Is the rate of water evaporation controlled by the sensible heat absorption process or the latent heat evaporation process? How to increase the spray evaporation rate?
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Two questions: 1. Is the rate of water evaporation controlled by the sensible heat absorption process or by the latent heat evaporation process? The heat absorbed for sensible heat is approximately one-tenth of that for latent heat; thus, evaporation seems to be primarily governed by the latent heat vaporization process. However, although the gasification process absorbs a large amount of heat, it does not necessarily do so at a fast rate, and it is also affected by other factors (steam pressure difference, droplet size, air pressure, air velocity, etc.). So, during spray evaporation, in the process of evaporation of the atomized droplets, does it happen faster that the droplets heat up to the boiling point (100°C), or does the vaporization process occur faster? What is the approximate ratio of their speeds? 2. How to increase the speed of the spray evaporation process? I am studying spray evaporation, with the main goal of ensuring that all the water vaporizes within 1 second. From which aspects can I start working on this?
@*nht1 @ylb913 @EvilHasReachedItsLimit @FishAgainstTheClock
The conversion of water into vapor should be controlled by sensible heat; reduced-pressure evaporation works. For water, flash evaporation is required, as increasing the flow rate helps; spraying might work as well. I don’t know for sure, so I’m just guessing.
There is some truth to that, but it takes about 20 minutes to heat water to a boil, while it generally takes another hour of heating to dry out an entire pot of water. In this case, although the heat absorption is 1:10, the rate is 1:2. Reducing pressure and increasing the relative flow velocity are not feasible under the existing process, but the atomization effect can be improved. However, a preheating unit can be added to heat the water to 100°C first. Considering that the heat absorbed during the preheating process accounts for only 1/10 of the latent heat of vaporization, it is feared that preheating will have little impact on increasing the vaporization rate; therefore, there is no need to invest in such a preheating system.
Thank you for your prompt reply; I don’t have any gold coins, so I’m unable to express my gratitude
What you say makes sense. I’m not sure exactly what material you’re referring to; the only thing that can evaporate instantly is vapor. A spray drying tower would be suitable, and it’s best to use a spraying method – you can choose whether to use steam or some other gas for spraying. What I say may not be correct; it’s just for reference, as I’m not an expert in this area. I’ve only seen fluidized bed drying.
So do you think it’s necessary to install a water pre-heating system? I know very little about the chemical industry; please feel free to advise me
To be honest, I have no experience with this; just taking a look doesn’t mean one knows how to do it. In my understanding, the material is injected at subsonic speed from the tangent direction, and due to the sudden loss of pressure, the water instantly changes from a liquid state to a gas state. The tower is designed in the form of a cyclone dust remover, with the gaseous medium and water vapor being discharged from the top of the tower. Afterwards, this residual heat is used to preheat the wet material, and the condensed water is recovered after it has condensed. I’m not sure whether this process will work. Without any experience in this area, I can only try to understand things by guessing. I hope it’s useful to you.
Could you please explain in detail what the background is? If specific names are involved, they can be replaced with something else. What exactly are the materials used, and what are the process conditions? What problems have arisen, and what are the current solutions? What measures have been taken, and what are the results of those measures? How effective have they been? Evaluation: Is further improvement needed? What are the goals for the improvement?
This post was last edited by woshishei007 on 2016-4-14 at 13:48. In spray drying, heat air is usually used as well. Using heat air is simple: firstly, it facilitates heat exchange; secondly, the water content in the air after heat exchange can be increased significantly, which allows for effective removal of moisture. With spraying, as long as the droplets are small enough and there is sufficient hot air that is hot enough, evaporation occurs quite rapidly ； In simple terms, the smaller the droplets, the larger the heat exchange area ； The more hot air there is, the more moisture it can carry away ； If there isn’t enough hot air or heat, it’s also a good idea to preheat the raw materials. Some of the things mentioned upstairs fall completely within the category of flashing.