Introduction: Portable Refrigeration System
The following Instructable shows the steps to follow in order to build a low cost portable refrigeration system.
Step 1: What Do You Need?
15 gallon paint bucket
1 m^2 polyurethane foam in sheets. 4 different sheets are needed, two of each density (20 and 26 kg/m3) and two thicknesses per density (1cm and 2cm)
1.5 kg of eutectic gel (the kind from coolers)
Large ziplock bags for the gel.
1 marker for the foam
Step 2: Cut the Foam
Different components should be obtained from the foam:
1. The sheet that covers the internal wall of the bucket. 1cm thickness
2. 4 layers (4cm per layer) that are designed to hold the vials. Each of these will be called a vaccine mold. A vaccine mold will be composed of two 2cm sheets glued together. For 4 layers, we need 8 sheets. Use the most dense foam for these.
3. Protective sheet layer in between each vaccine mold, 1cm thickness
4. Sheet for the base and the cap, 1cm thickness.
The exact internal wall measurements will depend on the bucket that is aquired. For example, for a bucket that measures 30cm in diameter and 35 in height, you would need a 35cm*94.3cm (which is the diameter * pi) sheet of foam.
The molds have a similar approach, if the bucket has a 30cm diameter, if the centimeter of insulation and approximately 1 cm of refrigerant are taken into account, the diameter of each mold should be 26cm or 25,5cm to have a little extra room. The molds don't need to be a perfect fit, there can be some wiggle room since the vials are to be safely kept in their individual slots in the mold.
The protective layers will have the same diameter as the molds. The sheets for the base and the cap should be the same diameter as the bucket.
Step 3: Manufature the Molds
Having cut the foam, the molds are to be manufactured by gluing the sheets together. Make 4 molds.
Mark the spots where the vial slots will go in the mold. The organization should be the following:
36 vials total per mold
18 in the outer circe
12 in the middle circle
6 in the center.
(Use the images for reference)
In order for the vials to penetrate the foam, X marks should be made in each slot, where the length of the cur should be the diameter of the vial.
Step 4: Freeze
The following components must be frozen:
- Protective sheets
- Vial molds
The gel must be frozen according to the manufaturer instructions, it shouldn't vary much from 0°C to 2°C and the amount of time should also be determined from the manufacturer. If the gel must be frozen in a temperature below 0°C, the gel can't be used. And if it must be cooled above 2°C, the system will have decreased autonomy.
The protective sheets and the molds must be cooled to 3°C for around an hour or the time needed for 3°C to be the stable temperature. The foams must be inserted in the system at this temperature.
Step 5: Assemble Base
While the materials are frozen, the base of the system is prepared.
The system must look like the image, where there is the circular sheet on the base of the bucket and on top of it is the radial sheet for the wall.
Step 6: Final Assembly
When everything is at its desired temperature it should be assembled in the following order:
1. Gel on the base
2. Protective sheet
3. Wall/Radial gel
4. Molds with their respective protective sheet
5. Cap sheet
Step 7: Seal the System
The system is sealed completely when the bucket cap is placed. For security, we recommend drilling a small hole on the cap where a thermocouple can fit in order to measure the internal temperature. It's important to keep this hole as small as possible in order to reduce heat transfer.
The internal temperatures should be measured periodically.