HEAT AND MASS TRANSFER CHARACTERISTICS OF TRANSPIRATION COOLING

The present work deals with an experimental study of the flow and heat transfer characteristics of transpiration cooling systems. The objective is to find appropriate correlation equations relating friction factor with Reynolds number and Nusselt number with Reynolds number (or Peclet number) for isothermal and non-isothermal flow through porous materials. The flow and heat transfer characteristics of the scaled-up models and the sintered porous materials were investigated in the laboratory under the countercurrent heat and mass transfer boundary conditions simulating the transpiration cooling phenomenon.; First, experiments were performed on sintered and unsintered packed beds of spheres and on sintered packed beds of rods (unit cell geometry). These were used as the scaled-up models for sintered powder metals and for sintered fiber metals respectively. The results of the isothermal and non-isothermal pressure drop data on these models are used to study their flow characteristics and the permeability. The pressure drop data is correlated in the form of friction factor vs. Reynolds number. It is clearly established that square root of permeability can be used as the characteristic length in defining the friction factor and Reynolds number. The heat transfer data is correlated on the basis of; (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI); In the case of non-Darcian flow through packed bed of spheres,; (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI); whereas for the packed bed of rods (unit cell geometry); (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI); Secondly, experiments were performed on nine different sintered powder metals and on one 'rigimesh' material. The sintered powder metal specimens were made of S.S. 316, Nickel 200 and Copper, having porosity of 26% to 65.3%. The 'rigimesh' specimen was made of S.S. 316 with a porosity of 5.4%. From the isothermal and non-isothermal pressure drop data on these specimens, permeability of each specimen is determined by Darcy's law. It is found that for sintered metals SQRT.(K can also be used as the characteristic length in defining the friction factor and the Reynolds number. The pressure drop data is correlated in the form of friction factor and Reynolds number. The detailed temperature distributions in the solid phase and in the gas phase of these specimens are measured. The heat transfer data is correlated on the basis of; (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI); In the case of Darcian flow through sintered powder metals,; (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI); It is found that for transpiration cooling purpose, Darcian flow through sintered material suffices to achieve required cooling. Furthermore, it is recognized that the effective thermal conductivity as well as the internal heat transfer coefficient of the porous medium play an important role in determining the wall temperature and the wall thickness.