I am wondering what exactly is it that makes R134a … The heat energy is used in breaking the hydrogen bonds which hold the molecules of … Clear editor. When the refrigeration system obtains the same cooling capacity, the large latent heat of vaporization can reduce the refrigerant circulation. It should be environment-friendly. 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. 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). High latent heat of vaporization to get more refrigeration effect. When there is a breeze, evaporative cooling is highly effective. Refrigerant R290 and R22 refrigerant performance comparison. Therefore, a refrigerant with a larger heat of vaporization is desirable. 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. High latent heat of vaporization to get more refrigeration effect. Ammonia refrigeration contractors explain that it is energy-efficient. It should be oil miscible. 5. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus 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 results in a high refrigerating effect and a low rate of refrigerant in circulation. 8. 5. More heat can be absorbed and ejected in each cycle of refrigeration. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. Latent heat is the amount of heat added to or removed from a substance to produce a change in phase. 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. 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….. 3. 3. You can answer this question. 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. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. by：Arkool 2021-01-18. Which of the following best describes the principle of latent heat of vaporization? Latent heat of vaporization is a physical property of a substance. 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 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. 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. 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. Refrigerant R134A −101 ... Heat is dissipated away from the body due to the high latent heat of vaporization of water.   Pasted as rich text. The latent heat of vaporization is a measure of the heat per pound that the refrigerant can absorb from an area to be cooled. The difference will give you the latent heat for the mixture. the higher the latent heat of fusion, the more heat it can absorb and eject in each cycle of refrigeration. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. Most of the heat transfer occurs because the refrigerant changes state. 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. 9. 4. A High Suction gas density and a Low Compression ratio. You can like the best answer. The gas refrigerant within the condenser rejects its latent heat of … In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke. 4. Therefore the refrigerant vapors should be easily condensible. 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 … × 4. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. It should be non-flammable, non-explosive and chemically stable. Thanks in advance :) Question is ⇒ Pick up the wrong statement. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. 2. Latent heat is the heat absorbed or released as the result of a phase change. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . More heat can be absorbed and ejected in each cycle of refrigeration. The latent heat of solidification is the heat involved in the phase change of a substance from liquid to solid. 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 latent heat of vaporization is desirable in a refrigerant. This video clearly explains why Latent heat of vaporization of a given substance is always larger Latent heat of fusion. 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. A High Suction gas density and a Low Compression ratio. 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. ; Example - Boiling Water at 100 o C, 0 bar (100 kPa) Atmospheric Pressure. Higher latent heat of vaporization of the refrigerant will result in lower mass flow rates according to the Heat transfer equation. Confused and have questions? 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. This brings us around to the most important characteristic of a refrigerant: the relationship between vapor pressure and temperature. High latent heat of vaporization to get more refrigeration effect. Large conductivity to reduce size of condenser and evaporator. June 14, 2014. Below are some of the reasons why the use of ammonia as a refrigerant has gained popularity. 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. Join us (login) to get full access : Please sign up to connect and participate. 8. 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. 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). 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. Why high latent heat of vaporization is desirable in refrigerant ? REFRIGERANTS By :- ENGINEER IN ... •Latent heat of vaporization :- It should have high latent heat of vaporization. All rights reserved. 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. 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. Why high latent heat of vaporization is desirable in refrigerant ? With. It should have low specific heat of liquid (to reduce vaporization during throttling). 6. 6. 3. When we raise the pressure, we also raise the temperature. ‘Specific Enthalpy of Vaporisation’ (latent heat) of refrigerant should be high. Latent Heat La- tent heat is the amount of heat required to change the refrigerant from a liquid to a gas. Evaporative cooling. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. Why manholes in vessel are elliptical in shape. © B-Cubed, 2003, 2005, 2006, 2014, 2018. Therefore ammonia cannot be used for small refrigeration systems. Heat is dissipated away from the body due to the high latent heat of vaporization of water. Most of the heat transfer occurs because the refrigerant changes state. R290 refrigerants, namely, propane, is a kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. High Latent Heat of Vaporization. The desirable properties of a refrigerant are as follows: 1. High latent heat of vaporization. and low freezing point, (E) , Leave your comments or Download question paper. EQ-COMP software is showcased on www.eq-comp.com website and the results of the software can be … Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. 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. - It must have low specific heat and high latent heat. Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. Latent heat of solidification. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. 5. The latent heat of vaporization is a key characteristic of a refrigerant. The gas refrigerant within the condenser rejects its latent heat of vaporization… When we raise the pressure, we also raise the temperature. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. 2. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. Enthalpy of vaporization: To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. Which means, that much heat is required to break inter-molecular forces and turn into gasoeus phase. At the same time, it can reduce the investment of refrigerators and equipment, reduce energy consumption and improve refrigeration efficiency. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. Why high latent heat of vaporization is desirable in refrigerant ? A refrigerant should have a high latent heat of vapour at the evaporator temperature. Dielectric strength: Advantages. A. 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 that case the chemical stability of the refrigerant may be an important property. Refrigerant 1. It should have high latent heat of vaporization (to reduce mass flow of refrigerant). 1. × Flip the page to see why this is so important. 2. 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. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. Specific heat capacity and heat of vaporization of water. Display as a link instead, × 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. 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. Cooling via perspiration is affected by latent and sensible heat. High latent heat of vaporization. High latent heat of vaporization is desirable in a refrigerant. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. Therefore the refrigerant vapors should be easily condensible. We've got answers. High suction gas density at the compressor suction means low sized compressor … The natural … 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. In other applications, recharging the system with refrigerant may be very difficult or expensive. It should be oil miscible. 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. Solution (By Examveda Team) -The refrigerant should have low boiling point and low freezing point. The difference will give you the latent heat for the mixture. (d) Low COP and low freezing point. There isn’t a single best refrigerant for all applications.   You cannot paste images directly. 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). It results in a high refrigerating effect and a low rate of refrigerant in circulation. The specific heat of …   Your link has been automatically embedded. •Thermal conductivity :- It should have high thermal conductivity. A corrosive refrigerant will require that all of the equipment, including piping and valves, be made of more exotic, expensive materials. 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. Heat transfer takes place from high temperature to low temperature, which is according to a temperature gradient. The heat of vaporization of water is about 2,260 kJ/kg, which is equal to 40.8 kJ/mol. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. Thanks in advance :) Fire Load Calculation: Latent Heat Of Vaporization - posted in Relief Devices Forum: Hi all, I have a question regarding latent heat of vaporization. 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 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. 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