nzben
24-09-2007, 10:25 AM
I'm building a prototype CO2 liquefying unit only quite small scale and I think i've stuffed it up even before I've begun.
I'm making 2 shell and tube exchangers and I think i have a couple of issues, firstly I'm making out of 316 stainless (man buying stainless hurts these days) And I'm welding the tubes in the endplates - not sure if this will result in weld cracking - I know people tend to expand the pipes in heat exchangers but I wasn't sure how to do it so I figured a bead of weld should seal it up, the exchanger should be running at about -30deg C.
My main issue as I see it is the tube size I've chosen is quite wee and I'm concerned about the tubes becoming bubblepumps for the liquid refigerant that's going to be inside them. The inside diameter of the tubes is only 4.5mm altho the heat load is not that much (3kW/m^2) I'm still concerned that the bubbles generated will be big enough to drive the refrigerant up to the top of the exchanger - the center pipe I've made 1/2" so if a small amount does make it up It'll hopefully run back down but - yah I don't really know wot I'm on about - can anyone give me any ideas/thoughts???
I'm using propane as the refrigerant on the inside of the tubes and a mixture of nitrogen and CO2 will be coming down the outside of the tubes at a rate of 30kg of CO2/hr - so really small quantities in the proto. I wanted the CO2 to be on the outside of the tubes to increase my residence times to allow more to condense. Have attached a pic of the tubes on my small exchanger would love to have some helpful input as I really don't know much of what I'm doing.
Thanks
I'm making 2 shell and tube exchangers and I think i have a couple of issues, firstly I'm making out of 316 stainless (man buying stainless hurts these days) And I'm welding the tubes in the endplates - not sure if this will result in weld cracking - I know people tend to expand the pipes in heat exchangers but I wasn't sure how to do it so I figured a bead of weld should seal it up, the exchanger should be running at about -30deg C.
My main issue as I see it is the tube size I've chosen is quite wee and I'm concerned about the tubes becoming bubblepumps for the liquid refigerant that's going to be inside them. The inside diameter of the tubes is only 4.5mm altho the heat load is not that much (3kW/m^2) I'm still concerned that the bubbles generated will be big enough to drive the refrigerant up to the top of the exchanger - the center pipe I've made 1/2" so if a small amount does make it up It'll hopefully run back down but - yah I don't really know wot I'm on about - can anyone give me any ideas/thoughts???
I'm using propane as the refrigerant on the inside of the tubes and a mixture of nitrogen and CO2 will be coming down the outside of the tubes at a rate of 30kg of CO2/hr - so really small quantities in the proto. I wanted the CO2 to be on the outside of the tubes to increase my residence times to allow more to condense. Have attached a pic of the tubes on my small exchanger would love to have some helpful input as I really don't know much of what I'm doing.
Thanks