 The first more industrial refrigeration system that we're going to look at is going to be the Cascade Cycle or the Cascade Vapor Compression Cycle. So the Cascade Vapor Compression Cycle is one whereby we have two different working fluids. Essentially what we have is two refrigeration systems, one sitting on top of another. And the reason why we have two working fluids is to enable us to get to lower temperatures than we could get to with just a single working fluid. And consequently the fluids would be selected carefully ensuring that we can get down to lower temperatures. And this is for what we would call moderately low temperatures. We're not looking at cryogenics, but we're looking at things minus 25 to minus 75 degrees C. That would be very difficult with our 134A. And consequently you have two different working fluids here. And what we'll do is we'll begin by looking at the process diagram and schematic. And then I'll write out an equation that shows us how to determine the coefficient of performance of our Cascade Vapor Compression Cycle. So here we have the process diagram and the process schematic for our Cascade refrigeration cycle. And the main difference between what we saw before is that we have two compressors. So we have compressor A and compressor B. And we have a heat exchanger operating between the two Cascades instead of what we had before with an evaporator. The evaporator is now down at the bottom. And so heat exchange is going on between the two working fluids. When we look at this on a process schematic or in terms of the process diagram, I should say above we have cycle A and then below we would have cycle B. Now in doing this we do attain a savings mainly in terms of reduced work. And so if we just had a single fluid we would have to add more work in here. And so this could be considered as being the reduced work. And we also attain increased refrigeration because if we only had the one fluid going through this cycle, the throttling process would bring it down to here somewhere. And so the difference between this and this is actually increased refrigeration. So what we're going to do now, we're going to take a look at basically the performance of the heat exchanger where what we have is evaporation going on here. And on the bottom part we have condensation or the condenser unit. We'll take a look at the heat exchanger and that will enable us to determine the coefficient of performance for this cycle. So that's what we'll do next. So looking at the performance of the heat exchanger, what we have is the mass flow rate of fluid from cycle A and the mass flow rate of fluid from cycle B. And we know the change in state or change in enthalpy between each of those fluids. So that's what we can write out. So fluid in cycle B times its change in enthalpy. And the coefficient of performance for this cycle would be whatever desired output, in this case it's refrigeration. So the low temperature heat transfer divided by the net work that we put in. The low temperature, if we look over here, is going to be what is going on in our evaporator here going from 4 to 1. And the net work in is going to be the work in to compressor A as well as B. So that is how we can determine the mass flow rates as well as the coefficient of performance. It depends on the problem that you're working and what is given. But that is an equation for the coefficient of performance. And what we find, no surprise, is that the coefficient of performance here for the cascade system. So we find that the coefficient of performance for the cascade system is higher than for a single fluid unit. And if we look back at our TS diagram, that's because of the savings that we get either through increased refrigeration or reduced work. So that is the cascade vapor refrigeration cycle. The next thing that we'll look at is a multi-stage vapor compression cycle.