US2020200490A1PendingUtilityA1
Method for Assessing Performance of Finned Tube Heat Exchanger under Non-uniform Face Velocity
Est. expiryDec 19, 2038(~12.4 yrs left)· nominal 20-yr term from priority
F28F 1/32F28D 1/053F28F 2200/00F28F 13/06F28F 1/42
45
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Claims
Abstract
A method for assessing and improving the performance of a finned tube heat exchanger under non-uniform face velocity is disclosed. First, a mathematical analysis method of the finned tube heat exchanger under the non-uniform face velocity is established. Second, a heat exchange amount and the heat resistance of the heat exchanger are obtained. Third, a quantitative relation between the non-uniform face velocity distribution and the performance of the finned tube heat exchanger are obtained. Finally, the heat exchange amount and the heat resistance of the heat exchanger are drawn in a rectangular plane coordinate system; and the coordinate system is partitioned in accordance with change rules of the curves, so that a performance assessment diagram of the finned tube heat exchanger under the non-uniform face velocity condition is obtained.
Claims
exact text as granted — not AI-modifiedWhat is claimed is:
1 . A method for assessing and improving the performance of a finned tube heat exchanger under non-uniform face velocity, wherein the method comprises:
1) determining a quantitative relation of face velocity non-uniformity to an air side average heat exchange coefficient of the finned tube heat exchanger;
(a) a quantitative relation between face velocity linear distribution and the air side average heat exchange coefficient of the finned tube heat exchanger is prescribed within an expression formula:
σ
=
Δ
h
h
uniform
=
1
6
m
(
1
-
m
)
ω
2
;
σ stands for a heat exchange coefficient loss factor, and Δh is change of the heat exchange coefficient of the heat exchanger caused by of face velocity non-uniformity, satisfying a formula:
Δ
h
=
h
uniform
-
h
nonuniform
=
t
(
t
+
1
)
(
2
t
+
1
)
6
n
m
(
1
-
m
)
k
Δ
u
2
u
a
m
-
2
;
wherein, h uniform form distribution and h nonuniform distribution are heat exchange coefficients of the heat exchanger under uniform air velocity and non-uniform air velocity; m is a coefficient in a relation of Nu: Nu=cRe m ; n stands for the quantity of heat exchange channels; and k is a constant;
ω is a defined dimensionless parameter velocity deviation factor, satisfying a relation:
ω
=
u
max
-
u
min
u
max
+
u
min
=
(
u
max
-
u
min
)
/
2
u
a
,
wherein u max , u min and u a respectively stand for the maximum value, the minimum value and an average value of the corresponding air velocity of a researched face side, satisfying relations:
Δ
u
=
(
u
max
-
u
min
)
/
n
,
u
a
=
(
u
max
+
u
min
)
/
2
,
n
=
2
t
+
1
and
n
2
-
1
n
1
≈
1
;
(b) a quantitative relation between face velocity arbitrary distribution and the air side average heat exchange coefficient of the finned tube heat exchanger is prescribed within an expression formula:
σ
=
Δ
h
h
uniform
=
1
-
∑
j
A
j
A
f
(
1
-
σ
j
)
ɛ
h
-
j
;
wherein, σ j , ω j and h uniform-j respectively stand for a heat exchange coefficient loss factor, a velocity deviation factor and a heat exchange factor corresponding to uniform velocity of the j<th> heat exchange unit (provided that the heat exchange units are in linear distribution);
ε h-j is a heat exchange coefficient discrete factor, satisfying a relation:
ɛ
h
-
j
=
h
uniform
-
j
h
uniform
=
(
u
a
-
j
u
a
)
m
;
2) determining a quantitative relation of the face velocity non-uniformity to heat exchange amount of the finned tube heat exchanger, prescribed within an expression formula:
η
=
Δ
Q
Q
uniform
=
1
-
∑
j
A
j
A
f
(
1
-
η
j
)
ɛ
Q
-
j
;
wherein, η is a heat exchange amount loss factor, satisfying a relation:
η
j
==
1
6
m
(
1
-
m
)
ω
j
2
,
ε Q-j stands for a heat exchange amount deviation factor, satisfying a relation:
ɛ
Q
-
j
=
Q
uniform
-
j
Q
uniform
-
cell
=
(
u
a
-
j
u
a
)
m
Δ
T
uniform
-
j
Δ
T
uniform
-
cell
;
Q uniform-j and ΔT uniform-j respectively stand for a heat exchange amount and a log mean temperature difference of the j<th> unit under a uniform velocity distribution condition; and Q uniform-cell and ΔT uniform-cell respectively stand for a heat exchange amount and a log mean temperature difference corresponding to each cell under uniform velocity after the heat exchanger is equally divided;
