Title of Invention

A MIXTURE OF REFRIGERANTS

Abstract

HCFC22 is used as refrigerant in air conditioners. As HCFC22 is an ozone depleting substance it has to be phased out. The substitute HFC407C consisting of difluoromethane (HFC32), pentafluoroethane (HFCI25), 1,1,1,2-tetrafluoroethane (HFCI34a) is immiscible with the conventional mineral oil. The immiscibility issue of HFC407C with mineral oil can be overcome with the addition of hydrocarbon to it. The present invention is a refrigerant mixture that comprises of difluoromethane (HFC32) as the first component, pentafluoroethane (HFCI25) as the second component, 1,1,1,2- tetrafluoroethane (HFCI34a)as the third component, isobutane (HC600a) as the fourth component, and Propane (HC290) as the fifth component. This refrigerant mixture of the invention is non ozone depleting and has performance characteristics similar to that of HCFC22 but with a higher energy efficiency. This would be of immense use to the RAC sector to retrofit window air conditioners in the event of phasing out of HCFC22 without changing the mineral oil.

Full Text

DESCRIPTION Field of invention: The present invention relates to refrigerants generally, and more specifically to eco-friendly, energy efficient, mixture of refrigerants that can be substituted for Monochlorodifluoromethane. Investigation details Background of the Invention Monochlorodifluoromethane (HCFC22), the generally accepted and more suitable refrigerant for air conditioners has to be phased out by 2030 in developed countries and by 2040 in developing countries (like India) because of its Ozone Depleting Potential (ODP). The, phasing out of ozone depleting refrigerants has led to the quest for eco-friendly alternative refrigerants. Therefore this invention as an alternative to HCFC22 is quite significant. Published literature revealed that the only drop-in substitute for HCFC22 is HFC407C, because it offers a close match to HCFC22 in its behaviour. HFC407C is a zeotropic refrigerant mixture of difluoromethane (HFC32) /pentafluoroethane (HFC 125)/1,1,1,2-tetrafluoroethane (HFC 134a) [23/25/52% by weight]. However, with HFC407C, Polyol Ester (POE) oil must be used instead of mineral oil. This POE is highly hygroscopic, expensive and it causes irritation if it comes in contact with our skin. On the other hand, this causes several service issues during retrofitting. If HFC407C could be made to work with mineral oil these service issues could be alleviated. It is possible to mix suitable Hydrocarbon (HC) Refrigerants with HFCs to solve the miscibility issues with mineral oil. Propane (HC290) is a common HC refrigerant that could be considered as a mixture constituent with HFC407C due to its higher latent heat, volatility and miscibility with mineral oil. However from the literature it is found that the discharge pressure of HFC134a/HC290 mixture itself is higher than that of HCFC22 and HC290 refrigerants. Hence adding HC290 to HFC407C will result in still higher pressures. It was also observed from the literature that isobutane (HC600a) could also be considered as mixture constituent with HFC 134a while the vapour pressure did not shoot up. But, the boiling point of HC600a was much higher when compared to that of the HFC407C and there would be a greater composition shift in the heat exchanger, which might lead to oil return problems in the evaporator. Hence to utilize the above advantages of HC290 and HC600a, a HC blend (readily available in the market) consisting of 45.2% of HC290 and 54.8% of HC600a was considered to mix with HFC407C. From the literature it was found that addition of 9% of HC blend with HFC 134a could solve the miscibility problem and also improves the performance of the system. Summary of the Invention One of the main objectives of the present invention is to provide a solution for replacing HCFC22 with an ozone friendly substance that uses mineral oil in a wider variety of applications. Another objective of the present invention is to improve energy efficiency of the system compared to HCFC22. Another objective of the present invention is to reduce the compressor discharge temperature compared to HCFC22. Another objective of the present invention is to keep the discharge pressure at lower levels or at least closer to HCFC22. Among the most preferred embodiments of the present invention are mixtures of refrigerants that are substitutes for monochlorodifluoromethane (HCFC22), comprising about 17.25 to 20.7 weight percent difluoromethane (HFC32); about 18.75 to 22.5 weight percent pentafluoroethane (HFC 125); about 39 to 46.8 weight percent 1,1,1,2-tetrafluoroethane (HFC 134a); about 5.48 to 13.7 weight percent isobutane (HC600a); and about 4.52 to 11.3 weight percent propane (HC290), with the weight percentage of the components of the mixture being