Skip to main content

Renin Angiotensin Mechanism.

Tray Dryers.

 

Definition

  • Drying is defined as the removal of liquid from a product usually with application of heat.

  • Equipment used for the purpose of drying are called “Dryers”.

Tray Dryers.

  • Also known as: Shelf dryers, Compartment dryers, Cabinet dryers.

  • Common example is Hot Air Oven.

Principle:

  • It's a static bed dryer where drying takes place by “Forced Convection”.

Construction:

  • It consists of a rectangular double layer stainless steel chamber whose walls are insulated. 

  • Inside layer is mirror polished. 

  • Door has a rubber lining. 

  • Dryers are fitted with a heating device, thermostat, fan and timer. 

  • Stainless steel trays are placed on the shelf of the drying chamber. 

  • Fresh air enters through an inlet, which is through a filter, a heater and a fan. 

  • In the corner of the chamber direction vanes can be placed to direct air in the expected path. 

  • The distance between the bottom of the upper tray and the upper surface of the material loaded in the subsequent tray must be 40 mm. 

  • Trays are usually loaded from 10 to 100 mm deep. 

  • Tray dryers are available in various sizes. 

  • The air with moisture absorbed from the substances leaves the dryer from an outlet as shown in the diagram below.

Working:

  • The material to be dried is placed in thin layers in trays. 

  • Trays are placed in the chamber as air is introduced through the inlet, which passes through the filters and heaters as it becomes hot. 

  • The hot air is circulated by means of fans at 2 to 5 meters per second. 

  • Air flows in the direction of the arrows over each shelf in turn as shown in the above figure. 

  • The moist air is removed through the outlet. 

  • Constant temperature and uniform airflow over the materials can be maintained for achieving uniform drying. 

  • In case of the wet granules, drying is continued until the desired moisture content is obtained. 

  • At the end of operation trays are pulled out of the chamber and the product is collected.

Uses:

  1. Used to dry variety of materials like,

    1. Sticky materials,

    2. Granules.

    3. Crystalline materials.

    4. Crude drugs.

    5. Precipitates.

    6. Some equipment and laboratory glassware.

Advantages:

  1. No loss of material while handling.

  2. Loading and unloading is easy.

  3. Easy to operate.

  4. Good for batch drying.

Disadvantages:

  1. Less efficient: only the surface of the product is exposed to heat.

  2. High labor cost.

  3. Not suitable for large scale drying.

  4. Liquids can not be dried.

  5. