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.

Turbulent Heat Transfer Augmentation and Friction in Periodic Fully Developed Channel Flows

1992 ◽  
Vol 114 (1) ◽  
pp. 56-64 ◽  
Author(s):  
T.-M. Liou ◽  
J.-J. Hwang
Keyword(s):  
Heat Transfer ◽  
Hot Spots ◽  
Channel Flows ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Relative Contribution ◽  
Friction Factors

Measurements are presented of the distribution of average friction factors (f) as well as local and average (Nu) heat transfer coefficients for fully developed channel flows with two rib-roughened opposite walls. The temperature measurements were made by using both a laser holographic interferometer and thermocouples. In addition, the reattachment length was determined by flow visualization. The Reynolds number (Re) was varied from 5.0 × 103 to 5.4 × 104; the rib pitch-to-height ratios (Pi/H) were 10, 15, and 20; and the rib height-to-hydraulic diameter ratios (H/De) were 0.063, 0.081, and 0.106. The detailed results allowed the peaks of heat transfer augmentation and the regions susceptible to hot spots to be located and allowed the relative contribution of the rib surface and the channel wall to the heat transfer augmentation to be determined. Moreover, relative to a smooth duct, the enhancement of both Nu and f at various Re, Pi/H, and H/De was documented in detail. Furthermore, compact correlations in terms of Re, Pi/H, and H/De were developed for both Nu and f.

Maldistributed Inlet Flow Effects on Turbulent Heat Transfer and Pressure Drop in a Flat Rectangular Duct

1983 ◽  
Vol 105 (3) ◽  
pp. 527-535 ◽  
Author(s):  
E. M. Sparrow ◽  
N. Cur
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Inlet Flow ◽  
Heat Transfer Coefficients ◽  
Flow Maldistribution

The effects of flow maldistribution caused by partial blockage of the inlet of a flat rectangular duct were studied experimentally. Local heat transfer coefficients were measured on the principal walls of the duct for two blockages and for Reynolds numbers spanning the range between 6000 and 30,000. Measurements were also made of the pressure distribution along the duct, and the fluid flow pattern was visualized by the oil-lampblack technique. Large spanwise nonuniformities of the local heat transfer coefficient were induced by the maldistributed flow. These nonuniformities persisted to far downstream locations, especially in the presence of severe inlet flow maldistributions. Spanwise-average heat transfer coefficients, evaluated from the local data, were found to be enhanced in the downstream portion of the duct due to the flow maldistribution. However, at more upstream locations, where the entering flow reattached to the duct wall following its separation at the sharp-edged inlet, the average coefficients were reduced by the presence of the maldistribution.

Experiments on Turbulent Heat Transfer in an Asymmetrically Heated Rectangular Duct

1966 ◽  
Vol 88 (2) ◽  
pp. 170-174 ◽  
Author(s):  
E. M. Sparrow ◽  
J. R. Lloyd ◽  
C. W. Hixon
Keyword(s):  
Heat Transfer ◽  
Rectangular Cross Section ◽  
Heated Wall ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
First Case ◽  
Symmetric Heating

An experimental investigation of the effect of asymmetrical heating on fully developed turbulent heat transfer has been carried out. The test apparatus was a rectangular duct of aspect ratio 5:1. The duct was constructed so that the two long sides of the rectangular cross section could be heated at different preselected rates, while the two short sides were unheated. Two cases of asymmetrical heating were studied: (a) One of the two long sides was heated, while the second was unheated; (b) both of the long sides were heated, with the heating rate at one side being twice that of the other. For the first case, the heat transfer coefficients are lower than those for the symmetrically heated duct. For the second case, the coefficients for the more strongly heated wall are also below the values for symmetrical heating, while the coefficients for the lesser-heated wall are greater than the symmetric heating results. These findings are in qualitative agreement with analytical predictions for the parallel-plate channel. Furthermore, by applying an analytically motivated correlation procedure (reference [10]), it was shown that overall Nusselt number results for asymmetric heating could be brought into virtual coincidence with those for symmetric heating.

Augmentation of Heat Transfer in Tubes by Use of Mesh and Brush Inserts

1974 ◽  
Vol 96 (2) ◽  
pp. 145-151 ◽  
Author(s):  
F. E. Megerlin ◽  
R. W. Murphy ◽  
A. E. Bergles
Keyword(s):  
Heat Transfer ◽  
Mass Velocity ◽  
High Heat ◽  
Equal Mass ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Large Pressure ◽  
Empty Tube

This paper summarizes the results of a study to determine the heat transfer and pressure drop characteristics of two types of tube inserts developed specifically for augmenting heat transfer and accommodating high heat fluxes. The best performing mesh-insert tubes exhibited heat transfer coefficients nine times the coefficients with empty tubes while brush-insert tubes had coefficients averaging five times the empty tube values, both comparisons being made at equal mass velocity. Both inserts produced very large pressure drops. Subcooled boiling curves and burnout points are presented; burnout heat fluxes are two to three times the empty tube values at equal mass velocity. For single-phase conditions and for burnout, the mesh and brush tubes have favorable performance characteristics, based on pumping power, which suggest use of these inserts in certain special cooling systems.

