scholarly journals Theory on the Heat Transfer Coefficient of a Sphere in a Uniform Stream at Low Reynolds Numbers

1950 ◽  
Vol 16 (54) ◽  
pp. 17-21
Author(s):  
Tatsuo YUGE
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
The Heat Transfer Coefficient ◽  
Uniform Stream

scholarly journals Experimental Study of Heat Transfer Enhancement through a Tube with Wire-Coil Inserts at Low Turbulent Reynolds Number

2018 ◽  
Vol 3 (3) ◽  
pp. 122-133
Author(s):  
Mohammad Zoynal Abedin ◽  
M. A. Rashid Sarkar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Test Section ◽  
Reynolds Numbers ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Low Reynolds Numbers ◽  
Wire Coil ◽  
Low Reynolds

This paper reports an experimental analysis to investigate the enhancement of turbulent heat transfer flow of air through one smooth tube and four different tubes with wire-coil inserts (Pitches, Pc = 12, 24, 40, and 50 mm with corresponding helix angles, a =100, 200, 350, and 450, respectively) at low Reynolds numbers ranging from 6000 to 22000. The test section of the tube was electrically heated and was cooled by fully developed turbulent air flow. The performance of the tubes was evaluated by considering the condition of maximizing heat transfer rate. From the measured data, the heat transfer characteristics such as heat transfer coefficient, effectiveness and Nusselt number, and the fluid flow behaviours such as friction factor, pressure drops and pumping power along the axial distance of the test section were analyzed at those Reynolds numbers for the tubes. The results indicated that for the tubes with wire-coil inserts at low Reynolds numbers, the turbulent heat transfer coefficient might be as much as two-folds higher, the friction factors could be as much as four-folds higher, and the effectiveness might be as much as 1.25 folds higher than those for the smooth tube with similar flow conditions. A correlation was also developed to predict the turbulent heat transfer coefficients through the tubes at low Reynolds numbers.

Effect of Pin Tip Dual Clearance on Flow and Heat Transfer at Low Reynolds Numbers

2014 ◽  
Vol 136 (7) ◽  
Author(s):  
Michael L. Seibert ◽  
Neal E. Blackwell ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat And Mass Transfer ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Microchannel Reactors ◽  
Pin Fins ◽  
The Heat Transfer Coefficient

This paper examines the augmentation of heat and mass transfer due to dual clearances on cylindrical pin fins, relative to a channel between parallel plates, in mini/microchannel reactors at low Reynolds numbers. In this work, diffusion limitations to heat and mass transfer in smooth-walled mini/microchannel reactors were minimized by the implementation of microcylinder pin fins with dual clearances that, (1) promote the production of instabilities in the wakes that enhance mixing and (2) reduce the viscosity dominated regions at pin-wall interfaces. A smooth catalyst coating is assumed on all exposed surfaces of the microchannel interior walls and pin fins. Due to the analogy of heat and mass transfer, augmentation of the Nusselt number is equivalent to the augmentation of the Sherwood number. Heat transfer augmentation is investigated in air (Pr = 0.705) at dual clearances ranging from 0 to 0.4 of the channel height and Reynolds numbers from 10 to 600. The pin fins and the clearance augmented the heat transfer coefficient by a factor of 4.0. The combination of the augmentation of the heat transfer coefficient and the increase in the surface area, by the clearances, results in an increase in the conductance over a plane channel, by a factor of 7.1. The results are extendable to overcoming laminar diffusion with laminar periodic wakes of fuel vapors such as methanol vapor in air where Scfuel ∼ Prair. For turbulent wakes impinging upon downstream pins, the results can be extended to fuel vapors with (Scfuel)turb ∼ (Prair)turb. A large eddy simulation (LES) approach was used in this study.

scholarly journals An Experimental Investigation of Heat Transfer Coefficients in a Spanwise Rotating Channel With Two Opposite Rib-Roughened Walls

1989 ◽  
Author(s):  
M. E. Taslim ◽  
A. Rahman ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient ◽  
Rotating Channel

