Inverse Determination of the Local Heat Transfer Coefficients for Nucleate Boiling on a Horizontal Cylinder

2003 ◽  
Vol 125 (6) ◽  
pp. 1087-1095 ◽  
Author(s):  
H. Louahlia-Gualous ◽  
P. K. Panday ◽  
E. A. Artioukhine
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pool Boiling ◽  
Gradient Methods ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Nucleate Boiling ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Iterative Regularization

This article treats the local heat transfer for nucleate pool boiling around the cylinder using the inverse heat conduction analysis. The physical model considers a half section of a cylinder with unknown surface temperature and heat flux density. The iterative regularization and the conjugate gradient methods are used for solving the inverse analysis. The local Nusselt number profiles for nucleate pool boiling are presented and analyzed for different electric heat. The mean Nusselt number estimated by IHCP is closed with the measured values. The results of IHCP are compared to those of Cornewell and Houston (1994), Stephan and Abdelsalam (1980) and Memory et al. (1995). The influence of the error of the measured temperatures and the error in placement of the thermocouples are studied.

Experimental Investigation of the Effect of Synthetic Jets in Minichannels With Subcooled Boiling Flow

2013 ◽  
Author(s):  
David M. Sykes ◽  
Andrew L. Carpenter ◽  
Gregory S. Cole
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Heat Transfer ◽  
Local Heat ◽  
High Heat ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation

Microchannels and minichannels have been shown to have many potential applications for cooling high-heat-flux electronics over the past 3 decades. Synthetic jets can enhance minichannel performance by adding net momentum flux into a stream without adding mass flux. These jets are produced because of different flow patterns that emerge during the induction and expulsion stroke of a diaphragm, and when incorporated into minichannels can disrupt boundary layers and impinge on the far wall, leading to high heat transfer coefficients. Many researchers have examined the effects of synthetic jets in microchannels and minichannels with single-phase flows. The use of synthetic jets has been shown to augment local heat transfer coefficients by 2–3 times the value of steady flow conditions. In this investigation, local heat transfer coefficients and pressure loss in various operating regimes were experimentally measured. Experiments were conducted with a minichannel array containing embedded thermocouples to directly measure local wall temperatures. The experimental range extends from transitional to turbulent flows. Local wall temperature measurements indicate that increases of heat transfer coefficient of over 20% can occur directly below the synthetic jet with low exit qualities. In this study, the heat transfer augmentation by using synthetic jets was dictated by the momentum ratio of the synthetic jet to the bulk fluid flow. As local quality was increased, the heat transfer augmentation dropped from 23% to 10%. Surface tension variations had a large effect on the Nusselt number, while variations in inertial forces had a small effect on Nusselt number in this operating region.

Local Heat Transfer Coefficients Under an Axisymmetric, Single-Phase Liquid Jet

1991 ◽  
Vol 113 (1) ◽  
pp. 71-78 ◽  
Author(s):  
J. Stevens ◽  
B. W. Webb
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Local Nusselt Number ◽  
Single Phase ◽  
Radial Distance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Plate Spacing

The purpose of this investigation was to characterize local heat transfer coefficients for round, single-phase free liquid jets impinging normally against a flat uniform heat flux surface. The problem parameters investigated were jet Reynolds number Re, nozzle-to-plate spacing z, and jet diameter d. A region of near-constant Nusselt number was observed for the region bounded by 0≤r/d≤0.75, where r is the radial distance from the impingement point. The local Nusselt number profiles exhibited a sharp drop for r/d > 0.75, followed by an inflection and a slower decrease there-after. Increasing the nozzle-to-plate spacing generally decreased the heat transfer slightly. The local Nusselt number characteristics were found to be dependent on nozzle diameter. This was explained by the influence of the free-stream velocity gradient on local heat transfer, as predicted in the classical analysis of infinite jet stagnation flow and heat transfer. Correlations for local and average Nusselt numbers reveal an approximate Nusselt number dependence on Re1/3.

Local Heat Transfer Coefficients for Condensation in Stratified Countercurrent Steam-Water Flows

1983 ◽  
Vol 105 (4) ◽  
pp. 706-712 ◽  
Author(s):  
H. J. Kim ◽  
S. G. Bankoff
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Heat Transfer Coefficients ◽  
Flow Parameters ◽  
Eddy Transport

A study of steam condensation in countercurrent stratified flow of steam and subcooled water has been carried out in a rectangular channel inclined 33 deg to the horizontal. The variables in this experiment were the inlet water and steam flow rates, and the inlet water temperature. Condensation heat transfer coefficients were determined as functions of local steam and water flow rates, and the degree of subcooling. Correlations are given for the local Nusselt number for the smooth and for the rough interface regimes, and also for the dimensionless wave amplitude. A turbulence-centered model is also developed. It is shown that better agreement with the data can be obtained if the characteristic scales in the turbulent Nusselt number and Reynolds numbers are related to measured interfacial parameters rather than the bulk flow parameters. The important effect of interfacial shear, missing in previous eddy-transport models, is thus implicitly included.

