Evaluation of local wall temperature, heat flux, and convective heat transfer coefficient from the near-wall temperature profile

A technique for determining local wall temperature, local surface heat flux and local convective heat transfer coefficient from a carefully-taken, near-wall temperature profile was evaluated. In most previous work, wall temperatures have been measured using embedded or surface-mounted instrumentation, and flow bulk or core temperature and surface heat flux are separately measured. With the present technique, profile measurements taken with very accurate near-wall values are substituted for these separate instruments. The profiles are extrapolated to the wall to determine the local surface temperatures and their slopes are used to calculate the local surface heat flux. This technique depends on accurate positioning of a traversing temperature sensor with respect to the wall. In the present paper, the technique is evaluated in two simple flows, a fully-developed tube flow and a simple boundary layer flow. In the tube flow, local wall temperatures determined from profile measurements agreed with those obtained with an embedded wall thermocouple to within 5.3% and 12% of the wall-to-bulk temperature difference for two cases of different Reynolds numbers. Nusselt numbers determined using the near-wall profile data were compared to values obtained from two standard pipe flow correlations. Agreement with the average of two correlations was within 7.2%. For the simple, unaccelerated boundary layer flow on a flat plate, Stanton numbers determined from temperature profile measurements agreed with standard flat plate correlation values to within 8%. To demonstrate the utility of the technique, it was also applied to an accelerated, transitional boundary layer on a concave wall under high free-stream turbulence conditions and to an oscillatory flow within a pipe. The temperature profiles from the curved, accelerated boundary layer case, when cast in terms of wall coordinates using the profile-determined wall temperature and heat flux, agreed well with analytically-predicted profiles. This technique provides greater flexibility in the design of test sections and measurement programs by allowing reasonably accurate (less than 10% uncertainty) determination of local heat transfer coefficient without embedded instrumentation.