Liquid crystals are used in this experimental investigation to measure the heat transfer coefficient in a spanwise rotating channel with two opposite rib-roughened walls. The ribs (also called turbulence promoters or turbulators) are configured in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90° for all cases. Results are presented for three values of turbulator blockage ratio, e/Dh (0.1333, 0.25, 0.333) and for a range of Reynolds numbers from 15,000 to 50,000 while the test section is rotated at different speeds to give Rotational Reynolds numbers between 450 and 1800. The Rossby number range is 10 to 100 (Rotation number of 0.1 to 0.01). The effect of turbulator blockage ratios on heat transfer enhancement is also investigated. Comparisons are made between the results of geometrically identical stationary and rotating passages of otherwise similar operating conditions. The results indicate that a significant enhancement in heat transfer is achieved in both the stationary and rotating cases, when the surfaces are roughened with turbulators. For the rotating case, a maximum increase over that of the stationary case of about 45% in the heat transfer coefficient is seen for a blockage ratio of 0.133 on the trailing surface in the direction of rotation and the minimum is a decrease of about 6% for a blockage ratio of 0.333 on the leading surface, for the range of rotation numbers tested. The technique of using liquid crystals to determine heat transfer coefficients in this investigation proved to be an effective and accurate method especially for nonstationary test sections.

Prediction of Heat Transfer and Friction for the Louver Fin Geometry

1992 ◽  
Vol 114 (4) ◽  
pp. 893-900 ◽  
Author(s):  
A. Sahnoun ◽  
R. L. Webb
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Friction Factor ◽  
Reynolds Numbers ◽  
Maximum Error ◽  
Transfer Coefficients ◽  
Mean Error ◽  
The Heat Transfer Coefficient

This paper is concerned with prediction of the air-side heat transfer coefficient of the louver fin geometry used in automotive radiators. An analytical model was developed to predict the heat transfer coefficient and friction factor of the louver fin geometry. The model is based on boundary layer and channel flow equations, and accounts for the “flow efficiency” in the array, as previously reported by Webb and Trauger. The model has no empirical constants. The model allows independent specifications of all of the geometric parameters of the louver fin. This includes the number of louvers over the flow depth, the louver width and length, and the louver angle. The model was validated by predicting the heat transfer coefficient and friction factor of 32 louver arrays tested by Davenport, which spanned hydraulic diameter based Reynolds numbers of 300–2800. At the highest Reynolds number, all of the heat transfer coefficients were predicted within a maximum error of −14 / + 25 percent, and a mean error of ± 8 percent. The high Reynolds number friction factors were predicted with a maximum error −22 /+ 26 percent, with a mean error of ± 8 percent. The error ratios were slightly higher at the lowest Reynolds numbers.

Forced Convective Heat Transfer From Helicoidal Pipes

2001 ◽  
Author(s):  
Ahmad Fakheri ◽  
Abdelrahman H. A. Alnaeim
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Characteristic Length ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Operating Conditions ◽  
Straight Pipe ◽  
Wide Range ◽  
The Heat Transfer Coefficient

Abstract Forced convection heat transfer from helicoidal pipes is experimentally investigated over a wide range of operating conditions. Based on the experimental results, a characteristic length incorporating the tube diameter, the coil diameter, and the coil spacing, is proposed as the relevant scale for defining Nusselt and Reynolds numbers. Based on this characteristic length, Nusselt number for helicoidal pipes can be predicated from the correlations available for cylinders in the range of available experimental data. It is shown that the performance of the coils depends on the Reynolds number. At high Reynolds numbers, the heat transfer coefficient is essentially equal to that of the straight pipe and the coil pitch has little influence on the heat transfer rate. On the other hand, at low Reynolds numbers, the heat transfer coefficient is lower than that of a straight pipe and its value is a strong function of the coil spacing.

