BMW turbosteamer concept

boudzmawed

guys ,i'm working on this project for my senior project , the tempreture is high enough to generate steam , however i'm facing a problem :
according to my design , the water flow rate is very low (0.54 l/min) and the pressure is up to 7 bars , so i'm finding it hard to allow water to be distributed equally in the 250 tubes tube side of the shell and tube heat exchanger , and i don't know how to do that or if it's possible or not can anyone help ? thank you :)

chris.roberts

I'm doing a similar kind of project, why does the water not distribute evenly? Could you turn the exchanger 90 degrees so the water fills the tubes and flows up, the water level will be equal in each tube . Why can you not increase the water flow rate?

russ_watters

Is the pressure drop high? Then you have too few/too small tubes.

boudzmawed

guys, imagine a flow rate of 9 ml/s and of pressure 7 bars going out of a pump, this flow will look like a thread ( very thin line ) , and it enters directly to the shell and tube exchanger that has 250 tubes , how will this flow be distributed equally in the tubes ?
i think i need a certain design of a distributor or a collector but i got no experience in that , i need help!
and i can't really increase the flow rate since water will not be superheated to steam then .

AlephZero

By my very rough calculation, that's about 20kW to vaporize the water at your pressure and flow rate.

So the "common sense" question might be, why do you need as many as 250 tubes to handle that power level?

20kW is roughly equivalent to about 10 electric kettles. So how much length of tubing does your 9ml of water need to flow through, in the 1s it takes to vaporize it? About 1m of 3mm diameter tube is the right sort of volume. Your heat exchanger doesn't need to be 1m long, you can coil the tube into a helix if you want...

That's about as far as I'm going to get "designing" this without using a calculator, so I'll stop there - it's your project not mine.

boudzmawed

as u know in heat transfer , Q depends on cross section aread and delta T mean, yes i need

to take around 26 kw heat , but since the maximum temp of hot fluid is 650 C , and i need

to heat water to around 400 C , then delta T mean is small , thats why i need big cross

area, based on HTRI exchanger program , this is the best design , to have 230 tubes of 6.4

mm diameter. the problem is stil ther, how to distribute the small flow to all those tubes ,

can you help ? thank you

AlephZero

Those numbers don't make "common sense" to me.
230 tubes 6.3mm diameter have a total area of 7400mm^2.
You have 9000mm^3 /s of fluid flow
That is a flow velocity of about 1.2mm/sec. How long is your fluid going to take to pass through the exchanger ???

For good heat transfer you don't need a big cross section area. You need a big surface area. I would forget about round tubes and start brainstorming for a completely different geometry of heat exchanger.

boudzmawed

fluid velocity is around 0.11 m/s , what do you by other design? can you help me in that ? so far i got no experience except in the normal round design of tubes , thank you

AlephZero

Are you sure?
0.0064^2 * pi/4 * 230 * 0.11 = 8*10^-4 m^3/s = 0.8 l/s
Previously you said 9 ml/s

Of course the steam velocity will be higher because of the greater volume, but I'm talking about the water velocity.

boudzmawed

My data is taken from the HTRI exchanger program , for a flow of water of 9 ml/s and diameter of tubes of 6.4 mm and tube length of 0.5 meters , and number of tubes of 215 tubes , the tube velocity is around 0.11 m/s . my question is , how to make that very low flow get equally distributed for all the tubes, or is there any other better design to allow me to take the 26 kw of heat from the exhause gases of the car? thank you

boudzmawed

I'm trying to do the concept of a turbosteamer that the bmw is workking on but i'm facing few problems :
the flow rate of water will be 9 ml/s and of pressure 6 bars . based on htri xchanger program , the best design of my shell and tube heat xchanger will be of 22 cm diameter and 6.4 mm tube diameter where number of tubes will be 215 and the length will be around 0.5 meters.

my problem is how to allow this very low flow rater ( 9 ml/s) enter the 215 tubes equally ?

my 2nd problems is that i have no experience with microturbines , i need to know how to design that turbine, ihope you can help guys

thank you

gmax137

Mount the heat exchanger vertically. Put the exhaust through the tubes (hot at the top and cooled exhaust leaving from the bottom). The water to be boiled is on the shell side. The upper portion of the heat exchanger will act like a superheater, and the water 'distribution' problem is solved. Put baffles in there so the water doesn't slosh around when you take a corner.

edit -- by the way I dont think that HRTI program is really for designing boilers.

boudzmawed

having the exhaust on tube side means huge pressure drop which means a back pressure. ur sure it wil work ?

boudzmawed

plus it's a bit difficult to place the hex vertical on the exhaust pipe of the care dont u think ?

gmax137

What's the pressure loss from pushing the exhaust through the shell side of your tube bundle? That's not a free ride either. By the way, how much backpressure is acceptable? I think you need to know that before you can decide what your boiler should look like.

No, but it's not my project. I'm just throwing ideas at you.

PS: You should get into the habit of typing out real words. Once you're out of school nobody wants to read text-speak.