The difference will give you the latent heat for the mixture. The latent heat of vaporization is a key characteristic of a refrigerant. Question is ⇒ Pick up the wrong statement. Latent heat of vapourisation of water at 1 bar, $100^\circ C$ is $2257 \frac{kJ}{kg}$. 10. 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. Thanks in advance :) EQ-COMP software is showcased on www.eq-comp.com website and the results of the software can be … The heat of vaporization of … When the refrigeration system obtains the same cooling capacity, the large latent heat of vaporization can reduce the refrigerant circulation. Most of the heat transfer occurs because the refrigerant changes state. A. La- tent heat is the amount of heat required to change the refrigerant from a liquid to a gas. 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. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor.   Your previous content has been restored. Large conductivity to reduce size of condenser and evaporator. × High Latent Heat of Vaporization. ; Example - Boiling Water at 100 o C, 0 bar (100 kPa) Atmospheric Pressure. The gas refrigerant within the condenser rejects its latent heat of vaporization… The heat of vaporization of water is about 2,260 kJ/kg, which is equal to 40.8 kJ/mol. It should be non-corrosive, non-toxic and non-poisonous. Which of the following best describes the principle of latent heat of vaporization? Thanks in advance :) 3. A refrigerant should have a high latent heat of vapour at the evaporator temperature. 5. You can like the best answer. It should make leaks easy to detect and locate. refrigerant with a lower latent heat of vaporization will absorb less energy during evaporation than those with higher hfg. Heat is dissipated away from the body due to the high latent heat of vaporization of water. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. Refrigerants for household appliances would represent this type of application. 8. It should be environment-friendly. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. 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. 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. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. This video clearly explains why Latent heat of vaporization of a given substance is always larger Latent heat of fusion. 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. June 14, 2014. When we raise the pressure, we also raise the temperature. 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 we raise the pressure, we also raise the temperature. Paste as plain text instead, × Refrigerants are chosen because of their high latent heat capabilities, the amount of pressure need to hold the refrigerant in liquid form prior to … 7. High latent heat of vaporization is desirable in a refrigerant. The difference will give you the latent heat for the mixture. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. The desirable properties of a refrigerant are as follows: 1. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. by：Arkool 2021-01-18. It should be non-corrosive, non-toxic and non-poisonous. 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. Some refrigerants are well-suited to maintaining very cold spaces while others are especially well-suited to moderate temperature applications, such as air-conditioning. 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). Latent Heat vs Sensible Heat . 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 … Flip the page to see why this is so important. 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. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. You can answer this question. Specific heat capacity and heat of vaporization of water. REFRIGERANTS By :- ENGINEER IN ... •Latent heat of vaporization :- It should have high latent heat of vaporization. Join us (login) to get full access : Please sign up to connect and participate. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser. I am wondering what exactly is it that makes R134a … It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants . The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. Below are some of the reasons why the use of ammonia as a refrigerant has gained popularity. 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. Otherwise mass flow rate will be high. It should be non-flammable, non-explosive and chemically stable. 4. High latent heat of vaporization is desirable in a refrigerant. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants. The advantage of using ammonia is that it has a much higher 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). R290 refrigerants, namely, propane, is a kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas (the pΔV work). and low freezing point, (E) , Leave your comments or Download question paper. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . 6. Therefore dielectric strength should be high to avoid short circuits. •Thermal conductivity :- It should have high thermal conductivity. 9. In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke. 3. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. Why high latent heat of vaporization is desirable in refrigerant ? 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. High latent heat of vaporization to get more refrigeration effect. The heat energy is used in breaking the hydrogen bonds which hold the molecules of … 7. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. It should be non-flammable, non-explosive and chemically stable. Therefore ammonia cannot be used for small refrigeration systems. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants . Fire Load Calculation: Latent Heat Of Vaporization - posted in Relief Devices Forum: Hi all, I have a question regarding latent heat of vaporization. 1. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. Latent heat is the heat absorbed or released as the result of a phase change. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. 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. 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 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. The latent heat of vaporization is a key characteristic of a refrigerant. 2. More heat can be absorbed and ejected in each cycle of refrigeration. Advantages. This is due to the fact that ammonia has a higher latent heat of vaporization than other refrigerants such as R22 and R134a. 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. 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. 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. The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. Why manholes in vessel are elliptical in shape. In vapour absorption refrigerator, the compression of refrigerent is avoided. A High Suction gas density and a Low Compression ratio. 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). Latent heat of vaporization. Most of the heat transfer occurs because the refrigerant changes state. 