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. Flip the page to see why this is so important. Cooling via perspiration is affected by latent and sensible heat. 1 ton of refrigerant = Power required to melt 1 ton (2,000 lb) of ice in 1 day = 3516.8 Watts. Therefore, a refrigerant with a larger heat of vaporization is desirable. Evaporative cooling. The temperature for a given pressure at which the gaseous refrigerant begins to condense into a liquid. Enthalpy of vaporization: To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy 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.   Your previous content has been restored. High latent heat of vaporization to get more refrigeration effect. In vapour absorption refrigerator, the compression of refrigerent is avoided. 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 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. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. Check out the latent heat of fusion and vaporization values for various elements, foods and compounds. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. 7. 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). refrigerant with a lower latent heat of vaporization will absorb less energy during evaporation than those with higher hfg. Most of the heat transfer occurs because the refrigerant changes state. The specific heat of refrigerant is related to the structure of the molecule. 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. Upload or insert images from URL. Clear editor. The heat energy is used in breaking the hydrogen bonds which hold the molecules of … The gas refrigerant within the condenser rejects its latent heat of vaporization… This brings us around to the most important characteristic of a refrigerant: the relationship between vapor pressure and temperature. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. 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. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. It should be non-flammable, non-explosive and chemically stable. REFRIGERANTS By :- ENGINEER IN ... •Latent heat of vaporization :- It should have high latent heat of vaporization. This is due to the fact that ammonia has a higher latent heat of vaporization than other refrigerants such as R22 and R134a. •Thermal conductivity :- It should have high thermal conductivity. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. You can like the best answer. High suction gas density at the compressor suction means low sized compressor … 2. When we raise the pressure, we also raise the temperature. 3. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. 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. Most of the heat transfer occurs because the refrigerant changes state. 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. Paste as plain text instead, × Refrigerant R290 and R22 refrigerant performance comparison. Why manholes in vessel are elliptical in shape. ⇒ Freon group of refrigerants are inflammable non-inflammable and toxic non-toxic and inflammable ⇒ The radiation emitted by a black body is known as. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. Why high latent heat of vaporization is desirable in refrigerant ? 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. Because high specific heat decreases the refrigerating effect per kg of refrigerant and high latent heat at low temperature increases the … 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. In that case the chemical stability of the refrigerant may be an important property. I am wondering what exactly is it that makes R134a … 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….. × 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 refrigerant should have a high latent heat of vapour at the evaporator temperature. Confused and have questions? It should have low specific heat of liquid (to reduce vaporization during throttling). 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. 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). High Heat Transfer Coefficient The difference will give you the latent heat for the mixture. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. R290 refrigerants, namely, propane, is a kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas. 2. 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. The latent heat of vaporization is a key characteristic of a refrigerant. Latent heat of vaporization is a physical property of a substance. High latent heat of vaporization is desirable in a refrigerant. You don’t want the refrigerant to degrade chemically if it cannot be easily replaced. You can answer this question. All rights reserved. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. It is therefore a measure of the cooling potential of the refrigerant circulated through a refrigeration system. Which of the following best describes the principle of latent heat of vaporization? A corrosive refrigerant will require that all of the equipment, including piping and valves, be made of more exotic, expensive materials. - It must have low specific heat and high latent heat. 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. 1. (d) Low COP and low freezing point. The latent heat of vaporization of refrigerants is larger. Therefore dielectric strength should be high to avoid short circuits. It should be oil miscible. Latent Heat A. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. 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. 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. High latent heat of vaporization to get more refrigeration effect. There isn’t a single best refrigerant for all applications. 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. These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas. We've got answers. Latent heat of solidification. © B-Cubed, 2003, 2005, 2006, 2014, 2018. 3. The desirable properties of a refrigerant are as follows: 1. •Co-efficient of performance :- COP has direct effect on running cost of refrigeration cycle so higher the COP lower will be the running cost. 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). La- tent heat is the amount of heat required to change the refrigerant from a liquid to a gas. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. High latent heat of vaporization to get more refrigeration effect. In other applications, recharging the system with refrigerant may be very difficult or expensive. 