3) determining a quantitative relation of the face velocity non-uniformity to the heat resistance of the finned tube heat exchanger, prescribed within an expression formula:
ψ
=
R
nonuniform
R
uniform
=
1
+
(
1
1
-
η
-
1
)
T
in
T
uniform
;
wherein, Ψ stands for an increasing rate of the heat resistance; R uniform and R nonuniform respectively stand for air side heat resistance of the heat exchanger corresponding to uniform velocity and air side heat resistance of the heat exchanger corresponding to non-uniform velocity; and T in and T uniform respectively stand for air side inlet temperature of the heat exchanger and air side inlet/outlet arithmetic mean temperature under an average air velocity condition;
4) calculating relation formulas on the influence of the obtained face velocity non-uniformity on performance, namely the air side average heat exchange coefficient, the heat exchange amount and the heat resistance, of the finned tube heat exchanger, and reflecting the relation formulas in a rectangular plane coordinate system, wherein based upon results, it is indicated that the influence of the non-uniform face velocity on the performance of the heat exchanger is quite small within a certain velocity deviation range; the heat exchange performance of the heat exchanger, under the influence of the non-uniform face velocity, drops along with increase in velocity deviation; and the heat exchange performance of the heat exchanger drops exponentially when velocity deviation reaches a certain degree; and
5) dividing the coordinate system into three regions, namely a performance stable region, a performance degradation region and a performance serious degradation region based upon conclusion obtained in the step 4), so that a performance assessment diagram under the non-uniform face velocity of the finned tube heat exchanger is defined; and assessing influence of various face velocity distribution on the performance of the finned tube heat exchanger on the basis of the diagram.
2 . The method for assessing and improving the performance of the finned tube heat exchanger under non-uniform face velocity of claim 1 , wherein the rectangular plane coordinate system takes the velocity deviation factor ω as transverse coordinate, and the heat exchange coefficient loss factor σ, the heat exchange loss factor η and the heat resistance increasing rate Ψ as vertical coordinates.
3 . The method for assessing and improving the performance of the finned tube heat exchanger under non-uniform face velocity of claim 2 , wherein the influence of the face velocity non-uniformity on the performance of the heat exchanger is quite small when the velocity deviation is within 20-30%; the influence of the face velocity non-uniformity on the performance of the heat exchanger becomes obvious along with increase in velocity variation; and the performance of the heat exchanger is presented in exponential attenuation along with further increase in the velocity deviation.
4 . The method for assessing and improving the performance of the finned tube heat exchanger under non-uniform face velocity of claim 3 , wherein heat exchange performance of the entire heat exchanger under non-uniform velocity can be accurately assessed just depending on the performance of a single fin under various working conditions, so that related performance parameters of the heat exchanger under the non-uniform velocity can be obtained by calculating the performance of the heat exchanger under uniform velocity.
5 . The method for assessing and improving the performance of the finned tube heat exchanger under non-uniform face velocity of claim 4 , wherein the rationality of face velocity distribution can be inspected, so as to offer certain guiding suggestions for the velocity of the heat exchanger and the arrangement of internal parts, and to provide reference for the optimization of the shape of the heat exchanger.Join the waitlist — get patent alerts
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