Page 303 - Mechanic Diesel - TT
P. 303
MECHANIC DIESEL - CITS
Preparation of heat balance sheet
Objectives: At the end of this lesson you shall be able to
• prepare of heat balance sheet.
Heat Balance Sheet
The heat generated inside the cylinder is not entirely used for external work. Some part of it goes into the cooling
system, some into the exhaust gas and some goes out through radiation. This reduces the thermal efficiency of
the engine. How much heat was generated in the cylinder, how much heat was spent in doing external work, how
much heat was lost, all these
The quantities are recorded in a table called heat balance sheet. To prepare the heat balance sheet of an engine,
it is run at a certain load and speed and from this the performance of the engine is known. To prepare heat
balance sheet the following items have to be known:
1 Heat supplied - Heat generated by burning of fuel = W x Q kJ/min Where, W = fuel supplied, kg/min Q = Lower
calorific value of fuel, kJ/kg
2 Heat converted to IP – = IP x 60 kJ
3 Heat Carried away by Cooling Water - = W (1-2) kJ W = Weight of cooling water, kg/min
Where,
11 = Temperature of cooling water at outlet, °C
12 = Temperature of cooling water at inlet, °C
4 Heat Carried away by Exhaust Gases -= W (T2-T1)= T8-Tambient [W (Tw2-T)] KJ Tg1-T82
This is determined from the exhaust gas calorimeter (Figure 6.7), in which
W = weight of water that flowed from the calorimeter, kg
12 = Water temperature at outlet, °C
T1 = water temperature at inlet, °C
T1 = temperature of exhaust gas at inlet, °C
T2 = temperature of exhaust gas at outlet, °C
Tambient = ambient temperature, °C
5 Heat Converted to BP = BP x 60 kJ
Heat to FP heat to IP-heat to BP
6 Unaccounted Heat – Add the values of formulas (1), (3) and (4). By subtracting these sums from the value
of (1), Agya heat is obtained.
The format of heat balance sheet is as follows.
S.No Item Heat Unit (KJ)
1 Heat supplied
2 Heat to IHP
3 Heat to cooling water
4 Heat to exhaust gases
5 Heat unaccounted (by
difference)
Total
290
CITS : Automotive - Mechanic Diesel - Lesson 87
