The Flow Of Gases In Furnaces

354 APPENDIX X
in mind that the heat appliance which works successfully and
economically with one form of fuel may not be adapted in any
way to the use of another form of fuel, unless extensive alterations
are made. There are great differences, not only in the amount of
heat released by different fuels, but in the temperatures obtained
by the different fuels. For instance, Table 22 compares several
gases, arranged in the order of the temperatures obtained through
their combustion with the theoretical air supply. It is interesting
to note that blue water gas comes first with a thermal value of less
than one-third that of natural gas, which comes third in calorific
intensity. Another interesting fact is that with 80 per cent
excess air, natural gas and a good producer gas are very nearly
on par. This tabulation also shows the number of volumes of air
supply, products of combustion and combustible mixture. The
gas cannot burn unless it has an opportunity to combine with
oxygen and it is the thoroughness of the mixing which governs the
length of the flame and its temperature. With too long a flame
and without good mixing, the temperature realized may be very
much lower than the potential temperature of the gas.
The working base necessary for the computation of any of these
curves is a complete analysis of the fuel, either by weight or by
volume. When the proportions are given by weight, each unit
per cent is taken as 10 grams or 10 ounces and divided by the
molecular weight to obtain the molecular proportions. Volu-
metric values may be considered as gram molecules or ounce
molecules or as cubic feet or cubic meters. As the chemical
equation of any substance fixes the relative weights of the sub-
stances and the relative volume when in the gaseous state as
well as the amount of heat released or absorbed in a reaction,
basing the computations on the molecular composition simplifies
the work of computation by eliminating a number of clumsy
conversion factors.
A further advantage of using molecular units arises from the
following facts:
When the weight is in grams the volume is..........22.32 liters
When the weight is in kilograms the volume is.......22.32 rn3
When the weight is in ounces the volume is.........22.32 cu ft
Another short cut is the assumption that the air consists of
1 volume of oxygen and 4 volumes of nitrogen, making 5 volumes