That internal temperature is fixed so long as the pressure remains the same across the coil and the refrigerant is a single component or azeotropic (no glide). Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. The temperature for a given pressure at which the gaseous refrigerant begins to condense into a liquid. Latent heat of vaporization is a physical property of a substance. Flip the page to see why this is so important. Therefore the refrigerant vapors should be easily condensible. It results in high ... Refrigerant Latent heat of vapour at 15 º C (Kcal/kg) R-12 (CCl 2 F 2) 37.97 R-717 (NH 4) 314.42 R.744 (CO 2) 65.44 R-764 (SO 2) 94.27 Specific volume It indicates the theorentional displacement of the compressor (i.e volume of suction vapour to compressor). A refrigerant should have a high latent heat of vapour at the evaporator temperature. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). A. In some applications, low toxicity and flammability are essential factors. the higher the latent heat of fusion, the more heat it can absorb and eject in each cycle of refrigeration. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. •Thermal conductivity :- It should have high thermal conductivity. It should be non-corrosive, non-toxic and non-poisonous. The ideal refrigerant should be: A) have a low latent heat capacity B) have a high boiling point C) have high condensing pressure D) be environmentally … This is due to the fact that ammonia has a higher latent heat of vaporization than other refrigerants such as R22 and R134a. Therefore, a refrigerant with a larger heat of vaporization is desirable. Upload or insert images from URL. (d) Low COP and low freezing point. Inside the evaporator, there is latent heat of vaporization as heat conducts into the coil and boils the refrigerant. With. The desirable properties of a refrigerant are as follows: 1. Why ice floats. R290 refrigerants, namely, propane, is a kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. Latent Heat Cooling via perspiration is affected by latent and sensible heat. Refrigerants are chosen because of their high latent heat capabilities, the amount of pressure need to hold the refrigerant in liquid form prior to … Therefore, a refrigerant with a larger heat of vaporization is desirable. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants . REFRIGERANTS By :- ENGINEER IN ... •Latent heat of vaporization :- It should have high latent heat of vaporization. © B-Cubed, 2003, 2005, 2006, 2014, 2018. Which of the following best describes the principle of latent heat of vaporization? Why high latent heat of vaporization is desirable in refrigerant ? 3. It should be oil miscible. Thanks in advance :) •Co-efficient of performance :- COP has direct effect on running cost of refrigeration cycle so higher the COP lower will be the running cost. The latent heat of freezing has the same numerical value as the latent heat of melting, but heat is released as a result of the change in phase from liquid to solid. High suction gas density at the compressor suction means low sized compressor … When we raise the pressure, we also raise the temperature. High latent heat of vaporization. The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke. × It should make leaks easy to detect and locate. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . When the energy of a system changes because of a temperature difference between the system and its surroundings, we say that energy has been transferred as heat (q). 2. 7. High heat of vaporization: For every kilogram of refrigerant that gets vaporized at the evaporator, it should take away a large amount of heat from the refrigerator.This is important because the higher the value of heat taken by the refrigerant, the greater the cooling effect accomplished. When the air moving over the evaporator has more moisture in it and therefore a higher RH and dewpoint the surface temperature of the coil is increased so long as the coil temperature is below the air dewpoint. 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. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. 6. The difference will give you the latent heat for the mixture. 9. Latent Heat vs Sensible Heat .   Your link has been automatically embedded. Enthalpy of vaporization: To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. The heat energy is used in breaking the hydrogen bonds which hold the molecules of … 2. 10. Latent heat of vaporization. A High Suction gas density and a Low Compression ratio. It should be non-flammable, non-explosive and chemically stable. It should be non-flammable, non-explosive and chemically stable. More heat can be absorbed and ejected in each cycle of refrigeration. High latent heat of vaporization is desirable in a refrigerant. Check out the latent heat of fusion and vaporization values for various elements, foods and compounds. 3. You can like the best answer. 8. Latent heat of solidification. High Latent Heat of Vaporization. Why high latent heat of vaporization is desirable in refrigerant ? La- tent heat is the amount of heat required to change the refrigerant from a liquid to a gas. 4. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. 7. High latent heat of vaporization to get more refrigeration effect. However, it's much harder to cool down in a sunny location than in a shady one because sensible heat from absorbed sunlight competes with the effect from evaporation. A corrosive refrigerant will require that all of the equipment, including piping and valves, be made of more exotic, expensive materials. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus Below are some of the reasons why the use of ammonia as a refrigerant has gained popularity. Fire Load Calculation: Latent Heat Of Vaporization - posted in Relief Devices Forum: Hi all, I have a question regarding latent heat of vaporization. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. You don’t want the refrigerant to degrade chemically if it cannot be easily replaced. A good refrigerant should have: (a) High latent heat of vaporization and low freezing point [IES-1992] (b) High operating pressure and low freezing point (c) High specific volume and high latent heat of vaporization. It is therefore a measure of the cooling potential of the refrigerant circulated through a refrigeration system. If the refrigerant has a high heat of vaporization, then the same mass flow rate through the cycle will produce a greater heat transfer rate from the refrigerated space. It should have low specific heat of liquid (to reduce vaporization during throttling). •Thermal conductivity :- It should have high thermal conductivity. The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas (the pΔV work). 