Air-Side Heat Transfer Enhancement and Pumping Power Penalty in Air-Cooled Heat Exchangers With Dimpled Fins

2017 ◽  
Author(s):  
Tung X. Vu ◽  
Lokanath Mohanta ◽  
Vijay K. Dhir
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Fold Increase ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Power Penalty ◽  
Flat Tubes

In this work, we focus exclusively on heat transfer enhancement techniques for the air-side heat transfer in air-cooled heat exchangers/condensers. An innovative dimpled fin configuration is explored. Experiments, in which both heat transfer and drag are measured, are conducted with flat tubes in three configurations: without fins, with plain fins and with dimpled fins. Reynolds numbers based on the hydraulic diameter of the finned passages are varied between 600 and 7000. Results indicate that fins are more advantageous at lower Reynolds numbers since the increase in drag at higher Reynolds numbers quickly erases any advantage due to an increase in heat transfer rate. As an example, for the plain fins versus a bare tube at a Reynolds number of 600, there is a 7 fold increase in heat transfer with only a 5 fold increase in drag. However, at a Reynolds number of 7000, both heat transfer and drag increase by approximately 6 times, indicating that the increase in drag has caught up with the heat transfer enhancement. Similarly, while dimpled fins do result in higher heat transfer compared with the plain fins, the advantage is also more prominent at lower Reynolds numbers where heat transfer enhancement is higher than the associated increase in pumping power.

Design and testing of energy-efficient heat exchangers for Newtonian and non-Newtonian fluids – A review

2021 ◽  
pp. 095765092110470
Author(s):  
Jayesh P ◽  
Mukkamala Y ◽  
Bibin John
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Internal Surface ◽  
Surface Modifications ◽  
Newtonian Fluids ◽  
Tube Surface ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
The Impact

Heat transfer enhancement, pumping power and weight minimization in enhanced heat exchangers has long been achieved by deploying tubes with internal surface modifications like microgrooves, ribs, fins, knurls, and dimples with and without tube inserts. This article presents a very extensive review of experimental and computational studies on heat transfer enhancement, which covers convectional and unconventional working fluids under different fluid flow conditions. Compound augmentation with tube surface modifications and inserts has yielded enhancements in the overall heat transfer coefficient of over 116% in the fully developed turbulent flow regime. Exotic fluids like nano-coolants deployed in spiral grooved mircofin tubes yielded 196% enhancement in tube side heat transfer rate for concentrations as low as 0.5% by volume, while the thermal efficiency index measuring the overall enhancement in relation to the pumping power was 75%. However, reviews that address the combined effect of unconventional fluids, surface modifications and tube inserts on the overall thermo-hydraulic performance of annular heat exchangers seem to be limited. Further, nano-coolants aren’t frequently used in the process industry. The goal of this study is to document and evaluate the impact of cost-effective and energy-saving passive enhancement techniques such as tube surface modifications, tube inserts, and annular enhancement techniques on annular heat exchangers used in the process industries with Newtonian and non-Newtonian fluids. This review should be useful to engineers, academics and medical professionals working with non-Newtonian fluids and enhanced heat exchangers.

Numerical Investigation of Heat Transfer Enhancement Due to Flow Agitators Between Fins

2021 ◽  
pp. 1-14
Author(s):  
Aditya Patki ◽  
Shankar Krishnan
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Visualization ◽  
Heat Transfer Enhancement ◽  
Time Scales ◽  
Reynolds Numbers ◽  
Critical Parameters ◽  
Transfer Enhancement ◽  
Oscillation Cycle

Abstract The paper investigates the heat transfer characteristics of a channel system consisting of mean axial flow and oscillatory cross flow components. A numerical model has been developed to solve the governing equations associated with the flow. The paper identifies advection, diffusion, and oscillation time scales and intensity of squeezing in the channel as critical parameters controlling system behavior. The total Reynolds number parameter is considered in the paper to understand the combined effect of axial and transverse Reynolds numbers on the Nusselt number. Flow visualization techniques are employed to understand the boundary layer changes that occur over an oscillation cycle. Nusselt number is found to increase with a reduction in advection and oscillation time scales. A linear relationship is observed between the Nusselt number and total Reynolds number when the axial and transverse Reynolds numbers are comparable. Non-dimensional pressure drop is primarily defined by only two parameters: axial Reynolds number and squeezing fraction. The flow visualization results indicate significant heat transfer enhancement in a small fraction of the oscillation cycle characterized by flow conditions similar to Couette flow.

Numerical Simulations of Heat and Fluid Flow in Grooved Channels With Curved Vanes

2003 ◽  
Author(s):  
Matthew McGarry ◽  
Antonio Campo ◽  
Darren L. Hitt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Exchangers ◽  
System Performance ◽  
Vortex Formation ◽  
Electronics Cooling ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Heat And Fluid Flow

The use of vanes in grooved channels for heat transfer enhancement has received more attention in the recent years due to applications in heat exchangers and electronics cooling. The current work focuses on characterizing the vortex formation around heated elements in grooved channels with curved vanes. A computational model is developed to examine the effect that the vortices have on heat transfer and system performance for a range of Reynolds numbers of 100 to 800. These vortices explain the previously observed characteristics in system performance for geometries with the use of curved vanes. At a Reynolds number of 400 these vortices inhibit heat transfer and increase pressure drop in the channel, resulting in significant decreases in system performance.

