A Comparative Study of Heat Transfer Characteristics and Pressure Drop in Matrix Structures

2019 ◽  
Author(s):  
Anjana N. Prajapati ◽  
Andallib Tariq
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Local Heat Transfer ◽  
Local Heat ◽  
The Matrix ◽  
Channel Aspect Ratio ◽  
Comparative Results

Abstract An experimental study on local heat transfer distributions and pressure loss in the closed matrix channels with an angle 45° has been conducted using liquid crystal thermography for a Reynolds number (Re) range 5800–14000. A total of five different configurations of matrixes have been considered for investigation. The thermo-hydraulic performance of the matrix structure with angle 45° is initially compared with that of the matrixes with angles 35° and 55° for a constant sub-channel aspect ratio (ARs) 0.8. Later, the sub-channel aspect ratio of matrix with angle 45° has been varied as 0.4 and 1.2 and the comparative results are presented. While comparing the performance parameters of different angles for the sub-channel aspect ratio 0.8, it is found that for lower Reynolds numbers (Re ≤ 8100), the angle 45° offers highest augmentation Nusselt number. However, for Re > 8100, the angle 55° showed the highest augmentation Nusselt number. It has been also observed that the sub-channel aspect ratio 0.8 presents the highest augmentation Nusselt numbers as compared to ARs = 1.2 and 0.4 for Re ≤ 12400. Whereas, the friction factor fairly decreases with the increase in the sub-aspect ratio. A significant effect of angle has been found for friction factor as compared to sub-channel aspect ratio. The highest thermal performance factor (1.13) is obtained for the matrix with angle 45° and sub-channel aspect ratio 0.8 at Reynolds number 8100.

Heat Transfer and Friction Characteristics in Rectangular Channels With Rib Turbulators

1988 ◽  
Vol 110 (2) ◽  
pp. 321-328 ◽  
Author(s):  
J. C. Han
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Side Wall ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Published Data ◽  
Number Range ◽  
Rectangular Channels ◽  
Channel Aspect Ratio

The effect of the channel aspect ratio on the distribution of the local heat transfer coefficient in rectangular channels with two opposite ribbed walls (to simulate turbine airfoil cooling passages) was determined for a Reynolds number range of 10,000 to 60,000. The channel width-to-height ratios (W/H, ribs on side W) were 1/4, 1/2, 1, 2, and 4. The test channels were heated by passing current through thin, stainless steel foils instrumented with thermocouples. The local heat transfer coefficients on the ribbed side wall and on the smooth side wall of each test channel from the channel entrance to the fully developed regions were measured for two rib spacings (P/e = 10 and 20). The rib angle-of-attack was kept at 90 deg. The local data in the fully developed region were averaged and correlated, based on the heat transfer and friction similarity laws developed for ribbed channels, to cover the ranges of channel aspect ratio, rib spacing, rib height, and Reynolds number. The results compare well with the published data for flow in a square channel with two opposite ribbed walls. The correlations can be used in the design of turbine airfoil cooling passages.

Effect of Laminarization and Retransition on Heat Transfer for Low Reynolds Number Flow Through a Converging to Constant Area Duct

1982 ◽  
Vol 104 (2) ◽  
pp. 363-371 ◽  
Author(s):  
H. Tanaka ◽  
H. Kawamura ◽  
A. Tateno ◽  
S. Hatamiya
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Parallel Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Parallel Plates ◽  
Number Range ◽  
Reynolds Number Flow ◽  
Turbulent Air Flow

A fully developed turbulent air flow between two parallel plates with the spacing of 15 mm was accelerated through a linearly converging passage of 200 mm in length, from which it flowed into a parallel-plate channel again. A foil heater was fastened on one wall surface over the entire channel, and local heat-transfer coefficient distribution was measured over the channel Reynolds number range of 5000 to 14,000 and also the slope of the accelerating section between 2/200 mm/mm and 10/200 mm/mm. (The acceleration parameter K ranged between 1.4 × 10−6 and 2 × 10−5.) The Nusselt number at the outlet of the accelerating section was considerably lower than in the initial fully turbulent state, suggesting laminarization of the flow. The measured Nusselt number continued to decrease in the first part of the downstream parallel-plate section to a minimum and then began to increase sharply, suggesting reversion to turbulent flow. Heat transfer along the parallel-converging-parallel plate system was reproduced fairly satisfactorily by applying a k-kL model of turbulence.

