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.

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.

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.

scholarly journals Overview of the innovative heat exchangers technologies

2020 ◽  
Vol XXIII (2) ◽  
pp. 32-36
Author(s):  
Avram Elena Rita
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Exchangers ◽  
Micro Channels ◽  
Flow Processes ◽  
Military Applications ◽  
Flow Through ◽  
Heat And Fluid Flow ◽  
Resistance To Heat ◽  
Similitude Theory

The current paper analyzed the new trends and challenges in heat exchanger technologies. The progress of the studies on mini and micro devices used in industry are presented. Particular attention is paid to the heat exchangers used in marine and chemical industries where the resistance to heat transfer increases due to the fouling or scaling. In the industry, there are very important the reduction in the size of devices, and the micro heat exchangers, due to its variety of advantages offered, are well recognized for their higher performance. The applications of them are ranging from process control to military applications. New engineering approaches for modeling the heat and fluid flow processes in micro heat exchangers are analyzed in the present paper. One of these is based on the dimensional analysis and principles of similitude theory that allow the modeling of microscale systems using a physical system at the mini scale. There are identified constant relationships between dimensions permitting the analysis of the fluid flow through micro channels.

scholarly journals Heat Transfer Enhancement by Perforated and Louvred Fin Heat Exchangers

Energies ◽  
2022 ◽  
Vol 15 (2) ◽  
pp. 400
Author(s):  
Miftah Altwieb ◽  
Rakesh Mishra ◽  
Aliyu M. Aliyu ◽  
Krzysztof J. Kubiak
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Flow Rates ◽  
Pressure Drops ◽  
Fin Design

Multi-tube multi-fin heat exchangers are extensively used in various industries. In the current work, detailed experimental investigations were carried out to establish the flow/heat transfer characteristics in three distinct heat exchanger geometries. A novel perforated plain fin design was developed, and its performance was evaluated against standard plain and louvred fins designs. Experimental setups were designed, and the tests were carefully carried out which enabled quantification of the heat transfer and pressure drop characteristics. In the experiments the average velocity of air was varied in the range of 0.7 m/s to 4 m/s corresponding to Reynolds numbers of 600 to 2650. The water side flow rates in the tubes were kept at 0.12, 0.18, 0.24, 0.3, and 0.36 m3/h corresponding to Reynolds numbers between 6000 and 30,000. It was found that the louvred fins produced the highest heat transfer rate due to the availability of higher surface area, but it also produced the highest pressure drops. Conversely, while the new perforated design produced a slightly higher pressure drop than the plain fin design, it gave a higher value of heat transfer rate than the plain fin especially at the lower liquid flow rates. Specifically, the louvred fin gave consistently high pressure drops, up to 3 to 4 times more than the plain and perforated models at 4 m/s air flow, however, the heat transfer enhancement was only about 11% and 13% over the perforated and plain fin models, respectively. The mean heat transfer rate and pressure drops were used to calculate the Colburn and Fanning friction factors. Two novel semiempirical relationships were derived for the heat exchanger’s Fanning and Colburn factors as functions of the non-dimensional fin surface area and the Reynolds number. It was demonstrated that the Colburn and Fanning factors were predicted by the new correlations to within ±15% of the experiments.

Numerical investigation of fluid flow structure and heat transfer in a passage with continuous and truncated V-shaped ribs

2015 ◽  
Vol 25 (1) ◽  
pp. 171-189 ◽  
Author(s):  
Shian Li ◽  
Gongnan Xie ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose – The employment of continuous ribs in a passage involves a noticeable pressure drop penalty, while other studies have shown that truncated ribs may provide a potential to reduce the pressure drop while keeping a significant heat transfer enhancement. The purpose of this paper is to perform computer-aided simulations of turbulent flow and heat transfer of a rectangular cooling passage with continuous or truncated 45-deg V-shaped ribs on opposite walls. Design/methodology/approach – Computational fluid dynamics technique is used to study the fluid flow and heat transfer characteristics in a three-dimensional rectangular passage with continuous and truncated V-shaped ribs. Findings – The inlet Reynolds number, based on the hydraulic diameter, is ranged from 12,000 to 60,000 and a low-Re k-e model is selected for the turbulent computations. The local flow structure and heat transfer in the internal cooling passages are presented and the thermal performances of the ribbed passages are compared. It is found that the passage with truncated V-shaped ribs on opposite walls provides nearly equivalent heat transfer enhancement with a lower (about 17 percent at high Reynolds number of 60,000) pressure loss compared to a passage with continuous V-shaped ribs or continuous transversal ribs. Research limitations/implications – The fluid is incompressible with constant thermophysical properties and the flow is steady. The passage is stationary. Practical implications – New and additional data will be helpful in the design of ribbed passages to achieve a good thermal performance. Originality/value – The results imply that truncated V-shaped ribs are very effective in improving the thermal performance and thus are suggested to be applied in gas turbine blade internal cooling, especially at high velocity or Reynolds number.

