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. High Heat Transfer Coefficient 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). Latent heat is the amount of heat added to or removed from a substance to produce a change in phase. (d) Low COP and low freezing point. 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. High suction gas density at the compressor suction means low sized compressor … Upload or insert images from URL. 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. Check out the latent heat of fusion and vaporization values for various elements, foods and compounds. 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 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). A High Suction gas density and a Low Compression ratio. 3. Every kilogram of liquid refrigerant vapourised at the evaporator coil should take away a large amount of heat, i.e. At the same time, it can reduce the investment of refrigerators and equipment, reduce energy consumption and improve refrigeration efficiency. Why manholes in vessel are elliptical in shape. The natural … The desirable properties of a refrigerant are as follows: 1. Sub-cooling can be achieved by circulating more quantity of cooling water through the condenser. 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. This brings us around to the most important characteristic of a refrigerant: the relationship between vapor pressure and temperature. 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. Refrigerant 1. Join us (login) to get full access : Please sign up to connect and participate. Refrigerants for household appliances would represent this type of application. 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. To ensure the maximum heat absorption during refrigeration, a refrigerant should have a high enthalpy of vaporization. 3. Dielectric strength: It results in a high refrigerating effect and a low rate of refrigerant in circulation. Cost is always a factor in selecting a refrigerant. •Critical pressure and temperature :- It should be above the condensing pressure and temperature. It should be environment-friendly. Therefore ammonia cannot be used for small refrigeration systems. 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. These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas. Latent heat of solidification. 1. When the refrigeration system obtains the same cooling capacity, the large latent heat of vaporization can reduce the refrigerant circulation. It results in a high refrigerating effect and a low rate of refrigerant in circulation. In vapour compression refrigeration, the vapour is drawn in the compressor cylinder during its suction stroke and is compressed adiabatically during the compression stroke. 8. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. Therefore dielectric strength should be high to avoid short circuits. The heat of vaporization of water is about 2,260 kJ/kg, which is equal to 40.8 kJ/mol. Hence why the heat absorption and heat rejection heat exchangers are called the evaporator and the condenser respectively. Cooling via perspiration is affected by latent and sensible heat. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. The gas refrigerant within the condenser rejects its latent heat of … You can share the question You can get updates of new questions on Facebook linkedin twitter & google plus Thanks in advance :) 9. 4. A refrigerant should have a high latent heat of vapour at the evaporator temperature. 4. EQ-COMP software is showcased on www.eq-comp.com website and the results of the software can be … More heat can be absorbed and ejected in each cycle of refrigeration. When we raise the pressure, we also raise the temperature. The heat energy is used in breaking the hydrogen bonds which hold the molecules of … 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….. 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. You can like the best answer. High latent heat of vaporization. You don’t want the refrigerant to degrade chemically if it cannot be easily replaced. Because of the relatively high temperature of the available cooling medium, the only way to make the vapor condense is to compress it. Paste as plain text instead, × A corrosive refrigerant will require that all of the equipment, including piping and valves, be made of more exotic, expensive materials. Two common forms of latent heat are latent heat of fusion and latent heat of vaporization . Why high latent heat of vaporization is desirable in refrigerant ? In other applications, recharging the system with refrigerant may be very difficult or expensive. Solution (By Examveda Team) -The refrigerant should have low boiling point and low freezing point. 5. This energy breaks down the intermolecular attractive forces, and also must provide the energy necessary to expand the gas (the pΔV work). All rights reserved. Refrigerants are chosen because of their high latent heat capabilities, the amount of pressure need to hold the refrigerant in liquid form prior to … Heat transfer takes place from high temperature to low temperature, which is according to a temperature gradient. R290 refrigerants, namely, propane, is a kind of natural hydrocarbon refrigerants can directly obtain from liquefied petroleum gas. High critical temperature to have large isothermal energy transfer. 5. A. 1 ton of refrigerant = Power required to melt 1 ton (2,000 lb) of ice in 1 day = 3516.8 Watts. 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? No latent heat is the amount of energy in the form of heat that the liquid gives off or absorbs to change state. High latent heat of vaporization is desirable in a refrigerant. We've got answers. 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. Flip the page to see why this is so important. •Latent heat of vaporization :- It should have high latent heat of vaporization. In that case the chemical stability of the refrigerant may be an important property. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. 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. 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). More heat can be absorbed and ejected in each cycle of refrigeration. Thermal Conductivity: Thermal conductivity of the refrigerant should be high for faster heat transfer during condensation and evaporation. The liquid refrigerant in the evaporator absorbs its latent heat of vaporization, and in the process changes from a liquid to a vapor. Question is ⇒ Pick up the wrong statement. The difference will give you the latent heat for the mixture. 7. 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. Therefore the refrigerant vapors should be easily condensible. High latent heat of vaporization to get more refrigeration effect. High latent heat of vaporization is desirable in a refrigerant. by：Arkool 2021-01-18. It is therefore a measure of the cooling potential of the refrigerant circulated through a refrigeration system. It should have high latent heat of vaporization (to reduce mass flow of 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. In vapour absorption refrigerator, the compression of refrigerent is avoided. Latent heat of vapourisation of water at 1 bar, $100^\circ C$ is $2257 \frac{kJ}{kg}$. 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. refrigerant with a lower latent heat of vaporization will absorb less energy during evaporation than those with higher hfg. Steel tubes are used for ammonia systems and copper tubes are used for Freon systems. Latent Heat vs Sensible Heat . In hermetically sealed compressors refrigerant vapor contacts with motor windings and may cause short circuits. When a refrigerant has a high latent heat of vaporization, it can effectively move more heat when it boils and condenses within the target ranges. 6. Trouton’s rule shows that the latent heat of vaporization will be high for refrigerants having lower molecular weight. 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. 10. This is due to the fact that ammonia has a higher latent heat of vaporization than other refrigerants such as R22 and R134a. 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). Nusselt number (NN) is given by A. NN = hl/k 4. 7. Since a refrigerant’s goal is to move heat, an ideal refrigerant should have a high latent heat of vaporization. The advantage of using ammonia is that it has a much higher latent heat of vaporization. Thanks in advance :) Most of the heat transfer occurs because the refrigerant changes state. The important properties such as latent heat of vaporization and specific heat depend on the molecular weight and structure of the molecule. 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. Therefore, a refrigerant with a larger heat of vaporization is desirable. 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? Latent heat of vaporization is a physical property of a substance.   You cannot paste images directly. 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. 6. Evaporative cooling. Latent heat of vaporization A refrigerant should have a high latent heat of vapour at the evaporator temperature. The gas refrigerant within the condenser rejects its latent heat of vaporization… In some applications, low toxicity and flammability are essential factors. If the mass flow is very small it is difficult to control the flow rates. When latent heat is added, no temperature change occurs. 4. 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 … 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.