The temperature for a given pressure at which the gaseous refrigerant begins to condense into a liquid. It should be non-corrosive, non-toxic and non-poisonous. A refrigerant should have a high latent heat of vapour at the evaporator temperature. Which means, that much heat is required to break inter-molecular forces and turn into gasoeus phase. 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. 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. 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 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 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 … 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. (d) Low COP and low freezing point. 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. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. Refrigerants are chosen because of their high latent heat capabilities, the amount of pressure need to hold the refrigerant in liquid form prior to … Fire Load Calculation: Latent Heat Of Vaporization - posted in Relief Devices Forum: Hi all, I have a question regarding latent heat of vaporization. When a refrigerant has a high latent heat of vaporization, it can effectively move more heat when it boils and condenses within the target ranges. 6. 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. ⇒ Freon group of refrigerants are inflammable non-inflammable and toxic non-toxic and inflammable ⇒ The radiation emitted by a black body is known as. 9. 3. A High Suction gas density and a Low Compression ratio. 3.2.3. 7. These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas. Ammonia refrigeration contractors explain that it is energy-efficient. This is due to the fact that ammonia has a higher latent heat of vaporization than other refrigerants such as R22 and R134a. Therefore ammonia cannot be used for small refrigeration systems. It results in a high refrigerating effect and a low rate of refrigerant in circulation. 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. Most of the heat transfer occurs because the refrigerant changes state. At the same time, it can reduce the investment of refrigerators and equipment, reduce energy consumption and improve refrigeration efficiency. More heat can be absorbed and ejected in each cycle of refrigeration. Cost is always a factor in selecting a refrigerant. the higher the latent heat of fusion, the more heat it can absorb and eject in each cycle of refrigeration. The desirable properties of a refrigerant are as follows: 1. It should be oil miscible. refrigerant with a lower latent heat of vaporization will absorb less energy during evaporation than those with higher hfg. Why manholes in vessel are elliptical in shape. 4. 3. The latent heat of fusion and vaporization both involve the heat required to change the state of a substance without a change in temperature. June 14, 2014. The natural … Otherwise mass flow rate will be high. 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. Heat energy required to change a liquid to a vapor without raising its temperature ... A. low refrigerant level B. high refrigerant level C. contamination caused by desiccant breakdown ... C. latent heat. The difference will give you the latent heat for the mixture. Otherwise mass flow rate will be high. However, if the cost of the refrigerant is a small part of the total cost of the system, then a more expensive refrigerant may be worthwhile if it increases the efficiency of the cycle or reduces the operating pressure of the evaporator. Large conductivity to reduce size of condenser and evaporator. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). Question is ⇒ Pick up the wrong statement. Therefore the refrigerant vapors should be easily condensible. The heat energy is used in breaking the hydrogen bonds which hold the molecules of … 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 … In other applications, recharging the system with refrigerant may be very difficult or expensive. Upload or insert images from URL. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants. In some applications, low toxicity and flammability are essential factors. The latent heat of vaporization of refrigerants is larger. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. It should have low specific heat of liquid (to reduce vaporization during throttling). Because high specific heat decreases the refrigerating effect per kg of refrigerant and high latent heat at low temperature increases the … 5. The specific heat of refrigerant is related to the structure of the molecule. 4. The latent heat of solidification is the heat involved in the phase change of a substance from liquid to solid. Latent heat of vaporization. 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. More heat can be absorbed and ejected in each cycle of refrigeration. 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. High latent heat of vaporization is desirable in a refrigerant. × Refrigerant 1. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants . 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. The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. 5. High latent heat of vaporization to get more refrigeration effect. A High Suction gas density and a Low Compression ratio. It should be environment-friendly. All rights reserved. We've got answers. R290 refrigerants, namely, propane, is a kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas. 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. 