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Re: [Phys-l] Copper and aluminum

On 12/13/2010 3:51 PM, Josh Gates wrote:
Hi everyone,

My HS chemistry is rusty, and my application of replacement reactions is non-existent. My goal is to insulate my hot water pipes in my cold basement. I have a few options:
- buy an expensive aluminum tape; the reflectivity helps with loss due to radiation, presumably.
- use foam "noodles" to insulate them, which presumably helps with loss from conduction (I guess)
- use Al foil around the pipe to help with radiation, and then foam around it, or
- use foam with Al foil around it.

I'm not sure if:
- having Al foil directly on the pipe will cause spontaneous corrosion of the pipe (I think that it may, given my cursory review of the chemistry). The tape stuff is coated with something to keep the metals apart, I believe.
- having Al foil around the noodles. This allays my fears about corrosion, but will it actually do anything now that it's outside of the foam insulator?

Thanks for the help!
Josh




--
Joshua Gates
Physics Faculty
Tatnall School (Wilmington DE)
JHU Center for Talented Youth
I would like to throw in some other thoughts. You have hot water pipes through the basement for a shower or handbasin.The noodles you have in mind are cost effective, but still they will leave the hot water running cold in the morning, unless.

The "unless" involves either a return flow pipe or an 'instantaneous' heater. The return pipe need only be narrow gauge, but still it wastes energy if it flows hot water to waste.It may be pumped back into the hot water tank feed, which itself has an appreciable energy cost, but still is a luxurious detail. Embellishments might include a timer to activate the pump for just a few minutes before the earliest time of use.

With or without return flow, I sincerely doubt that the life cost of using aluminum tape would be anywhere as low or as effective as using duct tape to close the axial and butt joints in the noodles, with the objective of stopping convective loss from leakage air.

The other alternative - the instant water heater - has been around in Europe for ever but the ones I see here are not specially cheap. Sited close to the point of use, this is as fast as any method.
The water starts hot, and stays hot, as it runs.

Brian W