Evaluation of the thermal design of a liquid-lens cooling system for projection picture tubes

The thermal design of a liquid-lens system for cooling picture tubes in projection television receivers is evaluated using an experimentally benchmarked numerical model. Because of the intense brightness in the visual image, excessive waste heat is generated as the by-product of light emission from the phosphor screen as the electron beam sweeps across the raster region at the back of the face panel. Projection tube specifications indicate a maximum allowable temperature at the face-panel center and a maximum allowable temperature differential between the center and perimeter points. To cool the tube's face, an optical liquid (liquid lens) fills the space between the face panel and a meniscus lens directly in front of it. A metallic enclosure frame serves as support for the meniscus lens and a container for the liquid. Heat is transferred by natural convection from the face panel to the enclosure frame and from there to the interior environment of the television cabinet by convection and radiation.; A boundary-fitted, finite-volume-based numerical model of the conjugate heat transfer and fluid flow processes within the liquid-lens system was developed and benchmarked with experimental data for nominal operation with the tube face oriented upward, making 30° with the horizontal. Results proved the thermal design adequate, with additional performance margin. Approximately 94% of the electrical input power is converted into heat at the phosphor screen (6% into visible light). Of that heat, 79% is transferred to the face-panel front by conduction, 19% to the tube interior by radiation, and 2% to the face panel sidewalls by conduction. Thermal performance is virtually unaffected by changes in the enclosure frame dimension, meniscus-lens design and position, or by variations in the tilt angle between 0° (face up) and 130°. Thermal performance is virtually insensitive to the meniscus lens thermal conductivity, but it can be enhanced using an optical liquid having higher thermal conductivity, density, specific heat, and volume expansivity or lower kinematic viscosity. If the need arises for enhancements in thermal performance; that is, lower temperatures or smaller temperature gradients on the tube face, forced convection cooling should be used instead of natural convection.