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How to make a peltier cooled cloud chamber. No dry ice!

Part 1: Shopping list and some design considerations.

These pages provide instructions on how to build the peltier cooled cloud chamber shown on my Youtube channel.

Part 1: Shopping list and some design considerations

Part 2: The electronics

Part 3: Assembly

Part 4: How to use

Part 5: Pictures, Videos and some explanations

'Shopping' list:

Only a few components need to be purchased, most items can probably be found 'lying around'.

Electronics: Two 12706 peltier cells - available from EBay at very reasonable prices. 12710's can be used for the 'hot' peltier. These will increase hot side power dissipation by 30% but only marginally increase cooling. See Pictures, Videos and Explanations

Note:  1206 and a 12706 peltier cell are the same - different numbering systems. (same for 1210 & 12710)

AT or ATX Computer Power Supply - this can be any old power supply that can provide 5V @ 2...3 amps & 12V @ 6...8 Amps. If larger peltier cells are used (eg: 1210) then the 12V needs to be able to supply 10...12 Amps. Most PC power supplies are rated over 16 Amps at 12V and over 20 Amps at 5V.

LED lamp - I used a 'Head' lamp - 5 white LED's. Any LED light will work, however a lamp with a row of LED's opposed to a 'cluster' will provide better illumination. Other light sources will work but LED's emit 'cold' light, ie no infra red (heat).

Two small computer fans - optional, used to keep the light and viewing areas of the dome clear of condensation.

Two 470K or 1M Ohm resistors (0.25W are OK) - these are for the optional ion scrubber.

One 0.5...1 watt resistor - optional, used to power the LED lamp from the PSU - exact value and rating will depend upon the LED lamp used. See LED lamp power supply

 

Metalwork: One computer heatsink - the type of heatsink selected will greatly affect the construction. See design considerations below.

Aluminium 'cold plate'. I used another computer heatsink cut all the fins off and ground the surface flat(ish).

Aluminium standoff - 40mm square by ? thickness - see design considerations below.

Thin steel strips (or similar) to make the strain relief fixings to mount the cold plate to the heatsink - see design considerations and Assembly

 

Plastics: NOTE:  Check all plastic materials for proof against the 'fuel' used - Isopropyl alcohol is very effective at producing clear results from -26C downwards but is a solvent and will attack many plastics.

Dome. I used a 1 polycarbonate 'pudding' bowl bought from a local 'cheap' shop (approx' 15cm diameter 11cm tall). Any clear bowl of these approx' dimensions will suffice. Glass has between 3 and 7 times the thermal conductivity of polycarbonate so a glass dome will significantly negatively affect the thermal performance.

Mounting plate. Any waterproof polycarbonate/plastic/fibreglass sheet to mount the assembly on and support it above the water tank.

Polycarbonate/perspex sheet - very thin and 'water clear'. This is for the 'fence'.

 

Insulation: Polystyrene sheet, 20mm thick or so, to make the dome base. See diagram below.

3mm (or so) thick closed cell foam sheet - as found protecting PC motherboards in their retail boxes.

4...5mm closed cell foam sheet/pieces - as found as transport protection in some PC peripheral retail boxes.

Note: Closed cell foam will not absorb water like a sponge (sponges are 'open cell foams'). Each 'bubble' in a closed cell foam is a sealed compartment - thus 'closed cell'.

 

Sundries: 4 x 25...35mm (length depends upon your heatsink/cold plate dimensions - see diagram below.) NYLON m3 countersunk screws with nuts. Use nylon threaded spacers if sufficiently long screws are not available.

2...4 short machine screws to mount the support plate to the stack - see diagram below.

Water container. I used a plastic 16 litre aquarium. Any container will suffice. The larger the capacity the slower the temperature rise of the water - approx' 1C/Min/Litre with this design.

Aquarium water pump (power head type) 5 Litre per minute or thereabouts. This is to force a continuous flow of water through the fins of the heatsink.

12...15mm inside diameter (exact size depends upon your pump) soft(ish) plastic tube, 10...20cm long - to direct the pumped water flow directly into the base of the heatsink fins.

