Improved Scaling Analysis for Heat Transfer in a Circular Tube With Various Supercritical Fluids Using Computational Fluid Dynamics Simulations

摘要

The operating conditions of supercritical water cooler reactor (SCWR) are well above the critical point of water, so it is not possible to investigate its heat transfer aspects through laboratory experiments without industry-scale support. The most feasible alternative can be to scale-down the operating parameters by fluid-to-fluid scaling with a suitably chosen scaling fluid. However, it is impossible to incorporate all phenomenological factors of an intricate system like the SCWR through simple analytical scaling. This study demonstrates the limitation of fluid-to-fluid scaling in such situations and suggests the incorporation of computational fluid dynamics simulation as a subsequent step for better scaling. A scaling methodology from the published literature is adopted. Carbon dioxide and R134a have been considered as scaling fluids to identify the parameter ranges suitable for lab-scale simulation of the SCWR. A circular tube of 8 mm diameter and 1500 mm length is taken for simulation. A grid dependency test is done and the standard k — ε turbulence model is selected. The developed computational model showed amicable agreement with existing experimental data. Analytically scaled-down parameters failed to simulate the axial and radial temperature profiles of the prototype. Increase in wall heat flux and reduction in mass flow rate are suggested as two possible options for achieving better profile matching. The modified values of scaled parameters with respect to a particular prototypical condition are reported. Profiles with CO_2 as model fluid show better agreement with water as compared to R134a and hence this is recommended for use in lab experiments.