Some Point Of Information And Practical Cases Involving Refrigeration Installations Frequently Used On Board Ship
The refrigeration system are becoming increasingly important on board ship both to achieve great Crew comfort and for better care of cargoes
The refrigetation installation that can be found on a ship are the following :
- Cargo hold refrigeration installation on refrigerated ship.
- Refrigeration installation for stores
- Centralized air conditioning installation for accomodations.
- Independent air conditioning installation.
Some point of information and parctical case involving refrigeration installations frequently used on board ship
- Compressors :
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In an installation ,it can happen that the system cools down but that the operating sequences of the compressor are very long or even that the compressor does not shut down .
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This is due to lack of coolant,so that coolant does not circulate properly through the installation,preventing the compressor’s shutoff system from being activated due to lack of pressure.
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When,after an extended shutdown of the refrigeration installation ,it has to be re-started and it noted that the compressor does not start,the most common cause of this problem is usually that the maximum protection device has been activated, thereby preventing the compressor from starting .
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Evaporators :
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In every refrigeration installation ,the cooling effect is produced in the evaporator. This is where boiling of the refrigerant ,the refrigerant vapor that flows from the compressor is condenced and consequently flows via an expansion valve into the evaporator where absorbtion of heat from the storage areas to be cooled will take place.
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The evaporator is normally installed inside a closed vessel with metal walls.
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To maintain a higher level of evaporator performance , a defrosting system is installed in it . If this system is electric and has a break-down ,it is recommended ,in order to proceed with defrosting ,to shut down the installation an flush the evaporator with hot water to lossen the ice, after which the moisture should be eliminated from the area close to the evaporator.
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In defrosting,scrapers or pointed tools or any other instrument,which by its nature,can damage the evaporator,should never be use
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Condensers :
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The compressor lubricating oil that circulates together with the coolant has a great effect on the performance of the condenser .This oil tends to adhere to the walls of the condenser tube and forms an insulating coating that reduces heat tramission and ,therefore ,condenser efficiency. To prevent excessive accumulation of oil in the system,an oil trap is installed at the compressor discharge.
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- Expansion Valve :
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In the event that the expension valve of a cold storage installation is opened too wide expansion will take place not only in the evaporator,but also much further away,causing the refrigerating effect to be extended through the entire compressorsuction line.This line would become coated with frost,reducing the performance level of the installation.
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Another of the problems that frequently occurs in refrigeration installations is the problem caused by the presence of moisture inside the system. This generally produces small particles of ice in the expansion valve,which cam eventually obstruct its opening, shutting off the flow of liquid refrigerant to the evaporator.
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On occasions ,this moisture is pulled into the evaporator due to the great velocity of flow through the expansion valve , and is then deposited in the bends and narrow areas in the evaporator itself and causing the formation of ice plugs that obstruct the tube when the temperature is blow zero.
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To eliminate moisture ,drier filters are installed in the liquid line.
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Safety Valve :
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The safety valve in a refrigeration installation is located in the system’s high pressure zoone between the outlet of the compressor and the intake of the condencer. In those cases where there is an oil trap , the valve is located in the section of line between the oil trap an the condencer.
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The valve communicates at its end point with the flow pressure zone,the two zones being separated by a membrane whose function it is to interconnect the high and low pressure zones in the event of a break due to overpressure.In this manner,loss gas in the circuit is prevented.
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