Establishing steady-state thermal conditions in flat slab specimens

The thermal response of flat slab specimens subjected to four sets of thermal boundary conditions is examined. The conditions are typical of thermophysical test apparatus, and the four sets of conditions are similar. Initial temperatures are uniform and the cold face temperature is stepped to the required value. There are four different hot face conditions: (1) constant temperature, (2) constant heat flow, (3) zero heat flow followed by constant temperature, and (4) zero heat flow followed by constant heat flow. Solutions are given for the heat transfer problems, and the equations are truncated, then inverted, to yield simple, approximate expressions for response time. The precision of the approximate equations is shown to be adequate for prediction purposes; the four sets of conditions are ranked in order of increasing response time; and the occurrence of optimum situations is noted.L'auteur examine la r\ue9ponse thermique d'\ue9chantillons de dalle sans nervure soumis \ue0 quatre s\ue9ries de conditions thermiques aux limites. Les conditions sont caract\ue9ristiques des dispositifs d'essai thermophysiques et les quatre s\ue9ries de conditions sont semblables. Les temp\ue9ratures initiales sont uniformes et la temp\ue9rature requise de la surface froide est atteinte par degr\ue9s. Les conditions de la surface chaude sont au nombre de quatre: ( 1) temp\ue9rature constante, (2) flux thermique constant, (3) flux thermique nul suivi d'une temp\ue9rature constante et (4) flux thermique nul suivi de flux thermique constant. L'auteur donne des solutions des probl\ue8mes de transmission de chaleur; les \ue9quations sont tronqu\ue9es, puis inverties, pour former des expressions simples et approximatives du temps de r\ue9ponse. L'auteur montre que l'exactitude des \ue9quations approximatives est convenable pour fins de pr\ue9diction; les quatre s\ue9ries de conditions sont rang\ue9es par ordre ascendant de temps de r\ue9ponse et l'on note l'existence de situations optimales.Peer reviewed: NoNRC publication: Ye