Anyone interested in helping me with my project? -40c cold plate

Hi everyone, i am about to begin a new projectwith a mate of mine, were going to design and build a -40c Cold Plate for "cooking" deserts similar to the "Anti Griddle"
http://en.wikipedia.org/wiki/Anti-griddle

Im a Refrigeration Mechanic and my mate is a Boilermaker so i think we should have enough resources to build this thing, Im just a bit confused about the design and the calculations to ensure everything runs smoothly.

We're building this "Cold Plate" for a mate (Chef) who is about to start a small boutique Bar/Cafe so were in no real rush. I think it will be great from what ive seen on you tube.

thats it for now ill upload some pics of what i think for the design and specs in the next couple of days, ill have to rap it up for tonight.

To anyone whos interested

Just like Cold Rock Icecream?

https://www.google.com.au/search?q=c...TySBP5R7HRM%3A

Looking forward to some pics Brad. I'm keen to lend a hand on this one.

Yeah just like cold rock. i havent measued it out yet but it will be a bench top or built in unit plate area roughly 600x300mm. ive been drawing up some pics and specs to discuss tonight i just need to put them on the pc and ill share them with you guys probably tomorrow night.

Hey Tesla! thanks for your help im bored out here. how you going?

Hi Brad I'm doing fine. Have not had a real job since redundancy last year but have got the website up and going. I am in the process of applying for a part time teaching job at Ultimo. I get bored sometimes but I have many things to do. Not enough time and money sometimes. Are you far from Mudgee? I could be heading out there in a few months for a mineral show for a weekend - we could catch up for a few beers.

Sorry Stu I havent earnt the privelage of private mail yet.

That sucks about work, good you got the website up and running i checked it out it looks sweet.
Im only an hour and a half from Mudgee, let me know when your comming out and ill bring the missus over for a getaway.
Would be awesome if you get in to teaching!

Cool Brad
Perhaps we should continue this conversation when you get your PM privilege and get back on track with the cold plate. Do you think we can achieve it with a single stage of refrigeration and will it be used much? Could also look at the use of Nitro cooling cause it looks so cool with all the fog stuff. They do use Nitro for some cooking.

Ok here is some stuff ive been working on.

Firstly the Application -

Flooded evaporater mounted to a stainless steel plate that runs at -35c constant temp.
The plate will be used to freeze/part freeze desert products like chocholate, creams and soft cheeses.

Some thoughts,

1. were building a static plate type evaporator and the plate is to be kept at -35c, the evaporator must be colder that the desired temp? What TD should be used to achive this plate temp?

-Properties of the steel plate
-Heat transfer between coil and the plate
-Heat load of the product

Can anyone else think of other factors?

Also what refrigerants would be suitable?
R22, R404a and R410a are readily availible to me and appear to be within the range, or are they?

Quote:

---

Originally Posted by Tesla

Cool Brad
Perhaps we should continue this conversation when you get your PM privilege and get back on track with the cold plate. Do you think we can achieve it with a single stage of refrigeration and will it be used much? Could also look at the use of Nitro cooling cause it looks so cool with all the fog stuff. They do use Nitro for some cooking.

---

I hope we could achive this temp with 1 stage, i havent had much experiance with low temp stuff, by the pt chart id like to think that one of the refrigerants ive mentioned above could do the job but as i said i havent done much with low temp.
the machine would run standard cafe/restraunt service hours, probably 6:00 - 10:00pm say 5-6 days per week.
(as long as the demand for the product remains a hit!)

ill look into the availibility and costing of nitro, is it dry ice? and maybe we can get some for a test run of the product and see how it goes and what sorts of recipes Sam can come up with.
I think a plug in unit would be best for a comercial kitchen application just due to ease of use, turn it on and away it goes.

Attachment 10364
basic drawing, Construction of evaporator

I met with the guys I'm building this with last night and we had decided that a fully flooded evaporator would be better than the convection coil that I'd drawn up earlier. Here's a pic of what we reckon, a folded stainless plate as a sealed vessel, with male flare connections for liquid and suction.

Question- Would an evap like this require a CPR valve to maintain evaporating pressure?

http://maps.google.com/maps/api/stat...00&sensor=true

Hi Brad, My two cents worth..

