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