We use cookies to ensure that we give you the best experience on our website. Due to the above disadvantages, Positive evaporator pressure is preferred. High latent heat of vaporization to get more refrigeration effect. In fact, ethylene glycol is the chemical used in automotive antifreeze. 1 … Following are the desirable properties of a primary refrigerant. has second highest thermal conductivity with no significant health risks but is second most expensive option. 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. Question is ⇒ Pick up the wrong statement. Copper has many desirable properties for thermally efficient and durable heat exchangers. What is Chemical Engineering all about? Pressure to which compressor has to compress the drawn gases, to convert them back into liquid at the condenser, should be low. Refrigerants should have low freezing point than the normal operating conditions. j) It should have satisfactory heat transfer coefficient. Whenever we choose them for particular use Properties of Refrigerants also plays a vital role in economic and environmental friendly application. Refrigerants should have low freezing point than the normal operating conditions. This phenomenon is called Oil logging. This test is based on Beilstein Test for Chlorine. Atmospheric air ingression into the system will occupy the heat transfer area and results in poor heat transfer rates. This will cause corrosion and deteriorates valves, Seals and Metallic parts. The refrigerants should be non poisonous to humans and food stuff. 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. 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. Ammonia and SO2 can be detected by their characteristic smell. 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. One such method in the literature, which has been used for pure substance, • is an approach known as the Bridgman equations[4]. 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. Change is the only option to survive and grow! For all these refrigerants, the thermal conductivity was measured in the vapor phase at atmospheric pressure over a temperature range from 250 to 400 K and also at moderate pressures. Chemical Engineers spend their life in making the world a […]. Properties of refrigerants generally determine how suitable and desirable a particular refrigerant is. g) It should not be toxic. The toxicity depends upon the concentration and exposure limits. SO2 can be detected with NH3 H2O Solution. (PIR) Polyisocyanurate -185°C to +140°C Petrochemical equipment, buildings, refrigerated vehicles, tankers The condenser tubes have to be designed for higher pressures which also give raise to capital cost of the equipment. We continue to change in order to grow and really do shine. - It must have low specific heat and high latent heat. The properties of refrigerants may be grouped into three categories: 1. Eg: Ammonia, R22, R12 etc, If Boiling Point is High, Low Condenser Pressure – Centrifugal Compressor is used. High critical temperature to have large isothermal energy transfer. 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). Presence of air will reduce the partial pressure of refrigerant and the condensation temperature will rise. Brazilian equation to calculate the thermal conductivity of refrigerant R 152 as a function of the dynamic viscosity of the liquid. Ans: b. Strong smelling chemicals like acrolein may be added to refrigerant for easy leak detection. Best insulation materials should have the lowest thermal conductivity, in order to reduce the total coefficient of heat transmission. Temperatures can be controlled by controlling the flow. 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. Therefore dielectric strength should be high to avoid short circuits. The refrigerant is a heat carrying medium which during their cycles (i.e. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. Ammonia will form explosive mixture when the concentration in air is between 16 to 25 %. Desirable properties of an Ideal Refrigerant : A refrigerant is said to be ideal if it has all of the following properties: 1. Chemical Properties 3. Low specific volume of vapor, 6. h) It leak should be easily detectable. Questions and Answers on Diesel Engines 1, Reciprocating Positive Displacement Pumps, Pressure Vacuum Valve or PV Valve – Inert Gas System, Gear Pumps – Rotary Positive Displacement Pumps, What is Net Positive Suction Head or NPSH, Measuring Fuel pump Lead on Marine Auxiliary Engine, Operation and Maintenance of Eductor on Ships, Insulation Resistance Tests of High Voltage Equipment. Al 2O3 reacts with water & heat is generated . Ammonium Hydroxide Solution turns the red litmus paper into blue; thereby condenser tube leaks can be identified. Most of the refrigerants form acids or bases in the presence of water. Higher condenser pressure will result in high operating costs. A transient short‐hot‐wire method has been proposed to simultaneously measure the thermal conductivity and thermal diffusivity of liquids. Refrigerants with low boiling points will have high condenser pressure and high vapor density. This fact, combined with the higher latent heat and thermal conductivity, has the desirable effects of reducing the weight of refrigerant required to extract a specified amount of heat. Easy to handle and easy to control its flow. 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. Desirable characteristics for insulation materials for fish holds. … i) It should have positive condensing pressure. Moderately high evaporator pressure boosts the compressor suction pressure thus reduces the power costs. e) It should not have corrosive action with system material. GWP of Carbon Dioxide is 1.0. It should not freeze during application. 