Thermal and hydraulic performance of a large scale printed circuit heat exchanger (PCHE)

Abstract

In present work, a printed circuit heat exchanger (PCHE), which was expected to be capable of heat exchange of 200 kW, was designed and manufactured, and its performance was evaluated by conducting experiments using nitrogen. Microchannels with a semi-circular cross section and a diameter of 2 mm were etched in the form of ‘N’ and ‘reverse N (RN)’ types on heat transfer plates made of STS316L and manufactured by diffusion bonding. Liquid nitrogen was vaporized and fed as gaseous state in hot side, and it was fed by pressurizing liquid nitrogen to the cold side. The mass flow rates were from 1531.8 to 2513.7 kg/h and from 407.2 to 980.5 kg/h in hot and cold side, respectively. The operating pressures were ranged from 0.51 MPa to 0.76 MPa and from 1.69 MPa to 9.38 MPa in hot and cold sides. Inlet temperature of nitrogen gas was ranged from 7.0 to 11.5 °C in hot side, and those of liquid nitrogen were from −165.9 to 178.3 °C. The phase change heat transfer coefficients of the cold side were calculated using the measured temperature and pressure values and compared with the existing correlation equations. The comparison showed a large discrepancy, so a new correlation equation, Nu = 0.09Reth0.79 Prv0.33(μ v/μ w)0.5, was developed and proposed. Also, through the measured pressure drop, the pressure coefficient, K value was calculated since the pressure drops appearing outside the main micro channel of the core is proportional to the square of the velocity, and it was confirmed that R2 = 0.99 when pressure coefficient, K was 15.7.