Dear Crispin, Stovers,
If I understand the problem, and with what I know about turbidity vs
weight for soil samples I am not surprised. I think the tests for soil
(silt-clay) can also be used for dust particles.
Turbidity is a measure of light reflecting off the sides of particles
and measured. The problem is if you have a cubic centimeter of particle
that weights one gram you have light reflecting off 6 one centimeter
surfaces. Cut that in half and you have 8 one centimeter surfaces
reflecting light- More light-Same weight! Cut again to make smaller
particles and you see the problem. Lots of light reflection with the
same weight particle.
In Silt-Clay: To measure the percentages of different fractions from
silt to clay (0.35um to 0.001 um) using reflecting light we mix a weight
of soil screened < 0.35um in a 15 cm high test tube with water. We add
detergent and sonicate to disperse the particles. We determine the
turbidity 10 cm down from the top and plot the decrease vs time as the
large heavy particles fall faster than the small ones. Based on the
first reflected reading after mixing as 100%, we can determine the
percent of each sub-fraction by time and decrease in reflected light. We
normalize the reflected light reading by assuming the particles all
being spheres and the change in surface (reflected) area as the particle
diameter decreases.
To do the same with stove emissions we need to know the total weight of
particles in a volume of gas. Done by weighing a filter paper before and
after. Then quickly pump some emission gas into a tank, stop all air
movement (seal the container) and measure the decreasing reflected light
as the particles fall over time. Assume all particles being the same
density (density determined using acetone method) and having the same
shape (sphere) and knowing the rate that weight falls in air, we can
come up with the diameter of particles passing through the light for
each time span. Could take a long time for the very small particles.
Convert the reflected light (normalize) to the diameter of the particle
so the weight is the same as if a gram of particle made of one chunk is
equal to that gram particle broken up into a million particles
reflecting a lot more light.
We need to know the grams/cc of the particles in the emissions gas.
We need to know the rate it falls in air.
We need to assume they are all the same shape being cube or sphere.
Not a fast flow-through procedure.
Thanks
Frank
.
Crispin Pemberton-Pigott wrote:
Dear Friends
Via Robert van der Plas..
In section 7 it says that others (for example Ryde and Johansson, 2007)
found condensable particle mass (which are picked up using a diluter) to
exceed solid particle mass by as much as 10:1. It kinda speaks against the
worthiness of running biomass stove tests using 'hot' dry dust measurements.
Regards
Crispin
http://www.ieabcc.nl/publications/Nussbaumer_et_al_IEA_Report_PM10_Jan_2008.
pdf
"For existing stoves and
boilers, ideal operation is regarded as a major target to reduce PM
emissions. Furthermore, the method
of ignition is important for the PM emissions of wood stoves and boilers.
For typical wood stoves,
ignition from the top of the batch of wood logs instead of ignition from the
bottom can often avoid
visible smoke during start-up and reduce the total PM emissions by more than
50%. For log wood
boilers, beside optimised ignition and start-up, the implementation of a
heat storage tank is essential,
as thanks to a heat storage, part-load operation related to high PM
emissions can be avoided. With
respect to the measurement of PM emissions, the mass on solid particles in
the hot flue gas (as
collected on filters) and the additional mass of condensables need to be
distinguished. Under poor
combustion conditions, the mass of condensables can exceed the mass of solid
particles and hence
should be considered in future immission inventories.
------------------------------------------------------------------------
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--
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA 95076
(831) 724-5422 tel
(831) 724-3188 fax
[email protected]
www.compostlab.com
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