Cooling of vegetables with water

[Ant85]

Hi all this is my first post , I have been using this forum for a while , but mostly directed here by Google and have found the answers to my questions.. until now .

I am trying to design a cooling system that will use chilled water around 1deg C to cool vegetables that have been cooked.

So far I have the vegetables leaving the cooker @ 70degC.
I need them to be cooled to 10degC .

I am struggling where to start with the maths for having the vegetables submerged in the water on a conveying system .And how long the conveyor will need to be to get the required outfeed temperature ,also the volume of water required to cool down the vegetables.

If someone could give me advice on where to start it would be greatly appreciated.

TIA

 

[scottdave]

The energy lost by the hot vegetables will be gained by the water.
One factor which will go into your final design would be determined by how much capacity you want to have.
You can search for heat transfer equations or tables, but something like vegetables, you probably will need to do some experimentation to get the necessary data.

 

[sophiecentaur]

If someone could give me advice on where to start it would be greatly appreciated.

The answer to your question will be very practically based and you would need to do some experimentation but one thing I can say that you will find useful is that you should pass the cooling water in the opposite direction to the veg. That means the veg at the output end will be in the contest water and the veg at the input end will have a significant temperature difference from the 9warmed up) exit water. All good heat exchangers use this principle (condensing central heating boilers etc.)
The speed of cooling will depend on the size of the veg pieces and the spaces in between the pieces, which only you will know.
You could do some simple 'static' experiments in which you immerse some hot veg in cold water for various times and measure the drop in temperature achieved.
The old fashioned "Method of Mixtures" would be worth reading up about but it tells you that heat lost by a hot object will equal the heat gained by in cold water water it's immersed in. If you assume the veg has the same Specific Heat Capacity as water (after all, it's all mainly water), the heat lost by the hot veg would be
(70-10) X Mass_veg
and the heat gained by the water will be
(10-1) X Mass_water
when equilibrium has been reached.
So you would need about 6.7 times the mass of cooling water (absolute minimum) as the mass of hot, wet veg. That means your steady rate of cold water mass flow would need to be more like at least ten times the mass flow of the veg. But I haven't included any time factor here; you would have to find that out by some kitchen tabletop experiments.
Would you be recirculating the cooling water or would it be fresh all the time? I know there can be issues in recirculating water around veg in some cases and the exit water could be very much luke warm - good for microorganisms.

 

[Ant85]

Thank you , I will have to do some experiments to gather the data.

Would you be recirculating the cooling water or would it be fresh all the time?

It would be fresh all the time, to avoid bacteria growth.