Andy Wade wrote:


As the final answer to this sort of calculation is usually needed in kW
or kWh I find it useful to remember the heat capacity of water as 1.16
Wh per litre per degree. 1.2 Wh is near enough for most purposes.

Cool (or, more exactly, warm ;-) For litres/min we transform 1.2Wh to
72, well, 70 Wmins; which tells us that for a 30 degree rise we need
70x30 = 2.1kWmins, agreeing with the previous sketch.

The best aide-memoire I've come across (and therafter remembered!) for
such "cached" intermediate results is "pi seconds is a nanocentury" -
i.e. in a year there's 3.gubbins x 10e7 seconds. Useful when you're
roughing out 'X things/sec, how many X in a year?' or similar.

Then there was Grace Hopper's visual-aid-memoi in some of her talks
she handed out 'nanoseconds' - one-foot lengths of wire, for such is a
(useful approximation to) the speed of light/electrical-signal
propagation - the relatively small (10-20%) differences between speed of
light in a vacuum, and electrical signal in copper, don't matter much
for these rule-o-thumb mnemonix; and it's kinda instructive to realise
that as memory buses in ordinary PCs approach GHz speeds, the distance
on the motherboard from CPU to RAM is 'significant' - half a cycle or
more...

Stefek