Thermo-Optics of Large Screen Plasma Display Panels

Avram Bar-Cohen – PI

Jeffry Kahn – Graduate Research Assistant

Objectives:

Plasma Display Panels (PDPs) are a popular technology for large size television displays.  Screen inefficiencies, which result in significant localized heat generation, necessitate the use of advanced thermal management materials to reduce the peak temperatures and spatial temperature variations across the screen.  In the current study, infrared thermography was used to obtain thermal maps of a typical, 42”, high-definition PDP screen for different illumination patterns and for several configurations of externally controlled heaters simulating PDP heat generation.  The results were used to validate a three-dimensional numerical thermal model of the PDP designed to predict the beneficial effects of anisotropic graphite heat spreaders on the temperature distribution.  In addition, a color analyzer was used to determine the spatial and temporal variations in luminosity across the PDP when operated continuously for 1750 hours.  The thermal model and experimental luminosity characteristics were used to evaluate the deleterious effects of temperature on PDP performance.

Current Effort:

Recent Publications:

Shooshtari, A., Kahn, J., Bar-Cohen, A., Dessiatoun, S., Ohadi, M., Getz, M., Norley, J.  “The Impact of a Thermal Spreader on the Temperature Distribution in a Plasma Display Panel.” ITherm, San Diego, CA, 2006.

Abstract: Plasma Display Panels (PDPs) are a leading technology for large size television displays. Screen inefficiencies result in considerable localized heat generation within the PDP and necessitate aggressive thermal management to reduce spatial temperature variations across the screen.  In the current study, experimental and numerical techniques were used to investigate the effect of a natural graphite heat spreader on hot spots and the temperature distribution across the screen. A commercial, 42” high-definition PDP, retrofitted with natural graphite heat spreaders with in-plane thermal conductivity varying from 140 to 440 W/m.K and thicknesses varying from 0.5 mm to 1.4 mm, served as the test vehicle for this study.  Infrared thermography was used to obtain a thermal map of the entire screen for different illumination patterns for each spreader configuration. Using a luminance meter, the luminosity of a selected point on the screen has been measured. A 3-D numerical model of this typical PDP, including the glass and spreader layers, as well as the chassis electronics, has been developed and the numerically obtained temperature distributions were compared to the experimental data.

Kahn, J., Bar-Cohen, A. “Thermal Modeling and Luminosity Characterizatin of a Plasma Display Panel.”  HT2007-33834.  ASME-JSME Thermal Engineering Summer Heat Transfer Conference. July 8-12, 2007, Vancouver, British Columbia, Canada.  

Abstract: Plasma Display Panels (PDPs) are a popular technology for large size television displays.  Screen inefficiencies, which result in significant localized heat generation, necessitate the use of advanced thermal management materials to reduce both the peak temperatures and the spatial temperature variations across the screen.  In the current study, infrared thermography was used to obtain thermal maps of a typical, 42”, high-definition PDP screen for different illumination patterns and for several configurations of externally controlled heaters, simulating PDP heat generation. The results were used to validate a 3-dimensional numerical thermal model of the PDP which was then used to predict the beneficial effects of anisotropic graphite heat spreaders on the temperature distribution of the PDP. In addition, a color analyzer was used to determine the spatial and temporal variations in luminosity across the PDP when operated continuously for 1750 hours with different illumination patterns. The thermal model and experimental luminosity characteristics are used to evaluate the deleterious effects of temperature on PDP performance.


LED Package Thermal Management

Avram Bar-Cohen – PI

Bongtae Han – Co-PI

Dae Whan Kim – Graduate Research Assistant

Objectives:

Recent Publications:

Kim, D.W., Rahim, E., Bar-Cohen, A., Han, B.T., 2007, “Thermofluid Characteristics Of Two-Phase Microgap Coolers, “Proceedings, ASME InterPack Conference, Vancouver, Canada, July 2007 (accepted)

Abstract: The thermofluid characteristics of a chip-scale microgap cooler, including single-phase flow of water and FC-72 and flow boiling of FC-72, are explored. Heat transfer and pressure drop results for single phase water are used to validate a detailed numerical model and, together with the convective FC-72 data, establish a baseline for microgap cooler performance. Experimental results for single phase water and FC-72 flowing in 120 µm, 260 µm and 600 µm microgap coolers, 31mm wide by 34mm long, at velocities of 0.1 - 2 m/s are reported. “Pseudo-boiling” driven by dissolved gas and flow boiling of FC-72 are found to provide significant enhancement in heat transfer relative to theoretical single phase values.


Thermo-Structural Influences on Optical Characteristics of Polymer Bragg Gratings

Avram Bar-Cohen – PI

Bongtae Han – Co-PI

Ilai Sher – Co-PI

Kyoung Joon Kim – Graduate Research Assistant

Background:

Bragg gratings incorporated into waveguide systems have broad application in filtering, control, and stabilization of optical signals, specifically in high capacity WDM networks and in photonic computing systems. The potential for low-cost fabrication and assembly makes Polymer Bragg gratings in waveguide systems a promising alternative to glass fiber optical systems, and they have been employed for WDM systems for the short haul data transmission with the wavelength tolerance of about 0.2 ~0.5 nm/K.

Temperature changes resulting from light absorption in the core of the waveguide can result in significant optical property variations, physical strain, and mechanical stress which, in turn, can lead to shifts in the Bragg wavelength. To facilitate the selection of waveguide, cladding, and substrate materials and the rational design of polymer Bragg gratings avoiding negative effects induced by Bragg wavelength shift, it is thus necessary to study the thermo-optic characteristics of these photonic components and quantify the relative magnitude of the thermally-induced deleterious effects on their performance. The goals of this study are defining thermo-optical issues in polymer Bragg gratings, quantifying thermally induced deleterious effects to its optical behaviors, and proposing thermally-robust (athermal) polymer Bragg gratings.

Objective:

Recent Publications:

Sher, I., Bar-Cohen, A. and Han, B.T. “Modeling of the non-isothermal effect on optical behavior of a Bragg grating.”

Abstract:A Modified Coupled-Mode model (M.C-M) is developed for the optical behavior of non-isothermal Bragg gratings. While the original Coupled-Mode model (C-M) predictions for polymer (PMMA) gratings under non-uniform temperature profiles deviate significantly from exact numerical calculations, the M.C-M model predictions coincide with the exact numerical results. The M.C-M model has revealed the importance of accounting for the thermo-mechanical effect of deforming the periodical shape of the grating, evident in gratings under a non-uniform temperature field. This effect is overlooked by the original C-M model, but while it may be negligible in glass gratings, it proves to be of significant magnitude in modern polymer gratings. The M.C-M model shares the simplicity benefit of the original C-M model, over the exact numerical calculation, in the requirement of three orders of magnitude less calculation steps.

Kyoung Joon Kim, Avram Bar-Cohen, Bongtae Han, “Thermo-Optical Characteristics of Bragg Grating Polymer Waveguides”, ISMNT-1, Honolulu, Hawaii, March 14-17, 2004

Kyoung Joon Kim, Avram Bar-Cohen, “Thermo-Optical Behavior of Passively-Cooled Polymer Waveguides”, Proceedings of IMECE2003-42342, Washington, D.C., November 15-21, 2003