scholarly journals Heat Transfer Enhancement by Detached S-Ribs for Twin-Pass Parallelogram Channel

Inventions ◽  
2018 ◽  
Vol 3 (3) ◽  
pp. 50 ◽  
Author(s):  
Shyy Chang ◽  
Wei-Ling Cai ◽  
Ruei-Jhe Wu
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Reynolds Numbers ◽  
Test Channel ◽  
Pressure Drops ◽  
Transfer Rates ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Measured Pressure

Detached S-ribs are proposed to arrange in the stagger manner along two parallelogram straight channels interconnecting with a 180° smooth-walled sharp bend for heat transfer enhancements. The detailed Nusselt number distributions over the two opposite channel endwalls at Reynolds numbers of 5000, 7500, 10,000, 12,500, 15,000 and 20,000 are measured using the steady-state infrared thermography method. The accompanying Fanning friction factors are evaluated from the measured pressure drops across the entire test channel. Having acquired the averaged heat transfer properties and Fanning friction factors, the thermal performance factors are determined under the criterion of constant pumping power consumptions. With the regional accelerated flows between the detached S-ribs and the channel endwall, the considerable heat transfer elevations from the Dittus–Boelter correlation levels are achieved. The comparative thermal performances between the two similar twin-pass parallelogram channels with detached 90° and S-ribs disclose the higher regional heat transfer rates over the turning region and the larger Fanning frictions factors, leading to the lower thermal performance factors, for present test channel with the detached S-ribs. To assist design applications, two sets of empirical correlations evaluating the regionally averaged Nusselt numbers and Fanning friction factors are devised for present twin-pass parallelogram channel with the detached S-ribs.

Latticework (Vortex) Cooling Effectiveness: Part 2 — Rotating Channel Experiments

2004 ◽  
Author(s):  
S. Acharya ◽  
Fuguo Zhou ◽  
Jonathan Lagrone ◽  
Gazi Mahmood ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators ◽  
Density Ratios

The heat transfer and pressure drop characteristics of latticework coolant blade passages have been investigated experimentally under conditions of rotation. Stationary studies with the latticework configuration have shown potential advantages including spatially-uniform streamwise distributions of the heat transfer coefficient, greater blade strength, and enhancement levels comparable to conventional rib turbulators. In the present study, a latticework coolant passage, with orthogonal-ribs, is studied in a rotating heat transfer test-rig for a range of Reynolds numbers (Res), Rotation numbers (Ros), and density ratios. Measurements indicate that for Res≥20,000, the latticework coolant passage provides very uniform streamwise distributions of the Nusselt number (Nus) with enhancement levels (relative to smooth-channel values) in the range of 2.0 to 2.5. No significant dependence of Nus on Ros and density ratio is observed except at lower Res values (≤10,000). Nusselt numbers are highest immediately downstream of a turn indicating that bend-effects play a major role in enhancing heat transfer. Friction factors are relatively insensitive to Ros, and thermal performance factors at higher Res values appear to be comparable to those obtained with conventional rib-turbulators. The present study indicates that latticework cooling geometry can provide comparable heat transfer enhancements and thermal performance factors as conventional rib-turbulators, with potential benefits of streamwise uniformity in the heat transfer coefficients and added blade strength.

Latticework (Vortex) Cooling Effectiveness: Rotating Channel Experiments

2004 ◽  
Vol 127 (3) ◽  
pp. 471-478 ◽  
Author(s):  
S. Acharya ◽  
F. Zhou ◽  
J. Lagrone ◽  
G. Mahmood ◽  
R. S. Bunker
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators ◽  
Density Ratios

The heat transfer and pressure drop characteristics of latticework coolant blade passages have been investigated experimentally under conditions of rotation. Stationary studies with the latticework configuration have shown potential advantages including spatially-uniform streamwise distributions of the heat transfer coefficient, greater blade strength, and enhancement levels comparable to conventional rib turbulators. In the present study, a latticework coolant passage, with orthogonal-ribs, is studied in a rotating heat transfer test-rig for a range of Reynolds numbers (Res), Rotation numbers (Ros), and density ratios. Measurements indicate that for Res⩾20,000, the latticework coolant passage provides very uniform streamwise distributions of the Nusselt number (Nus) with enhancement levels (relative to smooth-channel values) in the range of 2.0–2.5. No significant dependence of Nus on Ros and density ratio is observed except at lower Res values (⩽10,000). Nusselt numbers are highest immediately downstream of a turn indicating that bend-effects play a major role in enhancing heat transfer. Friction factors are relatively insensitive to Ros, and thermal performance factors at higher Res values appear to be comparable to those obtained with conventional rib-turbulators. The present study indicates that latticework cooling geometry can provide comparable heat transfer enhancements and thermal performance factors as conventional rib-turbulators, with potential benefits of streamwise uniformity in the heat transfer coefficients and added blade strength.

