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Tag Archives: cooling

Cup cooler #3

Build #3

In my continuing effort to build a working cooled cup holder, I’ve put together another unit. In this attempt, instead of using a plate and having the container cooled from the bottom I decided to attach it to the side, and have a small enclosure to attempt to insulate the beverage a little bit to help increase the cooling effect. Also, from my experimentation in part 1, I found that the cooling elements produce tons of heat, and so would need a quite large heat sink to keep things cool. Since these devices work by producing a certain temperature delta from one side to the other, keeping the hot side as cool as possible is key, and apparently very difficult. Cooling from the side allows for a large sink without holding the beverage up in the air. As you can see in the above picture, this build features a large Dell workstation CPU heat sink I scored off EBay for about $15. These are nice and feature a copper base fused with copper tubes that carry the heat into the aluminum fins. A salvaged fan forces some air through the fins.

The main design of this build features a printed cylindrical body with an opening on one side. Aluminum sheeting is cut and fit on the inside of the container to help transfer the cooling to all sides, and a piece of aluminum flat stock is used as the main contact with the cooling element and covers the opening. The cooling element used is a 12 volt, 16 amp version. Two large U brackets hold the assembly together and press the heat sink tight to the hot side of element. I’m using the same 10 amp, 12 volt power supply brick as the previous experiment.

Test Results

In this experiment I’ve powered on the element and placed a glass container of Diet Sun Drop, measured at about 38F to start, and let the unit run for approximately 30 minutes. The plate measured about 33 F inside the container while running, and the heat sink fins stabilized at around 100F. That’d a good step forward, as previous experiments seemed to just keep getting hotter. However, it did not manage to keep the soda cold. After the 30 minutes, with the ambient temperature around 70F, the soda measured about 45F, not a huge increase, but nowhere near our cooling goal.

Conclusions and Analysis

Reflecting on the experiment, I’ve already noticed several problems. One, I didn’t use a control. That is, I should have left another soda on the bench next to the experiment and measured its after temperature as well. This would give a measure of how much effect, if any, that the cooler had on the soda. Secondly, I was overloading my power supply. It measured about 145F after the experiment. What I didn’t measure was the voltage output of the supply to ensure the load wasn’t causing the output to sag.

In the next round, I will try a few improvements. My fan, while very quiet, could be a little faster to keep the heat sink temperature down, which should decrease the cold side temperature. I will use a higher current power supply to ensure the element is operating at full power and the supply can operate in a safe manner. I may try higher power cooling elements as well, and possibly experiment with stacking the elements to achieve colder temperatures.

This project is turning out to be more challenging than originally planned. However the prospect of keeping my soda cold with a high power home built contraption is enough to keep on trying. More to come…..

Genesis

A seemingly simple project, this is one I’ve been thinking of making for a long time now. Mostly because I had acquired a couple of thermoelctric cooling elements and wanted to use them for something. That, coupled with a desire to keep my soda cold while writing code, pushed me into this challenge. Now, while in theory, this device is pretty simple. In fact, I’m pretty sure a few already exist that I could probably just buy, but there is no fun in that. The challenge comes in that thermoelectric coolers suck. They eat power, are terribly inefficient compared to compressor based cooling systems, and generate a lot of waste heat. In fact, I own a thermoelectric powered travel cooler and at best it could maybe keep stuff slightly colder than a regular cooler. It certainly couldn’t chill anything. However, they are solid state and small, that is if you don’t count the heat sink and fan required. The challenge is not just to build one, but build one that actually works.

Criteria for Success

A good project always needs a sound criteria for reaching success. Otherwise, how will you know when you’ve succeeded? In this case I’m going to set my goals rather high. The primary goal will to be to keep a 20oz plastic soda bottle ice cold, for an indefinite period, at average room temperature. I’ll set the standard for ice cold as 35 degrees Fahrenheit, about the temperature of the average refrigerator. Once I feel I’m close to the goal, I’ll probably have to design a test rig to get an accurate measurement. That’s a pretty stiff requirement, but to make it easier, I will focus on keeping a cold soda cold, rather than trying to chill a warm one. Another tough aspect is using a plastic bottle. Bottles tend to not have a lot of surface area that contacts the surface they are on, and the plastic probably won’t conduct heat very well. As an alternative goal, I can attempt to do the same with a 12 ounce aluminum can. Presumably a metal can would get better thermal transfer from the cooling surface, but at the same time would leak more heat into the air than the plastic bottle would.

Experimentation

Stop the World and Melt with Me, Build #1

My first experiment will make use of a cooling element I aquired some time ago from All Electronics. Here’s the specsheet they provided. The basic operation of these modules is to create a temperature differential between the hot side and the cold side. The spec on this module give a max temperature delta of 79 C (174 F). I wasn’t quite sure how to read the graphs on the sheet, but I figure at 12 volts I could hope for a 60 – 70 C (140 -158 F) delta. Now, that temperature difference, I assume, is from side to side of the element. So given the temperature gradient from the element surfaces to the surfaces I’ll be measuring, I probably won’t see that big of a delta.

