09-10-2012, 05:51 PM
DOMESTIC LPG REFRIGERATOR
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INTRODUCTION
In India, more than 80% of the domestic refrigerator utilize HFC 134a as refrigerant, due to its excellent thermodynamic and thermo physical properties. But, HFC 134a has a high global warming potential (GWP) of 1300. There is a need of assess various refrigerant option considering the existing refrigerators in the field and for the future market.
CFC’s are principally destroyed by ultraviolet radiations in the stratosphere; the chlorine released in the high stratosphere catalyzes the decomposition of ozone to oxygen; and ultraviolet radiations penetrates to lower altitudes. Credible calculations of the magnitude of the effect (Hoffman 1987) and his team predicted 3% global ozone emissions of 700 thousand tonnes/year after a hundred years. The ozone impact of car air conditioners also can not be ignored. Hydrofluorocarbons (HFC’s) can be thought of as a replacement, but unfortunately the radiation properties of HFC’s like R-134a make them powerful global warming agents. HFC 134a and the HC blend have been reported to be substitutes for CFC 12, but they have their own drawbacks in energy efficiency, flammability and serviceability aspects of the systems. HFC 134a is not miscible with mineral oil, and hence, polyol ester oil is recommended, which is highly hygroscopic in nature. This hygroscopicity demands stringent service practices, which otherwise results in moisture entry into the system.
Thus, hydrocarbon refrigerants; particularly LPG serves as the best contender to replace CFC’s from domestic refrigerator as well as car air conditioners.
LPG consists mainly of propane (R-290) and butane (R-600), and LPG is available as a side product in local refineries. In Cuba for already several decades LPG is used as a drop-in refrigerant. LPG mixtures have composition of a commercial LPG mixture suitable as ‘drop-in’ replacement for R-12 was calculated crudely as 64% propane and 36% butane by mass. Liquefied petroleum gas (LPG) of 60% propane and 40% commercial butane has been tested as a drop-in suitable for R 134a in a single evaporator domestic refrigerator with a total volume of 10 ft3.
PROPERTIES
o Colourless.
o Odourless. (It’s normal to odorise LPG by adding an
o Odorant prior to supply to the user, to aid the detectionof any leaks).
o Flammable.
o Heavier than air.
o Approximately half the weight of water.
o Non-toxic but can cause asphyxiation.
o LPG expands upon release and 1 litre of liquid will form approximately 250 litres of vapour.
• A Good Mixture : LPG is mainly Propane (C3H8), Butane (C4H10) or a mix of Propane/Butane. Since LPG has such a simple chemical structure, it is among the cleanest of any alternative fuel.
• Boiling Point : LPG’s boiling point ranges from -42 ºC to 0 ºC depending on its mixture percentage of Butane and Propane.
• Combustion : The combustion of LPG produces carbon dioxide (CO2) and water vapour but sufficient air must be available. Inadequate appliances flueing or ventilation can result in the production of carbon monoxide which can be toxic.
• Vapour Pressure : LPG is a stored as a liquid under pressure. It is almost colourless and its weight is approximately half that of an equivalent volume of water. The pressure inside a closed container in which LPG is stored is equal to the vapour pressure of the liquid and corresponds to its temperature.
• Ignition Temperature : The temperature required to ignite LPG in air is around 500 ºC.
• Calorific Value : The calorific value of LPG is about 2.5 times higher than that of main gas so more heat is produced from the same volume of gas.
• Toxicity : LPG is a colourless, odourless and non-toxic gas. It is supplied commercially with an added odorant to assist detection by smell.LPG is an excellent solvent of petroleum and rubber product and is generally non-corrosive to steel and copper alloys.
• Safety : LPG is just as safe as any other fuel. In fact, it is safer than most fuels because neither LPG itself nor the end products that are produced by burning LPG in a suitable appliance are poisonous to inhale. Since LPG cannot burn without air, there can never be a ‘Flash-back’ into the cylinder.
You can feel safe with LPG as the most through precaution are taken to ensure your safety. All you have to do is to handle it correctly whilst adhering to the simple instructions provided.
» Propane : suitable for use in all conditions. It is the only
LPG product suitable for cold climates (such as the UK and
Canada) because of its low boiling point of -43.6 ºF
(-42 ºC).
» Butane : suitable for use in hot climate only because of its
higher boiling point of 22.9 ºF (-5 ºC).
» Propane/Butane mixtures : suitable for use in moderate
Climates
THE LPG REFRIGERATION CYCLE
i. LPG Gas Cylinder: The LPG gas cylinder, LPG flows through the pipe and reaches to the capillary tube. LPG gas pressure is approximate 80-100 psi.
ii. Capillary Tube: As the capillary tube, capillary tube downs the pressure up to less than 1 psi.
iii. Evaporator: In the evaporator LPG is converted into the vapour from with low pressure. After passing through the evaporator low pressure and temperature LPG vapour absorbs heat from the chamber system.
iv. Gas Burner: After performing the cooling effect, low pressure LPG gas goes into the burner where the burns.