scholarly journals Steady interaction of a turbulent plane jet with a rectangular heated cavity

2016 ◽  
Vol 20 (5) ◽  
pp. 1485-1498
Author(s):  
Farida Iachachene ◽  
Amina Mataoui ◽  
Yacine Halouane
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Structure ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Potential Core

Turbulent heat transfer between a confined jet flowing in a hot rectangular cavity is studied numerically by finite volume method using the k-w SST one point closure turbulence model. The location of the jet inside the cavity is chosen so that the flow is in the non-oscillation regime. The flow structure is described for different jet-to-bottom-wall distances. A parametrical study was conducted to identify the influence of the jet exit location and the Reynolds number on the heat transfer coefficient. The parameters of this study are: the jet exit Reynolds number (Re, 1560< Re <33333), the temperature difference between the cavity heated wall and the jet exit (DT=60?C) and the jet location inside the cavity (Lf, 2? Lf? 10 and Lh 2.5<Lh?10). The Nusselt number increased and attained its maximum value at the stagnation points and then decreased. The flow structure is found in good agreement with the available experimental data. The maximum local heat transfer between the cavity walls and the flow occurs at the potential core end. The ratio between the stagnation point Nusselt numbers of the cavity bottom (NuB0) to the maximum Nusselt number on the lateral cavity wall (NuLmax) decreased with the Reynolds number for all considered impinging distances. For a given lateral confinement, the stagnation Nusselt number of the asymmetrical interaction Lh?10 is almost equal to that of the symmetrical interaction Lh=10.

Shape Optimization of Partly Removed Straight Ribs in Turbine Internal Rectangular Cooling Channel With 45 Degree Ribs

2018 ◽  
Author(s):  
Jiangnan Zhu ◽  
Xiying Wang ◽  
Changxian Zhang ◽  
Hui Miao
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Friction Factor ◽  
Response Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Friction Loss ◽  
Cooling Channel ◽  
Number Ratio ◽  
Ansys Workbench

Angled ribs have been widely used in the rectangular internal cooling channel of gas turbine to enhance heat convection strength and the optimal rib parameters have been shown in the former investigations. However, the heat transfer strength of the wall near the terminal of angled ribs is less enhanced by the rib and the local Nusselt number ratio may be lower than 1, which means that the local heat transfer strength of the ribbed wall is lower than that of smooth wall. At the same time, the ribs also generate large friction loss. As a result, a part of ribs which provides little heat transfer enhancement effect are removed in order to both reduce friction loss and maintain or enhance local heat transfer strength. In order to find out the optimal geometry parameters of the removed part of the rib, the optimization study are conducted in this paper based on the ANSYS Workbench software. The channel width to height ratio is 1 and 4. The rib attack angle is 45 degrees. The length of removed part, the transverse location of the removed part and the angle between the flow direction and the incision edge are chosen as the design variables. The area-averaged Nusselt number ratio and temperature on the ribbed wall, the friction factor ratio of the channel and the thermal performance factor are chosen as the objectives. The samples are generated by Latin Hypercube Sampling method and the CFD calculation is conducted by ANSYS CFX module using SST turbulence model. The response surface is obtained by Kriging model based on the CFD results and the Pareto optimal solution of this multi-objective problem is conducted by Multi-Objective Genetic Algorithm (MOGA) in the Response Surface Optimization module of ANSYS Workbench. The results show that the removed part of rib could both maintain or slightly enhance the overall Nusselt number ratio and obviously reduce the friction factor at the same time. Furthermore, the Nusselt number ratio in the terminal region of original ribs is also largely enhanced.

