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Post by Andrew on Aug 30, 2013 3:20:12 GMT
I don't think there is any such thing as sky temperature. realizing that as I write this there may well be a translation imperfection. but regardless the point of this is that the mixing up of radiation with conduction is the issue. technically space has a temperature defined by the molecular velocity and mass of the very sparsely separated atmosphere out there. a thermometer will tell you nothing. I have solar panels that regularly show a low thermocouple temperature inside the units (there are several in the system)on a cloudless night after some hours of exposure to a dark clear sky relative to the surrounding environmental air. the conditions for such a 'Sky Fridge' to exist limits it real-world application, but the sky needs to be very dry and cloudless the solar units are well insulated from beneath the glass panel is sealed and is able to insulate from the top and it needs to be able to reradiate a significant portion of the IR from the surface of the copper panels. What I am calling the sky temperature, would be the 'temperature' measured by a thermometer if the sky was surrounding the thermometer. The lowest temperature i have got so far is 7C for an air temp of 12C and sky temp of -8C in 50% cloud conditions at 11pm. Freezing temperatures appear possible on a night with a clear sky even while the air temp remains around 10C.
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Post by numerouno on Aug 31, 2013 6:24:41 GMT
Ok, so now you only need to reproduce the historical Indian ice-making machinery, and we're making a NatGeo special!
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Post by Andrew on Aug 31, 2013 6:29:02 GMT
Ok, so now you only need to reproduce the historical Indian ice-making machinery, and we're making a NatGeo special! I am at a loss as to why you are making such a big deal about this. Warm dry air has a very very poor ability to transmit heat to other objects unless it is touching objects where the thermal conductivity of dry air is very low. The science involved in indian ice making in a relatively warm dry climate is not something to get so worked up about. What specifically is your objection to the idea?? Our dispute here can be solved with fairly simple maths where all we would need to make guesses about is the dryness of the atmosphere and the sky temperature available above india where Tyndall said parts of Asia in the himalayan area were not cold because of altitude but rather because of absence of water vapour. Tyndall said that NSW surveyor Mitchell recorded a temperature of -11C at sunrise and 19.4C at 4pm near the town now known as Mitchell in Queensland Australia on about the 20th of June 1845. Tyndall attributed this to the dry air. In dry conditions on earth exceptional cooling can occur where the local air has a poor ability to overcome the surface cooling to space. Finland is for example renowned as a place of numerous lakes rather than being thought of as being a particulary dry place like India must be or would have been before the arrival of widespread artificial irrigation from deep water resources, canals and pipes and so forth.
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Post by Andrew on Aug 31, 2013 7:15:20 GMT
Ok, so now you only need to reproduce the historical Indian ice-making machinery, and we're making a NatGeo special! Some further aspects of night cooling under clear skies W. E. Saunders Quarterly Journal of the Royal Meteorological Society Volume 78, Issue 338, pages 603–612, October 1952 Abstract The nature and cause of the evening temperature discontinuity near the ground is discussed, evidence being given that this is a result of the commencement of dew formation. Regression equations for forecasting the temperature of discontinuity are given. Methods of forecasting the subsequent cooling are discussed, and a detailed procedure given for Northolt. The relation between screen and grass minimum temperatures is briefly discussed. ------------------ ------------- www.cedarmountainsolar.com/nightskyradiantcooling.php-------------- www.ceen.unomaha.edu/solar/documents/sol_29.pdfMEASUREMENT OF NIGHT SKY EMISSIVITY IN DETERMINING RADIANT COOLING FROM COOL STORAGE ROOFS AND ROOF PONDS Passive Solar Research Group University of Nebraska
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Post by numerouno on Aug 31, 2013 10:48:49 GMT
Ok, so now you only need to reproduce the historical Indian ice-making machinery, and we're making a NatGeo special! I am at a loss as to why you are making such a big deal about this. I'm interested in the ice-making tehnique you had found told in a source. If it works, it could be very useful in the poorer segments of India and elsewhere who can't buy their own real electric refrigerator. Extra ice could be stored under sawdust, as the ancient Finns did, if the weather is not suitable during some nights. There could even be a NatGeo special on "the secrets of ancient India revealed".
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Post by Andrew on Aug 31, 2013 11:29:25 GMT
I am at a loss as to why you are making such a big deal about this. I'm interested in the ice-making tehnique you had found told in a source. If it works, it could be very useful in the poorer segments of India and elsewhere who can't buy their own real electric refrigerator. Extra ice could be stored under sawdust, as the ancient Finns did, if the weather is not suitable during some nights. There could even be a NatGeo special on "the secrets of ancient India revealed". I am more interested in why you think it cannot work. You seem to think you cannot have a colder ground surface than the air immediately near that surface. Fairly clearly that is wrong. The surface cools to space and dry air cannot easily cool to space. The surface therefore cools the air. I first heard of the technique as an ancient Persian technique. It is possible the British introduced the technique to India
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Post by numerouno on Aug 31, 2013 11:36:26 GMT
OK, so now let's see some real ice!
