Steam generator on the exhaust pipe of the car ( cogeneration )

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

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philrainey

IN refrigeration evapourators the refrigerant goes through a valve called the thermostatic expansion valve which measures the amount of liquid in to insure all liquid is boiled by the end of the evapourator then it goes through a distributor which is basically a orifice which then divides into evenly spaced tubes (this is suppose to be in a vertical plane) These tubes (about half the diameter of the tubes in the heat exchanger) are all of equal length and
each feeds into its heat exchanger tube Circuit( which is also of equal length) But I have never seen one with 215 circuits maybe you could have several passes. Another thing we do is if we have not got a distributor (say we have two circuits) is have a expansion valve for each circuit. I know refrigeration is not a steam boiler for a car but they are boilers, I don't know if you can apply some of the same rules.

philrainey

PS in cheap commercial units we use a capillary tube instead of a expansion valve but of course it does not adjust itself for differing conditions to maintain a constant superheat at the outlet of the evaporator but is designed for design temps/pressures and conditions. If a thermostat fails and the evaporator gets colder and colder (pressure in there lower) you get to the point where there is flooding back to the compressor (where you would have your turbine) I think the pressure drop across a distributer is important and has to be a lot more than the pressure drop through the evaporator to help insure even feeding. In the old days before they invented the expansion valve they used a automatic valve which governed to keep a constant pressure in the evaporator but as with the capillary if the pressure in the evaporator went below design conditions (or the heat load going into the evaporator)(your heat from the exhaust reduces) then it will flood over.
I guess another way of doing it would be to have two heat exchangers one where it is the exhaust gas that passes through the tubes and the water covers them and boils before going into a second heat exchanger to superheat the steam. Also you might want to investigate if other working fluids (such as refrigerants) could give more output power for the same input heat. In refrigeration they design /make working fluids for a job. Ie some refrigerants for freezers and others for chillers.

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SteamKing

Staff Emeritus
Science Advisor
Homework Helper
How will you harness the massive amount of power you expect to generate from this device? Could it be used to keep your coffee warm on cold mornings?

rollingstein

Gold Member
9ml/sec through 215 tubes? Something doesn't seem right. Your fluid's going to crawl at 0.001 m/sec I think.

I don't even think using a shell and tube at these sizes makes any sense.

SteamKing

Staff Emeritus
Science Advisor
Homework Helper
I wouldn't worry too much about it. It's necroposting since the OP has never responded in a year and a half.

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