Build a J-Tube Unpressurized Rocket Hot Water Heater - PEP BB rocket.wood.hotwaterrmh

Dave Burton wrote:This BB requires you to build a j-tube unpressurized rocket hot water heater.

To get certified for this Badge Bit you must provide:
  - 5 pics of build in progress
  - very clear description of how it is not pressurized (if steam happens it can't blow up)
  - 15 second long video of cold water going in and steaming hot water coming out
  - 2 minute video of starting the fire and proving there are no smoke leaks

I ran about 8-10 iterations of design concepts by my husband and every time my objective was to make it simpler and safer, simpler and safer, simpler... and safer. What I built is essentially a double boiler system. I have a ~20gal stock tank that is directly exposed to the hot air above the riser. I then dropped in a copper coil that exchanges heat with the hot stock tank water. If the stock water were to reach boiling point, the water in the copper coil would reach up to boiling but not exceed it since it isn't in direct contact with the heat source. I also installed a pressure relief valve above the section of copper that takes cold water vertically down as an added safety measure in the event that water wants to rise against the intended direction. Meanwhile, the water on the other side where the copper coils vertically up, the pressure would escape via the intended direction of the hot water. The diaphragmatic pump is on-demand and will turn off when the valves are closed. Until this system can be integrated into the neighboring structure differently, I put the valve in between the pump and the copper coil.

About the rocket: I built an 8in system with a 6in exhaust juice-boxed into the air void next to the j-tube. Take a look at the last photo attachment. I positioned the exhaust as low as possible to make the system as efficient as possible. Because of this, you'll see that I made sure the chimney was very primed before priming the riser in the 2min video below.

Stock tank water and cistern water (water supply) was at 54deg. After 2hrs11min run time of the rocket, the stock tank was at 187deg and the copper heat exchange output was 154deg (as noted in the video). I used about 2 5-gal buckets of wood.

I figured a water temp above 140deg would be considered safe from legionella bacterium and close to 160degFwould be even better.

15 second long video of cold water going in and steaming hot water coming out:


2 minute video of starting the fire and proving there are no smoke leaks: