Method for creep-fatigue strength of plate-fin heat exchanger

Patent metadata

Field	Value
Publication number	US-10289772-B2
Application number	US-201715737008-A
Country	US
Kind code	B2
Filing date	Sep 15, 2017
Priority date	Nov 9, 2016
Publication date	May 14, 2019
Grant date	May 14, 2019

Abstract

A design method for creep-fatigue strength of a plate-fin heat exchanger. The method includes preliminarily designing the plate-fin heat exchanger according to its service requirements, making a primary stress assessment for the plate-fin heat exchanger, calculating the equivalent mechanical and thermophysical parameters of the plate-fin heat exchanger core to satisfy the allowable stress requirement, performing a thermal fatigue analysis for the plate-fin heat exchanger based on these parameters and then calculating the fatigue life and creep life of the plate-fin heat exchanger to accomplish the comprehensive design of the plate-fin heat exchanger in the high-temperature service. The design method provides an effective method for the high temperature design of the plate-fin heat exchanger.

First claim

What is claimed is:

1. A design method for creep fatigue strength of a plate-fin heat exchanger, wherein the method comprises the following steps:
Step 1: preliminarily designing a structure of the plate-fin heat exchanger according to its design temperature and design pressure requirements and defining operating temperature, number of operating cycles and service life of the plate-fin heat exchanger;
Step 2: making a primary stress analysis for the plate-fin structure with a finite element software to identify stress concentration parts and determining allowable stress S t ;
Step 3: judging whether a stress level of the stress concentration parts satisfies the following conditions:
P m ≤S t ;P L +P b ≤K t *S t ;
wherein, P m means primary membrane stress, P L means local membrane stress, P b means the primary bending, stress, S t means time-dependent allowable stress and K t assumes a value between 1.05 and 1.16;
if these conditions are satisfied, then performing Step 4; and if the primary stress is assessed unsatisfactory, chancing the structure and plate thickness of the plate-fin heat exchanger core and going back to Step 2;

Step 4: carrying out creep rupture experiment and fatigue experiment on the plate-fin structure and on an aged base material in service environment, calculating stress magnification factor K σ and strain magnification factor K s and correcting fatigue design curve and creep rupture design curve for the base material according to the calculated results of K σ and K s ;

K
σ

=

σ
B

B
B
*

,

K
s

=

Δ
s

Δ
s
*

,

wherein, and σ B mean σ* B rupture strength of the base material and plate-fin structure in a same creep rupture time respectively,
Δ t and Δ* t mean a macro-strain range of the base material and plate-fin structure in a same fatigue life respectively;

Step 5: acquiring equivalent mechanical parameters and equivalent thermophysical parameters of the plate-fin structure thus to perform a finite element analysis for thermal fatigue for the plate-fin heat exchanger, finding a time history of micro-stress σ* th of the plate-fin heat exchanger core in a height direction and calculating a total strain Δε at a fillet,
Δε=Δε ph +K s Δε* th ,

wherein, Δε ph means a strain range that is derived from a stress range Δσ ph obtained from the primary stress analysis;
Δε* th means a ratio of a difference between a maximum value and a minimum value of the macro stress σ* th obtained from the thermal fatigue analysis to an elastic modulus of the plate-fin heat exchanger core in the height direction;

Step 6: calculating fatigue damage D f and creep damage D c of the plate-fin heat exchanger core,

D
f

=

N
t

N
f

⁡

(

Δɛ
*

K
s

)

,

wherein, N t means a number of fatigue cycles,
N f (ε) means a corresponding fatigue life on the corrected fatigue design curve if the strain range is ε;

D
c

=

N
i

*

∫
0

t
h

⁢

dt

tr
⁡

[

σ
e
*

⁡

(
t
)

*

K
σ

]

,

wherein, N i means a number of fatigue cycles,
t h means strain retention time,
σ ε *(t) means macro stress at the moment, t,
tr(σ) means a corresponding creep rupture life on the corrected creep rupture design curve if the stress is a:

Step 7: if D f +D c is less than 1, design requirements for the plate-fin heat exchanger are satisfied and then performing Step 8: if D f +D c is greater than or equal to 1, then performing Step 1 exchanger;
Step 8: completing the design of the plate-fin heat exchanger, based on satisfying the design requirements.

2. The design method for creep fatigue strength of a plate-fin heat exchanger according to claim 1 , wherein, the allowable stress S t as described in Step 2 and Step 3 includes allowable stress S t1 of a fin area and allowable stress S t2 of a seal area.

3. The design method for creep fatigue strength of a plate-fin heat exchanger according to claim 1 , wherein, the step of acquiring the equivalent mechanical parameters and equivalent thermophysical parameters of the plate-fin heat exchanger core as described in Step 5 comprises the substeps of:
a. dividing the plate-fin heat exchanger core into multiple plate-fin cells of a same shape;
b. considering the plate-fin cells equivalent to uniform solid plates;
e. acquiring equivalent mechanical parameters and equivalent thermophysical parameters of one of the multiple plate-fin cells, thus obtaining equivalent mechanical parameters and equivalent thermophysical parameters of the whole plate-fin heat exchanger core.

4. The design method for creep fatigue strength of a pla

Assignees

• Univ China Petroleum East China

Inventors

• Jiang Wenchun
• Ge Lei
• Zhang Yucai
• Gong Jianming
• Tu Shandong
• Xie Xuefang

Classifications

• G06F2119/08

  Thermal analysis or thermal optimisation · CPC title

• G06F30/23 Primary

  using finite element methods [FEM] or finite difference methods [FDM] · CPC title

• F28F3/025

  the means being corrugated, plate-like elements · CPC title

• G06F30/367

  Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods · CPC title

• B21D53/02 Primary

  heat exchangers {or parts thereof}, e.g. radiators, condensers {fins, headers}(making finned or ribbed tubes by fixing strip material or the like to tubes B21C37/22) · CPC title