Experimental investigation of the effects of transverse vibration on the supercritical CO2 heat transfer characteristics in vertical tubes

Mechanical motion is unavoidably accompanied by vibration, which has an effect on fluid heat transfer. However, few investigations have been conducted on the effects of vibration on heat transfer characteristics of supercritical CO₂ (SCO₂). In this paper, effects of transverse vibration on heat transfer characteristics of SCO₂ during upward flow in a vertical tube (d = 4.57 mm, 20379≤Re≤88285) are studied experimentally. The results show that vibration achieves heat transfer enhancement. Specifically, with the increase of vibration amplitude and vibration frequency, the wall temperature decreases, the heat transfer coefficient increases, and the heat transfer enhancement efficiency (HTE) shows an upward trend. HTE of amplitude outweighs that of frequency over the test range, with an HTE of up to 32.70%. Heat transfer enhancement of vibration mainly acts in the region before mainstream enthalpy reaches pseudo-critical enthalpy. Based on pseudo-boiling theory, the reason for vibration-enhanced heat transfer is analyzed. Vibration weakens the thickness of gas-like film near the wall, thus accelerating heat transfer between the cold mainstream and the wall. A heat transfer correlation for vertical tubes under vibration is proposed based on 3822 experimental data points, which captures 94.2 % of the experimental data within ±30 % error.