* Steam Jet Water Vapor Refrigeration–4–Analysis, Advantages and Disadvantages
Steam Jet Water Vapor Refrigeration–4–Analysis ,Advantages and Disadvantages
ηn nozzle efficiency
ηe en-trainment efficiency
ηc Compression efficiency
Ws = mass of steam required to eject 1 kg of water vapor
Ww = mass of water vapor for 1 ton of cooling per hour
N = Refrigeration effect or cooling effect
CALCULATION OF Ws/kg, Ws/ton/h, Ww
1. P2 = P2’ = P3 = P4 = P5
2. ηn = h1 –h’2)/(h1 –h2)
3. ηe = (h1 –h3)/ (h1 –h2)
4. ηc = (h6 –h5)/ (h’6 –h5)
5. v2 = 2gJ ηn(h1—h’2)
6. equating momentum Ws v2/g = (Ws + 1)v5/g
7. Equationg enthalpies Ws h3 + 1 h4 = (Ws + 1) (h5 + v52/2gJ)
8. Ws = (h6 –h5)/((h1 –h’2) ηn ηe ηc –(h6’ –h5))
9. N = h4 – h8
10. Ww/ton/h = 211 x 60/(h4 – h8)
11. Ws/ton/h = (wsfrom eq 8) x (211 x 60)/(h4 – h8)
1. It is flexible in operation; cooling capacity can be easily and quickly changed by varying the flow rate and pressure of the steam.
2. It has no moving parts. So it is vibration free.
3. No noise and maintenance is low.
4. The system is very reliable.
5. The operating cost is significantly lower than that for conventional vapor compression systems.
6. The weight of the system per ton of refrigerating capacity is less than vapor compression system light weight equipment.
7. It is installed out doors.
8. The system is applicable to the processing of cold water used in rubber mills, distilleries, paper mills, breweries, food processing plants, gas plants, refineries, vacuum pre-cooling of fruits and vegetables etc.
9. This system is particularly used in air-conditioning installations, because of the complete safety of water as refrigerant and ability to adjust quickly to load variations.
10. There is no hazard from the leakage of the refrigerant.
11. A single Unit up to 300 ton of refrigeration can be installed.
12. Cost of this system with 75 ton of refrigeration equals to that of vapor compression system. But for capacity greater than 75 tons, steam jet system is economical.
13. Overall electric consumption is less since it is required for pumps only.
1. The use of direct evaporation to produce chilled water is usually limited as tremendous volume of vapor is to be handled by the steam jet. It handles 665 m3/h/ton as compared to 7m3/h/ton for R-12. Centrifugal compression could have been used but would require a very very high speed, the steam jet has been found to be most economical.
2. The size of condenser is big in this system because heat removed in the condenser of the steam jet system is twice than in the vapor compression refrigeration system per ton of refrigeration.
3. The system is useful for comfort air-conditioning, but it is not practically feasible for water temperature below 50C because of the freezing point of water.
4. COP is less i.e. 0.4 to 0.6.