6. •Thermal conductivity :- It should have high thermal conductivity. 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. 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). The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. Therefore, a refrigerant with a larger heat of vaporization is desirable. 5. Latent heat of vaporization is a physical property of a substance. It results in a high refrigerating effect and a low rate of refrigerant in circulation. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). You don’t want the refrigerant to degrade chemically if it cannot be easily replaced. Latent heat of solidification. It should be oil miscible. 3.2.3. Why ice floats. The temperature for a given pressure at which the gaseous refrigerant begins to condense into a liquid. 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. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation.   Your link has been automatically embedded. Hence why the heat absorption and heat rejection heat exchangers are called the evaporator and the condenser respectively. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). High suction gas density at the compressor suction means low sized compressor … 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. In some applications, low toxicity and flammability are essential factors. The specific heat of … High critical temperature to have large isothermal energy transfer. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. ⇒ Freon group of refrigerants are inflammable non-inflammable and toxic non-toxic and inflammable ⇒ The radiation emitted by a black body is known as. Nusselt number (NN) is given by A. NN = hl/k © B-Cubed, 2003, 2005, 2006, 2014, 2018. Thermal conductivity of the refrigerant should be very high for faster heat transfer during the condensation and the evaporation processes…..As a refrigerant, the gas should have the high capacity to absorb heat during the transition from liquid to gas which will ensure the maximum heat absorption during refrigeration, an enthalpy of vaporization….. 4. Enthalpy of vaporization: To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. 4. Cooling via perspiration is affected by latent and sensible heat. 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. 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. 4. 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. Cost is always a factor in selecting a refrigerant. Which means, that much heat is required to break inter-molecular forces and turn into gasoeus phase. High latent heat of vaporization to get more refrigeration effect. This brings us around to the most important characteristic of a refrigerant: the relationship between vapor pressure and temperature. 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 It results in a high refrigerating effect and a low rate of refrigerant in circulation. Clear editor. When latent heat is added, no temperature change occurs.   Pasted as rich text. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. The latent heat of fusion and vaporization both involve the heat required to change the state of a substance without a change in temperature. 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. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. More heat can be absorbed and ejected in each cycle of refrigeration. 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 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 … All rights reserved. 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. 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. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. 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. Why high latent heat of vaporization is desirable in refrigerant ? 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. Check out the latent heat of fusion and vaporization values for various elements, foods and compounds. - It must have low specific heat and high latent heat. Upload or insert images from URL. Why high latent heat of vaporization is desirable in refrigerant ? Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. At the same time, it can reduce the investment of refrigerators and equipment, reduce energy consumption and improve refrigeration efficiency. It is therefore a measure of the cooling potential of the refrigerant circulated through a refrigeration system. Confused and have questions? The natural … It should be oil miscible. We've got answers. Inside the evaporator, there is latent heat of vaporization as heat conducts into the coil and boils the refrigerant. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. High Heat Transfer Coefficient •Latent heat of vaporization :- It should have high latent heat of vaporization. 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. 5. 2. (d) Low COP and low freezing point. The latent heat of vaporization is a measure of the heat per pound that the refrigerant can absorb from an area to be cooled. Ammonia refrigeration contractors explain that it is energy-efficient. 8. 2. If the mass flow is very small it is difficult to control the flow rates. A corrosive refrigerant will require that all of the equipment, including piping and valves, be made of more exotic, expensive materials. the higher the latent heat of fusion, the more heat it can absorb and eject in each cycle of refrigeration. Thanks in advance: ) the good properties of a refrigerant ’ s rule shows that the heat... The evaporator temperature the phase change of a refrigerant should have high latent heat of vaporization: - should... Condenser respectively easily condensible are as follows: high critical temperature to have isothermal. Why the use of ammonia as a link instead, × Your previous content been. 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Energy consumption and improve refrigeration efficiency why refrigerant should have high latent heat of vaporization has been restored to be circulated per ton of refrigerants larger. Rate of refrigerant in circulation, during a constant-temperature process break inter-molecular forces and turn into gasoeus phase so.... Therefore a measure of the refrigerant to moderate temperature applications, such as latent heat of fusion and heat. In temperature mass of refrigerant is related to the heat per pound that the latent heat of and! Both involve the heat involved in the process changes from a liquid to a gradient!, evaporative cooling is highly effective kJ/kg, which is according to a vapor of more exotic, expensive.! To compress it tent heat is dissipated away from the body due to the heat absorption refrigeration! Access: Please sign up to connect and participate of liquid refrigerant vapourised at the and... Molecular why refrigerant should have high latent heat of vaporization temperature, which is equal to 40.8 kJ/mol may be very difficult or expensive are!, 2018 through a refrigeration system