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Renin Angiotensin Mechanism.

Climbing film evaporators.

 

Definition:

  • The equipment used for carrying out the process of evaporation are called “Evaporators”.

  • Evaporators are classified according to the form of the heat movement,

    • Natural circulation evaporators. e.g Evaporating Pan.

    • Forced circulation evaporation. e.g. Modified evaporating pan.

    • Film evaporators. e.g Climbing film evaporator.

  • Film evaporators spread the material as a film over the heated surface, and the vapor escapes the film.

 Climbing film evaporators:

Construction and working Principle:

  • The heating unit consists of steam-jacketed tubes, having a length to diameter ratio of about 140 to 1, so that a large evaporator may have tubes 50 mm in diameter and about 7 m in length.

  • The liquor to be evaporated is introduced into the bottom of the tube, a film of liquid forms on the walls and rises up the tubes, hence it is called a climbing film evaporator. 

  • At the upper end, the mixture of vapor and concentrated liquor enters a separator, the vapor passes to a condenser, and the concentrated liquid to a receiver.

  • Cold or preheated liquor is introduced into the tube. Heat is transferred to the liquor from the walls and boiling begins. Ultimately sufficient vapor has been formed for the smaller bubbles to unite into a large bubble, filling the width of the tube and trapping a ‘slug’ of liquid above the bubble. 

  • As more vapor is formed, the slug of liquid is blown up the tube, the tube is filled with vapor, while the liquid continues to vaporize rapidly, the vapor escaping up the tube and, because of friction between the vapor and liquid, the film also is dragged up the tube upto a distance of 5 to 6 metres.

Advantages

  1. Good for thermolabile substances as residence time of the liquid feed is very short i.e. 5-10 sec.

  2. Comparatively high heat transfer rates hence good for viscous solutions.

  3. Higher surface area and hence higher heat transfer rate.

  4. Mixture of liquid and vapor enters the separator at a very high speed which improves separation efficiency, particularly helpful for foaming substances.

  5. High velocity decreases scale formations inside the tubes.

  6. Relatively economical operation.

Disadvantages:

  1. Lower efficiency compared to the falling film evaporators.

  2. Requires more driving force.

  3. Needs larger space.

  4. Purchase cost is higher.

  5. Difficult to clean and maintain.

  6. Maintaining feed rate is critical for effective evaporation.

Applications:

  1. In Industry used as,

    1. Reboiler for distillation.

    2. Pre-concentrators.

    3. Pre-heaters to remove volatile components.

Commonly Asked Questions.

  1. Define evaporation and write a short note on “Climbing Film Evaporators”.

  2. With help of a well labelled diagram, describe construction and working of “Climbing Film Evaporators”.
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