The desirable characteristics of ‘ideal’ re… This will cause corrosion and deteriorates valves, Seals and Metallic parts. This phenomenon is called Oil logging. Since a refrigerant absorbs and releases heat primarily through evaporation and condensation, a high latent heat of vaporization might seem to be desirable. Environmentalfactors. A. Therefore, the dielectric strength of refrigerant is an important property in hermetically sealed compressor units. Similarly if it is very low industry professional will not take necessary action to control the leaks. Whenever we choose them for particular use Properties of Refrigerants also plays a vital role in economic and environmental friendly application. SO2 can be detected with NH3 H2O Solution. Carbon dioxide is widely used as a refrigerant in mechanical systems refrigerant, marine services, hospitals, etc. The low stage also functions like any other low temperature system, with the exception being the pressure characteristics of the refrigerant. Visit our about section to know more. Curiously enough the use of air as a refrigerant is both older and more recent than the other vapour refrigerants. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. Short answer: NO. (adsbygoogle=window.adsbygoogle||[]).push({}); Home In other cases, it is desirable that liquid refrigerant should not enter the compressor. The year which will be remembered in the history has come to an end. The refrigerant should not make combustion mixture in Air. Water for example cannot be used below 0 Deg C. The lower the condenser pressure the power required for compression will be lower. Methane, butane and other hydrocarbons are flammable. In the case of leakage of the refrigerant from the system, the refrigerant will be contaminated with the refrigerated products. Contact. Learn epa refrigerant with free interactive flashcards. Most of the refrigerants form acids or bases in the presence of water. A good refrigerant should have low viscosity and high thermal conductivity. The ozone depletion potential (ODP) of a refrigerant is the relative amount of depletion to the ozone layer it can cause. HFO-1234yf (or YF) has been shown to be a desirable, lowenvironmental-impact alternative to the more common HFC-134a as a refrigerant [1][2][3][4] [5]. The liquid at the evaporator coil … Other refrigerants are best adapted to centrifugal or rotary compressors. Global Warming Potential (GWP) is a relative measure of how much heat a refrigerant  traps in the atmosphere. 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). CH3Cl reacts with Aluminium. There is no rule of thumb governing the selection of refrigerants. c) Latent heat of vaporization of refrigerant must be … It may accumulate in evaporator. What is the desirable characteristics of a refrigerant? 'ME Mechanical' is an online portal for mechanical engineers and engineering students. Long answer: This is a very bad idea for multiple reasons: * R22 & R404A have different pressure temperature characteristics. The refrigerants should not react with the materials used in refrigeration cycle like evaporators, condenser tubes, compressors, control valves etc. In addition, if the volume of charge is large, there should be no danger to health and property in case of its escape. In hermetic arrangements, the motor windings are cooled by refrigerants vapor on its way to the suction valve of the compressor. What is the desirable characteristic of a refrigerant? We continue to change in order to grow and really do shine. © Copyright 2020 ME Mechanical. This may also cause bursting of the tubes. 2. Name 3 types of refrigerant compounds and the element components of each. It makes white fumes of ammonium sulfide. Freon leak can be detected by a halide torch. Q2. a) Boiling point at atmospheric pressure should be low. Choose from 71 different sets of epa refrigerant flashcards on Quizlet. 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: Tag Index Sorry, you have Javascript Disabled! Therefore overflow drain is to be provided to remove oil. Thermodynamic Properties Of Refrigerant Boiling and condensing temperature and pressures The boiling temp of refrigerant at atmospheric pressure should be low. Lack of Toxicity. What is the desirable characteristic of a refrigerant? The liquid has to vapourise at the evaporator coil to cause cooling. Strong smelling chemicals like acrolein may be added to refrigerant for easy leak detection. In today's world, other properties of the refrigerant are more important. Shallow industry professional will not take necessary action to control the leaks. It increasers the condenser pressures and thereby the power consumption for the compressor will also rise. Critical pressure of the refrigerant should be higher than the condenser pressures. The toxicity depends upon the concentration and exposure limits. What is Chemical Engineering all about? It is highly toxic, non-flammable, non-explosive, non-corrosive and works at low pressures. The moisture inside the system will starts freezing at low temperature zones and clogs and chokes the system. DESIRABLE PROPERTIES OF REFRIGERANT OR SELECTION OF A REFRIGERANT. Ammonia and SO2 can be detected by their characteristic smell. Desirable refrigerants are those which possess chemical, physical, and thermodynamic properties that permit their efficient application and service, in practical designs of refrigerating equipment. Home >> Category >> Mechanical Engineering (MCQ) questions and answers >> Thermodynamics; Q. 16 Viscosity and Thermal Conductivity. If the mass flow is very small it is difficult to control the flow rates. The lubricating oils must be soluble in Refrigerants. Therefore, epoxy resin is not desirable for the use with those refrigerants. 