High-performance, simple cooling structures for optical disc drives compatible with the Blu-ray disc (BD) were developed using unsteady numerical flow simulation based on the Cartesian grid method. In the new structure, an additional hole in the tray outside of the disc induced a secondary upward flow, which is caused by a pressure difference and rotating-disc flow. The secondary flow decreases the ambient air-temperature of the laser diode below the hole, and furthermore it increases the velocity around the laser diode and enhances the heat transfer rate. The experimental results indicate that the cooling effect of the laser diode increases, and the disc vibration is not influenced by the additional hole in the tray. The cooling structures are applied to the so-called super-multi BD drive, which achieved 4X high-speed recording for the first time in the industry.
A system of numerical flow simulation with an automated mesh generator and parallelized solver was developed and applied to the flow-field inside an optical disc drive. In this simulation system, a uniformly spaced Cartesian grid is used to reduce time and automatically generate a mesh from CAD data for complicated geometries, such as optical disc drives. The simulation results of optical disc drives are validated by particle image velocimetry (PIV) and pressure-distribution measurements. The measured velocity distributions above a rotating disc and around a pick-up unit show quantitative agreement with the simulated distributions. For the pressure distributions on a top case of an optical disc drive, although there is an error of 10% between simulated and measured results, the position of the peaks and distribution of pressure show good agreement. Comparing both sets of measurements, the simulation results in a Cartesian grid system are sufficiently accurate to enable the flow-field to be quantitatively assessed. This numerical flow simulation is applied to investigate the detailed flow-field in a commercial optical disc drive.
We developed a voxel code using a finite difference method for unsteady three-dimensional thermal flows in a Cartesian grid system. This code enables us to predict flow fields around complicated geometries in a short pre-processing time. The code was used to predict flow fields around a flat plate that was heated to a constant temperature, and the results were within 20% of those obtained using analytical solutions. The code was also used to predict the flow field of a liquid crystal display (LCD) projector that has highly complicated internal structures such as a lamp, LCD panels, electric parts, etc.
A low-noise and high-performance “inclined fan-blowing-upward structure” for full high definition plasma display panel television sets was developed by using computational fluid dynamics with heat transfer based on a Cartesian grid system. In the conventional structure, the plasma panel and boards are cooled by fans and upward flow induced by natural convection. However, simulation results indicated that low-temperature flows between the bottom and rear inlets and fans are formed along the back cover, and the flows are not sufficiently supplied to the plasma panel and address-driver modules. Our solution is to mount the cooling fans inclined to the plasma panel so that the flows produced by the fans impinge on the panel to supply the low-temperature air to the panel and address-driver modules directly. In the new structure, larger fans can be used because fans are mounted inclined. With the larger fans, the rotation speed of the fans can be reduced, and the flow rate is increased. The experimental results show that the temperature of the panel and address-driver modules decreases respectively 3C and 8C at the same noise output level.
To achieve precise temperature control, Peltier devices, which are also called thermoelectric coolers, are widely used. However, simulating the unsteady temperature history caused by the Peltier devices is difficult because the amounts of heat absorption and generation are affected by their temperature. The temperature dependence reportedly can be calculated using the quadratic equation of temperature and the typical temperature characteristic coefficients. However, as the temperature dependence varied among the manufacturers, the temperature characteristic coefficients had to be modified for each of the devices. We developed a technique to determine the temperature characteristic coefficients of the Peltier device automatically by using data assimilation. We integrated the particle filter, one of the data assimilation algorithms, into the thermal network method and enabled estimating the suitable temperature characteristic coefficients. To demonstrate the estimation, we evaluated a Peltier device. The constant current 1.0 A and its inverse current were applied to the sample device repeatedly, and the temperature of the control object fluctuated repeatedly between 40 °C and 90 °C was measured. The temperature change was simulated using the thermal network method with the typical temperature characteristic coefficients and the history was compared with the measurement results. The root mean square error of temperature between the measurement and the calculation results was 3.20 K. Then, we estimated the applicable value of the temperature characteristic coefficients by applying the particle filter combined with the thermal network model. When the estimated coefficients were applied to the thermal network model, the root mean square error of temperature decreased to 1.39 K. Key words
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