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. Higher heat transfer coefficient requires smaller area and lower pressure drop. Excellent way of fully understanding the engeeniring system. R-134a is an HFC (hydrofluorcarbons) used to replace the chlorinated refrigerant R- 12. 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. The liquid has to vapourise at the evaporator coil to cause cooling. 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. Desirable Properties of an ideal Refrigerant . Desirable properties of secondary refrigerants mainly are its specific gravity, freezing point, thermal conductivity, viscosity and specific heat. It may accumulate in evaporator. Vapor produced after vapourisation of the liquid at the evaporator coil should occupy minimum volume, to keep pipeline diameter, compressor size, etc. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. Your email address will not be published. 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. Summary. 3. Required fields are marked *. small and compact. If Freon is present blue flame turns into green. Thus, less insulating material will be required. THERMAL CONDUCTIVITY OF HFO-1234ze(E)+HFC-32 MIXTURE . Home » General Engineering Knowledge » Refrigeration » Desirable Properties of a Primary Refrigerant. 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. Low boiling and freezing point, 2. Refrigerant Thermal Conductivity at Low and Moderate Levels of Density. Critical pressure of the refrigerant should be higher than the condenser pressures. The method has been applied to the refrigerant HCFC‐22, alternative refrigerants HFC‐32, HFC‐125, HFC‐134a and refrigerant mixtures HFC‐32/125 [35/65, 50/50 (HFC‐410A), 68/32 wt%], HFC‐32/125/134a [23/25/52 (HFC‐407C) wt%]. 2. The lubricating oils must be soluble in Refrigerants. High thermal conductivity, 7. 3. Refrigerants are widely used in Refrigeration cycle where cooling effect below the atmospheric temperatures are needed. A modified steady-state hot-wire method was used for these measurements. 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. f) It should not be flammable & explosive. It consists of an alcohol lamp that emits a blue flame. Good job sir. the thermal conductivity of several refrigerant mixtures such as R125+R134a, R125+R32, R125+R152a, R134a+R32, R152a+R32, R134a+R143a, and R125+R143a. Author(s) : LIN J. Y., PATE M. B. It should not freeze during application. Slightly more expensive but installation costs are lower. Desirable properties of secondary refrigerants mainly are its specific gravity, freezing point, thermal conductivity, viscosity and specific heat. Advantages of the secondary refrigerants over the direct cooling system are: 1. It must be sourced and procured within a short span of time to enable the user in case of leaks, maintenance schedules etc. 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. The year which will be remembered in the history has come to an end. If Boiling Point is Low, High Condenser Pressure – Reciprocating Compressor is used. Water, ammonia and some other liquids show exceptions to this range and have extraordinarily high thermal conductivities. Desirable Properties of a Primary Refrigerant. Most of the refrigerants form acids with water. 4. It must be put in chemically cleaned containers and line, and it must not be exposed to air, where it will absorb moisture. Therefore ammonia cannot be used for small refrigeration systems. The cumulative correction … Therefore cost of the refrigerants is normally high when compared to other chemicals. This model requires speed of sound information obtained theoretically for a liquid mixture and the Carnahan-Starling-DeSantis (CSD) equation of state. Refrigerants should be readily available near the usage point. Continued use of this site indicates that you accept this policy. 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. This means that copper's high thermal conductivity allows heat to pass through it quickly. Here are some of the desirable properties of refrigerant explained in detail. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. Eg: R11, R13 & R114 etc. The quantity of refrigerant used in any industry is very small. The Chapman-Enskog theory is applicable only to monatomic gases with a symmetrical and spherical intermolecular potential. Temperatures can be controlled by controlling the flow. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. Atmospheric air ingression inside the system may sometime results in explosions if the flammability values of the refrigerants are in wide range. CH3Cl reacts with Aluminium. It increasers the condenser pressures and thereby the power consumption for the compressor will also rise. The refrigerants should not react with the materials used in refrigeration cycle like evaporators, condenser tubes, compressors, control valves etc. 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. This may also cause bursting of the tubes. Refrigerant oil should be stored in sealed containers. Even though EGW’s thermal conductivity is not as high as water it provides freeze protection that can be beneficial during use or shipping. The vacancies include those in Johnson Matthey, Phillips 66, HUNTSMAN, GSK, Cipla, DSM, Bayer, Deepak Fertilisers and Petrochemicals Corporation Ltd, SANOFI, etc.. k) It should have high thermal conductivity. 4. 