CN104992048A - Fatigue life estimation method of air heat exchanger tube bundle - Google Patents

Abstract

The invention discloses a fatigue life estimation method of an air heat exchanger tube bundle, which belongs to the fatigue strength field, wherein the method specifically comprises that, step one, a three-dimensional finite element calculation model of an air heat exchanger is established; step two, velocity distribution and pressure distribution of shell-side fluid and the temperature distributions of a tube plate and the tube bundle are obtained through numerical calculation; step three, the result obtained at step two is used as a boundary condition and the boundary condition is applied to the three-dimensional finite element calculation model for performing coupling calculation, thus the stress distribution and the strain distribution of the air heat exchanger are obtained; the maximum equivalent plastic strain range Delta Lambda pmax at a dangerous part of the air heat exchanger tube bundle is obtained according to the strain distribution; and step four, the fatigue life of a sample material is firstly obtained and the service life of the air heat exchanger tube bundle can be obtained by multiplying the fatigue life of the sample material with a safety coefficient. According to the invention, by adopting the estimation method provided herein, the result is reliable; the logic is clear; the detection means and method are simple; and the fatigue life estimation method can also be used to estimate the service life of the air heat exchanger tube bundle.

Description

A kind of air heat exchanger tube bank estimating method for fatigue life

Technical field

The present invention relates to a kind of air heat exchanger tube bank estimating method for fatigue life, be specifically related to a kind of air heat exchanger tube bank estimating method for fatigue life calculated based on heat-fluid-wall interaction.Belong to fatigue strength field.

Background technology

Energy shortage problem has become countries in the world and has very paid close attention to and urgent problem of wishing to solve.For this reason, country 12 plan proposes energy-saving and emission-reduction strategy, economize energy is used as a real urgent task and implements.Heat interchanger is as the exchange heat core cell in high energy consumption national economy production field, and be widely used in the industries such as aviation, oil, chemical industry, electric power, food, the reliability of equipment work and the stability of heat transfer efficiency have great impact to commercial production.In heat interchanger operational process, the vibration of heat transfer element is caused to be called heat interchanger inner fluid induced vibration due to the flowing of heat exchanger media.This vibration can cause heat interchanger additional pressure losses, causes violent noise and the destruction of heat transfer element simultaneously.Heat interchanger causes the phenomenon of vibration to increase significantly because of fluid flowing, governs further developing of heat exchanger technology.

Because the tectonic stress of heat interchanger is complicated; condition of work is severe; weld defects is difficult to the reasons such as control; microfissure even cracking phenomena is often there will be in air heat exchanger tube bank; can cause heat interchanger partial failure even entirety scrap; bring huge economic loss to enterprise and country, this problem has certain ubiquity.

In order to solve the problem, need to adopt the tube bank of estimating method for fatigue life heat exchanger to carry out Fatigue Life Assessment, once there is fatigue crack in heat-exchanging tube bundle, the method can be adopted to assess fast and accurately its residual life, and then science decision is made to the production of follow-up heat interchanger, use and maintenance, this is for guaranteeing that the normal work of air heat exchanger is significant.

Summary of the invention

In view of this; a kind of air heat exchanger is the object of the present invention is to provide to restrain estimating method for fatigue life; described method assessment result is reliable, clear logic, detection means, method are simple; can assess the life-span of air heat exchanger tube bank; and then provide reference for the decision scheme of designer, guarantee the normal work of heat interchanger.

Object of the present invention is realized by following technical scheme:

A kind of air heat exchanger tube bank estimating method for fatigue life, step is as follows:

Step one, sets up air heat exchanger dimensional Finite Element model;

Be specially the three-dimensional model first setting up air heat exchanger, then stress and strain model is carried out to described three-dimensional model, obtain air heat exchanger dimensional Finite Element model;

Step 2, numerical evaluation

(1) numerical evaluation is carried out to air heat exchanger shell side flow field, obtain velocity distribution and the pressure distribution of shell-side fluid;

(2) Numerical Temperature calculating is carried out to air heat exchanger, obtain the Temperature Distribution of air heat exchanger tube sheet and tube bank.

Step 3, coupling calculates

Utilize finite element analysis software, velocity distribution step 2 obtained, pressure distribution, Temperature Distribution are applied in dimensional Finite Element model as boundary condition carries out coupling calculating, obtain heat interchanger stress distribution and Strain Distribution, obtain the maximum equivalent plastic strain ranges Δ ε of air heat exchanger tube bank dangerous position according to Strain Distribution _pmax.