Black cardboard - 0.5mm thick or so - to provide a black base to the area around the cold plate, and optionally for constructing the light 'mask' and condensation fan shrouds.

Felt, or similar material, to act as the 'fuel' reservoir in the dome.

One or two small powerful magnets - used to hold the felt fuel reservoir in place.

Thermal paste - available from Ebay.

4 way terminal block (10 amp minimum rating) - optional.

Computer AT extension cables - optional.

Ringmain cable (solid core mains cable) for the ion scrubber - optional.

Fuel: Isopropyl alcohol is very effective as the 'fuel' for a cloud chamber, however many low 'boiling' point solvents can be used. Please check ALL your plastic components against attack by the 'fuels' used. This design has produced results with water as the 'fuel', but the cold plate rapidly built up a 'frost garden'. See Pictures, Videos and Explanations

'PVA' Wood/paper glue - water based so solvent resistant.

Epoxy resin adhesive - optional

Mat black spray paint - for the top of the cold plate to improve contrast.

 

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Design Considerations.

There are a few design considerations to take into account before starting to cut material.

This section describes some of the design process and provides guidance for sorting out your own system dimensions etc.

The selection of the heatsink is the main factor in the design of the 'Heatsink/Peltier/Peltier/Cold Plate' stack.

Modern PC's (Intels and AMDs) all use a 'circular' heatsink design, these are NOT suitable. Top pic' on right.

Older PC's have flat based rectangular heatsinks. Lower pic' on right.

The old style flat based straight finned heatsink will allow water to flow freely through the fins. The flat base also provides full contact across the peltier cells. If part of the cell is not in direct contact with the heatsink it WILL overheat (locally) and degrade rapidly. Hotspots are death to peltier cells.

If a machined flat aluminium cold plate is not available cutting all the fins off and smoothing down an old heatsink will provide a suitable cold plate. Ensure that you do not damage the 'good' surface of the heatsink during the process - that needs to be as smooth and flat as possible to prevent damage to the peltier cells, as it will be compressing those cells.

 

 
I was lucky in that I found a old Dell Dimension E5 computer with a 'vented fan' system which provided the perfect heatsink for this project. See pic' on right. I would be surprised if these were readily available so I will describe an alternative approach here.

Assuming a heatsink similar to those 'old style' shown above:

Take a block of aluminium at least 40mm x 40mm (to match the size of the peltier cells). The exact thickness will depend upon the materials used later - see diagram below. This can be cut from another heatsink base if one of suitable thickness can be sourced (and if no other aluminium sheet/block is available). The top and bottom surfaces of this block MUST be ground flat. This can be achieved either by machining or hand filing and finishing using fine grade wet&dry paper and a truly flat surface - I used a polished marble block. Note: Copper could be used to replace this aluminium block.

The standoff provides space to place insulation between the cold plate and the heatsink. The temperature difference between the heatsink and cold plate is at a maximum in this area (60C or so), so thick insulation of 15mm+ is recommended. Minimising heat transfer is the key to good operation.

Note: Each material junction - Al...Al or Al...Peltier - will reduce the thermal efficiency, even with properly applied thermal paste. So use as few layers of material as possible to provide the standoff required by your materials.

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Cross section diagram through the device.

From the above diagram it can be seen that the aluminium block does not appear to be necessary. However if it is removed the space between the cold plate and the heatsink would be reduced to 7mm (each peltier is 3.5mm thick). Add the support plate and the insulation layer would only be about 3.5mm thick (assuming 3.5mm support plate.) 3.5mm of insulation is NOT sufficient with the temperature difference between the two surfaces of around 60C.

The ideal position for the coldplate is 0.5mm to 1mm above the level of the black card/polystyrene insulation.

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Closed cell foam is used for insulation between the heatsink and coldplate. This resilient foam will compress elastically (unlike polystyrene) and will maintain a good fit through assembly/disassembly and temperature cycles.

