condensor- temp effect on amount of liquid

[kfjoe]

hoping you guys can help me out please,as im getting a little confused

If the condensor temp is increased by say one fan not running and so the rise in temp/pressure , will this mean more liquid in the condensor as it is condensing at a higher temperature and therfore less laten heat is required to be removed to turn to a liquid as per PH diagram ?
and if so does this mean there will be more sub cooling ??

thanks in advance for any help

Joe

[The MG Pony]

ya but you'll all so have a higher over all liquid temp thus loos more to flash gass on the way to the metering device over the pipes internal pressure drop! How ever the side with a dead fan will still reject small amounts of heat due to convection.

(Now don't take this too heavily as I am still a student, but so far that would be my understanding)

[kfjoe]

Thanks

yeah i realize the overall liquid temp will be high and so a negative effect , just trying to get into my head (amongst over things )weather with a very high condensing pressure you could read a high subcooling and so would get the same effect as if the system was overcharged , when it could be air flow etc to the condensor .
also cant get into my head quite where the new point of inlet to the expansion valve would be on a PH diagram

thanks
Joe

[Josip]

Hi, Joe

hoping you guys can help me out please,as im getting a little confused

If the condensor temp is increased by say one fan not running and so the rise in temp/pressure , will this mean more liquid in the condensor

Compression pressure will increase - HPS (high pressure switch) functions and unit will stop.

Evaporting pressure will slightly increase.

Discharge temp will increase - oil deterioration -compressor failure.

Suction temperature will slightly increase.

Amount of superheat remains constant.

Amount of subcool remains constant.

Compression ratio increase - weight of refrigerant circulated decrease.

Refrigerating effect will decrease - cooling capacity decrease - COP will decrease

Thermal equivalent of compression work increase - running current increase

Best regards, Josip

[kfjoe]

Thanks Josip

so subcooling would remain the same then

so what governs subcooling in a system other than the refrigerant charge ,no condensables , is there anything else than can effect it ?

thanks

[Josip]

Thanks Josip

so subcooling would remain the same then
so what governs subcooling in a system other than the refrigerant charge ,no condensables , is there anything else than can effect it ?

thanks

Some examples:

Insufficient refrigerant circulation

a) amount of ref in a system is insufficient
1. undercharge of refrigerant
2. refrigerant leakage

.....SC decreases

b) amount of ref passing through a metering device is insufficient
1. choked filter, drier or metering device
2. faulty metering device

....SC increases

Excessive refrigerant circulation
With TXV - SC decrease
With capilary tube - SC increase

Excessive cooling load
SC - decrease

That's all folks

Best regards, Josip

[Dan]

Tricky questions.I would say that the amount of liquid in the condenser will decrease if you lose a fan. The subcooling question is a good one. I can see it actually increasing. Once the liquid has condensed, it does not take much work to finish the sensible cooling, thus you might have a liquid at 95 degrees at the outlet of the condenser both with the fan on and with the fan off. The pressure will be higher with the fan off, thus the 95 deg liquid will be more subcooled under the higher pressure.

I see it as similar to a phenomenon I puzzled over for years regarding noncondensibles in a system. The discharge pressure would be very high, but the liquid return line would feel cool. Actually, the liquid return line was the same temperature as other liquid return lines.

Noncondensibles in essence take away valuable condensing surface from a condenser, thus the pressure will be higher. But surprisingly, the liquid return temperature is not as significantly higher, thus, the return liquid is more subcooled in the situation of noncondensibles. Why not the same pattern with a fan disabled?

Not so simple questions, Joe.

[kfjoe]

thanks guys
that helps .

but it sure does confuse me why reducing the capacity of a condensor by non condensables , which to me means the condensor has to work at a higher TD so therefore presure, is different to reducing the capacity of a condensor by say less airflow as this also raises the pressure , so why does one have high subcooling and not the other

maybe im missing something

thxs

[Dan]

so why does one have high subcooling and not the other

Subcooling is the amount of sensible heat below saturation temperature: If you have a liquid at 95 degrees F with a saturated condensing temperature of 105 deg F, you have 10 deg of subcooling. You can increase the subcooling in any of two ways: By lowering the liquid temperature, or by raising the saturated condensing temperature. So if you raise the saturated condensing temperature to 115 deg F, and you still have 95 deg liquid, you now have 20 deg subcooling. Same as if you lowered the liquid temperature to 85 deg F. Don't confuse subcooling with enthalpy or net refrigerating effect. Subcooling is simply a relative term indicating the relationship of a liquid to its saturated pressure and temperature conditions.

