cooling design problem

[foza_11]

dear all
i have designed the radiator with about 20 KW ,and inlet water temp. 85 C ,water mass flow rate =0.15 kg/sec at idling for air side inlet temp. 40 C and mass flow 0.45 kg/sec this calculations estimate a core size about 354 X 330 mm .
if the engine raised to 60 KW max.power in this cause water mass flow rate increased so it will compansat the rise in Q as Q = m dot X cp X delta T SO, Q increased and m dot increased no problem in this cause .
for air side CFM of the fan is constant (the car is at rest ) and inlet air temp. is 4o C SO to compansate that increase in Q i should increase the air flow rate so it will increase to a value say 2 kg /sec ,the question here is can i have a fan with various CFM out put and how i can relate it's speed to the rpm of the engine ?
thanks in advance http://fsae.com/groupee_common/emoticons/icon_smile.gif
regards
mostafa shawky
CURT-2012

[foza_11]

dear all
i have designed the radiator with about 20 KW ,and inlet water temp. 85 C ,water mass flow rate =0.15 kg/sec at idling for air side inlet temp. 40 C and mass flow 0.45 kg/sec this calculations estimate a core size about 354 X 330 mm .
if the engine raised to 60 KW max.power in this cause water mass flow rate increased so it will compansat the rise in Q as Q = m dot X cp X delta T SO, Q increased and m dot increased no problem in this cause .
for air side CFM of the fan is constant (the car is at rest ) and inlet air temp. is 4o C SO to compansate that increase in Q i should increase the air flow rate so it will increase to a value say 2 kg /sec ,the question here is can i have a fan with various CFM out put and how i can relate it's speed to the rpm of the engine ?
thanks in advance http://fsae.com/groupee_common/emoticons/icon_smile.gif
regards
mostafa shawky
CURT-2012

[Jay Lawrence]

Mostafa,

There are a number of ways to alter the CFM of your fan (power signal modifications, vane alterations, ducting alterations, etc), which can be linked to a control system based on your engine RPM that your ECU is reading, but these (I believe) are impractical. Typically, you just want to have the fan come on when your engine reaches a certain temperature and then come off when it goes below a certain temperature.

Design your cooling system for maximum expected power output to be safe (or for average power used on track to be light). At UoW we use an electric water pump with PWM control, rather than trying to control the fan CFM.

I am not a sparky, so I can't really help any further.

[TMichaels]

Mostafa,
if you go for Jay's proposal to switch the fan on and off depending on your engine temperature (which is actually the most common way), make sure to add some hysteresis, otherwise your fan will "jitter" around the set point.
You may also go for PWM to control the CFM of the fan, but this is overcomplicating a simple problem in my opinion and usually less efficient as well.

[foza_11]

ok, the question here is that the max. load for cooling is 20 KW ( 1/3 HP of engine ) OR 60 KW (=HP of engine ).
for the second case i want fan with 1811 CFM which is unlogic .
thanks for your help