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re: mills, etc (was heating with wood)
19 sep 2005
christina peterson  wrote:

>"ed earl ross"  wrote:

>> >  wrote...

>> >>>the description pete uses to describe the way our house conserves
>> >>>temperature (it's cooler in summer too, though by fall the logs are
>> >>>thoroughly warm) is "heat sink".  what you are calling thermal mass.
>> >>
>> >>to me, a heat sink is a gadget with fins that clips onto an ic or some
>> >>other power electronic device to dissipate heat with no heat storage,
>> >>vs thermal mass, which stores heat with no dissipation. a car radiator
>> >>is a heat sink, altho it also stores some heat in the coolant...

>> though nick's definition is commonly used, it is not technically correct.

a sentence beginning "to me" cannot be incorrect :-)
to most engineers, a heat sink dissipates energy.

>> a heat source emits heat and a heat sink absorbs heat.

a stiff voltage source, in a thermodynamic context. do we "absorb" via
storage or dissipation? this thermodynamic definition implies storage
in an infinite lake.

>so the logs in my house are a heat sink when they absorb heat (from the sun
>in summer, from the fire in winter), and a heat source at other times.  and
>can be both when there are fluctuations in temperature.  also walls are a
>heat sink inside the house and a heat source outside in winter.  just like
>rocks absorb heat from the sun, and are later warm under foot.

that's an accurate energy flow description, but i wouldn't use the words
"heat sink" in this case. what matters is the nature of energy flow, vs
the nomenclature.
>so what is the difference between "heat sink" and "thermal mass"?

heat sinks dissipate energy and thermal masses store and release energy,
like resistors and capacitors, from an engineer's point of view. people
who understand physics talk about heat sources and sinks differently,
eg in a carnot context, but they agree on the basic energy flows.


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