TECHNICAL
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The physics of solar water geysers
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Heat capacity can easily be understood using
the example of the beach and the sea. Early in
the morning the sand is relatively cool and in the
afternoon the sand may become very hot – but the
sea remained at the same temperature although
both were exposed to the same sunlight. The
answer lies in the heat capacities of water versus
sand. Much more energy is needed to heat up
water than sand.
The heat capacity of water is very important and
is the amount of heat it requires to raise the
temperature of 1mℓ of water with 1 degree Celsius:
cw = 4,186 Joules/gK.
Heat always flows from a warmer body to the
cooler body and this is called heat flow.
The heat transfer, Q is the measured solar energy
absorbed in terms of the increase in temperature of
the water: Qgain = Qloss, where Qloss is the sun
energy absorbed and Qgain is temperature rise of
the water.
The heat gained can be calculated by using the
simple heat flow equation: Q = mc∆T, where Q is
the heat flow and is measured in joules, m is the
mass of the water, c is the heat capacity of the
water and ∆T is change of the water temperature.
One Joule is equivalent to one Watt of power
radiated or dissipated per one second, so
1W = 1J/s. There are many practical examples in
nature, and one is one second of sunlight shining
on a 10 cm 2 piece of earth surface.
Images 1-4: Geysers undergoing testing.
"A self-sampled system may not be used
for certification purposes because there
is no traceability back to a batch that was
manufactured. "
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November 2019 Volume 25 I Number 9
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