exchanger SAR1 is higher than that in the second one, i.e. SAR2. However, the variation in the convective heat transfer coefficient from the first to the third element along the heat exchanger SAR2 is less significant than that observed for SAR1. Moreover, SAR2 causes a higher pressure drop, especially when Re>1000, and provides a less uniform temperature field at the outlet.

Convective Heat Transfer Coefficient and Pressure Drop of Al2O3-Water Nanofluid in a Single-Phase Microchannel for Cooling of High Heat Output Devices

2008 ◽  
Author(s):  
Guillermo E. Valencia ◽  
Miguel A. Ramos ◽  
Antono J. Bula
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Convective Heat Transfer Coefficient ◽  
Heat Output ◽  
Flux Boundary Condition

The paper describes an experimental procedure performed to obtain the convective heat transfer coefficient of Al2O3 nanofluid working as cooling fluid under turbulent regimen through arrays of aluminum microchannel heat sink having a diameter of 1.2 mm. Experimental Nusselt number correlation as a function of the volume fractions, Reynolds, Peclet and Prandtl numbers for a constant heat flux boundary condition is presented. The correlation for Nusselt number has a good agreement with experimental data and can be used to predict heat transfer coefficient for this specific nanofluid, water/Al2O3. Furthermore, the pressure drop is also analyzed considering the different nanoparticles concentration.

Convective Heat Transfer Characteristics of Silver-Water Nanofluid Under Laminar and Turbulent Flow Conditions

2012 ◽  
Vol 4 (3) ◽  
Author(s):  
Lazarus Godson ◽  
B. Raja ◽  
D. Mohan Lal ◽  
S. Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Pure Water ◽  
Convective Heat Transfer Coefficient ◽  
Experimental Results

The convective heat transfer coefficient and pressure drop of silver-water nanofluids is measured in a counter flow heat exchanger from laminar to turbulent flow regime. The experimental results show that the convective heat transfer coefficient of the nanofluids increases by up to 69% at a concentration of 0.9 vol. % compared with that of pure water. Furthermore, the experimental results show that the convective heat transfer coefficient enhancement exceeds the thermal conductivity enhancement. It is observed that the measured heat transfer coefficient is higher than that of the predicted ones using Gnielinski equation by at least 40%. The use of the silver nanofluid has a little penalty in pressure drop up to 55% increase 0.9% volume concentration of silver nanoparticles.

Condensation Pressure Drop and Heat Transfer in 5-mm-OD Micro-Fin Tubes

2012 ◽  
Author(s):  
Wei Li ◽  
Dan Huang ◽  
Zan Wu ◽  
Hong-Xia Li ◽  
Zhao-Yan Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Condensation Heat Transfer ◽  
Transfer Enhancement ◽  
Mass Fluxes ◽  
Fin Tubes ◽  
Condensation Heat Transfer Coefficient

An experimental investigation was performed for convective condensation of R410A inside four micro-fin tubes with the same outside diameter (OD) 5 mm and helix angle 18°. Data are for mass fluxes ranging from about 180 to 650 kg/m2s. The nominal saturation temperature is 320 K, with inlet and outlet qualities of 0.8 and 0.1, respectively. The results suggest that Tube 4 has the best thermal performance for its largest condensation heat transfer coefficient and relatively low pressure drop penalty. Condensation heat transfer coefficient decreases at first and then increases or flattens out gradually as G decreases. This complex mass-flux effect may be explained by the complex interactions between micro-fins and fluid. The heat transfer enhancement mechanism is mainly due to the surface area increase over the plain tube at large mass fluxes, while liquid drainage and interfacial turbulence play important roles in heat transfer enhancement at low mass fluxes. In addition, the experimental data was analyzed using seven existing pressure-drop and four heat-transfer models to verify their respective accuracies.

Applied Pulsed Flow for Single-Phase Convective Heat Transfer Enhancement in a Laminar Flow Cooling System

2008 ◽  
Author(s):  
Bolaji O. Olayiwola ◽  
Gerhard Schaldach ◽  
Peter Walzel
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Cooling System ◽  
Transfer Enhancement ◽  
Flow Rates ◽  
The Heat Transfer Coefficient

Experimental and CFD studies were performed to investigate the enhancement of convective heat transfer in a laminar cooling system using flow pulsation in a flat channel with series of regular spaced fins. Glycerol-water mixtures with dynamic viscosities in the range of 0.001 kg/ms–0.01 kg/ms were used. A steady flow Reynolds number in the laminar range of 10 &lt; Re &lt; 1200 was studied. The amplitudes of the applied pulsations are in the range of 0.25 &lt; A &lt; 0.55 mm and the frequency range is 10 &lt; f &lt; 60 Hz. Two different cooling devices with active length L = 450 mm and 900 mm were investigated. CFD simulations were performed on a parallel-computer (Linux-cluster) using the software suit CFX11 from ANSYS GmbH, Germany. The rate of cooling was found to be significant at moderate low net flow rates. In general, no significant heat transfer enhancement at very low and high flow rates was obtained in compliance with the experimental data. The heat transfer coefficient was found to increase with increasing Prandtl number Pr at constant oscillation Reynolds number Reosc whereas the ratio of the hydraulic diameter to the length of the channel dh/L has insignificant effect on the heat transfer coefficient. This is due to enhanced fluid mixing. CFD results allow for performance predictions of different geometries and flow conditions.

Influence of Various Nanofluid Types on Wavy Microchannels Heat Sink Cooling Performance

2013 ◽  
Vol 420 ◽  
pp. 118-122 ◽  
Author(s):  
Prem Gunnasegaran ◽  
Noel Narindra ◽  
Norshah Hafeez Shuaib
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Heat Sink ◽  
Convective Heat Transfer Coefficient ◽  
Volume Fractions ◽  
The Impact

This paper discusses the impact of using various types of nanofluids and nanoparticle volume fractions on heat transfer and fluid flow characteristics in a wavy microchannel heat sink (WMCHS) with rectangular cross-section. Numerical investigations using three different types of nanofluids including Al2O3-H2O, CuO-H2O, and diamond-H2O with a fixed nanoparticle volume fraction of 3% and using a diamond-H2O with nanoparticle volume fractions ranging from 0.5% to 5% are examined. This investigation covers Reynolds numbers in the range of 100 to 1000. The three-dimensional steady, laminar flow and heat transfer governing equations are solved using the finite-volume method (FVM). The computational model is used to study the variations of convective heat transfer coefficient, pressure drop and wall shear stress. It is inferred that the convective heat transfer coefficient of a WMCHS cooled with the nanofluid flow showed marked improvement over the pure water with a smaller pressure drop penalty.

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