The Structural Optimization of Dimple in Microchannel for Heat Transfer Enhancement

2020 ◽  
Author(s):  
Xiuping Chen ◽  
Jiabing Wang ◽  
Kun Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Flow Direction ◽  
Turbine Blades ◽  
Transfer Enhancement ◽  
Factors Affecting ◽  
Transfer Unit ◽  
Comprehensive Performance ◽  
The Impact

Abstract Dimple on the surface is widely used in electronic cooling equipment, turbine blades, and combustion chamber gaskets and so on, which is a good structure for heat transfer enhancement. In this paper, taking comprehensive performance parameters of flow and heat transfer PEC as an evaluation parameter, numerical simulation and multi-island genetic algorithm are combined to optimize the shape of the dimple in microchannel under fully developed laminar condition. The results show that the optimal dimple is asymmetric along the flow direction, and the deepest position of which shifts downstream, which is dependent on the Reynolds number, the dimple diameter, and the periodic length. With the increase of the Reynolds number and the dimple diameter, the Nusselt number ratio, the Fanning fraction factor ratio, and the comprehensive performance parameter PEC increase for the optimal dimple. The separation of the fluid in the front edge of dimple is not conducive to heat transfer. The number and size of the vortex, the impact and the reattachment are found to be the key factors affecting the heat transfer in the dimple. As the periodic length L of the heat transfer unit decreases, the heat transfer is enhanced and the flow resistance increases, and the comprehensive performance of the microchannel becomes better.

scholarly journals Heat Transfer and Pressure Loss Measurements of Matrix Cooling Geometries for Gas Turbine Airfoils

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Carlo Carcasci ◽  
Bruno Facchini ◽  
Marco Pievaroli ◽  
Lorenzo Tarchi ◽  
Alberto Ceccherini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Flow Direction ◽  
Western World ◽  
Open Area ◽  
Transfer Enhancement ◽  
Test Models

Matrix cooling systems are relatively unknown among gas turbines manufacturers of the western world. In comparison to conventional turbulated serpentines or pin–fin geometries, a lattice–matrix structure can potentially provide higher heat transfer enhancement levels with similar overall pressure losses. This experimental investigation provides heat transfer distribution and pressure drop of four different lattice–matrix geometries with crossing angle of 45 deg between ribs. The four geometries are characterized by two different values of rib height, which span from a possible application in the midchord region up to the trailing edge region of a gas turbine airfoil. For each rib height, two different configurations have been studied: one having four entry channels and lower rib thickness (open area 84.5%), one having six entry channels and higher rib thickness (open area 53.5%). Experiments were performed varying the Reynolds number Res, based on the inlet subchannel hydraulic diameter, from 2000 to 12,000. Heat transfer coefficients (HTCs) were measured using steady state tests and applying a regional average method; test models have been divided into 20 stainless steel elements in order to have a Biot number similitude with real conditions. Elements are 10 per side, five in the main flow direction, and two in the tangential one. Metal temperature was measured with embedded thermocouples, and 20 thin-foil heaters were used to provide a constant heat flux during each test. A specific data reduction procedure has been developed so as to take into account the fin effectiveness and the increased heat transfer surface area provided by the ribs. Pressure drops were also evaluated measuring pressure along the test models. Uniform streamwise distributions of Nusselt number Nus have been obtained for each Reynolds number. Measurements show that the heat transfer enhancement level Nus/Nu0 decreases with Reynolds but is always higher than 2. Results have been compared with previous literature data on similar geometries and show a good agreement.

scholarly journals Heat Transfer and Pressure Loss Measurements of Matrix Cooling Geometries for Gas Turbine Airfoils

2014 ◽  
Author(s):  
Carlo Carcasci ◽  
Bruno Facchini ◽  
Marco Pievaroli ◽  
Lorenzo Tarchi ◽  
Alberto Ceccherini ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Flow Direction ◽  
Western World ◽  
Open Area ◽  
Transfer Enhancement ◽  
Test Models

Matrix cooling systems are relatively unknown among gas turbines manufacturers of the western world. In comparison to conventional turbulated serpentines or pin-fin geometries, a lattice-matrix structure can potentially provide higher heat transfer enhancement levels with similar overall pressure losses. This experimental investigation provides heat transfer distribution and pressure drop of four different lattice-matrix geometries with crossing angle of 45 deg between ribs. The four geometries are characterized by two different values of rib height which span from a possible application in the mid chord region up to the trailing edge region of a gas turbine airfoil. For each rib height two different configurations have been studied: one having four entry channels and lower rib thickness (open area 84.5%), one having six entry channels and higher rib thickness (open area 53.5%). Experiments were performed varying the Reynolds number Res, based on the inlet sub-channel hydraulic diameter, from 2000 to 12000. Heat transfer coefficients were measured using steady state tests and applying a regional average method; test models have been divided into 20 stainless steel elements in order to have a Biot number similitude with real conditions. Elements are 10 per side, 5 in the main flow direction and 2 in the tangential one. Metal temperature was measured with embedded thermocouples and 20 thin-foil heaters were used to provide a constant heat flux during each test. A specific data reduction procedure has been developed so as to take into account the fin effectiveness and the increased heat transfer surface area provided by the ribs. Pressure drops were also evaluated measuring pressure along the test models. Uniform streamwise distributions of Nusselt number Nus have been obtained for each Reynolds number. Measurements show that the heat transfer enhancement level Nus/Nu0 decreases with Reynolds but is always higher than 2. Results have been compared with previous literature data on similar geometries and show a good agreement.

