Turbulent Flow Friction and Heat Transfer Characteristics of Single- and Multistart Spirally Enhanced Tubes

1986 ◽  
Vol 108 (1) ◽  
pp. 55-61 ◽  
Author(s):  
R. Sethumadhavan ◽  
M. Raja Rao
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Evaluation Criteria ◽  
Helix Angle ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Aspect Ratios ◽  
Friction Factors ◽  
Enhanced Tubes ◽  
Momentum And Heat Transfer

Investigations have been carried out on heat transfer and frictional characteristics of five spirally corrugated tubes of one to four corrugation starts, having the same helix angle, but of varying geometrical aspect ratios, for the turbulent flow of water and 50 percent glycerol. The thermal performance of these tubes was found to be superior compared to a smooth tube. Friction factors and heat transfer coefficients in these rough tubes were analysed on the basis of momentum and heat transfer analogy, and the correlation obtained was tested with the present data and also the published results of previous investigators. Performance evaluation criteria were used for the quantitative demonstration of the benefits offered by these spirally corrugated tubes for heat exchanger applications.

Turbulent Flow in Closely-Pitched Internally Enhanced Tubes

2000 ◽  
Author(s):  
T. S. Ravigururajan ◽  
J. Srinivasan
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Helix Angle ◽  
Independent Study ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Flow Parameters ◽  
Wide Range ◽  
Enhanced Tubes

Abstract General correlations are developed and verified for friction factor and heat transfer coefficients for single-phase turbulent flow in internally augmented tubes, with low pitch to height ratios. Data from existing investigations were collected for a wide range of tube parameters with e/d: 0.01 to 0.2; p/e: < 8; α/90: 0.2 to 1.0, and flow parameters; Re: 2000 to 250,000 and Pr: 0.66 to 37.6. The data were applied to a linear model to get normalized correlations that were then modified to approach smooth tube correlations, as the roughness variables became very small. The correlations predicted 92% of data from an independent study on microfin tubes within ± 30%. For closely-pitched enhanced tubes, the proposed correlations predict heat transfer/friction factor with better overall accuracy and are suitable for different types of internal enhancements. The heat transfer increases with decreasing p/e ratio and increasing helix angle. The effects of roughness height and pitch on both friction and heat transfer are similar to that experienced in traditional enhancement design (p/e > 8).

Thermally Developing Single-Phase Flows in Microtubes

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Mehmed Rafet Özdemir ◽  
Ali Koşar
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Single Phase ◽  
High Mass ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Friction Factors ◽  
Developing Flow ◽  
Theoretical Predictions

The pressure drop and heat transfer due to the flow of de-ionized water at high mass fluxes in microtubes of ∼ 254 μm and ∼ 685 μm inner diameters is investigated in the laminar, transition and the turbulent flow regimes. The flow is hydrodynamically fully developed and thermally developing. The experimental friction factors and heat transfer coefficients are respectively predicted to within ±20% and ±30% by existing open literature correlations. Higher single phase heat transfer coefficients were obtained with increasing mass fluxes, which is motivating to operate at high mass fluxes and under thermally developing flow conditions. The transition to turbulent flow and friction factors for both laminar and turbulent conditions were found to be in agreement with existing theory. A reasonable agreement was present between experimental results and theoretical predictions recommended for convective heat transfer in thermally developing flows.

SINGLE-PHASE HEAT TRANSFER AND PRESSURE DROP INSIDE INTERNALLY HELICAL-GROOVED HORIZONTAL SMALL-DIAMETER TUBES

2012 ◽  
Vol 20 (04) ◽  
pp. 1250022 ◽  
Author(s):  
NORIHIRO INOUE ◽  
JUNYA ICHINOSE
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Single Phase ◽  
Small Diameter ◽  
Flow Region ◽  
Helix Angle ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental study on pressure drop and heat transfer in single-phase was carried out using 10 types of internally helical-grooved and smooth small-diameter tubes with an outside diameter of 4 mm. The results are listed below: (1) In the turbulent flow region, fin height had the greatest effect, helix angle had only a minor effect, and the number of grooves had almost no effect upon the pressure drop versus the mass flow rate of the 4-mm grooved small-diameter tubes. In the laminar flow region, except for fin height, the shapes of the internal grooves had scarcely any effect upon pressure drop. (2) In the turbulent flow region, the heat transfer coefficients of the 4-mm grooved small-diameter tubes were greatly affected by fin height. The heat transfer coefficients became the maximum when a helix angle was near 15°, and there is a different tendency in the experiments of the pressure drop. On the other hand, there is almost no effect of the number of grooves. In the laminar flow region, there were no large differences in the heat transfer coefficients between the internally helical-grooved tubes and smooth small-diameter tube. (3) New empirical correlations for the friction factor and heat transfer coefficient in the laminar and turbulent flow regions were developed based on the experimental values. (4) The performance assessment in consideration of both heat transfer and pressure drop was indicated by using Colburn's analogy.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

Characterization of the Effect of Corrugation Angles on Hydrodynamic and Heat Transfer Performance of Four-Start Spiral Tubes

2001 ◽  
Vol 123 (6) ◽  
pp. 1149-1158 ◽  
Author(s):  
X. D. Chen ◽  
X. Y. Xu ◽  
S. K. Nguang ◽  
Arthur E. Bergles
Keyword(s):  
Heat Transfer ◽  
Evaluation Criteria ◽  
Geometry Optimization ◽  
Longitudinal Direction ◽  
Experimental Results ◽  
Neural Network Modeling ◽  
Transfer Coefficients ◽  
Correlation Models ◽  
Friction Factors ◽  
Double Pipe

A series of four-start spirally corrugated tubes has been subjected to heat transfer and hydrodynamic testing in a double-pipe heat exchanger. The study has been focused on the non-symmetric nature of the corrugation angles along the longitudinal direction. Both friction factors and heat transfer coefficients inside the tubes have been correlated against various process parameters. It can be shown that by altering the internal non-symmetric wavy shapes of the tubes, one is able to manipulate heat transfer and friction characteristics. The experimental results have been compared with some popular correlation models developed previously for both friction and heat transfer for corrugated tubes. Considerable differences between the experimental results and the predictions made using the existing correlations have been found and the probable causes have been discussed. Performance evaluation criteria are presented using the standard constant power criterion. A neural network modeling approach has been taken so that, based on the limited data, one can generate the contour showing the effect of corrugation angle on heat transfer coefficient for geometry optimization purposes.

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