What is a Bomb- or Combustion
Calorimeter?
A Bomb-Calorimeter is used to measure the heat created by
a sample burned under an oxygen atmosphere in a closed vessel,
which is surrounded by water, under controlled conditions.
The
measurement result is called the Combustion-, Calorific-
or BTU-value. The BTU value is more common in the USA.The
result allows the user to make certain important quality,
physiological, physical and chemical as well as financial
conclusions and/or decisions on the product, for the company.
There
are many different types of Calorimeters available on the
market. You might have heard of Solution Calorimeter, Differential
Scanning Calorimeter (DSC), Titration Calorimeter, Gas Calorimeter
and Reaction Calorimeter for example.
IKA
manufactures so called “Bomb-“ or “Combustion
Calorimeter”. The term “Bomb” is misleading,
but it is the most commonly used description of this kind
of equipment. We will use the term “decomposition
vessel” instead of bomb in this Guidebook.
About
1g of solid or liquid matter is weighed into a crucible,
and placed inside a stainless steel container (the “Decomposition
vessel”) filled with 30 bar (435 PSI) of oxygen (Quality:
technical oxygen 99.98%). Than the sample is ignited through
a cotton thread connected to an ignition wire inside the
decomposition vessel and burned (combusted).
During
the combustion the core temperature in the crucible can
go up to 1000oC (1800 oF), and the pressure rises for milliseconds
to approximately 200 bar (2900 PSI). All organic matter
is burned under these conditions, and oxidized. Even inorganic
matter will be oxidized to some extend.
The heat created during the burning process can be determined
in different ways.
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A vessel filled with water (inner vessel) surrounds
the Decomposition vessel. |
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| The
heat created by the combustion process is transferred
into the surrounding water. |
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| To
ensure that the heat created during the combustion does
not get out of the system or heat gets into the system
from the environment (room temperature changes), another
water filled vessel (outer vessel) is used as an isolation. |
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Many
customers often ask for a specific kind of Calorimeter.
You will hear and read terms like “adiabatic”,
“isoperibol”, “isotherm”, “aneroid”
and “dynamic”.These
are different principles used to describe the working
principles of the Calorimeter in terms of the temperature
control between the inner- and outer vessel surrounding
the decomposition vessel.
I just want to focus on the most common measurement
principles “adiabatic”, “isoperibol”
and “dynamic IKA”. |
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| Isoperibol
Calorimeter |
In
the USA and Canada 95% of all customers prefer to work
with an isoperibol Calorimeter.
In
an isoperibol Calorimeter the temperature in the outer
vessel (Tov) is kept constant throughout the whole
experiment.
The
isolation by keeping the outer vessels temperature
constant does not allow creating a “perfect
isolation”. There are small temperature exchanges
between inner and outer vessel. The influence from
the environment (room) has to be kept small by using
air-condition to keep the error as little as possible.
A correction factor will be calculated after the experiment
that takes these temperature exchanges in account.
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| Adiabatic
Calorimeter |
This
Calorimeter measuring principle is used mainly in
Europe and South America.
In
an adiabatic Calorimeter the temperature in the outer
vessel (Tov) follows the temperature of the inner
vessel (Tiv) throughout the whole experiment.
The
isolation is as close to a “perfect isolation”
as possible. The influence from the environment (room)
has to be kept very small by using air-condition to
keep the error as little as possible. No correction
calculations need to be done like in the isoperibol
Calorimeter. |
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| Dynamic
IKA Calorimeter |
This
Calorimeter measuring procedure is not actually a
principle. It is more precisely described a measurement-mode
designed for customers that need to get results faster
than the official Standards allow.
The
dynamic modes are basically short versions of the
original adiabatic and/or isoperibol measuring principles.
The measurement results are still conforming to the
required precision of the official standards. |
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