Visualization of Flow Phenomena Near Enhanced Surfaces

1994 ◽  
Vol 116 (1) ◽  
pp. 54-57 ◽  
Author(s):  
T. S. Ravigururajan ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Working Fluid ◽  
Hydraulic Characteristics ◽  
Transfer Enhancement ◽  
Flow Phenomena ◽  
Augmentation Techniques ◽  
Simultaneous Existence ◽  
Physical Phenomena

Passive augmentation techniques such as surface disruptions are being increasingly used in heat exchangers. Although many working correlations have been suggested to predict their thermal-hydraulic characteristics, the physical phenomena governing the heat transfer enhancement have not been clearly understood. The paper describes a qualitative study on the flow phenomena near an enchanced surface. Water was used as the working fluid. Experiments were conducted for different coil wire diameters and for a Reynolds number of 150-2600. The results show the simultaneous existence of different flow patterns in enhanced flow. Also, the study confirmed that the developing length is very much smaller than that of a smooth tube, even for laminar flow.

Single-Phase Heat Transfer and Pressure Drop of Water Cooled Inside Horizontal Smooth Tubes in the Transitional Flow Regime

2010 ◽  
Author(s):  
Josua P. Meyer ◽  
Leon Liebenberg ◽  
Jonathan A. Olivier
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Transition Region ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Transitional Flow ◽  
Working Fluid ◽  
Tube Heat Exchanger ◽  
Smooth Tubes

Heat exchangers are usually designed in such a way that they do not operate in the transition region. This is usually due to a lack of information in this region. However, due to design constraints, energy efficiency requirements or change of operating conditions, heat exchangers are often forced to operate in this region. It is also well known that entrance disturbances influence where transition occurs. The purpose of this paper is to present experimental heat transfer and pressure drop data in the transition region for fully developed and developing flows inside smooth tubes using water as the working fluid. The use of different inlet disturbances were used to investigate its effect on transition. A tube-in-tube heat exchanger was used to perform the experiments, which ranged in Reynolds numbers from 1 000 to 20 000, with Prandtl numbers being between 4 and 6 while Grashof numbers were in the order of 105. Results showed that the type of inlet disturbance could delay transition to a Reynolds number as high as 7 000, while other inlets expedited it, confirming results of others. For heat transfer, though, it was found that transition was independent of the inlet disturbance and all commenced at the same Reynolds number, 2 000–3 000, which was attributed to secondary flow effects.

Effect of Twist Ratio on Heat Transfer Enhancement by Swirl Impingement

2019 ◽  
Author(s):  
Kishore Ranganath Ramakrishnan ◽  
Srivatsan Madhavan ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Heat Transfer Enhancement ◽  
Experimental Work ◽  
Working Fluid ◽  
Transfer Enhancement ◽  
Average Heat ◽  
Twist Ratio ◽  
Single Jet

Abstract Steady state experimental work has been carried out to compare a conventional single jet of diameter 12.7mm with a swirling impinging jet. In this study swirl inserts with three different twist ratios 3, 4.5 and 6 were used to induce the swirling motion to the working fluid. The Reynolds number based on conventional impinging jet’s diameter is varied from 10000 to 16000. It is observed that with increase in twist ratio, the average heat transfer enhancement is reduced. However, with higher twist ratios more uniform distribution of heat transfer enhancement is observed.

Experimental Study on Heat Transfer Performances of Flat Tube Bank Fin Heat Exchanger Using Four Different Fin Patterns

2018 ◽  
Vol 140 (4) ◽  
Author(s):  
Feng-Cai Zheng ◽  
Song Liu ◽  
Zhi-Min Lin ◽  
Jaafar Nugud ◽  
Liang-Chen Wang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Transfer Enhancement ◽  
Tube Bank ◽  
Number Range ◽  
Flat Tube ◽  
Louvered Fin ◽  
Delta Winglet ◽  
Better Than

Air-side heat transfer and flow friction characteristics of four different fin patterns suitable for flat tube bank fin heat exchangers are investigated experimentally. The fin patterns are the fin with six dimples, the fin with nine dimples, the double louvered fin, and the fin with delta-winglet vortex generators (VGs). The corresponding plain fins (plain fin I and plain fin II) are used as the references for evaluating the thermal performances of these fin patterns under identical pump power constraint. The performance of the fin with the six dimples is better than that with nine dimples. The performance of the fin with delta-winglet VGs is better than that of the double louvered fin, and the performance of the latter is better than that of the fins with six or nine dimples. In the tested Reynolds number range, the heat transfer enhancement performance factor of the fin with six dimples, the fin with nine dimples, the double louvered fin, and the fin with delta-winglet VGs is 1.2–1.3, 1.1–1.2, 1.3–1.6, and 1.4–1.6, respectively. The correlations of Nusselt number and friction factor with Reynolds number for the fins with six/nine dimples and the double louvered fin are obtained. These correlations are useful to design flat tube bank fin heat exchangers.

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.

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.

scholarly journals What dominates heat transfer performance of a double-pipe heat exchanger

Open Physics ◽  
2021 ◽  
Vol 19 (1) ◽  
pp. 863-866
Author(s):  
Dan Zheng ◽  
Zhenwei Hu ◽  
Liting Tian ◽  
Jin Wang ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchangers ◽  
Heat Transfer Performance ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Corrugated Tube ◽  
Helical Corrugation ◽  
Double Pipe ◽  
Pipe Heat

Abstract ZnO–water nanofluid in an inner pipe was experimentally investigated to improve the thermal efficiency of double-pipe heat exchangers. In this work, a 57.6% increase in the Nusselt number was obtained at Re = 14,340 when the ZnO–water nanofluid flowed through a helically corrugated tube. It was found that helical corrugation played a more important role in heat transfer enhancement than thermophysical properties of the nanofluid at the Reynolds number below 10,221. In addition, with the increase of the Reynolds number, the advantages of nanofluids in thermal performance become obvious, and Nusselt numbers increase by 28.5 and 30.6% with the effects of helical corrugation and ZnO–nanofluid, respectively, at Re = 14,349.

Experimental Investigation of Nanofluid Heat Transfer in a Plate Heat Exchanger

2012 ◽  
Author(s):  
Matthew Taws ◽  
Cong Tam Nguyen ◽  
Nicolas Galanis ◽  
Iulian Gherasim
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Hydraulic Characteristics ◽  
Transfer Enhancement ◽  
Cold Side ◽  
Particle Volume ◽  
Nusselt Numbers ◽  
Turbulent Transition ◽  
Corrugated Plates ◽  
Two Fluid

An experimental study was carried out to determine the forced convective heat transfer and hydraulic characteristics of a chevron-type two-channel industrial PHE when used with a nanofluid. The PHE is composed of two fluid passages formed by three corrugated plates, which have a herringbone pattern and the corrugations are of a trapezoidal shape. Heated water is used on the hot side. On the cold side a mixture of 29nm-diameter CuO nanoparticles in suspension in water is forced. Collected data for the nanofluid side covers two particle volume fractions, 2% and 4.65%, and the range of Reynolds number up to 1000. Results have shown that, for a given Reynolds number, CuO-water nanofluid clearly exhibits a higher friction factor compared to that of water. Calculated Nusselt numbers have shown no significant heat transfer enhancement when using the 2% nanofluid. A decrease of heat transfer was even observed with the 4.65% nanofluid. The laminar-turbulent transition was also observed for the nanofluids studied.

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