AN EXPERIMENTAL INVESTIGATION OF THE HEAT TRANSFER TO TURBULENTLY FLOWING PRESSURIZED AIR

1954 ◽  
Vol 32 (2) ◽  
pp. 190-200 ◽  
Author(s):  
A. W. Marris
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Low Velocity ◽  
Eddy Diffusivities ◽  
Factor Measurement ◽  
Radial Heat ◽  
The Heat Transfer Coefficient

Employing a counter-flow figure-of-eight heat exchanger, direct measurements are made of the Nusselt modulus for radial heat transfer to air pressurized up to 20 atmospheres for Reynolds numbers up to 1.20 × 105. For each heat transfer determination a simultaneous friction factor measurement is made and it is found that the latter is independent of heat transfer.Results in reasonable agreement with the momentum transfer theory are obtained for Reynolds numbers less than 0.75 × 105, provided the ratio of the eddy diffusivities for heat and momentum is taken as unity. For such values of the Reynolds number, the same value of the heat transfer coefficient was obtained irrespective of whether the Reynolds number was obtained by having high pressure (density) and low velocity, or high velocity and low pressure. For higher values of the Reynolds number, however, the value of the heat transfer coefficient appeared to become dependent on the over-all heat transfer rate.

An Experimental Investigation of Heat Transfer Coefficients in a Spanwise Rotating Channel With Two Opposite Rib-Roughened Walls

1991 ◽  
Vol 113 (1) ◽  
pp. 75-82 ◽  
Author(s):  
M. E. Taslim ◽  
A. Rahman ◽  
S. D. Spring
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Blockage Ratio ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Heat Transfer Coefficient ◽  
Rotating Channel

Liquid crystals are used in this experimental investigation to measure the heat transfer coefficient in a spanwise rotating channel with two opposite rib-roughened walls. The ribs (also called turbulence promoters or turbulators) are configured in a staggered arrangement with an angle of attack to the mainstream flow, α, of 90 deg for all cases. Results are presented for the three values of turbulator blockage ratio e/Dh (0.1333, 0.25, 0.333) and for a range of Reynolds numbers from 15,000 to 50,000 while the test section is rotated at different speeds to give rotational Reynolds numbers between 450 and 1800. The Rossby number range is 10 to 100 (rotation number of 0.1 to 0.01). The effect of turbulator blockage ratios on heat transfer enhancement is also investigated. Comparisons are made between the results of geometrically identical stationary and rotating passage of otherwise similar operating conditions. The results indicate that a significant enhancement in heat transfer is achieved in both the stationary and rotating cases, when the surfaces are roughened with turbulators. For the rotating case, a maximum increase over that of the stationary case of about 45 percent in the heat transfer coefficient is seen for a blockage ratio of 0.133 on the trailing surface in the direction of rotation and the minimum is a decrease of about 6 percent for a blockage ratio of 0.333 on the leading surface, for the range of rotation numbers tested. The technique of using liquid crystals to determine heat transfer coefficients in this investigation proved to be an effective and accurate method especially for nonstationary test sections.

Measurement of Surface Heat Transfer Due to Particle Impact

1995 ◽  
Vol 117 (4) ◽  
pp. 1028-1035 ◽  
Author(s):  
J. G. Sun ◽  
M. M. Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Particle Impact ◽  
Impact Flux ◽  
The Difference ◽  
The Heat Transfer Coefficient ◽  
Particle Impact Velocity

Heat transfer coefficients for a surface continuously impacted by a stream of falling particles in air and in helium were measured as functions of particle flux and particle velocity. The purpose was to provide well-controlled data to clarify the mechanisms of heat transfer in particle suspension flows. The particles were spherical glass beads with mean diameters of 0.5, 1.13, and 2.6 mm. The distribution of the particle impact flux on the surface was determined by deconvolution from the measurement of the total solid masses collected at both sides of a movable splitter plate. The particle velocity was calculated from a simple, well-established model. The experimental results showed that in air, the heat transfer coefficient increases approximately linearly with particle impact flux. At high impact fluxes, the heat transfer coefficient decreases with particle impact velocity, and at low impact fluxes, it increases with particle impact velocity. Furthermore, the heat transfer coefficient decreases drastically with the particle size. In helium gas, it was found that at low particle impact fluxes, the difference between the coefficients in helium and in air is small, whereas at high fluxes, the difference becomes large. A length scale, V/n˙dp2, was used to correlate the data. At low particle Reynolds numbers, gas-mediated heat conduction was identified as the dominant particle/surface heat transfer mechanism, whereas at high particle Reynolds numbers, induced gas convection was the dominant mechanism.

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