weight percentages of the overall mixture. Description of the preferred embodiments To improve the system performance and solve the immiscibility issue of existing refrigerant mixture HFC407C with conventional mineral oil, a hydrocarbon blend (isobutane/propane) was considered to mix with HFC407C. Accordingly the performance tests were conducted for the mixtures comprising about 17.25 to 20.7 weight percent difluoromethane (HFC32); about 18.75 to 22.5 weight percent pentafluoroethane (HFC125); about 39 to 46.8 weight percent 1,1,1,2-tetrafluoroethane (HFC134a); about 5.48 to 13.7 weight percent isobutane (HC600a); and about 4.52 to 11.3 weight percent propane, with the weight percentage of the components of the mixture being weight percentages of the overall mixture. Initially, the REFPROP software was used to analyse the performance of refrigerant mixtures. It was indicated that with increase in the mass percentage of HC blend, the suction and discharge pressure shoots up. To decrease the discharge pressure of HFC407C/HC blend refrigerant mixture the condenser length had to be altered. Therefore in the present invention, the condenser surface area was increased by about 19% for the mixtures to control the increase in discharge pressure. This can reduce the pressure ratio and also realize superior heat transfer in the condenser. It was also indicated that the mixtures have higher latent heat than HCFC22 and thus there is scope for the mixtures to have better refrigeration capacity than HCFC22. It was also observed that with the increase of HC blend in the mixture the density decreases, which will reduce the charge quantity while retrofitting HCFC22 systems. Test rig used for the invention A test rig as shown in figure was constructed to measure the mineral oil return characteristics, energy efficiency, and other performance such as compressor discharge temperature and pressure in an actual operating system. This test rig consists of a room calorimeter, a window air conditioner of 1050 W capacity, instruments and accessories fitted to facilitate performance study as detailed in the following sections. Room Calorimeter The outer dimensions of the room calorimeter are 2300 mm x 2300 mm x 2800 mm. The walls of the room were insulated with glass wool of thickness 200 mm in order to maintain the heat infiltration to be less than 5% of the air conditioner capacity [BIS (Bureau of Indian Standards): 1391-1992]. A 2000W heating capacity air heater was placed inside the room calorimeter as the source for heating load. The heater was connected through a dimmerstat and wattmeter (±0.5% accuracy) to the power supply, to facilitate variation and measurement of heat load. In order to have a uniform temperature throughout the calorimeter room, a fan (40 W) was used to circulate the air inside the calorimeter. Window Air-Conditioner To periodically check the oil level in the compressor an oil level indicator was attached suitably to the compressor as shown in figure. To optimize the capillary, 8 capillaries of different diameter and length viz. 1.1176 mm diameter: 1.25 m, 1.5 m, 1.75 m, 2 m, 2.25 m long and 1.27 mm diameter: 1.5 m, 1.75 m, 2 m long were fixed to a header. Suitable ball valves were used to select the required capillary to be included in the circuit. A thermally insulated duct was used to control the temperature of air passing over the condenser to simulate various ambient conditions without obstructing the flow of air. Instrumentation To monitor the mass flow of the refrigerant in the system, a mass flow meter with ± 0.25% accuracy was installed next to the condenser. To measure the compressor power a wattmeter with ±0.5% accuracy was used. The energy consumption per day was also measured with an energy meter with ±0.5% accuracy. Pressure transducers with ±0.25% accuracy and film type PT100 RTD temperature sensors with ± 0.1 °C accuracy were fixed appropriately to measure the respective parameters across each component. Since the mixture is zeotropic in nature, to measure the temperature distribution along the evaporator coil 8 temperature sensors were fixed suitably. Computerized data acquisition system (Agilent 3 4970A - polling frequency 60 channels / second) was used to record the entire temperatures (T) and pressures (P). Five temperature sensors were fixed at various state points inside the room calorimeter to ensure that the variations in the temperature inside is not exceeding 1°C at steady state conditions before making observations. Test procedure The entire test was conducted according to the BIS standard 1391 (1992). In this test, refrigerant side performance of the air conditioner was measured. Before starting the experiment, heat infiltration test was carried out for a temperature differential between evaporator inlet air temperature