On 12/20/2010 06:43 AM, Ken Brown wrote:
>
>> To further prove my point, you have a black car and a white car out
>> in the sun on a hot day.
>> You know the black car is going to be hotter, but why is this when
>> black is apparently such a good radiator that it should just radiate
>> all that excess heat right out of that car, as quick as its absorbing
>> it?.
>>
> Radiant heat (which is essentially light, mostly at longer than
> visible wavelengths) travels from the higher temperature mass ( sun
> for instance ) to the lower temperature mass (car for instance) A flat
> black automobile will collect radiant heat from the sun more
> effectively than a shiny white car. When the sun goes down, you can
> take two cars heated up to the same temperature out under the cold
> (about 3 to 4 Kevin ) clear sky and the heat flow will be in the
> opposite direction than it was in the daytime. The flat black car will
> lose heat faster than the shiny white car.
>
> Black absorbs AND radiates heat more efficiently.
>
Ok try this idea in a perfect vacuum and see how you go regarding the
black car losing heat in the dark faster than the white car. If
radiation is the method of heat release then having no air/gas present
will not matter will it?
If your theory of radiation loss is correct then the black HWS solar
collector will be cooling down the water bigtime at night, as the glass
air pocket enclosure which keeps the trapped air temperature high as an
air insulator will not stop radiation loss, , but that's not the case,
but it slows convection heat loss bigtime.
Please place a piece of hot black material in a perfect vacuum and see
how long it takes to cool down via radiation loss.
Adrian ... vk4tux
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