Sweet Buns, Katanas and Heat Exchanges

Sweet Buns ((1))

I am a youtube hair style enthusiast. It's my guilty pleasure to spend an unnecessary amount of time getting ready for parties so that I can learn a new hairstyle. Often I don't even care about doing my makeup.
Hair is both ridiculous and crazy cool. I've always found it weird that unlike most other animals our hair doesn't seem to stick around to keep us warm at all. The fact that our hair pretty much only has an aesthetic use says a lot about people I think. But isn't it cool that somehow, when we twist it into some knots and smooth it down or whatever, this somehow means that we can make ourselves more "attractive". That's whacked, its not just me, right?? But then the general public does seem to like a lot of whacked things that aren't entirely natural or practical. So although its whacked, its not at all surprising.
I would really like to get into doing hair for balls and weddings and things when I get a bit older so hit me up if you are willing to trade me some baking for a hair style for x event in the future. I love that stuff, weird as it is.

Katana ((1))

I bought my first Larp-safe weappon today!! MUCH EXCITE! It's a katana and its beautiful. I have no idea how I am going to be able to use it but man it is cool. Its got a weighted hilt so it feels like you are wielding the real thing except that you're in no danger of splitting flies in half mid air. I will post photos when i get it :) And then I will have to start learning how to use it.

Heat Exchanges ((2))

So heat exchangers are a pretty common place thing for a mechanical engineer. They are basically a component through which flows two fluids which do not mix (i.e. they are in separate pipes). They will be separated by some conductive metal so that heat is conducted between the two streams. This heats on of the streams and cools the other. 

The reason I am telling you about heat exchangers is because they are relevant to my fourth year project. My fourth year project is all about waste heat recovery cycles. This means that take some hot fluid created in an industrial process e.g. some hot water. Then we put it through a thermodynamic cycle in order to turn the heat into electricity. In order to extract energy from heat you need to transfer the heat from the waste fluid into the fluid that you use to drive a turbine (a device which a flow of fluid rotates in order to generate electricity). In our project, the fluid we are investigating is carbon dioxide. I want to see how well heat can be transferred between my waste fluid and carbon dioxide when the carbon dioxide is at different pressures. 

It gets a wee bit more complicated than that but for the sake of simplicity and the time it takes me to write a blog post just keep all of that in mind. 

((3))

One method of calculating the heat transfer rate (how fast heat energy can be passed between streams) is called the Log Mean Temperature Difference Method or LMTD for shorts.This is what it looks like:

• Qdot is just the heat transfer rate
• U is the overall heat transfer coefficient (which basically says how easy or hard it is to transfer heat between the two fluids)
• A is the area over which heat transfer between the two fluids occurs 
• Triangle Tlm is the log mean temperature difference defined in the second equation
• ln is a natural log (basically an operation which is a little more complex than multiplication and stuff)
• Th,in is the temperature of the hot stream at the inlet of the heat exchanger
• Th, out is the temperature of the hot stream at the outlet of the heat exchanger
• Tc, in and Tc,out are the corresponding cold stream values

Creating a Model 

So the tricky thing about the model that I have to create is that the above equation is only viable for constant specific heat (Cp). But at certain pressures (close to the critical pressure, where unfortunately our project's cycle is operating at) the Cp of carbon dioxide changes a lot! By the way, specific heat is pretty much a measure of how much energy it takes to increase the temperature of a fluid by one degrees. Ever wondered why it takes water about twice as long to boil as it does for oil? Yeah oil has about half the Cp value as water. Try it out yourself if you can spare a pot full of oil! 

This variation of cp means that I need to break the heat exchanger up into many very small parts so that I can assume constant specific heat across these tiny sections. Then I can integrate over all of these sections in order to get the overall heat transfer rate. This is why they teach us integration in high school by the way! Because of applications like this. Your teacher wasn't just doing it to see you suffer! 

But anyhow! I will have to talk more about this later because its getting late and university is tomorrow! Goodnight!