Information on frost top prep table

I am about to design and build a frost top pizza table. I have previously built one but, in the name of R&D, would like to compare notes. Information needed on all aspects such as different surface materials, mounting evap tubes, superheat, ect. The one I built was 22"x37". Copper tubing was clamped to 3/8" thick alumnum. I used a thermal mastic to help improve transfer between tubing and Alum plate. Thermal mastic was then trowled on the alum plate ,non tubing side, and then tightly anchored to granite. the tubing was then enclosed in a SS box which was foamed in insulation. It works well but is very labor intensive at this stage of developement. Any suggestions? Ken

That's how we are doing it with very good results

it gives you anyhow an idea of th process

You don't get any reaction with the metal clamps and the copper? "electroplating"?

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That's how we are doing it with very good results

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It looks to be about the same as mine but I still have some questions;
1. how many circuts do you use and if there are multiple circuts how do you determine the breakdown ?
2. If the frost top is to be contained to a particular section of the entire top do you use heat wire to control it. This idea has been sugested to me and it was adopted for production but wasn't sure it was needed.
3. How did you determine the CI and CO pres/tenp. We are using both 134A & 404A.
4. How did you do all the bending, I do it the old fashioned way by hand, and what size tubing was used.
Ken

Ken,

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How did you do all the bending?

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Look for the tube benders made by Imperial Eastman. They manufacture hand held tube benders for soft copper. It takes a little practice to make the offsets correctly, but I can assure you the job will look very professional with no kinks or wrinkles.

You can bend 180 degree bends that have a pretty tight radius with these.

Hi Ken:
I used to work at a factory (back in the 70's). After the initial R&D (where a hand bender was used for all the intricate piping), we used a pattern. This pattern was constructed on a 1/2" Plywood backboard, and using a bunch of 2 to 2-1/2" circles also cut from 1/2" plywood for the inside radius, for each of the bends. This system worked well for tubing up to 3/8" to 180 deg. It is much quicker, and easier than using a hand bender. Also, if you premeasure and cut the tubing length of each run before starting the bending, there is less waste.
Rick

That sounds like a plan. The nest one I have to build Is quite large and a patern with the radius' laid out might just be the way to go. I'll give it a try.

Anyone have anyadvise on where the CI/CO should be?
Ken

Ken,

What is a CI or CO? I am not familiar with this terminology.

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Originally Posted by kengineering

1. how many circuts do you use and if there are multiple circuts how do you determine the breakdown ?
2. If the frost top is to be contained to a particular section of the entire top do you use heat wire to control it. This idea has been sugested to me and it was adopted for production but wasn't sure it was needed.
3. How did you determine the CI and CO pres/tenp. We are using both 134A & 404A.
4. How did you do all the bending, I do it the old fashioned way by hand, and what size tubing was used.
Ken

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Just read your post
1 max lenght of 1 section = 25m. Otherwise to much pressure drop. We already used 3/8 and 1/2 (now only 3/8 tube)
Same principle is used in every evaporator, therefore they invented distributors if a section becomes too long.
2. I don't understand this question (frost top contained to a particular section of the entire top'
..top and frost top? :confused:
3. What is CI and CO? How we determine temperature: trial and error and knowledge we gathered from previous work.
You can't calculate this.
Take +/- 200 to 250 W/m² as a start, and install a CVP if precise control is necessary.
If it's for mass production, then make a test counter like we did for our last market truck to gather information.
4. The old fashioned way, with a tube bender from Imperial Eastman. (3/8 tube, 7 cm spacing) Every counter is different.

We don't have any problems with the stainless steel against the copper. And even then, copper is higher ranked in the galvanic table, so i should say that the stainless steel will rust. :confused:

Yeah sorry guys my question was unresearched. These fandangles are foamed in place aren't they?
Spoke to a guy the other day who told me about a "cold rock" top that was made. 2" marble, chilled bench for ice cream. Was a one off and cost a shed load. But it works still 10 yrs later.

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What is a CI or CO? I am not familiar with this terminology.

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I would hazard a guess that it stands for Coil In - Coil Out :)

what exactly is a table top like this used for?

finger skating? :D


but seriously, I'm clueless here

Ken

I'll take a shot at several of your questions.

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1. how many circuits do you use and if there are multiple circuits how do you determine the breakdown ?

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and,

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3. How did you determine the CI and CO press/temp.? We are using both 134A & 404A.

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These are both related. I am using Frank's definition of CI and CO. That makes sense.

The first thing you need to find out is how much evaporator surface do you need to cool the table top?

You will need a certain amount of heat transfer surface to provide the required cooling of the top.

The number of circuits is determined by the maximum pressure loss of each circuit. Obviously, we cannot use a very long single tube since the pressure drop through the tube would be too high. Therefore we find the need to use multiple circuits to minimize the pressure drop.

Each circuit is in parallel, not series.

As the pressure drop increases, the saturated temperature at the end of the tube decreases (lower suction pressure at the compressor). This goes back to the pressure temperature chart. Lower pressure equals a lower saturated temperature.

We are trying to minimize the pressure drop of the individual circuits. By minimizing the pressure loss, we are in effect minimizing the temperature difference across the evaporator surface. This in turn defines the CI and CO pressure/temeprature relationship.

If we want to say the maximum temperature loss is 1 degree F, then we have to find out what the 1 degree F temperature loss is equal to in pressure loss.

This equivalent pressure loss is what the evaporator circuit is being designed for. Once you have the required heat transfer surface and the total length of tubing, you need to divide the total length of tubing into multiple circuits of equal length.

The length of tubing used to provide the design pressure drop is the circuit length.

It is important that all circuit lengths are the same. Otherwise the TXV will not control correctly.

To distribute the refrigerant evenly into each circuit you will need a refrigerant distributor of course.

Take a look at the Sporlan brochure link below. This should expand on the ideas discussed above.

http://www.sporlan.com/20-10.htm

Hope that helps...:)

Ken,

I re-read once thoroughly your first post and indeed, you're doing it exact the same way we're making it.

Just at the other side of my street, there is a counter manufacturer (http://www.atsprojects.be/NL/projects/projects2.aspx , click on the pictures i'm living in number 16 and they have 9 in the same street) since +/-20 years but they came from another location and started around 1960.
So, they have a lot of experience and I did many years there install at the clients and the service afterward.
They remodel shops, especially bakeries, fish vending shops and butcheries.
There main job is making the counters.

They tried also several techniques to produce their counters and it's there that i learned how you have to do it.
I think you can still learn the most from the older and experienced techs, driven by their job.

Many times, a test counter is made with the length of 1 glass before they make the final counter, especially if it's a special ventilated one.

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If the frost top is to be contained to a particular section of the entire top do you use heat wire to control it. This idea has been sugested to me and it was adopted for production but wasn't sure it was needed.

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We were commisioned to build a granite top unit. One piece of stone 10 feet long, but only a 2 foot by 3 foot section to get frosted. To insure the frost stayed within the outline we installed a heat wire ( similar to a mullion heater, around the perimeter. It works but didnt think it nessesary. Never used it I gather. As far as the Cut-in / Cut-out I figured it would by trial by ice. Ken