Step 4, air heat exchanger tube bank Fatigue Life Assessment

${\mathrm{\Δ\ϵ}}_p\·{N_f}^a=C---\left(1\right)$

Life appraisal adopts the Strain Method in Manson-Coffin formula, and concrete formula is:

Wherein: Δ ε _pfor plastic strain ranges; N _ffor the fatigue lifetime of sample material; A, C are respectively material constant;

Taken the logarithm in above formula both sides and arrange:

${\mathrm{logN}}_f=\frac{1}{a}\left(\log C-{\mathrm{log\Δ\ϵ}}_p\right)---\left(2\right)$

After being found out taken the logarithm by above formula, plastic strain ranges Δ ε _pwith N fatigue lifetime _flinear;

The maximum equivalent plastic strain ranges Δ ε of the air heat exchanger tube bank that step 3 is calculated _pmaxbring in formula (2), obtain N fatigue lifetime of sample material _f, by N fatigue lifetime of sample material _fbe multiplied by safety coefficient and calculate air heat exchanger tube bundle life.

Beneficial effect

Method of the present invention, by first setting up air heat exchanger dimensional Finite Element model, calculates through numerical evaluation, coupling the fatigue lifetime obtaining sample material, then by N fatigue lifetime of sample material _fbe multiplied by safety coefficient and calculate air heat exchanger tube bundle life; assessment result is reliable, clear logic, detection means, method are simple; can assess the life-span of air heat exchanger tube bank, for the decision scheme of designer provides reference, guarantee the normal work of heat interchanger.

Embodiment

Below in conjunction with specific embodiment in detail the present invention is described in detail, but is not limited thereto.

A kind of air heat exchanger tube bank estimating method for fatigue life, step is as follows:

Step one, sets up air heat exchanger dimensional Finite Element model;

Air heat exchanger modeling: be specially the three-dimensional model first being set up air heat exchanger by drawing modeling software, then by CAE software, stress and strain model is carried out to described three-dimensional model, obtain air heat exchanger dimensional Finite Element model;

Step 2, numerical evaluation

(1) numerical evaluation is carried out to air heat exchanger shell side flow field, obtain velocity distribution and the pressure distribution of shell-side fluid;

Be specially: adopt the companied with k-s equation being applicable to large Reynold number turbulence state, obtain velocity field and the pressure field distribution in air heat exchanger shell side flow field:

$\mathrm{\κ}=\stackrel{\‾}{\frac{{u_i}^{\′}{u_i}^{\′}}{2}}=\frac{1}{2}(\stackrel{\‾}{u^{\′2}}+\stackrel{\‾}{v^{\′2}}+\stackrel{\‾}{w^{\′2}})$

$\mathrm{\ϵ}=\frac{\mathrm{\μ}}{\mathrm{\ρ}}\stackrel{\‾}{\left(\frac{\∂{u_i}^{\′}}{\∂x_{\mathrm{\κ}}}\right)\left(\frac{\∂{u_i}^{\′}}{\∂x_{\mathrm{\κ}}}\right)}$

In formula, k is tubulence energy, u _i' be time averaged velocity, u ', v ', w ' they are speed component, and ε is dissipative shock wave, and μ is turbulence viscosity, and ρ is fluid density, x _kfor direction vector.

(2) Numerical Temperature calculating is carried out to air heat exchanger, obtain the Temperature Distribution of air heat exchanger tube sheet and tube bank.

Step 3, coupling calculates

Utilize finite element analysis software, velocity distribution step 2 obtained, pressure distribution, Temperature Distribution are applied in dimensional Finite Element model as boundary condition carries out coupling calculating, obtain heat interchanger stress distribution and Strain Distribution, obtain the maximum equivalent plastic strain ranges Δ ε of air heat exchanger tube bank dangerous position according to Strain Distribution _pmax.

Step 4, air heat exchanger tube bank Fatigue Life Assessment

This lifetime estimation method adopts the Strain Method in Manson-Coffin formula, and concrete formula is:

${\mathrm{\Δ\ϵ}}_p-{N_f}^a=C$

Wherein: Δ ε _pfor plastic strain ranges; N _ffor the fatigue lifetime (sample is obtain according to GB/T26077-2010 standard) of sample material; A, C are respectively material constant, are generally measured by test.

Taken the logarithm in above formula both sides and arrange:

${\mathrm{logN}}_f=\frac{1}{a}(\log C-{\mathrm{log\Δ\ϵ}}_p)$

After taking the logarithm as can be seen from the above equation, plastic strain ranges Δ ε _pwith N fatigue lifetime _flinear.

According to the coupling result of calculation of step 3, obtain the maximum equivalent plastic strain ranges Δ ε of air heat exchanger tube bank _pmax, carry it in the equation of above-mentioned fatigue lifetime, obtain N fatigue lifetime of sample _f, according to the relevant regulations about fatigue design in mechanical design handbook, consider the factors such as structural stress is concentrated, surface condition, operating environment, get safety coefficient, by N fatigue lifetime of sample _fbe multiplied by safety coefficient and calculate air heat exchanger tube bundle life.

The present invention includes but be not limited to above embodiment, every any equivalent replacement of carrying out under the principle of spirit of the present invention or local improvement, all will be considered as within protection scope of the present invention.

Claims (2)

1. an air heat exchanger tube bank estimating method for fatigue life, it is characterized in that, described method step is as follows:

Step one, sets up air heat exchanger dimensional Finite Element model;

Be specially: the three-dimensional model first setting up air heat exchanger, then stress and strain model is carried out to described three-dimensional model, obtain air heat exchanger dimensional Finite Element model;

Step 2, numerical evaluation

(1) numerical evaluation is carried out to air heat exchanger shell side flow field, obtain velocity distribution and the pressure distribution of shell-side fluid;

(2) Numerical Temperature calculating is carried out to air heat exchanger, obtain the Temperature Distribution of air heat exchanger tube sheet and tube bank;

Step 3, coupling calculates

Velocity distribution step 2 obtained, pressure distribution, Temperature Distribution are applied in dimensional Finite Element model as boundary condition carries out coupling calculating, obtain heat interchanger stress distribution and Strain Distribution, obtain the maximum equivalent plastic strain ranges Δ ε of air heat exchanger tube bank dangerous position according to Strain Distribution _pmax;

Step 4, air heat exchanger tube bank Fatigue Life Assessment

Be specially: life appraisal adopts the Strain Method in Manson-Coffin formula, and concrete formula is:

Δε _p·N _f ^a＝C (1)

Wherein: Δ ε _pfor plastic strain ranges; N _ffor the fatigue lifetime of sample material; A, C are respectively material constant;

Taken the logarithm in above formula both sides and arrange:

${\mathrm{logN}}_f=\frac{1}{a}(\log C-{\mathrm{log\Δ\ϵ}}_p)---\left(2\right)$

After being found out taken the logarithm by above formula, plastic strain ranges Δ ε _pwith N fatigue lifetime _flinear;

The maximum equivalent plastic strain ranges Δ ε of the air heat exchanger tube bank that step 3 is calculated _pmaxbring in formula (2), obtain N fatigue lifetime of sample material _f, by N fatigue lifetime of sample material _fbe multiplied by safety coefficient and calculate air heat exchanger tube bundle life.

2. a kind of air heat exchanger tube bank estimating method for fatigue life according to claim 1, it is characterized in that, in described step 2 (1), numerical evaluation is carried out to air heat exchanger shell side flow field, obtain velocity distribution and the pressure distribution of shell-side fluid, concrete grammar is: adopt the companied with k-s equation being applicable to large Reynold number turbulence state, obtains velocity field and the pressure field distribution in air heat exchanger shell side flow field:

$\mathrm{\κ}=\stackrel{\‾}{\frac{u_i^{\′}{u}_i^{\′}}{2}}=\frac{1}{2}(\stackrel{\‾}{u^{\′2}}+\stackrel{\‾}{{\mathrm{\ν}}^{\′2}}+\stackrel{\‾}{w^{\′2}})$

$\mathrm{\ϵ}=\frac{\mathrm{\μ}}{\mathrm{\ρ}}\stackrel{\‾}{\left(\frac{\∂u_i^{\′}}{\∂x_{\mathrm{\κ}}}\right)\left(\frac{\∂u_i^{\′}}{\∂x_{\mathrm{\κ}}}\right)}$

In formula, k is tubulence energy, u _i' be time averaged velocity, u ', v ', w ' they are speed component, and ε is dissipative shock wave, and μ is turbulence viscosity, and ρ is fluid density, x _kfor direction vector.