I could have left the vacuum pump running and eventually all the alcohol would evaporate. The same with the water, but all the moisture ends up in the vacuum pump oil. It's very hard on vacuum pumps.
It is a different substance so It has a different saturation (boiling temperature) it is still changing state (evaporating) , it's just doing so slower than boiling. I don't have a pressure chart for alcohol.
@@love2hvac I thought so I just wanted to make sure. Thank you for your prompt replies and your videos and explanations are great, wish I had this platform when I first came into the industry. Thank you
Because the temperature of the alcohol dropped. It was still changokgnstate, evaporating, just not boiling. I would need to lower the pressure again to make boil again.
That's a great question. water has a table that shows what vacuum and what temperature boiling would be at. Alcohol It would depend on what kind of alcohol and %. I'm sure someone out there has this data. Wine would me more difficult with the sugar content and other stuff in it.
I think I may be over thinking all this. I understand that when a substance boils/evaporates heat is removed from it by being carried away by the vapor. But the whole latent heat thing I thought i understood until this example, If latent heat is a change of state without a change in temp, and the temp of the water or alcohol drops when this change in state is happening, how does that definition make sense? But i also understand that latent heat is the extra energy needed to change state after a substance gets to that change of state temp. So Im a bit lost.
Have you watched the videos before this point? They help build the ground work to this example. Let's start with you first statement. "A substance boils/evaporates heat is removed from it" In reality it is the opposite. When a substance boils or evaporates it the substance ABSORBS heat! It changing state from a liquid to a vapor will absorb heat from what ever is around it. However dropping the pressure we drop the boiling point. Now as it boils it absorbs heat from itself. It's taking the heat that it already has in sensible and moves it to latent. The heat is still there it's now hidden. Bu taking away sensible heat the temperature drops, but the heat has to go somewhere, so it goes to the change of state latent heat. It absorbed the heat into itself. It has to do this to maintain a saturated temperature. Every time we change the pressure we change the boiling point and latent heat point. Think of a propane tank. As you use vapor propane more liquid has to boil into a vapor to maintain the ballance. But as propane changed from a liquid to a vapor it absorbs heat also dropping it's temperature. As the temperature drops the pressure also drops. Sometimes you will even see a frozen propane tank in summer because of this. Temperature, pressure and saturation. I define things in a very specific way to help with each step. So make sure to write them down so when you get to the next part you can reference it . Latent heat, a change of state without a change in temperature, latent heat. Sensible heat change of temperature without a change of state. Boiling / evaporating a substance changing state from a liquid to a vapor absorbs heat, latent heat. It is a cooling effect. Condensing changing state from a vapor to a liquid rejecting heat, latent heat. It's a heating effect. Temperature pressure, by changing the pressure we can change the boiling/condensing temperature.
@@love2hvac Thanks for the reply. I think i get what your trying to say, its just that I think of it differently maybe. When you say absorbing heat from itself you mean The vapor is absorbing heat from the liquid but I was taught that whats actually happening during the liquid to gas change is the molecules in the liquid substance are heated up to the point that they seperate/break there bonds and then are released in the form of vapor molecules which carry away the heat that was applied to them to break those bonds. And the molecules that are left behind in the liquid have a lower energy than the ones leaving which causes the cooling effect, the liquid will now be cooler because theres less thermal energy left over. I guess it depends on how you think about it. Thats what I meant when i said when a liquid boils/evaporates heat is removed. I meant removed from the liquid. I think we are coming at it from two different angles here haha. I totally understand the refrigeration cycle and what is happening at every stage and how pressure/temp and boiling points work. Now, I do agree that when rifrigerant is boiling in the evaporator it is absorbing heat from the air passing over it and that is occuring because of heat transfer from warmer air to a colder coil,and i understand that all the heat absorbed is latent untill it is 100% vapor where it will become sensible therafter measured as superheat. Also Ive always thought when lets say you have high humidity in the space your cooling, you have a lower delta t because most of the heat being removed from the air passing over the evap is latent heat coming from the phase change from vapor to liquid in the form of condensate so you wont be able to measure all of the heat transfer taking place even though theres more transfer than it seems. After reviewing what you wrote here, Im pretty sure I understand everything you said now and let me know if Im wrong please
That is correct. After the metering device you have flash gas. The refregerant that changes state from a liquid to a vapor also absorbed heat from itself causing the saturated mixture to drop even before absorbing heat from the air. Yes moisture in the air condensing has a big effect on the evaporator. I have a video on this also. It also proves why the "20delta T" is not correct. It can be measured but not with a sensible thermometer. If we know the volume of air, the wet bulb in and the wet bulb (delta WB) out we can calculate the BTU, Alternatively we can measure the volume of air with delta T and measuring the quantity of condensate. Or even measure the delta T at the condensor with the volume but that will also include suction line and compressor heat.
thank you for writing your speck
i follow you from Iraq
Really happy to see such experiment..gained much knowledge today..Ty thnx.
That's great to hear!
Yes violent boil but it did not get very cold. Not a great refrigerant substance in this case. Lower pressure?
Uncle Ty's HVAC and science show -
Remember kids, be sure you have adult supervision before doing experiments with alcohol.
Great videos, thank you. What does it mean when the alcohol stopped boiling and the water example you did kept boiling until the water was gone?
I could have left the vacuum pump running and eventually all the alcohol would evaporate.
