Heat Exchange in airconditioner

[Varon]

I let the aircon cleaning crew wash my window airconditioner.. and after it was washed.. it is less cool.. maybe from a micro leak they caused. Bad.

Anyway. I'm researching how aircon work and went to over a dozen sites. I'll summarize it thus and ask something.

The compressor turns the gas into high pressure. While it is passing thru the condenser coil, the gas turns into liquid? I think it's because the evaporated freon become cools again and become liquid, right?

In the expansion valve. The liquid turns to low pressure liquid. (Can you give example of other liquid that is high or low pressure? Water can't seem to do this). When heat is encountered in the evaporator coil, the liquid boils to gas. Right?

Then the boiled gas enters the compressor and everything starts again.

 

[Varon]

Years ago. I had aircon in the office that has ice on the front grill due to low refrigerant levels. At that time. I wasn't interested in the physics of it. Now I do. After searching many sites. I still haven't found the full details. So any knows the exact cascade that occurs after low refrigerant that can make ice form at the front grill? Thanks.

 

[Drakkith]

In the expansion valve. The liquid turns to low pressure liquid.

When the hot refrigerant first enters the condenser the gas loses heat and thanks to the pressure and lower temperature it condenses into a liquid. When the liquid goes through the expansion valve, that pressure it was under is suddenly reduced. This causes part of the liquid to quickly evaporate, turning into a gas and carrying further energy from the liquid, cooling it further. Then this mix of cold liquid and gas enters the evaporating coil and absorbs heat from the air. As the refrigerant absorbs heat, more and more turns to gas until all of the liquid is into a gas again, at which point it enters the compressor to repeat the cycle.

Years ago. I had aircon in the office that has ice on the front grill due to low refrigerant levels. At that time. I wasn't interested in the physics of it. Now I do. After searching many sites. I still haven't found the full details. So any knows the exact cascade that occurs after low refrigerant that can make ice form at the front grill? Thanks.

I had to look this up, and I'm still not sure it's 100% correct, but I'll use it. Apparently when you have a low amount of refrigerant, the pressure in the system drops. This causes more evaporation in the liquid than usual, and since evaporating requires heat, this cools the refrigerant below it's normal temperature. If it becomes low enough the temperature will fall below freezing and ice will form.

 

[Varon]

When the hot refrigerant first enters the condenser the gas loses heat and thanks to the pressure and lower temperature it condenses into a liquid. When the liquid goes through the expansion valve, that pressure it was under is suddenly reduced. This causes part of the liquid to quickly evaporate, turning into a gas and carrying further energy from the liquid, cooling it further. Then this mix of cold liquid and gas enters the evaporating coil and absorbs heat from the air. As the refrigerant absorbs heat, more and more turns to gas until all of the liquid is into a gas again, at which point it enters the compressor to repeat the cycle.

What do you think is the main purpose of the Compressor? Is it to make the refrigerant higher in temperature than the outside air so there would be flow of hot air to outside? But isn't it just like wasting energy by further increasing the temperature of the refrigerant?

Why do you think the Expansion Valve can reduce pressure? What's the principle?

I had to look this up, and I'm still not sure it's 100% correct, but I'll use it. Apparently when you have a low amount of refrigerant, the pressure in the system drops. This causes more evaporation in the liquid than usual, and since evaporating requires heat, this cools the refrigerant below it's normal temperature. If it becomes low enough the temperature will fall below freezing and ice will form.

How come if pressure drops, there would be more evaporation in the liquid than usual?

 

[Drakkith]

What do you think is the main purpose of the Compressor? Is it to make the refrigerant higher in temperature than the outside air so there would be flow of hot air to outside? But isn't it just like wasting energy by further increasing the temperature of the refrigerant?

When the gas is compressed it heats up. Since the gas is not warmer than the outside air, heat will flow from the gas into the cooler environment. The MUST happen. If you did not compress the gas, then there would be no heat flow from the gas to the environment, AND there would also be no cooling from the expansion valve since the gas wouldn't be pressurized.

Why do you think the Expansion Valve can reduce pressure? What's the principle?

Do a quick wikipedia or google search for the details on the valve.

How come if pressure drops, there would be more evaporation in the liquid than usual?

I THINK that the expansion valve is set to keep a certain pressure in the evaporator coil. The lower pressure of the refrigerant means that a larger percentage of the liquid is evaporated to fill up the coil. I'm not really sure though. Also, when you pressurize a liquid, it increases the temperature that it will boil at. So having a lower than normal pressure liquid should lower the boiling point and let more of the liquid evaporate in the expansion valve. Again, I'm not 100% sure on all this.

 

[Varon]

When the gas is compressed it heats up. Since the gas is not warmer than the outside air, heat will flow from the gas into the cooler environment. The MUST happen. If you did not compress the gas, then there would be no heat flow from the gas to the environment, AND there would also be no cooling from the expansion valve since the gas wouldn't be pressurized.



