{"id":215,"date":"2022-03-16T07:05:26","date_gmt":"2022-03-15T22:05:26","guid":{"rendered":"https:\/\/chemical-engineering-review.com\/en\/?p=215"},"modified":"2022-03-22T06:40:24","modified_gmt":"2022-03-21T21:40:24","slug":"post-215","status":"publish","type":"post","link":"https:\/\/chemical-engineering-review.com\/en\/pv\/","title":{"rendered":"P\/V(power per unit volume)\uff1aScale-up indicator for mixing vessel"},"content":{"rendered":"

Outline<\/span><\/h2>\n

The power required to agitate per unit volume (liquid volume) is called P<\/em>\/V<\/em> value.<\/p>\n

P<\/em>\/V<\/em>[kW\/m3<\/sup>] is expressed by the following equation\uff1a<\/p>\n

$$P\/V=\\frac{P}{V}$$<\/p>\n

where P<\/em> is the agitation power, V<\/em> is the liquid volume.<\/p>\n

P<\/em>\/V<\/em>\u00a0is often used as an indicator to determine if sufficient power is being applied to the liquid in the mixing vessel.<\/p>\n

When evaluated simply by the required agitation power P<\/em>, the larger the mixing vessel and agitation impeller, the higher the value.<\/p>\n

If this is the case, it is impossible to determine whether power is excessive or insufficient.<\/p>\n

Therefore, the effect of scale is eliminated by dividing by the liquid volume in the mixing vessel.<\/p>\n

P\/V Guideline<\/span><\/h2>\n

Below is P<\/em>\/V<\/em> guideline for each mixing system.<\/p>\n

P\/V value for each viscosity<\/h3>\n

Low liquid viscosity\uff1a0.1\u2266P<\/em>\/V<\/em>\u22661.0<\/strong><\/p>\n

High liquid viscosity\uff1a1.0\u2266P<\/em>\/V<\/em>\u22665.0<\/strong><\/p>\n

Low-viscosity liquids that do not require much agitation power are often designed with P<\/em>\/V<\/em> of 1.0 or less.<\/p>\n

P<\/em>\/V<\/em> of 0.1 or less is unlikely to be selected for a stirred reaction tank because the agitation power is too low and mixing performance is poor. It may be possible in an mixing vessel that does not require uniform mixing.<\/p>\n

On the other hand, operating P<\/em>\/V<\/em> at 1.0 or higher is not recommended because the mixing performance does not change much for the power required.<\/p>\n

High viscosity agitation requires more power for agitation, resulting in higher P<\/em>\/V<\/em>.<\/p>\n

When the P<\/em>\/V<\/em> exceeds 5.0, the liquid is no longer agitated as generally imagined. It will be mixed with a liquid that has properties similar to a solid, such as syrup.<\/p>\n

It may no longer be better to use a kneader in that area than to use an mixing vessel.<\/p>\n

The P<\/em>\/V<\/em> is separated by up to 5.0, meaning that liquids that are too viscous are difficult to mix in the mixing vessel.<\/p>\n

P\/V value for each type of mixing<\/h3>\n

Liquid-liquid mixing\uff1a0.1\u2266P<\/em>\/V<\/em>\u22662.0
\nSolid-liquid mixing\uff1a0.5\u2266P<\/em>\/V<\/em>\u22662.0
\nGas-liquid mixing\uff1a1.0\u2266P<\/em>\/V<\/em>\u22665.0<\/strong><\/p>\n

For each agitation systems, P<\/em>\/V<\/em> is a value assuming the liquid is of low viscosity.<\/p>\n

As is usual with agitation, it is very difficult to uniformly mix materials with different densities, and power is required.<\/p>\n

 <\/p>\n

Liquid-liquid agitation is a relatively easy system for uniform mixing. However, when mixing two phase-separating liquids such as water and oil, it may take up to 1.0 to 2.0 P<\/em>\/V<\/em>.<\/p>\n

Furthermore, it is difficult to achieve completely uniform dispersion.<\/p>\n

 <\/p>\n

Solid-liquid agitation depends on the density of solid particles.<\/p>\n

If the density of the solid particles is close to the density of the liquid, the P<\/em>\/V<\/em> is low. The density of polymer particles is often close to the density of the liquid, so not much power is required.<\/p>\n

On the other hand, heavier particles such as metals require more energy to lift, so their P<\/em>\/V<\/em> tends to be higher.<\/p>\n

However, it is important to note that if the P<\/em>\/V<\/em> is set too high, the metal particles are likely to hit the impellers and vessel walls, causing wear or erosion.<\/p>\n

 <\/p>\n

Gas-liquid mixing is the most difficult of all multiphase systems.<\/p>\n

In solid-liquid mixing, the density difference is a few times at most, but in gas-liquid mixing, the difference is about 1,000 times.<\/p>\n

Since the gas will escape upward in a matter of seconds, it is necessary to agitate vigorously to keep as much gas in the liquid as possible.<\/p>\n

Also, P<\/em>\/V<\/em> in gas-liquid mixing depends on the process.<\/p>\n

If the gas must be absorbed into the liquid in one pass, the P<\/em>\/V<\/em> must be set higher.<\/p>\n

If some of the gas from the top of the tank is recycled and returned to the feed line, it does not need to be mixed so vigorously.<\/p>\n

P\/V constant scale-up<\/h2>\n

P<\/em>\/V<\/em>\u00a0is also often used as a criterion in scale-up (or down) considerations.<\/p>\n

Scaling up with P<\/em>\/V<\/em>=constant allows for constant energy to be added per unit liquid volume. As a result, it is easier to obtain similar mixing performance after scale-up.<\/p>\n

In particular, scale-up that meets the following three conditions is known to provide the same mixing performance as before scale-up.<\/p>\n

    \n
  • P<\/em>\/V<\/em>=constant<\/li>\n
  • Mixing vessel and impeller shape are similar<\/li>\n
  • Turbulent field with baffles<\/li>\n<\/ul>\n

    In conclusion<\/h2>\n

    The P<\/em>\/V<\/em> value of the required agitation power per unit volume was explained.<\/p>\n

    This is a basic indicator for agitation tank design, so be sure to keep it in mind.<\/p>\n","protected":false},"excerpt":{"rendered":"

    The power required to agitate per unit volume (liquid volume) is called P\/V value. P\/V\u00a0is often used as an indicator to determine if sufficient power is being applied to the liquid in the mixing vessel.<\/p>\n","protected":false},"author":1,"featured_media":222,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9],"tags":[],"class_list":["post-215","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-mixing"],"_links":{"self":[{"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/posts\/215","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/comments?post=215"}],"version-history":[{"count":9,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/posts\/215\/revisions"}],"predecessor-version":[{"id":229,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/posts\/215\/revisions\/229"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/media\/222"}],"wp:attachment":[{"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/media?parent=215"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/categories?post=215"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/chemical-engineering-review.com\/en\/wp-json\/wp\/v2\/tags?post=215"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}