Experimental work for the performance of a printed circuit heat exchanger (PCHE) using nitrogen under trans-critical states

Abstract

Experiments were carried out for the manufactured a printed circuit heat exchanger (PCHE) using nitrogen on the super-critical state. For the core of the PCHE, ‘N’ and reverse N, ‘RN’ shape microchannels were etched on stainless steel 316L plates, and total 120 plates were diffusion bonded. Then, for the PCHE evaluation in which the headers were welded, liquid nitrogen of below -170 °C and about 0.8 MPa was pressurized to about 3.42 ∼4.59 MPa, then was injected to the inlet on the cold side, and nitrogen gas of 72.7 ∼75.1 °C and about 0.6 ∼0.75 MPa was flowed through channels on the hot side. The flow rates were 2401 ∼3211 kg/h and 1592 ∼2357 kg/h on the hot and cold sides, respectively. In particular, the nitrogen on the cold side was pressurized by a pump, and state changes occurred over pseudo critical point. In order to evaluate performance of the PCHE with the super critical state nitrogen, the channels were simplified and discretized, then, effectiveness-number of transfer units (e-NTU) method was applied. Then, a new correlation expecting the thermal-hydraulic performance of PCHE was developed as Nu = 0.023Re0.78Pr0.4.