Numerical study on the thermal-hydraulic performance of a circular-arc-wavy helically coiled heat exchanger developed based on chaotic advection

A circle-arc-wavy helically coiled pipe heat exchanger (CAWC) was proposed and numerically studied. The CAWC is formed by dividing a conventional helically coiled heat exchanger into several (N-bend) segments uniformly and rotate each segment upward and downward alternatively around the chord of the arc with an angle phi. Water under atmosphere pressure was employed as the working fluid. The results showed that the local convective heat transfer coefficient was extremely sensitive to the inlet boundary conditions and showed stochastic characteristics. The mechanism of convective heat transfer enhancement induced by chaotic advection was analyzed using an improved field synergy analytical method. The results showed that the local and total convective heat transfer coefficients always coincided with the variation of the h' (rho uC(p)cos(theta);theta: synergy angle) field, suggesting that the enhancement of the h' field is the main reason for convective heat transfer enhancement induced by chaotic advection. Parameter analyses on the CAWC were conducted with N-bend = 4, 6, and 8; phi = 30 degrees, 60 degrees, 120 degrees, and 180 degrees; Re = 200, 400, 800, 1600 and 3200. It was found that under the same pumping power and heat exchanging area, the total convective heat coefficient of the CAWC can be increased by 40%, relative to the conventional coiled heat exchanger. (C) 2020 Elsevier Ltd. All rights reserved.