Heat Transfer and Pressure Drop in a Helically Coiled Rectangular Duct

1986 ◽  
Vol 108 (2) ◽  
pp. 343-349 ◽  
Author(s):  
V. Kadambi ◽  
E. K. Levy ◽  
S. Neti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Reynolds Numbers ◽  
Rectangular Duct ◽  
Number Range ◽  
Rectangular Wave ◽  
Friction Factors ◽  
Sudden Transition ◽  
The Heat Transfer Coefficient ◽  
Straight Duct

The present paper deals with experiments using air in three helically coiled rectangular ducts of mean diameters 12.7 cm, 17.8 cm, and 22.8 cm, respectively, made of rectangular wave-guide tubing of dimensions 1.27 cm × 0.64 cm. Pressure variations observed around the ducts were qualitatively in agreement with the expectations for secondary flow. The friction factors change gradually with increasing Reynolds numbers over the range 1200–10,000 without exhibiting a sudden transition from laminar flow to turbulence. At all Reynolds numbers, these are higher than those for a straight duct by 20–100 percent. The heat transfer coefficient is also higher than that for straight ducts ranging between 20–300 percent, depending on the Reynolds number. The largest increases are seen in the Reynolds number range 1200–2500.

Heat Transfer for High Aspect Ratio Rectangular Channels in a Stationary Serpentine Passage With Turbulated and Smooth Surfaces

2013 ◽  
Author(s):  
Matthew A. Smith ◽  
Randall M. Mathison ◽  
Michael G. Dunn
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Behavior ◽  
Reynolds Numbers ◽  
Hydraulic Diameter ◽  
Internal Cooling ◽  
Number Range ◽  
Aspect Ratios ◽  
Parallel Configuration

Heat transfer distributions are presented for a stationary three passage serpentine internal cooling channel for a range of engine representative Reynolds numbers. The spacing between the sidewalls of the serpentine passage is fixed and the aspect ratio (AR) is adjusted to 1:1, 1:2, and 1:6 by changing the distance between the top and bottom walls. Data are presented for aspect ratios of 1:1 and 1:6 for smooth passage walls and for aspect ratios of 1:1, 1:2, and 1:6 for passages with two surfaces turbulated. For the turbulated cases, turbulators skewed 45° to the flow are installed on the top and bottom walls. The square turbulators are arranged in an offset parallel configuration with a fixed rib pitch-to-height ratio (P/e) of 10 and a rib height-to-hydraulic diameter ratio (e/Dh) range of 0.100 to 0.058 for AR 1:1 to 1:6, respectively. The experiments span a Reynolds number range of 4,000 to 130,000 based on the passage hydraulic diameter. While this experiment utilizes a basic layout similar to previous research, it is the first to run an aspect ratio as large as 1:6, and it also pushes the Reynolds number to higher values than were previously available for the 1:2 aspect ratio. The results demonstrate that while the normalized Nusselt number for the AR 1:2 configuration changes linearly with Reynolds number up to 130,000, there is a significant change in flow behavior between Re = 25,000 and Re = 50,000 for the aspect ratio 1:6 case. This suggests that while it may be possible to interpolate between points for different flow conditions, each geometric configuration must be investigated independently. The results show the highest heat transfer and the greatest heat transfer enhancement are obtained with the AR 1:6 configuration due to greater secondary flow development for both the smooth and turbulated cases. This enhancement was particularly notable for the AR 1:6 case for Reynolds numbers at or above 50,000.

Heat Transfer And Pressure Drop Of An Angled Discrete Turbulator At Elevated Reynolds Numbers Up To 900,000

2021 ◽  
pp. 1-29
Author(s):  
Sam Ghazi-Hesami ◽  
Dylan Wise ◽  
Keith Taylor ◽  
Peter Ireland ◽  
Étienne Robert
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Friction Factor ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Enhance Heat Transfer ◽  
Near Surface ◽  
Number Range ◽  
Smooth Channel

