Investigating the Effect of Geometry on Micro-Channel Heat Exchangers Using CFD Analysis

Micro-channel heat exchangers (MCHEs) are compact and robust heat exchangers with high surface area per unit volume facilitating closer temperature of approach. MCHE is conventionally fabricated using photochemical etching followed by diffusion bonding (PCED). Though PCED allows various flow path designs for improved heat exchange, it is not deployed for MCHE with cross sections other than semi-circular. Laser additive manufacturing (LAM) can overcome this limitation. The present study is focused on thermo-hydraulic simulation of LAM built MCHE with various cross sections. A 3D steady-state computational fluid dynamics (CFD)-based analysis is performed using CFD code ANSYS CFX to estimate the temperature, pressure drop and velocity distribution across the length of channel and variation of friction factor with Reynolds number. The working fluid is supercritical helium and material of construction of MCHE is Inconel 617 (IN 617). The temperature-dependent thermo-physical properties of helium and IN 617 are taken into account for the above simulation. To validate the simulation output, the results for conventionally fabricated PCHE are compared with that of previously published results and are found to be within 5%. The study of MCHE with cross sections other than semi-circular (i.e. square and circular) is also done using the same CFD code. From this numerical analysis, it is found that the heat transfer is maximum in square geometry while pressure drop, velocity across the channel and friction factor are the least for square geometry.