Computational and Experimental Research of
Combustion Processes
Task 3: Local heat flux measurement
from membrane water wall
4th Flame Day 23.1.2008
Cumulus Koskikatu, Tampere
Timo Leino
VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Fuel blend
availability
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Fouling
and corrosion
Slagging
Bed agglomeration
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
The objective of the project
• The aim of the project is to find/develop heat
flux density measurement for furnace membrane
water wall
• To enable information from the heat flux density
profile the measurement method should be:
• Inexpensive
• Easy to install
• Possible to install non-destructively (old
plants)
• If a heat flux instrument is to measure the
absorbed heat correctly, it must resemble the
tube as closely as possible
However the sensor cannot be placed
• On the tube (erosion)
• In the pipe wall (weaker pressure durability)
• Inside the pipe (pressure loss)
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
The novelty values
• The novelty value of the measurement:
• Heat flux measurement gives information on the water wall heat load
More accurate heat transfer correlations
• The design of furnace improves with new measurement information
(dimensions, etc..)
• The parameters in the CFD-models can be enhanced
Better modeling results
• The novelty values for the existing boilers:
• The measurements give information on combustion profile
• Water wall slagging and boiler load on different locations of the boiler
can be obtained
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Tasks
1. Background information
• Literatury search on developed heat flux
measurements
Sensors, accuracy, installation, total cost
• Modelling work
Background information on heat transfer
phenomena in water wall
2. Measurement development / testing
• Possible further development of the measurement
method
• Testing
3. Researcher exchange
• 6 Month visit to the Budapest University of
Technology and Economics in Hungary
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Heat flux density measurements:
There are two broad categories of heat flux density measurements:
1. Direct measurements using nonperturbing heat flux density sensors
placed in the thermal field. The sensor can be mounted on the membrane
wall or in the head of a probe
Can have disturbing effect on flow fields and/or the temperature field in
the metal.
Expensive
Conductive type sensors
Thin membrane sensors
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Heat flux density measurements:
Radiative heat transfer
Radiative and convective
heat transfer
2. Indirect measurements made by calculating
heat transfer rates, using fundamental theories
together with measurements of temperature and
thermophysical properties,
Do not affect on temperature field
The results are as good as the
thermophysical properties and the
model from the case
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Modeling work
Objectives
• Obtain background information on
temperature distribution in water wall
How the temperature field changes in
different boundary conditions
How accurate should the temperature
measurement be
How small sensor is needed
Where the sensor/s should be placed
What kind of sensor fulfills the conditions
given for the measurement
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VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Future work: Measurement development and testing
In the previous studies the heat flux has been calculated among others with FEM/FVMmethods offline
There is a need for online calculation
Analytical model development
0.006
0.0055
0.005
0.0045
0.0035
0.003
0.0025
0.002
0.0015
0.001
0.0005
Evän pituus (m)
Fluent
Analytical model
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0.0085
0.008
0.0075
0.007
0.006
0.0065
0.0055
0.005
0.0045
0.004
0.003
0.0035
0.0025
0.002
0.0015
0.001
0
0.0005
0
Evän paksuus (m)
0.004
VTT TECHNICAL RESEARCH CENTRE OF FINLAND
Thank you
for your attention!
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