Do a quick wikipedia or google search for the details on the valve.




I THINK that the expansion valve is set to keep a certain pressure in the evaporator coil. The lower pressure of the refrigerant means that a larger percentage of the liquid is evaporated to fill up the coil. I'm not really sure though. Also, when you pressurize a liquid, it increases the temperature that it will boil at. So having a lower than normal pressure liquid should lower the boiling point and let more of the liquid evaporate in the expansion valve. Again, I'm not 100% sure on all this.

Ok. Thanks. After the cleaning crew wash the aircon. The blower got cracked and it wiggled. I managed to turn the aircon on for a few hours. But there is decrease cooling which I presume was because the blower couldn't absorb more air from the room. But after they replaced the blower fan. The cooling didn't increase or not the same as before washing but lessened. Of course washing crew won't admit they damaged the unit. They left already and won't claim responsibility.

So I have to analyze it on my own before calling for repairs next week. What I'd like to know at this point is whether the fan motor can be damaged when the load is uneven.. that is.. the blower fan wiggles to one side. So when it rotates, there is torque effect. In this case, would the motor slow down (it's not automatic) or would it be damaged. Or let's just take the example of a normal electric fan in the room. If you hold the blades while turning the fan on. Would it damage the motor or not with force holding the blades down (hence resisting rotation)?

 

[Drakkith]

I can't say for certain, as I am not very familiar with a blower. Sorry.

 

[Varon]

I can't say for certain, as I am not very familiar with a blower. Sorry.

Do you know why a bigger compressor produce more cooling? I was wondering if it simply speeds up the refrigerant or because the evaporator and condensor are bigger hence the compressor needs to be bigger. If so. This means big or small compressor, the speed of the refrigerant is the same. Any ideas?

 

[Drakkith]

Do you know why a bigger compressor produce more cooling? I was wondering if it simply speeds up the refrigerant or because the evaporator and condensor are bigger hence the compressor needs to be bigger. If so. This means big or small compressor, the speed of the refrigerant is the same. Any ideas?

On it's own it wouldn't. A bigger compressor would be used with a larger system, which would be able to cool a larger amount of air.

 

[ZealScience]

A great group of halogen alkanes (CFCs is one of them) are good gases for refrigerator, you can look for them.

 

[Drakkith]

A great group of halogen alkanes (CFCs is one of them) are good gases for refrigerator, you can look for them.

Umm, was this one of the questions asked and I somehow missed it?

 

[ZealScience]

Umm, was this one of the questions asked and I somehow missed it?

I mean the question in the bracket

 

[timothy1875]

When the gas is compressed it heats up. Since the gas is not warmer than the outside air, heat will flow from the gas into the cooler environment

Surely the temperature within the condenser has to be higher than the external temperature in order for the condenser to reject heat. Within the evaporator the temperature is lower to allow the heat from the warm environment (the room etc) to be absorbed. Heat will only flow from a region of high temp to a low, not vice versa.

Don't forget the superheating and subcooling also.

 

[Drakkith]

Surely the temperature within the condenser has to be higher than the external temperature in order for the condenser to reject heat. Within the evaporator the temperature is lower to allow the heat from the warm environment (the room etc) to be absorbed. Heat will only flow from a region of high temp to a low, not vice versa.

Don't forget the superheating and subcooling also.

You are correct. The coolant is compressed inside the compressor, which also has the effect of heating it.

 

[Drakkith]

I mean the question in the bracket

Oh, I see. In addition to that, just remember that all liquid can be pressurized. It cannot be COMPRESSED, but it can be under pressure. The coolant is in a gas state when it enters the compressor, which allows it to be compressed. It only forms a liquid in the condensor thc to the pressure it is under along with the drop in temperature.

 

[Varon]

So the heat coming out from condenser is more than the heat absorbed by the evaporator because the compressor is adding heat, right?

Anyway is the following sequence correct? If the evaporator inputs say 15 Celsius (just as example for comparison purposes). After the gas enters the compressor, it becomes 100celsius. After it passes by the condenser.. it becomes say 30 celsius. After it enters the expansion valve. Would it become 10 Celsius (just as an example)?

 

[Varon]

I can't say for certain, as I am not very familiar with a blower. Sorry.

I'm asking about electric fan that we have in our living room. Or maybe electric fan are already faced out in the US? Do you mostly use portable aircondioner there now here in the present generation? For those who haven't seen electric fan. These ancient device is like those propellers in world word II tora tora airplanes that the japanese use. After the war, it is mass produced in third world countries after it is discovered it can be used to introduce or move wind within a living room. Now if one holds the blade while the motor is running. Would the motor be damaged? Hope others with actual experience in electric fan can share this.


