Will a laboratory freezer be suitable for a slow freezing project?

[iceman31]

I want to get some items and freeze them slowly. The more time the item spends between -2c to -5c the better.

Most domestic freezers do not go this high and I do not want to modify my freezer unless absolutely required. I thought of renting a lab freezer as these can be set to high temps e.g. -2c to -4c. However I am concerned that lab freezers are high performance and they may bring the items to say -4c in very quick times.

Is this the case or are lab freezers just as suitable as domestic freezers to slow freeze an item. I'd imagine that a lab freezer freezes fast when set to very low temps but then I wouldn't know and perhaps there is something i'm missing as I believe the freezer system can determines the rate of freezing.

Is a lab freezer suitable, if not why not, would a lab freezer bring an item to say -4c very quickly when set at that temp?

Thanks

[chemi-cool]

I think that any freezer will be suitable as long as you can control the temp.
If you set set it to -4 with 2k differential, you shoud get what you want

[Brian_UK]

Would an environmental chamber be a better option, ignoring cost of course, as they normally have a time element as well as temperature control.

Use a slow ramp down and then set to hold the temperature.

[frank]

As Brian says, it's not the final temperature that is important it's the rate of pull down.
This will be determined by the cooling capacity of the freezer and the amount of product to be frozen

[monkey spanners]

What sort of weight of product are you looking to freeze?

[r.bartlett]

deja vu all over again...

[iceman31]

What sort of weight of product are you looking to freeze?

Chicken, 1 bird is 1kg. Would start with 1 bird just for testing however if I could get many in and got the results that would be great.

[install monkey]

http://www.refrigeration-engineer.com/forums/showthread.php?39580-How-to-make-freezer-slow-freeze-poultry&p=280704&highlight=#post280704:D

chest freezer 3/4 filled with water- chuck ur feathery friends in and it will take ages to freeze- and they can absorb as much water as possible

[iceman31]

As Brian says, it's not the final temperature that is important it's the rate of pull down.
This will be determined by the cooling capacity of the freezer and the amount of product to be frozen

Frank, in your sentence, does cooler capacity refer to the size capacity e.g. freezer x has a 100 litre capacity or does it refer to the engine capacity e.g. freezer x can freeze 2kg of food in 12 hours? Which is it. I asked this elsewhere however was given some awkward answers. Please clarify, which is it?

Thanks

[iceman31]

http://www.refrigeration-engineer.com/forums/showthread.php?39580-How-to-make-freezer-slow-freeze-poultry&p=280704&highlight=#post280704:D

Yes, that was one question however this question was specifically about a lab freezer which nobody addressed in the other thread. Also nobody answered my questions about size/engine capacity.

[Josip]

Hi, iceman31 :)


Chicken, 1 bird is 1kg. Would start with 1 bird just for testing however if I could get many in and got the results that would be great.

just an idea to help, if ;)

you can try to make some kind of shelf within domestic freezer chamber to put 4 or 6 birds simultaneously in - that will increase the load and reduce the freezing speed ... in the same time you can use some electronic thermostat with small hysteresis to use it as on-off control of your freezer ... coming down to -2oC switch your freezer of ... rising temp for 0,3oC switch it on ... then when you want set the temperature to -3oC .. etc... the problem you can face is the mass of your chicken ... i.e. position of your temperature sensor is very important ...maybe you'll need two thermostats ... one for air temperature within freezing chamber another one for chicken itself ... you must observe both temperature air and meat to get a good product ... big water crystals and soft meat if I am right ....

This is some idea and it is far from something for very precise long time freezing but basically it is the same what we use within freezing tunnels ... observing air and product temperature in the same time to get a good frozen product ...

Best regards, Josip :)

[install monkey]

Endocube!
:D
mimicks product load and saves u money- allegedly

[frank]

Frank, in your sentence, does cooler capacity refer to the size capacity e.g. freezer x has a 100 litre capacity or does it refer to the engine capacity e.g. freezer x can freeze 2kg of food in 12 hours? Which is it. I asked this elsewhere however was given some awkward answers. Please clarify, which is it?

ThanksI am referring to the cooling capacity of the fridge, not it's physical size.
i.e. the heat absorption and heat rejection, measured in Watts

[iceman31]

I am referring to the cooling capacity of the fridge, not it's physical size.
i.e. the heat absorption and heat rejection, measured in Watts

Thanks Frank. Can you clarify something else for me. I asked the question of what determines the rate of freezing to somebody else and I believe he said cooler capacity and product load. However he made some references which I didn't fully understand. Below is my question to him and his answer, please could you clarify what he meant:

My question to him: I believe you said the rate at which the meat will freeze will depend upon the 'size and load' of the freezer. I thought the temperature of the freezer alone e.g. -5c would be enough to ensure slow freezing regardless of size and load of freezer. Can you explain if this is not the case and if so how, technically speaking, the freezers size and load affect the rate of freezing? I note you said that a normal freezer may achieve slow freezing at -5c wheareas a deep freezer may achieve it at -10c.

His reply: Temperature alone will assure it only if the capacity of the freezer is very high. If the load is high in a refrigerator situation, it will not be able to maintain the -5C. It can warm even to + tempeatures in order to cool down the product.
The rate of freezing depends on the rate of heat removal and hence they are dependent on the cooler capacity and product load. By increasing one over the other you can make it depend either on the cooler capacity or product load.

1) What did he mean in the sentence highlighted in bold? Surely if the cooler capacity is much higher then the load, it will freeze fast/normal.
2) Also if temperature doesn't affect rate of freezing, why does he say 'temperature will only assure it if the freezer capacity is high?
3) Why did he also mention that a normal freezer can produce slow freezing at -5c while a deep may do it at -10c. Is he saying size is important in some way.

Would be very grateful if you could answer these for me.

Thanks.

[iceman31]

Duplicate post.

[frank]

Your product to be frozen will have a specific heat capacity expressed as kj/kg. To determine the amount of energy needed to reduce its heat from initial temperature to final temperature you use the formula Q=m c dt where
Q = energy required
m = mass of product in kg
C = specific heat capacity of product
dt = start temperature minus end temperature expressed in K

When you are freezing a product it will have a specfic heat above and below freezing and both calculations have to be carried out.

Once you have the value of Q (in joules or kilojoules) your divide this by the time you want the freezing process to take. This value in Watts (1 joule/s = 1Watt) gives you the size of the equipment needed to do the job.
Obviously, this isn't taking account of any other heatloads which must be added in.

[TERRENAS]

And if.... you use a digital thermostate to control temperature and an inverter to control the power/capcity of your compressor...?