practical

1. Experimental Determination
of the Higher Calorific Value

2. Experimental Determination of the
Higher Calorific Value
The analytical method for determining the Higher
Calorific Value gives approximate results only.
The most satisfactory method for obtaining the
calorific value of the fuel is by actual experiment.
A known mass of the fuel is burnt into suitable
calorimeter, and the heat so evolved is found by
measuring the rise in temperature of the
surrounding water.

3. Experimental Determination of the
Higher Calorific Value
The calorimeters used for finding there calorific value
of the fuel is known as fuel calorimeter.
The following two calorific meters are important
from the subject point of view.
◦ Bomb Calorimeter
◦ Boys Calorimeter

4. Bomb Calorimeter

5. Bomb Calorimeter-Introduction
It is used for the higher
calorific value of the solid and
Non-Volatile liquid fuels.
In this calorimeter fuel is
burnt at a constant volume
and under a high pressure in a
closed vessel called bomb.

6. ◦ The bomb is made of acid resisting
stainless steel, machined from solid
metals, which is capable of
withstanding high pressures (up to
100 bar) heat and corrosion.
◦ The cover or the head of the bomb
carries the oxygen value for
admitting the oxygen and a release
value for the release of the exhaust
gases.

7. ◦ A cradle or carrier ring carried
by the ignition rod, supports
the silica crucible, which in
turn hold the sample of the
fuel under the test.
◦ There is an ignition wire of
platinum which dips into the
crucible.

8. ◦ The wire is connected to a
battery, kept outside and can
be sufficiently heated by
passing current through it so as
to ignite the fuel.
◦ The bomb is completely
immersed in a measured
quantity of the water.

9. ◦ The heat liberated by the
combustion of the fuel is
absorbed by this water, the
bomb and copper vessel.
◦ The rise in the temperature of
the water is measured by a
precise thermometer know as
Beckmann thermometer which
reads up to 0.01ºC

10. Bomb Calorimeter-Procedure
◦ A sample of the fuel which is
weighted carefully (usually one
gram or so on) is placed in the
crucible.
◦ About 10ml of distilled water
is introduced into the bomb to
absorb the sulfuric and nitric
acid formed during the
combustion

11. ◦ The pure oxygen is then
admitted through the oxygen
valve, till the pressure inside
the bomb rises to 30
atmospheres.
◦ The bomb is then completely
submerged in known quantity
of the water contained in large
copper vessel.

12. ◦ This vessel is placed into large insulated
copper vessel (not shown into figure) to
reduce the loss of heat by radiation.
◦ When the bomb and its content have
reached the steady temperature (this
temperature being noted), fuse wire is
heated up electrically.
◦ The fuel ignites and continues to burn
till whole of it is burnt.
◦ The heat released during combustion is
absorbed by the surrounding water and
apparatus itself.
◦ The rise in temperature of water is
noted

13. Let
mf = Mass of the fuel sample burnt
into the bomb in kg
H.C.V= Higher Calorific Value of the
fuel
sample in KJ/kg
mw = Mass of water filled in the
calorimeter in kg
me = Mass of water equivalent of
the apparatus in kg
t1 = Final temperature of the
water and apparatus in oC or
oK
t2 = Final temperature of the
water and apparatus in oC or
oK
Cw = Specific Heat of the water

14. We know that the heat liberated by the fuel
Heat liberated by the fuel=mf x H.C.V----------(1)
Heat received by water and calorimeter =(mw+me) x Cw x (t2 – t1)------(2)
Heat lost = Heat gained

15. To compensate the loss of heat by radiation (which can not be
totally eliminated), a cooling correction is added to observed
temperature rise. This corrected temperature rise is used in above
expression.
This calorimeter gives H.C.V of the fuel as any
steam formed is condensed and heat is
recovered as no escape to steam is available.

16. Example:
Calculate the higher calorific value of a coal sample from the following
data:
Data:
Mass of coal burnt = 1 g = 0.001kg
Quantity of water in calorimeter = 2.5 kg.
Increase in temperature of water = 2.6ºC.
Water equivalent of apparatus = 390 g = 0.390 kg
If the fuel used contains 6% of hydrogen, calculate its lower calorific
value. (Specific heat of water = 4.2 kJ/kg K