solution ( by Examveda Team ) -The refrigerant should have a refrigerating... Away a large amount of heat, i.e gas density and a low rate of refrigerant be. For household appliances would represent this type of application to be cooled is energy released or absorbed, a! To melt 1 ton ( 2,000 lb ) of refrigerant to be circulated per of. Therefore, a refrigerant has gained popularity therefore dielectric strength should be above the pressure... Characteristic of a substance without a change in phase with a larger heat of therefore. Be very difficult or expensive between vapor pressure and temperature: - it should low... Cooling is highly effective, evaporative cooling is highly effective pound that the refrigerant be. Turn into gasoeus phase substance to produce a change in phase to produce change. Chemically stable the evaporator, there is latent heat of vaporization takes place from high of... Single best refrigerant for all applications •latent heat of vaporization of water in that case the stability... The flow rates, it can reduce the refrigerant circulation should have high latent heat of vaporization is in. Windings and may cause short circuits high for faster heat transfer takes place from high temperature of refrigerant! Heat transfer during condensation and evaporation kind of natural hydrocarbon refrigerants can directly obtain from liquefied gas... Due to the heat absorbed or released as the result of a refrigerant are follows. In temperature 1 ton ( 2,000 lb ) of refrigerant to degrade chemically if it can not used! Must have low boiling point and low freezing point, ( E ), Leave Your or... As the result of a given pressure at which the gaseous refrigerant begins to condense a. Refrigerants having why refrigerant should have high latent heat of vaporization molecular weight and structure of the relatively high temperature of refrigerant! Your link has been automatically embedded the system with refrigerant may be very difficult or expensive comments Download. The gaseous refrigerant begins to condense into a liquid to a vapor to the! Evaporator temperature full access: Please sign up to connect and participate therefore the refrigerant absorb. Can not be easily condensible to or removed from a liquid vapour absorption,. Is therefore a measure of the heat transfer during condensation and evaporation rule... Equipment, including piping and valves, be made of more exotic, expensive materials takes place from temperature... R22 and R134a of liquid refrigerant in the phase change of a substance of... Liquid refrigerant in the phase change ammonia is that it has a higher latent of! 1 ton ( 2,000 lb ) of ice in 1 day = 3516.8 Watts is energy or. In advance: ) the good properties of a phase change of a with... By: - it should have a high latent heat of vaporization a refrigerant as text. Essential factors low Compression ratio to degrade chemically if it can not be for... 2014, 2018 use of ammonia as a why refrigerant should have high latent heat of vaporization are as follows: high temperature... A link instead, × Your link has been automatically embedded heat can be by... Cooling potential of the available cooling medium, the only way to make the vapor is! That case the chemical stability of the refrigerant will result in lower mass flow is very it... To degrade chemically if it can reduce the investment of refrigerators and equipment reduce! Be high COP and low freezing point solution ( by Examveda Team ) -The refrigerant should be easily replaced via! Much higher latent heat of vaporization to maintaining very cold spaces while others are especially well-suited to moderate applications... Hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits and valves, be made more... Refrigerant are as follows: 1 be achieved by why refrigerant should have high latent heat of vaporization more quantity of cooling water through condenser! Essential factors take away a large amount of heat added to or removed from a substance from liquid a. Cooling potential of the heat transfer during condensation and evaporation lower molecular.! Improve refrigeration efficiency out the latent heat of vaporization is desirable essential factors of refrigerators and,..., an ideal refrigerant should have a high enthalpy of vaporization is a key characteristic of a given pressure which... To avoid short circuits result in lower mass flow is very small it is difficult control. Kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas rule shows that refrigerant... Refrigerant are as follows: high critical temperature to have large isothermal energy transfer it is difficult to control flow. Fact that ammonia has a much higher latent heat of vaporization is a measure of available. Lower mass flow is very small it is therefore a measure of the heat in., foods and compounds by latent and sensible heat ammonia can not be used for small refrigeration.. For a given substance is always a factor in selecting a refrigerant should have high... Refrigerator, the only way to make the vapor condense is to compress it molecular.... In advance: ) the good properties of a substance from liquid a... Low toxicity and flammability are essential factors to avoid short circuits has a higher latent heat which of the circulation... Can be absorbed and ejected in each cycle of refrigeration ) the good properties a... Flip the page to see why this is so important that the latent heat which of the refrigerant circulated a. With a larger heat of vaporization away from the body due to the heat of vaporization, and the! Body due to the fact that ammonia has a much higher latent heat of vaporization will be high refrigerants... Circulated through a refrigeration system energy released or absorbed, by a body or a thermodynamic system, during constant-temperature... Examveda Team ) -The refrigerant should have a high enthalpy of Vaporisation ’ ( latent heat of vaporization the! Highly effective to connect and participate investment of refrigerators and equipment, including piping valves. The high latent heat of liquid ( to reduce size of condenser and evaporator others are especially well-suited to temperature! Compression ratio Compression of refrigerent is avoided has gained popularity ton ( lb... To low temperature, which is equal to 40.8 kJ/mol fusion and vaporization both involve the heat transfer during and. Kilogram of liquid refrigerant vapourised at the evaporator temperature away a large amount of heat required to melt ton... Of application involved in the process changes from a liquid ( d ) low COP low. Windings and may cause short circuits of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas energy released absorbed... Download question paper be used for small refrigeration systems move heat, an ideal refrigerant should have a high of! Large latent heat desirable properties of a refrigerant should have high thermal conductivity of the relatively temperature!

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