The effect of geometry parameters on the heat transfer performance of supercritical CO2 in horizontal helically coiled tube under the cooling condition

摘要

Experimentally and numerically studied the heat transfer performance of supercritical CO2 (S -CO2) cooled in small (d <= 4 mm) horizontal helically coiled tube (HCT). Five HCTs with fixed coil pitch b = 34 mm, coil diameters D ranging from 36-140 mm and tube diameters d ranging from 2 to 4 mm were used. The results showed that the heat transfer coefficient (HTC) has tripled as the tube diameter decreases from 4 to 2 mm. HTC increases up to 30% with the coil diameter decreasing from 140 to 36 mm. Based on the modified theory derived from the straight tube (ST) with upward flow, the onset value of buoyancy effect in horizontal HCT was obtained, which confirmed that the buoyancy in the present experimental study can be neglected. Totally, 33 test runs and 426 points were performed, and from which a new correlation was proposed to evaluate the HTC of S-CO2 in the horizontal HCT under cooling condition. (C) 2019 Elsevier Ltd and IIR. All rights reserved.