Abstract

Heat Exchangers are one of the most important engineering systems with various applications like power plants, nuclear reactors, refrigeration and air conditioning, heat recovery systems, chemical processing and food industries. Basic advantage of helical Coil heat exchanger is its higher heat transfer with compact size, due to secondary flow generation in coil. One of the passive methods of heat transfer enhancement is used here, by changing the design of helical coil. Few investigators have introduced Critical Reynolds number to identify the transition from laminar to turbulent flow in helical coils which is given by Schmidts Co-relation. An attempt is made to change the curvature ratio continuously throughout the coil by using a conical shaped coil in order to decrease the critical Reynolds number. Then fabrication of both straight and conical coil heat exchangers is done for experimentation work. The mass flow rate range through coil is taken 0.01 kg/s,0.02 kg/s, 0.05 kg/s,0.07 kg/s,0.09 kg/s, 0.1 kg/s keeping mass flow rate through shell 0.05 kg/s constant also tube inlet and shell inlet temperatures maintained same 42ºC and 27 ºC respectively for all mass flow rate. This experimentation is done in parallel as well as in counter flow arrangement. Experimental results of conical coil are compared with straight helical coil. As mass flow rate through coil increases there is increment in shell outlet temperature by enhancement of heat transfer by 2.78%, average heat transfer and LMTD by 12%, heat transfer coefficient by 4%, overall heat transfer coefficient by 11% and decrement in friction factor and pressure drop by 40% in conical coil heat exchanger counter arrangement as compare to straight coil heat exchanger.

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