Expansion of a Modified Transient Liquid Crystal Method for Thin Plates of Different Materials

2004 ◽  
Author(s):  
Alison K. Reed ◽  
Kenneth Van Treuren
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Temperature Distribution ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Plexiglas Plate ◽  
Coefficient Distribution

The purpose of this research is to apply a modified transient liquid crystal method to a thin flat plate to determine the local temperature distribution and heat transfer coefficient. This research examines three different plates: 1) 1/8 inch thick Plexiglas plate, 2) 1/2 inch thick Plexiglas plate, and 3) 1/8 inch thick aluminum plate. Each plate is approximately 6 inches in length by 3 inches in width. The temperature distributions on a flat plate are viewed over time using a liquid crystal thermography (LCT) technique. The plates are coated with a wide band liquid crystal (R30C5W) and fixed in a vertically oriented wind tunnel. For any thickness plate, the speed of the tunnel was adjusted for a Reynolds number within the range of approximately 22100 and 23100. For the theoretical analysis, the thin flat plate used a convective surface boundary condition and a 2-D transient finite-differencing conduction scheme. An initial local heat transfer coefficient distribution is selected based upon flat plate theory and is used to calculate an initial streamwise temperature distribution. The local heat transfer coefficient distribution is readjusted until the theoretical temperature distribution matches the experimental temperature distribution over the center surface of the plate. This technique allows a wider application of transient LCT and for heat transfer coefficients to be mapped on thin surfaces of different materials.

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.

Overall Thermal Performance of a Rectangular Channel With an Array of Elongated Pedestals

2013 ◽  
Author(s):  
S. Huang ◽  
Y. Y. Yan ◽  
J. D. Maltson ◽  
E. Utriainen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Flow Area ◽  
Coefficient Distribution

Experiments have been conducted to investigate the overall thermal performance of a rectangular channel implemented with an elongated pedestal array. The staggered pedestals were elongated in the spanwise direction in order that the jet flow from between the pedestals impinges at the centre of the pedestals in the downstream row. The average heat transfer coefficient of the pedestal and the local heat transfer coefficient distribution of the bottom channel wall were investigated for different geometrical arrangements. The pressure drop across the pedestal bank was measured. The transient liquid crystal method was used to obtain the local heat transfer coefficient distribution on the bottom channel wall and the lumped capacitance method was used to measure the average heat transfer coefficient of the pedestals in the last two rows of the bank. Five pressure taps were arranged on the centerline of each gap between two pedestal rows to measure the pressure drop. The heat transfer coefficients were measured over the Reynolds number range from 10,000 to 30,000. The minimum flow area to the channel cross-section flow area ratio ranged from 0.149 to 0.333. The effects of pedestal geometry and array distribution were investigated in detail showing the relationship between the pedestal array geometry, heat transfer enhancement and pressure drop. Conclusions were drawn on the effects of geometry and flow conditions on overall thermal performance of the respective channels.

Verification and Validation Studies for Laminar Hypersonic Flow Over a Blunted Cone and a Flat Plate

2006 ◽  
Author(s):  
S. Gokaltun ◽  
P. V. Skudarnov ◽  
C. X. Lin ◽  
Hugh Thornburg
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Hypersonic Flow ◽  
Surface Pressure ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Numerical Results ◽  
Verification And Validation

In this paper, verification and validation analysis for laminar hypersonic flow fields is presented. The simulations include a Mach 8 flow of calorically perfect gas over a spherically blunted cone and a Mach 14 flow over a flat plate. Numerical results were obtained using the finite volume method on structured grids. The verification of the numerical solutions was performed by calculating the Grid Convergence Index (GCI) for both test cases. A set of three different grids is used to calculate the discretization uncertainty, where each grid was generated by doubling the number of cells in each direction of the coarser grid. The value of GCI allows calculating the observed order of accuracy of the numerical method for local values of surface pressure at various points and the net drag force for the blunted cone case and for the local heat transfer coefficient for the flat plate case. The error band was observed to be 2.4% for the surface pressure in the blunted cone problem and 0.5% for the heat transfer coefficient in the flat plate problem. Finally the numerical results were validated with experimental data using the local surface pressure measurements for the hypersonic cone and the local heat transfer coefficient measurements for the hypersonic flat plate.

Local Heat Transfer Coefficient Distribution With Air Impingement Into a Cavity

1972 ◽  
Author(s):  
F. Burggraf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Local Heat Transfer Coefficient ◽  
Cavity Surface ◽  
Transfer Coefficients ◽  
Coefficient Distribution

Impingement heat transfer coefficients are presented for a row of holes impinging into an oval cavity with the spent air leaving through holes on one or both sides of the cavity. The distribution around the cavity surface is obtained and is correlated with a survey of the recent literature. In addition, local heat flux gages were used with an impingement jet air supply which could be changed in location along the axis of the test section. This permitted the determination of local heat transfer coefficient distribution over the surface both around the cavity and also in the region between the impinging jets. This two-dimensional distribution is shown to be influenced by the bleed geometry and the shape of the impinging jet holes.

Effects of Cooling Films on the Heat Transfer Coefficient on a Flat Plate With Zero Mainstream Pressure Gradient

1985 ◽  
Vol 107 (1) ◽  
pp. 105-110 ◽  
Author(s):  
N. Hay ◽  
D. Lampard ◽  
C. L. Saluja
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flat Plate ◽  
Polymer Surface ◽  
Flux Ratio ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

The influence of injection of cooling films through a row of holes on the heat transfer coefficient on a flat plate is investigated for a range of mass flux ratio using a heat-mass transfer analogy. Injection angles of 35 deg and 90 deg are covered. The experimental technique employed uses a swollen polymer surface and laser holographic interferometry. The results presented show the change in local heat transfer coefficient over the no-injection values at the centerline and off-centerline locations for various streamwise stations. The effect of injection on laterally averaged heat transfer coefficients is also assessed.

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