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