Pressure Drop And Boil-Up Rate Research

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Explain the relationship

1. Pressure drop and boil-up rate

As seen from graph 2, pressure drop increases as the boil-up rate increases.
The reflux ratio is kept constant so the liquid flowing down has uniform flow and only the power input to the reboiler can be adjusted. The boil-up rate is obtained by varying the heat energy to the reboiler and this affects the velocity of the vapour passing up the column. As the velocity of the vapour passing up the column increases, the vapour flow will generate more pressure drop due to the resistance force that is acting against the holes in the sieve tray and the liquid that is flowing down the column. In addition, increasing the vapour flow means that increasing the contacting time between liquid and vapour phase inside the column resulting in higher pressure drop. This is proven clearly from the graph that the pressure drop is linearly related with boil-up rate.

Therefore, the relationship between pressure drop and boil-up rate means that more volume of vapour educed per unit time results in more restriction of the holes in the sieve tray and that caused by passing of vapour through the liquid on top of the tray. Hence, the higher the velocity, the higher the boil-up rate and so does the overall pressure drop.

2. Purity and boil-up rate

From the graph 2, it is seen clearly that the relationship between purity and boil-up rate is inversely proportional to each other. In order to achieve a good separation and high purity between the liquid and the vapour must be brought to an intimate contact by counter-current flow. Increasing the vapour flow actually means decreasing the interaction time between the down flowing liquid and up flowing vapour inside the column. Hence, if ...

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...mes more violent and spread out.

4. Pressure drop and foaming

As the pressure drop increases in the column, it is observed that the degree of foaming becomes more violent and more spread out. When the pressure drop is relatively high, it means that the pressure exerted by the vapour is insufficient to hold up the liquid in the tray, causing the gas bubbles to appear on top of the sieve trays. To add on, the higher the pressure drop, the higher the velocity of the vapour passing up the column. As a result, more vapour will penetrate the liquid and more bubbles formation is observed. Due to more bubbles formation, the degree of foaming are more agitated, rapid and spread out.

The bubbles forms become more spread out when the pressure drop increases because the pressure acting on the holes of the sieve trays causes to push the bubbles against the other bubbles.

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