Author Topic: Window screens  (Read 4821 times)

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Offline EPAIII

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Re: Mosquitoes
« Reply #75 on: June 12, 2023, 10:19:20 am »
OK, Mosquitoes! Never mind any of the exaggerated stories about mosquitoes big enough to saddle and ride. Never mind about 10,000 pounds of fuel being loaded in one. How about a 100% real and COMPLETELY TRUE mosquito story. Mine, and it really did happen. And no exaggeration on the size of them. They were little, small, standard mosquitoes.

I was born and lived the first two decades of my life in Louisiana, on the outskirts of New Orleans. And we had mosquitoes. Just plain, ordinary, smallish mosquitoes. It was a fact of life there and no big deal. Window screens? Heck yes. There were even trucks with fogging machines that would try to eliminate them in your neighborhood if someone paid for it. It did not work well, but people still paid.

One day in the 1960, probably a Friday, after finishing my last class at college I decided to take a ride outside of town. I came to an old fort on the shore line of the Gulf of Mexico a short time before sunset. I got out of the car and walked toward the water. I got half way there (50 meters/yards) and looked at my arm. I am a white skinned and was wearing a short sleeve shirt. And my arm was BLACK. Both my arms were SOLID BLACK. Both arms were almost completely covered with mosquitoes. And they were all biting me.

I wiped them off while turning around and RUNNING as fast as I could back to the car. I don't know how many times I wiped them off my arms but the number got less as I approached the car and got further from the water. I was seriously worried for my very life. I had no idea how many mosquito bites I could endure. I didn't count, but must literally have killed many thousands of them in only a minute or two.

When I got in the car I wiped them off my arms and face and scrambled for the spray can of flying bug spray I had. I probably came close to choking on the bug spray, but I only wanted to kill every last one inside the car. And I drove back home as fast as I could.

Not monsters. Not even the largest mosquitoes I have ever seen. I have seen far larger ones. But thousands and thousands and thousands of them; the shear number of them scared the daylights out of me.

I have traveled around and lived in other parts of the country (the US) and even visited/lived in a couple of others, but have never, ever seen mosquitoes like that any where else. And I never, ever want to.

That's my mosquito story. It is 100% true. I swear it. Not a single syllable of exaggeration. And I really was scared for my very life.

So you can have your Texas mosquitos. Your western mosquitos. Your eastern mosquitos. Your mosquitos from any other area of the world. I don't care about how big they are. Louisiana mosquitos have them beat in shear NUMBERS. And if you don't believe me, I will take you to that coastal Louisiana fort one summer afternoon. But I am staying in the car.
Paul A.  -   SE Texas
And if you look REAL close at an analog signal,
You will find that it has discrete steps.
 

Offline MK14

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Re: Window screens
« Reply #76 on: June 12, 2023, 10:42:15 am »
Five words:

The second law of thermodynamics.




Pity we can't just invent something, which can turn heat (temperature) as opposed to temperature differences, into electricity.  Saving burning so much fossil fuels and reducing the global temperatures (maybe or maybe not, as that electricity would eventually be turned back into heat, when it is used, typically).

That's kind of how physics works though. Heat is a bit like static electricity, unless the heat (or electricity) is flowing somewhere, no work is getting done.

My understanding, is that it might be theoretically possible.

Example:
You use a very high efficiency heat pump, to turn the existing temperature into a temperature difference, perhaps using a fifth (or hopefully higher) of the electrical energy, that would have been needed, to create the heating (temperature increase) using resistive heating elements.

You then use that temperature difference to power a thermopile  https://en.wikipedia.org/wiki/Thermoelectric_generator  with perhaps an ...
 
Quote
efficiency is approximately 33-37%

can be used.  Then it might be possible, eventually, to make realistic ones, which can 'profitably' extract electricity, out of pure/fixed temperature.

Just that they need to invent, practicable heat-pumps and thermopiles, with the necessary high enough efficiencies, over compatible temperature ranges.

But don't worry.  I've heard about and/or spoken to one or more people, who strongly think that the Physics of what I just said, is relatively impossible and it would never work.

Anyway, as a backup solution.  Perhaps fusion power will be invented one day (by that I mean our own fusion generators, excluding calling solar cells/panels fusion as they use the suns natural fusion energy system).