The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib-Roughened Walls

1999 ◽  
Vol 122 (2) ◽  
pp. 386-392 ◽  
Author(s):  
Hector Iacovides ◽  
David C. Jackson ◽  
George Kelemenis ◽  
Brian E. Launder
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Separation Bubble ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Experimental Investigations ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Cfd Validation ◽  
Secondary Motion

The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-bends of square cross section, with and without artificial wall roughness, are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is presented. Tightly curved U-bends generate strong secondary motion and cause flow separation at the bend exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-bend, where it is over two times higher than in a straight duct. The local heat transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs results in a further increase in turbulence levels, a reduction in the size of the curvature-induced separation bubble, and a complex flow development after the bend exit with additional separation regions along the outer wall. Heat transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the bend on the overall levels of Nusselt number are not as strong as in the smooth U-bend, but are still significant. The effects of the bend on the perimetral variation of local heat transfer coefficients within the ribbed downstream section are also substantial. [S0889-504X(00)00802-3]

Local Heat Transfer in Turbine Disk Cavities: Part II—Rotor Cooling With Radial Location Injection of Coolant

1992 ◽  
Vol 114 (1) ◽  
pp. 221-228 ◽  
Author(s):  
R. S. Bunker ◽  
D. E. Metzger ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Computer Assisted ◽  
Transfer Coefficients ◽  
Disk Radius ◽  
Radial Location ◽  
Heat Transfer Coefficients

Detailed radial distributions of rotor heat transfer coefficients are presented for three basic disk-cavity geometries applicable to gas turbines. The experimental apparatus has been designed to obtain local heat transfer data on a number of easily interchangeable rotor surfaces. The method employs thin thermochromic liquid crystal coatings upon the rotor surfaces together with video system data acquisition and computer-assisted image analysis to detect surface color display and to extract heat transfer information. A thermally transient, aerodynamically steady technique is used, which attains consistent thermal boundary conditions over the entire disk cavity. Cooling air is introduced into the disk cavity via a single circular jet mounted perpendicularly into the stator at one of the three radial locations: 0.4, 0.6, or 0.8 times the rotor radius. Rotor heat transfer coefficients have been obtained over a range of parameters including disk rotational Reynolds numbers of 2 to 5 × 105, rotor/stator hub spacing-to-disk radius ratios of 0.025 to 0.15, and jet mass flow rates between 0.10 and 0.40 times the turbulent pumped flow rate of a free disk. The rotor surfaces include a parallel rotor-stator system, a rotor with 5 percent diverging taper, and a similarly tapered rotor with a rim sealing lip at its extreme radius. Results are presented showing the effects of the parallel rotor, which indicate strong variations in local Nusselt numbers for all but rotational speed. These results are compared to associated hub injection data of Part I of this study, demonstrating that overall rotor heat transfer is optimized by either hub injection or radial location injection of coolant dependent upon the configuration. Results with the use of the tapered rotor show significant variations in local Nusselt number compared with those of the parallel rotor, while the addition of a rim sealing lip appears to increase the Nusselt number level.

Nucleate boiling heat transfer coefficients of halogenated refrigerants up to critical heat fluxes

2009 ◽  
Vol 223 (6) ◽  
pp. 1415-1424 ◽  
Author(s):  
K-J Park ◽  
D Jung ◽  
S E Shim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Nucleate Pool Boiling ◽  
Transfer Coefficients ◽  
Average Deviation ◽  
Heat Transfer Coefficients

In this work, nucleate pool boiling heat transfer coefficients (HTCs) of five refrigerants of differing vapour pressures are measured on a horizontal, smooth copper surface of 9.53×9.53 mm. The tested refrigerants are R123, R152a, R134a, R22, and R32 and HTCs are taken from 10 kW/m2 to the critical heat flux (CHF) of each refrigerant. Wall and fluid temperatures are measured directly by thermocouples located underneath the test surface and in the liquid pool, respectively. Test results show that nucleate pool boiling HTCs of halogenated refrigerants increase as the heat flux and vapour pressure increase. This typical trend is maintained even at high heat fluxes above 200 kW/m2. Zuber's prediction equation for CHF is quite accurate showing a maximum deviation of 21 per cent for all refrigerants tested. For all refrigerants, Stephan and Abdelsalam's well-known correlation underpredicted nucleate boiling HTC data up to the CHF with an average deviation of 21.3 per cent, while Cooper's correlation overpredicted the data with an average deviation of 14.2 per cent. On the other hand, Gorenflo's and Jung et al.'s correlations showed 5.8 and 6.4 per cent deviations, respectively, in the entire nucleate boiling range up to the CHF.

