The compression ratio affects discharge temperature more than anything else. A major parameter in the determination of the magnitude of this "optimum" pressure level is the refrigerant temperature at the outlet of the heat rejecting heat exchanger 2, i.e. In HVAC/R we are in the business of moving BTUs of heat and we move these BTUs on the back of pounds of refrigerant. This site uses Akismet to reduce spam. Derived from refrigeration grade lubricants. This is where the suction gas enters the compressor. The ideal working fluid or often called refrigerant would have favorable thermodynamic properties, be noncorrosive to mechanical components, and be safe, including freedom from toxicity and flammability.It would not cause ozone depletion or climate change.Since different fluids have the desired traits in different degree, choice is a matter of trade-offs. Rubber and plastics are used extensively in the refrigeration system. This compression ratio calculator can be used to work out the compression ratio of your engine. High critical temperature to have large isothermal energy transfer. Taking these three factors into account, the T-s and p-h diagrams of an ideal refrigerant would be as shown in the figures below: These properties are practically not found in any refrigerant. As the refrigerant is changed from a liquid vapor mix to fully liquid in the condenser it travels from right back left between points #4 and #5 as heat is removed from the refrigerant into the outside air (on an air cooled system). Here i am talking with respect to vapor compression refrigeration cycle. Get the (near) daily Tech Tip email right in your inbox! compression, condensation, expansion, evaporation) in the refrigeration system absorb heat from a low temperature system and discard the heat so absorbed to a higher temperature system. Direct material compatibility is less problematic. Hence, it is desirable that the refrigerant has a pungent smell so that its leakage can be detected immediately. smaller pressure ratio have been obtained with liquid injection flows between 40 and 80 g/s. Refrigerants should have low freezing point than the normal operating conditions. When a low temp freezer is functioning on on a very hot day it will run high compression ratios. Absolute Pressures. The metering device then creates a pressure drop that is displayed between points #6 and #7. A High Suction gas density and a Low Compression ratio. In a 404a medium temp refrigeration (cooler) 3.0:1 – 5.5:1  is a common ratio range, In a typical 404a 0°F to -10°F freezer application 6.0:1 – 13.0:1 is a common ratio range. In the case of R-502, the compression ratio is almost 10 percent less than that of R-22 and 3 percent less than R-115. Desirable Properties of a Refrigerant: 1. The conductivity of the refrigerant should be as high as possible so that the size of the evaporator and condenser is manageable. 3.16.2 Should. Threshold and Ratio. In such a case, the mass flow rate has to be controlled in such a manner that only superheated vapour leaves the evaporator. Figure 1 depicts a typical, single-stage vapor-compression system. Vapor-compression uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Generally, the refrigerant or the required volume of cooling capacity will determine the kind of compressor that is needed. The density of the refrigerant should be as large as possible. (b) evaporation of the refrigerant liquid (c) compression of the refrigerant vapour (d) metering of the refrigerant liquid (e) none of the above. Absolute pressure is just gauge pressure + atmospheric pressure. It also continually circulates the refrigerant through the refrigerating system. ** The vapour compression cycle as above and with 70% efficient compression with R134a and no other losses. ANALYSIS OF VAPOUR COMPRESSION REFRIGERATION SYSTEM WITH SUB- COOLING AND SUPER HEATING WITH THREE DIFFERENT REFRIGERANTS FOR AIR-CONDITIONING APPLICATIONS Dr. Boda Hadya* * Assistant Professor, Mechanical Engineering Department, U.C.E., Osmania University, Hyderabad, A.P-500007 DOI: 10.5281/zenodo.164904 ABSTRACT This paper presents the simulated results of vapour compression … It should be chemically stable for the operating ranges of temperature. Again in centrifugal compressors pressure rise is related to the density of the vapor. If the outdoor air temperature is high or if the condenser coils are dirty, blades are improperly set or the condenser coils are undersized point #2 (condensing temperature) will be higher on the chart and therefore will put more heat strain on the compressor and will result in lower compressor efficiency and capacity. On the other hand, the specific heat of vapor should be high to have less superheating of the vapor. Solid lines are Simple Mixtures. The compression ratio will change as the evaporator load and the condensing temperature change but in general, under near design conditions, you will see the following compression ratios on properly functioning equipment depending on the efficiency and conditions of the exact system. Plus, when you order through my link, it helps me to continue to offer you lots of free stuff. So, a trade-off has to be done in order to achieve as high a COP as possible. The refrigerant should not react with them or else there might be leakage of refrigerant from the system or loss of functioning of the compressor. The desirable properties of a refrigerant are as follows: 1. During trans-critical cycle operation of such circuit, a high-side pressure providing a maximum ratio between refrigerating capacity and compressor shaft power should be provided. Download our mobile app and study on-the-go. When servicing the unit; A. the compressor should be valved off. You'll get subjects, question papers, their solution, syllabus - All in one app. A lower compression ratio is desirable in all respects. The compression ratio can also be used as a diagnostic tool to analyze whether or not the compressor is providing the proper compression. Go ahead and login, it'll take only a minute. 