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. Cryogenic refrigerants are those refrigerants which produce minus temperature in between range -157°C to -273°C in the refrigerated space. refrigerant flow. While able to follow the load better than fixed restrictors or capillary tubes, their operating characteristics are The most reliable way to be safe is to choose a refrigerant that is neither toxic nor flammable. It is normally mentioned as 20 years or 100 years period. R-22 for example, has an ODP of 0.055. Higher condenser pressure will result in high operating costs. Halocarbons. All Rights Reserved. Viscosity; It should be as small as possible to ensure that the pressure drop in the system is as small as possible. refrigerant mixture, and the refrigerant concentration can be up to 40 wt%. A boiling-point temperature low enough that air … If the refrigerant velocity is not sufficient, then it cannot carry all oil back into the compressor. The cryogenic refrigerants have a shallow boiling point at atmospheric pressure. 3. Published hundreds of articles on various engineering topics. Otherwise the zone of condensation decreases and the heat rejection occurs. But, I really wants to download it. It is widely used in … To see this page as it is meant to appear, please enable your Javascript! Eg: Ammonia, R22, R12 etc, If Boiling Point is High, Low Condenser Pressure – Centrifugal Compressor is used. The price of the refrigerants is generally high when compared to other chemicals in the industry. HFCs. The characteristics of some refrigerants make them desirable for use with reciprocating compressors. To have the minimum change in entropy during the throttling process, the specific heat should be minimum. It is odorless, non-toxic, non-flammable, non-explosive and non-corrosive. 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. The refrigerant used in air conditioning, food preservation, etc. a. it should not be toxic b. it should not be non-corrosive c. it should have minimum enthalpy of vaporization d. all of the above View Answer / … About Us Toxicity is the important properties of refrigerants. Refrigerants should have low freezing point than the normal operating conditions. Distinction between Work and Internal Energy, Some of the widely used cryogenic refrigerants are Helium, Nitrogen, Oxygen, Hydrogen. Learn how your comment data is processed. - Published on 20 Aug 15. a. it should not be toxic. due to its excellent safety properties. Insufficient refrigerant C. Air in the system D. Stuck discharge valve ANS: B 240. Refrigerants with low boiling points will have high condenser pressure and high vapor density. When can you say a System is in Thermodynamic Equilibrium ? Desirable properties 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. Safety is perhaps the most important single factor in the selection of a refrigerant. List 6 desirable characteristics of a refrigerant. Theoretically, almost any liquid can be used as a refrigerant if its pressure/temperature relationship is suitable for the conditions. Eg: R11, R13 & R114 etc. Therefore cost of the refrigerants is normally high when compared to other chemicals. High latent heat Non Toxic Non Flammable Non Corrosive Chemically stable Lubricant soluble. However, there are five criteria should be taken into account: 1. Sulfur dioxide was widely used as refrigerant during the early 20th century. It is highly chemically stable. Freon-11 (Trichlorofluoromethane) is used under low operating pressures; it is non-toxic, non-corrosive and non-flammable. However, the oil in the refrigeration system is a contaminant that lowers the efficiency of the refrigeration system. Usertraining requirements should be taken into account. A refrigerant must also possess certain thermodynamic characteristics for it to function. Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. This makes the equipments compact and reduced the operating cost. 5. Critical pressure of the refrigerant should be higher than the condenser pressures. If Boiling Point is Low, High Condenser Pressure – Reciprocating Compressor is used. Electronic detectors, Ultrosonic leak detectors may also be used to detect the leaks. The desirable characteristics of “ideal” refrigerants are considered to be as follows: Normal boiling point below 0 °C; Non-flammable; Non-toxic; Easily detectable in case of leakage; Stable under operating conditions; Easy to recycle after use; Relatively large area for … Therefore ammonia cannot be used for small refrigeration systems. ODP of R11 is fixed as the maximum value of 1.0. The quantity of refrigerant used in any industry is very small. Ammonia reacts with Copper and Cuprous alloys and forms copper complexes. In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. The refrigerant may leak out of the system. should not be toxic as they will come into contact with human beings. - Thermodynamics. Which of the following characteristics that is not desirable in a refrigerant? It consists of an alcohol lamp that emits a blue flame. Name a Chlorine-free refrigerant. The condenser tubes have to be designed for higher pressures which also give raise to capital cost of the equipment. Each refrigerant has different material compatibility. 