Refrigerants should be available near the usage point. In an example with R-12, assume the compressor is of the right size to deliver one ton of refrigeration when refrigerant evaporates at 0 deg. What is the desirable characteristic of a refrigerant? CCl2F2, CH4Cl can form HCL with water which dissolves the copper from condenser tubes and deposits them on compressor pistons and deteriorates the life of the machinery. Epoxy resin has relatively strong solubility in these refrigerants. The quantity of refrigerant used in any industry is very small. To ensure the maximum heat absorption during refrigeration, a refrigerant … Distinction between Work and Internal Energy, https://me-mechanicalengineering.com/about/. Which of the following characteristics that is not desirable in a refrigerant? The refrigerants should not react with the materials used in refrigeration cycle like evaporators, condenser tubes, compressors, control valves etc. To enable the use of smaller compressors and other equipment the refrigerant should have smaller vapor density. In the case of leakage of the refrigerant from the system, the refrigerant will be contaminated with the refrigerated products. It is odorless, non-toxic, non-flammable, non-explosive and non-corrosive. Cryogenic refrigerants are those refrigerants which produce minus temperature in between range -157°C to -273°C in the refrigerated space. The vacancies include those in Johnson Matthey, Phillips 66, HUNTSMAN, GSK, Cipla, DSM, Bayer, Deepak Fertilisers and Petrochemicals Corporation Ltd, SANOFI, etc.. If the refrigerant velocity is not sufficient, then it cannot carry all oil back into the compressor. It must be sourced and procured within a short period to enable the user in case of leaks, maintenance schedules, etc. It would not cause ozone depletion or climate change. List 6 desirable characteristics of a refrigerant. The proportions of the components are chosen based on the exact characteristics desired in the final product. If the mass flow is very small it is difficult to control the flow rates. This makes the equipments compact and reduced the operating cost. Freon, Carbon Dioxide, SO2 are non flammable. The toxicity depends upon the concentration and exposure limits. Sulfur dioxide was widely used as refrigerant during the early 20th century. The quantity of refrigerant used in industries is very less. Water for example cannot be used below 0 Deg C. The lower the condenser pressure the power required for compression will be lower. A hot crankcase and cylinder head accompanied by a low suction pressure would be caused by A. Topic Index Usertraining requirements should be taken into account. It consists of an alcohol lamp that emits a blue flame. It is widely used in … However, its use has been restricted nowadays because of its many inherent disadvantages. Leakage can be identified quickly if the refrigerant has a distinct color or odor. Q2. Refrigerants with low boiling points will have high condenser pressure and high vapor density. due to its excellent safety properties. It may accumulate in evaporator. But, I really wants to download it. The most reliable way to be safe is to choose a refrigerant that is neither toxic nor flammable. Similarly if it is very low industry professional will not take necessary action to control the leaks. The capacity of the system depends on how often a pound of refrigerant evaporates and this depends on compressor size and on properties of the refrigerant at refrigerant cycle temperatures. What is the desirable characteristic of a refrigerant? When can you say a System is in Thermodynamic Equilibrium ? A boiling-point temperature low enough that air … In addition, if the volume of charge is large, there should be no danger to health and property in case of its escape. HFCs. CH3Cl reacts with Aluminium. As a refrigerant, it possesses completely stable thermal characteristics, has low toxicity, and is non-corrosive and non-combustible. In other cases, it is desirable that liquid refrigerant should not enter the compressor. Here are some of the desirable properties of refrigerant explained in detail. should not be toxic as they will come into contact with human beings. What is the desirable characteristics of a refrigerant? Atmospheric air ingression inside the system may sometime results in explosions if the flammability values of the refrigerants are in wide range. Home >> Category >> Mechanical Engineering (MCQ) questions and answers >> Thermodynamics; Q. It is normally mentioned as 20 years or 100 years period. Therefore dielectric strength should be high to avoid short circuits. Although no perfect refrigerant is known, there are certain factors which determine a refrigerant's desirability for a particular duty and the one selected should possess as many as possible of the following characteristics: Economic considerations: The refrigerant used in the vapor compression cycle of the refrigeration or air-conditioning system should produce maximum refrigerating effect. Therefore, epoxy resin is not desirable for the use with those refrigerants. Privacy Policy The detection of leaks should be easy to loss of refrigerant. Published hundreds of articles on various engineering topics. Chemical Engineers spend their life in making the world a […]. For this, the liquid saturation line should be almost vertical. Some of the widely used cryogenic refrigerants are Helium, Nitrogen, Oxygen, Hydrogen. Thermophysical properties. 