Extended surface convective cooling studies of engine components using the transient liquid crystal technique

1997 ◽  
Vol 211 (3) ◽  
pp. 273-287 ◽  
Author(s):  
A J Neely ◽  
P T Ireland ◽  
L R Harper
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Convective Heat Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Finned Tube ◽  
Correct Selection ◽  
Transfer Coefficients ◽  
Cooling Performance ◽  
Convective Cooling

A heat transfer tunnel used for local convective heat transfer coefficient measurements on liquid crystal instrumented models is described. The tunnel uses the new mesh heater device to produce a good approximation to a step change in the test section flow temperature. A simple analytical model of the cooling performance of cylindrical extended surfaces is derived from empirical relations obtained from the literature. Experiments conducted on a smooth cylinder and selected cylindrical finned geometries are discussed. In the configurations investigated, the relative sizes of the fin diameter to the fin array greatly exceed any geometries previously reported. The use of liquid crystal mapping techniques is shown to provide the full distribution of local heat transfer coefficients across the fin surface. This enables a greater understanding of the convective cooling process than could be obtained from the simple average measurements of h previously reported in the literature. Existing finned tube correlations are shown to be unable to predict the measured heat transfer levels. The investigation shows that correct selection of fin geometry can result in a significant increase in overall convective cooling performance.

Three-Dimensional Transient Heat Conduction Equation Solution for Accurate Quantification of Heat Transfer Coefficient in Transient Liquid Crystal Experiments

2019 ◽  
Author(s):  
Shoaib Ahmed ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Conduction Model

Abstract Liquid crystal thermography and infrared thermography techniques are typically employed to measure detailed surface temperatures, where local heat transfer coefficient (HTC) values are calculated by employing suitable conduction models. One such practice, which is very popular and easy to use, is the transient liquid crystal thermography using one-dimensional semi-infinite conduction model. In these experiments, a test surface with low thermal conductivity and low thermal diffusivity (e.g. acrylic) is used where a step-change in coolant air temperature is induced and surface temperature response is recorded. An error minimization routine is then employed to guess heat transfer coefficients of each pixel, where wall temperature evolution is known through an analytical expression. The assumption that heat flow in the solid is essentially in one-dimension, often leads to errors in HTC determination and this error depends on true HTC, wall temperature evolution and HTC gradient. A representative case of array jet impingement under maximum crossflow condition has been considered here. This heat transfer enhancement concept is widely used in gas turbine leading edge and electronics cooling. Jet impingement is a popular cooling technique which results in high convective heat rates and has steep gradients in heat transfer coefficient distribution. In this paper, we have presented a procedure for solution of three-dimensional transient conduction equation using alternating direction implicit method and an error minimization routine to find accurate heat transfer coefficients at relatively lower computational cost. The HTC results obtained using 1D semi-infinite conduction model and 3D conduction model were compared and it was found that the heat transfer coefficient obtained using the 3D model was consistently higher than the conventional 1D model by 3–16%. Significant deviations, as high as 8–20% in local heat transfer at the stagnation points of the jets were observed between h1D and h3D.

A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

1989 ◽  
Vol 111 (4) ◽  
pp. 877-881 ◽  
Author(s):  
J. W. Baughn ◽  
P. T. Ireland ◽  
T. V. Jones ◽  
N. Saniei
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux, while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

Heat Transfer Coefficient Distributions for the Convective Cooling of Non-Cylindrical Geometries in Crossflow Using Extended Surfaces

1997 ◽  
Author(s):  
Andrew J. Neely ◽  
Peter T. Ireland ◽  
Les R. Harper
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Convective Cooling ◽  
Heat Transfer Coefficients ◽  
Cylindrical Geometries

An experimental investigation of the performance of extended fin surfaces for the forced convective cooling of a range of engine component geometries in crossflow is reported. The experiments were undertaken to measure the surface heat transfer coefficient distributions of external finning around non-cylindrical geometries for use in aviation gas turbines in which the cooling performance/mass ratio must be maximised. The geometries examined were a box (square with rounded corners), a flute (rectangle with circular ends) and a 30° wedge. These models were sized to have equivalent cross sectional area to allow a direct comparison of performance. Perspex models coated with thermochromic liquid crystal were tested at a range of Reynolds numbers in a heat transfer wind tunnel in which a step change in flow temperature was used to measure the transient thermal behaviour of the fins. This technique enables the full surface mapping of local heat transfer coefficients on the surface of the fins. These measurements are compared with those for the equivalent smooth geometries and also with empirical calculations from the literature where available. A comparison with previous cylindrical measurements is also made. Knowledge of the distributions of local heat transfer coefficients enables the optimisation of the geometry through strategies such as baffling of the fins. Some examples of these strategies have been implemented and the results are reported. The finned geometries are seen to outperform the unfinned geometries (by factors greater than 3) though by factors less than simply the increase in area. The enhancement in h results because the increased surface area of the fins more than outweighs the decrease in local h on the fin surface as compared to the smooth geometries.

Improved Accuracy in Jet Impingement Heat Transfer Experiments Considering the Layer Thicknesses of a Triple Thermochromic Liquid Crystal Coating

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Alexandros Terzis ◽  
Stavros Bontitsopoulos ◽  
Peter Ott ◽  
Jens von Wolfersdorf ◽  
Anestis I. Kalfas
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Thickness Gauge ◽  
Thermochromic Liquid Crystal ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Paint Thickness

This paper examines the applicability of a triple layer of thermochromic liquid crystals (TLCs) for the determination of local heat transfer coefficients using the transient liquid crystal (LC) technique. The experiments were carried out in a narrow impingement channel, typically used for turbine blade cooling applications. Three types of narrow bandwidth LCs (1 °C range) of 35 °C, 38 °C, and 41 °C were individually painted on the target plate of the cooling cavity and the overall paint thickness was accurately determined with an integral coating thickness gauge. The 1D transient heat conduction equation is then implicitly solved for each individual TLC layer on its realistic depth on the painted surface. Local heat transfer coefficients are therefore calculated three times for the same location in the flow improving the measurement accuracy, especially at regions where the LC detection times are too short (stagnation points) or too long (wall-jet regions). The results indicate that if multiple LC layers are used and the paint thickness is not considered, the heat transfer coefficients can be significantly underestimated.

scholarly journals A Comparison of the Transient and Heated-Coating Methods for the Measurement of Local Heat Transfer Coefficients on a Pin Fin

1988 ◽  
Author(s):  
J. W. Baughn ◽  
P. T. Ireland ◽  
T. V. Jones ◽  
N. Saniei
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Uniform Heat Flux ◽  
Fluid Temperature ◽  
Transfer Coefficients ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Difference

Measurements of the local heat transfer coefficients on a pin fin (i.e., a short cylinder in crossflow) in a duct have been made using two methods, both of which employ liquid crystals to map an isotherm on the surface. The transient method uses the liquid crystal to determine the transient response of the surface temperature to a change in the fluid temperature. The local heat transfer coefficient is determined from the surface response time and the thermal properties of the substrate. The heated-coating method uses an electrically heated coating (vacuum-deposited gold in this case) to provide a uniform heat flux while the liquid crystal is used to locate an isotherm on the surface. The two methods compare well, especially the value obtained near the center stagnation point of the pin fin where the difference in the thermal boundary condition of the two methods has little effect. They are close but differ somewhat in other regions.

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.

Sign in / Sign up

Export Citation Format

Share Document