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. Change is the only option to survive and grow! Due to the above disadvantages, Positive evaporator pressure is preferred. Figures 5-11 shows the test results. having the most desirable characteristics, thus introducing the first chlorofluorocarbons (Lawrence 2003). To ensure the maximum heat absorption during refrigeration, a refrigerant … Hence, it is desirable that the refrigerant has a pungent smell so that its leakage can be detected immediately. This site uses Akismet to reduce spam. Safety. For Methane GWP is 72, it means that if the same mass of CH4 and CO2 were introduced into the atmosphere, that methane will trap 72 times more heat than the carbon dioxide. High Vapor Density In some applications, toxicity is of negligible importance whereas in others, such as comfort cooling, a non-toxic and non-flammable refrigerant is essential. Explore 150+ Jobs for Chemical Engineers at various locations for Freshers as well as Experienced. Get unlimited access to 5,000+ magazines, newspapers and curated premium stories at flat 55% off, Cooling Tower Efficiency Calculations – 75,000+ Views, Chemical Engineering Jobs Digest January 2021. A hot crankcase and cylinder head accompanied by a low suction pressure would be caused by A. So, please make it downloadble format. It must be sourced and procured within a short span of time to enable the user in case of leaks, maintenance schedules etc. Therefore oil separators are to be employed. Submit Guest Post Excess refrigerant B. Technological issues. Other desirable characteristics of a refrigerant include being nontoxic, noncorrosive, nonflammable, and chemically stable; having a high enthalpy of vaporization (minimizes the mass flow rate); and, of course, being avail-able at low cost. It is used for air-conditioning applications. Presence of air will reduce the partial pressure of refrigerant and the condensation temperature will rise. To enable the use of smaller compressors and other equipment the refrigerant should have smaller vapor density. If Freon is present blue flame turns into green. Higher heat transfer coefficient requires smaller area and lower pressure drop. Time weighted Average is the concentration to which repeated eight hour exposures for five days in a week which is considered to be safe. It must be sourced and procured within a short period to enable the user in case of leaks, maintenance schedules, etc. Ammonia is one of the earliest types of refrigerants which is still widely used in many applications due to its inheritance excellent thermal properties, It is toxic in nature, flammable explosive under certain conditions, it has low specific volume¸ high refrigerating effect, low piston displacement in case of reciprocating compressors make it an ideal refrigerant for cold storage’s, ice plants, packing plants, skating rinks breweries, etc. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. Economic aspects. It has not only excellent safe properties but also condenses at moderate pressure under normal atmospheric conditions. These characteristics could include vapor pressure, transport properties, lubricant and material compatibility, thermodynamic performance, cost, flammability, toxicity, stability, and environmental properties. If the oil is not miscible in the refrigerant used and it is heavier it will settle down in the evaporator and reduces the heat transfer. The quantity of refrigerant used in industries is very less. Miscibility with Oil; The refrigerant should not be miscible with the oil else the lubricating strength will be reduced. This is the most important property of refrigerant. Enthalpy of vaporization:. Refrigerants should be readily available near the usage point. Ammonia will form explosive mixture when the concentration in air is between 16 to 25 %. The refrigerants should be non poisonous to humans and food stuff. Insulation of windings in hermatic compressors will also get damaged. This feature is not available right now. The free water apart from the dissolved water in refrigerant freezes below 0 Deg C and chokes the narrow orifice of expansion valve. b) Freezing point at atmospheric pressure should be low. However, its use has been restricted nowadays because of its many inherent disadvantages. Privacy Policy As a refrigerant, it possesses completely stable thermal characteristics, has low toxicity, and is non-corrosive and non-combustible. Here are some of the desirable properties of refrigerant explained in detail. boiling points are small. The problems with a leakage are wearing out of joint or the material used for the fabrication of the system. 386 Freon, Carbon Dioxide, SO2 are non flammable. Sometimes, the product to be cooled is such that a constant evaporator temperature has to be maintained. 