and the atmosphere ranging from 15°C to 0°C. It was found that for the maximum temperature differential of 15°C, the heat leak was 47.1 W, which was less than 5% of the air conditioner capacity. During tests, condenser inlet air temperature was varied from 30 to 45°C in steps of 5°C, whereas evaporator inlet air temperature was varied from 21 to 29°C in steps of 2°C. The evaporator inlet air temperature and condenser inlet air temperature were the main variables in the test matrix. The refrigerating capacity of the system for a particular evaporator inlet air temperature and condenser inlet air temperature was obtained by reading the room heater load, which was controlled by a dimmerstat to maintain steadily the required evaporator inlet air temperature. At each test condition the respective heat infiltration was added to the heater load to get the actual refrigeration capacity. To have a realistic comparison of the performance of the proposed mixtures, the test was carried out initially with the conventional refrigerant HCFC22. The capillary tube diameter, length and the refrigerant charge were optimised as the refrigerant flow volume had changed due to alterations made to fix instruments, receiver etc. During capillary tube optimisation, the system was initially charged with 750 g of HCFC22 (as per the manufacturer's catalogue). An evaporator inlet air temperature of 27°C and a condenser inlet air temperature of 35°C were maintained during testing. In the test the COP of the system was maximum with 1.1176 mm diameter capillary tube at 1.75 m length and it was selected. Subsequently for the selected capillary tube the charge quantity of HCFC22 was optimised for maximum COP by varying charge from 600g to 1100 g in steps of 50g. The optimal charge of HCFC22 was found to be 950g. After that, the performance test [mineral oil return to the compressor, energy efficiency, discharge temperature and pressure] was carried out for various sets of condenser and evaporator inlet air temperatures with optimal capillary and optimal charge. COP and per day energy consumption of window air conditioner was considered to rate the energy efficiency of refrigerants. COP was calculated from the actual refrigeration capacity and compressor power. To measure the per day energy consumption of window air conditioner, the thermostat inside the room was adjusted to cut-in at 28°C and cut-off at 26°C while the condenser inlet air temperature was varied from 30 to 45°C in steps of 5°C. Once the system reached steady cut-in and cut-off cycles, for a set of test condition the energy consumption was noted for 24 hours using energy meter. Also at each test condition the discharge temperature and pressure were noted for all the refrigerants. To conduct the experiment using mixtures, they were prepared separately in four different cylinders, which were initially cleaned and flushed thoroughly. For each mixture the equivalent charge quantity for 950gm of HCFC22 was obtained along with % composition of HFC407C and HC blend considering the specific volume ratios at suction condition. Each mixture component was weighed individually in an electronic balance with an accuracy of ±0.1 gm and filled in the respective cylinders with the help of a suitable charging manifold. While doing experiments with mixtures after realizing the higher condenser pressure the tube length was increased by 19% from that of HCFC22 so that the discharge pressure was maintained within 27 bar. The capillary tube optimization for the mixtures was carried out as mentioned earlier with equivalent charge of mixtures. The COP for the mixtures was found to be maximum for a capillary tube diameter of 1.1176 mm and length 1.5 m. Hence the same capillary tube was considered for all the mixtures to evolve the equivalent charge corresponding to maximum COP. Further the same system performance study carried out with HCFC22 was repeated with the equivalent charge for all the considered mixtures. Test performance observation The oil level was continuously noted on the oil level indicator during the operation of the system for all the refrigerants. Compared to the initial level, a small reduction (2mm) in height was observed. This could be due to oil lost with the refrigerant during change over of mixtures. Thus from the above observation it was proved that the miscibility issue of HFC407C refrigerant with mineral oil can be over come with the addition of HC blend. From performance tests it was observed that the improvement in refrigeration capacity of mixtures was 9.54 to 12.76% higher than that of HCFC22 at the various condenser inlet air temperatures. This increase in refrigeration capacity can be attributed to the higher latent heat of evaporation and the mass flow rate. For the mixtures the mass flow rate was found to be 4.64 