Help for selection of cap tube for Single stage cooling

[tosunermc]

I have made single stage cooler for PC. I have problems wih cap
tube


System Components:
Tecumseh cdj2464z lbp hermetic compresor,50 Hz 1,5 HP
5,8kBTU
580 Wats Cooling at -40C Te,40C Tc

0,75 kW condenser 5m2 ,220V,50 Hz 75 W fan
0,031" 2,2 m cap tube
Castell Drier
Special evap for CPU
Vapour / gas separator 2lt at suction
Cap tube is at the round of suction pipe 12mm ID
Ref: 404a
Pressure gauges at exit point of drier and suction port
K Type Temp. Sensor at the top of the evap
250 W Heat load cell at the bottom of evaparator


Results 250 Watts Heat Load Off
Static charge :7 bars
Operation pressure:13 bars at high side , deep vacuum at suction
Idle Temp at the top of evap -55C/-56C (From ambient temp 25C to -56C It takes 2 minutes)

When System is 13 bars,-55C at top of evap I give current to heat load cell

The temperature at top starts to drop down, High side pressure rises 14 bars, Suction pressure is still deep vacuume
Within 100 secs temp at top of evap reaches -18C and If I dont cut energy of cell evap reaches +C's.

I have used rotary compressors before this cooling with 1 HP 12000BTU rotary compressors I can handle 350W's at lower than -40C with %90 r404A+ %10 R410a. Cap tube was same 2,1m-2,2m 0,031".
Since rotary compressors are too loud I wanted to use Hermetic one.


Hermetic Compressor is weak in terms of BTU but According to Tecumseh documents Thic compressor have to hanle 400W Pe at -40C's

I have checked Tecumseh's cap sizin program and Danfoss Cap sizing program. They gives me 1,9 m 0,042" cap tubes.

My rotary' are ok with 0.031" 2 meters but this hermetic systems fail?


I have already check oil, re vacuum system, change drier. Result is same


How will I modify system If you help me I will be very glad.


Adding more gas: I think I can add little amount of R404A or R410A Static cahrge to 7,5 bars

Changing cap tube to which size?

Thx Memet Can from Istanbul/Turkey

[tosunermc]

44 wieving and no reply:(

Today I have shortened cap tube to 1,8 meters, Increased condenser temperature with adding more gas to 45C, Unit is stable at 300Wats at -42C, If I change cape tube to 0.9meters I can pump more refrigerant to cpu block and unit will be able to hold 350-400W at required temperature.

Any way if you help me I will be glad

[monkey spanners]

Hi Tosunermc,

I have never worked one of these PC coolers, they are very specialist equipment.

If I read your post correctly, the hermetic compressor failed when the rotatry didn't. I also notice the system runs in a very deep vacuum, both these styles of compressor motors are cooled by the refrigerant they pump, with the hermetic the steel body opperates at the suction pressure, in a deep vacuum there is not enough refrigerant to cool the motor.
In the rotary comp the body of the compressor is at discharge pressure, so it has a better chance of being cooled in your application.
Neither compressor is designed to be opperated in a vacuum, many have warning labels to that effect.

You can't accuratly charge a system to a static pressure as the pressure will depend on the temperature of the system. It needs to be charged by wieght.
Imagine a pan of boiling water, it could be full or nearly empty and its temperature and pressure would be the same, so it is with refrigerants.

Jon

[tosunermc]

Hi Tosunermc,

I have never worked one of these PC coolers, they are very specialist equipment.

If I read your post correctly, the hermetic compressor failed when the rotatry didn't. I also notice the system runs in a very deep vacuum, both these styles of compressor motors are cooled by the refrigerant they pump, with the hermetic the steel body opperates at the suction pressure, in a deep vacuum there is not enough refrigerant to cool the motor.
In the rotary comp the body of the compressor is at discharge pressure, so it has a better chance of being cooled in your application.
Neither compressor is designed to be opperated in a vacuum, many have warning labels to that effect.

You can't accuratly charge a system to a static pressure as the pressure will depend on the temperature of the system. It needs to be charged by wieght.
Imagine a pan of boiling water, it could be full or nearly empty and its temperature and pressure would be the same, so it is with refrigerants.

Jon



The rotary cooler was succescull with cap 0.8 but with hermetic compressor It doesnot hold load. Everything same I am changing only compressor. The temperature of compressor is rlow . System has been put in the very well ventilated box. Air velocity at compressor top is very high)


I think that amount of the coolant is not enough with hermetic. For more refirigerant I have to decrease pressure lost at capillary either I will cut some of the cap or I will change it with bigger size.