Increase in flow rate decrease in Outlet pressure.

trovilb1 · November 2, 2017, 10:01

I've run into an interesting problem with testing a heater core system for a vehicle. I instrumented the system(instrumentation included inlet/oulet pressure, thermo couples, and flow meters). There is only one fluid path in this heater core and no leaks were observed. As i increased fluid flow through the system the pressure differential did increase, but what confused me was the outlet pressure dropped. i would assume the outlet pressure would increase with the increase or stay constant. I can't seem to explain why it would decrease. They heater core was a double pass so it has a high restriction. I don't know if that could account for outlet pressure decreasing with an increase in flow rate. assume all instrumentation is operating correctly.

Ravindra Shende · December 5, 2017, 08:22

I know this is a late reply, but still....

Yes, you are right in thinking that the outlet pressure is decreasing because of the high restriction in the heater core.
This is because the pressure drop in a system is proportional to the square of the velocity.
So, as you increase the fluid flow, the velocity will increase linearly but the pressure drop will increase parabolically.

November 2, 2017, 10:01	Increase in flow rate decrease in Outlet pressure.	#1
trovilb1 New Member North Carolina Join Date: Nov 2017 Posts: 1 Rep Power: 0	I've run into an interesting problem with testing a heater core system for a vehicle. I instrumented the system(instrumentation included inlet/oulet pressure, thermo couples, and flow meters). There is only one fluid path in this heater core and no leaks were observed. As i increased fluid flow through the system the pressure differential did increase, but what confused me was the outlet pressure dropped. i would assume the outlet pressure would increase with the increase or stay constant. I can't seem to explain why it would decrease. They heater core was a double pass so it has a high restriction. I don't know if that could account for outlet pressure decreasing with an increase in flow rate. assume all instrumentation is operating correctly.

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December 5, 2017, 08:22		#2
Ravindra Shende Member Ravindra Shende Join Date: Feb 2011 Location: Pune, India Posts: 45 Rep Power: 15	I know this is a late reply, but still.... Yes, you are right in thinking that the outlet pressure is decreasing because of the high restriction in the heater core. This is because the pressure drop in a system is proportional to the square of the velocity. So, as you increase the fluid flow, the velocity will increase linearly but the pressure drop will increase parabolically.