Investigation of a tube in tube conically coil heat exchanger thermal and fluid flow performance characteristics

Abstract The thermal and fluid flow characteristics of a tube in tube conical coiled heat exchanger ( TTCCHE) were experimentally conducted. This research tends to improve the thermal performance characteristics of a curved tube. The effects of different design parameters, including coil torsions, λ ; inclination angles, α ; the Dean number, Dn ; and flow arrangements for both the inner and annulus fluid sides were examined. Three test samples with different torsions, λ , values of 0.0352, 0.0713, and 0.1115 were designed, manufactured, and tested in both parallel and counterflow arrangments. Three different inclination angles, α , values of 0°, 45°, and 90° were also examined. The experimental runs were carried out in at from 2000 ≤ Dn i ≤ 10,833 (corresponding to 12,300 ≤ Re i ≤ 62,600) for the inner tube side and from 430 ≤ Dn o ≤ 3200 (corresponding to 2500 ≤ Re o ≤ 18,500) for the annulus. The results revealed that the TTCCHE coil torsion of λ = 0.0352 results in a significant increase in the Nu for both the inner and the annulus sides by 40.9% and 32.2%, respectively. The coil inclination angle of 90° has a noticeable influence on increasing Nu for both the inner and annulus fluid sides by 23.7% and 21.6%, respectively, compared with that of 45°. The maximum thermohydraulic performance criteria reach 1.45 and 2.26 for the inner tube and annulus sides at α = 90° and λ of 0.0352, respectively. New correlations to predict the Nu and f for both the inner tube and the annulus were presented.