Last week we had very cold weather; and as a result there were lots of frosted pipes (iron and plastic). I spent a lot of time defrosting metal pipes with a torch, but could not do the same with plastic ones.
Could a practical gadget be made to thaw the ice trapped inside metal/plastic pipes based on induction? What would a blueprint of such look like?
Induction uses magnetic fields to move free electrons in a regular lattice (ie: a conductor). Ice doesn't have very many free electrons or a regular lattice, so no. It does have a few large ions and protons, but they are at least 1600X more massive, so they don't move much. In this YouTube video, iron filings are dispersed in ice in order to provide a conductive heat sink -- otherwise it would not heat.
An inductive heating device could be used to heat the pipe directly, though.
Something that could heat the ice directly is microwaves. I don't recommend it, however, as there wouldn't be much stopping the energy from bouncing around and heating you!
An non-electronic solution to a similar problem in Canada, which is that mobile homes and cottages can have exposed water or waste (sewage) pipes that can freeze in winter. The majority of this piping is plastic now.
The most common approach is to use a thermostat controlled electric heat "tape", which has a waterproof coated heating element (high resistance wire, such as used in electric blankets) which is based on Joule heating rather than induction.
Ad-hoc solutions could include using hair dyers or heat lamps. Even incandescent light bulbs could be used.
How about a good old fashioned heating blanket? That would use electricity to get hot without having to fish heating coils either in or around the pipe and wouldn’t be as dangerous as playing with a microwave’s magnetron.
Induction from a standard electromagnet wouldn't be able to cause normal water to get hot. If you had something of high enough frequency such as a magnetron you would be able to use dielectric heating to slowly melt the water.
Microwaves are actually rather ineffective in ice. Water molecules in ice are in a crystalline structure and will not polarize at microwave frequencies like liquid water will. They more easily resonate in the kHz region, which I suppose you would make the design frequency of any induction based system.
See http://www1.lsbu.ac.uk/water/microwave_water.html for much more info on water's response to RF radiation, especially the graph right after Figure 1.
Induction can thaw ice if metal were dissolved in the water, so say you had the water pass through a metal filter that allowed the water to pick up some metal particles then you could. With a metal pipe you can simply heat the pipe with induction pretty efficiently.
It would look like a thick coil of wire.
The melting point of ice is somewhat lower than that of plastic - all you need to do is use hot air with a controlled temperature. Like a hairdryer or fan-heater. Or hot water.
Would microwave work? It would be safe on plastics while heating the water as it does with food in a microwave.
