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--- projects:vacuum_drier:work_logs:3_second_try [2022/10/28 03:35] – tjhowse
+++ projects:vacuum_drier:work_logs:3_second_try [2022/10/28 07:02] (current) – tjhowse
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 The kiwi fruit developed a split across the middle.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-033616.png}}
+Frost forming in the cold trap.
+===== Stop =====
-===== Video =====
+Several problems arose. My improvements to the inside diameter of the vacuum pump fittings meant I needed to leave out a one-way valve that prevented vacuum oil flowing back along the pipe if the pump turned off. The pump turned off and vacuum oil flowed back along the pipe, into my cold trap.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-033754.png}}
+Vacuum oil in the cold trap.
+I disassembled the pump to try to work out whether it had been damaged by running with insufficient oil. I couldn't find any significant damage inside, just a bit of wear. I think the motor has a thermal cutout, as it started up again by itself after a short time of being off.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-035748.png}}
+The pump, disassembled.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-034857.png}}
+The food in the chamber when the pump failed. We fed it to the possums.
+===== Tangent =====
+Heating the food is necessary to drive the sublimation of the ice into gas. Heating the food from the bottom works, however the top of the food dessicates normally rather than vacuum-drying like the heated bottom. I want to shine some infra-red radiation onto the food to heat it from above. I ran a tungsten-filament floodlight bulb off my benchtop powersupply at 31.8VDC, however this only gave off a dull glow.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-034404.png}}
+Safer than it looks.
+I don't want to die from electricity, so I don't want to run 240VAC into the vacuum chamber. I could shine the light down from above, but I don't think much IR would transmit through the 15mm transparent plastic on the top of the vacuum chamber.
+I had good success with some nichrome wire. Ideally I could build some kind of rack system that interspersed layers of food and heating elements.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-034451.png}}
+Giving off lots of IR.
+Building this IR heating system would take too long to implement before my dry ice disappeared. Maybe next time.
+===== Success! =====
+Once I'd rebuilt the pump and got everything up and running again I put in some 10mm thick mango slices and ran it overnight. The result was delicious vacuum-dried mango slices!
+{{:projects:vacuum_drier:work_logs:pasted:20221028-035147.png}}
+Foamy, crunchy texture.
+The texture was definitely crispier on the bottom, where the food could absorb heat from the pot. The top side was chewier, more like sun-dried food.
+{{:projects:vacuum_drier:work_logs:pasted:20221028-035319.png}}
+I weighed the cold trap afterwards and it held 105g of water. I did not weigh the fruit before I put it in, or after I took it out. That would've been helpful.
+===== Future =====
+The next step is working out how to get heat into the food uniformly and in a controlled way. I essentially need a toaster inside the vacuum chamber. A rack to hold the food and heating elements to radiate IR onto it.
+===== Videos =====
 {{youtube>Uoaib2deHbw?large }}
+{{youtube>KkSbQajeCC8?large }}
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