buletinul institutului politehnic din iaşi - Universitatea Tehnică ...

154 Marius Receanu et al.
where: qr – the coolant flow rate in the radial loop, cl – the heat capacity of unit
coolant, Tri – the coolant temperature at the inlet of the radiator, Tre – the
coolant temperature at the outlet to the radiator.
According to Eq. (1) it results that the heat Qr of car-engine cooling
system can be modified through the coolant flow, qr or cooling air flow,
ΔT=Tri-Tre. A method for the cooling air flow control is the utilization of blind,
who obturates the radiator of car-engine for the ambient temperature < +5 ˚C.
2. Experiments Results
For two situation of the radiator the heat balances are:
a) is not obturated
b) is obturated
h l e r l
( ri re)
exh rest
Q C Q Q q c T T Q Q
= − + − + + ; (2)
( ri re)
Q C Q Q q c T T Q Q
' '
h l e r l
= − + − + + (3)
exh rest
where: Ch is the fuel mass flow, Ql – specific energy content.
The experiment was performed in the same conditions: the speed of
motor vehicle has (approximately) constant value and the segment of direction
is identically and it results: Qe=const. heat converted into mechanical energy,
Qexh=const. heat lost in exhaust gases, Qrest=const.
After the substraction of Eqs. (2) and (3) it results
' '
( Ch Ch) cl( T re T re)
Q q
− = − .
(4)
l r
Because the temperature T’re>Tre, when the radiator is obturated
'
Ch> Ch.
(5)
The fuel economy is evidently in the case b) when the radiator is partial
or total obturated. The Eq. (4) has valability when the radiator is partial or total
obturated and the process has practical validity when the ambient temperature is
Tamb