2. The compression ratio needs to be as small as possible otherwise the leakage of refrigerant occurs across the piston. A compression ratio of 5:1 indicates that_____. Receiver. Horizontal (left to right) is the heat content scale, the further right the more heat contained in the refrigerant (heat, not necessarily temperature). The performance of refrigeration plant is expressed as "Co-efficient of Performance (COP)" which is defined as the ratio of refrigerating effect produced to the work of compression. Calculating this ratio can be a big help when it comes to troubleshooting a system. Calculating this ratio can be a big help when it comes to troubleshooting a system. This should be as small as possible in order to have a small size of the compressor. It is desirable to operate above atmospheric pressure to avoid moisture and air leakage into the system. These properties can be divided into favourable thermodynamic, chemical and physical properties. Vapor density: To enable the use of smaller compressors and other equipment the refrigerant should have smaller vapor density. For the evaporator, the refrigerating capacity is (9) Q e = m 3 ( h 7 − h 3) = m 3 ( h | p = p e, q = 0 − h 3) To facilitate the performance comparisons between the hybrid cycle and the conventional vapor-compression cycle, the coefficient of performance (COP) of … CO2 has a very low COP. Very low compression ratios coupled with low amperage and low capacity are often an indication of mechanical compressor issues. In order to determine a system’s compression ratio, we must deal in absolute pressures, not gauge pressure readings, since a … Non-hardening, non-drying fluid which bonds tenaciously to many different substrates. The Coefficient of performance or COP has a direct bearing on the running cost of the refrigeration system. refrigerant for a vapor compression ~achine is a long and elaborate process. When a customer sets their A/C down to 69°F(20.55°C) on a 100°(37.77°C) day they will simply have high compression ratios. Ten times the logarithm to the base ten of the ratio of the sound power radiated by the source to a reference power, expressed in decibels (dB). Also, due to presence of moisture in air, acids or other corrosive compounds may form and this may affect the tubing of the refrigeration system. A: A1 refrigerant ANSI/ASHRAE 34 published in 2001 and entitled "Designation and Safety Classification of Refrigerants". refrigerant temperature must be lower than 253 K; in order to transfer heat from the cold room to the refrigerant. For the larger pressure ratio an injection flow of 100 g/s has been assumed. This ensures that the irreversibilities associated with throttling are small and there is greater sub-cooling of the liquid. Desirable properties of an Ideal Refrigerant : A refrigerant is said to be ideal if it has all of the following properties: 1. The LNG is reduced in pressure and may be sent to an endflash drum before it is sent to the storage tank. Hence, it is not suitable for use as a refrigerant. † SEI is the ratio between the actual COP and the Carnot COP with reference to the cooling load and outside air temperatures, that is when the heat exchanger … The refrigerant is compressed and cooled using air or cooling water prior to providing the refrigeration duty. Desirable Properties of an ideal Refrigerant Refrigerant: The refrigerant is a heat carrying medium which during their cycles (i.e. Seasonal Energy Efficiency Ratio. The design coil temperature is dictated by the requirements of the space being cooled as well as the load on the coil but the LOWER the pressure and temperature of the evaporator the less dense the vapor will be at point #2 when it re-enters the compressor and the higher the compression ratio will need to be to pump it back up to point #3 and #4. Mass flow ratio of NH3 in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of (a) 1 : 1 (b) 1 : 9 (c) 9 : 1 (d) 1 : 3 (e) 3 : 1 Ans: b 67. An operating unit that has a receiver/storage tank requires refrigerant system service. Freezing Point It should be as low as possible or else there will be a possibility of blockage of passages during flow of fluid through evaporator. Sometimes, the product to be cooled is such that a constant evaporator temperature has to be maintained. Both the evaporator and condenser pressures need to be above atmospheric pressure otherwise there is a possibility of air leaking into the system. It should not be soluble in the oil else there will be reduction in the viscosity of the lubricating oil. All components of vapor cycle system should check to ensure for any damage, misalignment, or visual signs of leakage. A potential replacement must satisfy a number of qualifying (or gate) properties as well as possess favorable the~odynamic and transport ~roperties (Threlk~l? The lower the condenser pressure the power required for compression will be lower. It should be as low as possible or else there will be a possibility of blockage of passages during flow of fluid through evaporator. D. a gauge pressure of "Ol/psi should be achieved by venting. (2001). The inventors have determined that a ratio of voltage-to-frequency for the motors of the components in a refrigerant system such as a compressor, fan or pump should vary with operating and environmental conditions. Find answer to specific questions by searching them here. Ethane, butane, isobutene are highly undesirable as they catch fire quickly. refrigerant for a vapor compression ~achine is a long and elaborate process. 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