Polystyrene is used for most of the base due to it's very effective insulation properties and it is resilient to isopropyl alcohol.

I used a perspex disk (a failed Wimshurst machine disk that was available) for the mounting plate, 3.5mm thick.

A good fit of the mounting plate to the heatsink is required to prevent excess water leakage, since the heatsink will be immersed in water and water will be pumped rapidly through the fins. This area could be sealed with a sealant.

Mounting plate is fitted to the heatsink via machine screws. The cold plate is fixed using nylon screws passed through the insulating foam and mounting plate to 'spring bars' passed through the heatsink fins. If the cold plate and heatsink are the same size mount the heatsink at 90 degrees to the cold plate so the nylon screws do not directly touch the heatsink. See diagram above right. The 'spring' bars allow for thermal expansion/contraction during operation keeping the stack compressed.

Nylon screws MUST be used here. Metal screws will conduct heat directly from the heatsink/outside environment into the cold plate. These 4 thermal paths would conduct far more heat into the chamber than all other paths combined - it may not even work at all with metal screws - I won't waste my time to find out.

 

The 'Fence' is a barrier to help trap the coldest air over the cold plate. Without the fence the densest cold air will spill over the edge onto the polystyrene insulation base and warm up a little. Without the 'fence' the active zone is only about 1...2mm deep. With the fence this is increased to upto 5mm. Sketch on right is exaggerated!

'Water clear' 0.5mm thick perspex is used for the 'fence'. It needs to be clear as the optimum light angle is parallel to the surface of the cold plate. See Assembly

A 'fence' higher than about 5mm does not appear to increase the active layer depth and starts to have a significant effect on imaging - light flares etc!

Watercooling. I selected a watercooled system for two reasons. The first was the expense of a suitable aircooled heatsink that would provide sufficient cooling. Second, with watercooling the temperature of the heatsink can be controlled much more finely. The water can be refreshed or topped up with ice to keep the temp' in suitable range. With water at between 10C and 20C I can easily keep the cold plate between -45C and -38C. See explanations

In a run with salt water brine at the cold plate achieved -58.5C! (Everything thoroughly rinsed in fresh water afterwards to prevent corrosion and salt buildup.) Peltier cells become less efficient when cooled! See explanations

A 5 litre/minute water pump pushes water directly through the base of the heatsink fins. The water rises approx' 0.2C on exiting the fins with an input power of approx' 60 Watts. Overall temperature rise can be calculated at 1C/Litre/Minute, my 16L tank rises approx' 4C/Hour.

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Part 1: Shopping list and some design considerations

Part 2: The electronics

Part 3: Assembly

Part 4: How to use

Part 5: Pictures, Videos and some explanations

 

How to make a CD wimshust machine - A 9.3 minute video providing full instructions on how to make a wimshurst machine from CD blanks and household items.

CD wimshurst machine 1 - wimshurst machine, cobbled together in an afternoon from scraps and a couple of CD's.

CD winshurst machine 2 - Short video of the wimshurst machine made in the 'How to build a CD wimshurst machine' showing max sparks of 15mm and overloads.

32cm wimshurts machine - A short video of a wimshurst machine with 32cm disks, this produced over 130mm sparks and is a very reliable wimshurst machine.

Cloud chamber 1 - 1 short video of an Alpha source (Am241) and background radiation in a homemade peltier cooled cloud chamber without dry ice.

Cloud chamber with Water as the 'fuel' - a short video demonstrating water as active vapour, very quickly frosted up! How to make a cloud chamber without dry ice.

Poorly Lit homemade cloud chamber- contrasting good and bad lighting in my homemade peltier cloud chamber! No dry ice.

Granite in a cloud chamber - no dry ice - some activity from a piece of granite. No dry ice, peltier cooled.

Background radiation in a peltier cloud chamber - no active sources anywhere near, just background radiation. Peltier cooled, homemade cloud chamber not using dry ice.

How to make a cloud chamber - a 5 minute video on how to build a simple cloud chamber in less than an hour. How to build a cloud chamber without dry ice, peltier cooled.

 

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