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convection-why hot body becomes colder after some time?-how convection happens?-difference between conduction and convection-types of convection-

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Convection: Did you ever notice when we leave a hot cup of tea for some time it did not remains hot as before? Why? It is due to heat being transferred from the cup to the surrounding. As we already know if the temperature difference between two bodies is present then heat transfers from the hot to the cold body. Heat can transfer by different modes. In the case of a hot cup, heat is transferred by convection. Due to the motion of air, warm air rises, and cold air replaced it that’s why after some time hot cup of tea becomes relatively cold. What is convection? Convection is a mode of heat transfer. In convection heat transfer between a solid surface and the adjacent liquid or gas that is in motion. Convection involves the combined effect of conduction and fluid motion. That’s why convection is also known as conduction with fluid flow. How convection happens? cooling of block by convection. Consider the cooling of a hot block by convection. As we know convection is the transfer o
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Fourier's law or heat transfer by conduction.

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Conduction: Heat transfer by molecular contact (collision) is conduction. Conduction is the heat transfer by molecular collision. Conduction takes place in solids, liquids, and gasses but works best in solids.  Why does conduction occur best in solids? Because in the case of solids, atoms or molecules are located closer together. That’s why the transfer of kinetic energy from a hot system to a cold is easier than liquids and gases. So, conduction occurs best in conduction. Mechanism of heat conduction in solid: In solids, heat is conducted by 2 methods. • By lattice vibration • By transport of free electron In the case of gases, the heat conduction mechanism is simple. The molecules of gases are in continuous random motion exchanging energy and momentum. When a molecule from the high-temperature region (with high kinetic energy) collides with a molecule from the lower temperature region (with low kinetic energy) it loses energy by collision and heat transfer occurs. In the case of
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Heat-Facts about the heat. -Heat transfer.- Why does heat transfer from the hot to the cold body? -Three types of heat transfer.- Example with a combination of 3 modes or types of heat transfer.

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Table of content 1.  Heat. 2.  Facts about the heat. 3.  Heat transfer. 4. Why does heat transfer from the hot to the cold body? 5. Three types of heat transfer. 6. Example with a combination of 3 modes or types of heat transfer. Heat: Heat is a form of energy that travels from one system to another because of temperature differences. Facts about heat: There are some facts about the heat that are explained by theories of heat. ·       Whenever heat exchange occurs, heat is consumed (heat lost by the hot body always equals heat gained by the cold body). ·       Heat flow from hot to a cold body. ·       Substance expands on heating. ·       Weight of the body did not vary if the body was heated or cooled. ·       To change the phase of material from solid to liquid or liquid to gases without temperature rise, a certain amount of heat is required. Heat transfer The science that deals with the determination of the rate of energy transfer are heat transfer. What is meant by heat transfer?
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construction-working-types of evaportor-open kettle or pan-falling film-forced circulating evaporator-multiple effect evaporator-feed mode arrangement-foward feed-backward feed-mixed feed

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  Table of content: 1.1           Evaporator and Why evaporation is a cooling process ? 1.2           Construction of evaporator : 1.3           Working of the evaporator : 1.4           Is there any difference between evaporator and condenser? 1.5           Types of evaporators : 1.6           Open kettle or pan evaporator : 1.7           Falling film evaporator : 1.8           Forced circulating evaporator : 1.9           Multiple effect evaporator : 1.10         Feed mode arrangements : 1.11         Why backward feed mode is more give more economy than forward feed mode? what is evaporators and why evaporation is a cooling process? As we all know, the evaporator is a device that turns liquid into a gaseous state and causes cooling. Evaporation is a process which turns liquid into vapours.   Why does evaporation cause cooling?  Evaporation is a cooling process because it absorbs energy (which is in the form of heat) from surrounding to make the evaporation p
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Is vaporization and evaporation the similar thing?

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    When we talk about evaporation then there a question arises, are evaporation and vaporization similar? So here is the simple answer. Evaporation is not exactly similar to vaporization. Evaporation is the type of vaporization. Both are phase transitions (where the liquid turns into vapors) but both are occurring at different temperatures (at which phase changes occur) and on different surfaces. Further vaporization is a bulk phenomenon but evaporation is a surface phenomenon. Vaporization takes place at a particular temperature where liquid reaches its boiling point, but evaporation can be carried out at any temperature where the temperature difference is observed mostly below the boiling point.
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Performance of evaporator-capacity-steam economy-methods to increase steam economy-heat transfer in evaporators-boiling point rise BPR-boiling point elevation-duhring’s rule

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  Performance of evaporator Two basic criteria for performance of evaporator.   Capacity Steam economy Capacity of evaporator “Number of kilogram of water evaporated per hour.” Or; “ Amount of water evaporated per hour.” Steam economy “Number of kilogram of water evaporated per kilogram of steam fed to evaporator.” Or; “Amount of water which is converted into vapors through steam.” Steam economy is the ratio of capacity and consumption. Steam economy is unitless quantity. Steam economy for single effect evaporator is 0.8.   That means 80 percent   of that steam is used to generate water. Methods to increase steam economy: The operation cost of evaporator can be reduced by increasing steam economy. There are two methods to increase steam economy. 1.      By use of multiple effect evaportaors.   2.      By vapor recompression. In Multiple effect evaporators the vapors which is generated in first effect can be used as heating media for second effect. Simila
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Evaporator and Evaporation. Purpose and applications of evaporation.

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  Evaporators A device that is used to convert liquid into gaseous form (vapors) by heat transfer. Evaporation Evaporation is a process in which the removal of water takes place by boiling the liquor. Purpose of evaporation? •    To increase the concentration of liquid. •    Evaporation is not only used for the concentration of liquor it is also used to generate vapors and to recover solvent. How to recover solvent? In evaporation, the solvent is converted into vapors. Vapors of solvent are comparatively pure because impurities did not evaporate. By condensing these vapors we can get pure solvent. This recovery solution can be used for further different methods.
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