Testing Pope 2 litre-per-hour dripper

I am conducting some experiments to find out how to obtain better control of the dripper rate for my solar water distiller. Prototype #2 has three 1mm holes drilled in an aluminium pipe, which does not give much control.

I posted about testing of the Carocell 1000, which has custom drippers:

http://bkhome.org/news/201906/testing-f-cubed-carocell-1000-solar-distiller.html

The documentation for the Carocell 1000 states a nominal input flow rate of 2 litres/hour is required. There are five drippers, so each will be outputing 0.4 litres/hour.

As my prototype has just under half the surface area, I expect to need an input flow rate of around 1 litre/hour.

Drippers used in garden irrigation have higher rates. Bunnings sell drippers rated at 2, 4 and 8 litres/hour.

But today I thought, I wonder how those Bunnings drippers would perform at lower water pressures? So, I bought a pack of these 2 l/h drippers (they are not sold singly):

https://www.bunnings.com.au/pope-easy-clean-dripper-2-l-h-10-pack_p3120447

Bunnings also sell Pope 2 l/h "precision drippers", designed for constant output with different water pressures, which I did not buy.

A very simple test setup, for differing heads of water, a dripper attached to the bottom of the pipe:

Only took three readings, at heads of 260, 590 and 1300mm:

Very interesting. Goes to show, must not just assume that because it is advertised as "2 l/h", that's what we will get. At low pressure, the flow drops right down.

I am rethinking the design. It will not be good to have the drippers inside the distiller, as many plastics become soft at around 60degC. Instead, thinking now will have just one dripper, outside the distiller. In that case, want one that will give about 1 l/h, so tomorrow plan to test the Pope 4 l/h and maybe 8 l/h drippers. I would like it to work with fairly low water head. 

Tags: nomad