6 replies to this topic

[process705]

Hi,
Can anyone please explain me the difference between residence time and hold up time?
Thank you very much

[clarenceyue]

If there're better people to correct me I would gladly stand aside, but here is what I have understood from my classes.

Hold-up/Residence time: Average amount of time a fluid spends in a reactor/tank.

Residence time and hold-up time are essentially similar, although there are distinctions, to me it is a distiction without significant differences.

[djack77494]

I don't know how rigorous this definition would be, and I'm not speaking from an academic point of view, but I can tell you how I understand the two. To me, residence time refers to the time when an action can occur. In our context, it might be the time that a fluid was in contact with a solid catalyst and therefore able to react. Hold up time is more like a surge time or (say) the clock time that a substance in contained within a vessel. If you subscribe to my way of thinking, then we could envision a reactor that contains an active volume where catalyst is loaded and other volume for supports, distributors, etc. A fluid passing through the reactor would spend more time within the walls of the reactor than it would spend in contact with the catalyst. The former time could be thought of as hold up time, while the latter would be residence time.

[clarenceyue]

djack77494:

I should think what you said made absolute sense. I stand corrected and glad that you provided all of us a good and practical understanding of what residence/hold-up time.

[fallah]

If the vessel isn't contained catalyst,support,....and not being known as a reactor/contactor/...,we can say the hold up time and residence time are equal.

Please correct me if i am wrong.

[djack77494]

If the vessel isn't contained catalyst,support,....and not being known as a reactor/contactor/...,we can say the hold up time and residence time are equal.
Please correct me if i am wrong.

fallah,
We are in agreement.

[riven]

Residence time defines how fast something moves through a system (usually the system is in equilibrium) e.g.

residence time of bacteria in a Steady State reactor= volume of reactor/volumetric flowrate of bacteria through reactor

In terms of chemical engineering I am at a lost exactly how to define holdup time so see above. But from computing/electrical
The amount of time that a power supply's output remains within the specified voltage ranges after its input ceases.

According to that definition holdup time is simply a specific non equilibrium state of residence time.