LAUSR

Abstract In this paper, the thermal performance of three different models includes novel torsion step-pitch step, three-bladed spiral tube-triple turbinate tube (TTT), and elliptical spiral tube-oval turbinate tube-elliptical helical tube (TOT) are investigated. Through comparing different turbulence models (RNG k-e, realizable k-e, RSM, standard k-ω, and SST k-ω) with the experimental value, the SST k-ω model with high precision is selected to estimate Nusselt number and friction coefficient in a triple spiral tube a uniform torsion step. In this model, the maximum error between numerical and experimental results are 2.7% and 4.7%, respectively. This comparison focused on the tube's thermal performance for heat exchangers; therefore, Nusselt number, pressure drop, and PEC number are considered as critical factors for analyses. The results show that the variable twist spiral tube dramatically enhances thermal performance compared to other cases. The study also confirmed that a constant pitch step in the helical tube has better performance than a variable pitch step.