Re: Efficient condensing
Posted by:
Peter Brow (IP Logged)
Date: May 06, 2003 08:15AM
<HTML>Hi Peter,
Personally, I don't plan to try vacuum pumps or vacuum condensing. In a car, I think that the pump(s) and fan required would eat more horsepower than the vacuum would produce, under almost all conditions except high-speed cruising. Full-time vacuum condensing would probably require too large a condenser and/or fan to be practical in a standard car. With atmospheric condensing, it seems possible that reduced condenser size/drag could compensate for the increased exhaust backpressure needed to accomplish them. It also looks like one of those things that would be difficult to measure and calculate, maybe more difficult than the small gains/losses (in an optimized system) involved would justify.
Yes, finned heat exchangers are everywhere, including condensers. In stationary applications, the reduced cost (fewer tube joints) is probably crucial. Also, for an unfinned heat exchanger to compete with a finned type, much smaller tubing has to be used in the unfinned type. Standard practice is larger tubing, fins, and fewer tube joints. I have some ideas for making "smaller tube/more joints" type heat exchangers competitive in price. These involve new fabrication methods/materials; if those don't work out, then the finned type will remain more cost-effective. One thing to note is that finned tubing is more expensive per square foot of heat exchange area than unfinned.
I like your idea for a multi-pass condenser. Not sure if it would be practical to convert a std. radiator core to multi-pass design (depends on the available flowpath area), but your comments inspired a redesign of the "V-front" condenser type which I think is an improvement. Basically a stack of small V-front condensers, the same size/shape as a standard car radiator (~1" x 12" x 24"), plumbed together in series. Header size and tube numbers in each of the plumbed-together modules would be tuned to keep total steam/water flow path cross-section area constant from one end to another. I am thinking approximately the same flowpath area as the exhaust steam pipe from the engine, though a larger flowpath, maybe 2x that or more, might be necessary to compensate for the flow resistance imposed by all the small tubing and twists and turns.
However, if a fan, controls, etc were worked out so that exhaust steam never blows through, or only a small amount, then the flowpath area could be reduced toward the outlet as you suggested. I am currently designing for a system with no condenser fan.
Finned tank is one way to cool the tank; I came up with one idea where ram-air blows over a duct-encased water tank with a deeply corrugated wall. In freezing weather, the air inlet ports could be closed, partly or fully, by an automatic thermostatic shutter, and the duct would be insulated to prevent freezing when air shutter is completely closed.
Peter</HTML>