Heat water in a pipe, non contact

[fastline]

Just trying to think outside the box here but we need to heat water moving through a pipe electrically. I realize resistance heating would likely be the most economical and efficient but the issue is having to open the pipe and build a device to run in series in the pipe to heat the water. I am curious if anyone has thoughts on an inexpensive non-contact solution similar to microwave? I want to say RF will be rather involved and will require a rather large boost transformer to obtain our target 1000W power input.

 

[ronv]

If there is much flow a 1000w won't heat it much. Is it a metal pipe or plastic. How hot?

 

[fastline]

plastic pipe, approx 100F, will just have to modulate flow rate to achieve temp.

 

[user_88]

What diameter is the pipe?

 

[picbits]

Personally I'd experiment with either a few lengths of copper tubing - maybe brake pipe which I'd pass a high current through (and have the water running or trickling through it) or a coated/lined iron or steel pipe and have a play with induction heating.

I wouldn't try it with plastic pipe.

 

[ronv]

The microwave is the best one I can think of. Induction heating needs metal.

 

[MikeMl]

I'll bet that you are way underestimating the power input to get a specific temperature rise at a specific flow rate. **broken link removed** which has the equations required to figure that out.

 

[fastline]

Yeah, I have run a lot of numbers for water heating in the past so I am familiar with the btu loads for this. However, the tube in this case is pretty small so 1000W can work. However, from what I recall, microwave is actually pretty inefficient compared to direct resistive heating of water? In the order of 70% eff? Obviously due to the limited about of power, I need all of it.

 

[MikeMl]

Provided you can come up with an insulating jacket to put around the heat exchanger where the only thing carrying heat out of the exchanger is the fluid being heated, then a resistance heater would be nearly 100% efficient. The only losses would be I^2R heating of the wires going to the heater...

 

[alec_t]

You didn't answer the question: what size pipe (id, od, length)?

 

[dr pepper]

I've messed with induction heating, it doesnt necessarily only work with metal non conductiing mediums can also be heated, but thats complex and over my head, and probably would cost a lot to do.
You cant use ultrasound as that would melt the pipe.

 

[user_88]

There was some nichrome ribbon available on Ebay. Get a transformer, wrap some of the nichrome around the pipe and measure the delta T. You will have to account for the transformer power capacity and your output amperage. I think the Ebay nichrome ribbon came out to be about 120 ohms for a 20 ft. length. If you require additional temperature increase, add another section of nichrome ribbon and transformer.