Numerical Study on the Effect of Diameter on Supercritical CO₂ Heat Transfer and Flow in Horizontal Tubes

In order to seek optimal heat transfer and flow characteristics of supercritical CO₂ flow in a tubular receiver characterized by high temperature, high operating pressure, and non-uniform heat flux, the heat transfer and flow characteristics of supercritical CO₂ flow in 5 tubes with different section shape were studied. The enhanced structures with excellent heat transfer and flow characteristics, heat receiving characteristic, lower and more uniform wall temperature were acquired. The results indicated that: 1) For the comprehensive criterion (j/f)(q'/q), ellipse section tubes are best. As K (ratio between long and short axes) increases, (j/f)(q'/q) increases first, and then decreases; 2) For the maximum wall temperature and wall temperature distribution uniformity, ellipse section C (K=2.5) tube is the best and becomes better as K increases.