Supplies:

  • Power Supply, 12 volt 10 amp, brick style (for monitor or TV) via Ebay, $12.99 USD.
  • Aluminum Plate, 3 inch diameter, 1/4 inch thick, via Ebay, $13.15 for 2.
  • Long machine screws and nuts, #10 x 1.5 inch, via TrueValue, $3.58 for 4 bolts and 14 nuts.
  • Printed parts, via myself, (STL Files: Top, Bottom)
  • Heatsink, via Newegg, $11.99
  • Thermoelectric cooler, 40mm X 40mm, 80 Watt max, via AllElectronics, $14.75.

Here’s what it looked like:

Unfortunately, this build had a couple issues from the start, which is a shame since it was rather small and quiet. First and foremost, the little chip set cooler heat sink/fan combo was ridiculously undersized. While it did cool the top side, the bottom side quickly rose to a fairly high temperature around 150 Fahrenheit. This not only above the max temperature rating for the element, but it also deformed the PLA frame.

With the high temperature on the hot side, and the heat capacity of the top aluminum plate, I was only getting slightly less than 50 F on the plate. As a side note, I was having a difficult time measuring the temperature of the plate with my IR thermometer, as the reflectivity of the plate caused it to just return the room temperature. I finally figured out that a small piece of tape on the surface would give me the ability to measure it better. Since the aluminum discs I bought came in quantities of 2, I repeated the experiment with the extra disc between the element and the heat sink. This made it work better for a short period, but the heat quickly built up and the same situation occurred. The simple conclusion was that my heat-sinking was insufficient, and that a larger heat sink would be required to whisk away all the waste heat fast enough to keep the element working effectively.

Now I did try the same setup a second time with a different element that I also had. I also bought this from All Electronics a long time ago, but unfortunately they don’t sell that unit any more, so the specs are unknown. The only things I know is that the unit itself is smaller, 30mm square as compared the the other unit at 40mm square, and the smaller unit drew about 2.5 A when first powered on as opposed to about 5.5 A that the other unit drew at 12 V. This configuration was at least stable, the hot side topped out at about 110 F, and the top disc dropped to about 45 F. I would have expected a higher temperature difference to have developed, but I think the smaller unit lacked the cooling power to get the 1/4 inch thick disc any colder.

Build #2

Armed with the knowledge that I was not sinking enough heat, I got a slightly larger, cheap CPU heat sink, about $9.99 from NewEgg. I also purchased two more of the 3 inch diameter aluminum discs from eBay, just in case. After a few experiments, I was having the same issue with the large cooler, heat would build up extremely fast on the hot side, limiting the temperature drop on the top side. I also had the same issue with the small cooler, not being able to drop the temperature of the disc very well. Although testing the small unit on the new heatsink, without the top disc revealed that the units were reaching a good temperature, just below 30 F, cold enough to form a bit of frost on the top.

I experimented more with the large unit, using the 3 spare discs in increase the mass of the heat sink. Although I used quite a bit of thermal paste, I feel that the effectiveness was limited by the heat transfer between the discs. But it did seem to work better.

As you can see, I didn’t bother making a frame for this experiment, I may have been a bit premature on printing a frame for the first build. With this setup, it initially worked fairly well with the big element, dropping the top plate temperature down to about 25 F. This seemed promising, but the hot side rose to around 140 F after
5 minutes or so, which brought the top disc up to around 40 F. I shut it down around then, because i didn’t know when or if it would achieve a stasis. I did test this with the smaller cooler, which did reach a static state, just under 100 F on the hot side, and about 50 F on the cold disc. I removed the top plate to measure the unit directly, and showed about 30 F on the top of the unit. A similar direct measurement of the top of the larger unit showed an initial temperature of -10 F, again that quickly rose with the heat buildup on the other side.

General Observations

While part 1 of this project has not left us with a unit that can meet the project goal, we have learned a lot that will hopefully lead to that. Let’s review.

  1. The large 40mm square, 80 Watt max cooling power element should have the cooling power required for this application, it demonstrated the ability to quickly cool the aluminum disc, and showed a fairly high temperature delta.
  2. The heatsink needs to be larger to support the large cooling element. It generated tons of waste heat, that all heat sink configurations in the experiment failed to dissipate quickly enough to reach a static state.
  3. The small cooling element, of unknown spec, did not have the cooling power required to keep the aluminum disc at a low enough temperature for the application.
  4. All the tested heasink configurations were enough to bring the small cooling element to a static state.

Conclusions

  1. The large cooling element needs to be tested with larger, more effective heat sinks.
  2. The small cooling element will not be used in further experiments.
  3. I should explore different cooling elements to use.

That’s it for now. Hopefully in the next installment I can demonstrate a working unit!