Post by Linda on Feb 14, 2011 19:22:09 GMT -5
Hi Everyone
I've had a few questions about the pressure drop calculation. I'll make the key points here and if you need clarification, let me know at rotman789@yahoo.com. I am happy to check your calculations if you are concerned.
Key points:
1. the calculations on pressure drop are there just for you to get some insight as to what Process Engineers do when they are make decisions in their design. So, don't stress over them too much.
2. the purpose of the pressure drop thing is to make sure the process will work ie. the air supply can supply more pressure than is required to fluidize the bed. That's really it. You can't assume it - you have to calculate it.
3. our air supply is a monster - it can fluidize just about anything as long as your diameter isn't too big. You should calculate the bed requires about 10 in wc to fluidize. The air supply can generate about 28 in wc depending on where you are on the flow curve.
4. you should not expect to find the 10 in wc on the curve. The 10 in wc calculation is about the bed and the curve is about the vacuum. two different things.
5. if you know the vacuum can give 28 in wc but you only need 10 in wc to fluidize, then that means you can use up 'up to' 18 in wc in the design of your piping and gas diffusion. Using less is fine. Using more would be a disaster.
6. don't even think about how to get your pressure drop to match a number - you don't have the tools to figure out what the pressure drop will be and we can't measure it anyways.
7. we can control the discharge pressure of the air supply to a lower value by leaking air (but we can't make it higher) to keep your bed in control.
We purposely designed our air supply so the end result is that the pressure drop calculation is somewhat 'bogus'. By that I mean we made sure our vacuum was powerful enough it could fluidize probably anything you can design.
If you can understand that in real life, Process Engineers have to take restrictions into account - I'll be really happy. Generally Process Engineers are faced with having so much inlet pressure available (28 in wc in our case) and need at least a certain outlet pressure to get the gas out of the process (in this case 10 in wc) and they then have to make SURE they don't exceed a pressure drop of more than 18 in wc in their design. Getting this wrong would cost a company a lot of money to fix.
This is great stuff. I hope you get the idea that Chemical Engineering is more than just Chemistry - understanding Fluid Dynamics is often what makes a successful Industrial Career out of a Chemical Engineering degree.
Have fun!
Linda
I've had a few questions about the pressure drop calculation. I'll make the key points here and if you need clarification, let me know at rotman789@yahoo.com. I am happy to check your calculations if you are concerned.
Key points:
1. the calculations on pressure drop are there just for you to get some insight as to what Process Engineers do when they are make decisions in their design. So, don't stress over them too much.
2. the purpose of the pressure drop thing is to make sure the process will work ie. the air supply can supply more pressure than is required to fluidize the bed. That's really it. You can't assume it - you have to calculate it.
3. our air supply is a monster - it can fluidize just about anything as long as your diameter isn't too big. You should calculate the bed requires about 10 in wc to fluidize. The air supply can generate about 28 in wc depending on where you are on the flow curve.
4. you should not expect to find the 10 in wc on the curve. The 10 in wc calculation is about the bed and the curve is about the vacuum. two different things.
5. if you know the vacuum can give 28 in wc but you only need 10 in wc to fluidize, then that means you can use up 'up to' 18 in wc in the design of your piping and gas diffusion. Using less is fine. Using more would be a disaster.
6. don't even think about how to get your pressure drop to match a number - you don't have the tools to figure out what the pressure drop will be and we can't measure it anyways.
7. we can control the discharge pressure of the air supply to a lower value by leaking air (but we can't make it higher) to keep your bed in control.
We purposely designed our air supply so the end result is that the pressure drop calculation is somewhat 'bogus'. By that I mean we made sure our vacuum was powerful enough it could fluidize probably anything you can design.
If you can understand that in real life, Process Engineers have to take restrictions into account - I'll be really happy. Generally Process Engineers are faced with having so much inlet pressure available (28 in wc in our case) and need at least a certain outlet pressure to get the gas out of the process (in this case 10 in wc) and they then have to make SURE they don't exceed a pressure drop of more than 18 in wc in their design. Getting this wrong would cost a company a lot of money to fix.
This is great stuff. I hope you get the idea that Chemical Engineering is more than just Chemistry - understanding Fluid Dynamics is often what makes a successful Industrial Career out of a Chemical Engineering degree.
Have fun!
Linda