I've enlarged and set bold, for the bit, I'm replying to, at the very top.

Here is an explanation, of why the heat pumps, I was describing, don't violate the second law of thermodynamics.

Quote
Heat pumps operate as a heat engine in reverse, as they do work from an input of electricity to push heat from a cold place to a warm place. This would seemingly violate the Second law of thermodynamics, but the key reason it doesn't is because this heat transfer is not spontaneous; it requires an input of energy to do so.

Source:
https://energyeducation.ca/encyclopedia/Heat_pump
« Last Edit: June 12, 2023, 10:49:12 am by MK14 »
 

Offline MK14

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Re: Window screens
« Reply #77 on: June 12, 2023, 10:45:25 am »
CO2 is not a pollutant. It is an absolute necessity for plant life.

CO2 levels are just barely just above their all time, in the entire history of the planet, low level. If we remove much of it, we will need a new food source because the plants will start dying out. And then the animals. And then, guess who!

Oh, and the oxygen, which the plants make, will run out too! Choke! Gasp!

Somebody needs to actually think this thing out. NOW!

It really needs someone who can explain the details of global warming, which also is getting too off-topic.

I was only suggesting reducing the CO2 levels, down to whatever it needs to be, to restore this planet back to normality.  NOT a total elimination of all CO2.
 

Online Zero999

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Re: Window screens
« Reply #78 on: June 12, 2023, 02:11:41 pm »
Here is an explanation, of why the heat pumps, I was describing, don't violate the second law of thermodynamics.

Quote
Heat pumps operate as a heat engine in reverse, as they do work from an input of electricity to push heat from a cold place to a warm place. This would seemingly violate the Second law of thermodynamics, but the key reason it doesn't is because this heat transfer is not spontaneous; it requires an input of energy to do so.

Source:
https://energyeducation.ca/encyclopedia/Heat_pump
But the overall system you've described would violate the second law of thermodynamics, because the end result would be perpetual motion.

Quote
You use a very high efficiency heat pump, to turn the existing temperature into a temperature difference, perhaps using a fifth (or hopefully higher) of the electrical energy, that would have been needed, to create the heating (temperature increase) using resistive heating elements.

As I stated in previous post the maximum efficiency of a heat engine is determined by the temperature differential, between the hot and cold sides, with respect to absolute zero. The reverse is also true with a heat pump. The closer the cold side is to absolute zero and the hotter, the hot side is, the more energy is required to shift the same amount of heat, which is also why it's impossible to cool something to 0 K because it would take an infinite amount of energy.

Note Carnot's theorem only determines the maximum efficiency. Real life heat engines never achieve the same efficiency. This means your heat engine wouldn't be able to make enough electricity to power your heat pump, to produce a great enough temperature difference.
 
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Offline MK14

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Re: Window screens
« Reply #79 on: June 12, 2023, 02:27:04 pm »
Here is an explanation, of why the heat pumps, I was describing, don't violate the second law of thermodynamics.

Quote
Heat pumps operate as a heat engine in reverse, as they do work from an input of electricity to push heat from a cold place to a warm place. This would seemingly violate the Second law of thermodynamics, but the key reason it doesn't is because this heat transfer is not spontaneous; it requires an input of energy to do so.

Source:
https://energyeducation.ca/encyclopedia/Heat_pump
But the overall system you've described would violate the second law of thermodynamics, because the end result would be perpetual motion.

Quote
You use a very high efficiency heat pump, to turn the existing temperature into a temperature difference, perhaps using a fifth (or hopefully higher) of the electrical energy, that would have been needed, to create the heating (temperature increase) using resistive heating elements.

As I stated in previous post the maximum efficiency of a heat engine is determined by the temperature differential, between the hot and cold sides, with respect to absolute zero. The reverse is also true with a heat pump. The closer the cold side is to absolute zero and the hotter, the hot side is, the more energy is required to shift the same amount of heat, which is also why it's impossible to cool something to 0 K because it would take an infinite amount of energy.

Note Carnot's theorem only determines the maximum efficiency. Real life heat engines never achieve the same efficiency. This means your heat engine wouldn't be able to make enough electricity to power your heat pump, to produce a great enough temperature difference.

I agree with you. (with some lingering doubts, which could probably be resolved, if I spent ages researching it and perhaps performing experiments).

