Environmental Engineering Reference
In-Depth Information
Figure 7: Core unit of a cross-current plate-fi n heat exchanger [17]: (A) air-fl ow
passage; (B) ethylene glycol aqueous solution channel; (a) the width of
the core unit; (b) height of the core unit; (c) thickness of the core unit.
4.1.3.1 Selection of the fi n unit and related dimension calculation
1.
Calculation of the heat transfer area of air side and liquid side.
Assuming that the density, thermal coeffi cient, constant-pressure specifi c heat
capacity and kinetic viscosity of air and ethylene glycol aqueous solution stay
constant in the heat transfer, their values are selected according to the inlet and
outlet mean temperature.
Calculation of heat transfer temperature difference and heat transfer coeffi cient .
2.
3.
Fin effi ciency and surface effi ciency of the air side and liquid side.
4.
Total heat transfer coeffi cient of the air side and liquid side.
5.
Checking and calculating heat exchanger thickness.
After obtaining the heat transfer coeffi cient and logarithmic mean temperature
difference of both air side and liquid side, the real transfer area and heat exchanger
thickness can be calculated. If the actual calculated thickness
c
real
of heat exchanger
does not equal the given
c
, the value of
c
should be reassumed and calculated following
steps (1)-(5) of the fl ow path until the calculated
c
real
equals the default
c
.
4.1.3.2 Calculation to other parameters of the heat exchanger
1.
Pressure loss on the liquid side.
In order to meet the technological requirement and the pump selection require-
ment, the resistance of the heat exchanger should be checked in the design
process. When the fl uid is in a pump circulation in the plate-fi n heat exchanger,
the resistance calculation can be divided into three parts, i.e. inlet tube, outlet
tube and central part of the heat exchanger [17].
Calculation of heat exchanger effi ciency and weight.
2.
4.1.3.3 Selection of the head plate for the plate-fi n heat exchanger
According to Liu
et al.
[19] and Zhou
et al.
[20], staggered perforated plate header
is selected in order to obtain well-proportioned fl ux distribution and well-controlled
fl uid friction loss.
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