 When we first analyze open systems we commonly sort reality into a sequence of models that we refer to as steady flow devices. And those steady flow devices are useful in the same way that learning simple geometric shapes is useful. For example if I were to draw for you a circle and I told you that the diameter of that circle was 2 inches and I asked you a question like what is the area of that circle? You would tell me well the area of a circle is pi times radius squared. The radius of that circle is 1 inch, 1 inch squared is 1 square inch, therefore the area of that circle is pi square inches. If I gave you a triangle and I told you its height was 2 inches and its width was 2 inches and I asked you for the area of that triangle you would tell me well I learned that the area of a triangle is 1 half times its base times its height, 2 times 2 is 4 divided by 2 is 2, therefore the area of that triangle is 2 square inches. If I drew a square and I told you that each side of the square was 2 inches and I asked you to calculate the area of that square you would tell me that well I learned that the area of a square is its side squared. 2 inches squared would be 4 square inches therefore the area of that square is 4 square inches. You learned those simple shapes not because you necessarily encounter only those shapes all the time but if I were to give you an abstract piece of geometry like this and ask you to calculate its area even though you didn't learn how to analyze this specific arbitrary shape you can break it into shapes that you are familiar with and analyze those. You could split it into a triangle, 3 rectangles and half a circle and if you knew all the dimensions you could figure out the area of each of those components and add them together. Similarly if I were to give you a schematic like this and ask you consider this power plant in Platt, Iowa and figure out its thermal efficiency or its power output well this overview schematic has quite a lot going on it might be difficult to try to quantify everything that's happening all at once but we don't have to we can break it into small chunks just like we did with our geometry and analyze each of those individually and by summing those together come up with an analysis of the whole. The steady state open system equivalent to these simple shapes are the study flow devices. I have them grouped together in a table which is by no means exhaustive it's just going to be some of the simple study flow devices that we encounter frequently. I would encourage you to get into the habit of analyzing these devices by considering first what that device is intended to do. From that you can figure out where energy needs to go and from that you can figure out where the energy to do that has to have come from. For example the first two devices on the list are nozzles and diffusers. The goal of a nozzle and a diffuser is to convert back and forth between enthalpy and kinetic energy. In a nozzle we want to increase the kinetic energy of a substance. When energy to increase the kinetic energy of the substance has to come from somewhere the source of energy for it is the enthalpy. We'll try a few of those now.