Agitator calculation

[Rio69]

We will try to build our own agitator for ice bank tanks.
How to calculate water flow of agitator.
Input data:
Diameter and pitch of propeller, and rpm of motor.


Thnx
Rio

[monkey spanners]

Hi Rio,

Most of the ice builders i've worked on the iced water pumps are sized to suit the cooling duty required (plate heat exchanger in the milk line) and the return water is sprayed on to the ice at the top, through spray rails. An air blower is fitted to agitate the water to ensure even melting and the air from this is fed to a row of pipe at the bottom of the ice builder. On one make the return water and air are fed into the same row of pipes at the bottom of the icebuilder with the water/air mix exiting the same holes (the air blower needs a check valve to prevent it filling with water incase of a fault), this make seems to suffer less from uneven ice melting, but this is just an obsevation, nothing technical.

What are using your ice bank tank for?

Jon

[Rio69]

Hi Jon,
we are using our tank for diary industry, for cooling milk. Agitator is for internal water circulation.
Look at the attachment.

Dario

[monkey spanners]

Wow, thats a bit bigger than the stuff i usually work on!
I would not have a clue about working out the flow required for the agitator.
It would need to move more water than the pump to the heat exchanger in the milk line to avoid the warm return water short circuiting.

If the iced water supply pipe was sealed to the centre section at the bottom then when the pump is running the warm water would have to flow through the ice bank without the need for the agitator, unless you need the extra flow to ensure even melting.

Jon

[Samarjit Sen]

Hi Rio,

Please give me a couple of days. We used to design and install Ice making plants, where the brine had to be circulated. There is velocity at which the brine has to be recirculated. I have it, but will have to do a bit of hunting.

Meanwhile I find your Ice Bank Tank quite interesting. Could you please provide some more details of the same.

[Samarjit Sen]

Hello Rio,

The agitator should ne designed so as to maintain a water flow of 16 to 18 ft. per minute. The agitator could be propellor blades or water pumps depending onthe volume of the fluid and the tank size.

I would advice you to purchase the agitator blade from the supplier of such components.

[Rio69]

Hello Samarjit Sen,
you can find more about ice bank on w3.frigoterm.com/silos/icebanksilotanks

We are purchasing blades from marine equippment supplier, and they do not know how much flow I am getting. They can help me if boat is in question (i.e. they can calculate thrust), but for my application they have no clue about it.
We have built many silos, and many agitators, but this is the issue where we need some improvements.

[Samarjit Sen]

Hi Rio,

You have contacted the correct people. The propellor blades use in the boats are the right ones. What is the height of the silo and the volume of water. Based on these, I can tell you the diameter of the propellor blades.

[Rio69]

Hi,
the diameter of silo is 3700mm, and inner tube for downstream is 600mm. Height of the silo is 10m.
Can you show the calculation?

Rio

[Samarjit Sen]

Hello Rio,

From the datas provided by you and my personal experience in such similar application, the diameter of the propellor blade should be about 550 mm. It is the HP of the electric motor that is going to drive the propellor. The HP for this would be about 10 HP. The purpose of the blade is to force the water down and at the same time draw the same from the top. I am sorry I do not have any calculation. It is just what I had done for the Ice Plants where similar water circulations are required.

[chemi-cool]

With all respect,
Why waist energy?
Why not use direct cooling?

Haet transfer of Glycol is lower then refrigerant!
And with the Glycol you cool water [another energy lost].


I install milk cooling tanks for may years now and every time this argument arise, it is clear that indirect cooling is a waist of energy.

Chemi

[monkey spanners]

Chemi cool,

You are right, DX is more efficient, but ice builders/plate coolers can cool quicker. On a recent training course i went on by one of the milk tank manufactures they stated that as the tanks get bigger, some are now 30,000L in the uk, the available surface are per litre gets less.
Quick cooling is an issue here now as the milk is often on the farm for two days, and possibly going to three days in the future. With a plate cooler the milk can be brought down to temperature much quicker ensuring better keeping quality.
Also here the cost of electricity is less at night so if you run the icebuilder overnight it can be cheaper to run even though its less efficient
Many farms in the uk have poor electrical supplies and cannot run the bigger compressors a DX tank needs.

Personaly i like DX stuff as i get to play with bigger equipment

What make tanks do you fit and work on?

Jon

[Samarjit Sen]

Hello Chemi Cool,

I do some projects for Ice Cream manufacturers. They always want a Milk Cooling with Ice Bank Tank. Moreover I have seen a number of Milk Chilling centres prefer to have Ice Bank Tank so that they may form the Ice in the night and in the morning circulate the cold water over Milk Tanks. This would have been feasible if the electricity rates in the night would have been cheaper. It is not so in our country.

I agree that DX system would be more proper to chill the Milk directly.