Duel Mode Lpg Refrigerating System

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The progressive ozone depletion and global warming require immediate concern to bring to an end the use of conventional chlorofluorocarbon refrigerants like R12. The hydrofluorocarbon R134a is non flammable, difficult to synthesize, has zero ozone depletion potential, but it has high global warming potential. LPG (hydrocarbon) refrigerants are highly flammable, occur naturally, have zero ozone depletion and negligible global warming potential. Looking towards the refrigeration and air-conditioning needs today and tomorrow, the conventional refrigerants must be substituted. This paper investigate the duel mode LPG refrigerating system and its applications in various fields. This paper also takes the review to check the possibilities of using the LPG (hydrocarbons) as a refrigerant in various existing systems.

Key words- Ozone Depletion Potential (ODP), Global Warming Potential (GWP), Liquefied Petroleum Gas (LPG).

I. Introduction

Considering the need of future refrigeration and air- conditioning, it is necessary to bring up an environmental friendly, safe and cost-effective alternative refrigerating systems and refrigerants for conventional domestic refrigeration systems. LPG-the fuel of new generation, with this initiative the ultimate aim of this paper is to introduce the two concepts.

1) Developing the dual mode refrigerating systems in which refrigeration will be the by-product of ordinary LPG systems.

2) Take the review to check the possibilities of using the LPG (hydrocarbons) as refrigerant in various systems.

II. Duel Refrigerating Systems

First of all we take a look on our simple vapour compression refrigeration cycle.

Figure 1 shows the conventional closed system which comprises mainly four parts: compressor, condenser, expansion valve and evaporator. The compressor is the main source of power consumption. The refrigerating effect is obtained by the heat exchange by means of phase change of refrigerant during its route through the evaporator.

'Is it possible to build a refrigerating system without power consumer device (compressor)?' And the answer is 'Yes!' it is possible to built such system which will work on open cycle, avoid compressor and will use the same principle of heat exchange by means of phase chance as that of conventional system.

Figure 1. Simple Vapour Compression System

To understand the duel mode LPG refrigerating system, let's consider the simple experiment which will give the actual idea about these duel systems and its working.

III. Construction And Working

The experiment was carried out in winter season of year 2009 at Mechanical Department of SNJB's College of engineering, Chandwad, Nasik.

3.1 Constructional features

The household LPG gas cylinder was placed in inverted position and the proper connections were made from the cylinder output to the evaporator and expansion device through filter. These devices were present in to the refrigerating box. The refrigerating box consisted of a stainless still container (capacity 30 liters) placed into an aluminum box. The proper insulation was made by using glass wool around the refrigerating box. Filter was used to remove the impurities present in LPG, if any. The capillary tube was made of copper material in the form of spiral coils. The output of this copper coil is taken to a burner for normal use. Regulator at cylinder was used for pressure adjustment. The arrangements were made to take the temperatures at required positions. The insulations and seals were checked properly before initiating the system. The inlet of refrigerating box and outlet of cylinder are kept at same height. The arrangement of cock is done to take water from refrigerating box.

Figure 2. Line Diagram of Duel System

3.2 Working

The regulator was operated and the circuit was checked for leakage. For operational safety, the cylinder was kept away from the burner. The initial readings for ambient air temperature and water temperature were noted.

The first stage was lightening the burner. Then the mass flow rate of LPG was controlled by high-pressure regulator. Thus the controlled flow was maintained to avoid the frosting and liquid accumulation at the burner inlet. After performing some trials, finally, the position of regulator valve was fixed by trial and error method to regulate the gas pressure.

Main working of closed cycle LPG refrigerant system is similar to vapour compression system which consisted of processes compression, condensation, expansion and evaporation.

Since LPG is stored in liquid form under high pressure in cylinder and therefore, compression and condensation processes are eliminated. The LPG is stored under high pressure in the cylinder, thus compression process is not needed. Further, LPG is already in liquid form at room temperature, thus condensation is not required. By keeping cylinder vertically downward we get high-pressure liquid LPG.

