Experimental heat/mass transfer studies of turbulent wall-bounded jets associated with mechanicallly ventilated enclosures

Abstract

The development and use of a'n experimental test rig is reported which is capable of modelling two- and three-dimensional wall-bounded air jets. This test rig was primarily produced in order to facilitate the experimental verification of computer codes for calculating convective heat transfer within mechanically- ventilated enclosures. Special attention was therefore given in the design of the rig to heat transfer measurements within such enclosures. The analogy between heat and mass transfer and the application of the naphthalene sublimation technique are explained. Also use of phase change paints in heat transfer measurements in general, and wall-jets in particular, is discussed and experimentally demonstrated. The boundary conditions for the application of each of the above two methods are then specified. The mass transfer method may be used for the case of a heated plate and a jet at ambient temperature while the phase change paint method is applicable to a heated jet. Heat/mass transfer studies are carried out for two different geometries. First beneath a plane wall-jet- obstructed by a normal flat-plate (Alamdari, Hammond and Montazerin (1986 bound paper)), where the data are compared with the computations of the 'intermediate-level' convection model of Alamdari and Hammond (1982) and the high-level 'elliptic' finite domain flow model of Pun and Spalding (1977). The comparison has been a clear demonstration of the capabilities of the computer codes and has shown that although their results over flat surfaces are in good agreement with the test data, their predictions for jets flowing round corners need further research. Secondly the flow and heat transfer characteristics of a three-dimensional jet parallel to a flat plate has been studied. In this case the flow field and mass transfer are modelled and an equation is finally derived which estimates the average heat transfer over a plate parallel to a bluff-jet for a variety of off-set heights, Reynolds numbers and nozzle aspect ratios and can readily be used by design engineers handling such flows.