Typically, one drop of Nylog can be stretched about three feet before breaking. Furthermore, there is no need of production of natural refrigerants, and hence no production related pollution or negative effect. Ltd. | Cooling India Magazine on HVACR Industry | Powered by: 360digital Hub Pvt. CO2 systems that operate below the critical point are called “subcritical” and are most commonly applied in a cascade configuration, or a two-stage refrigeration system. © Chary Publications Pvt. This is because high specific heat decreases the specific refrigerating effect and high latent heat at low temperature increases the specific refrigerating effect, The pressures required to be maintained in the evaporator and condenser should be low enough to reduce the material cost and must be positive to avoid leakage of air into the system, It must have high critical pressure and temperature to avoid large power requirements, It should have low specific volume to reduce the size of the compressor, It must have high thermal conductivity to reduce the area of heat transfer in evaporator and condenser, It should be non-flammable, non-explosive, non-toxic and non-corrosive, It should not have any bad effects on the stored material or food, when any leak develops in the system, It must have high miscibility with lubricating oil and it should not have reacting property with lubricating oil in the temperature range of the system, It should give high COP in the working temperature range. Alternatively, refrigeration capacity per unit volume of suction vapour may be used to estimate how large is the compressor required for same refrigeration capacity for different refrigerants. All the selections have been made based on an optimum intermediate temperature for an individual pair. Also many cascade systems use a very refined purified butane as a lubricant for the refrigerant. Direct Global Warming Impact (GWI) is the direct effect of released refrigerant emission in equivalent tonnes of carbon dioxide. Attainment of holistic environmental safety is the call of the day.... - Dr J Sarkar. Figure 3. In cascade systems: a) Different refrigerants are used in individual cascade cycles b) There is no mixing of refrigerants and no migration of lubricating oil c) Higher COPs compared to multi-stage systems can be obtained d) Operating pressures need not be too high or too low Ans.  The refrigerant pair selection procedure involves the following two major steps: The natural refrigerants which have been considered here are: Ammonia, Carbon dioxide, Propane, Propylene, n-Butane, Isobutane, Ethane & Ethylene. Key Performance and Design Parameters Attainment of holistic environmental safety is the call of the day, and this has facilitated the recent emergence of natural refrigerants as the more benign working fluid in refrigeration and heating systems. The other refrigerant used for the high side of the system can vary. These systems are sometimes called auto cascade systems. The use of ammonia as a refrigerant started in the 1870s. Hence, the refrigerant has to be selected for a certain application in such a way that the most of the basic properties should be favourable for that application. A typical R-717/CO2 cascade system. The Optimized Cascade process is based on three multi-staged, cascaded refrigerant circuits using pure refrigerants, brazed aluminum heat exchangers and insulated cold box modules. Hence, natural refrigerants can be assumed as next generation refrigerant for cooling and heating applications. Centrifugal or turbo compressors are used with refrigerants with low pressures and large volumes of suction vapour. The HT and LT circuits are thermally connected to each other through a cascade-condenser, which acts as an evaporator for the HT cycle and a condenser for the LT cycle. Refrigerant Pair Selection Guidelines R-22 refrigerant was made in the late 1990’s to temporarily replace R-12 due to its lower ODP. The ozone hole and ozone depletion result from CFCs, HCFCs, Halons, methyl bromide and other ODS released to the atmosphere. The load at -40°C is absorbed by a unit using R-22 as the refrigerant and is rejected to a cascade condenser at -10°C. Environmentally Friendly. The Ozone Depletion Potential (ODP) reflects the combination of percentage (by weight) of chlorine atoms and the lifetime of the compound in the atmosphere. :) Thank you, in advance for your support! GWPs (Global Warming Potential) are used to compare the impact on the climate system of emission of different greenhouse gases with respect to carbon dioxide (normalized at 1). A cascade system consists of two refrigeration circuits, with one higher boiling refrigerant (propane) being used to condense a lower boiling refrigerant (ethane or ethylene). A refrigerant is a substance, often a fluid, used in a refrigeration cycle to cool a space. The two-stage cascade absorption refrigeration system (CARS) is a type of CRS that can operate with two or more di erent refrigerants; the performance of CARS with R744 and R717 as working fluids has been analyzed to realize the cold energy production at lower temperatures. Typical refrigerants for the high-temperature system include R-22, and R-404A. Selection of suitable refrigerant mainly depends on its thermodynamic properties, physical properties and chemical properties. This approach is usually used for temperature levels below –90°F, when light hydrocarbon gases or other low boiling gases and vapors are being cooled (Lee et al., 1999). It also completely screens out lethal UV-C radiation. Carbon dioxide is also both plentiful and inexpensive. 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