It seems, one of the effects is called COP (Coefficient of performance), see here:
https://en.wikipedia.org/wiki/Coefficient_of_performance

Which (after my rather quick read up on it, so could be a bit or more mistaken) limits the maximum efficiency of heat-pumps, to values which CAN'T exceed 100% over-all efficiency.  Because if it did, it would violate a number of laws of Physics.

So in summary, I agree with you.  It seems, it would break some fundamental laws of Physics, even if I don't yet 100% understand the full Physics explanations, on why it CAN'T happen.
 

Offline tom66

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Re: Window screens
« Reply #80 on: June 12, 2023, 03:13:21 pm »
Which (after my rather quick read up on it, so could be a bit or more mistaken) limits the maximum efficiency of heat-pumps, to values which CAN'T exceed 100% over-all efficiency.  Because if it did, it would violate a number of laws of Physics.

No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.
 
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Offline MK14

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Re: Window screens
« Reply #81 on: June 12, 2023, 03:19:50 pm »
Which (after my rather quick read up on it, so could be a bit or more mistaken) limits the maximum efficiency of heat-pumps, to values which CAN'T exceed 100% over-all efficiency.  Because if it did, it would violate a number of laws of Physics.

No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

I didn't write/explain it well enough.

I meant, 100% efficiency of the overall system, with a combination of the heat-pump and the thermopile, to turn the heat-difference back into electrical energy.  The idea being to generate more electricity (by inventing much high efficiency heat-pumps and thermopiles, than perhaps are available today), than you initially put into the heat-pumps.
Essentially making a device which turns pure temperate back into electricity, while absorbing some background temperature.

I.e. If a room is at 25 deg C, and you have a discharged car battery.  The car battery could be charged up, but the room temperature would fall to perhaps 10 degrees C.

But as Zero999 (and at least one other in this thread), are pointing out.  The existing laws of Physics, don't allow for this.

I.e. You can't do it, it wouldn't work.  (ok, you can try it, but you would end up putting in more energy (electricity) into the heat-pump, than the thermopile, returns as generated electricity.

Because otherwise, it would be more than 100% efficient, overall (i.e. comparing input electricity into mainly the heat-pump, with the generated/outputted electricity from the thermopile).
« Last Edit: June 12, 2023, 03:25:20 pm by MK14 »
 

Online IanB

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Re: Window screens
« Reply #82 on: June 12, 2023, 03:24:37 pm »
No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

But CoP is not efficiency.

To relate to what MK14 was saying, you have a hypothetical Black Box, connected to various high temperature sources on one side, various low temperature sinks on other side, and the box does useful work (mechanical work, electrical work, whatever). Heat flows through the box from the hot sources to the cold sinks. Inside the box can be any contrivances you like, including the use of heat pumps.

The efficiency is the amount of heat converted to work divided by the total amount of heat flowing through the device. Conservation of energy says that the maximum efficiency cannot be greater than 100%. Other laws of thermodynamics say you cannot even reach 100%.
 
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Offline tom66

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Re: Window screens
« Reply #83 on: June 12, 2023, 03:26:52 pm »
No.  The theoretical maximum CoP for a heat pump is around 8.5.   Real world units are limited to about 5 in ideal conditions, and around 3.5-4 in real world conditions.  Those are all above 100% efficiency.  The efficiency figure can exceed 100% because the energy to the room includes that which is extracted from the outdoor environment, which you don't pay for.  I guess you could try to measure the thermal efficiency of the whole system including that outdoor heat source but I'm not sure exactly what that would tell you or if it would be that useful as a figure.

But CoP is not efficiency.

To relate to what MK14 was saying, you have a hypothetical Black Box, connected to various high temperature sources on one side, various low temperature sinks on other side, and the box does useful work (mechanical work, electrical work, whatever). Inside the box can be any contrivance you like, including the use of heat pumps.

The efficiency is the amount of heat converted to work divided by the total amount of heat flowing through the device. Conservation of energy says that the maximum efficiency cannot be greater than 100%. Other laws of thermodynamics say you cannot even reach 100%.