Abstract Turbulators are a promising avenue to enhance heat transfer in a wide variety of applications. An experimental and numerical investigation of heat transfer and pressure drop of a broken V (chevron) turbulator is presented at Reynolds numbers ranging from approximately 300,000 to 900,000 in a rectangular channel with an aspect ratio (width/height) of 1.29. The rib height is 3% of the channel hydraulic diameter while the rib spacing to rib height ratio is fixed at 10. Heat transfer measurements are performed on the flat surface between ribs using transient liquid crystal thermography. The experimental results reveal a significant increase of the heat transfer and friction factor of the ribbed surface compared to a smooth channel. Both parameters increase with Reynolds number, with a heat transfer enhancement ratio of up to 2.15 (relative to a smooth channel) and a friction factor ratio of up to 6.32 over the investigated Reynolds number range. Complementary CFD RANS (Reynolds-Averaged Navier-Stokes) simulations are performed with the κ-ω SST turbulence model in ANSYS Fluent® 17.1, and the numerical estimates are compared against the experimental data. The results reveal that the discrepancy between the experimentally measured area averaged Nusselt number and the numerical estimates increases from approximately 3% to 13% with increasing Reynolds number from 339,000 to 917,000. The numerical estimates indicate turbulators enhance heat transfer by interrupting the boundary layer as well as increasing near surface turbulent kinetic energy and mixing.

Heat Transfer Enhancement in Axial Taylor-Couette Flow

2005 ◽  
Author(s):  
S. Gilchrist ◽  
C. Y. Ching ◽  
D. Ewing
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Couette Flow ◽  
Reynolds Numbers ◽  
Taylor Number ◽  
Number Range ◽  
Taylor Couette ◽  
Number Case ◽  
Taylor Couette Flow

An experimental investigation was performed to determine the effect that surface roughness has on the heat transfer in an axial Taylor-Couette flow. The experiments were performed using an inner rotating cylinder in a stationary water jacket for Taylor numbers of 106 to 5×107 and axial Reynolds numbers of 900 to 2100. Experiments were performed for a smooth inner cylinder, a cylinder with two-dimensional rib roughness and a cylinder with three-dimensional cubic protrusions. The heat transfer results for the smooth cylinder were in good agreement with existing experimental data. The change in the Nusselt number was relatively independent of the axial Reynolds number for the cylinder with rib roughness. This result was similar to the smooth wall case but the heat transfer was enhanced by 5% to 40% over the Taylor number range. The Nusselt number for the cylinder with cubic protrusions exhibited an axial Reynolds number dependence. For a low axial Reynolds number of 980, the Nusselt number increased with the Taylor number in a similar way to the other test cylinders. At higher axial Reynolds numbers, the heat transfer was initially independent of the Taylor number before increasing with Taylor number similar to the lower Reynolds number case. In this higher axial Reynolds number case the heat transfer was enhanced by up to 100% at the lowest Taylor number of 1×106 and by approximately 35% at the highest Taylor number of 5×107.

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.

Two-Phase Heat Transfer for Flow in Tubes and Over Rod Bundles With Blockages

1984 ◽  
Vol 106 (4) ◽  
pp. 856-864 ◽  
Author(s):  
M. I. Drucker ◽  
V. K. Dhir ◽  
R. B. Duffey
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Coefficient ◽  
Rod Bundles ◽  
Two Phase ◽  
Number Range ◽  
Transfer Data ◽  
Void Fractions ◽  
Two Phase Heat Transfer ◽  
The Heat Transfer Coefficient

A study of single- and two-component, two-phase heat transfer mechanisms for vertical flow inside of tubes and over rod bundles with blockages has been made. Existing heat transfer data for air–water flow in tubes with a liquid Reynolds number range of 2000 to 150,000 and void fractions up to 0.40 have been correlated as a function of αGr/Re2. The correlation has also been found to compare well with limited high Prandtl number data obtained with liquids other than water and for flow over rod bundles when an empirical constant is modified. Correlations have also been developed for the heat transfer coefficient in the vicinity of flow blockages in rod bundles. The heat transfer data have been obtained on a four rod bundle with sleeve-type blockages for a Reynolds number range of 230 to 6900 and void fractions up to 0.15. Significant enhancement of the heat transfer coefficient has been observed downstream of the blockages.

