THE AIR FLOW DEBATE
Davies, Craig weighs in on this hot topic
Davies, Craig says many a debate has been held relating to air flow in an engine’s cooling system and what is an adequate volume of air and what is not.
Radiators assist with heat transfer from the core to air via coolant flow to and from the engine and adequate air flow and coolant circulation are crucial to the radiator’s effectiveness and efficiency.
Scoops, lips, deflectors and recessed panels can be used to improve air flow when the frontal area of a vehicle is less than ideal. To function efficiently, the air stream on the front side of the radiator/needs to be higher than the air stream behind it.
The next issue is the fan. Engine-driven fans must have a circular shroud to be fully effective, says Davies, Craig, which states the blades should have no more than one inch in clearance to the shroud. Some mechanical fans can reach a blade stall at high RPM, causing a ‘wall’ which prevents air from passing through it. Davies, Craig says the installation of a temperature-controlled, radiator mounted electric fan in the majority of cases is far more efficient.
For this reason, consideration should be given to vehicle use for both low speed cruising and higher speed operation to ensure the effective channeling of air to the radiator while operating in both circumstances.
Nearly all modern-day vehicles have an electric, temperature-controlled fan as standard equipment at the rear of the radiator and all modern electric fans have a standard circular shroud to maximise efficiency.
Davies, Craig says you should pay attention the fan’s motor power (watts) and the published CFM (Cubic ft3/min) the specific fan produces; usually, the larger the electric fan, the higher the CFM. Davies, Craig publishes all the specifications and dimensions on its website: www.daviescraig.com.au
Some electric fans may be enclosed in a metal or nylon cowling (or shroud) which is designed to be rear radiator mounted only. At speeds of 60kmh or under, electric fans are most effective due to their total operating independence from engine revs.
With ram air intake driving above 60kmh, a fan is not as necessary, says Davies, Craig, which states the use of a cowling can be problematic as encompassing the entire rear radiator core can inhibit air flow at speed. If there is a build-up of air pressure in the fan cowling or engine compartment, air flow across the radiator can stall, causing higher engine temperatures.
For example, Davies, Craig notes an electric fan and cowling which covers the entire core should have “trap doors”, usually made of silicone, rubber or nylon installed to assist cooling efficiency. When cruising at low speed these trap doors will stay closed to prevent bypass while at speed, the doors will open to allow more air flow and prevent the cowling from damming the air.
Since the engine compartment must be able to maintain pressure differential as vehicle speed increases, many OEMs install air dams or other wind deflector devices to increase the pressure at the face of the radiator and block the air from passing under the car.
Davies, Craig says an electric fan’s operation is not ‘complete’ without an appropriate Digital Thermatic Switch, stating using either a Davies, Craig Thermatic Switch or LCD EWP/Fan Controller will activate the electric fan/s at set/targeted temperatures.
For more information, visit www.daviescraig.com.au