I reckon scavenge a compressor, condenser & capillary tube from an old domestic refrigerator. Then experiment with a coil of 1/4" copper tubing as the evaporator - you would need to experiment with the length, obliviously start long & cut it down progressively.

For the plate, I'd go for some sort of tile (or fancy garden paver), sandwich the copper coil between two of them & sikaflex around the edges to stop the cold from falling out.

Some sort of suction accumulator probably wouldn't hurt.

As for the refrigerant I'd go for one of those hydrocarbons that have been talked about in other threads, at least during the development stage you can charge, blow off, cut, braze, purge & all over again without the procedure / expense of regular *****..

As you can see, my general gist is to use cheap readily available materials that can be experimented with, chopped, modified, try this, try that, shorter, longer, three bags full & s h 1 t canned with no big cost if it don't work out.. Or you might get lucky on the first go, then all the money you've saved can help pay for diabetes medication after eating too many cold cooked deserts!!!! :D

Im designing a evaporator for an appliance some freinds and i are going to build.
Its a -35c plate used for freezing deserts like cold rock sort of.

Anyway this is the design weve come up with, its a stainless steel folded and sealed to make a vessel with male flare connections attached to the bottom for liquid in and suction out.

Im thinking of running R404a at about 9psi which would meann the plate/vessel temp should be about -35c.

Does this make sense?

Attachment 10366

I will have my 2 cents as well.
I would not go the mechanical refrigeration at all, I would go total wastage with CO2, your plate could be very close to -55C.
Cheap to make.
As a luxury item, the running cost could be negated by the sale price of the product.

Brad to run your plate at around -35 you would need to have a colder refrigerant so it would be on it's limits at around 2 psi. Here is an example of liquid Nitro (at the chemistry building)
Attachment 10367

Quote:

---

Originally Posted by HVACRsaurus

Hi Brad, My two cents worth..

I reckon scavenge a compressor, condenser & capillary tube from an old domestic refrigerator. Then experiment with a coil of 1/4" copper tubing as the evaporator - you would need to experiment with the length, obliviously start long & cut it down progressively.

For the plate, I'd go for some sort of tile (or fancy garden paver), sandwich the copper coil between two of them & sikaflex around the edges to stop the cold from falling out.

Some sort of suction accumulator probably wouldn't hurt.

As for the refrigerant I'd go for one of those hydrocarbons that have been talked about in other threads, at least during the development stage you can charge, blow off, cut, braze, purge & all over again without the procedure / expense of regular *****..

As you can see, my general gist is to use cheap readily available materials that can be experimented with, chopped, modified, try this, try that, shorter, longer, three bags full & s h 1 t canned with no big cost if it don't work out.. Or you might get lucky on the first go, then all the money you've saved can help pay for diabetes medication after eating too many cold cooked deserts!!!! :D

---

Hey HVACRsaurus haha yeah I hope we get to that stage, not the diabeties but the cooking!

Thats a great idea about the scavenging and tinkering Ive already started scouring the work shop and scrappies up the road for a donk, havent found anything suitible yet.
Have you ever heard of R134a running this low in a vacuum?

Ive been doing some home work and ive come up with the unit capacity so ive got a fair idea of what parts im looking for, ill post the working out soon.

Thanks for your involement talk soon.

oh ps, as for the Hydrocarbons, thats a top idea as well Ive never used or seen them before but i think ill look into it hey, Im pretty keen on learning more about it.

Quote:

---

Originally Posted by mad fridgie

I will have my 2 cents as well.
I would not go the mechanical refrigeration at all, I would go total wastage with CO2, your plate could be very close to -55C.
Cheap to make.
As a luxury item, the running cost could be negated by the sale price of the product.

---

Hey Mad Fridgie, Im hearin ya, just started gathering some prices to compare for a condensing unit today. I had to reduce my the desired capacity from 4kw to .5kw just to be within sight of affordability to begin with.
I like HVACRsaurus's idea about knocking a few random bits together and mess about till i find something that works.

Im gonna speak to BOC tommorow about getting hold of some liquid nitrogen and do a bit of reasearch on equipment and fittings required, its sounds a whole lot cheaper.


Thanks for your advice!