Turbulent Convective Heat Transfer in Forced Cooled Underground Electric Transmission Systems

1985 ◽  
Vol 107 (2) ◽  
pp. 327-333 ◽  
Author(s):  
R. Ghetzler ◽  
J. C. Chato ◽  
J. M. Crowley
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Scale Model ◽  
Transfer Coefficients ◽  
Transmission Systems ◽  
Number Range ◽  
Heat Transfer Coefficients ◽  
Electric Transmission ◽  
Friction Factors ◽  
High Reynolds

Heat transfer and friction factors were experimentally determined in a scale model of high-voltage, pipe-type underground transmission systems for Reynolds numbers to 8000. Dielectric insulating oil (Sun No. 4) with a Prandtl number of 120 was utilized for the coolant. Two ratios of cable to enclosure pipe diameters, corresponding to standard and oversize enclosure pipes, were examined for the three-cable system. Helical wire wrap was included to simulate protective skid wires around the cables. Three configurations of cable positioning were considered—open triangular, close triangular, and cradled. A method of generalizing the heat transfer coefficients was developed and tested for rough pipe cables based on extensions of previous work in the literature. The generalized correlation, without correction factors, was found to be applicable only in two cases with appropriate flow pattens and geometries. Heat transfer to the pipe wall could be correlated by standard methods in the high Reynolds number range.

Augmented Heat Transfer in a Recovery Passage Downstream From a Grooved Section: An Example of Uncoupled Heat/Momentum Transport

1995 ◽  
Vol 117 (2) ◽  
pp. 303-308 ◽  
Author(s):  
M. Greiner ◽  
R.-F. Chen ◽  
R. A. Wirtz
Keyword(s):  
Heat Transfer ◽  
Reynolds Numbers ◽  
Pumping Power ◽  
Power Performance ◽  
Velocity Measurements ◽  
Cross Sectional ◽  
Number Range ◽  
Transverse Grooves ◽  
Pressure And Velocity Measurements ◽  
The Heat Transfer Coefficient

Earlier experiments have shown that cutting transverse grooves into one surface of a rectangular cross-sectional passage stimulates flow instabilities that greatly enhance heat transfer/pumping power performance of air flows in the Reynolds number range 1000 < Re < 5000. In the current work, heat transfer, pressure, and velocity measurements in a flat passage downstream from a grooved region are used to study how the flow recovers once it is disturbed. The time-averaged and unsteady velocity profiles, as well as the heat transfer coefficient, are dramatically affected for up to 20 hydraulic diameters past the end of the grooved section. The recovery lengths for shear stress and pressure gradient are significantly shorter and decrease rapidly for Reynolds numbers greater than Re = 3000. As a result, a 5.4-hydraulic-diameter-long recovery region requires 44 percent less pumping power for a given heat transfer level than if grooving continued.

scholarly journals The Effect of Inclination Angle and Reynolds Number on the Performance of a Direct Contact Membrane Distillation (DCMD) Process

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2824 ◽  
Author(s):  
Adnan Alhathal Alanezi ◽  
Mohammad Reza Safaei ◽  
Marjan Goodarzi ◽  
Yasser Elhenawy
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Inclination Angle ◽  
Temperature Difference ◽  
Direct Contact ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Membrane Distillation ◽  
Number Range ◽  
Direct Contact Membrane Distillation

In this numerical study, a direct contact membrane distillation (DCMD) system has been modeled considering various angles for the membrane unit and the Reynolds number range of 500 to 2000. A two-dimensional model developed based on the Navier–Stokes, energy, and species transport equations were used. The governing equations were solved using the finite volume method (FVM). The results showed that with an increase in the Reynolds number of up to 1500, the heat transfer coefficient for all membrane angles increases, except for the inclination angle of 60°. Also, an increase in the membrane angle up to 90° causes the exit influence to diminish and the heat transfer to be augmented. Such findings revealed that the membrane inclination angle of 90° (referred to as the vertical membrane) with Reynolds number 2000 could potentially have the lowest temperature difference. Likewise, within the Reynolds numbers of 1000 and 2000, by changing the inclination angle of the membrane, temperature difference remains constant, however, for Reynolds numbers up to 500, the temperature difference reduces intensively.

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.

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