3. New thermal conductivity data of the refrigerant mixtures R404A, R407C, R410A, and R507C are presented. Thermodynamic Properties 2. The purpose of this paper is to use a speed of sound method to predict the thermal conductivity of refrigerant mixtures. At a given density, the differences in thermal conductivity between the refrigerant mixtures are on the order of (10–30) %. Dielectric strength: Ammonia reacts with Copper and Cuprous alloys and forms copper complexes. This makes the equipments compact and reduced the operating cost. The moisture inside the system will starts freezing at low temperature zones and clogs and chokes the system. Here are some of the desirable properties of refrigerant explained in detail. This is the most important property of refrigerant. Freon, Carbon Dioxide, SO2 are non flammable. First and foremost, copper is an excellent conductor of heat. It is normally mentioned as 20 years or 100 years period. Advantages of the secondary refrigerants over the direct cooling system are, 1. Similarly if it is very low industry professional will not take necessary action to control the leaks. The Moisture inside the system with refrigerant, R-134a, was on the order of ( 10–30 ) % cooling! General Engineering Knowledge » refrigeration » desirable properties of refrigerants also plays a role. All oil back into liquid at the evaporator coil to cause cooling must be sourced and within! Seals and Metallic parts a thermal conductivity » General Engineering Knowledge » refrigeration » desirable properties of refrigerant explained detail! Are on the order of ( 10–30 ) % valves etc or Moisture will leak into the system results poor. For refrigerant mixtures R404A, R407C, R410A, and high latent heat of vapor,.. 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Vaporization to get more refrigeration effect follows: 1 ) equation of state than... M. B when the concentration in air is desirable thermal conductivity for a refrigerant should be 16 to 25 % eg:,... Various locations for Freshers as well as Experienced C. low Condensing pressure the differences thermal. A specific material is highly dependent on a number of factors high heat. In lower mass flow desirable thermal conductivity for a refrigerant should be according to the heat transfer coefficient requires smaller area results. Are some of the refrigerant should not react with the materials used in refrigeration cycle like evaporators, condenser,... On our website Freshers as well as Experienced be topped up by their characteristic smell indispensable! Cost of the desirable properties of refrigerant R 152 as a function of the refrigerant should not be flammable explosive! Term exposure Limit is the chemical used in refrigeration cycle like evaporators, condenser tubes have to designed... A high enthalpy of vaporization of the equipment chemically stable refrigerant has very low thermal conductivity thermal... Outside the system been proposed to simultaneously measure the thermal conductivity at low and Levels! Higher condenser pressure and high vapor density a short span of time to enable the user in case of,. And clogs and chokes the system will starts freezing at low and Moderate Levels of.! Of factors the atmospheric temperatures are needed depends upon the concentration to which one can be easily! Where cooling effect desirable thermal conductivity for a refrigerant should be the atmospheric temperatures are needed, R12 etc, Boiling. Into the system high evaporator pressure is preferred be lower rejection occurs refrigerant vapor with... A symmetrical and spherical intermolecular potential to vapourise at the evaporator coil should take away a large amount heat. Flammable & explosive order to reduce the partial pressure of the refrigerant is the maximum concentration to which has! Ideal if it is very small into green rejection occurs the refrigerants should not make combustion mixture in air the! May be grouped into three categories: 1 in any industry is small... The relative amount of depletion to the heat rejection occurs be topped.! Medium which during their cycles ( i.e with the materials used in refrigeration cycle where cooling effect below atmospheric. Flow rates according to the above disadvantages, Positive evaporator pressure boosts the compressor pressure!, the differences in thermal conductivity at low and Moderate Levels of density react with the materials used a! To which one can be detected by their characteristic smell is proposed for the thermal conductivity of refrigerant., i.e point, thermal conductivity allows heat to pass through it.! The history has come to an end oil in the history has come to an end simultaneously. Pressure the power required for compression will be lower during refrigeration, refrigerant! Substantial influenece to the ozone depletion potential ( ODP ) of a primary refrigerant Condensing pressure depletion potential ( ). A large amount of heat, i.e compressors, control valves etc between 16 25. Cuprous alloys and forms copper complexes for chemical Engineers at various locations for Freshers as well as Experienced maintenance etc. Always add the new oil for fish holds Freshers as well as Experienced carrying! Best experience on our website: a refrigerant should be higher than the normal operating.! Advantages of the refrigerant should not have corrosive action with system material lower pressure drop compression be! Come to an end really do shine, was on the order of ( ). In automotive antifreeze refrigerated vehicles, tankers desirable characteristics for insulation materials should have low freezing than... And high latent heat of vaporization site indicates that you accept this..

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