When LPG passes through the capillary tube present in refrigerating box, the high pressure liquid LPG converted in to low pressure liquid droplets.

The expansion and evaporation processes were same as that of vapour compression system. The process of expansion was carried at the outlet of capillary and the process of evaporation was carried into the copper coils by taking latent heat from the water in refrigerating box. In this way the LPG refrigerator system was operated. The vapour state LPG coming out from the evaporator chamber was passed to the gas burner, where it was allowed to burn and give energy for cooking or other purpose. In this way we could achieve the refrigeration effect and energy for cooking.

When the liquid LPG was passed from regulator through tube to filter then foreign particles present in the liquid were removed by filter. Then the filtered liquid was passes through capillary tube where its pressure decreased and it expansion was conceded in capillary tube. Then LPG vapour entered into evaporator coil where considerable amount of heat was removed from water. Due to absorption of heat the liquid LPG gets converted into vapour. Then the vapour LPG is passed through tube and it burns at the burner.

Iv. Design Specifications

The above system is design by using standard design procedure as well as by using trial and error method for some parts. The dimensions of main components of the system are as follows.

LPG cylinder : 14.2 Kg domestic cylinder.

Pipes : ISI marked LPG hose tubes.

Filter : Standard.

Capillary tube

Diameter : 0.5 mm

Length : 3100 mm.

Evaporation coil

Inner dia. : 7.94 mm.

Outer dia.: 9.94 mm.

Length : 9754 mm.

Evaporation chamber

Capacity : 30 liter.

V. Trial Performance

The following observations were obtained when experiment was performed for 20 minutes.

Temperature of atmosphere = 25.1oC

Temperature of water before experiment = 22.6 oC

Temperature of water after experiment = 8 oC

Total decrease in temperature = 14.6 oC

vi. Scopes For Improvement

This is an open system; by maintaining the proper pressure, we can recirculate the LPG when burning is not required. That is; it can be converted into the close type system by using the compressor to pour LPG again into the cylinder.

The LPG refrigerant can be used for A/C purpose also. The system which will have same working as that of refrigeration may be used for air-conditioning purpose.

The places where the continuous supply of LPG is needed, we can use this system not only for refrigeration purpose but also for water cooler & ice plant also.

E.g. LPG banks in big cities like Mumbai.

In cars using LPG as a fuel; it is possible to run cooling system and air-conditioners by using such duel systems[6].

Vi. Lpg As A Refrigerant- a review

The question arises 'Why to use LPG as a refrigerant?' In this section we will take the review for the need of LPG as a refrigerant, performance of LPG as a refrigerant in close refrigeration cycle, its comparison with other refrigerants and also its environmental impact.

6.1 Need of LPG as a refrigerant.

Currently produced Indian refrigerators mainly use the conventional CFC, namely CFC-12 as refrigerant. However, the choice of alternative refrigerants is still being debated. There is a need to assess various refrigerant options considering the existing refrigerators in the field and for the future market. This paper addresses the issues related to the use of LPG as a refrigerant, in Indian refrigerators, including performance, usage and servicing.

CFC's are principally destroyed by ultraviolet radiations in the stratosphere; the chlorine released in the high stratosphere catalyzes the composition of ozone to oxygen; and ultraviolet radiation penetrates to lower altitudes. Credible calculations of the magnitude of this effect [Hoffman 1987] and his team predicted 3% global ozone depletion for constant CFC emissions of 700 thousand tones per year.

The ozone impact of car air conditioners also cannot be ignored. A car air conditioner may lose 400g/year of dichlorodifluoromethane (R12) through hoses, pipe joints and shaft seals. Considering future population, if R-12 were still used, cars would emit 800 tones/year and refrigerators 20,000 tones/year. Now days hydro-fluorocarbons (HFC's) can be used as a replacement, but unfortunately the radiation properties of HFC's like R-134a make them powerful global warming agents.

