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--- projects:vacuum_drier:work_logs:2_first_try [2022/10/15 01:57] – tjhowse
+++ projects:vacuum_drier:work_logs:2_first_try [2022/10/18 06:43] (current) – [Attempt 3] tjhowse
@@ Line 44: / Line 44: @@
 Beans.
-I put my spare jar (two is one, one is none) into the big esky with the dry ice, along with the stainless pot and ice cream, to pre-chill. After another half an hour or so I set everything up again, turned on the vacuum and everything held.
+I put my spare jar (two is one, one is none) into the big esky with the dry ice, along with the stainless pot and ice cream, to pre-chill. After another half an hour or so I set everything up again. The pre-chilled glass jar didn't crack when submerged into the cold bath. I turned on the vacuum and waited.
 ==== Waiting ====
-After an hour or so
+After an hour the ice cream had started to melt a little as the pot absorbed heat from the environment. I put the pot into another esky and filled it with the water ice to slow down the melting. There was some condensation on the outside of the cold trap esky so I put a sheet of insulation foam underneath it to slow down conduction from the tabletop. Once the pot goes onto the hotplate I will put the cold trap into the bigger esky to insulate it further.
+After about three hours the ice cream melted into a undifferentiated beige sludge. Poo.
+==== Attempt 2 ====
+I suspected the first attempted failed due to the small size of the pipe between the food chamber and the cold trap. I went to Bunnings (hardware store) and bought some fittings to make a 25mm interconnect between the two.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-043948.png}}
+Luckily this pack had most of the bits I needed.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-044024.png}}
+Mark 2.
+After a few false starts I managed to get the leakage under control. I pre-chilled the second batch of ice cream by putting it in the esky with the dry ice, rather than in the cold bath, to reduce the chance of contamination by methylated spirits. I bought a fresh bag of water ice and packed it around the food chamber, and sprinkled some salt into the ice to lower the melting point. I left it under a vacuum in the ice bath an hour or so until the surface of the ice cream began to develop a kind of foamy, crusty appearance. I took this as a sign that things were progressing well. About an hour later I took it the food chamber out of the ice bath and left it running overnight.
+In the morning I found the ice cream entirely melted, and the pressure at about 0.4 atmospheres.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-050527.png}}
+Sigh.
+I vented the food chamber and tried to disassemble the cold trap, only to find it still under a vacuum. A solid plug of ice had formed at the top of the cold trap.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-050546.png}}
+Plug'd
+The pipe fitting kit I bought had two crude filters inside. I estimate they would let through an 8mm sphere. I didn't think these would cause a problem since the pipe fittings wouldn't be cold enough to condense the water into ice. I was wrong. I cleared the ice out and chiselled out the filter and set the system up again.
+==== Attempt 3 ====
+This would be the last attempt, as I was nearly out of dry ice. I pre-chilled about four strawberries and a dozen raspberries, then put them into the system with the last of my dry ice in the cold trap. After a few hours there was a fair bit of berry juice on the bottom of the food chamber. I put the food chamber into a 40°C water bath and the juice began to boil spectacularly. I could hear the dry ice in the cold trap bubble vigourously as it tried to keep up with the heat flux.
+After a few hours the dry ice was gone and the cold trap was at around -50°C. I assumed it would not be able to do its job anymore so I shut it down and disassembled the cold trap.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-051739.png}}
+I was too excited to get a proper photo.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-051806.png}}
+p-o-vision.
+The cold trap was full of feathery frost and solid ice! Exactly as I'd hoped. This confirmed that the cold trap was at least kinda working.
+{{:projects:vacuum_drier:work_logs:pasted:20221018-052859.png}}
+Berry sludge.
+I ate some of the strawberries, they weren't nice.
+===== Next time =====
+I am going to try this again with less water volume in the food chamber, and a bigger pipe between the cold trap and the vacuum pump.
 ===== Video =====
-{{youtube>yC4Bo7wB_ug?large }}
+{{youtube>fu1aIfAKpM8?large }}
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