The differences and connections between airspeed and linear velocity
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This post was last edited by jordan569 on 2013-1-6 20:16. What is the difference between air speed and linear speed? In pilot tests, the space velocity is generally considered, while in industrial applications, the linear velocity is used instead. What are the differences and connections between the two? I think the space velocity usually refers to the inlet velocity of the reactor. In pilot tests, the residence time of the material within the reactor is primarily controlled by adjusting the feed rate, which in turn controls the space velocity. In such tests, the outlet velocity of the reactor is roughly equal to the inlet velocity; therefore, it is sufficient to consider only the space velocity. In other words, the space velocity in the pilot test is the same as the linear velocity. In the case of large-scale reactors, controlling only the feed rate is not sufficient to determine the residence time of the material inside the reactor; factors such as porosity and pressure drop in gas-solid reactions can affect the residence time (which is much longer than in pilot-scale experiments). Therefore, it is necessary to measure the residence time by examining the exit velocity or linear velocity of the material from the reactor, so that the reaction conditions can be adjusted accordingly. I’m not sure if I understand correctly Please point out any mistakes; it would be best if examples could be provided. . Note $ # , $ $
Airspeed and linear velocity are the same; they essentially refer to the same thing. Higher air velocity and linear velocity result in a shorter residence time ； With a low air velocity and low linear velocity, the residence time is longer.
The space velocity considered in the pilot experiment should be the amount of reactant processed per unit of catalyst. In industrial reactors, in order to control the adiabatic temperature rise or other factors, non-reactants need to be added; the linear velocity refers to that of the mixture as a whole, rather than just that of the reactants. For example, consider the reaction of ethanol dehydration to produce ethylene; if the reaction feed is pure ethanol, then linear velocity and space velocity should be the same thing. If the reaction feed is ethanol and water, at the same ethanol space velocity, the linear velocity should be much higher and the residence time much lower compared to a feed consisting solely of ethanol.
3# happydays Oh, so linear velocity is a concept that applies to all materials, while space velocity applies only to a specific material, right? What about using that speed as a benchmark? Are they all related to the import speed?
Space velocity refers to the amount of reactant that passes through a unit volume of catalyst bed per unit time in a continuously flowing reactor, and is measured in s-1. Reducing the space velocity increases the reaction time of the feedstock, enhances the reaction depth, and raises the conversion rate. Space velocity is generally not adjusted; it is determined by the properties of the feedstock and the volume of material to be processed, as well as the characteristics of the catalyst. Linear velocity is the flow rate of a fluid within a system, representing the volume of fluid that passes through a unit cross-sectional area per unit time, and is measured in m/s. Space velocity and linear velocity are two distinct concepts that should not be confused.
I strongly agree with what was said on floor 5; the explanation was very professional
5# wu_pb Since they are two different concepts, why is only the space velocity considered in pilot tests, while the linear velocity is not taken into account? And why is it the linear velocity that is considered in industrial applications, rather than the space velocity? I think these two concepts are still related! Please give me some advice!
5# is supported, but I also have questions about 7#; is it related to engineering calculations?
Reply to t18l: \"Since they are two different concepts, why is only the volumetric flow rate considered in pilot tests, without taking linear velocity into account, while in industrial applications it is the linear velocity that is considered rather than the volumetric flow rate?\" " In industrial production, when a device is in operation, space velocity and linear velocity are generally not used as evaluation parameters. Firstly, space velocity is typically measured at the inlet of the equipment (the location where physical, chemical, or physicochemical reactions take place); it reflects the performance of the equipment and is a manually defined value. It relates to the equipment itself, whereas linear velocity applies to pipes or channels. Secondly, space velocity indicates the processing capacity of the equipment as well as the apparent properties of catalysts, while linear velocity can be measured and is used in engineering design to determine pipe sizes!!! Additionally, let’s explain a few concepts: 1. Space time is obtained by dividing the volume of the reactor by the volumetric flow rate at the reactor inlet. It represents the time required for the fluid within the entire reactor volume to be processed under given conditions. It is also known as residence time or average stay time. Its physical meaning is the time needed for the reactor to process an amount of material equal to its volume under specified conditions. 2. Space velocity (SV) in a continuous-flow reactor is the ratio of the volumetric flow rate of the fluid at the inlet to the volume of the reactor (in continuous-flow reactors, it represents the amount of material that reacts per unit time per unit of catalyst bed, with units of s-1). Its physical meaning is the amount of material that can be processed per unit time per unit of reaction volume in a continuous-flow reactor. The higher the space velocity, the greater the production capacity of the equipment. Both space time and space velocity are artificially defined quantities that do not change depending on the nature of the reaction process or operating conditions!! The definitions of space time and space velocity, along with the specified conditions, are also determined arbitrarily. In heterogeneous systems, the mass of the catalyst can be used to replace the reactor volume in these formulas. In industrial production, space velocity is generally not used as a means of regulation; nor is linear velocity used for this purpose. The most common and convenient means of regulation in industrial production are pressure and temperature :) Due to time constraints, it’s not possible to cover everything in detail. Please feel free to point out any shortcomings or errors!!!
Got it! Thank you! :victory: