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THE STRESS ANALYSIS OF A BUFFER AIR HEAT EXCHANGER YONGSHENG GEa, IGOR DOKLESTICb

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Title: THE STRESS ANALYSIS OF A BUFFER AIR HEAT EXCHANGER YONGSHENG GEa, IGOR DOKLESTICb


1
THE STRESS ANALYSIS OF A BUFFER AIR HEAT
EXCHANGER YONGSHENG GEa, IGOR DOKLESTICb
STEVE HUGHESa a Serck Aviation, Oscar House,
Wharfdale Road, Tyseley, Birmingham, B11 2DGb
Stirling Dynamics Ltd, 2 Tyndalls Park Road,
Clifton, Bristol, BS8 1PG
16th ABAQUS USER GROUP CONFERENCE UK-- 2002
2
Outlines
  • Introduction to Serck Aviation products
  • Certification requirements for the new product
  • FE modelling by Stirling Dynamics Ltd
  • The validation of the FE model
  • The Fatigue Life Prediction
  • Conclusions

3
Introduction
Traditional heat exchangers
4
Introduction
Newly developed heat exchangers
5
Introduction
Newly developed heat exchangers
Cold air outlet
Cold air inlet
Hot air inlet
Hot air outlet
6
Introduction
Newly developed heat exchangers
baffles
Tubes in matrix
7
Flight Certification Requirement
  • The flight certification requirement for this
    new product would have been meet by Pressure,
    Temperature and Flow (PTF) testing at a
    representative flight cycle for 80,000 cycles.
  • With the flight cycle compressed into 600
    seconds, the test duration would have been
    approximately two years, which was beyond the
    service introduction date and would have been
    very expensive.
  • The purpose of the PTF test is to demonstrate
    the ability of the design and construction to
    meet the fatigue life requirements. An
    alternative to the full scale PTF test was agreed
    that a fully calibrated FEA model can be used for
    the fatigue life predictions.

8
The Finite Element Model
Tube plate
Baffles
9
The Finite Element Model
Basic assumptions
  • It was assumed that geometry and loading of the
    heat exchanger are symmetrical therefore, only
    one half of the cooler was modelled.
  • Tubes and areas where the tubes are brazed into
    the tube sheet were not modelled.
  • Calculation of the stress concentration around
    the tube holes was not part of this analysis.
  • The tube matrix (tube plate) was modelled as a
    continuous plate. For this area effective
    material properties were defined to account for
    the reduction in conductivity, density and
    Youngs modulus.
  • Baffles were additionally modelled to stiffer
    the casing.

10
The Finite Element Model
Loading conditions
Thermal Thermal transient loading was applied to
the surfaces of the model via a film heat
transfer coefficient and fluid temperatures.
This loading was implemented with the user
subroutines FILM and DFLUX, specified in the
ABAQUS input file. Formulas and constants for
the heat transfer coefficients and temperatures
were supplied by SERCK Aviation. The FILM
subroutine was applied to all surfaces except the
top of the tube plate for which the equivalent
material properties were used. The DFLUX
subroutine was applied to the volume of elements
in the tube plate area with equivalent material
properties.
11
The Finite Element Model
Loading conditions
Pressure   Pressure transient loading was applied
to the internal surfaces of the model via the
DLOAD subroutine specified in the ABAQUS input
file. Pressure distribution was defined by SERCK
Aviation.
12
The Validation of the FE Model
Temperature data-match at steady-state points
13
The Validation of the FE Model
Temperature data-match of a simple transient
cycle
294 sec pressure dwell, Wh0.32pps max Wh0.09pps
min
225
Buffer Pressure (psi)
50
292 second temperature dwell
600
Buffer Temperature (deg.F)
200
0 2 6 8 300
315
Time (seconds)
Constant coolant air inlet temperature of 100
deg.F Wc0.52pps with 32psia inlet.
14
The Validation of the FE Model
Temperature data-match of a simple transient
cycle
15
The Validation of the FE Model
Temperature data-match of a simple transient
cycle
16
The Validation of the FE Model
Strain data-match of a simple transient cycle
17
The Fatigue Life Prediction
Fatigue life prediction using FE Safe, based on
the results from the validated FE model
18
Conclusions
  • Good temperature data match has been obtained
    for both steady-state and transient conditions.
    Reasonably good strain match is observed to give
    further confidence in the FE model.
  • The model is recognised by Serck Aviations
    customer for further fatigue life prediction. It
    is time and cost efficient to certificate the
    product by using FE model than by carrying out
    full test.
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