Another thing. Does anyone know of electron fan RPM sensor that can count the revolution per minute? The aircon service in my country are very dumb. They may not have the equipment to check for fan speed. So I have to measure it myself by maybe pointing a laser at it that can count the RPM and compare it with the same model in my house that is working.

 

[Drakkith]

I'm asking about electric fan that we have in our living room. Or maybe electric fan are already faced out in the US?

I should have said I don't know enough about fans and motors and such in general to make a decent guess, sorry.

Do you mostly use portable aircondioner there now here in the present generation? For those who haven't seen electric fan. These ancient device is like those propellers in world word II tora tora airplanes that the japanese use. After the war, it is mass produced in third world countries after it is discovered it can be used to introduce or move wind within a living room. Now if one holds the blade while the motor is running. Would the motor be damaged? Hope others with actual experience in electric fan can share this.

I have multiple fans in my house and I've never ever met anyone who didn't know what a fan was.

Also, I'm about 90% certain that the electric fan was in use in households before world war 2, and the fan in general has been around a long time.

I know that the box fan I had as a kid could easily be damaged if the blades couldn't turn, but I don't know why.

Another thing. Does anyone know of electron fan RPM sensor that can count the revolution per minute? The aircon service in my country are very dumb. They may not have the equipment to check for fan speed. So I have to measure it myself by maybe pointing a laser at it that can count the RPM and compare it with the same model in my house that is working.

Even if you had one, installing it would most likely require dissassembly of the fan motor. Are you sure you want to go through all that trouble? Removing the fan, the motor, taking it apart, then putting it all back together and installing it all again.

 

[Varon]

I should have said I don't know enough about fans and motors and such in general to make a decent guess, sorry.



I have multiple fans in my house and I've never ever met anyone who didn't know what a fan was.

Also, I'm about 90% certain that the electric fan was in use in households before world war 2, and the fan in general has been around a long time.

I know that the box fan I had as a kid could easily be damaged if the blades couldn't turn, but I don't know why.




Even if you had one, installing it would most likely require dissassembly of the fan motor. Are you sure you want to go through all that trouble? Removing the fan, the motor, taking it apart, then putting it all back together and installing it all again.

No. The laser will count the rotations of the blades. But the blower has many blades. Now I count 9 blades in the evaporator blower. So if the laser can output say 900 RPM for each blade detected. It means the blower runs at 900/9 = 100 RPM. Now I can compare this to a standard working airconditioner of the same model and I can know if my blower is defective. I wonder if the aircon service crew has other methods to know if a blower is detective (it's subtle because it is still running high speed but not sure it is optimal full speed).

Anyway. In message before it. I wrote.

So the heat coming out from condenser is more than the heat absorbed by the evaporator because the compressor is adding heat, right?

Anyway is the following sequence correct? If the evaporator inputs say 15 Celsius (just as example for comparison purposes). After the gas enters the compressor, it becomes 100celsius. After it passes by the condenser.. it becomes say 30 celsius. After it enters the expansion valve. Would it become 10 Celsius (just as an example)? What do you think?

 

[Drakkith]

No. The laser will count the rotations of the blades. But the blower has many blades. Now I count 9 blades in the evaporator blower. So if the laser can output say 900 RPM for each blade detected. It means the blower runs at 900/9 = 100 RPM. Now I can compare this to a standard working airconditioner of the same model and I can know if my blower is defective. I wonder if the aircon service crew has other methods to know if a blower is detective (it's subtle because it is still running high speed but not sure it is optimal full speed).

Sure, but I was talking about getting an electronic counter for the fan itself, not using a laser. Your way seems to be effective.

So the heat coming out from condenser is more than the heat absorbed by the evaporator because the compressor is adding heat, right?

Yes.

Anyway is the following sequence correct? If the evaporator inputs say 15 Celsius (just as example for comparison purposes). After the gas enters the compressor, it becomes 100celsius. After it passes by the condenser.. it becomes say 30 celsius. After it enters the expansion valve. Would it become 10 Celsius (just as an example)? What do you think?

I believe that is pretty much correct.

 

[Varon]

Sure, but I was talking about getting an electronic counter for the fan itself, not using a laser. Your way seems to be effective.




Yes.


I believe that is pretty much correct.

I let the cleaning crew washed it because it's dirty and cooling is not efficient. After cleaning, it's even worse and parts got broken. I should be very angry at them. That's why I'm trying to understand the physics of how aircon work so I won't be so mad.. at least I learned something. I didn't even know the principle of airconditioner a week before this.

Anyway. If we could put a pack of ice (like dry ice) outside, the compressor is not necessary. How do you circulate the refrigerant then. Know any device that can merely circulate gas? Or a gas pump? I only know of liquid pump. Do you know of a gas pump (when I searched at internet.. i only found gas pump as in gasoline pump... lol)