Raypak whistling help

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Don’t have a flue! Inside my vent is smooth without any corrosion. Smooth.

I didn’t get that the condensate issue was in the flue! I thought it was the heat exchanger, and have been scratching my head for a couple months on how you could condensate on the heat exchanger that would cause corrosion. Now it all makes sense. Aha moment.

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PoolStored said:
I thought the air over the heat exchanger was 300F?
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That's average air temperature.

Not all exhaust air makes contact with the copper metal.

The air that makes direct contact will lose more heat than the air not making contact.

Think of the air moving through the channels as a fluid moving through a pipe.

The air making contact with the pipe/channel walls will have direct conduction and then the heat moves by conduction and convection through the air .

The smaller the diameter, the greater the ratio of circumference to area or total direct surface area contact to total volume.

This is why they try to make the channels as small as possible without restricting the flow of air too much.

Diameter = 1 mm.

Circumference/Area = 4.

Surface Area/Volume = 4 (Length cancels).

Diameter = 10 mm.

Circumference/Area = 0.4.

Surface Area/Volume = 0.4 (Length cancels).

The exhaust moves through the channels between the fins.

A 1 mm channel has 10 times more surface area contact than a 10 mm channel, but the resistance to airflow is also increased.

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Adding 332,000 BTU of heat to 1132 pounds of air will raise the temperature by approximately 1221.5°F.

So, the exhaust temperature will be about 1,300°F before it hits the heat exchanger.

The exhaust temperature past the heat exchanger is about 300°F, which is about 1,000°F drop.

The exhaust that makes contact with the copper might be about 150 degrees Fahrenheit and the exhaust that does not make contact might be at 450 degrees.

However, for a really cold heat exchanger, the exhaust temperature might drop below 132 Fahrenheit and then condensation can occur.

Past the heat exchanger, the air is mixing and homogenizing.

The temperature sensor will read an average temperature.

There are hundreds of tiny short channels that the exhaust moves through, so the exhaust is separated into hundreds of parts each with a temperature gradient from coldest to hottest.

By the time that the exhaust has exited the heater, the temperature difference between the hottest and coldest molecules might be pretty low.

If you have a super high resolution FLIR Camera, you can zoom in and see the temperature difference between the molecules of air.
 
PoolStored said:
You know, funny. Didn't connect the dots until just now. When I was by the heater when I first started it up, I thought "This thing puts off a lot of heat, I don't remember it being this hot." Now it makes sense.
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When the heater is running the heat has to go somewhere- either into the water or out the exhaust or the heater overheats and the safeties shut it down.

With the bad UG limiting the water flow through the heat exchanger more heat went up the exhaust. That is as designed to keep the exhaust warmer than normal when the heater thinks the water is cold.
 
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