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. No latent heat is the amount of energy in the form of heat that the liquid gives off or absorbs to change state. High Heat Transfer Coefficient Steel tubes are used for ammonia systems and copper tubes are used for Freon systems. When a material in liquid state is given energy, it changes its phase from liquid to vapor; the energy absorbed in this process is called heat of vaporization. High latent heat of vaporization. The latent heat of vaporization is a measure of the heat per pound that the refrigerant can absorb from an area to be cooled. I am wondering what exactly is it that makes R134a … Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. I have been comparing values of latent heat of vaporization - R12 is about 166 kj/kg and r134a is 215kg/kg, which means for R134a that for any given liquid amount in the evaporator, it can absorb more energyfrom the incoming air from the blower until it evaporates compared to R12, which would mean it can cool more air for a longer time. More heat can be absorbed and ejected in each cycle of refrigeration. Because high specific heat decreases the refrigerating effect per kg of refrigerant and high latent heat at low temperature increases the … The heat of vaporization of water is about 2,260 kJ/kg, which is equal to 40.8 kJ/mol. Heat is dissipated away from the body due to the high latent heat of vaporization of water. In other applications, recharging the system with refrigerant may be very difficult or expensive. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. The enthalpy of vaporization (symbol ∆H vap), also known as the (latent) heat of vaporization or heat of evaporation, is the amount of energy that must be added to a liquid substance to transform a quantity of that substance into a gas.The enthalpy of vaporization is a function of the pressure at which that transformation takes place. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. Display as a link instead, × When choosing a refrigerant, it is suggested to have a high heat of evaporation, as it keeps the mass flow rate low...why is this? In addition, latent heat storage has the capacity to store heat of fusion at a constant or near-constant temperature that corresponds to the phase transition temperature of the phase change material (PCM). Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. You can answer this question.   You cannot paste images directly. High critical temperature to have large isothermal energy transfer. Otherwise mass flow rate will be high. Water has latent heat of vaporization of 540 calories per gram, the amount of heat energy that is necessary to convert 1 g of liquid water at 100°C to steam at 100°C, or 40.71 kJ/mol or about 2,260 kJ/kg water. •Latent heat of vaporization :- It should have high latent heat of vaporization. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. Confused and have questions? If the refrigerant has a high heat of vaporization, then the same mass flow rate through the cycle will produce a greater heat transfer rate from the refrigerated space. the vaporized refrigerant can be made to give up the latent heat of vaporization that it absorbed in the evaporator is by cooling and condensing it. Dielectric strength: Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. Otherwise mass flow rate will be high. ; Example - Boiling Water at 100 o C, 0 bar (100 kPa) Atmospheric Pressure. As pressure on molecules increases they require more heat to overcome the pressure force acting or to escape and thus latent heat required is more. Hence why the heat absorption and heat rejection heat exchangers are called the evaporator and the condenser respectively. 4. High latent heat of vaporization to get more refrigeration effect. It results in a high refrigerating effect and a low rate of refrigerant in circulation. A High Suction gas density and a Low Compression ratio. The specific heat of refrigerant is related to the structure of the molecule. High latent heat of vaporization is an asset for refrigerants, because most of the heat absorption and heat rejection in the vapor-compression refrigeration cycle occurs as a phase change. The specific heat of … Join us (login) to get full access : Please sign up to connect and participate. 4. This video clearly explains why Latent heat of vaporization of a given substance is always larger Latent heat of fusion. Clear editor. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. Latent heat is the amount of heat added to or removed from a substance to produce a change in phase. The natural … There isn’t a single best refrigerant for all applications. Therefore the refrigerant vapors should be easily condensible. 8. 1) 1 bar abs = 0 bar gauge = 100 kPa abs = atmospheric pressure Vacuum steam is the general term used for saturated steam at temperatures below 100°C. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. In the case of the latent heat of fusion it is the heat required to change a substance from a solid (ice) to a liquid (water) or vice versa while the latent heat of vaporization from a liquid (water) to a gas (steam) or vice versa. June 14, 2014. In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. Latent heat energy storage is a near-isothermal process that can provide significantly high storage density with smaller temperature swings in comparison with sensible storage systems. Why manholes in vessel are elliptical in shape. This temperature change during a phase change is due to the energy released from the potential energy stored in the bonds between the particles, and not due to the energy release from the kinetic energy of the particle. Solution (By Examveda Team) -The refrigerant should have low boiling point and low freezing point. In that case the chemical stability of the refrigerant may be an important property. As previously stated, the molecules of a substance in the liquid phase have more internal energy than solid ones, so in solidification energy is released instead of absorbing it, as an infusion. These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas. EQ-COMP software is showcased on www.eq-comp.com website and the results of the software can be … the vaporized refrigerant can be made to give up the latent heat of vaporization that it absorbed in the evaporator is by cooling and condensing it. Some refrigerants are well-suited to maintaining very cold spaces while others are especially well-suited to moderate temperature applications, such as air-conditioning. The heat of vaporization of … Similarly, the latent heat of vaporization or evaporation ( L v ) is the heat that has to be given to a unit mass of material to convert it from the liquid to the vapor phase without a change in temperature. Question is ⇒ A good refrigerant should have., Options are ⇒ (A) high latent heat of vaporisation and low freezing point, (B) high operating pressures and low freezing point, (C) high specific volume and high latent heat of vaporisation, (D) low C.O.P. 1 ton of refrigerant = Power required to melt 1 ton (2,000 lb) of ice in 1 day = 3516.8 Watts. We've got answers. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. 3. A high latent heat of vaporization is desirable in refrigerant, because it results in high refrigerating effect per unit weight of the refrigerant and low rate of circulation of the refrigerant. The gas refrigerant within the condenser rejects its latent heat of vaporization… Be non-flammable, non-explosive and chemically stable point and low freezing point explains why latent heat of in... 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