i'm Michael Crowley from Fluid Mechanics and in this video i'm going to tell you about our new
heat pump technology which we call the near isothermal sterling heat pump and this is our
prototype machine. Heat pumps move or pump heat from a cold space to a hot space and they're the
core part of any refrigeration or air conditioning system and they are very widely used. Today almost
all heat pumps use the vapor compression cycle as it is the most effective way to pump heat
however thermodynamically speaking the vapor compression cycle is only 40% efficient on cooling
compared to the Carnot efficiency and often is significantly lower than that particularly
when operating away from the design duty points or the design operating temperatures.
Our technology is based on an alternative cycle called the Stirling cycle
however we've modified the Stirling cycle to incorporate our near isothermal technology.
With this prototype machine we have demonstrated thermal efficiencies on cooling of 70% of Carnot
but in a practical machine I would expect that we would be able to achieve 60% efficiency. So
if the vapor compressor is 40% efficient and our technology is 60% efficient for a given input
power we can get an extra 50% of cooling. So for the consumer or end user they'll be able to reduce
their energy bill and CO2 emissions by a third. Normally when a gas is compressed it heats up
and it cools down when it's expanded this is called adiabatic compression and expansion.
In our heat pump we use our near isothermal technology to compress and expand the gas at
near isothermal conditions. Isothermal means at constant temperature and because we can compress
and expand the gas at near isothermal condition it means we can significantly improve the heat
pumps efficiency. So how does our isothermal technology work. Well inside the heat pump
we have pistons which go up and down and this is the type of piston that we have we have a simple
piston that goes up and down inside a cylinder and at the bottom of the piston we have attached
a series of fins collectively we call these the HARS which means heat absorbing and releasing
structure. Each of these fins is got a 2mm spacing the piston goes up and down inside
the cylinder so if you can imagine that being the cylinder inside the machine and in the bottom of
the cylinder we have a hydraulic fluid in this case it is water. Basically the piston
goes up and down and the gas there will be a seal between the cylinder and the piston and the gas is
compressed between the piston and the fluid in the bottom but as the gas is compressed and expanded
the gas is contained between those fins. Now if the gap between the fins is 2mm that means
that the distance the average distance a gas molecule is away from what any of the surfaces
is only 0.5mm so as the gas is compressed and it tries to heat up
the heat of compression is rapidly transferred into the fins conversely when the gas expands
as the gas tries to cool down heat is transferred back into the fins so by using that we can get
near isothermal compression expansion. Now this is a 16 bar pressure vessel
which is filled with helium gas and i've got a short video clip which shows you what's actually
happening inside the machine. This is the main working part of the machine. It is temporarily
sitting in a tub of silicon oil. Normally this oil is contained in the pressure vessel the oil
fills up the bottom half of the cylinders the oil is used to ensure near isothermal conditions
inside the cylinder and it's also used to transfer the heat to the external environment.
The prototype machine is quite large and fairly heavily instrumented but for a production machine
of say 10kW I would expect its size to be about a third of the size of this this machine. Up here
we have the drive motor in a production machine this would normally be inside the pressure vessel
but for the prototype that was going to be quite difficult because we've got electrical
cables feeding the motor and trying to get those through into the pressure housing was going to be
complicated. Also we've got torque transducers which is these electrical connections to it and
they were going to be quite difficult to put inside the pressure chamber we need the torque
transducer so that for the prototype we could actually measure how much power we're putting
into the thing which allows us to calculate its performance. This is quite heavily instrumented
we've got various tappings down here which are for pressure sampling so that we can measure
the pressure in each of the eight cylinders that make up this machine. We've also got
various temperature probes which again allow us to measure the temperature inside again all
of this is required so that we could actually work out what the performance of the machine
is. Can I please ask that you give me a like on YouTube click the link down here. That does help
us get the message out about the technology and so i'd like to thank you in advance for doing that.
I'm Michael Crowley from Fluid Mechanics and thank you very much for watching.