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

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