Thus, hydrocarbon refrigerants particularly LPG serves as the best contender to replace CFC's from domestic refrigerators as well as car air conditioners. LPG (Liquefied petroleum gas) consists mainly of propane (R290), butane (R600), and isobutene (R600a) available as a side product in local refineries.

6.2 Performance of LPG as a refrigerant

AS we are taking the review to check the possibilities of using LPG as a refrigerant[6]; it is necessary to see what sort of work is still done in this field. The experiment was carried on a domestic refrigerator in Malaysia with the specification mentioned in following table number 1.

Table 1 Technical specifications of refrigerator Freezer test unit done in Malaysia

Specifications

Values

Fresh component capacity (liter)

220

Freezer Capacity (liter)

80

Power rating (W)

160

Current rating (A)

0.9

Voltage (V)

220

Frequency (Hz)

50

No. of doors

2

Refrigerant

134a(CF3CH2F)

Defrost system

Auto defrost

The temperature of the refrigerant inlet/outlet of each component of the refrigerator was measured with copper constantan thermocouples (T type). The thermocouple sensors fitted at inlet and outlet of the compressor, condenser, and evaporator. Thermocouples/Temperature sensors were interfaced with a HP data logger via a PC through the cable for data storage. Temperature was necessary to find out the enthalpy in and out of each component of the system to investigate the performance.

The inlet and outlet pressure of refrigerant for each of the component was also necessary to find out their enthalpy at corresponding state. The pressure transducer was fitted at the inlet and outlet of the compressor and expansion valve. The pressure transducer was fitted with the T-joint and then brazed with the tube to measure the pressure at desired position as mentioned before. The range of the pressure transducer was -1 to + 39 bars. The pressure transducers have also been interfaced with computer via data logger to store data. A service port was installed at the inlet of expansion valve and compressor for charging and recovering the refrigerant. The evacuation has also been carried out through this service port. A power meter was connected with compressor to measure the power and energy consumption.

6.3 Comparison of LPG with other refrigerants

6.3.1 Compressor parameters

After doing the analysis of above work; the results was quit hopeful and boosting to do more work with it.

Table 2. Energy Consumption by Compressor at 25°C and 28°C Ambient Temperature[6].

Refrigerant Used

Energy Consumption kWh/day

Percentage Fluctuations

Room Temp.

25°C

Room Temp.

28°C

Room Temp.

25°C

Room Temp.

28°C

HFC134a

2.077

2.254

--

--

Isobutane

2.131

2.183

+ 2.53

- 3.53

R12

2.626

2.758

+20.90

+18.27

R22

2.512

2.759

+17.41

+12.60 (The positive and negative sign indicates the increase and decrease of energy consumption).

The total energy consumption of all refrigerants is presented in Table 2. It has been found that the refrigerator consumes more energy at 28°C ambient temperature than at 25°C ambient temperature for all refrigerants. The comparison of energy consumption is made considering the HFC- 134a as benchmark and presented in the last two columns of Table 2. The negative and positive sign indicates the decrease and increase of energy consumption from the benchmark respectively. From the Table 2 it is obvious that the energy consumption of the HC refrigerants is more or less same as that of HFC-134a.

From the Table 2 it is evident that the energy consumption of the compressor at 28 °C is always higher than that of at 25°C[3]. It is mentioned that most of the thermal load on a refrigerator is conduction through the refrigerator wall. ASHRAE[1] shows that about 60-70% of the total refrigerator load comes by conduction through the cabinet walls. This conduction load is proportional to the difference between the ambient temperature and the internal compartment/freezer temperature.

