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Design and Fabrication Of LPG Refrigeration System Report Download

ABSTRACT

This work investigates the result of an experimental study carried out to determine the performance of domestic refrigerator when a propane-butane mixture is liquefied petroleum gas (LPG) which is locally available and comprises 24.4% propane, 56.4% butane and 17.2% isobutene which is very from company to company. The LPG is cheaper and possesses an environmental friendly nature with no ozone depletion potential (ODP). It is used in world for cooking purposes. The various methods of refrigeration on the basis of standard refrigerant discussed. He refrigerator used in the present study is of medium size with a gross capacity of 125 litre and is designed to work on LPG. The performance parameters investigated is the refrigeration effect in certain time. The refrigerator worked efficiently when LPG was used as refrigerant instead of CFC 12. The evaporator temperature reached -5 ºC with and an ambient temperature of 12 ºC. Also from the experiment which done in atmospheric condition, we can predict the optimum value of cooling effect with the suitable operating condition of regulating valve and capillary tube of the system. The results of the present work indicate the successful use of this propane-butane mixture
as an alternative refrigerant to CFC 12 in domestic refrigerant.

INTRODUCTION

The term ‘refrigeration’ in a broad sense is used for the process of removing heat (i.e. cooling) from a substance. It also includes the process of reducing and maintaining the temperature of a body below the general temperature of its surroundings. In other words, the refrigeration means a continued extraction of heat from a body, whose temperature is already below the temperature of its surroundings.

For example, if some space (say in cold storage) is to be kept at -2 ºC, we must continuously extract heat which flows into it due to leakage through the walls and also the heat, which is brought into it with the articles stored after the temperature is one reduced to -2 ºC. Thus in a refrigerator, heat is virtually being pumped from a lower temperature to a higher temperature. According to second law of thermodynamics, this process can only be performed with the aid of some external work. It is thus obvious, that supply of power (say electrical motor) is regularly required to drive a refrigerator. Theoretically, the refrigerator is a reversed heat engine, or a heat pump which pumps heat from cold body and delivers to a hot body.
The substance which works in a heat pump to extract heat from a cold body and to deliver it to a hot body is called refrigerant.

TYPES OF DOMESTIC REFRIGERATOR

There are two types of domestic refrigerator.
1. Single door fresh food refrigerator
2. Double-door refrigerator-freezer

Most domestic refrigerator are of two types – either a single door fresh food refrigerator or a two-door refrigerator-freezer combination, with the freezer compartment on the top portion of the cabinet, or a vertically split cabinet (side-byside), with the freezer compartment on the left side of the cabinet. They are completely self-contained units and are easy to install. Most refrigerators use R-22 refrigerant, normally maintaining temperatures of 0 ºF in the freezer compartment and about 35 ºF to 45 ºF in the refrigerator compartment.

LPG REFRIGERATION

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.

PROPERTIES

» Colourless.
» Odourless. (It’s normal to odorise LPG by adding an odorant prior to supply to the user, to aid the detection of any leaks).
» Flammable.
» Heavier than air.
» Approximately half the weight of water.
» Non toxic but can cause asphyxiation.
» 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.

THE LPG REFRIGERATION CYCLE

(1). LPG Gas Cylinder:

From the LPG gas cylinder, LPG flows through the pipe and reaches to the capillary tube. LPG gas pressure is approximate 80-100 psi.

(2). Capillary Tube:
As the capillary tube, capillary tube downs the pressure up to less then 1 psi.

(3). 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.

(4). Gas Burner:
After performing the cooling effect, low pressure LPG gas goes into the burner where the burns.

WORKING LPG REFRIGERATOR

The basic idea behind LPG refrigeration is to use the evaporation of a LPG to absorb heat. The simple mechanism of the LPG refrigeration working is shown in figure.

» LPG is stored in the LPG cylinder under high pressure. When the gas tank of regulators is opened then high pressure LPG passes in gas pipe. This LPG is going by high pressure gas pipe in capillary tube.

» High pressure LPG is converted in low pressure at capillary tube with enthalpy remains constant.

» After capillary tube, low pressure LPG is passed through evaporator. LPG is converted into low pressure and temperature vapour from and passing through the evaporator which absorbs heat from the chamber. Thus the camber becomes cools down. Thus we can achieve cooling effect in refrigerator.

» After passing through the evaporator low pressure LPG is passed through pipe by burner. And we can uses the low pressure of LPG is burning processes.

ADVANTAGES OF LPG REFRIGERATION

» The cooling capacity of LPG is 10% higher than R-12 and the vapour pressure is appropriate.
» LPG is naturally occurring and non-toxic.
» Use of LPG as a refrigerant also improves the overall efficiency by 10 to 20%.
» The ozone depletion potential (ODP) of LPG is 0 and Global warming potential (GWP) is 8 which is Significantly negligible as compared to other refrigerant.
» Apart from environment friendly, use of also LPG gives us lot of cost advantages.
» LPG does not form acids and thereby eliminates the problem with blocked capillaries.
» There is 60% reduction in weight of the system due to higher density of LPG.
» The fridge works when electricity off.
» It is efficient to save fuel.
» No pollution
» The units are effectively silent in operation.
» Running cost is zero.
» Eliminates the compressor and condenser.

DISADVANTAGES OF LPG REFRIGERATION

» LPG is explosive in nature.
» Do not maintain constant pressure in LPG cylinder.
» Put the LPG cylinder is inverted position.
» After the refrigeration processes, the exhaust of LPG is burn into burner. Because of the exhausted vapour LPG can not converted again liquid phase , because the this process is very costly.
» The prevention of leakage of the LPG is the major problem in LPG refrigeration system. Because of the LPG is highly flammable.

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