HEAT TRANSFER STUDIES IN AGITATED NON-NEWTONIAN SYSTEMS

Abstract

This thesis presents an experimental investigation for heat transfer for heated inner wall surface to agitated water and 0.5 % and 1 % CMC-Water solution. The agitation was caused by a turbine-type impeller. The vessel and the impeller geometry confirm closely to the standard geometrical configuration. Heating of the vessel wall surface was carried out electrically. Experiments were conducted at 180, 225, 305, 400 rpm impeller speed and 100,-125, 150 and 180 mm impeller submergence. The heater was energized at 2000 watts. Heat transfer coefficient was measured at eight different locations lying in a vertical plane on the vessel surface. Water was circulated as a coolant in the helical coil immersed in the liquid to maintain steady state condition. The flow rate of the water was reassured by calibrated rotameter. As a result of data analysis, the wall surface is found to be composed of two distinct regions — stagnation region and wall jet region. The stagnation region has been found just opposite to the impeller blade position in the liquid. Increasing in impeller speed has been found to increase heat transfer coefficient at a position on the wall surface. Similarly, impeller submergence has also been found to increase heat transfer coefficient at all the position of the wall surface. The local value of heat transfer coefficient has been obtain quantitatively in the following dimensionless correlations: iv For water, (a) Wall jet region 0.4 ( -0.36 Nu x = 1.6212(Re)o.55 (Pr)0.33(2-) D D This correlation holds true within an error of ± 35%. (b) Stagnation region Nu ss = 0.8966(Re)(165 (Pr)o.33 This equation is true within an error of ±10%. (5.1) (5.2) For CMC-water (a) Wall jet region Nu x = I .5593(Re)0." (P00.33 0.4 x -0.22 ) ( ) K -014 (5.5) (5.6) 3 an error of ±43%. The equation is valid within (b) Stagnation region. Nu ss = 3.0268(Re)° 6 (Pr)° 33 This correlation holds true within range of an error of ±40%. Average value of heat transfer coefficient has been obtained by the following equation -0.14 0.40 0.78 X. Jan 1.5593 0 Arux = (Re) •67 (Pr)0 33 K (—Kw ) ()SD) [(f)) + (1 – 0.78 (5.10) This equation has been obtained on the basis of negligible stagnation region developed over the wall surface.