Preface - kmutt

KMUTT Annual Research Abstracts 2005
Paisarn Naphon, Somchai Wongwises
Experimental Thermal and Fluid Science,
Vol. 29, No. 4, 2005, pp. 511-521
The heat transfer characteristics and the
performance of a spiral coil heat exchanger
under cooling and dehumidifying conditions are
investigated. The heat exchanger consists of a
steel shell and a spirally coiled tube unit. The
spiral-coil unit consists of six layers of
concentric spirally coiled tubes. Each tube is
fabricated by bending a 9.27 mm diameter
straight copper tube into a spiral-coil of five
turns. Air and water are used as working fluids.
The chilled water entering the outermost turn
flows along the spirally coiled tube, and flows
out at the innermost turn. The hot air enters the
heat exchanger at the center of the shell and
flows radially across spiral tubes to the
periphery. A mathematical model based on mass
and energy conservation is developed and solved
by using the Newton–Raphson iterative method
to determine the heat transfer characteristics.
The results obtained from the model are in
reasonable agreement with the present
experimental data. The effects of various inlet
conditions of working fluids flowing through the
spiral coil heat exchanger are discussed.
IJ-038 HEAT TRANSFER COEFFICIENTS
UNDER DRY- AND WET-SURFACE
CONDITIONS FOR A SPIRALLY COILED
FINNED TUBE HEAT EXCHANGER
Paisarn Naphon, Somchai Wongwises
International Communications in Heat and Mass
Transfer, Vol. 32, No. 3-4, February 2005,
pp. 371-385
In the present study, the average tubeside
and air-side heat transfer coefficients in a
spirally coiled finned tube heat exchanger
under dry- and wet-surface conditions are
experimentally investigated. The test section is a
spiral-coil heat exchanger, which consists of six
layers of concentric spirally coiled tube. Each
tube is fabricated by bending a 9.6-mm outside
diameter straight copper tube into a spiral coil of
four turns. Aluminium fins with thickness 0.6
mm and outside diameter 28.4 mm are placed
helically around the tube. The chilled water and
the hot air are used as working fluids. The test
runs are done at the air and water mass flow
rates ranging between 0.02 and 0.2 kg/s and
between 0.04 and 0.25 kg/s, respectively. The
15
inlet-air and -water temperatures are between 35
and 60 °C and between 10 and 35 °C,
respectively. The effects of the inlet conditions
of both working fluids flowing through the heat
exchanger on the heat transfer coefficients are
discussed. New correlations based on the data
gathered during this work for predicting the
tube-side and air-side heat transfer coefficients
for the spirally coiled finned tube heat exchanger
are proposed.
IJ-039 TWO-PHASE FLOW OF
REFRIGERANTS DURING EVAPORATION
UNDER CONSTANT HEAT FLUX IN
A HORIZONTAL TUBE
Wisis Sripattrapan, Somchai Wongwises
International Communications in Heat and Mass
Transfer, Vol. 32, No. 3-4, February 2005,
pp. 386-402
This paper presents the results of
simulations using a two-phase separated flow
model to study the heat transfer and flow
characteristics of refrigerants during evaporation
in a horizontal tube. A one-dimensional annular
flow model of the evaporation of refrigerants
under constant heat flux is developed. The basic
physical equations governing flow are
established from the conservation of mass,
energy and momentum. The model is validated
by comparing it with the experimental data
reported in literature. The present model can be
used to predict the variation of the temperature,
heat transfer coefficient and pressure drop of
various pure refrigerants flowing along a
horizontal tube. It is found that the refrigerant
temperature decreases along the tube
corresponding to the decreasing of its saturation
pressure. The liquid heat transfer coefficient
increases with the axial length due to the
reducing thickness of the liquid film. The
evaporation rate of liquid refrigerant tends to
decrease with increasing axial length, due to the
decreasing latent heat transfer through the
liquid–vapor interface. The developed model
can be considered as an effective tool for
evaporator design and can be used to
choose appropriate refrigerants under designed
conditions.
IJ-040 A TUBE-BY-TUBE REDUCTION
METHOD FOR SIMULTANEOUS HEAT AND
MASS TRANSFER CHARACTERISTICS FOR
PLAIN FIN-AND-TUBE HEAT EXCHANGERS
IN DEHUMIDIFYING CONDITIONS
International Journal