scholarly journals Investigation of Thermal-Flow Characteristics of Pipes with Helical Micro-Fins of Variable Height

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2048
Author(s):  
Piotr Bogusław Jasiński ◽  
Michał Jan Kowalczyk ◽  
Artur Romaniak ◽  
Bartosz Warwas ◽  
Damian Obidowski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Evaluation Criteria ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Working Fluid ◽  
Pressure Drops ◽  
Nusselt Numbers ◽  
Heat Transfer Efficiency ◽  
Friction Factors ◽  
Regular Roughness

The results of numerical investigations of heat transfer and pressure drops in a channel with 30° helical micro-fins are presented. The main aim of the analysis is to examine the influence of the height of the micro-fins on the heat-flow characteristics of the channel. For the tested pipe with a diameter of 12 mm, the micro-fin height varies within the range of 0.05–0.40 mm (with 0.05 mm steps), which is equal to 0.4–3.3% of its diameter. The analysis was performed for a turbulent flow, within the range of Reynolds numbers 10,000–100,000. The working fluid is water with an average temperature of 298 K. For each tested geometry, the characteristics of the friction factor f(Re) and the Nusselt number Nu(Re) are shown in the graphs. The highest values of Nusselt numbers and friction factors were obtained for pipes with the micro-fins H = 0.30 mm and H = 0.35 mm. A large discrepancy is observed in the friction factors f(Re) calculated from the theoretical relationships (for the irregular relative roughness values shown in the Moody diagram) and those obtained from the simulations (for pipes with regular roughness formed by micro-fins). The PEC (Performance Evaluation Criteria) heat transfer efficiency analysis of the geometries under study is also presented, taking into account the criterion of the same pumping power. The highest PEC values, reaching 1.25, are obtained for micro-fins with a height of 0.30 mm and 0.35 mm and with Reynolds numbers above 40,000. In general, for all tested geometries and for large Reynolds numbers (above 20,000), the PEC coefficient reaches values greater than 1, while for lower Reynolds numbers (less than 20,000), its values are less than 1.

scholarly journals Execution of a Smart Prediction Tool to Evaluate Thermal Performance in a heat exchanger by using Single Elliptical Leaf Strips with altered Angle

2019 ◽  
Vol 8 (11) ◽  
pp. 123-131
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Industrial Applications ◽  
Generalized Regression Neural Network ◽  
Prediction Tool ◽  
Pressure Drops ◽  
Transfer Rates ◽  
Mass Flow Rates

Heat exchangers are prominent industrial applications where engineering science of heat transfer and Mass transfer occurs. It is a contrivance where transfer of energy occurs to get output in the form of energy transfer. This paper aims at finding a solution to improve the thermal performance in a heat exchanger by using passive method techniques. This experimental and numerical analysis deals with finding the temperature outlets of cold and hot fluid for different mass flow rates and also pressure drop in the tube and the annular side by adding an elliptical leaf strip in the pipe at various angles. The single elliptical leaf used in experiment has major to minor axes ratios as 2:1 and distance of 50 mm between two leaves are arranged at different angular orientations from 0 0 to 1800 with 100 intervals. Since it’s not possible to find the heat transfer rates and pressure drops at every orientation of elliptical leaf so a generalized regression neural network (GRNN) prediction tool is used to get outputs with given inputs to avoid experimentation. GRNN is a statistical method of determining the relationship between dependent and independent variables. The values obtained from experimentation and GRNN nearly had precise values to each other. This analysis is a small step in regard with encomiastic approach for enhancement in performance of heat exchangers

Influence of Short Helical Tape on Local Convective Heat Transfer and Thermal Performance Characteristics in Turbulent Decaying Swirl Flow