Flow and Heat Transfer Enhancement of Nanofluids in Microchannel With Blocks and Grooves

2013 ◽  
Author(s):  
Ping Li ◽  
Jianhui Chen ◽  
Huancheng Qu ◽  
Yonghui Xie ◽  
Di Zhang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Heat Transfer Enhancement ◽  
Energy Transport ◽  
Recirculation Zone ◽  
Volume Concentration ◽  
Flow Analysis ◽  
Transfer Enhancement ◽  
Flow And Heat Transfer

A code based on the lattice-Boltzmann method was programmed. At various Reynolds numbers, simulations of the Cu/water nanofluid flow structure and heat transfer performance in a two dimensional microchannel with blocks (Re = 10–100) and grooves (Re = 50–200) were conducted, and the factors affecting the flow and heat transfer were explored. The flow and heat transfer of nanofluids with nanoparticle volume concentration of 0.5%, 1.0%, 1.5% and 2.0% were simulated, obtaining the velocity and temperature distributions to compare with the results of base fluid. Flow analysis showed that recirculation zones formed behind the blocks and in the grooves when nanofluids flowed in the microchannel, and the size of recirculation zone increased with the increase of Reynolds number and nanoparticle volume concentration. The core of the recirculation zone in the groove gradually moved to the right wall as Reynolds number increased at the same nanoparticle volume concentration, and the direction of the main flow was getting horizontal. Heat transfer results indicated that the addition of nanoparticles could promote fluid flow and energy transport, so that the thermal boundary layer thickness decreased and the heat transfer was enhanced. The heat transfer enhancement increased with the increase of Reynolds number and nanoparticle volume concentration. It was also shown that the heat transfer enhancement by increasing the Reynolds number was limited. The results could give a fundamental understanding for designing highly efficient heat exchangers.

Heat Transfer and Pressure Loss Measurements in a Turbulated High Aspect Ratio Channel With Large Reynolds Number Flows

2014 ◽  
Vol 6 (4) ◽  
Author(s):  
Shantanu Mhetras ◽  
Je-Chin Han ◽  
Michael Huth
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Steady State ◽  
Aspect Ratio ◽  
Compressible Flow ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Transfer Enhancement ◽  
High Reynolds ◽  
Wide Wall

Experiments to investigate heat transfer and pressure loss are performed in a rectangular channel with an aspect ratio of 6 at very high Reynolds numbers under compressible flow conditions. Reynolds numbers up to 1.3 × 106 are tested. The presence of a turbulated wall and the resultant heat transfer enhancement against a smooth surface is investigated. Three dimpled configurations including spherical and cylindrical dimples are studied on one wide wall of the channel. The presence of discrete ribs on the same wide wall is also investigated. A steady state heat transfer measurement method is used to obtain the heat transfer coefficients while pressure taps located at several streamwise locations in the channel walls are used to record the static pressures on the surface. Experiments are performed for a wide range of Reynolds numbers from the incompressible (Re = 100,000–500,000; Mach = 0.04–0.19) to compressible flow regimes (Re = 900,000–1,300,000, Mach = 0.35–0.5). Results for low Reynolds numbers are compared to existing heat transfer data available in open literature for similar configurations. Heat transfer enhancement is found to decrease at high Re with the discrete rib configurations providing the best enhancement but highest pressure losses. However, the small spherical dimples show the best thermal performance. Results can be used for the combustor liner back side cooling at high Reynolds number flow conditions. Local measurements using the steady state, hue-detection based liquid crystal technique are also performed in the fully developed region for case 1 with large spherical dimples. Good comparison is obtained between averaged local heat transfer coefficient measurements and from thermocouple measurements.

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.

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.

Investigations on Fluid Flow and Heat Transfer Performances Within a Real Turbine Blade Channel

2014 ◽  
Author(s):  
Zhaoqing Ke ◽  
Jian Pu ◽  
Jianhua Wang ◽  
Lei Wang ◽  
Zhiqiang Zhang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Secondary Flow ◽  
Reynolds Numbers ◽  
Numerical Investigations ◽  
Serpentine Channel ◽  
Flow And Heat Transfer ◽  
Working Medium

The characteristics of fluid flow and heat transfer within a smooth three-pass channel of a real low pressure (LP) turbine blade have been investigated through experimental and numerical approaches. The serpentine channel consists of two inlet passes, two dividing walls, two 180 degree bends, twenty-five exits at the trailing edge, and two exits at the blade tip. In the experiments, purified water was used as working medium, the secondary flow patterns at five cross-sections were captured by a particle image velocimetry (PIV) system, the inlet Reynolds number was controlled by a turbine flow meter, and the mass flow rate ejected from each exit was measured by rotameters. Using the commercial software ANSYS CFX 13.0, numerical investigations were carried out. The practicability of four turbulence models, the SSG RSM, SST k-ω, RNG k-ε and standard k-ε models, were estimated. Through qualitative and quantitative comparisons of the secondary flow patterns, local velocity variation trends and mass flow rates between the experimental data and numerical results, the SSG RSM was selected as the most appropriate model in the following numerical investigations. Using ideal gas as working medium, the impacts of Reynolds numbers and rotation numbers on the heat transfer performances were numerically investigated. The numerical results predicted three interesting phenomena: 1) The locally averaged Nusselt number increases generally with the inlet Reynolds numbers. However, the increasing amplitude is significantly different from the correlation suggested by Dittus-Boelter, Nuo = 0.023Re0.8Pr0.4. The effect of the Reynolds number on the Nusselt number is substantially enhanced due to the serpentine channel design with two 180 degree-bends. The enhancement amplitude is described by two fitted coefficients based on Dittus-Boelter correlation. 2) Under a rotation condition, in the 1st and 3rd passes, the enhancement amplitude of the average Nusselt number on the pressure side (PS) is more significant than that on the suction side (SS), whereas in the 2nd pass, the enhancement amplitude on the PS is lower than that on the SS. 3) In the 3rd pass, a higher rotation number leads to a more uniform distribution of the local Nusselt number along the streamwise direction on both the PS and SS.

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