Heat used in raising the temperature of oven or furnace.
Heat used in raising the temperature of the containers carriers.
Heat conducted through the walls.
Escapement of heat due to opening the door.
In addition to heat required temperature of the charge to the required value, the above factors should be considered. The efficiency of the oven= (Heat required to raise the temperature of the charge to the required value / Heat required to raise the temperature of the charge to the required value + losses )
The heat required to raise the temperature of the charge to the required value, W = mass of charge in kg X specific heat of charge in J/kg 0C X temperature rise W = m X s X t Joules
The heat used for raising the temperature of the oven or furnace can be calculated in a similar way by knowing the weight of the refractory material and its specific heat.
In case the oven is used continuously, this loss becomes negligible.
Heat used for raising the temperature of container is calculated in exactly the same way as for the oven or furnace.
The container usually has to be heated up afresh for each charge.
Since, the heat is continuously conducted through the walls so this source of loss is most important.
It can be determined by knowing the mean value of the inside and outside surface areas A in square meters; the thickness of walls t in metre; inside and outside temperatures T1 and T2 in 0c and thermal conductivity of walls K in MJ per hour per square metre, per metre, from the following expression. Heat loss by conduction through walls : (KA/t)*(t3-t2) – MJ/hour
Though there is no specific formulae for determination of loss occurring due to opening of door for inspection of the charge. however. this loss may be taken as O.575 to 1.15 MJ/m2 of the door area if the door is opened for a period of 20 to 30 seconds.
The efficiency defined above lies between 60 and 80 percent.