Enhanced cooling in compact helical tube cross-flow heat exchanger through higher area density and flow tortuosity

摘要

A novel configuration of compact cross-flow helical tube (CFHT) heat exchanger for cooling applications is proposed, in view of its inherent high surface area density and tortuous flow path. The cooling potential of such a configuration is assessed against that of its straight tube counterpart i.e., cross-flow straight tube (CFST) heat exchanger for similar volumetric air flow rates under laminar regime. Cross-flow experiments are conducted on CFST and CFHT unit systems for different helix angles ranging from 46° ≤ φ ≤ 72°. CFHT exhibits superior cooling potential, with a manifold increase in heat extracted per unit volume of heat exchanger, as high as 1.5-3.3 times, and heat exchanger efficiency as high as 70% (for φp = 72°). The comparative assessment is extended to an array of (3 × 3) tubes in an inline arrangement, through CFD analysis, for a wider range of helix angles from 17° ≤ φ ≤ 72°. Analysis reveals (ⅰ) flow intensification reflected in ~2.3 times increase in Re and (ⅱ) 3D flow that eliminates dead zones otherwise observed behind the straight tubes. The flow features result in 1.4-2.5 times increase in Nu, 2-4 times increase in the rate of heat extracted and higher heat exchanger efficiency upto 90%. Thereby, the efficacy of CFHT heat exchanger in cooling applications is established.