2010 ◽  
Vol 8 (1) ◽  
Author(s):  
Smith Eiamsa-ard ◽  
Vichan Kongkaitpaiboon ◽  
Khwanchit Wongcharee
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Swirl Flow ◽  
Transfer Rates ◽  
Friction Factors ◽  
Plain Tube ◽  
Uniform Wall ◽  
Uniform Wall Heat Flux

This paper reports the experimental investigation of local convective heat transfer enhancement, flow friction and thermal performance factor behaviors in the tube fitted with the short helical tapes (SHTs) acting as decaying swirl flow generators. The tapes with three different helical tape angles (? = 90°, 135° and 180°) and three different channel numbers (N = 2, 3 and 4 channels) were tested under the uniform wall heat flux condition. The performance of each tape is compared with the performance of the plain tube subject to the same pumping power. The experimental results show that the heat transfer rates and friction factors of the tube with SHTs are respectively in range of 1.15 to 1.9 and 1.49 to 2.31 times of those in the plain, corresponding to thermal performances between 0.98 and 1.46. The correlations for Nusselt number (Nu) as a function of Reynolds number (Re), Prandtl number (Pr), helical tape angle (?) and the number of channel (N) are also developed.

Heat Transfer Enhancement Using a Convex-Patterned Surface

2003 ◽  
Vol 125 (2) ◽  
pp. 274-280 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
R. Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Patterned Surface ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer rate from a smooth wall in an internal cooling passage can be significantly enhanced by using a convex patterned surface on the opposite wall of the passage. This design is particularly effective for a design that requires the heat transfer surface to be free of any augmenting features (smooth). Heat transfer coefficients on the smooth wall in a rectangular channel, which had convexities on the opposite wall were experimentally investigated. Friction factors were also measured to assess the thermal performance. Relative clearances δ/d between the convexities and the smooth wall of 0, 0.024, and 0.055 were investigated in a Reynolds number ReHD range from 15,000 to 35,000. The heat transfer coefficients were measured in the thermally developed region using a transient thermochromic liquid crystal technique. The clearance gap between the convexities and the smooth wall adversely affected the heat transfer enhancement NuHD. The friction factors (f ), measured in the aerodynamically developed region, were largest for the cases of no clearance δ/d=0). The average heat transfer enhancement Nu¯HD was also largest for the cases of no clearance δ/d=0, as high as 3.08 times at a Reynolds number of 11,456 in relative to that Nuo of an entirely smooth channel. The normalized Nusselt numbers Nu¯HD/Nuo, as well as the normalized friction factors f/fo, for all three cases, decreased with Reynolds numbers. However, the decay rate of the friction factor ratios f/fo with Reynolds numbers was lower than that of the normalized Nusselt numbers. For all three cases investigated, the thermal performance Nu¯HD/Nuo/f/fo1/3 values were within 5% to each other. The heat transfer enhancement using a convex patterned surface was thermally more effective at a relative low Reynolds numbers (less than 20,000 for δ/d=0) than that of a smooth channel.

Measurement and Analysis of Laminar Heat Transfer Coefficients in Micro and Mini-Scale Ducts and Channels

2014 ◽  
Author(s):  
Y. S. Muzychka ◽  
M. Ghobadi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Reynolds Numbers ◽  
Transfer Coefficients ◽  
Constant Wall Temperature ◽  
Fully Developed Flow ◽  
Transfer Rates ◽  
Heat Transfer Coefficients ◽  
Advantages And Disadvantages ◽  
Nusselt Numbers

Heat transfer in micro and mini-scale ducts and channels is considered. In particular, issues of thermal performance are considered in systems with constant wall temperature at low to moderate Reynolds numbers or small dimensional scales which lead to conditions characteristic of thermally fully developed flows or within the transition region leading to thermally fully developed flows. An analysis of two approaches to representing experimental data is given. One using the traditional Nusselt number and another using the dimensionless mean wall flux. Both approaches offer a number of advantages and disadvantages. In particular, it is shown that while good data can be obtained which agree with predicted heat transfer rates, the same data can be problematic if one desires a Nusselt number. Other issues such as boundary conditions pertaining to measuring thermally developing and fully developed flow Nusselt numbers are also discussed in detail.

