 In the last segment, we took a look at the different forms of condensation and we said that there is film or droplet condensation and we also said that droplet condensation was the more efficient from the heat transfer perspective. Now in order to achieve droplet condensation in systems, quite often coatings will be added to the surface and what these coatings do is they have an impact upon the surface tension characteristics between the solid and the liquid that is being condensed and so coatings such as silicones, so silicones, teflon, waxes and fatty acids, those are examples of coatings that will change the surface tension characteristics between the solid and the liquid and that helps prevent film condensation and then it enables droplet condensation to occur. Now when we're doing engineering calculations, typically what we will do is we will assume that film condensation is occurring and that gives us a bit of a factor of safety in our engineering design calculations and it's basically a worst-case scenario type of estimate for the calculations so you wouldn't be undersizing a condensing unit for example. Okay so in what we're now going to do we're going to take a look at some engineering applications where condensation is quite prominent and is used in part of the system so what we're going to do though we're going to begin with the most general and that's looking at condensation that we experience in our everyday lives and so what we're going to begin with here we can see condensation on the window of an automobile that has been placed outside overnight and when it gets cool at night the condensation occurs on the surface there you can see some more condensation on a mirror and you'll see the droplets form together and then they run down the surface. Now in Calgary in Northern climate sometimes what happens is it freezes and there you can see evidence with frost, frost patterns form and essentially what's happening is the moisture in the air condenses and then it freezes. This is an example in China where the floor is actually below the dew point of the atmospheric air and so what happens is you get puddles forming on the floor due to the fact that the floor itself is cooler than the dew point in the air and you have condensation occurring on the surface. So sometimes what they do is they'll put cardboard down and that minimizes people from slipping while walking on surfaces like that but if you're walking around in China or other very very humid climates and you're wondering why the floor is wet and that is probably the reason it's due to condensation. Now another type of application that we're going to look at is that of the heat pipe and and so heat pipes are used in many different types of applications now and we're going to begin with this one. This is a bubble light and it has methylene chloride on the inside. On the right we have high speed video you can see there is boiling occurring the bubbles moving up they get to an interface and then there's condensation from the tip that then runs back down. So with the IR camera we can see the bulb temperature is around 58 57.5 degrees Celsius and then we can go into the stem region and then the temperature drops down a bit it's around 41.6 degrees C where the bubbles are rising up and then at the tip the temperature is around 39.7 degrees Celsius and and when you look at the saturation temperature for methylene chloride it's 39.75 which agrees very very well with what we're seeing and so it's because there is condensation of of the methylene chloride occurring on the inside of the tip and it would make sense that we would be measuring the saturation temperature within that device. So the bubble light is a bit of a novelty it's an interesting thing to look at but that very same system is used in many engineering applications and so what we're going to do now we're going to take a look at a few of those and we're going to begin with computing computers. Processes generate enormous amounts of power and heat well they don't generate power they generate heat and we have to dissipate that and so these are coolers that are used for central processing units and they're a bunch of different varieties of shapes sizes but you can see the heat pipes there they're the copper pipes that are coming up into the fins there it is on the side there you can see the top of the heat pipes that extend up through the fins and then there you can see the side profile again with the heat pipes going up so essentially this is the same as the bubble light but inside you would have a working fluid that would boil and then it would go up and condense and come down and so what we're doing here is an experiment where we put that heat pipe apparatus onto a hot plate heat is on and so it's heating up I have a fan blowing through it in order to provide cooling because otherwise it would overheat and then when you look at the heat off what's happening is that the fluid in the the pipes is cooling off due to the fins and so you can see the fact that the temperature drops as the the pipes go to a lower and lower temperature this is a railroad in Shanghai to tie that railroad and there there are heat pipes on the side to deal with the permafrost and here's a similar application in Alaska where we have heat pipes and what they're doing if there is anything on the surface in permafrost they put those heat pipes under the surface and that maintains a low frozen temperature of the permafrost and so it doesn't thaw and if it thaws what would happen is the railroad would either sink or it shift and you'd have all kinds of geotechnical problems going on so heat pipes are used not only in computers but they're also used with pipelines or railroads like we saw with that one particular application now another application that we have for condensing is in refrigeration and so here is a picture of a refrigerator it's an older fashion refrigerator where we have coils on the back but what's happening on the inside of those coils is we have condensation occurring so the refrigerant becomes a superheated vapor after the compression process and then we reject heat and it's going through a condensing process and so that's essentially what we're looking at as the refrigerant flows through those coils and and so that would be where you have condensation on the tube side that the condensation is occurring within the tube and it's going from being a superheated vapor down to the saturation temperature and then it would go through a phase change and then you would have a liquid coming out at the bottom but that is typically the cycle used for any kind of refrigeration system and then finally and the last application we're going to look at are very large-scale industrial condensing units and so here we can see a picture of a condensing unit being fabricated sometimes it's hard to tell the difference between a condensing unit and a shell and tube heat exchanger they're very very big and you got a lot of tubes on the inside but in this particular one this was one where it was tube side condensation and so they are relatively large tubes they're the tubes there they're probably one and a half to two inches in diameter and and so what is happening is you have condensation occurring within the tubes and and if i sketched that out you would have a system like this and usually they'll incline the tubes at a bit of an angle but you would have a vapor going through and and you would get condensation forming and you would get a film forming like this you want to use gravity to draw that down sometimes you'll also have your vapor so you have velocity vapor coming through the central core that essentially what happens is this here would be your liquid and you would have gravity driving that you want to be careful because as the tube gets with more and more liquid building up so eventually you're going to get to some point like this ideally you want to keep it as being stably stratified flow and and so you'll have your vapor up here going through the this is if we have what we refer to as being tube side condensation you need to be careful because what can happen is if the vapor velocity is high with respect to the liquid velocity so this is our liquid here you can actually get instability waves that start to form on here and that can transition into slug flow and it could cause a very very high pressure drop a multi-phase flow physics can be rather complicated now sometimes you're okay with this but sometimes you're not for example if if the vapor has to go through another stage ideally you don't want to be in training a liquid drop let's say you would get with multi-phase flow or plugs coming out of it so anyways though those are examples of condensing units that are used in industrial applications as well as many other types of condensing applications that we use in not only in engineering but also that we see in everyday life and so what we're going to be doing in the next segment is we're going to be taking a look at some of the correlations we'll derive the Reynolds number and then we'll move into some analysis that New Salt did coming up with very early correlations enabling us to determine the convective heat transfer coefficient for these types of systems