Heat transfer enhancement in round tubes using three different tube inserts : non-Newtonian liquids

Experiments are described in which three types of turbulator are used: a copper wire coil in light contact with the tube, a stainless steel twisted strip and the Cal Gavin patent wire matrix insert. The liquids are solutions of sodium carboxymethylcellulose (SCMC) in water, which are pseudoplastic in character. Measurements of both heat transfer and pressure drop are made; the Prandtl and Reynolds number ranges covered are 30-90 and 20-2000 respectively. Heat transfer enhancement by factors up to four are obtained when using the wire matrix inserts; these are matched by copper coil insert data only at high Reynolds numbers. Overall, Cal Cavin inserts give the best heat transfer results. Twisted strip inserts increase heat transfer by factors up to 2.1. The relative increase in pressure drop caused by the turbulators is typically 20 for wire matrix inserts, 5 for the copper coil and 4 for the twisted strip. A form of effective viscosity first used by Oliver and Aldington is used in calculating Reynolds numbers for non-Newtonian liquids and the data for Cal Gavin inserts are shown to be in broad agreement with earlier data for Carbopol solutions