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. 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. Excellent way of fully understanding the engeeniring system. Thus, less insulating material will be required. It makes white fumes of ammonium sulfide. Chemical Properties 3. Question is ⇒ Pick up the wrong statement. Continued use of this site indicates that you accept this policy. This means that copper's high thermal conductivity allows heat to pass through it quickly. Ammonia and SO2 can be detected by their characteristic smell. Ans: b. has second highest thermal conductivity with no significant health risks but is second most expensive option. Here are some of the desirable properties of refrigerant explained in detail. Thermodynamic Properties 2. Water, ammonia and some other liquids show exceptions to this range and have extraordinarily high thermal conductivities. Following are the desirable properties of a primary refrigerant. 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 Brazilian equation to calculate the thermal conductivity of refrigerant R 152 as a function of the dynamic viscosity of the liquid. Eg: R11, R13 & R114 etc. Slightly more expensive but installation costs are lower. i) It should have positive condensing pressure. 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. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. Pressure to which compressor has to compress the drawn gases, to convert them back into liquid at the condenser, should be low. (PIR) Polyisocyanurate -185°C to +140°C Petrochemical equipment, buildings, refrigerated vehicles, tankers The thermal conductivity of a specific material is highly dependent on a number of factors. 1 … Best insulation materials should have the lowest thermal conductivity, in order to reduce the total coefficient of heat transmission. Freon leak can be detected by a halide torch. The cumulative correction … Electronic detectors, Ultrosonic leak detectors may also be used to detect the leaks. small and compact. High latent heat of vaporization, 4. High thermal conductivity, 7. Presence of air will reduce the partial pressure of refrigerant and the condensation temperature will rise. Refrigerants should be readily available near the usage point. The toxicity depends upon the concentration and exposure limits. 2. For … The desirable properties of a refrigerant are as follows: 1. 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. If the refrigerant velocity is not sufficient, then it cannot carry all oil back into the compressor. Change is the only option to survive and grow! This test is based on Beilstein Test for Chlorine. Desirable properties of an Ideal Refrigerant : A refrigerant is said to be ideal if it has all of the following properties: 1. e) It should not have corrosive action with system material. Water for example cannot be used below 0 Deg C. The lower the condenser pressure the power required for compression will be lower. R-22 for example, has an ODP of 0.055. Required fields are marked *. It is normally mentioned as 20 years or 100 years period. High latent heat of vaporization to get more refrigeration effect. This may also cause bursting of the tubes. Low specific volume of vapor, 6. We use cookies to ensure that we give you the best experience on our website. At a given density, the differences in thermal conductivity between the refrigerant mixtures are on the order of (10–30) %. The vacancies include those in Johnson Matthey, Phillips 66, HUNTSMAN, GSK, Cipla, DSM, Bayer, Deepak Fertilisers and Petrochemicals Corporation Ltd, SANOFI, etc.. Global Warming Potential (GWP) is a relative measure of how much heat a refrigerant  traps in the atmosphere. Therefore ammonia cannot be used for small refrigeration systems. This follows the same trend as observed for the thermal conductivities of the … Due to the above disadvantages, Positive evaporator pressure is preferred. 2. When recharging the system with refrigerant, always add the new oil. 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. Advantages of the secondary refrigerants over the direct cooling system are: 1. Atmospheric air ingression inside the system may sometime results in explosions if the flammability values of the refrigerants are in wide range. Moderately high evaporator pressure boosts the compressor suction pressure thus reduces the power costs. We continue to change in order to grow and really do shine. Higher heat transfer coefficient requires smaller area and lower pressure drop. In a negative pressure evaporator Atmospheric air or Moisture will Leak into the system. Desirable properties of secondary refrigerants mainly are its specific gravity, freezing point, thermal conductivity, viscosity and specific heat. If Boiling Point is Low, High Condenser Pressure – Reciprocating Compressor is used. Similarly if it is very low industry professional will not take necessary action to control the leaks. ODP of R11 is fixed as the maximum value of 1.0. the thermal conductivity of several refrigerant mixtures such as R125+R134a, R125+R32, R125+R152a, R134a+R32, R152a+R32, R134a+R143a, and R125+R143a. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. 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. Al 2O3 reacts with water & heat is generated . Department of Mechanical Engineering, Saga University . If Freon is present blue flame turns into green. 3. The refrigerant should not make combustion mixture in Air. Following are the desirable properties of a primary refrigerant. Strong smelling chemicals like acrolein may be added to refrigerant for easy leak detection. 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. Therefore overflow drain is to be provided to remove oil. High critical pressure and temperature, 3. Water for example cannot be used below 0 Deg C. Low Condensing Pressure. This will cause corrosion and deteriorates valves, Seals and Metallic parts. 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. Insulation of windings in hermatic compressors will also get damaged. Critical pressure of the refrigerant should be higher than the condenser pressures. Properties of refrigerants generally determine how suitable and desirable a particular refrigerant is. k) It should have high thermal conductivity. Therefore dielectric strength should be high to avoid short circuits. j) It should have satisfactory heat transfer coefficient. Temperatures can be controlled by controlling the flow. The lubricating oils must be soluble in Refrigerants. It increasers the condenser pressures and thereby the power consumption for the compressor will also rise. Refrigerants with low boiling points will have high condenser pressure and high vapor density. Explore 150+ Jobs for Chemical Engineers at various locations for Freshers as well as Experienced. 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. 3. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. 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. Chemical Engineers spend their life in making the world a […]. Desirable properties of secondary refrigerants mainly are its specific gravity, freezing point, thermal conductivity, viscosity and specific heat. Special pressure pumps can be used to pump oil in the low parts of the system. 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. This is the most important property of refrigerant. In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. f) It should not be flammable & explosive. 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. Most of the refrigerants form acids or bases in the presence of water.

desirable thermal conductivity for a refrigerant should be 2021