Volume 54

A comparative numerical study on heat transfer analysis between singlechannel- type large diameter heat exchanger with that of multi-channel-type small hydraulic diameter heat exchanger using Super-critical CO2 Samir Nanda, Sourav Mitra

Abstract

The supercritical carbon dioxide (s-CO2) Brayton cycle is one of the recommended power cycles for next generation high efficiency power plants. An additional benefit of using this working fluid is the miniaturised moving parts when compared to conventional Rankine or Brayton cycle. However, one of the challenges is the
miniaturised design of heat exchangers used in gas cooler, gas heater and regenerators. This can be achieved by reducing the hydraulic diameter of fluid flow channel. However, heat transfer coefficients for supercritical CO2 flow through such miniaturised channels are yet to be studied. In any heat exchanger, the decrease in hydraulic diameter of the channel leads to a higher heat transfer coefficient at the expense of higher pumping power. This study deals with the comparison of a large-diameter single-channel type (SCT) heat exchanger and a small hydraulic diameter multichannel type (MCT) heat exchanger using s-CO2. A numerical investigation is done on a tube-in-tube type heat exchanger, and the effect of mass flow rate and channel diameter at the given inlet temperature and pressure is depicted. At 3 different mass flow rates, such as 1 kg/hr, 3 kg/hr, and 4 kg/hr, the percentage enhancement in the rate of heat transfer for MCT is found to be higher w.r.t. SCT, by 33.4%, 30.34%, and 25%, respectively.

Keywords Brayton cycle, Heat Exchanger, Super-critical CO2