As mentioned in previous blog posts, the biggest unresolved problem was connecting the secondary heat exchanger to the mains water tap. It was necessary to join a standard garden hose to 3/4" qualpex - this is a very unusual combination and it is almost certainly not available as a standard fitting in a plumbing shop. I decided to quickly machine a small insert on my lathe that would allow me to join the flexible pipes. Whilst not very aesthetic the jubilee clip/rubber tubing has proven to be extremely effective and simple to use.
Machining the part from a piece of scrap aluminium
Finished part
Preparing to join the two hoses
The garden hose fits tightly around the insert
The larger diameter hose also fits well. This larger hose just connects onto the qualpex.
Jubilee clips added for additional safety. The interference fit is probably sufficient
I replaced the fitting on the tap with a standard garden hose quick release
With the last of the plumbing problems solved, I hooked up the inverter and a small 250W heater load. I intend on replacing this with an 800W heater in the coming days to act as the proper load for the engine to slow the rate of battery charging.
Batteries and inverter setup
View of the test area (note MicroMon running on the computer)
All of the major systems work on the engine is now completed. There are only minor jobs remaining, mostly related to adding various sensors to the setup which will be logged by LabView.
These include:
- Pressure Transducer - To view the pressure levels inside the engine and keep an eye on any leakage
- Water Flow Meter - T measure the flow rate of mains water pressure through secondary heat exchanger
- Water Flow Meter - To measure the flow rate inside the cooling loop (possibly unnecessary)
- Multiple Thermocouples - To measure heat rejected to cooling circuit and to mains water dump
I also tested the engine with the new secondary heat exchanger dump. It significantly slowed the heating rate of the cooling system. It appeared to stabilise at around 40°C even with around 10 amps going into the heater clamp (the batteries had switched to absorption charge). I ran the engine for a total of about 30 minutes and logged the run using MicroMon.
Today's data. Tblock (blue) is a proxy for the cooling system temperature as both were in rough equilibrium. The key thing to notice is that even with the clamp heater activated, the secondary heat exhanger is able to dump enough heat out of the system to maintain more or less constant coolant temperature.
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