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Choice of refrigerants for ship refrigeration systems

Choice of refrigerant: Mechanical refrigeration makes possible the control of the pressure and therefore, the temperature at which a refrigerant boils (within the limits of critical pressure and temperature). The closed circuit ensures repeated use of the same refrigerant with little or no loss to atmosphere.

Theoretically, almost any liquid can be used as a refrigerant if its pressure/temperature relationship is suitable for the conditions. Although no perfect refrigerant is known, there are certain factors which determine a refrigerant's desirability for a particular duty and the one selected should possess as many as possible of the following characteristics:




Finally the refrigerant should preferably be non-toxic, have satisfactory heat transfer characteristics, and leakages should be easy to detect either by odour or by the use of suitable indicators.

It is not proposed to list or deal with all known refrigerants, only those likely to be encountered on board. These refrigerants are referred to by their trade name, chemical name or their internationally recognized numbers,

Commonly used refrigerants and possible replacements

Rll is a CFC which is included in the Montreal protocol having an ozone depletion potential (ODP) of 1 and a greenhouse potential (GP) of 3300. The formula for Rll is CC13F and it has the chemical name trichloromonofluoromethane. It was found suitable for air conditioning installations.

R12 is a CFC which, with an ODP of 1 and a GP of 10 000 is also to be phased out by the Montreal protocol. The formula for R12 is CC12F2 and the chemical name dichlorodifluoromethane.

R22 is an HCFC with a much lower ODP of 0.05, is much less of a threat to the ozone layer and has been used in place of R12 in some recent installations. The formula for R22 is CHC1F2 and its chemical name is rnonochlorodifluoromethane. It has a GP of 1100.

R502 is an azeotropic mixture composed of 48.8% R22 and 51.2% of Rl.15. Details of R22 are given above and R115 is a CFC with the formula CC1F^CF3 which is used only in R502. As a CFC, with an ODP of 0.6 and a GP of 25 000 the R115 is included in the Montreal convention and this implies that R502 is also included. R502 is particularly suited for use with hermetic compressors.

Replacement refrigerants

A number of new refrigerants have been developed by the large chemical companies as potential replacements for refrigerants commonly in service. Three refrigerants considered as candidates to replace R12 are referred to as HFC-134a, Blend MP33 and Blend MP39. The two blends are both made up from the same three other compounds but in different proportions by weight.

Thus Blend MP33 consists of 40% HCFC-22 plus 17% HFC-152a plus 43% HCFC-124 and Blend MP39 is made up from 52% HCFC-22 plus 15% HFC-152a plus 33% HCFC-124. These gases are stated to have very low ozone depletion potential when compared with R12 and the two blends are less toxic with TLVs of 750 ppm for Blend MP33 and 800 for MP39, The HFC-134a has a TLV of 1000 ppm which is the same as that of R.12.

Any replacement refrigerant must compare in performance with existing gases, for direct economy of operation as well as in respect of the amount of fossil fuel consumed.

There have always been minor problems with refrigerant and oil miscibility, Some problems with lubricants are being experienced with the new gases. Rl34a is seriously considered as the best replacement for R12, It is an HFC with the chemical formula CF3CH2F an OOP of 0 and a GP of 900.

R123 is being considered as a replacement for Rl 1. It is an HCFC with the chemical formula CHC12CF3 an OOP of 0.02 and a GP of only 50.

R125 is being tested as a potential replacement for R22 and the gas with similar properties R502. The gas R125 is an HFC with the chemical formula CHF2CF? an OOP of 0 and a GP of 1900.

Liquid indicators

These can be either cylindrical or circular glasses installed in the liquid line, providing a means of ascertaining whether or not the system is fully charged with refrigerant. If undercharged, vapour bubbles will appear in the sight glass. To be most effective indicators should be installed in the liquid line as close to the liquid receiver as possible. Some types incorporate a moisture indicator which, by changing colour indicates the relative moisture content of the liquid passing through.


Summarized below various refrigeration system components, working process and maintenance guideline:
  1. Automatic direct expansion refrigeration- vapour compression

  2. The basic components of any refrigeration system (Figure 11.1) working on the vapour compression cycle, are the compressor, condenser, expansion valve, evaporator and the refrigerant fluid which is alternately vaporized and liquefied during the refrigeration cycle. The temperature at which a fluid boils or condenses, is known as the saturation temperature and varies with pressure....more

  3. Choice of refrigerants

  4. Theoretically, almost any liquid can be used as a refrigerant if its pressure/temperature relationship is suitable for the conditions. Although no perfect refrigerant is known, there are certain factors which determine a refrigerant's desirability for a particular duty and the one selected should possess as many as possible of the following characteristics.....more

  5. Refrigeration systems - Chamber cooling arrangements

  6. To avoid having an extended refrigeration circuit for cargo cooling, a brine system can be used. The brine is cooled by the evaporator and in turn cools grids or batteries. Grids provide cooling which relies on convection and conduction but air circulated through brine batteries provides a positive through cooling effect. .....more

  7. Refrigeration system components

  8. Marine condensers are generally of the shell and tube type, designed for high pressures. There may a few coil-in-casing or other types still in use. The coolant passes through the tubes with refrigerant condensing on the outside......more

  9. Refrigeration system compressors

  10. Refrigeration compressors are usually either reciprocating, or of the rotary screw displacement type. Centrifugal and rotary vane compressors have also been used.....more

  11. Refrigeration systems expansion valves

  12. The expansion valve is the regulator through which the refrigerant passes from the high pressure side of the system to the low pressure side. The pressure drop causes the evaporating temperature of the refrigerant to fall below that of the evaporator. .....more

  13. Monitoring instruments,CO2 measurement & Heat leakage and insulation test

  14. All necessary cargo temperature readings are obtained on modern reefers and container ships on a data logger which makes an automatic record. The temperatures and pressures relating to refrigerant gas and liquid, cooling water, brine and the ambient are also required. Most of these are obtained from direct reading instruments. .....more

  15. Marine condenser assembly

  16. The temperature of the refrigerated spaces with a direct expansion system is controlled between limits through a thermostatic switch and a solenoid valve which is either fully open to permit flow of refrigerant to the room evaporator, or closed to shut off flow. The solenoid valve is opened when the sleeve moving upwards due to the magnetic coil hits the valve spindle tee piece and taps the valve open.....more

  17. Comparison between refrigerants R717 ammonia & R744 carbon dioxide

  18. The ammonia used for refrigeration systems based on the use of a compressor, condenser, expansion valve and an evaporator (Figure 11.2) is dry (anhydrous) in that there is no water in solution with it. It has the chemical formula NH3 but as a refrigerant, it is coded with the number R717....more

  19. Container cooling system

  20. The air is cooled either by brine or direct expansion batteries and the containers are arranged so that one cooler can maintain a stack of containers at a given temperature. The temperature of the return air duct for each container is monitored.....more



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