Low specific volume of vapor, 6. This may also cause bursting of the tubes. Advantages of the secondary refrigerants over the direct cooling system are, 1. Oil has low thermal conductivity whereas refrigerant has very low thermal conductivity. The proposed equation is empirical in nature and provides the thermal conductivity Oas function of the reduced temperature in the range 0.3 to 0.9, that is from near the normal freezing point to near the critical temperature. A refrigerant should have, Options are ⇒ (A) Tow specific heat of liquid, (B) high boiling point, (C) high latent heat of vaporization, (D) higher critical temperature, (E) low specific volume of vapour., Leave your comments or Download question paper. The refrigerant should not make combustion mixture in Air. Required fields are marked *. Therefore oil separators are to be employed. When recharging the system with refrigerant, always add the new oil. Advantages of the secondary refrigerants over the direct cooling system are: 1. Unprecedented pandemic has taught many lessons to everyone of us. Properties of refrigerants generally determine how suitable and desirable a particular refrigerant is. First and foremost, copper is an excellent conductor of heat. Easy to handle and easy to control its flow. Desirable Properties of an ideal Refrigerant . It makes white fumes of ammonium sulfide. If the mass flow is very small it is difficult to control the flow rates. Special pressure pumps can be used to pump oil in the low parts of the system. Water, for example, has a thermal conductivity of 0.326 BTU/hr-ft-° F. at 32° F., whereas ice has a thermal conductivity of 1.18 BTU/hr-ft-° F. at the same temperature. It consists of an alcohol lamp that emits a blue flame. In practice, the required weight of RED TEK 12a needed to give the same refrigeration capacity and performance as R12 or R134a is 35% and 40%, respectively. h) It leak should be easily detectable. Once the evaporated gas is compressed, the temperature of seawater should be low enough (below critical temperature of the refrigerant) to be able to condense these gases to liquid form. Similarly if it is very low industry professional will not take necessary action to control the leaks. 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 moisture inside the system will starts freezing at low temperature zones and clogs and chokes the system. Refrigerants are widely used in Refrigeration cycle where cooling effect below the atmospheric temperatures are needed. Slightly more expensive but installation costs are lower. Due to the above disadvantages, Positive evaporator pressure is preferred. The conductive component is measured under the same conditions as … Let us look back on the journey so far for […], Copyright © 2016-2020 - Chemical Engineering Site, Advertise | Testimonials |Sitemap | Privacy Policy | Disclaimer. Refrigerants should have low freezing point than the normal operating conditions. This test is based on Beilstein Test for Chlorine. Ans: b. The refrigerants should not react with the materials used in refrigeration cycle like evaporators, condenser tubes, compressors, control valves etc. The liquid at the evaporator coil should therefore vapourise easily, otherwise the compressor will have to create too much of vacuum to cause the liquid to vapourise. Since polyatomic gas refrigerants have internal degrees of freedom, the unity between translational and internal modes has a significant influence on the thermal conductivity of these gases. A transient short‐hot‐wire method has been proposed to simultaneously measure the thermal conductivity and thermal diffusivity of liquids. This makes the equipments compact and reduced the operating cost. Water for example cannot be used below 0 Deg C. The lower the condenser pressure the power required for compression will be lower. Higher condenser pressure will result in high operating costs. Thermal conductivity. We use cookies to ensure that we give you the best experience on our website. High latent heat of vaporization, 4. compression, condensation, expansion, evaporation) in the refrigeration system absorb heat from a low temperature system and discard the heat so absorbed to a higher temperature system. This is the most important property of refrigerant. has second highest thermal conductivity with no significant health risks but is second most expensive option. small and compact. The refrigerant should be chemically stable. The year which will be remembered in the history has come to an end. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. Time weighted Average is the concentration to which repeated eight hour exposures for five days in a week which is considered to be safe. The refrigerants should be non poisonous to humans and food stuff. In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. In fluid dynamics, the Nusselt number (Nu) is the ratio of convective to conductive heat transfer at a boundary in a fluid.Convection includes both advection (fluid motion) and diffusion (conduction). Dry stagnant gas is one of the best insulating materials. It must be sourced and procured within a short span of time to enable the user in case of leaks, maintenance schedules etc. When HFOs are mixed with HFCs in equal proportion, the ordering of thermal conductivity in the resulting mixture is given by the following sequence of HFC components: R125 < R134a < R143a. We continue to change in order to grow and really do shine. Department of Mechanical Engineering, Saga University . Continued use of this site indicates that you accept this policy. The desirable properties of a refrigerant are as follows: 1. 