Simultaneous Determination of Reference Free-Stream Temperature and Convective Heat Transfer Coefficient
This paper deals with the development of a new method that can obtain heat transfer coefficient and reference free stream temperature simultaneously, The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is found that the errors could be reduced more than 2 times less. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.
Impingement of a circular jet with and without cross flow
Abstract Measurements are reported for the local heat transfer to an impinging air jet with and without a cross flow of air. At large jet-to-plate spacing the cross flow diminishes the peak heat transfer coefficient ; at a smaller spacing cross flow can increase the peak heat transfer coefficient. A correlation is obtained for the average heat transfer in the absence of cross flow.
Transient Liquid Crystal Measurement of Local Heat Transfer on a Rotating Disk With Jet Impingement
All experimental technique has been developed for measurement of local convection heat transfer characteristics on rotating surfaces, utilizing thin liquid crystal surface coatings in a thermal transient test procedure. The encapsulated liquid crystal coatings used are sprayed directly on the test surface and their response is observed and processed during the transient with automated computer vision and data acquisition systems. Heat transfer coefficients are calculated from the thermal transient response of the test surface, as determined from the color indication from the thin coating. A significant advantage of the method, especially for convection in disk/shroud cavities that may contain recirculating fluid regions, is that appropriate thermal boundary conditions are naturally imposed on all of the boundary surfaces. The method is also relatively fast and inexpensive, and allows the geometry of the disk and stator surfaces to be changed easily, without the expenses of mounting discrete heat flux and temperature sensors and equipment to transfer information to a stationary frame of reference. Application of the experimental technique is demonstrated with detailed radially local surface Nusselt number distributions acquired for cases involving jet impingement onto a plane smooth disk, rotating in close proximity to a parallel plane stator disk. A single circular jet, with nozzle exit flush mounted in the stator, is oriented normal to the disk surface at various radii and flowrates. Local Nusselt numbers are presented nondimensionally as functions of both disk and flow Reynolds numbers. The results indicate that the local radial heat transfer distribution can be controlled by varying the impingement radius, but maximum radially averaged heat transfer is obtained with impingement at the disk center.Copyright © 1989 by ASME