Transport 2 Project
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Conduction
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- What a beautiful day in the wonderful city of Philadelphia
- Now that I finished my morning pop its time to do my daily wall touches
- Hey Charlie... Could you stop hugging the walls again
- Hey Dennis man, I'm really scared man. I think my hands are different temperatures
- Stop hugging the walls you are scaring all of the customers
- Charlie, your hands are not different temperatures
- What customers? We couldn't get people in here if we paid them
- SHUT UP D! Dumb bird
- When I touch the walls my hands feel different temperatures, but when I hold them to my face they feel the same...
- Hmmm, maybe I'm dying guys, I'm really scared.
- You aren't dying you, idiot! You are feeling the effects of heat transfer at work
- Of course, not drugs are bad and this is a college learning tool ;)
- Heat Transfer... Frank are you on drugs again??
- I'm telling you, Charlie, this is heat transfer at work. My friend Lucas gave a lecture about it during Transport II
- Well alright, if this heat transfer thing is real what is it? And will it kill me?
- Let's see if I remember correctly, heat transfer is the movement of thermal energy from one thing to another
- No Charlie, shut up and listen!
- Oh, so heat transfer is some sort of superpower. I want it!
- Heat transfer is caused by a temperature gradient and works to reach equilibrium
- Where'd you get the chalkboard from, Frank?
- I found it in the dumpster around back, what a steal right? Now stop interrupting and pay attention! There are three modes of heat transfer
- Hmm. I think im just going to go kill some rats. This seems too complicated
- Conduction
- Stay or I'll fire you
- Which is the random molecular motion of adjacent particles Can be found using-
- Convection
- Which is the bulk motion of a fluid or particles Can be found using-
- Radiation
- Heat Transfer by electromagnetic waves or particles Can be found using-
- So what you are feeling is the combination of conduction and convection through the walls.
- Wait so you are telling me that the walls are broken?
- Let's punch it see if that fixes it
- No Charlie, look at the wall. It is being heated on one side by the warm summer air
- The wall is made up of 3 components; paint, sheet rock, and wood.
- Each component of the wall has a different K value for conduction. K is the thermal conductivity coefficient
- Which material do you think would conduct heat better; steel or wood?
- Wood right? My rat club is made of wood and those rats sure feel the heat
- Thats wrong Charlie
- The Thermal Conductivity coefficient (K)- is a measure of a materials ability to conduct heat. Metals generally conduct heat better than many other materials
- Wood
- Steel
- Similarly, each of the fluids that interact with the wall has a heat transfer coefficient, h
- The summer air is being pushed to the wall and will transfer more heat to the wall than its cold counterpart on the other side
- You lost me, Frank, what does any of this mean and why is it important?
- Turbulent
- The Heat Transfer Coefficient (h)- is a characteristic of convective heat transfer between a fluid medium and the surface flowed over by the fluid. h for turbulent air flow is greater than h for laminar flow due to higher fluid mixing
- Laminar
- From Professor Landherr's lecture we can talk about a few equations
- Frank, i stopped doing math when I failed the 5th grade for the third time. Sorry but no thank you sir
- Here is the important part though, Charlie. In order to do a lot of these calculations, we need to make assumptions.
- I'm great at assuming Frank!
- The Energy Equation
- Now let's simplify
- The Energy Equation Cont.
- CHARLIE! Wake up! I am almost done
- ZZZZZ....ZZZZZ
- This means that the flux is the same between all parts of the wall! This makes the math so much easier
- Watch this Charlie
- One final assumption that we need to make is that the system is continuous. This means that there is no contact resistance. - The walls are perfectly aligned
- Now let's go back to your problem with the wall
- Let's find the conduction components for the wall
- Wait Wait, I'm lost frank! Why is this part conduction?
- Its conduction because we have direct contact between the different layers of the wall. This is also why we are using k.
- Now let's look at the convective part for this problem
- Before you ask why this is convection it is because the bulk warm air is coming into contact and flowing over the cooler wall
- I understood that part, Frank. Please treat me with respect
- Here's the bread and butter Charlie. We can combine all the equations! !
- I really could go for some bread and butter right about now
- This can be reduced using the overall Heat Transfer Coefficient, U.
- Wait, Frank, I think I get it! = U
- No Charlie!
- Oh darn so close
- Just a few finishing touches Charlie. Let's talk about resistance!
- No Charlie, shut up and listen!
- I'm having a hard time resisting sleep right now. Does that count?
- Thermal Resistance is the ability of an object to resist heat flow. Here are the equations for both types of heat transfer
- Do you understand now why your hands feel different temperatures and that you aren't dying?
- Well not really, I just know I have to clean the bathrooms during my lunch break now. Thanks, Frank.
- Well before you do that lets summarize
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