Thermodynamic analysis of optimal mass flow rate for fully developed laminar forced convection in a helical coiled tube based on minimal entropy generation principle

The present paper analyzes the optimal mass flow rate for steady, laminar, fully developed, forced convection in a helical coiled tube with fixed size and constant wall heat flux by the thermodynamic second law based on the minimal entropy generation principle. Two working fluids, including air and water, are considered. The entropy generation analysis covers a coil curvature ratio (δ) range of 0.01-0.3, two dimensionless duty parameters related to fluid properties, wall heat flux and coiled tube size, α 1 range of 0.01-3.0 and α 2 range of 0.1 x 10-6-1.2 x 10-6. The optimal mass flow rate, denoted by a dimensionless parameter, β opt, for cases with various combinations of the design parameters is given in the present paper. In addition, a correlation equation for β opt as a function of α 1, α 2 and δ is proposed through a least square error analysis. For a thermal system composed of helical coiled tubes with fixed wall heat flux and tube size, the optimal mass flow rate β opt should be selected so that the system can have the least irreversibility and the best exergy utilization