Why Is Water Flow Uneven in My DIY Pool Heater?

[novop]

Hi,

I'm having a problem building a sort of pool heater for my backyard. I've assembled some black tubing into 9 spirals, making 3 groups of 3, and then attaching the groups of spirals to a manifold, to supply equal pressure to each group, see pic below.

The water is pumped up to my roof, where the manifold is, by a pump at about 6 psi, and then the water (is supposed to) runs through the hot tubes back into the pool. The problem is this: only the group of 3 spirals on the right get water flowing through them. The other 2 groups (or 6 spirals) get no water flow.

By disconnecting the group on the left and then connecting just ONE spiral, the pressure is so weak it doesn't even flow through the one spiral. Doing the same to the middle group, I find that the water can flow through one spiral.

Shouldn't the manifold be supplying equal pressure to each group? Why is it then that the pressure on the leftmost group is very weak, the middle intermediate, and the best pressure is on the right? What can I do to improve this? Thanks in advance.

 

[jack action]

The fluid travels too fast in your manifold. When it arrives at the first group of spirals, it goes so fast and there is so little resistance to keep going forward that it takes this path instead of "turning" at the junction. Of course, once it arrives at the end of the manifold, it doesn't have a choice and it does turn into your third group of spirals.

The fluid will always take the path of least resistance, unless you force it to.

Solution:

Add restrictions. Best way would be to have the diameter of your manifold decreasing between each set of spirals (1, 2 and 3 starting from the inlet of the manifold).

Quick intuitive calculations of manifold area (Needs could vary according to the way your junctions are designed):

A_in = A₁ + A₂ + A₃;
A_1-2 = A₂ + A₃;
A_2-3 = A₃.

Otherwise, you can put some restrictions (like a valve) on section 1-2 and 2-3 of your manifold and adjust them until you get the flow characteristics you want.

 

[novop]

Thanks!

 

[emiltr]

And you can try the following:
On entering each group of two spiral you put one restriction,identical
This ensures equal pressure to entry for each group of two spirals,therefore equal flow.

 

[sneakindeacon]

Dont know how feasible it is for you to do, but some small diameter, say 3/8-5/8" ID aluminum or copper tubing, painted black and put into a zig zagging manner would seem to be more efficient. Slower water travel would also help to heat the water a little more quickly...also, if you have a charcoal grill or wood burning grill, something to that effect, you could make something to size and it would warm it even quicker and not cost you anything really, just a couple swings of an axe and a match and lighter fluid.

 

[novop]

Thanks for the tips. I attached a valve to each entry point from the manifold and played around with the openings until I had water flow in each group. Works like a charm now =)