Some studies on heat transfer in diverging-converging geometries

Abstract

Transport phenomena in diverging-converging geometries have created a lot of interest recently. The present paper highlights the specific advantages of diverging-converging geometries in the augmentation of heat transfer at the expense of a negligible increase in the pressure drop penalty.The work is confined to Newtonian, incompressible, and steady-state flow through the annular space between a diverging-converging tube and an outer straight column and also to heat transfer at constant wall temperature. The work also highlights the dependence of heat-transfer augmentation on the design parameters such as the angle of constriction and segment length.

Experimental studies on heat transfer with phase change on diverging‐converging surfaces

“…Though q decreases with increase in 8, hi increases with increase in 8. However, it has been reported by Narayanan and Bhattacharyya (1985, 1986, 1988 that if the angle of constriction is too large, the pressure drop in the system will also be substantially large. They have proposed a reasonable choice of 8 to be 5 " , at which the heat transfer coefficient is at an appreciable magnitude and the pressure drop is within reasonable limits.…”

“…However, it has been established that such diverging-converging systems provide excellent enhancement in heat transfer coefficient (300-400%) even at low Reynolds numbers (less than 1300) with relatively very little increase in the pressure drop (108-110%). The phenomena have been evidenced both for Newtonian (Narayanan and Bhattacharyya, 1985, 1986, 1988 and non-Newtonian (Gagan et al, 1985) flow, for constant wall heat flux (Narayanan and Bhattacharyya, 1986) as well as constant wall temperature Bhattacharyya, 1985, 1986) and also for heat transfer in falling liquid films (Narayanan, 1987). It was therefore of great interest to study the heat transfer with phase change in such geometries so as to analyse the enhancement that can be achieved t (Chakravarty, 1985).…”

“…The methods fall chiefly into three categories, namely (i) change of heat transfer surface geometry to increase the available area or to promote more rapid removal of condensate, such as using artificially roughened surfaces (Medwell and Nilcol, 1965) or employing finned tubes (Edwards et al, 1973;Fujii and Honda, 1978) or fluted surfaces (Lustanader et al, 1959;Nabavian and Bromley, 1963); (ii) incorporation of centrifugal forces (Sparrow and Hartnett, 1961), acoustic (Mathewson and Smith, 1963) or mechanical (Haughey, 1965) vibrations or an electrostatic field (Didkovsky and Bologa, 1981) in the flow field; (iii) use of surface coatings to promote dropwise condensation (Osmet and Tanner, 1962). Considerable work has been done to study heat transfer characteristics in diverging-converging system by Narayanan and Bhattacharyya (1985, 1986, 1988 and Gagan et al (1985), though most of the studies have been confined to liquid-liquid heat transfer and practically no significant work has been reported on condensation heat transfer in such geometrics. However, it has been established that such diverging-converging systems provide excellent enhancement in heat transfer coefficient (300-400%) even at low Reynolds numbers (less than 1300) with relatively very little increase in the pressure drop (108-110%).…”

Thermal stress analysis in annular duct resembling gas turbine transition piece

“…He indicated that initial swirl had significant effect on the flow reversal. Heat transfer rates due to the flow in diverging-converging shapes of metallic casings were investigated by Narayanan and Bhattacharyya [4]. They highlighted the importance of heat transfer augmentation on the design parameters such as the angle of constriction and segment length.…”