Detailed Heat Transfer Distributions and Pressure Drop Measurements for a Rotating Parallelogram Channel With Radially Outward Flow

2011 ◽  
Author(s):  
S. W. Chang ◽  
T.-M. Liou ◽  
T.-H. Lee
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Test Channel ◽  
Transfer Data ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Test Conditions ◽  
Present Test ◽  
First Time ◽  
Rotating Channel

This experimental study examines the pressure drop coefficients (f) and the detailed Nusselt numbers (Nu) distributions over two opposite leading and trailing walls roughened by 45° ribs for a rotating parallelogram channel with radially outward flow. For the first time the isolated effects of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers on local and area averaged Nusselt numbers (Nu and Nu) measured from the infrared thermography method were successfully examined at the parametric conditions of 5000≤Re≤15000, 0≤Ro≤0.3 and 0.001≤Bu≤0.23 for the single-pass parallelogram channel. A set of selected heat transfer data illustrates the Coriolis and rotating-buoyancy effects on the detailed Nu distributions and the area-averaged heat transfer performances of the rotating parallelogram channel. With the consideration of the f data generated at the isothermal conditions, the thermal performance factors (η) for this radially rotating channel were evaluated. The Nusselt numbers obtained from the leading and trailing walls of the rotating test channel fall in the respective ranges of 0.78–1.34 and 1.09–1.38 times of the stationary levels; while the η factors are in the range of 0.979–1.575 for the present test conditions.

Experimental and Numerical Investigation of Flow and Heat Transfer in Stationary Two-Pass Rectangular Duct (AR = 1:2) with Continuous and Broken V- shaped ribs

2021 ◽  
pp. 1-37
Author(s):  
Ramesh Erelli ◽  
Arun Saha
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Heated Surface ◽  
Reynolds Analogy ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Performance Factor ◽  
Thermal Performance Factor ◽  
Friction Factors ◽  
Local Temperature Distribution

Abstract The combined experimental and Large Eddy Simulations (LES) were performed in the stationary two-pass duct of aspect ratio (AR) 1:2. The experiments were conducted with three different rib arrangements, namely 60° V, 60° V-IV, and broken 60° V-IV ribs, and analysis was carried out with Reynolds numbers of 45,000, 60,000, and 75,000. The infrared thermography (IRT) technique is employed to obtain the local temperature distribution on heated smooth and ribbed surfaces. In all ribbed cases, the copper ribs are glued to the heated surface with a fixed rib height-to-hydraulic diameter (e / Dh) ratio is 0.125 and the rib pitch-to-height ratio (P / e) is 10 and 5 for continuous and broken ribs, respectively. In addition, LES turbulence model was adopted for carrying out simulation to understand the flow and heat transfer behavior in ducts populated with all three V-shaped ribs. The comparison of the time-averaged thermal fields generated using computations has been made with experimentally measured Nusselt numbers, friction factors, thermal performance factor (TPF), and Reynolds analogy performance parameter (RAPP) for all cases. The overall thermal performance factor was found to be quantitatively within 8.0 - 10.66% between experimental and numerical results. Among all the cases, the 60° V-IV ribbed duct provides the best TPF and RAPP than the other two ribbed ducts, whereas the smooth duct shows poor TPF.

Influence of Crossflow-Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

2000 ◽  
Vol 122 (3) ◽  
pp. 587-597 ◽  
Author(s):  
S. V. Ekkad ◽  
G. Pamula ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Feed System ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique ◽  
Measured Pressure

Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The impingement and passage crossflow are generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180-deg U-bend. The holes direct the flow laterally from one passage to another and generate different secondary flow patterns in the second pass. These secondary flows produce impingement and swirl and lead to higher heat transfer enhancement. Three different lateral hole configurations are tested for three Reynolds numbers (Re=10,000, 25,000, 50,000). The configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is used to measure the detailed heat transfer coefficient distributions inside the passages. Results with the new crossflow feed system are compared with the results from the traditional 180-deg turn passage. Results show that the crossflow feed configurations produce significantly higher Nusselt numbers on the second pass walls without affecting the first pass heat transfer levels. The heat transfer enhancement is as high as seven to eight times greater than obtained in the second pass for a channel with a 180-deg turn. The increased measured pressure drop (rise in friction factor) caused by flow through the crossflow holes are compensated by the significant heat transfer enhancement obtained by the new configuration. [S0022-1481(00)03103-0]

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