Cooling of Material Using Screw Conveyor
Cooling of material using jacketed type screw conveyor
I want to convey the seeds from one machine to Storage silo through screw conveyor . After coming from that machine temp. of material is 90 deg.
I want to reduce the temp. of material from 90 deg cel. to 40 deg cel. using jacketed type screw conveyor . Then it will go to storage silo I will circulate cooled water around the jacket to drop down the temp. of material
Capacity of material conveyed through screw conveyor is 3000 kg/hr. Material is Seeds having Bulk Density - 800 Kg/Hr So I want the calculation for the same. i. e. How to calculate the length of screw conveyor? How much quantity of water is required to down the temp. of material?
How much will be the residence time?
Cooling of material using screw conveyor
There is pneumatic conveying system from one machine to Storage Silo. capacity is 3000 Kg/ Hr. Material density is 800kg/m3
But material temp after coming from machine is 90 deg. Cel. & want to cool it up to 40 deg. cel. i.e. in storage silo it should be of 40deg. cel.
we are thinking to keep Jacketed type screw conveyor after machine to cool it up to 40deg. cel. . I want to know , what will be the calculation for the same to calculate length of conveyor ? What will be the quantity of water required to cool it ?
Kindly help for the same .
You have posted this thread under “Pneumatic Conveying”.
However, you are asking for information about a screw conveyor, also working as a cooler.
Calculating the screw conveyor alone is not so difficult but calculating the heat transfer from the conveyed material through the screw tube to the cooling water in the jacket is something that should be done by a manufacturer with knowledge.
They should know the field parameters, based on their field experience.
A pneumatic conveying system, working with cooled compressed air and a cooling jacket could also be an option.
Take care of condensation of water, when cooling seeds.
Originally Posted by Teus Tuinenburg
Thank u for your reply.
31st August 2012, 15:42
heat transfer screws
The residence time through a heat transfer screw cooler depends on the equipment specification so it may be useful to set out a few design parameters. The writer does not identify the type of seed, so a basic value needed is the specific heat of the seeds, conductivity and seed dimensions.
The total heat burden can then be related to the heat transfer characteristics of the mode of equipment selected and temperature of the water intake and discharge, to determine the heat transfer surface contact area and the water capacity needed. Iterative comparison of the required cooling area with the handling capacity relative to screw size will establish the necessary size and speed of the equipment. Attention will then be given to whether the feed is controlled by prior equipment or is self-regulated by the machine.
The final temperature required would seem a non-starter on a horizontal screw conveyor as the thermal efficiency is low due to employing only a section of the casing periphery, and even that is insulated by a residue layer in the flight tip clearance that suffers poor inter-particle heat transfer by static contact. A steep, jacketed screw elevator will generate full use of the casing circumference, maximum thermal homogenisation of the contents and generate intense surface wiping of the cooled surface. A courageous design would incorporate a spiral chute around the cooling jacket for the returning grains. In summary, I would expect even a specialist supplier to conduct some trials, unless he had specific experience with the product, and the costs of a custom-built unit to compare unfavourable with a simple, standard pneumatic system that also offers easier testing for cooling in transit.
Screws are great for reducing high temperature products to a degree that leaves a decent differential with the cooling medium, but the combination of high thermal loads and low temperature differences to the cooling media seriously drives up the scale of equipment required. On the other hand, heating or cooling is relatively inexpensive to add to equipment that is necessary for material transport.
Calculation of Transit time in a screw conveyor
I would appreciate your assistance in determining the required calculation for Transit time in any given conveyor.
As an example:
6" screw conveyor turning at 16 RPM will deliver 34 FT^3/Hr. (Material mass is 59Lbs/Ft^3)
I need to heat this material for a predetermined amount of time, so I must determine the length of the conveyor to transfer the amount of heat needed
I have seen the formula (length / (pitch x rpm) = minutes) In our example above with Standard pitch (Pitch = Diameter of Screw), would the calculation look like this, using 20 feet as an example?
Originally Posted by ScottC
20ft/6 x 16 = .033 ft/min
Your formula is correct you are just executing it wrong. The length and pitch need to be in the same unit of measure.
length in ft / (pitch in ft x rpm) = minutes
20' / (.5'x16RPM) = M
20' / 8 FPM = M
Therefore retention time is 20/8 = 2.5 minutes assuming that the inlet and outlet are 20' apart.
President - Bulk Handling Technology Inc.
Offering DEM Flow Simulation Services, Conveyor Transfer Design Services, SolidWorks Design Services for equipment layout, Books & Software to the Bulk Handling Industry
heat transfer of screw conveyors
As Gary noted, the transit rate of 8 ft/min gives a residence time in mins. of - conveyor length,(ft)/8.
However, to assess the amount of heat transmitted is much more involved. Classical heat transfer equations apply, but the factors used are sensitive to fine design details and may require verification by trials. This is generally a specialist suppliers task.
25th August 2013, 7:12
Cooling of Material through the screw conveyor
You could cool the temperature of the material in a few ways, yes a water jacket around the outside but also down the middle of the screw conveying shaft depending on how big the shaft of the screw conveyor is.
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