A Periodic Transient Method Using Liquid Crystals for the Measurement of Local Heat Transfer Coefficients

1998 ◽  
Vol 120 (3) ◽  
pp. 772-777 ◽  
Author(s):  
J. W. Baughn ◽  
J. E. Mayhew ◽  
M. R. Anderson ◽  
R. J. Butler
Keyword(s):  
Heat Transfer ◽  
Liquid Crystals ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transient Method ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

scholarly journals Local Heat-Transfer Measurements on a Large Scale-Model Turbine Blade Airfoil Using a Composite of a Heater Element and Liquid Crystals

1985 ◽  
Vol 107 (4) ◽  
pp. 953-960 ◽  
Author(s):  
S. A. Hippensteele ◽  
L. M. Russell ◽  
F. J. Torres
Keyword(s):  
Heat Transfer ◽  
Liquid Crystals ◽  
Turbine Blade ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Scale Model ◽  
Test Surface ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Local heat-transfer coefficients were experimentally mapped along the midchord of a five-times-size turbine blade airfoil in a static cascade operated at room temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a mylar sheet with a layer of cholesteric liquid crystals, which change color with temperature, and a heater sheet made of a carbon-impregnated paper, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat-transfer coefficients were mapped over the airfoil surface. The local heat-transfer coefficients are presented for Reynolds numbers from 2.8×105 to 7.6×105. Comparisons are made with analytical values of heat-transfer coefficients obtained from the STAN5 boundary layer code. Also, a leading-edge separation bubble was revealed by thermal and flow visualization.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

scholarly journals Heat Transfer Coefficient Determination in a Gravity Die Casting Process with Local Air Gap Formation and Contact Pressure Using Experimental Evaluation and Numerical Simulation

2021 ◽  
Author(s):  
T. Vossel ◽  
N. Wolff ◽  
B. Pustal ◽  
A. Bührig-Polaczek ◽  
M. Ahmadein
Keyword(s):  
Heat Transfer ◽  
Contact Pressure ◽  
Local Heat Transfer ◽  
Casting Process ◽  
Local Heat ◽  
Air Gap ◽  
Gap Formation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Die Casting Process

AbstractAnticipating the processes and parameters involved for accomplishing a sound metal casting requires an in-depth understanding of the underlying behaviors characterizing a liquid melt solidifying inside its mold. Heat balance represents a major factor in describing the thermal conditions in a casting process and one of its main influences is the heat transfer between the casting and its surroundings. Local heat transfer coefficients describe how well heat can be transferred from one body or material to another. This paper will discuss the estimation of these coefficients in a gravity die casting process with local air gap formation and heat shrinkage induced contact pressure. Both an experimental evaluation and a numerical modeling for a solidification simulation will be performed as two means of investigating the local heat transfer coefficients and their local differences for regions with air gap formation or contact pressure when casting A356 (AlSi7Mg0.3).

scholarly journals Condensation inside smooth horizontal tubes: Part 1. Survey of the methods of heat-exchange prediction

2015 ◽  
Vol 19 (5) ◽  
pp. 1769-1789 ◽  
Author(s):  
Volodymyr Rifert ◽  
Volodymyr Sereda
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Film Condensation ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

Survey of the works on condensation inside smooth horizontal tubes published from 1955 to 2013 has been performed. Theoretical and experimental investigations, as well as more than 25 methods and correlations for heat transfer prediction are considered. It is shown that accuracy of this prediction depends on the accuracy of volumetric vapor content and pressure drop at the interphase. The necessity of new studies concerning both local heat transfer coefficients and film condensation along tube perimeter and length under annular, stratified and intermediate regimes of phase flow was substantiated. These characteristics being defined will allow determining more precisely the boundaries of the flow regimes and the methods of heat transfer prediction.

Heat Transfer and Pressure Drop Correlations for Square Channels With 45 Deg Ribs at High Reynolds Numbers

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Akhilesh P. Rallabandi ◽  
Huitao Yang ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Turbine Blade Cooling ◽  
Square Channel ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Cooling Passage

Systematic experiments are conducted to measure heat transfer enhancement and pressure loss characteristics on a square channel (simulating a gas turbine blade cooling passage) with two opposite surfaces roughened by 45 deg parallel ribs. Copper plates fitted with a silicone heater and instrumented with thermocouples are used to measure regionally averaged local heat transfer coefficients. Reynolds numbers studied in the channel range from 30,000 to 400,000. The rib height (e) to hydraulic diameter (D) ratio ranges from 0.1 to 0.18. The rib spacing (p) to height ratio (p/e) ranges from 5 to 10. Results show higher heat transfer coefficients at smaller values of p/e and larger values of e/D, though at the cost of higher friction losses. Results also indicate that the thermal performance of the ribbed channel falls with increasing Reynolds numbers. Correlations predicting Nusselt number (Nu) and friction factor (f¯) as a function of p/e, e/D, and Re are developed. Also developed are correlations for R and G (friction and heat transfer roughness functions, respectively) as a function of the roughness Reynolds number (e+), p/e, and e/D.

Experimental Investigation of Local Heat Transfer Distribution on Smooth and Roughened Surfaces Under an Array of Angled Impinging Jets

2001 ◽  
Author(s):  
Lamyaa A. El-Gabry ◽  
Deborah A. Kaminski
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Roughened Surface

Abstract Measurements of the local heat transfer distribution on smooth and roughened surfaces under an array of angled impinging jets are presented. The test rig is designed to simulate impingement with cross-flow in one direction which is a common method for cooling gas turbine components such as the combustion liner. Jet angle is varied between 30, 60, and 90 degrees as measured from the impingement surface, which is either smooth or randomly roughened. Liquid crystal video thermography is used to capture surface temperature data at five different jet Reynolds numbers ranging between 15,000 and 35,000. The effect of jet angle, Reynolds number, gap, and surface roughness on heat transfer efficiency and pressure loss is determined along with the various interactions among these parameters. Peak heat transfer coefficients for the range of Reynolds number from 15,000 to 35,000 are highest for orthogonal jets impinging on roughened surface; peak Nu values for this configuration ranged from 88 to 165 depending on Reynolds number. The ratio of peak to average Nu is lowest for 30-degree jets impinging on roughened surfaces. It is often desirable to minimize this ratio in order to decrease thermal gradients, which could lead to thermal fatigue. High thermal stress can significantly reduce the useful life of engineering components and machinery. Peak heat transfer coefficients decay in the cross-flow direction by close to 24% over a dimensionless length of 20. The decrease of spanwise average Nu in the crossflow direction is lowest for the case of 30-degree jets impinging on a roughened surface where the decrease was less than 3%. The decrease is greatest for 30-degree jet impingement on a smooth surface where the stagnation point Nu decreased by more than 23% for some Reynolds numbers.

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

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