I agree, ultimately the heat is just moved so it has to come from somewhere.  I guess such a system would probably approach 100% efficiency at a CoP of >8.5 (haven't done the maths, just intuition).   However, I'm not sure what that would tell you.  Maybe give you a figure of merit for the performance of such a system?  Sounds more like a scientific curiosity than a useful measurement.
 
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Online IanB

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Re: Window screens
« Reply #84 on: June 12, 2023, 03:30:14 pm »
I agree, ultimately the heat is just moved so it has to come from somewhere.  I guess such a system would probably approach 100% efficiency at a CoP of >8.5 (haven't done the maths, just intuition).   However, I'm not sure what that would tell you.  Maybe give you a figure of merit for the performance of such a system?  Sounds more like a scientific curiosity than a useful measurement.

Engineering comes into it. Every improvement in efficiency comes at a cost (of design, of manufacture, of materials). At some point, the increased cost outweighs the benefit.
 

Offline MK14

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Re: Window screens
« Reply #85 on: June 12, 2023, 03:38:43 pm »
I agree, ultimately the heat is just moved so it has to come from somewhere.  I guess such a system would probably approach 100% efficiency at a CoP of >8.5 (haven't done the maths, just intuition).   However, I'm not sure what that would tell you.  Maybe give you a figure of merit for the performance of such a system?  Sounds more like a scientific curiosity than a useful measurement.

Presumably, if someone had a great understanding of the gas (Physics) laws.  They could use that (and maybe some other stuff), to calculate the theoretical maximum CoP, at a given input (source) temperature.

I.e.  https://en.wikipedia.org/wiki/Gas_laws

Hence we would know (out of curiosity), what the highest possible CoP value, could be for a perfect heat-pump.  Without violating any laws of Physics, even though technologically speaking, we wouldn't be able to produce a device with such high efficiency ratios.
« Last Edit: June 12, 2023, 03:40:19 pm by MK14 »
 

Offline tom66

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Re: Window screens
« Reply #86 on: June 12, 2023, 03:40:27 pm »
I agree, ultimately the heat is just moved so it has to come from somewhere.  I guess such a system would probably approach 100% efficiency at a CoP of >8.5 (haven't done the maths, just intuition).   However, I'm not sure what that would tell you.  Maybe give you a figure of merit for the performance of such a system?  Sounds more like a scientific curiosity than a useful measurement.

Engineering comes into it. Every improvement in efficiency comes at a cost (of design, of manufacture, of materials). At some point, the increased cost outweighs the benefit.

But why not just measure the CoP?  That is a far more useful figure for the application of a heat pump. 
 

Offline SeanB

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Re: Window screens
« Reply #87 on: June 12, 2023, 05:37:50 pm »
Mosquitos I have many, and you can hear the difference between possibly getting Zika virus, West Nile virus, Chikungunya virus, dengue, and malaria, just from the different varieties of mosquito that fly year round.
 

Online mendip_discovery

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Re: Window screens
« Reply #88 on: June 12, 2023, 06:02:13 pm »
CO2 is not a pollutant. It is an absolute necessity for plant life.

CO2 levels are just barely just above their all time, in the entire history of the planet, low level. If we remove much of it, we will need a new food source because the plants will start dying out. And then the animals. And then, guess who!

Oh, and the oxygen, which the plants make, will run out too! Choke! Gasp!

Somebody needs to actually think this thing out. NOW!

I had a quick google and the data I saw states there has been a massive rise in CO² levels. Given how much we have deforested the planet to further our industrial revolutions. It's not surprising. We need to plant more green stuff.
https://earth.org/data_visualization/a-brief-history-of-co2/

Anyhow, I live in the UK and we don't have a need for window or door screens. We do have occasional spates of lots of flies but not had that for a few years. Though I live in a house where on the hottest day of the year the living room doesnt get beyond 21°C so no need to have the windows open. We do get bees in the house and wasps when it's that time of year but we just learn to let them out.

I have heard of the Scottish "wee midge" but avoided being that far north in the summer so far. I have met thier cousins "Manx Midge" it's all ok being up on the mountain course in the Isle of Man until the wind drops and much like scene from Pitch Black all things change and they begin to devour all life.

Motorcyclist, Nerd, and I work in a Calibration Lab :-)
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So everyone is clear, Calibration = Taking Measurement against a known source, Verification = Checking Calibration against Specification, Adjustment = Adjusting the unit to be within specifications.
 
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