LAMINAR FLOW HEAT TRANSFER AUGMENTATION BY USING INSERTS

Abstract

Heat transfer augmentation techniques are used to increase rate of heat transfer without affecting much on
overall performance of system. This paper presents the result obtained from experimental investigation of heat transfer
and friction factor characteristics in horizontal tube by means of twisted tape inserts of various twist ratios with Non
Newtonian solution (0.2 wt . percent CMC solution) as working fluid. The experiments are conducted in Reynolds
number range 87 to 347 with twisted tape inserts of different twist ratio(y=H/D) in the range 6.11 to 7.77. The inner tube
is made of copper with inner and outer diameter 19.5x10-3m and 24.5x10-3m respectively. Twisted tape is made up of
stainless steel of 1 mm thickness and 1.9 m length. Hot and cold fluid flow though tube and shell side respectively Hot
fluid is Non Newtonian fluid & is used as a test fluid . The results obtained from twisted tape are compared with plain
tube results. The result obtained for Non Newtonian solution conforms that twisted tapes are more effective with Non
Newtonian solution than for water. For non-Newtonian solution heat transfer coefficient increases with decrease in twist
ratio. Maximum value of Nusselt number is obtained for twist ratio y = 6.11 which is 40% higher than plain tube and
friction factor increases by 56.86% than plain tube value. If we compare the experimental results for water and nonNewtonian solution, it is clear that, twisted tape inserts are more effective with Non-Newtonian solution than water as
working fluid. From performance ratio we can say that twisted tape performs effectively at low Reynolds number range.
Finally new generalized correlations function for predicting heat transfer and friction factor for laminar flow of Non
Newtonian solution are proposed with tape inserts.