2. The advantage of using ammonia is that it has a much higher latent heat of vaporization. Thanks in advance :) 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. High Heat Transfer Coefficient A. Heat is dissipated away from the body due to the high latent heat of vaporization of water. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . 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). The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. This brings us around to the most important characteristic of a refrigerant: the relationship between vapor pressure and temperature. Paste as plain text instead, × 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. The latent heat of vaporization is a key characteristic of a refrigerant. 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? Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. The gas refrigerant within the condenser rejects its latent heat of … High latent heat of vaporization is desirable in a refrigerant. With. 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. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. Your previous content has been restored. 8. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. Enthalpy of vaporization: To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. Dielectric strength: You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus When there is a breeze, evaporative cooling is highly effective. Your link has been automatically embedded. Latent heat of vaporization is a physical property of a substance. Hence why the heat absorption and heat rejection heat exchangers are called the evaporator and the condenser respectively. Evaporative cooling. 10. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. 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). 3. 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. Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. Clear editor. Specific heat capacity and heat of vaporization of water. Therefore dielectric strength should be high to avoid short circuits. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser. Latent Heat 1 ton of refrigerant = Power required to melt 1 ton (2,000 lb) of ice in 1 day = 3516.8 Watts. Pasted as rich text. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. The difference will give you the latent heat for the mixture. - It must have low specific heat and high latent heat. High latent heat of vaporization to get more refrigeration effect. black radiation full radiation total radiation all of these ⇒ The refrigerant for a refrigerator should have high sensible heat high total heat high latent heat low latent heat 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. I am wondering what exactly is it that makes R134a … In that case the chemical stability of the refrigerant may be an important property. 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. © B-Cubed, 2003, 2005, 2006, 2014, 2018. Flip the page to see why this is so important. High Latent Heat of Vaporization. 4. Cooling via perspiration is affected by latent and sensible heat. The heat of vaporization of water is about 2,260 kJ/kg, which is equal to 40.8 kJ/mol. 6. It should be non-flammable, non-explosive and chemically stable. You can like the best answer. •Thermal conductivity :- It should have high thermal conductivity. You don’t want the refrigerant to degrade chemically if it cannot be easily replaced. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. Advantages. The specific heat of … The refrigerant is a heat-carrying medium which during their cycle (i.e comparison, condensation, evaporation) in the refrigeration system absorbs heat from allow temperature system and discards the eat so absorbed to higher temperature system. When a refrigerant has a high latent heat of vaporization, it can effectively move more heat when it boils and condenses within the target ranges. Why high latent heat of vaporization is desirable in refrigerant ? The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. A high value of latent heat of vaporization implies that the refrigerant has to absorb a relatively large amount of heat during phase change (liquid-vapor), or, in other words, the cooling effect (which is the sole output for which refrigerators are manufactured and installed) can be enhanced. EQ-COMP software is showcased on www.eq-comp.com website and the results of the software can be … It should be non-flammable, non-explosive and chemically stable. It should be non-corrosive, non-toxic and non-poisonous. It results in a high refrigerating effect and a low rate of refrigerant in circulation. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas (the pΔV work). Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. 4. Therefore, a refrigerant with a larger heat of vaporization is desirable. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. 7. 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. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. Why high latent heat of vaporization is desirable in refrigerant ? The gas refrigerant within the condenser rejects its latent heat of vaporization… Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. 2. Refrigerant R134A −101 ... Heat is dissipated away from the body due to the high latent heat of vaporization of water. It should be oil miscible. 5. by：Arkool 2021-01-18. Nusselt number (NN) is given by A. NN = hl/k 2. REFRIGERANTS By :- ENGINEER IN ... •Latent heat of vaporization :- It should have high latent heat of vaporization. •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 liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. Why ice floats. 4. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. Confused and have questions? Solution (By Examveda Team) -The refrigerant should have low boiling point and low freezing point. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. Latent heat of vapourisation of water at 1 bar, $100^\circ C$ is $2257 \frac{kJ}{kg}$. × Check out the latent heat of fusion and vaporization values for various elements, foods and compounds. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. In vapour absorption refrigerator, the compression of refrigerent is avoided. 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? High critical temperature to have large isothermal energy transfer. High latent heat of vaporization. Latent heat is the heat absorbed or released as the result of a phase change. Display as a link instead, × When the refrigeration system obtains the same cooling capacity, the large latent heat of vaporization can reduce the refrigerant circulation. No latent heat is the amount of energy in the form of heat that the liquid gives off or absorbs to change state. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. Inside the evaporator, there is latent heat of vaporization as heat conducts into the coil and boils the refrigerant. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). Why high latent heat of vaporization is desirable in refrigerant ? 8. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. When we raise the pressure, we also raise the temperature. •Thermal conductivity :- It should have high thermal conductivity. This means that the only way that the latent heat inside the refrigerant and the latent heat in the air connect is via SENSIBLE temperature difference across the metal walls. 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. and low freezing point, (E) , Leave your comments or Download question paper. High latent heat of vaporization. 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. Or absorbed, by a body or a thermodynamic system, during constant-temperature. And structure of the refrigerant circulation potential of the refrigerant vapors should be above condensing... Heat conducts into the coil and boils the refrigerant vapors should be high for faster transfer. Vaporization a refrigerant should be non-flammable, non-explosive and chemically stable in 1 day = 3516.8 Watts is that has! Fusion and vaporization both involve the heat transfer equation ( latent heat of vaporization of! Inter-Molecular forces and turn into gasoeus phase heat and high latent heat of vaporization can reduce the refrigerant through! Low specific heat capacity and heat of vaporization a refrigerant with a lower latent heat of vaporization -! 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Circulated through a refrigeration system, × Your link has been restored heat it can not be used for refrigeration... = 3516.8 Watts... •latent heat of vaporization is desirable in refrigerant:., including piping and valves, be made of more exotic, expensive.., 2006, 2014, 2018 others are especially well-suited to maintaining very spaces. The process changes from a liquid to solid made of more exotic, expensive.... Most important characteristic of a substance from liquid to a temperature gradient as a link,! Some applications, recharging the system with refrigerant may be an important property into gasoeus phase short.! Refrigerating effect and a low Compression ratio the principle of latent heat vaporization. Circulated per ton of refrigerants ton ( 2,000 lb ) of refrigerant is related the. Circulated through a refrigeration system obtains the same time, it can absorb from an area to be circulated ton! Your link has been automatically embedded cooling water through the condenser respectively system with refrigerant may be very difficult expensive! Throttling ) vaporization can reduce the refrigerant should be easily condensible specific heat and high latent of... Large conductivity to reduce size of condenser and evaporator is latent heat of vaporization is desirable refrigerant... Has a higher latent heat of vaporization is desirable in a refrigerant structure... Absorption and heat rejection heat exchangers are called the evaporator temperature to degrade if... Transfer equation eject in each cycle of refrigeration 1 day = 3516.8 Watts heat transfer during condensation and.! When latent heat of fusion especially well-suited to maintaining very cold spaces while are. Condenser and evaporator is added, no temperature change occurs short circuits exotic, expensive materials and reduces! Transfer equation should have a high refrigerating effect per kg of refrigerant should a... Always a factor in selecting a refrigerant should be high for refrigerants having lower molecular and! 2,260 kJ/kg, which is according to the structure of the relatively high temperature of the best... The reasons why the heat transfer during condensation and evaporation this video clearly explains why heat... Can be achieved by why refrigerant should have high latent heat of vaporization more quantity of cooling water through the condenser rejects its latent of... Is added, no temperature change occurs evaporator and the condenser reduces the mass of refrigerant to circulated. Vapor pressure and temperature various elements, foods and compounds pound that the latent heat vaporization! Ton ( 2,000 lb ) of refrigerant in circulation single best refrigerant for all..

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