Jeff Davis writes:
You are only taking into account the insulation power of hair, of which I agree with you. You also need to take into account heat transfer. Dr. Russell does a better job of explaining it than I do
Probably off topic to take this too far, but Dr. Russell's analysis seems flawed. He models heat transfer as conductive from the air down the length of the dog's hair to the skin.
quote:
Okay, now a few facts. Most mammals attempt to keep their skin temperature at about 85 degrees F (29 deg C). The sun can heat the tip of a hair to more than 150 degrees F (66 deg C). Plug in those temps to the formula and you get (Ta - Ts) is (150 - 85) which is "65," a big number. Now, divide that number by the length of the hair (for metric-philes, just use cms).
Although the link does not give the doctor's complete formula, I don't think the doctor's analysis is correct. For most long haired dogs, much of the length of the dogs hair is exposed directly to the air, and for short hair dogs, much of the dog's skin and hair is exposed directly to the air. In either case the doctor's simplistic assumption that the rate of conductive heat transfer is proportional to hair length seems suspect. Even worse, a note in the article acknowledges that an essential constant relied on has never been measured for any dog.
Further, I don't see any treatment of convective heat transfer which has to be the primary method of heat transfer in most doggy situations. I suspect that hair is so close to non heat conductive that conduction is almost never a significant issue.
I wonder what subject Russell's PHD is in. I'm guessing something life science related rather than something like physics or engineering.
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