[kfjoe]

thanks Dan

yes that makes sence to me

but lets say you have a system running at 105 degf
with a 95 degf liquid so a 10 degf subcooling and then raise the condensing temp to 115 degf by say blocking off part of the condesor air flow , what would be the subcooling or how would it change if at all ?
thats the bit i cant get mt head around

thxs for all the help

[johnyfreon]

thanks Dan

yes that makes sence to me

but lets say you have a system running at 105 degf
with a 95 degf liquid so a 10 degf subcooling and then raise the condensing temp to 115 degf by say blocking off part of the condesor air flow , what would be the subcooling or how would it change if at all ?
thats the bit i cant get mt head around

thxs for all the help

As far as I know when you push the condenser beyond the design temperatures the efficiency of it will decrease resulting on less subcooling, condenser are designed to serve as desuperheaters, condensers and subcoolers under normal operating conditions, as the temperature of the air/water increases it takes more of condensers surface to desuperheat refrigerant vapors moving the condensation process further down towards the bottom of the condenser that under normal circumstances would had been using for subcooling purposes.

[chistine]

how are you ?

[Samarjit Sen]

With a fan being off in an air cooled condenser, there will be reduced condensation, which means that the temperature and pressure shall be high and there will more vapour at hihg temperature than liquid. This will result in flash gas formation ahead of the TEV resulting in reduction of capacity in refrigeration capacity.

For any refrigeration system it is very important that proper condensation is there and the subcooling is maintained. In air cooled condenser a seperate section is usualy set aside for subcooling, but it is better to install a liquid suction heat exchanger as it will offer a better subcooling and also maintain proper superheat. However everything depends on proper design.

With best wishes,

Samarjit

[yangchenchen]

hello,friends, i'm a new comer. it's a very good forum.

[Dan]

but lets say you have a system running at 105 degf
with a 95 degf liquid so a 10 degf subcooling and then raise the condensing temp to 115 degf by say blocking off part of the condesor air flow , what would be the subcooling or how would it change if at all ?
thats the bit i cant get mt head around

Subcooling equals Saturated Condensing Temperature (SCT) (converted from pressure per your T/P chart) minus your actual liquid temperature. Thus, in an R22 system:

Condensing pressure: 210 psig = 105 deg F SCT
Temperature of liquid refrigerant at outlet of condenser: 95 deg F
105 SCT minus 95 = 10 deg F subcooling.

If you are condensing at 115 SCT,

115 SCT minus 95 = 20 deg F subcooling.

As far as I know when you push the condenser beyond the design temperatures the efficiency of it will decrease resulting on less subcooling, condenser are designed to serve as desuperheaters, condensers and subcoolers under normal operating conditions, as the temperature of the air/water increases it takes more of condensers surface to desuperheat refrigerant vapors moving the condensation process further down towards the bottom of the condenser that under normal circumstances would had been using for subcooling purposes.

Well spoken, and I don't really disagree, other than the fact you haven't considered the new dynamic of increasing the condenser TD. By going from a 10 deg TD (105 F condensing - 95 deg air, for example) to a 20 deg TD, you have doubled the capacity of the remaining active suface of the condenser. But that is a quagmire I don't want to step into.

My point is that it is entirely possible you will not get an increase in liquid temperature even though you have raised the condensing pressure. I am not denying that at some point you will get an increase in liquid temperature as you turn fans off, but I have seen instances where you can cycle fans off on a multifan condenser and you do not get as large an increase in liquid temperature as you do in Saturated condensing temperature, thus you gain subcooling.

Here are some other examples of reducing the condensers capacity that will show up as increases in subcooling:

Condenser flooding valves. They will not open until the condensing pressure exceeds their setting. The way they do this is to fill or "flood" the condenser with lquid until the pressure rises as a result of the reduced condensing surface.

An overcharged self-contained refrigerator. The condensing pressure again rises because liquid is backed up into the condenser, but as in the case of the previous example, more tubes are now dedicated to subcooling as the liquid fills more of the tubing from the outlet inward - thus, more subcooling.

Just speculations on my part.

[Sridhar1312]

thanks guys
that helps .

but it sure does confuse me why reducing the capacity of a condensor by non condensables , which to me means the condensor has to work at a higher TD so therefore presure, is different to reducing the capacity of a condensor by say less airflow as this also raises the pressure , so why does one have high subcooling and not the other

maybe im missing something

thxs

When non condensibles are in system the surface area available for condenser gets affected consequently effect the temperature.If non condensibles present the pressure gauge needle will oscillate.
other reason could be due to refrigerant over charge then both suction and discharge will be high.

[chillyblue]

I would have thought losing one fan, is the same as high ambient temperatures or fouled condenser which causes a reduction in condenser capacity. The condenser can no longer reject enough heat, for it to operate efficently. If theres not enough heat rejection then surely you cannot condense the same amount of gas into a liqiud.
Systems which have operated fine in lower ambient conditions then fail under high ambient conditions, because the liquid in the condenser is reducing the surface area for heat rejection.
What would the symptons of a undersized condenser be??

CB

[skinnymanpig]

ive got a similar question, didnt want to make a new thread. what would happen if the heat transfer to the evaporator was reduced?