Detailed Heat Transfer Characteristics of Matrix Cooling Channels With Rib Angle 35° Using Liquid Crystal Thermography

2019 ◽  
Author(s):  
Anjana N. Prajapati ◽  
Andallib Tariq
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Aspect Ratio ◽  
Friction Factor ◽  
Hydraulic Performance ◽  
Liquid Crystal Thermography ◽  
Aspect Ratios ◽  
Factor Ratio ◽  
Channel Aspect Ratio

Abstract Matrix cooling is relatively newer cooling technique and preferred over the conventional rib turbulators or pin fin cooling due to its capacity to provide the structural rigidity and higher heat transfer enhancement. The present investigation addresses the detailed study of local and averaged heat transfer augmentation distributions within the sub-channels of matrixes with rib angle 35° and varying sub-channels aspect ratios using liquid crystal thermography. The effects of varying sub-channel aspect ratios 1.2, 0.8 and 0.4 on averaged Nusselt number augmentation, friction factor ratio and thermo-hydraulic performance factor have been also verified within the Reynolds numbers range 5800–14000. The flow trend within the sub-channels is typically found to be eccentric and attributed to the possible vortical flow within the sub-channels and this eccentricity reduces as the sub-channel aspect ratio decreases. Results have shown that the highest Nusselt number augmentation and the lowest friction factor ratio are obtained for the highest sub-channel aspect ratio i.e., the best thermo-hydraulic performance factor (≥ 1) has been found for sub-channel aspect ratio 1.2. The sub-channel aspect ratio is found to have significant effect on both Nusselt number augmentation and friction factor ratio as compared to Reynolds number.

Heat Transfer Prediction of a Jet Impinging a Cylindrical Deadlock Area

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Yacine Halouane ◽  
Amina Mataoui ◽  
Farida Iachachene
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Flow Behavior ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Potential Core ◽  
Numerical Predictions

The turbulent heat transfer by a confined jet flowing inside a hot cylindrical cavity is investigated numerically in this paper. This configuration is found in several engineering applications such as air conditioning and the ventilation of mines, deadlock, or corridors. The parameters investigated in this work are the Reynolds number (Re, 20,000 ≤ Re ≤ 50,000) and the normalized distance Lf between jet exit and the cavity bottom (Lf, 2 ≤ Lf  ≤ 12). The numerical predictions are performed by finite volume method using the second order one-point closure turbulence model (RSM). The Nusselt number increases and attains maximum values at stagnation points, after it decreases. For an experimental test case available in the literature Lf = 8, the numerical predictions are in good agreement. Processes of heat transfer are analyzed from the flow behavior and the underlying mechanisms. The maximum local heat transfer between the cavity walls and the flow occurs at Lf = 6 corresponding to the length of the potential core. Nusselt number at the stagnation point is correlated versus Reynolds number Re and impinging distance Lf; [Nu0=f(Re,Lf)].

Local Heat Transfer in a Rotating Square Channel With Jet Impingement

1999 ◽  
Vol 121 (4) ◽  
pp. 811-818 ◽  
Author(s):  
S.-S. Hsieh ◽  
J.-T. Huang ◽  
C.-F. Liu
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Average Nusselt Number ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient

The influence of rotation and jet mass flow rate on the local heat transfer coefficient for a single confined impinging round jet with a fixed jet-to-wall spacing of H/d = 5 was studied for the jet Reynolds number from 6500 to 26,000 and the rotational Reynolds number from 0 to 112,000. The local heat transfer coefficient along the surface is measured and the effect of the rotation on the stagnation (peak) point, local and average Nusselt number, is presented and discussed. Furthermore, a correlation was developed for the average Nusselt number in terms of the parameters of Rej and ReΩ. In general, the combined jet impingement and rotation effect are shown to affect the heat transfer response. Rotation decreases the average Nusselt number values from 15 to 25 percent in outward and inward radial flow, respectively. Finally, comparisons of the present data with existing results for multijets with rotation were also made.

