Abstract
ABSTRACT A series of experimental investigations with stringent measurement methods on the studies related to transient natural/mixed convection from a horizontally unconfined/confined stationary/rotating ceramic-based MCM disk have been successfully performed. The relevant parameters influencing heat transfer performance are (1) purely natural convection －steady-state Grashof number and ratio of the confinement spacing to disk diameter; (2) mixed convection due to disk rotation and buoyancy －steady-state Grashof number, ratio of the confinement spacing to disk diameter and rotational Reynolds number. In the study, the transient heat transfer behavior on an unconfined/confined stationary/rotating MCM disk surface has been systematically explored. It includes the transient temperature distribution on the MCM disk surface, transient heat flux distribution of input power, transient convective heat flux distribution of chips, and transient chip and average heat transfer characteristics on the MCM disk. In addition, an effective time, ton, representing a certain transient time when the natural or mixed convection effect due to disk rotation becomes significant relative to heat conduction, is introduced in the study. Both the transient chip and average Nusselt numbers on the MCM disk surface decrease with time in a very beginning period of 0□ t < ton, whereas it gradually increases or keeps at constant with time and finally approaches the steady-state value in the period of ton□ t < ts. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t □ ton in the power-on transient period. Nevertheless, significant deviations can be observed by using the existing steady-state correlations to predict the transient data in a very beginning of the transient period, say t < ton because the heat transfer behavior is mainly dominated by pure heat conduction at that time; while the steady-state correlation can be used at t □ ton when the thermal behavior is dominated by natural or mixed convection due to disk rotation. In the present study, the effective time, ton, can be observed to be 10 min and 7 min for the natural convection from a stationary disk and for mixed convective from a rotating disk, respectively.