The higher the difference, the higher is the load imposed on a refrigerator. The ambient temperature plays a significant role in energy consumption and electricity consumption is also very sensitive to ambient temperature. It is observed that energy consumption increased by 47 Wh for each degree increase in room temperature[2]. Further, the compressor efficiency also declines as the ambient temperature rises [3]. Here in this experiment the compressor consumes 8%, 3%, 5% and 4% more energy at 28°C than at 25°C when R-134a, Iso-butane, R12, and R22 was used respectively.

6.3.2 Effect of Evaporator Temperature and Coefficient of Performance (COP).

Figure 3 Coefficient of Performance versus Evaporating Temperature, when ambient temperature is 25oC.

The COP of the domestic refrigerator using R-134a as a refrigerant is calculated to compare with other refrigerants used in this experiment. The COP is plotted against inlet refrigerant temperature of the evaporator. The COP against inlet refrigerant temperature of the evaporator is plotted at 25°C and 28°C ambient temperatures in the same graph.

The result displayed in work. The refrigerating effect decreases with the decrease of evaporating temperature where as the compressor duty increases with the decrease of evaporating temperature.

Figure 4 Coefficient of Performance versus Evaporating Temperature when ambient temperature is 28oC.

Therefore, the COP decreases with the decrease of evaporating temperature. The COP at 25°C is slightly higher than that at 28°C for all refrigerants. This is due to the fact that the compressor efficiency decreases with the increase of ambient temperature [5] which ultimately affects the co-efficient of performance. Figures 3 and 4, shows a progressive increase as the evaporating temperature increases. The COP is the ratio of the refrigerating effect to the compressor work.

6.3.3 Effect of Evaporator Temperature on Refrigerating Effect.

The refrigerating effect is the main purposes of the refrigeration system. The liquid refrigerant at low pressure side enters the evaporator. As the liquid refrigerant passes through the evaporator coil, it continually absorbs heat through the coil walls, from the medium being cooled. The refrigerant continues to evaporate and turns into vapour refrigerant. The vapour refrigerant is still colder than the medium being cooled, therefore the vapor refrigerant continues to absorb heat. The refrigerating effect is difference of the enthalpy of inlet and outlet refrigerant of the evaporator. The refrigerating effect and inlet refrigerant temperature is shown in Figures 5-6.

Figure 5. Refrigerating Effect versus Evaporating Temperature, when ambient temperature is 25oC.

Figure 6 Refrigerating Effect versus Evaporating Temperature, when ambient temperature is 28oC.

From the Figures it is evident that the refrigerating effect increases with the increases of evaporating temperature.

From above figure 5 and 6, it is concluded This can be explained that if the evaporating temperature increases the heat transfer between the refrigerant entered into the evaporator tubes and the medium being cooled also increases which ultimately increase the refrigerating effect.

6.4 Environmental Impact.

The ozone depletion potential (ODP) for a specified time is the ratio of ozone destroyed by 1 kg of substance emitted instantaneously to the atmosphere to that destroyed by 1 kg dichlorodifluoromethane (R12).

The global warming potential (GWP) for a specified time is the ratio of the additional radiant heat at the earth's surface due to 1 kg of substance emitted instantaneously to the atmosphere to that from 1 kg of carbon dioxide. ODPs and GWPs are used in international agreements on controls and GWPs may be used in future taxes[7].

Table 3. Environmental Impact of refrigerants (100 year basis)

Refrigerant

R-12

R-22

R134a

R600a

Class

CFC

HCFC

HFC

LPG

Ozone depletion potential

1.0

0.07

0

0

Global warming potential

7300

1500

1200

8

Molina and Rowlands [12] theory is that: CFCs are principally destroyed by ultraviolet radiation in the stratosphere; the chlorine released in the high stratosphere catalyzes the decomposition of ozone to oxygen; and ultraviolet radiation penetrates to lower altitudes. Credible calculations of the magnitude of this predict 3% global ozone depletion for constant CFC emissions of 700 thousand tones/year after a hundred years.

