Optimal pressure drop in condensers and evaporators

[MrReds]

Hallo to everybody.
Please, can anybody tell me if there are optimal pressure drops in a condenser and an evaporator as a function of different refrigerants ?
Is there a preferable circuit disposition depending on refrigerant type (ex: R407-C, R410A)...

thanks in advance for your help

 

[insult2injury]

It's not only dependent on working fluid, but also strongly dependent on the heat exchanger geometry.

I2I

 

[AbbyNormal]

It really matters to the expansion device selection.

I am a rusty now, especially with the newer refrigerants, but 407C must be similar to 22. No clue on the 410A

With R22 through the serpentine coils probably want a minimum of 10000 btu/circuit. I would guess about 3 psi max on the evap plus then you allow for the distributor tubes,distributer orifice, probably 30 to 60 psi drop with evap coil, distributor tubes and orifice.

Sporlan used to have a bulletin 20-10 on the distributers etc.

Maybe 5 psi on the condenser.

You allow for the pressure leaving the condenser, the drops through filter dryers, site glasses, solenoids,the piping to the evap.

You also subtact the suction piping loss, suction pressure in coil(what you hope it evaporates at}, then the coil/distributer pressure drop, and what you have left is the pressure to push the liquid through the expansion valve.

Pick out your valve based on the capacity at that much pressure and you are done like dinner.

 

[MrReds]

thanks to everybody

1 - Mr. Insulttoinjury,

please, what do you mean for dependent on the heat exchanger geometry ? that for a pattern there is an optimum pressure drop while for a second one there is a second optimum pressure ?

2 - Mr. AbbyNormal
Thanks a lot.


For everybody: do you think that exist an optimal circuitation for every kind of refrigerant ?

Thanks in advance

 

[insult2injury]

Different heat exchanger geometries produce different ranges of pressure drops. For instance, the tube-side pressure drop in a shell and tube heat exchanger will be significantly different than that of a plate heat exchanger accomplishing the same task. For that matter, the tube-side and shell-side pressure drops within an shell and tube heat exchanger will be different as well. For evaporating/condensing flows, the range of pressures in the HEXs determine the temperature of the condensed or evaporated fluid. The pressures also have an effect on the total cooling/heating capacity of the heat exchanger as well.

I2I

 

[AbbyNormal]

My comments were all based on coils.

 

[tbedford]

isn't the design standard for pressure drop the temperature equivalent of 2 degrees F... pressure drop slightly different for each refrigerant.

TAB

 

[sterl]

The ideal pressure drop through either side is zero. All kinds of guidelines out there on what is an economical pressure drop, and for the condenser, the numbers are much the same and will tend to correspond to about 2-3 Deg F for air cooled tubulars on AC type duties....that means they are considerably lower in PSID for R-134 than for R-404, largely without penalizing the compressor inordinately. But that same 2-3 Deg is a mountain if you are trying to make 0-deg. F. brine with R-134; unless your system is such that the compressor capacity can vary and you only will encounter the max load, 3% of real time....Obviously, with the system turned down, the mass flow and pressure drop for High Side and Low Side will be lower. If the basis of control is to shut the compressor off once a set point is reached, the heat exchanger pressure drop will be largely the same every time the compressor is running...

So its a duty cycle and application driven answer. For AC duties, in a climate with 7000-plus HDD, first cost is going to drive the equation....If its case and storage cooling for a supermarket, the criteria will be different even in that climate.