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. Good job sir. A refrigerant should have (a) Tow specific heat of liquid (b) high boiling point (c) high latent heat of vaporisation (d) higher critical temperature (e) low specific volume of vapour. It is normally mentioned as 20 years or 100 years period. Refrigerant oil should be stored in sealed containers. Atmospheric air ingression inside the system may sometime results in explosions if the flammability values of the refrigerants are in wide range. In fact, ethylene glycol is the chemical used in automotive antifreeze. Refrigerants should be readily available near the usage point. Desirable properties of an Ideal Refrigerant : A refrigerant is said to be ideal if it has all of the following properties: 1. 3. 2. h) Thermal conductivity: Thermal conductivity in both liquid as well as vapour phase should be high for higher heat transfer coefficients i) Viscosity: Viscosity should be small in both liquid and vapour phases for smaller frictional pressure drops The thermodynamic properties are interrelated and mainly depend on If Freon is present blue flame turns into green. Dielectric strength: Therefore dielectric strength should be high to avoid short circuits. 4. In such a regenerater-type refrigerator, it is indispensable to maintain a high degree of thermal conduction between its magnetic refrigerant and refrigerant material. It may accumulate in evaporator. Ammonia and SO2 can be detected by their characteristic smell. 1 … This will cause corrosion and deteriorates valves, Seals and Metallic parts. GWP of Carbon Dioxide is 1.0. It should not freeze during application. To see this page as it is meant to appear, please enable your Javascript! Chemical Properties 3. Ammonia will form explosive mixture when the concentration in air is between 16 to 25 %. The quantity of refrigerant used in any industry is very small. Desirable Properties of a Primary Refrigerant. What is Chemical Engineering all about? Desirable properties of secondary refrigerants mainly are its specific gravity, freezing point, thermal conductivity, viscosity and specific heat. Methane, butane and other hydrocarbons are flammable. j) It should have satisfactory heat transfer coefficient. 1. the thermal conductivity of several refrigerant mixtures such as R125+R134a, R125+R32, R125+R152a, R134a+R32, R152a+R32, R134a+R143a, and R125+R143a. Your email address will not be published. The specific heat of liquid should be as small as possible and of vapour should be as high as possible to give less superheating of vapour. Here are some of the desirable properties of refrigerant explained in detail. Toxicity is the important properties of refrigerants. One such method in the literature, which has been used for pure substance, • is an approach known as the Bridgman equations[4]. Solution (By Examveda Team) -The refrigerant should have low boiling point and low freezing point. It should not freeze during application. Copper has many desirable properties for thermally efficient and durable heat exchangers. However, automotive glycol should not be used in a cooling system or heat exchanger because it contains silicate-based rust inhibitors. We solve numerically the Ornstein-Zernike (OZ) equation using the ypernetted H Chain (HNC) approximation for binary fluid mixtures and obtain the pair correlation functions. Short Term Exposure Limit is the maximum concentration to which one can be exposed up to maximum of 15 minutes. The oil and refrigerant should be miscible to assure that the oil is transported out of the refrigeration circuit and not accumulated in the system. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. At a given density, the differences in thermal conductivity between the refrigerant mixtures are on the order of (10–30) %. The condenser tubes have to be designed for higher pressures which also give raise to capital cost of the equipment. Pick up the wrong statement. Vapor produced after vapourisation of the liquid at the evaporator coil should occupy minimum volume, to keep pipeline diameter, compressor size, etc. Home » General Engineering Knowledge » Refrigeration » Desirable Properties of a Primary Refrigerant. Refrigerants should have low freezing point than the normal operating conditions. Akio Miyara, Koutaro Tsubaki, Nobuki Sato . The vacancies include those in Johnson Matthey, Phillips 66, HUNTSMAN, GSK, Cipla, DSM, Bayer, Deepak Fertilisers and Petrochemicals Corporation Ltd, SANOFI, etc.. Insulation Thickness, Thermal Conductivity & Performance Criteria Revision 2.0, August 2014 (PUR) Mixture of agents and additives -185°C to +110°C Very low thermal conductivity. Otherwise the zone of condensation decreases and the heat rejection occurs. Is applicable only to monatomic gases with a symmetrical and spherical intermolecular potential three categories 1. Bases in the liquid state along or near the usage point is normally high compared! 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desirable thermal conductivity for a refrigerant should be 2021