Environmental Engineering Reference
In-Depth Information
Vacuum tube collectors consist of a series of glass tubes, each containing a second
light-absorbing tube. Between the two tubes is a vacuum, which allows light to pass
through but prevents heat from escaping. The inner tube, which is sealed, contains a
heat-transporting fluid similar to that used in the flat-plate collector (see
Figure 4.19
). The
main difference to the flat-plate collector is that the pressure in the inner tube is very
low. Pressure exerts a cohesive influence on all matter, so when it is absent or reduced,
molecular bonds break more easily. As a result, the fluid vaporizes at a lower temperature
than it would under normal atmospheric pressure, and travels upwards where the heat
is transferred to another fluid (usually water). This secondary fluid carries heat to the
house. This system is more efficient and considerably more complex and expensive than a
flat-plate collector, involving different tubes and fluids to capture and transport the heat.
Figure 4.19.
Mechanism by which a vacuum tube collector absorbs and transmits solar
energy.
