Expansion noise - capillary tube into evaporator

[desA]

When you calc the charge in operation you will need to know in what phase the cap tube is operating in. For instance if it will always have SC then there will be more liquid in the condenser but if it runs mainly with X then there will be far less liquid in the condenser.

With this kind of coil condenser, the coil winds its way from top, to bottom, with a vertical up-leg for the outlet fluid. Judging from the sight-glass, with its clouds of bubbles, the SC would appear to be in the range 0-4K. Since the temp gradient over such a tank is some 10K different from bottom-to-top, an amount of liquid sub-cooling, could be expected - subject to adequate coil surface area (never a sure thing).

Choose your operating cycle on a PH diagram, get the value of X (or SC) for h3 and X for h4.
Lets assume X=0.0 at h3,
then using a simple linear condensation through the condenser Vol liquid = 0.5*Vc

Ok, that's an elegant way to look at it. Decent rule-of-thumb. Thanks for that.

It may be more accurate to use a logarithmic formulae for the condensate and most certainly in the case for SC.

Can I ask you to perhaps expand on this point a little further?

Once X is 0.1 or 0.2 then the volume of liquid falls dramatically and can be found using
vol liquid =(Vc-X*Vgas*Vc)/(1-X) where Vgas is specific gas volume and Vc is condenser volume.

Ok. Understood. I had to re-read a few times. Condenser.

Again doing it logarithmically and in finite elements down the condenser would be better. You can see it falls to below 10% of the value at X=0 very quickly.

If you explain the logarithmic part? dTlm? Which temperatures? The finite element part I understand.

The evap can similarly be treated and also for the piping but only you can determine this as you have the geometry.

Good point.

As for the SH - is this SH out of the evap or into the compressor, it is important as cap systems can have SH as low as 1C at design conditions at evap exit.

SH at evap discharge & SH' at compressor inlet. Surely with an SH ~ 1K at evap discharge, the evap would be very close to flooding - with some droplet carryover? This could be a little tricky. In my system, the operating SH today, at mid cycle is ~ 6.5K at evap discharge. Observing the evap tube hairpins also gives a reasonable 'feel' for the amount of the core involved in super-heating. Currently this is in the range of around 24-26.5% of core tube count.

Any cap dimensions, pressures and temps yet?

I've got the pressure & temps parts moving & should have a set of results tomorrow. I've been running rough trials to check on the evap behaviour in regards to flooding. I'll have to go off & get a decent micrometer to measure the cap tube diameter.