Can we see a picture/link of you sky temp probe please? Interested am I.
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Post by Andrew on Aug 31, 2013 12:19:20 GMT
OK, so now let's see some real ice! Can we see a picture/link of you sky temp probe please? Interested am I. If i can get 7C in 12C air at 11pm for a sky temp of -8C and 50% cloud and when the rest of the night was lost to cloud cover it seems possible to get ice if I can get a clear night. All i have is a crude space about 4cm by 6cm by 7cm deep using 7cm thick DOW 300AN polystyrene, that is crudely lined with a single piece of aluminium foil i have pushed down into the space, with cling film over the opening and a temp probe inside. It looks like a shoe box from the outside. I will load a picture soon
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Post by numerouno on Aug 31, 2013 12:52:56 GMT
I actually meant the probe you are measuring the sky temp with.
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Post by Andrew on Aug 31, 2013 13:00:48 GMT
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Post by nonentropic on Aug 31, 2013 19:14:51 GMT
I think India will go fine with the reliability of electricity.
I'm just imagining the hazards of being in a hot sometimes cloudy country and wanting a milk in my coffee.
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Post by sigurdur on Aug 31, 2013 20:01:09 GMT
I think India will go fine with the reliability of electricity. I'm just imagining the hazards of being in a hot sometimes cloudy country and wanting a milk in my coffee. Depends how warm you prefer your milk..
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Post by Andrew on Sept 1, 2013 3:28:33 GMT
books.google.fi/books?id=C3JBAAAAcAAJ&printsec=frontcover&dq=fanny+parks+wanderings+of+a+pilgrim+in+search+of+the+picturesque&hl=en&sa=X&ei=m6kiUvHrKITOsgbE_YHACQ&ved=0CDEQ6AEwAA#v=onepage&q=fanny%20parks%20wanderings%20of%20a%20pilgrim%20in%20search%20of%20the%20picturesque&f=falsefanny parks: wanderings of a pilgrim in search of the picturesque. Vol 1 Chapter 9 Residence at Allahabad "The Ice pits January 22nd-—My husband has the management of the ice concern this year. It is now in full work, the weather bitterly cold, and we are making ice by evaporation almost every night. I may here remark, the work continued until 19th of February when the pit was closed with ...80 pounds weight" "The highest temperature at which ice was made in 1846, at Cawnpore, was 43 degrees fahrenheit or 11 degrees above freezing point" ---------------- books.google.fi/books?id=B-4HAAAAQAAJ&pg=PA324&dq=persian+ice+pit&hl=en&sa=X&ei=SLIiUpS1IIrGtAaYj4HQAg&ved=0CEEQ6AEwAg#v=onepage&q=persian%20ice%20pit&f=falseHistory of inventions and discoveries. 1817 Egyptians heated water during the day in Earthen jars then cooled them at night on roof tops and then placed them in cool cellars where they froze further. ---------------- www.hemmingjorgensen.com/Full catalogue of Iranian ice houses, 71 of which had an associated ice making plant. Sunday 31st August. Finally a clear night so far: 22:45 6.3C, 12.4C air, -13C sky 00:19 6.2C, 11.7C, -14C quite a bit of cloud to west and south still clear to North East 00:35 5.0,11.2 no clouds visible.
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Post by Andrew on Sept 2, 2013 4:08:24 GMT
Almost there! Only one degree from 0C
Sunday 31st August. Finally a clear night:
22:45 6.3C, 12.4C air, -13C sky 00:19 6.2C, 11.7C, -14C quite a bit of cloud to west and south still clear to North East 00:35 5.0,11.2 no clouds visible. 06:30 1.0, 8.1, -17C a clear looking sky with very few very high clouds but with a murky looking veil of what is possibly very fine moisture levels very high in the atmosphere.
I will leave the set up as it is for a few more days then remove the cling film and see what difference it makes.
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Post by icefisher on Sept 2, 2013 5:10:42 GMT
fanny parks: wanderings of a pilgrim in search of the picturesque. Vol 1 Chapter 9 Residence at Allahabad "The Ice pits January 22nd-—My husband has the management of the ice concern this year. It is now in full work, the weather bitterly cold, and we are making ice by evaporation almost every night. I may here remark, the work continued until 19th of February when the pit was closed with ...80 pounds weight" "The highest temperature at which ice was made in 1846, at Cawnpore, was 43 degrees fahrenheit or 11 degrees above freezing point" Living at the side of the sea I have seen frost appear on my windshield when the temp was around 40F. When I lived in the desert you don't see much of that because the air is so dry. But it gets colder because of that, so if you have a thousand slaves scrapping frost off of slabs of glazed rock you might be able to produce a bit of ice. Wow 80lbs out of how many many days? One manager with 29 man days and how many slave man days?
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