Investigation of the Effects of Flow Swirl on Heat Transfer Inside a Cylindrical Cavity

1991 ◽  
Vol 113 (2) ◽  
pp. 348-354 ◽  
Author(s):  
A. Salce ◽  
T. W. Simon
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cylindrical Cavity ◽  
Flow Direction ◽  
Axial Flow ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Sensitive ◽  
Transfer Coefficients ◽  
Cavity Bottom

Experiments were conducted to determine local heat transfer coefficients on the inside surfaces of a cylindrical cavity that is cooled by a swirling air flow. Temperature-sensitive liquid crystals were used as temperature sensors. Five blowing (cooling) modes were tested: three with swirl numbers of 0.36, 0.84, and 1.73; a fourth with no swirl (axial flow), and a fifth that was similar to the fourth but had the flow direction reversed. Flow visualization and static pressure measurements were performed to improve understanding of the situation. The smoke-wire technique was successfully used to picture the flow patterns. Plots of local Nusselt number along the cavity surfaces were obtained for the five blowing modes and for three different Reynolds numbers. The swirling cases had similar flow fields with higher heat transfer rates near the cavity top and lower rates near the cavity bottom (the opposite of the nonswirling cases). A tornadolike structure on the cavity bottom was observed in the swirling cases. This structure became stronger and more violent as the degree of swirl and the Reynolds number were increased. The Nusselt number curves for the two nonswirling cases were of similar shape, although the flow direction was reversed.

The Measurement of Local Wall Heat Transfer in Stationary U-Ducts of Strong Curvature, With Smooth and Rib Roughened Walls

1999 ◽  
Author(s):  
Hector Iacovides ◽  
David C. Jackson ◽  
George Kelemenis ◽  
Brian E. Launder
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Separation Bubble ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Experimental Investigations ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Cfd Validation ◽  
Secondary Motion

The paper presents some of our recent experimental investigations of convective heat transfer in flow through stationary passages relevant to gas-turbine blade-cooling applications. The main objective of this effort is to produce local heat transfer data for CFD validation. Local Nusselt number measurements in flows through round-ended U-bends of square cross-section, with and without artificial wall roughness are presented. Our earlier LDA measurements of flows through these passages are first briefly reviewed and then the liquid-crystal technique for the measurement of local wall heat transfer inside passages of complex geometries is then presented. Tightly curved U-bends generate strong secondary motion and cause flow separation at the bend exit, which substantially raise turbulence levels. Wall heat transfer is significantly increased, especially immediately downstream of the U-bend, where it is over two times higher than in a straight duct. The local heat-transfer coefficient around the perimeter of the passage is also found to vary considerably because of the curvature-induced secondary motion. The introduction of surface ribs, results in a further increase in turbulence levels, a reduction in the size of the curvature induced separation bubble and a complex flow development after the bend exit with additional separation regions along the outer wall. Heat-transfer levels in the straight sections are more than doubled by the introduction of ribs. The effects of the bend on the overall levels of Nusselt number are not as strong as in the smooth U-bend, but are still significant. The effects of the bend on the perimetral variation of local heat-transfer coefficients within the ribbed downstream section are also substantial.

Experimental Study of Countercurrent Steam Condensation

1981 ◽  
Vol 103 (2) ◽  
pp. 307-311 ◽  
Author(s):  
A. Segev ◽  
L. J. Flanigan ◽  
R. E. Kurth ◽  
R. P. Collier
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Nusselt Number ◽  
Liquid Film ◽  
Rectangular Cross Section ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Liquid Films ◽  
Steam Condensation ◽  
Transfer Coefficients

An experimental study of steam condensation on subcooled liquid films in countercurrent flow has been conducted in a small inclined test apparatus having a rectangular cross-section. Condensation heat transfer coefficients were determined and the dependence on steam and water flow rates, the degree of subcooling, and test section inclination were all studied. The results were correlated in terms of local parameters for the complete penetration and bypass regions. It was found that the local Nusselt number increases with steam and liquid Reynolds numbers and liquid Prandtl number when no bypass occurs. In the bypass region the Nusselt number drops sharply due to the strong effects of the reduced liquid film flow rate. It is shown that the local heat transfer coefficient may be related to the turbulence intensity in the liquid film which suggests that a general turbulence-centered model can be constructed.

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