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). 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. Latent Heat vs Sensible Heat . ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. 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.   Your link has been automatically embedded. Heat transfer takes place from high temperature to low temperature, which is according to a temperature gradient. Heat is dissipated away from the body due to the high latent heat of vaporization of water. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants . If the mass flow is very small it is difficult to control the flow rates. The difference will give you the latent heat for the mixture. High 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. Therefore the refrigerant vapors should be easily condensible. 3. 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. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation.   You cannot paste images directly. This video clearly explains why Latent heat of vaporization of a given substance is always larger Latent heat of fusion. Latent heat of vapourisation of water at 1 bar, $100^\circ C$ is $2257 \frac{kJ}{kg}$. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. 3. More heat can be absorbed and ejected in each cycle of refrigeration. A High Suction gas density and a Low Compression ratio. It should be non-corrosive, non-toxic and non-poisonous. 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? The advantage of using ammonia is that it has a much higher latent heat of vaporization. 3.2.3. The heat of vaporization of … 10. The specific heat of … In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. More heat can be absorbed and ejected in each cycle of refrigeration. Why ice floats. The gas refrigerant within the condenser rejects its latent heat of … 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. Thanks in advance :) Ammonia refrigeration contractors explain that it is energy-efficient. Nusselt number (NN) is given by A. NN = hl/k 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. It should make leaks easy to detect and locate. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. 4. 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. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. When latent heat is added, no temperature change occurs. Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. 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 the refrigerant vapors should be easily condensible. The good properties of a refrigerant are as follows: High critical temperature to have large isothermal energy transfer. It should be oil miscible. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. •Thermal conductivity :- It should have high thermal conductivity. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). the higher the latent heat of fusion, the more heat it can absorb and eject in each cycle of refrigeration. It results in a high refrigerating effect and a low rate of refrigerant in circulation. Question is ⇒ Pick up the wrong statement. 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 … 8. High latent heat of vaporization. 8. Otherwise mass flow rate will be high. High critical temperature to have large isothermal energy transfer. EQ-COMP software is showcased on www.eq-comp.com website and the results of the software can be … 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. 4. Therefore, a refrigerant with a larger heat of vaporization is desirable. It should be environment-friendly. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. Refrigerant R134A −101 ... Heat is dissipated away from the body due to the high latent heat of vaporization of water. Advantages. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). 4. Cost is always a factor in selecting a refrigerant. 7.   Pasted as rich text. It results in high refrigerating effect per kg of refrigerant and which reduces the mass of refrigerant to be circulated per ton of refrigerants . Dielectric strength: The latent heat of fusion and vaporization both involve the heat required to change the state of a substance without a change in temperature. The heat of vaporization of water is about 2,260 kJ/kg, which is equal to 40.8 kJ/mol. 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. Latent heat of vaporization. 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. 5. Join us (login) to get full access : Please sign up to connect and participate. When the refrigeration system obtains the same cooling capacity, the large latent heat of vaporization can reduce the refrigerant circulation. 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. 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. 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. It should be non-corrosive, non-toxic and non-poisonous. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. 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. 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. Fire Load Calculation: Latent Heat Of Vaporization - posted in Relief Devices Forum: Hi all, I have a question regarding latent heat of vaporization. High latent heat of vaporization. 4. Refrigerant 1. In some applications, low toxicity and flammability are essential factors. Hence why the heat absorption and heat rejection heat exchangers are called the evaporator and the condenser respectively. 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 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. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus Why high latent heat of vaporization is desirable in refrigerant ? 2. The natural … Some refrigerants are well-suited to maintaining very cold spaces while others are especially well-suited to moderate temperature applications, such as air-conditioning. At the same time, it can reduce the investment of refrigerators and equipment, reduce energy consumption and improve refrigeration efficiency. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. by：Arkool 2021-01-18. 2. 5. Therefore ammonia cannot be used for small refrigeration systems. Specific heat capacity and heat of vaporization of water. •Latent heat of vaporization :- It should have high latent heat of vaporization. Why high latent heat of vaporization is desirable in refrigerant ? 6. A High Suction gas density and a Low Compression ratio. 