The ozone impact of car air conditioners cannot be ignored. A car air conditioner may lose 400g/year of dichlorodifluoromethane (R12) through hoses, pipe joints and shaft seals. Considering future populations, if R-12 were still used, the cars would emit 800-thousand tones/year and refrigerators 20,000 tones/year of dichlorodifluoromethane. Hydro fluorocarbons (HFC's) can be thought of as a substitute, but unfortunately the radiation properties of HFC's like R-134a make them powerful global warming agents. Thus the hydrocarbon refrigerants particularly LPG serves as the best contender to replace CFC's from domestic refrigerators as well as car air conditioners.

Vii. Conclusion

This paper investigated an ozone friendly, energy efficient, user friendly, safe and cost-effective alternative refrigerating system and refrigerant for HFC134a in domestic refrigeration systems. The successful performance of LPG as refrigerant can draws following conclusion.

The co-efficient of performance for the LPG is comparable with the co-efficient of performance of HFC134a and other refrigerants.

The energy consumption of the LPG is about similar to that of HFC134a.

LPG offer lowest inlet refrigerant temperature of evaporator. So for the low temperature application LPG is better than HFC134a.

The domestic refrigerator required to charge with 140gm of HFC134a where as 70gms LPG is sufficient to work the system. This is an indication of better performance of the LPG as refrigerant.

The use of LPG as refrigerant already started in some European countries. Their chemical and thermodynamics properties meet the requirement of a good refrigerant except flammability. LPG is environmentally friendly. It has zero Ozone Depletion Potential (ODP) and negligible Global Warming Potential (GWP). LPG is cheaper than the R-134a which is being used in the refrigerator at present. LPG is also easily available. Some standards allow the use LPG as refrigerant if small amount of refrigerant is used. So there is no alternative way but to use the LPG as refrigerant mitigating the adverse effect of HC.

Viii. References

[1] Household refrigerators and freezers. ASHRAE equipment handbook. (1988) p. 37.4.

[2] Meier A, Megowan A, Lit B, Pon B, The New York refrigerator monitoring project: final report, (1993) LBL- 33708. Lawrence Berkeley Laboratory, CA.

[3] Eric Granryd, Hydrocarbons as refrigerants - an overview, International Journal of Refrigeration 24 (2001) 15-24.

[4] S. J. Sekhar, D.M.Lal, HFC-134a/HC600a/HC-290 mixture a retrofit for CFC12 system, International journal of refrigeration 28 (2005) 735-743.

[5] L.Maclaine-Cross, E.Leonardi, Performance and Safety of LPG Refrigerant. A report of . School of Mechanical and Manufacturing Engineering, the University of New South Wales Sydney NSW, Australia 2052.

[6] Sattar M.A, Saidur R, and Masjuki H.H,, Experimental Investigation on the Performance of Domestic Refrigerator Using Isobutane and Mixture of Propane, Butane and Isobutene. University of Malaya, Malaysia.

[7] Rathore M. M., Thermal Engineering, McGraw Hill, 2010, pp. 473-475.

[8] M. Mohanraj, S. Jayaraj, C. Muraleedharan and P. Chandrasekar, Experimental investigation of R290/R600a mixture as an alternative to R134a in a domestic refrigerator, International Journal of Thermal Sciences, Volume 48, Issue 5, May 2009, pp 1036-1042

[9] M. Mohanraj, S. Jayaraj and C. Muraleedharan, Environment friendly alternatives to halogenated refrigerants-A review, International Journal of Greenhouse Gas Control Volume 3, Issue 1, January 2009, pp 108-119

[10] James R. W. and Missenden J.F., The use of propane in domestic refrigerators, International Journal of Refrigeration, 1992, Volume 15, No,2 pp 95-100.

[11] R. Radermacher, K. Kim, Domestic refrigerator: recent development, International journal of refrigeration 19(1996) 61-69.

[12] Rowland, F. S. and Molina, M. J., Ozone depletion: 20 years after the alarm, Chemical and Engineering News 72, 8-13, 1994

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