Design, Construction and Performance of an Ohmic Fruit Juice Evaporator
A fruit juice ohmic evaporator (FlOE) was designed and constructed. The design was done in accordance with the basic principle of ohmic heating to provide heat for evaporation instead of steam or conventional direct heating, to overcome problems arising through these methods of heating. The FlOE...
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| Format: | Thesis |
| Language: | English English |
| Published: |
1999
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/10279/1/FK_1999_13_A.pdf |
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| Summary: | A fruit juice ohmic evaporator (FlOE) was designed and constructed. The
design was done in accordance with the basic principle of ohmic heating to provide
heat for evaporation instead of steam or conventional direct heating, to overcome
problems arising through these methods of heating.
The FlOE was constructed mainly from stainless-steel. A cylinderical heating
vessel of internal diameter 20.5 cm and length of 3 1 cm was constructed to enclose
electrodes supplying the heat for evaporation. The heating vessel was coated
internally with epoxy resin to isolate the wall of the vessel from electric current
passing through the fluid. Three sets of electrodes connected to the three-phase
alternating current supply were used. Each set of electrodes composed of a three
parallel stainless-steel plates. A vacuum pump was used to lower the boiling point of
the juice below 65°C and as low as 45°C to prevent the nutrient material from
damage.
Salt-water solution and pineapple juice were used to study the performance of
the FlOE. Three types of tests were done. Preliminary tests were conducted to ensure that the FJOE operates within the design limits and to check for fluid and electric
leakage. Performance of the FlOE was computed by testing the system in both batch
and continuous operation using salt-water solution and pineapple juice.
Electric conductivity of the dilute pineapple juice was first measured to find
the maximum allowable level of the juice inside the FlOE to prevent current overload
or high temperatures during evaporations.
Four tests using salt-water solution, two of them in batch mode and two in a
continuous mode were conducted. Another four test using pineapple juice of initial
concentration of 10% were conducted to achieve a final concentration of 40%, two of
them were batch tests and the others in continuous mode operation.
Results of all tests were tabulated and illustrated in graphs. Electric current
and the total area of electrodes used was found to be the controlling factors during
evaporation using the FlOE. Increasing the total contact area between electrodes and
the fluid was found to increase the average apparent current and hence the power
consumption.
Energy cost using the FJOE was found to be relatively cheap and of low cost
and the evaporation economy was found to be 0.7. The FlOE was found to be a
suitable evaporation equipment for concentrating fruit juices and other food materials
in a small scale industries without any need of steam boilers and of low energy cost. |
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