A typical minichannel evaporator used in AC&R applications
is made of stacked parallel aluminum extruded multiport
plates and louvered fins placed between them. In this configuration
cold refrigerant flows inside the ports, and hot air passes
though the louvered fins. Heat flux variation between neighboring
minichannels, in the direction from the leading to the trailing
edge, may be expected since warmer air enters the louvered fins
domain and its temperature is reduced at the outlet.
The possible nonuniformity of the heat flux from channel to
channel was studied numerically using ANSYS Fluent as a threedimensional
time-dependent heat transfer problem of louvered
fins bounded with multiport aluminum plates. While the fin geometry
was kept constant in all simulations, two different multiport
plate configurations (11 round ports, D= 1.2 mm; and 22
square ports, 0.54 0.54mm2) were analyzed at air face velocities
from 1 m/s to 5 m/s. The wall temperature of all channels was
set to be constant 10 oC, which corresponds to the typical saturation
temperature of refrigerants used in AC&R applications. The
incoming air flow temperature considered was 20 oC and 30 oC.
Results illustrate that both air velocity and temperature play
a profound role on heat flux variation from the leading to the
trailing edge of the multichannel plate. The heat flux varies drastically
in the case of the slower incoming air flow due to the
significant change in the driving potential along the air flow, and
it varies less at higher air velocities due to the heat transfer recovery
effect behind the turning louver along with the smaller
driving temperature difference between mixing cup and saturation
temperature. The overall heat flux difference between the
leading channel and the trailing one reaches almost 94% at free
stream air velocity 1 m/s and 69% at air velocity of 5 m/s.
This numerical modeling of the conjugate heat transfer problem
proves the presence of heat flux difference among channels
which was overlooked in the literature. Understanding of the
channel-to-channel heat flux variation is valuable for understanding
the flow boiling behavior in parallel non-uniformly heated
minichannels and the two-phase flow maldistribution.
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .