Automotive Cooling System Design

[commonbrick]

Hi

I was wondering if some one could describe the technical benefits/differences between two automotive cooling systems. Additionally if there are specific names for these two systems I would be interested to know what they are.

The first system would be one consisting of a radiator and expansion bottle system where the expansion bottle is pressurized and has a radiator cap. Additionally this system has two hoses connected to the expansion bottle, one that allows the water pump to draw coolant from the expansion bottle and a small hose (5/16") that permits coolant to enter the expansion bottle from the top of the radiator. In this system the expansion bottle has air in it and is the highest point in the system. the system is also allowed to draw atmospheric air back into the system on cool down if needed.

The second system is a cooling system that consists of a radiator and two coolant bottles. One bottle is the expansion tank and the other bottle is an over flow tank. There is no air in this system and the radiator cap is on the expansion bottle. As the system pressurizes the radiator cap valve opens to permit coolant to enter the bottom of the over flow tank. Upon system cool down the vacuum valve on the radiator cap opens to allow the system to draw coolant back into the expansion bottle but, permits no air to be drawn into the system.

jonathan

 

[ivymike]

I think that the expansion tank variety allows a slightly higher pump inlet pressure for a given relief pressure, which helps to avoid pump cavitation. It is probably less prone to coolant spillage too, which would make it a better choice for marine / fire hazard applications.

 

[commonbrick]

InHiding could you eleborate on what might make the expansion tank set up have a slightly higher inlet pressure for a given relief pressure?

Also I have managed to come up with another question. Does any one know, or could you tell me where I could reference data on what volume or at what speed an automotive coolant system vents to the atomosphere when it over heats. My goal here is to properly size a "blow-off" valve on a system that I am currently working on. I have an existing 10mm threaded orifice and I am wondering if that is large enough to plumb a hight pressure blow off to, or whether I need to have a larger diameter orifice.

 

[ivymike]

Take a 15psi relief valve (radiator cap) for this example.

Case 1: Expansion tank feeds directly into pump inlet via large tube, tank pressure is 15psi (regulated by valve). Pump inlet pressure is close to 15psi.

Case 2: Relief valve is at the top of the radiator. Pump inlet is separated by the radiator, a tube or two, etc. There is significant flow restriction through the radiator, so pressure at the pump inlet is less than 15psi.