The same with the water, but all the moisture ends up in the vacuum pump oil. It's very hard on vacuum pumps.
@@love2hvac so why need the alcohol stop boiling when the temp dropped?
It is a different substance so It has a different saturation (boiling temperature) it is still changing state (evaporating) , it's just doing so slower than boiling.
I don't have a pressure chart for alcohol.
@@love2hvac I thought so I just wanted to make sure. Thank you for your prompt replies and your videos and explanations are great, wish I had this platform when I first came into the industry. Thank you
Hello, very instructive video. A question : why the alcohol stops boiling at some point even that more vacuum is made?
Because the temperature of the alcohol dropped. It was still changokgnstate, evaporating, just not boiling.
I would need to lower the pressure again to make boil again.
I saw an expriment where water boiled at seas level and about 70* f with about 28 in HG. How many HG does it take for alcohol? What about say wine?
That's a great question.
water has a table that shows what vacuum and what temperature boiling would be at.
Alcohol It would depend on what kind of alcohol and %. I'm sure someone out there has this data.
Wine would me more difficult with the sugar content and other stuff in it.
Like a swap cooler cool
I have the same thermometer. Harbor freight special lol. Works great. Just slow
They really are not bad. I burn threw a lot in classes haha but its fun!
Start the Learn HVAC playlist in sequential order here
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I think I may be over thinking all this. I understand that when a substance boils/evaporates heat is removed from it by being carried away by the vapor. But the whole latent heat thing I thought i understood until this example, If latent heat is a change of state without a change in temp, and the temp of the water or alcohol drops when this change in state is happening, how does that definition make sense? But i also understand that latent heat is the extra energy needed to change state after a substance gets to that change of state temp. So Im a bit lost.
Have you watched the videos before this point? They help build the ground work to this example.
Let's start with you first statement.
"A substance boils/evaporates heat is removed from it"
In reality it is the opposite. When a substance boils or evaporates it the substance ABSORBS heat!
It changing state from a liquid to a vapor will absorb heat from what ever is around it.
However dropping the pressure we drop the boiling point. Now as it boils it absorbs heat from itself.
It's taking the heat that it already has in sensible and moves it to latent.
The heat is still there it's now hidden.
Bu taking away sensible heat the temperature drops, but the heat has to go somewhere, so it goes to the change of state latent heat.
It absorbed the heat into itself. It has to do this to maintain a saturated temperature.
Every time we change the pressure we change the boiling point and latent heat point.
Think of a propane tank. As you use vapor propane more liquid has to boil into a vapor to maintain the ballance. But as propane changed from a liquid to a vapor it absorbs heat also dropping it's temperature. As the temperature drops the pressure also drops. Sometimes you will even see a frozen propane tank in summer because of this. Temperature, pressure and saturation.
I define things in a very specific way to help with each step. So make sure to write them down so when you get to the next part you can reference it .
Latent heat, a change of state without a change in temperature, latent heat.
Sensible heat change of temperature without a change of state.
Boiling / evaporating a substance changing state from a liquid to a vapor absorbs heat, latent heat. It is a cooling effect.
Condensing changing state from a vapor to a liquid rejecting heat, latent heat. It's a heating effect.
Temperature pressure, by changing the pressure we can change the boiling/condensing temperature.
@@love2hvac Thanks for the reply. I think i get what your trying to say, its just that I think of it differently maybe. When you say absorbing heat from itself you mean The vapor is absorbing heat from the liquid but I was taught that whats actually happening during the liquid to gas change is the molecules in the liquid substance are heated up to the point that they seperate/break there bonds and then are released in the form of vapor molecules which carry away the heat that was applied to them to break those bonds. And the molecules that are left behind in the liquid have a lower energy than the ones leaving which causes the cooling effect, the liquid will now be cooler because theres less thermal energy left over. I guess it depends on how you think about it. Thats what I meant when i said when a liquid boils/evaporates heat is removed. I meant removed from the liquid. I think we are coming at it from two different angles here haha. I totally understand the refrigeration cycle and what is happening at every stage and how pressure/temp and boiling points work. Now, I do agree that when rifrigerant is boiling in the evaporator it is absorbing heat from the air passing over it and that is occuring because of heat transfer from warmer air to a colder coil,and i understand that all the heat absorbed is latent untill it is 100% vapor where it will become sensible therafter measured as superheat. Also Ive always thought when lets say you have high humidity in the space your cooling, you have a lower delta t because most of the heat being removed from the air passing over the evap is latent heat coming from the phase change from vapor to liquid in the form of condensate so you wont be able to measure all of the heat transfer taking place even though theres more transfer than it seems. After reviewing what you wrote here, Im pretty sure I understand everything you said now and let me know if Im wrong please
That is correct.
After the metering device you have flash gas. The refregerant that changes state from a liquid to a vapor also absorbed heat from itself causing the saturated mixture to drop even before absorbing heat from the air.
Yes moisture in the air condensing has a big effect on the evaporator.
I have a video on this also. It also proves why the "20delta T" is not correct.
It can be measured but not with a sensible thermometer.
If we know the volume of air, the wet bulb in and the wet bulb (delta WB) out we can calculate the BTU,
Alternatively we can measure the volume of air with delta T and measuring the quantity of condensate.
Or even measure the delta T at the condensor with the volume but that will also include suction line and compressor heat.
@@love2hvac all great info,thank you