scholarly journals Efficiency Improvement of Miniaturized Heat Exchangers

Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 25
Author(s):  
Iris Gerken ◽  
Thomas Wetzel ◽  
Jürgen J. Brandner
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Exchangers ◽  
Assessment Method ◽  
Flow Path ◽  
Transfer Enhancement ◽  
Pressure Losses ◽  
Pin Fin ◽  
Additional Pressure ◽  
The Impact

Micro heat exchangers have been revealed to be efficient devices for improved heat transfer due to short heat transfer distances and increased surface-to-volume ratios. Further augmentation of the heat transfer behaviour within microstructured devices can be achieved with heat transfer enhancement techniques, and more precisely for this study, with passive enhancement techniques. Pin fin geometries influence the flow path and, therefore, were chosen as the option for further improvement of the heat transfer performance. The augmentation of heat transfer with micro heat exchangers was performed with the consideration of an improved heat transfer behaviour, and with additional pressure losses due to the change of flow path (pin fin geometries). To capture the impact of the heat transfer, as well as the impact of additional pressure losses, an assessment method should be considered. The overall exergy loss method can be applied to micro heat exchangers, and serves as a simple assessment for characterization. Experimental investigations with micro heat exchanger structures were performed to evaluate the assessment method and its importance. The heat transfer enhancement was experimentally investigated with microstructured pin fin geometries to understand the impact on pressure loss behaviour with air.

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

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.

scholarly journals Review on Heat Transfer Enhancement by Louvered Fin

2021 ◽  
Vol 6 (1) ◽  
pp. 60-80
Author(s):  
Samsul Islam ◽  
Md. Shariful Islam ◽  
Mohammad Zoynal Abedin
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Vortex Generator ◽  
Transfer Enhancement ◽  
Maximum Heat ◽  
Louvered Fin ◽  
Heat Transfer Improvement ◽  
Better Than

The heat transfer enhancement is recycled in many engineering uses such as heat exchangers, refrigeration and air conditioning structures, chemical apparatuses, and automobile radiators. Hence many enhancing extended fin patterns are developed and used. In multi louvered fin, in this segment for multi-row fin and tube heat exchanger, an increase in heat transfer enhancement is found 58% for ReH = 350. When the Reynolds number is 1075, the temperature gradient is more distinct for greater louver angle that is the higher heat transfer enhanced for large louver angle. For variable louver angle heat exchanger, the maximum heat transfer improvement achieved by 118% Reynolds number at 1075. In the vortex generator for the delta winglet vortex generator, the extreme enhancement of heat transfer increased to 16% compared to the baseline geometry (at ReDh = 600). For a compact louvered heat exchanger, the results showed that a regular arrangement of louvered fins gives a 9.3% heat transfer improvement. In multi-region louver fins and flat tubes heat exchanger, the louver fin with 4 regions and the louver fin with 6 regions are far better than the conventional fin in overall performance. At the same time, the louver fin with 6 regions is also better than the louver fin with 4-region. The available work is in experimental form as well as numerical form performed by computational fluid dynamics.

Falling Film Evaporation of Water on Horizontal Configured Tube Bundles

2010 ◽  
Author(s):  
Wei Li ◽  
Xiaoyu Wu ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Inlet Temperature ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Film Evaporation ◽  
Tube Bundles ◽  
Falling Film Evaporation

This paper reports an experimental study on falling film evaporation of water on 6-row horizontal configured tube bundles in a vacuum. Three types of configured tubes, Turbo-CAB-19fpi and −26fpi, Korodense, including smooth tubes for reference, were tested in a range of film Reynolds number from about 10 to 110. Results show that as the falling film Reynolds number increases, falling film evaporation goes from tubes partial dryout regime to fully wet regime; the mean heat transfer coefficients reach peak values in the transition point. Turbo-CAB tubes have the best heat transfer enhancement of falling film evaporation in both regimes, but Korodense tubes’ overall performances are better when tubes are fully wet. The inlet temperature of heating water has hardly any effects on the heat transfer, but the evaporation pressure has controversial effects. A correlation with errors within 10% was also developed to predict the heat transfer enhancement capacity.

Full Surface Heat Transfer Measurement of a Turbine Internal Cooling System Using a Large Scaled Model

2018 ◽  
Author(s):  
Nojin Park ◽  
Changmin Son ◽  
Jangsik Yang ◽  
Changyong Lee ◽  
Kidon Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Cooling System ◽  
Surface Heat ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Scaled Model ◽  
Surface Heat Transfer

A series of experiments were conducted to investigate the detailed heat transfer characteristics of a large scaled model of a turbine blade internal cooling system. The cooling system has one passage in the leading edge and a triple passage for the remained region with two U-bends. A large scaled model (2 times) is designed to acquire high resolution measurement. The similarity of the test model was conducted with Reynolds number at the inlet of the internal cooling system. The model is designed to simulate the flow at engine condition including film extractions to match the changes in flowrates through the internal cooling system. Also, 45 deg ribs were installed for heat transfer enhancement. The experiments were performed varying Reynolds number in the range of 20,000 to 100,000 with and without ribs under stationary condition. This study employs transient heat transfer technique using thermochromic liquid crystal (TLC) to obtain full surface heat transfer distributions. The results show the detailed heat transfer distributions and pressure loss. The characteristics of pressure loss is largely dependent on the changes in cross-sectional area along the passages, the presence of U-bends and the extraction of coolant flow through film holes. The local and area averaged Nusselt number were compared to available correlations. Finally, the thermal performance counting the heat transfer enhancement as well as pressure penalty is presented.

Sign in / Sign up

Export Citation Format

Share Document