IR temp thermometer

[ss]

Just got this delivered a cheap £9 one off ebay and having fun with it, already shown a few `weak spots` around the house but I have a question, probably obvious to those in the know but I dont understand the technical side of this.... In a bog standard house cavity wall insulation, double glazing. Does the cold external temp leak in to a house or does hot internal temp leak out? In other word which way does temperature dissapate from cold to hot or hot to cold or does it make any difference as it will diminish in any case.

[polygonum]

It's the pholigiston, I tell ye...

[Roger Mills]

You obviously need to study the Laws of Thermodynamics, as expounded by Flanders & Swann:

"The First Law of Thermodymamics: Heat is work and work is heat Heat is work and work is heat Very good! The Second Law of Thermodymamics: Heat cannot of itself pass from one body to a hotter body (scat music starts) Heat cannot of itself pass from one body to a hotter body Heat won't pass from a cooler to a hotter Heat won't pass from a cooler to a hotter You can try it if you like but you far better notter You can try it if you like but you far better notter 'Cos the cold in the cooler with get hotter as a ruler 'Cos the cold in the cooler with get hotter as a ruler 'Cos the hotter body's heat will pass to the cooler 'Cos the hotter body's heat will pass to the cooler"

[John Rumm]

The nett flow of heat is from hot to cold. The greater the temperature difference or the higher the thermal conductance of the wall the faster the flow.

Alas temperature is not a direct indication of heat flow. However you can generally assume that a well insulated wall will read a higher temperature on the heated side, and a lower one on the unheated side.

[Brian Gaff]

Not sure we really needed that though.. The next question is no doubt about moisture retention of different temperature air.

Brian

[Graham.]

When medical / industrial gas fitters are installing a vacuum line, do they think of the flow of the vacuum, as if it was the commodity, or air flow in the opposite direction?

[John Rumm]

Seems like they were not too well up on black body radiation or the theory of exchanges ;-)

[PeterC]

Nothing worth thinking about.

At work (Plessey) a chap in the lab designed a circuit based on electron flow - it worked, apparently.

[Roger Mills]

Maybe, but everything my wife knows about thermodynamics comes from F&S

- including their definition of "entropy"!

[Bob Minchin]

Ah! another ex plessey man on here. (Roke Manor 1974-2009)

[newshound]

Exactly. In the case of heat, it is just a (convenient) convention, the maths and temperature distribution for a "flow" of cold would be exactly the same. Doesn't Terry Pratchett have some sort of "source of dark" which works by hoovering up light?

[John Rumm]

I am sure there ought to be a Kenneth Williams joke there somewhere.... "entropy entropy, I am sure they have it..."

[John Rumm]

Much like any discipline where you use whatever works for the situation much as we use flow of negative charge in the reverse direction of conventional current. P type semiconductors using flow of (non moving) positive "holes" etc.

[The Natural Philosopher]

which are in themselves abstractions rather than 'real things'

[PeterC]

Caswell/Water Lane, Towcester, '67 - '89. Redundancy, so 'retired' :-))

[docholliday93]

I thought I recognised the name. (Southleigh 1979-1983, Roke Manor 1983-88 then Caswell...)

[ARW]

Best cat toy I have every owned:-)

--Adam

[Kevin]

Some of the more pedantic amongst us might even query the concept of heat flowing. The first head of the Engineering Science department at Durham, Russell Hoyle, made it very clear: temperature is a property; heat is an occurrence. Energy transfer can occur "by heat".

The analogy is perhaps money: it only does anything when being transferred. Energy is analogous to wealth.

Warning: I remember little enough about thermodynamics, and never did know anything about economics. But I do know "All the heat in the universe, is gonna cooool down - 'cos it can't increase. That's entropy, man". Or so F&S say.

[PeterC]

Used to have people asking me if I knew so-and-so. When I started there were

35,000 employees across 105 establishments! I did Caswell, Wood Lane and Water Lane and an odd week on Malta (shock to the system - week's cycle touring in Wales, in shorts, in October and 3 days later in 'hot' (cool to the natives) Malta.

[Bob Minchin]

G'day Mike! I also wondered when I saw Doc Holiday as your username. Happy memories of wine tastings at your place in Alma road. Incidentally the people who bought your house now live next door to me! Small world eh? Bob