to 9.04 % higher than that of HCFC22 at various condenser inlet air temperatures. This increased mass flow rate could be attributed to the higher volumetric efficiency that might result due to lower pressure ratio. The discharge pressure of HCFC22 was found to be lowest among the refrigerants. For the mixtures the discharge pressure was found to be 3.73 to 11.46 % higher than that of HCFC22 for different condenser inlet air temperatures. Even though the discharge pressure of HCFC22 was lower it was observed that the pressure ratio of HCFC22 was the highest and it could be attributed to the lower suction pressure of the HCFC22 as compared to that of mixtures. It was observed that the compressor power was lowest for HCFC22. This can be due to the lower mass flow rate than other mixtures. However for the mixtures, with the increase in HC blend, the compressor power was found to be decreasing and approaching that of HCFC22. This is due to the lower pressure ratio for the mixtures. It was observed that even though with mixtures the power consumed by the compressor was higher than that of HCFC22, the COP was also higher because of the higher mass flow rates and possibly better heat transfer characteristics. At all test conditions, uncertainty analyses were carried out and the uncertainty in COP was less than 2.3%. From the test it was observed that the per day energy consumption of the mixtures is less than that of HCFC22. Even though the compressor power is higher than HCFC22 the reduced running time due to higher refrigerating capacity has resulted in lower energy consumption for mixtures. Mixtures show 5.08 to 10.45 % less energy consumption than that of HCFC22 for various condenser inlet air temperatures. From the above observation it is inferred that as the proportion of HC blend increases in the considered mixture the mass flow rate, refrigerating capacity and COP increases whereas compressor power, compression ratio, discharge temperature and per day energy consumption decreases. This can be due to the fact that as HC blend proportion increases density of the refrigerant mixture decreases. This can reduce the mass flow rates but the lower pressure ratio results in a better volumetric efficiency leading to higher mass flow rates and thence better system performance. Thus it is better to use the proposed mixtures to retrofit the HCFC22 refrigeration and air conditioning systems in the event of phasing out of HCFC22. Conclusion Based on the above observation it is concluded that this invention of the mixtures 1) is significant because of the mechanism by which the oil miscibility issue of HFC407C with mineral oil is tackled. 2) is innovative by virtue of the fact that the new mixture solves the service issue associated with HFC system due to hygroscopicity of POE oil. 3) has got good applicability as in the event of HCFC22 phase out the existing millions of window Air conditioners, split Air conditioners, water coolers and bottle coolers operating with HCFC22 reciprocating hermetic compressors can be retrofitted. The test has been conducted with a window air conditioner in a room calorimeter with standard operating conditions prescribed by the compressor manufacturers. Since the test conditions prescribed by the manufacturers for the other appliances mentioned above are also same, the refrigerant mixtures of this invention could be also used other appliances that use HCFC22 hermetic compressors. I Claim: 1. A mixture of refrigerants that substitutes monochlorodifluoromethane (HCFC22), comprises of difluoromethane (HFC32) as the first component, pentafluoroethane (HFC 125) as the second component, 1,1,1,2-tetrafluoroethane (HFC 134a) as the third component is characterized in that isobutane (HC6G0a) as the fourth component and propane (HC290) as the fifth component. 2. The mixture according to claim 1 wherein said mixture comprises 17.25 to 20.7% by weight difluoromethane (HFC32). 3. The mixture according to claim 1 wherein said mixture comprises 18.75 to 22.5% by weight pentafluoroethane (HFC 125). 4. The mixture according to claim 1 wherein said mixture comprises 39 to 46.8% by weight 1,1,1,2-tetrafluoroethane (HFC 134a). 5. The mixture according to claim 1 wherein said mixture comprises 5.48 to 13.7% by weight isobutane (HC600a). 6. The mixture according to claim 1 wherein said mixture comprises 4.52 to 11.3% by weight propane (HC290).

Documents:

0941-che-2005 abstract duplicate.pdf

0941-che-2005 claims duplicate.pdf

0941-che-2005 description (complete) duplicate.pdf

0941-che-2005 drawings duplicate.pdf

941-che-2005-abstract.pdf

941-che-2005-claims.pdf

941-che-2005-correspondnece-others.pdf

941-che-2005-correspondnece-po.pdf

941-che-2005-description(complete).pdf

941-che-2005-drawings.pdf

941-che-2005-form 1.pdf

941-che-2005-form 9.pdf