3.1 Specific heat of combustion Ho,n
The heating value of a material is measured using the following system:
The sample of natural gas is passed through a wet gas meter for measuring and humidifying before being burned.
The air for combustion is also humidified before combustion.
The air and natural gas are then mixed in the Junkers Calorimeter and burned.
The exhaust gas is passed through a cooling spiral in the calorimeter and cooled to ambient temperature. The heat produced during combustion is passed completely into the coolant. The water formed during combustion is also condensed and measured.
The following values are measured every 60 seconds for a period of 10 minutes:
The coolant is collected in a bucket during the test and weighed afterwards. The gas meter is read before the test and after 10 minutes. The quantity of condensate at the end of the test is also noted.
The First Law gives for Ho,n:
Partial pressure of water P s,H2O
Gas pressure Pg:
Converting the volume to STP using the ideal gas formulae:
Calculation of cpmw:
Specific heat of combustion:
The heating value is the specific heat of combustion less the specific heat of evaporation for the condensate.
This is the measurement of stated heating power and efficiency of a domestic gas boiler, together with the losses due to heat and chemical inefficiency.
The gas boiler used was a standard household boiler from Junkers/Wernau.
Gas and air pass into the unit and are burnt there. The flue gas passes out through a chimney.
Part of the water circulation system lies above the combustion chamber. This is kept in motion by a circulation pump, which is also part of the gas boiler.
The heat produced is sent to various heat consumers in the laboratory (radiators, heat exchangers).
The following values are recorded every minute for 10 minutes for calculation of heat output, efficiency and stack losses:
- Gas temperature ΘGas
- Water outlet temperature Θvl
- Water inlet temperature Θrl
- Ambient temperature Θa
- Flue gas temperature Θrg
- O2 level in flue gas ΨO2
- Gas gauge pressure Pgas
- Ambient pressure Pa
- Time Δt
The following meter readings are recorded at the beginning and end of the period:
- Gas ΔVgas
- Coolant Vkw
Flue gas temperature, ambient temperature and CO2 content are recorded with a flue gas analyser.
The heating power is calculated as follows:
ρ(Sw) and cpm values are taken from standard tables.
Hu,n taken from the calculation of heating value
The practical measurement and evaluation of combustion efficiency is described more fully on the linked page, and the calculations carried out by a combustion analyzer to determine stack loss, combustion efficiency and other combustion parameters are to be found in the section on calculations.
The value Hu,n for heating value was used in the calculation of heating power, taking over any errors.
The values for cpm are very close together due to the
slight rise of the curve at this point. This reduces the accuracy with which
they can be read. 
would be
larger if the coolant water could be reduced to room temperature. This would
also increase ΔΘ and hence reduce the effects
of inexact readings from the curve.
|
t [min]
|
Vgas [m³]
|
Θgas [°C]
|
Water column [mm]
|
Θluft [°C]
|
Θwein [°C]
|
Θwaus [°C]
|
mw [kg]
|
Θrgas [°C]
|
Vkondensat [ml]
|
p∞ [bar]
|
|
0
|
3.4295
|
19
|
35
|
11.5
|
10.6
|
25.8
|
0
|
15
|
0
|
|
|
1
|
|
19.5
|
35
|
11.4
|
10.6
|
25.8
|
|
15
|
|
|
|
2
|
|
19.5
|
35
|
11.4
|
10.6
|
25.8
|
|
15
|
|
|
|
3
|
|
19.5
|
35
|
11.3
|
10.6
|
25.8
|
|
15
|
|
|
|
4
|
|
19.5
|
35
|
11.3
|
10.6
|
25.8
|
|
15.1
|
|
|
|
5
|
|
19.5
|
35
|
11.2
|
10.6
|
25.8
|
8.26
|
15
|
|
|
|
6
|
|
20
|
35
|
11.3
|
10.6
|
25.8
|
|
15
|
|
|
|
7
|
|
20
|
35
|
11.2
|
10.6
|
25.8
|
|
15
|
|
|
|
8
|
|
20
|
35
|
11.3
|
10.6
|
25.8
|
|
15
|
|
|
|
9
|
|
20
|
35
|
11.4
|
10.6
|
25.8
|
|
15
|
|
|
|
10
|
4.45785
|
20
|
35
|
11.3
|
10.6
|
25.8
|
8.28
|
15
|
42
|
|
|
Average
|
|
19.682
|
35
|
11.327
|
10.6
|
25.8
|
|
15.009
|
|
1.0048
|
|
Total
|
0.028350
|
|
|
|
|
|
16.54
|
|
42
|
|
|
t [min]
|
Vgas [m³]
|
Θgas [°C]
|
Vkw [m³]
|
Θvl [°C]
|
Θrl [°C]
|
Θluft [°C]
|
Θrg [°C]
|
ΨO2 [vol%]
|
Pgas [ml]
|
p∞ [bar]
|
|
0
|
2518.9135
|
21
|
62.89
|
81.2
|
71.5
|
21
|
176.6
|
3.6
|
0.015
|
|
|
1
|
|
|
|
81.2
|
71.5
|
|
|
|
|
|
|
2
|
|
21.2
|
|
81.3
|
71.6
|
|
|
|
0.016
|
|
|
3
|
|
|
|
81.3
|
71.7
|
21.7
|
174.4
|
3.5
|
|
|
|
4
|
|
21.3
|
|
81.4
|
71.7
|
|
|
|
|
|
|
5
|
|
|
|
81.4
|
71.7
|
|
|
|
0.016
|
|
|
6
|
|
21.3
|
|
81.4
|
71.7
|
21.4
|
172.6
|
3.5
|
|
|
|
7
|
|
|
|
81.4
|
71.7
|
|
|
|
|
|
|
8
|
|
21.3
|
|
81.5
|
71.8
|
|
|
|
0.016
|
|
|
9
|
|
|
|
81.5
|
71.8
|
|
|
|
|
|
|
10
|
2519.284
|
21.3
|
63.151
|
81.5
|
71.8
|
21.3
|
172.5
|
3.5
|
0.016
|
|
|
Average
|
|
21.233
|
|
81.373
|
71.682
|
21.35
|
174.025
|
|
0.0158
|
1.0048
|
|
Total
|
0.3705
|
|
0.261
|
|
|
|
|
|
|
|
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