I am a food engineer curious about refrigeration system in my plant.

I have several scraped surface heat exchangers (cylinder within cylinder), kind of flooded type evaporator.There is refrigerant, ammonia, outside the inner cyclinder.
Inside the inner cylinder there is high temperature fat to be cooled down to be solidfied and make margarine.
You can see the very simple illustration here ; https://ibb.co/3YPt350

There is motorized danfoss icm valves for ammonia inlet and outlet.
inlet valve keeps liquid ammonia at constant level.
I increase or decrease degree of cooling by controlling outlet valve.
My evaporation temperature depends on aperture of it. So, i change boiling point of ammonia from 0 C to -20 C /3.3 bar to 0.8 barg dependent on the fat product.

My question is, where is expansion valve in my refrigeration cycle?
Is it my evaporataor inlet valve that i keeps constant level?
Is it my ammonia outlet valve that i change degree of cooling?
Is it somewhere else after condenser outside the building?

If it is my outlet valve it means expension valve is after evaporator, or evaporator itself
which doesnt make sende in terms of reverse carnot cycle, it should be befor evap.


So as you see i am in a deep confusing, may be you can help me.

Thank you in advance.