EXPERIMENTAL INVESTIGATIONS ON HEAT TRANSFER ENHANCEMENT FOR HORIZONTAL HELICAL COIL HEAT EXCHANGER WITH DIFFERENT CURVATURE RATIOS USING CARBOXYMETHYL CELLULOSE-BASED NON-NEWTONIAN NANOFLUIDS
Prabhakar Zainith, Niraj Kumar Mishra
Abstract
In the present study, the heat transfer, friction factor, and thermal performance factor (TPF) of the coil side for a helical coil heat exchanger by using non-Newtonian nanofluids for various modified Dean numbers ranging from 10 to 300 with three different curvature ratios δ equal to 0.072, 0.083, and 0.098 were investigated experimentally. The two-step method was adopted for the preparation of non-Newtonian nanofluids. For the same, the carboxymethyl cellulose (CMC) in concentration of 0.4 wt.% was added to distilled water with three different nanoparticles, viz., CuO, Al2O3, and TiO2, for particle concentrations ranges from 0.01 vol.% to 0.04 vol.%. The present investigation reveals that with increasing particle concentration the Nusselt number increases for all the nanofluids, while with increase in the curvature ratio the heat transfer rate decreases. The maximum enhancement in the Nusselt number was found to be 31.8% for CuO-based nanofluids at 0.04% particle concentration for coil 1, while the least enhancement of 21% was reported for TiO2-based nanofluids for coil 3. Moreover, the friction factor was also increased when particle concentration increases. Therefore, the TPF was evaluated and it was found greater than unity for all combinations. The above conclusion ensures that losses by pressure do not overcome the enhanced value of the heat transfer rate. The maximum value of TPF was found to be 1.30 for CuO-based nanofluids at 0.04 vol.% particle concentration.