The weather has turned cloudy and cool which has put the experiment on hold.

A couple of recent nights showed the effect of the dew point.  The first night the temp was 35 and the box was 32 and covered with heavy dew.  The next tight the temp was 36 and the box was 20 but no ice.  The bottom of the box was covered with frozen dew.  The third night the temp was 34 and the box was 17 with the water frozen hard and the saline mix slushy.  The box was dry.

It is looking like a dT of 17 degrees is attainable under the right conditions which would allow ice formation at 47-49 degrees.  Hope to resume the experiment in January.

This morning the "box" was 20 F with the ice frozen hard.  The outside temp was 35 F. with calm winds.  This 15 degree temp difference should get me close to my goal.

Recent trials included building a Styrofoam chimney around the box but this actually raised the interior temps above the outside air temps.  Adding a small amount of salt water brine to the pvc cap and using a small enamel cup for the distilled water definitely improved the ice formation.  An identical cup placed inside the box did not freeze.  The improved conduction must have overcome the phase change energy requirements. (I must credit my brother for this idea.)

Next step is to add some insulation to the outside of the box and raise the pvc cap up in the box to improve circulation.  Then I just need to wait for the perfect night with clear skies, low humidity, calm winds and the right temperature profile.

A fun experiment with no practical use...at least for now.

The wind finally calmed and the OAT was 36 F so I assumed the ice would be well frozen.  The water in the PVC cap was liquid but the box was 21.5F.  I put the temperature probe in the water and it caused slushy ice to form immediately.  Seems I had made super-cooled water.

Tonight I am going to try a copper plate with a center well which is painted flat black.  The shiny copper was a complete failure.

A slight haze last night with OAT of 43F.  Box was at 30.5F but no ice.  Seems I have gone as far as I can with my present setup.  Will try and construct a continuous black plastic bottom.  From the data it looks like rusted steel bight be my best bet.  Better conduction and almost the same emissivity as the black PVC.

I wonder if higher sides might allow better cooling?  The surface area of the base seems critical because when I tried dividing it in half, the results were worse.

Removed the fancy heat sink and made more ice at 42F OAT.  The box interior was 26 F.

Thinking that the floor of the box should be a piece of rusted metal to act as a better conductor of the heat to a larger radiant surface.

Still see no use for the concept but it does make me question the concept of "white" roofs.

Update on experiment

16 March 2016

The high thin overcast has started to dissipate with the approaching high pressure.

The clearer skies have allowed better radiant cooling and the temperature dropped to 42 F last night.  I had a small amount of ice on one of the black PVC pieces but none with the fancy radiant cooler.  The interior of the box was 28 degrees with the OAT of 42.  Only a small amount of ice formed which would imply that the temperature did not drop quick enough to allow for better ice formation.  I am using a glass bowl as a control and it was 40 degrees.

I need to figure out a method of improving the heat transfer to dissipate the heat of fusion to produce faster freezing.  It is interesting that the simple black PVC surface seemed to be better that the fancy carbon coated radiant fins of the computer CPU cooler.  This may be an artifact of the quantity of water involved.

The intent of this blog is to share my efforts at making ice at 50 degrees.  I am not sure their is any practical reason for my ongoing experiment other than cold beer while camping.  My interest was aroused when I came across an article about making ice in India and Syria during ancient times.  They would dig a deep dry well and place pans of water at the bottom. The water would freeze and be harvested.  If they could do it why can't I?

The theory is that we have access to the cold of space if we can control the frequency of the outgoing infrared radiation to take advantage of the gap in the water absorption of infrared.  Air currents must be controlled.

At present my device consist of an 8 x 12 inch Styrofoam box with 2 inch thick walls which is divided into two chambers.  After trying dozens of containers I have had my best results with a black PVC 4" pipe cap.  The PVC provides a pretty good infrared spectrum of radiation but is a poor conductor.  I am in Cottonwood Arizona at 3400 feet and can dependably make ice at 40 F. but only at night.  This is still 10 degrees below my goal.

I will provide a list of those things that I have tried and hope to try in a future posting.  Here is a good link:  http://www.asterism.org/tutorials/tut37%20Radiative%20Cooling.pdf.

Here is a list of common materials and their emissivity:  http://www.infrared-thermography.com/material-1.htm

Here is a description of the infrared window:  https://en.wikipedia.org/wiki/Infrared_window

I would appreciate any advice you may have.

Charlie