EFFECT OF PERTURBATION ON THE CRITICAL REYNOLDS NUMBER IN NON-ISOTHERMAL PIPE FLOW

Abstract

Heat transfer tests with perturbed flow indicate that the nature or the function Nu = f(Re) for the main Nusselt number permits to distinguish between laminar, transient and turbulent domains of non-isothermal air flow. Values of critical Reynolds numbers Recr and Re' cr separating laminar from transient, and transient from turbulent domains, resp., have been found to depend on the perturbation frequency. \With increasing frequency, Recr values decrease. A relationship has been given for determining Recr Experimental observations agree with conclusions drawn from the Tollmien - Schlichting theory or stability of laminar flows.