386 Moderately high evaporator pressure boosts the compressor suction pressure thus reduces the power costs. The condenser tubes have to be designed for higher pressures which also give raise to capital cost of the equipment. Higher condenser pressure will result in high operating costs. It is highly toxic, non-flammable, non-explosive, non-corrosive and works at low pressures. This may also cause bursting of the tubes. 16 Viscosity and Thermal Conductivity. The refrigerant should not make combustion mixture in Air. So, please make it downloadble format. Therefore ammonia cannot be used for small refrigeration systems. Carbon dioxide is widely used as a refrigerant in mechanical systems refrigerant, marine services, hospitals, etc. It is used for air-conditioning applications. Methane, butane and other hydrocarbons are flammable. What type of refrigerant are R-11 and R-12. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. Otherwise the zone of condensation decreases and the heat rejection occurs. Refrigerants with High vapor density/ Low specific volume will require a smaller compressors and velocity can be kept small and so the condenser tubes used will also be in smaller diameter. Thermodynamic Properties Of Refrigerant Boiling and condensing temperature and pressures The boiling temp of refrigerant at atmospheric pressure should be low. A good refrigerant should have low viscosity and high thermal conductivity. Due to the above disadvantages, Positive evaporator pressure is preferred. Under ideal conditions, the mass flow rate of refrigerant in the system should be proportional to the cooling load. Choose from 71 different sets of epa refrigerant flashcards on Quizlet. While able to follow the load better than fixed restrictors or capillary tubes, their operating characteristics are In a negative pressure evaporator Atmospheric air or Moisture will Leak into the system. Automatic expansion valves maintain a pressure in the evaporator, and open in response to a drop in suction pressure. Other refrigerants are best adapted to centrifugal or rotary compressors. The moisture inside the system will starts freezing at low temperature zones and clogs and chokes the system. Learn epa refrigerant with free interactive flashcards. Leak outside the system results in refrigerant loss and it can be identified easily and refrigerant loss can be topped up. The low stage also functions like any other low temperature system, with the exception being the pressure characteristics of the refrigerant. It increasers the condenser pressures and thereby the power consumption for the compressor will also rise. This feature is not available right now. Ammonia and SO2 can be detected by their characteristic smell. The ozone depletion potential (ODP) of a refrigerant is the relative amount of depletion to the ozone layer it can cause. 4. Ammonia reacts with Copper and Cuprous alloys and forms copper complexes. Freon-12 (Dichloro difluoromethane) is non-flammable, non-toxic and non-explosive. Halocarbons. What is Chemical Engineering all about? boiling points are small. Most of the refrigerants form acids or bases in the presence of water. Excess refrigerant B. This is the most important property of refrigerant. Eg: Ammonia, R22, R12 etc, If Boiling Point is High, Low Condenser Pressure – Centrifugal Compressor is used. Enthalpy of vaporization:. The refrigerant used in air conditioning, food preservation, etc. It must be sourced and procured within a short span of time to enable the user in case of leaks, maintenance schedules etc. One of the most famous displays of its non-toxic properties occurred when Thomas Midgely filled his lungs with Freon and blew out a candle (Lawrence 2003). To see this page as it is meant to appear, please enable your Javascript! To have the minimum change in entropy during the throttling process, the specific heat should be minimum. Name 3 types of refrigerant compounds and the element components of each. Visit our about section to know more. - Published on 20 Aug 15. a. it should not be toxic. Critical pressure of the refrigerant should be higher than the condenser pressures. The free water apart from the dissolved water in refrigerant freezes below 0 Deg C and chokes the narrow orifice of expansion valve. Due to low operating pressure and high displacement, it is used in systems employing centrifugal compressors. Let us look back on the journey so far for […], Copyright © 2016-2020 - Chemical Engineering Site, Advertise | Testimonials |Sitemap | Privacy Policy | Disclaimer. This site uses Akismet to reduce spam. 5. Freon-11 (Trichlorofluoromethane) is used under low operating pressures; it is non-toxic, non-corrosive and non-flammable. Therefore, the dielectric strength of refrigerant is an important property in hermetically sealed compressor units. Toxicity is the important properties of refrigerants. Eg: R11, R13 & R114 etc. It has not only excellent safe properties but also condenses at moderate pressure under normal atmospheric conditions. Insufficient refrigerant C. Air in the system D. Stuck discharge valve ANS: B 240. A denser refrigerant will have fewer tendencies to leak as compared to higher density refrigerant. 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