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Heat Transfer 101....

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Posted by: BoaMorph at Mon Jun 19 19:21:43 2006   [ Email Message ] [ Show All Posts by BoaMorph ]  

Allow me to lay a little chemical engineering on you....

There are three mechanisms by which heat transfer can occur:

1. Conduction - heat can be conducted through solids, liquids and gases by the transfer of kinetic energy (energy of motion) between adjacent molecules,

2. Convection - the transfer of heat due to bulk transport and mixing of macroscopic elements of liquid or gas; in other words, heat transfer related to motion of a fluid and thus partially governed by the laws of fluid mechanics, and

3. Radiation - energy transfer by electromagnetic radiation, or photons, having a certain range of wavelengths largely within the infrared part of the spectrum; electromagnetic radiation produces heat when absorbed.

It is radiation which conventional wisdom suggests is more strongly absorbed by darker-colored objects, though it actually is much more strongly dependent upon how reflective the surface is. Radiation can be transmitted, absorbed, or reflected. Opaque objects (such as a boa) do not transmit radiation, and so all of the radiation incident on an opaque object is either reflected or absorbed. Thus, the more reflective the surface of the object, the less radiant energy it absorbs. A darker object may be more absorptive than a lighter-colored one, but it is interesting to note that the absorptivities published for black lacquer and white lacquer are identical over the same temperature range. It is also interesting to note that the same qualities that make a surface/object a good absorber also make it a good emitter. Is it possible that the conventional wisdom is incorrect, and that there is another evolutionary reason that gravid boas darken?

Also of note is the fact that a boa in a cage typically receives heat primarily by conduction; for example, from heat tape attached to the cage bottom through the cage bottom to the boa, heat tape in direct contact with cage bottom in direct contact with boa - and color has zero effect on conduction. The exception here would be the use of a radiant heat panel; nevertheless, such panels also heat the cage material and surroundings such that even if albino boas are "electromagnetic radiation absorption-challenged," the boa would easily be able to maintain the desired temperature.

Most relevant is a principle called Kirchhoff's law, which states (in part) that in a system at thermal equilibrium, all bodies will have the same temperature. This means that if you provide an area of the cage that is 90F, and your boa camps out in that spot, it's body temperature will reach 90F, regardless of color, albinism, planet of origin, or anything else.

Too much science - what's the point? The point is that an albino boa provided with an appropriate hot spot in the cage will have no more trouble maintaining it's desired body temperature than a normally colored boa, and so I don't buy the theory that because of lower heat retention baby albino boas are often born undercooked despite a full-length gestation term. Our friend Kirchhoff tells us boa breeders that as long as we provide appropriate temperatures in our enclosures, our albino or any other colored boas will be able to reach and maintain those temperatures.

My understanding of the historical problems with female albino boas as breeders is that many of them were producing deformed offspring, throwing slugs, and/or dropping litters early. Breeders appear to have attributed these problems largely to "inbreeding-related genetic weakness," though as far as I know this is based solely on conjecture. As with most such issues in our hobby there is not much real science behind it, and in the end, an informed guess is still only a guess.

I do agree that the reputable breeders have done a better job outcrossing albinos to diversify bloodlines - including crossing albino Bci with various locality Bcc, and even some argentines. Even so, I wouldn't figure on purchasing a pair of albino littermates and breeding them to each other....

Steve Reiners


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>> Next Message:  The description relates well to me... - ChrisGilbert, Mon Jun 19 21:21:17 2006
>> Next Message:  Very very good explanation..... - robertmcphee, Tue Jun 20 07:00:16 2006

<< Previous Message:  Well... - ChrisGilbert, Mon Jun 19 15:15:46 2006