Flow Structure and Heat Transfer During Free Liquid Jet Impingement on a Hemispherical Plate

2006 ◽  
Author(s):  
Muhammad M. Rahman ◽  
Cesar F. Hernandez ◽  
Jorge C. Lallave
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Jet ◽  
Fluid Interface ◽  
Solid Plate

The flow structure and convective heat transfer behavior of a free liquid jet impinging on a hemispherical solid plate of finite thickness have been examined using a numerical analysis. The simulation model included the entire fluid region (impinging jet and flow spreading out over the convex surface) and solid plate as a conjugate problem. Solution was done for both isothermal and constant heat flux boundary conditions at the inner surface of the hemispherical plate. Computations were done for jet Reynolds number (ReJ) ranging from 500 to 2000 and the dimensionless nozzle to target spacing ratio (β) from 0.75 to 3. Results are presented for local heat transfer coefficient and the local Nusselt number using the following working fluids: water (H2O), flouroinert (FC-77), and oil (MIL-7808) and for various solid materials namely aluminum, Constantan, copper, silicon, and silver. It was observed that plate materials with higher thermal conductivity maintained a more uniform temperature distribution at the solid-fluid interface. A higher Reynolds number increased the Nusselt number and local heat transfer coefficient distributions over the entire solid-fluid interface.

scholarly journals Experimental investigation of flow and heat transfer characteristics on matrix ribbed channel

2020 ◽  
Vol 24 (3 Part A) ◽  
pp. 1593-1600
Author(s):  
Bo Zhang ◽  
Quan Hong ◽  
Yuanyuan Dou ◽  
Honghu Ji ◽  
Rui Chen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Turbine Blades ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Channel Height ◽  
Height Ratio ◽  
Ribbed Channel ◽  
The Matrix

The effect of the rib width to height ratio t/e and width to pitch ratio t/p on the local heat transfer distribution in a rectangular matrix ribbed channel with two opposite in line 45? ribs are experimentally investigated for Reynolds numbers from 54000 to 150000. The rib height to channel height ratio e/H is 0.5, t/p and t/e both varies in range of 0.3-0.5. To simulate the actually situation in turbine blades, and provide useful direct results for turbine blade designers, the parameters are same with the blade. The experiments results show that, in comparison to fully developed flow in a smooth pipe of equivalent hydraulic diameter, the Nusselt number inside the matrix-ribbed rectangular channel is increased up to 5 to 9 times higher, while total pressure drop is enlarged by up to significant magnitude. The Nusselt number ratio increases with t/p and t/e increased. Semi-empirical heat transfer is developed for designing of cooling channel.

Local Heat Transfer Distribution in a Rotating Serpentine Rib-Roughened Flow Passage

1993 ◽  
Vol 115 (3) ◽  
pp. 560-567 ◽  
Author(s):  
N. Zhang ◽  
J. Chiou ◽  
S. Fann ◽  
W.-J. Yang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Performance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Performance ◽  
Height Ratio ◽  
Nusselt Numbers ◽  
Rayleigh Numbers ◽  
Rib Roughened

Experiments are performed to determine the local heat transfer performance in a rotating serpentine passage with rib-roughened surfaces. The ribs are placed on the trailing and leading walls in a corresponding posited arrangement with an angle of attack of 90 deg. The rib height-to-hydraulic diameter ratio, e/Dh, is 0.0787 and the rib pitch-to-height ratio, s/e, is 11. The throughflow Reynolds number is varied, typically at 23,000, 47,000, and 70,000 in the passage both at rest and in rotation. In the rotation cases, the rotation number is varied from 0.023 to 0.0594. Results for the rib-roughened serpentine passages are compared with those of smooth ones in the literature. Comparison is also made on results for the rib-roughened passages between the stationary and rotating cases. It is disclosed that a significant enhancement is achieved in the heat transfer in both the stationary and rotating cases resulting from an installation of the ribs. Both the rotation and Rayleigh numbers play important roles in the heat transfer performance on both the trailing and leading walls. Although the Reynolds number strongly influences the Nusselt numbers in the rib-roughened passage of both the stationary and rotating cases, Nuo and Nu, respectively, it has little effect on their ratio Nu/Nuo.

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