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equation to work out temperature rise please?

Hello,

I would like to create a transparent chilled micro studio space: this is to photograph insects (which won't move if the temperature is cold so I can take a photo without harming them).

My *basic* idea is 2 cube tanks from plexiglass, one approx 30*30*30cm (the smaller, in which the insect sits) and the larger 50*50*50, 2 tubes between them in a one way system to let air cycle between them, the larger with lots of freezerblocks and an aquarium pump to circulate the cold air through the system.

I'm after a sustainable temperature (for approx 1 hr) of 1-3 degrees C. The sides have to be clear to let light from the flashes through, and there's a special slot in area into which a lens will poke through into the smaller cube.

It's all perfectly doable and would in all honesty be a godsend if I could get it working.

The thing is... I don't have the foggiest idea if it'll be cold enough, ie stay at the 1-3 deg C for an hr with a bunch of freezer blocks and a pump. And before making it it'd be good to know that theoretically it should work.

Before I embark, would anyone knowledgable about such things be able to do a 'back of an envelope' rough guesstimate of whether it's likely to work or to be a miserable failure?

Many thanks!!!

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ingleslenobel (author) 4 years ago
This is my proposed gadget, what do people think. Any obvious problems?

Thanks!

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Well, Although I appreciate the drawing, I have trouble reading the handwriting. Think I get about 70% of it.

I see you plan on a glove box. this seems like a good idea to keep box sealed.
Toga_Dan4 years ago
I say try it and see. If necessary, put styrofoam lid on box between shots. Try to avoid holes in the sides or bottom thru which cold air can leak out. A small fan (from a computer?) will probably move more air than a pump. Perhaps convection would be adequate if there were a hose at top of box and at bottom connecting to the ice box.

Are these exotic insects? If they die from exposure to too much CO2 from dry ice, would you be heartbroken and set back monetarily?

Cold blooded critters don't need as much air as warm bloodeds.

Simplest/ cheapest prototype: Make a cube with coat hangers and tape, secure a white trash bag to it (it lets light thru) If it works... good, if not... you've lost 20 minutes build time plus the scraps you made it from.
ingleslenobel (author)  Toga_Dan4 years ago
No, not exotic, just common garden insects (moths). CO2 won't kill them, that's actually another method that's used a lot but I'd rather try this one.

I wonder, I've been reading about 'dessicants' that remove humidity by having water stick to them (silica gel). I wonder if drawing the air through this would help a bit in removing some condensation as well.
Seems like it would. I get packs of dessicant in seaweed sheets for wrappin sushi. I bake em on warm to re- activate em.

Another thought: what if you made 2 plexi boxes, 1 fits WITHIN the other. Thus you have an ice water jacket around the habitat. You could even add salt to the ice to make it more coolerific (just like an ice cream maker)

Have you done solvent welding on plexi? It requires a fairly tight joint, but makes a nice strong watertight joint if you have tools + skills to do it.
ingleslenobel (author)  Toga_Dan4 years ago
Never tried solvent welding, no. But I've used araldite positioned with a stick for other jobs and although it's a little tricky to position precisely, it's done wonders for me. So attaching things to each other wouldn't seem to be an obstacle I think.

Someone on Twitter also suggested putting one inside the other and although it might seem a very nice solution in fact it wouldn't work because the flashes (I use 4) are positioned round this whole contraption (and there's a field monitor behind to give background). For example that's how I did this, at http://www.flickr.com/photos/jingleslenobel/7191333770/in/set-72157623492127788/

I think I've got the design of the thing down on paper, I'll scan it at the w/e and put it up here for a final sanity check before I acquire the neccessary materials. Thanks everyone for your input!
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While you don't have the foggiest idea it will be the fog or rather the condensation that will make this hard to pull off. Cooling a little clear plastic box to 1 - 3 C will draw every bit of moisture around it to the outside of the container. Much like any cold drink you have builds up condensation on the outside of the cup. Every time you open the lid to get to the inner box you'll be introducing more moisture to it and fogging up the plastic again. This will eventually clear if you have good circulation of the cold air through the refrigeration unit. You also need to consider using an insulated double pain glass. Otherwise the cold air will penetrate the small box and chill the larger one as well so the larger box and your lens will be covered in condensation.

Think of this like the freezer isle of your local grocery store. The glass doors are double pained and insulated with argon or some other gas between the pains. When you open the door you allow fresh moist air into the unit and it condensates on the inside of the glass. In time that moisture will be taken out of the unit as the cold air is fully circulated through the refrigeration coils. But it takes time. You also have to worry about shooting through that glass and any possible glare from it. Cutting a hole for your lens will allow moisture into the system and fogging your lens. So you would need a good seal around the lens and window and hope the lens itself is well sealed or moisture will get trapped inside and ruin it.

Overall your idea is doable but you have a lot more things to consider and a whole lot of trial and error before you'll find the ideal setup.

I think a better option would be to have a small freezer and freeze the bugs for a couple of hours then take the pictures. If you are worried about killing the bug, don't! They would have to stay in the freezer for over a week before they will die. If you give them time to thaw out they will come back to life.
ingleslenobel (author)  mpilchfamily4 years ago
Hello mpilchfamily

many thanks for the imput as well! Yes I'm very familiar with condensation issues because of startrail photography on freezing nights! Something I didn't write down in the initial description was the addition of a fan in the smaller cube flowing air over the optical surface to the outside - this is how we keep condensation from forming when we're doing a startrail.

Glare is not a problem - I already work with shooting into a highly reflective field monitor using a micro stage and diffusers. In terms of lens protection though I'm tending towards the hole (& tube) that the lens is fitted into having a large cover slip over the end - these are optically perfect but will at least keep humidity away from the lens.

But, assuming the above is sorted, is there any maths to support the idea that 30cm^3 of cooler blocks + pump will keep 20cm^3 between 1 and 3?

Thanks!
quatch4 years ago
Have a look at peltier coolers, they are nice and small and simple.
ingleslenobel (author)  quatch4 years ago
Hello quatch,

Many thanks for your input! I had a long look at peltier coolers first but was advised against this due to their inefficiency and need for large cooling fin things. This was the most obvious initial path but apparently imparctical.