scholarly journals Augmentation of Heat Transfer in a Duct with Rotating Turbulator using Al2o3 Nanofluid

2019 ◽  
Vol 8 (3) ◽  
pp. 3059-3062
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Twist Ratio ◽  
Al2o3 Nanofluid

The heat transfer enhancement is one of the essential factors to be considered in the design of heat exchangers. The rate of heat transfer can be enhanced by inserting and modifying the geometric configuration of the turbulators in the tube of heat exchangers. In our present work we conducted the experiment to investigate the rate of heat transfer enhancement in a tubular in a heat exchanger by using rotating twisted tape turbulator of twist ratio 3.27 using water and Al2O3 nanofluid as a testing fluid at the flow rate of 1, 2, and 3 LPM. The range of Reynolds number used is 2000<Re<10000, the heat transfer rate calculated for each case of rotating TTT with the speed of 0 to 300 RPM with the step of 100 RPM. The obtained results are compared between water and Al2O3 nanofluid, with and without rotating TTT. From the comparisons, it was found that the TTT with U-cut and the use of Al2O3 nanofluid gives the better rise in the heat transfer rate of about 39.63%. The augmented rate of heat transfer is due to the more turbulence when the rotating TTT is used and replacing the water with nanofluid as the testing fluid which of high thermal properties.

The Spacer Grid Effect on Heat Transfer at Low Flow Rate in a 5×5 Rod Bundles

2016 ◽  
Author(s):  
Da Liu ◽  
Hanyang Gu ◽  
Shengjie Gong
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Flow Rate ◽  
Reynolds Numbers ◽  
Low Flow ◽  
Transfer Enhancement ◽  
Spacer Grid ◽  
Maximum Enhancement ◽  
Low Reynolds Numbers

It is widely acknowledged that the spacer grid has great effect on heat transfer downstream of it. The conventional correlations to predict the augmentation of the spacer were carried out on high Reynolds numbers. However, recent studies have shown that Reynolds number on the heat transfer enhancement is not negligible when the Reynolds number is lower than about 10000. An experiment to investigate the single-phase convective heat transfer downstream of the spacer grid at low flow rate has been performed in a 5×5 rod bundle. The test section was uniformly heated by a DC power and cooled by water. The Reynolds number covered from about 2000 to 10000. The experiment showed that the existing correlations for heat transfer enhancement by a spacer grid underestimated the maximum enhancement at the grid exit of the spacer grid at low Reynolds numbers. As the Reynolds number decreases, the maximum enhancement increases, nevertheless, when Reynolds number decreases to about 4300, the maximum enhancement tend to converge at a certain value. A new correlation has been proposed to account for the Reynolds number effect on heat transfer enhancement downstream of the spacer grid at low Reynolds numbers and which gave good predictions.

Using Computational Fluid Dynamics to Design Heat Transfer Enhancement Methods for Cooling Channels

1995 ◽  
Author(s):  
Aaron M. Plotnik ◽  
Ann M. Anderson
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Transfer Enhancement ◽  
Low Reynolds Numbers ◽  
Cooling Channels ◽  
Dimensional Measure

Abstract This paper presents the results of a study to enhance heat transfer in a short narrow cooling channel (7.9 mm high by 30.9 mm wide by 109 mm long). The study was performed using a computational fluid dynamics (CFD) code. Flotherm, by Flomerics, Inc. The work emphasizes the usefulness of CFD in the design process. The heat transfer enhancement was accomplished by placing thin rib-like protrusions in the channel. Simulations were run for two protrusion spacings, with a range of protrusion heights from 0.5 to 1.5 mm and a range of channel Reynolds number from 500 to 40,000. The results of a grid dependence study are presented and baseline comparisons are made to validate the computational model. The results show increases in channel Nusselt number of 10–160% while the friction factor increases by 10–5200%. The different configurations are compared using a non-dimensional measure of the pumping power and this shows that devices are most effective at low Reynolds numbers. The enhancement in heat transfer, the increase in friction loss and the worth in terms of pumping power would all have to be weighed with respect to the needs of a particular application before any choice is made to apply the techniques studied in this report.

Heat Transfer Investigation of the Channels With Rib Turbulators and Double-Row Bleed Holes

2011 ◽  
Author(s):  
Tao Guo ◽  
Huiren Zhu ◽  
Dunchun Xu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Liquid Crystal ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Double Row ◽  
Average Heat ◽  
Rib Turbulators ◽  
Transient Liquid Crystal Technique

The detailed heat transfer distributions are measured for the wall of a channel with rib turbulators and double-row bleed holes by transient liquid crystal technique. The effects of the relative positions of rib turbulators and bleed holes, rib angles, channel Reynolds numbers and bleed ratios on heat transfer character are studied. The bleed holes are located near the upstream ribs, equidistant between ribs and near the downstream ribs. Three different rib angles of 60°, 90° and 120° are selected with the holes equidistant between ribs. The channel Reynolds numbers are changed from 30000 to 120000. The bleed ratios are between 0.09 and 0.22. The results show that angled ribs produces higher heat transfer enhancement in conjunction with the effect of bleed holes. The heat transfer characters are best when the bleed holes are located near the upstream ribs in the channels with 90° ribs. The change of bleed holes locations does not change the position of the flow reattachment, but affect the heat transfer distribution and intensity in the region. The average heat transfer enhancement decreases with the increasing of Reynolds number, and slight increases as the bleed ratio increases.

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