| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 95 === A series of experimental investigations with stringent measurement methods on the studies related to fluid flow and heat transfer characteristics of a stationary or rotating MCM disk with various cooling techniques have been performed. The total experimental cases for a stationary or rotating MCM disk with various cooling techniques are statistically designed by the Design of Experiments (DOE) together with Central Composite Design method (CCD). The relevant parameters influencing fluid flow and heat transfer performance for a stationary or rotating MCM disk with various cooling techniques include: steady-state Grashof number (Grs), ratio of the confinement spacing to disk diameter (H/D), ratio of jet separation distance to nozzle diameter (H/d), jet Reynolds number (Rej) and rotational Reynolds number (Rer). The ranges of the above-mentioned parameters are: Grs = 2.32 ×105 - 2.57×106, H/D = 0.083 - 1.2, H/d = 0.83 - 14.4, Rej = 89 - 17364 and Rer = 0 - 2903. Their effects on fluid flow and heat transfer characteristics for a stationary or rotating MCM disk with various cooling techniques have been systematically explored. In addition, a sensitivity analysis, the so-called “ANOVA”, for the design factors has been performed. An effective optimal method with the RSM and SQP techniques for performing the thermal optimization of a stationary or rotating MCM disk with various cooling techniques under multi-constraints has been successfully developed. Six subtopics of thermal optimization have been systematically explored. They are (1) a confined stationary MCM disk in natural convection; (2) a confined rotating MCM disk; (3) a stationary MCM disk with confined single round jet impingement; (4) a confined rotating MCM disk with single round jet impingement;(5) a confined stationary MCM disk with round jet array impingement; and (6) a confined rotating MCM disk with round jet array impingement.
In hydrodynamic aspect, the fluid flow characteristics including the streamwise velocity and turbulence intensity distributions at nozzle exits, jet potential core length, streamwise velocity decay along jet centerline and turbulence intensities evolution along jet centerline are investigated. The flow behaviors for single round jet and for jet array impingement have been experimentally verified as a symmetrical flow and an unsymmetrical flow, respectively. Based on the measurement of the above-mentioned jet flow characteristics for jet array impingement, the jet flow behaviors at nozzle exits can be classified into two regimes such as “initially transitional flow regime” and “initially turbulent flow regime.” Additionally, new correlations of the ratio of potential core length to nozzle diameter, Lpc/d, in terms of relevant influencing parameters for a confined stationary or rotating MCM disk with single round jet and round jet array impingement at various nozzle jets are presented.
In heat transfer aspect, from all the experimental data measured for transient-/steady-state local and average heat transfer characteristics, the thermal behavior has been verified to be axisymmetrically maintained and the results have been achieved in an axisymmetric form. The stagnation, local and average heat transfer characteristics for a stationary or rotating MCM disk with various cooling techniques are successively explored. Besides, the mutual influences among buoyancy, disk rotation and jet impingement on the heat transfer performance of a confined stationary or rotating MCM disk with round jet array impingement have been quantitatively evaluated. New correlations of stagnation, local and average Nusselt numbers in terms of relevant parameters are proposed. To interpret the convective heat transfer characteristics on the confined stationary or rotating MCM disk surface due to the mutual effects among jet impingement and disk rotation, the heat transfer behavior can be classified into two distinct heat transfer regimes such as disk rotation-dominated regime and jet impingement-dominated regime for the cases with a specified ratio of rotational Reynolds number to jet Reynolds number, i.e., . Two empirical correlations of classifying these two distinct regimes are proposed for the single round jet and jet array impingement, respectively. The steady-state heat transfer enhancement for jet array impingement compared with single round jet impinging onto a confined stationary or rotating MCM disk has been systematically explored; and a new correlation of the heat transfer enhancement ratio, , in terms of relevant influencing parameters is reported.
Furthermore, a series of thermal optimizations with multiple constraints such as space, jet Reynolds number, rotational Reynolds number, nozzle exit velocity, disk rotational speed and total power consumption constraints for a stationary or rotating MCM disk with various cooling techniques have been performed and discussed. New correlations of the optimal steady-state average heat transfer performance for the cases of a confined stationary or rotating MCM disk with single round jet or jet array impingement are finally presented.
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