Re: Radiator Flow ?

Posted by carla on April 20, 1998 at 14:47:03

In Reply to: Radiator Flow ?
posted by Bob Johnson on April 20, 1998 at 11:24:05

: While trying to figure out how to replace the tubes in a 1930-1931 Model A radiator I have discovered something interesting. After removing the core I decided to test it for water flow. I cleaned out one of the tubes until it was clear of all obstructions.I then formed a bowl on top of the core with clay. I centered the bowl over the tube that I had cleaned. I made sure that the tube that I had cleaned was the only one that was open in the bowl. Then I turned on the garden hose and ran water into the bowl and down through the tube. I turned up the water until the bowl was overflowing to be sure that the maximum water flow would go through the tube. Next I put a container under the core to collect the water running through the tube. The overflow water was directed away from the container. Here is the interesting part. The flow rate through the tube was about one gallon per miniute. Since there are 102 tube the flow through a clean core would be about 100 gallons per miniute.The accepted flow rate of a 'good' radiator should be 30 to 35 gallons per miniute. These two number do not agree. So what is going on here ?I checked the size of the tubes and the size of the opening at the bottom of the radiator. The tubes are hard to measure since they vary from one to another. But they are about 0.43" by 0.13". This computes to a cross section of 0.056 square inches. Since there are 102 of them the total cross section for all the tubes is aprox. 5.7 square inches. Now the outlet at the bottom of the radiator is about 1.5" in diameter. Thus it's cross section would be 1.77 square inches. (pi r squared you know). This is very interesting since the flow rate of the tubes is about 3 times higher than the flow rate of the radiator and the cross section of the tubes is about three times the cross section of the outlet at the bottom of the radiator.
: So what does this mean ? If you were to close up 67 of thetubes the remaining 35 would pass enough water to give you a flow rate of 35 gallons per miniute. In other words more than 2/3s of the tubes must be blocked before the flow rate of the radiator drops below 35 gallons per miniute.
: I think that a better test would be to fill the radiator up to the top of the tubes, drain it and see how much water it holds. If you subtract off the water from the bottom tank you would just have the water volume from the tubes. I calculate this number as about 0.55 gallons.

: So what do you guys think ?I was thinking of writing this up as an article for the Model A News or Restorer.

thats fascinating, bob,---and that might explain why some rads
would still cool properly with a number of leaking or damaged
tubes pinched off--has anyone ever researched cooling capacity
vs. flow rate??---for example, could a person try fitting
various sizes of restrictors in one of the hoses, and then
observing time-to temp, and stabilised running temp under
load?




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