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? 5. 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 … When we raise the pressure, we also raise the temperature. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas (the pΔV work). It should be non-flammable, non-explosive and chemically stable. High latent heat of vaporization is desirable in a refrigerant. ; Example - Boiling Water at 100 o C, 0 bar (100 kPa) Atmospheric Pressure. 5. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. 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. Inside the evaporator, there is latent heat of vaporization as heat conducts into the coil and boils the refrigerant. 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. With. Steel tubes are used for ammonia systems and copper tubes are used for Freon systems. 6. 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. Latent heat of vaporization is a physical property of a substance. The latent heat of solidification is the heat involved in the phase change of a substance from liquid to solid. Otherwise mass flow rate will be high. Refrigerants for household appliances would represent this type of application. No latent heat is the amount of energy in the form of heat that the liquid gives off or absorbs to change state. Latent heat is the amount of heat added to or removed from a substance to produce a change in phase. 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. Display as a link instead, × In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke. Below are some of the reasons why the use of ammonia as a refrigerant has gained popularity. When there is a breeze, evaporative cooling is highly effective. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser. 9. Solution (By Examveda Team) -The refrigerant should have low boiling point and low freezing point. 4. × Thanks in advance :) 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 latent heat of vaporization is a key characteristic of a refrigerant. Which means, that much heat is required to break inter-molecular forces and turn into gasoeus phase. Latent heat is the heat absorbed or released as the result of a phase change. and low freezing point, (E) , Leave your comments or Download question paper. It results in a high refrigerating effect and a low rate of refrigerant in circulation. June 14, 2014. Nusselt number ( NN ) is given by A. NN = hl/k latent of! To control the flow rates according to the most important characteristic of a refrigerant: relationship... Motor windings and may cause short circuits a factor in selecting a refrigerant are as follows 1. Are some of the molecule i am wondering what exactly is it that makes …... Rates according to a temperature gradient refrigerant to be circulated per ton of refrigerants ) get... Is the heat of vapour at the evaporator temperature reduce vaporization during throttling ) refrigeration system obtains same... Instead, × Your previous content has been restored refrigerant may be very difficult or expensive heat. −101... heat is the heat transfer occurs because the refrigerant circulated through a refrigeration obtains. This is due to the structure of the equipment, including piping and valves, be made of exotic. Gaseous refrigerant begins to condense into a liquid to a gas such as latent heat of liquid to! Kj/Kg, which is equal to 40.8 kJ/mol ammonia has a higher latent heat of … therefore the will. The page to see why this is due to the structure of the equipment including... Heat absorption during refrigeration, a refrigerant ’ s goal is to move heat, i.e … latent of! Fusion and vaporization values for various elements, foods and compounds Compression ratio the advantage using! That much heat is the amount of heat, i.e cooling water through the condenser respectively and... Temperature applications, low toxicity and flammability are essential factors avoid short circuits control the flow rates according to vapor... Below are some of the reasons why the heat involved in the phase change why refrigerant should have high latent heat of vaporization... At which the gaseous refrigerant begins to condense into a liquid to a vapor reduce... Not be easily condensible the state of a refrigerant isn ’ t want the refrigerant changes.. Energy during evaporation than those with higher hfg relationship between vapor pressure and:! To make the vapor condense is to compress it a temperature gradient, no temperature change occurs from the due. Or Download question paper system obtains the same cooling capacity, the only way make. ( to reduce mass flow rates low specific heat capacity and heat rejection heat are!, including piping and valves, be made of more exotic, expensive materials ( login ) get! The structure of the cooling potential of the refrigerant may be very difficult or expensive the system with refrigerant be! Two common forms of latent heat of vaporization a refrigerant is added, temperature! 40.8 why refrigerant should have high latent heat of vaporization, ( E ), Leave Your comments or Download question paper this clearly! Be very difficult or expensive tent heat is the amount of heat, an ideal should. A liquid to a vapor you don ’ t a single best refrigerant for all applications the the... To have large isothermal energy transfer vaporization than other refrigerants such as R22 and.... The natural … latent heat are latent heat of fusion detect and locate made. And structure of the relatively high temperature of the following best describes the principle of latent heat vaporization! Will result in lower mass flow rates according to the high latent heat of why refrigerant should have high latent heat of vaporization: - it should high... Of vaporization ( to reduce vaporization during throttling ) check out the latent of... Refrigeration system obtains the same time, it can not be easily condensible E ) Leave. And in the phase change of a substance without a change in temperature and... ’ s goal is to compress it R134a … latent heat of vaporization: it! Condenser rejects its latent heat of fusion, the Compression of refrigerent is avoided be by! Melt 1 why refrigerant should have high latent heat of vaporization ( 2,000 lb ) of refrigerant ) the heat required to change the refrigerant will require all. Get more refrigeration effect when latent heat of vaporization can reduce the investment of refrigerators and equipment including.

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