tx valve bulb location

[freddyng]

Dear All

Let's clearly define the purpose of having a HE in a system:
1. To acheive high refrigeration capacity in evaporator.
2. Maximize utilisation of evaporator on setting the thermostatic expansion valve for minimum superheat.
3. To prevent sweating and iced-up of suction lines.

If the bulb is placed after the HE:
* Suction line will be iced-up
* More non-useful superheat will be pick up along the suction line outside the refrigerated box(higher TD between ambient & suction line)
* The net refrigerating effect will be decrease
* Higher risk of liquid flooding back

Please correct me if I am wrong.
Cheers
Freddy

[adam]

Dear All

Let's clearly define the purpose of having a HE in a system:
1. To acheive high refrigeration capacity in evaporator.
2. Maximize utilisation of evaporator on setting the thermostatic expansion valve for minimum superheat.
3. To prevent sweating and iced-up of suction lines.

If the bulb is placed after the HE:
* Suction line will be iced-up
* More non-useful superheat will be pick up along the suction line outside the refrigerated box(higher TD between ambient & suction line)
* The net refrigerating effect will be decrease
* Higher risk of liquid flooding back

Please correct me if I am wrong.
Cheers
Freddy

i can't see how you could have liquid flooding back if you have measured a superheat of 5k

[freddyng]

Hi Adam
You are absolutely right. There shouldn't be any floodback if you are measuring 5 degree K superheat. But, when during a warm start-up(with sensing bulb located after HE), the evaporator pressure will drop rapidly when the compressor is started and the bulb pressure remains high until the temperature of the bulb is cooled to the normal operating temperature by the suction vapor.
Naturally, because of the high bulb pressure, the valve will be unbalanced in the open direction during this period and overfeeding of the evaporator will occur until the bulb pressure is reduced. This will eventually cause liquid slugging in the compressor.

Hope my reply does make sense.

Cheers
Freddy