Experiments on Turbulent Heat Transfer in a Tube With Circumferentially Varying Thermal Boundary Conditions

1967 ◽  
Vol 89 (3) ◽  
pp. 258-268 ◽  
Author(s):  
A. W. Black ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boundary Conditions ◽  
Wall Heat Flux ◽  
Turbulent Heat Transfer ◽  
Working Fluid ◽  
Turbulent Heat ◽  
Turbulent Diffusivity ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental investigation, supported by analysis, was performed to determine the heat transfer characteristics for turbulent flow in a circular tube with circumferentially varying wall temperature and wall heat flux. Air was the working fluid. The desired boundary conditions were achieved by electric heating within the wall of a tube whose thickness varied circumferentially. In this way, ratios of maximum-to-minimum wall heat flux as large as two were attained. Local heat transfer coefficients, deduced from the experimental data, display a circumferential variation that is substantially smaller than the heat flux variation. In general, lower heat transfer coefficients correspond to circumferential locations of greater heating, while higher coefficients correspond to locations of lesser heating. The predictions of prior analyses appear to overestimate the circumferential variation of the heat transfer coefficient. A specially designed probe was employed to measure the radial and circumferential temperature distributions within the flowing airstream. On the basis of these measurements, as well as from the heat transfer results, it is concluded that, in the neighborhood of the wall, the tangential turbulent diffusivity is greater than the radial turbulent diffusivity. The axial thermal development was found to be more rapid on the lesser-heated side of the tube than on the greater-heated side. Experimentally determined circumferential-average heat transfer coefficients agreed well with the predictions of analysis.

Experimental Investigation of Thermal and Hydrodynamic Performances of a Partial Cross-Wavy Recuperator for Microturbine Applications

2012 ◽  
Author(s):  
L. X. Du ◽  
P. Q. Yu ◽  
M. Zeng ◽  
Q. W. Wang
Keyword(s):  
Heat Transfer ◽  
Flow Distribution ◽  
Reynolds Numbers ◽  
Experimental Results ◽  
Hydrodynamic Performance ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
High Efficient

In order to improve the thermal efficiency of the microturbines, the compact and high efficient primary surface heat exchangers are mandatory. Recently, the thermal and hydrodynamic performances of a cross-wavy (CW) primary surface recuperator are experimentally investigated. The recuperator tested in the experiment is only 1/3 part of the whole recuperator which is designed for a 100kW microturbine. The experimental results have shown that the comprehensive thermal and hydrodynamic performances of the CW primary surface recuperator are competitive. The overall heat transfer coefficients and the pressure drops of the recuperator are tested in the experiments. And the range of the Reynolds number is from 150 to 400. The corresponding correlations between heat transfer coefficients and Reynolds numbers and the correlations between friction factors and Reynolds numbers are obtained. The Genetic Algorithm (GA) has been used to separate the coefficients of heat transfer correlations in the hot and cold sides of the partial recuperator by separating the overall heat transfer coefficient without experimentally knowing wall temperatures. In order to improve the hydrodynamic performance, the flow arrangement is also carefully designed. Furthermore, the experimental results have also confirmed that the flow distribution in the recuperator is quite uniform.

Heat Transfer and Pressure Drop Characteristics Induced by a Slat Blockage in a Circular Tube

1980 ◽  
Vol 102 (1) ◽  
pp. 64-70 ◽  
Author(s):  
E. M. Sparrow ◽  
K. K. Koram ◽  
M. Charmchi
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Pipe Flow ◽  
Turbulent Pipe Flow ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Cross Sectional ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Flow Experiments

Complementary heat transfer and fluid flow experiments were performed to determine transfer coefficients and pressure drops associated with the presence of a slat-like blockage in a tube. Water was the working fluid for the heat transfer studies (Pr = 4), while for the fluid flow experiments, which were performed under isothermal conditions, air was employed. The flow was turbulent in all cases, with the Reynolds number ranging from 10,000 to 60,000. Three blockage elements were used which respectively blocked 1/4, 1/2, and 3/4 of the tube cross-sectional area. Downstream of the blockage, heat transfer coefficients were measured around the circumference of the tube as well as along its length. The heat transfer coefficients in the region just downstream of the blockage were found to be several times as large as those for a corresponding conventional turbulent pipe flow. With increasing downstream distance, the coefficients diminish and thermal development is completed (to within five percent) at about 10, 15, and 18 diameters from the respective blockages. The blockage-induced circumferential variations of the heat transfer coefficient are dissipated by about five diameters. The pressure losses induced by the blockage are high, with values for the respective blockages that are 1.2, 5.2, and 33.2 times the velocity head in the pipe flow in which the blockage is situated. These losses are comparable to those for a gate valve.

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