Experimental and numerical study of an innovative twined tube HX design

An innovative twined tube heat exchanger (HX) design is proposed, which is simple, robust, and efficient for use in advanced nuclear reactors. The heat exchanger is designed with two tubes twined around each other. Multiple modules can be assembled within a shell to meet the necessary heat load. Thermal-hydraulic investigations of the novel design are performed through experiments and numerical simulation. The experimental investigations of the twined tube HX are carried out on a laboratory-scale thermal-hydraulic rig commissioned at the Pakistan Institute of Engineering & Applied Sciences (PIEAS). The primary loop contains water at a high temperature and a pressure of 4.0 bar pressure, while the secondary loop operates at atmospheric pressure. Single-phase forced convection heat transfer characteristics of the twined tube HX are investigated experimentally. Pressure drop is measured for mass fluxes ranging from 350 kg/m2s to 1376 kg/m2s. A correlation for the estimation of friction factor is developed based on the experimental studies. Heat transfer measurements are carried out for mass fluxes ranging from 244 kg/m2s to 419 kg/m2s. Based on these experiments, the Nusselt number is evaluated for the mass flux range mentioned above. The numerical simulations of a twined tube HX are performed on a full-scale STAR-CCM + model. The model is validated against the experimental results. The performance factor of the twined tube HX is higher than that of straight tube HX, with a maximum performance enhancement of 60%. The thermal-hydraulic performance of the twined tube HX is comparable with helical coil HX designs. However, the proposed HX design is easier to fabricate and maintain than the helical coiled HX. Overall, the study provides valuable insights into the thermal-hydraulic performance of the twined tube HX, which could be useful in the design of compact and efficient heat exchangers for small modular reactors.