Quote:

---

Originally Posted by Tesla

Brad to run your plate at around -35 you would need to have a colder refrigerant so it would be on it's limits at around 2 psi. Here is an example of liquid Nitro (at the chemistry building)
Attachment 10367

---

Hey Stu, good old Bondi Pipe Freezing i assume what were you doing isolating fire pipes?

Ive done some calcs ill put up soon, you can have a look over my working out for capacity.

obviously theres a lot missing but for example if we were running a freezer system with a static plate evap on
404a at 9.75psi , in theory shouldn't the evaporator temp be -35c?
how did you get a 7k TD? Is the TD to do with the stainless steel heat transering properties?

the evaps gonna be a tricky one, ive got a heap more reasearch to do on evap types and dynamics.
The evap ive got in my head will look something like the last pic i put up, constructed of 2m steel plate folded and sealed as a box with a connection for in and out.
the thing thats worrying me about that is the eddy currents of the flow and how it will affect the superheat. Also locations of the liquid/Suctions pipes to ensure liquid stays at the bottom and the gas boils off.
If it doesn't work like a finned evap usually does ill need to allow for a float chamber and baffle the thing inside to run like a temprite.
I guess i really need to have an even surface temp for this thing to work properly, just working out how to engineer the insides is a pain.

ps im working on the nitro idea, just gotta get a price and availibility and ill get my mate matt to knock up a plate and frame to use it with.

.

Be aware that if you use the flooded type you show in the drawing,
it will have to be constructed in sections with welded sections holding
the two flat plates together.

Any pressure inside that thing without these welded braces will result
in the plate "ballooning" with the pressure of the refrigerant inside and
be very careful when you pressure test to prove it is sealed.

This is the voice of experience, I have made a similar flooded plate evap
in stainless (for a different reason than yours) and it distorted when we
tested it with N2.

Regards

Rob

.

Ok here’s what vie been working on lately, Heat load calcs of product to determine unit capacity.

All products are to be chilled in a fridge between 2-5c to remove sensible heat, so I reckon we only need to remove the latent heat. Is that right?

• Cream – Latent heat 308kj/kg
• Chocolate – 93kj/kg
• Cheese (Ricotta) – 265kj/kg
So I chose the product with the most energy to base the capacity on so that we are oversized rather than undersized. To begin with I thought I’d design this unit to serve a max capacity restaurant (better looking at it than looking for it).

So I calculated service to 2 tables, 4 serves per table at 50g per serve.
Using the latent heat for cream I worked out;

KW = Product Mass (kg) x Latent Heat (kj/kg) / Time (seconds)
50g x 8 serves = 400g of product (cream)
.400kg x 308jg/kg = 123.2
123.2 x 30 seconds = 4.1KW, fair enough.
Then I looked in a catalogue and saw the list price on a condensing unit at -35 SST. Wow.

Scale it back a bit then, 1 table, 2 serves 25g a serve.
.050kg x 308kj/kg = 15.4
15.4 x 30 seconds = 0.51KW much better. And at -35 SST the C/unit would cost me $375, if I wanted to buy one that is, I’d much rather collect all of the parts and build one from scrap.

So that’s how I've calculated the capacity of the unit, this is my first time apart from at TAFE 7 years ago, wish id payed attention.
If I've gone wrong any help will be most welcome

Whew.

Asuming the calcs are correct, does anyone have any suggestions for the evaporator?
ive posted 2 ideas a fair way above, i pretty much scraped the first idea its simple but im not confident in the heat transfer.
So that leaves me with idea two a hollow stainless vessel, but should i run it as a standard finned evap would, where the liquid enters and boils off about halfway, or use it as a Flooded evaporator (not Shell and tube water cooled type) like a temprite and have a ball valve to controll the flow in and let it boil off at its own rate, using a EPR valve to maintain pressure?

??? the big questions in life. its late i gotta go to bed.

I would be using a L'Unite Hermetique CAJT2446ZBR Condensing unit (or parts made to suit).

Brad I was lying in bed last night thinking about the plate and I thought the ideas were good but a little complicated to manufacture. so I thought the simplest method would be to use a serpentine coil of 1/4" cu tube (just like an electric stove element) brazed to the stainless plate. The calcs above not quite right need sensible heat but I have to get back to study. Talk soon.