4. Advances in mechanical valves led toautomatic expansion valves. Otherwise the zone of condensation decreases and the heat rejection occurs. If the oil density is less than the refrigerant used and it if it is immiscible, the oil will float on the surface of the refrigerant. Therefore dielectric strength should be high to avoid short circuits. It should not freeze during application. Automatic expansion valves maintain a pressure in the evaporator, and open in response to a drop in suction pressure. That’s means it should have high coefficient of performance and consume less power for producing certain refrigerating effect. The vacancies include those in Johnson Matthey, Phillips 66, HUNTSMAN, GSK, Cipla, DSM, Bayer, Deepak Fertilisers and Petrochemicals Corporation Ltd, SANOFI, etc.. What type of refrigerant are R-11 and R-12. Chemical Engineers spend their life in making the world a […]. Most of the halogenated refrigerants meet these requirements. If it is brought into contact with open flame or heater elements, it decomposes into highly toxic constituents. In a negative pressure evaporator Atmospheric air or Moisture will Leak into the system. Let us look back on the journey so far for […], Copyright © 2016-2020 - Chemical Engineering Site, Advertise | Testimonials |Sitemap | Privacy Policy | Disclaimer. Thermophysical properties. Epoxy resin has relatively strong solubility in these refrigerants. Under ideal conditions, the mass flow rate of refrigerant in the system should be proportional to the cooling load. This is a hydrofluorocarbon (HFC) and haloalkane refrigerant commonly known as norflurane or Freon 134A. Therefore, it is important that the oil and the refrigerant are miscible with each other so that oil following the refrigerant out in the system is In order to have a broad range of isothermal energy transfer, the refrigerant should have a critical temperature above the condensing temperature. Unprecedented pandemic has taught many lessons to everyone of us. Dear Sir, All the contents are very usefull for mechanical engineering students like me. For this, the liquid saturation line should be almost vertical. Leakage can be identified quickly if the refrigerant has a distinct color or odor. Please try again later. The high specific heat of vaporization High suction gas density Positively, but not excessive pressure, the boiling point and condensation conditions The critical temperature and the triple point are far beyond the operating range Economic considerations: The refrigerant used in the vapor compression cycle of the refrigeration or air-conditioning system should produce maximum refrigerating effect. Refrigerants should be available near the usage point. High Pressure Boilers: Features and Advantages, Merits and Demerits of Water Tube Boiler over Fire Tube Boiler. The detection of leaks should be easy to loss of refrigerant. Due to low operating pressure and high displacement, it is used in systems employing centrifugal compressors. Topic Index Short Term Exposure Limit is the maximum concentration to which one can be exposed up to maximum of 15 minutes. Atmospheric air ingression inside the system may sometime results in explosions if the flammability values of the refrigerants are in wide range. It would not cause ozone depletion or climate change. According to Wikipedia, Chemical engineering is a branch of engineering that applies physical sciences (physics and chemistry), life sciences (microbiology and biochemistry), together with applied mathematics and economics to produce, transform, transport, and properly use chemicals, materials and energy. 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. Refrigerants are widely used in Refrigeration cycle where cooling effect below the atmospheric temperatures are needed. Characteristics of a Good Refrigerant Boiling Point. This test is based on Beilstein Test for Chlorine. Most of the refrigerants form acids with water. Refrigerants will affect human health if they are poisonous. Moderately high evaporator pressure boosts the compressor suction pressure thus reduces the power costs. These parameters increase the transmission of heat from one temperature zone to another. Desirable Properties of Refrigerant: Desirable refrigerant possess such chemical, physical and thermodynamic properties which permit their practical application in … Atmospheric air ingression into the system will occupy the heat transfer area and results in poor heat transfer rates. 1 Answer. A denser refrigerant will have fewer tendencies to leak as compared to higher density refrigerant. Freon-12 (Dichloro difluoromethane) is non-flammable, non-toxic and non-explosive. Ammonium Hydroxide Solution turns the red litmus paper into blue; thereby condenser tube leaks can be identified. The proportions of the components are chosen based on the exact characteristics desired in the final product. In addition to these criteria, other considerations such as; local regulations and standards, maintainability and capability (such as having staff with skills to support the units). GWP of Carbon Dioxide is 1.0. Stability. Leak outside the system results in refrigerant loss and it can be identified easily and refrigerant loss can be topped up.

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