Experimental study of the influence of perforated circular-ring on pressure loss and heat transfer enhancement using sensitivity analysis

•Perforated circular rings are used in an air to water heat exchanger.•Friction factor rises with increase of pitch ratio.•Nusselt number is an increasing function of pitch ratio.•Thermal performance rises with increase of open area ratio.

Experimental analysis on pressure loss and heat transfer improvement in an air to water double pipe heat exchanger is presented. Typical circular-ring (TCR) and perforated circular-ring (PCR) turbulators, assumed as turbulators. Water and air move through inner and outer pipes, respectively. Experimental analysis is conducted for various values of open area ratio (0, 0.0208, 0.0416 and 0.0833), Reynolds number (6000, 8000, 10,000 and 12,000) and pitch ratio (1.83, 2.92 and 5.83). According to experimental data, correlations for Nusselt number, friction factor and thermal performance are presented as functions of Reynolds number, pitch ratio and open area ratio. Sensitivity analysis is used to find the effect of each active parameter. Results indicated that using PCRs leads to obtain lower heat transfer enhancement than the CRs. Thermal performance increases with increase of open area ratio but it reduces with rise of pitch ratio and Reynolds number. The most effective parameter for thermal performance is open area ratio.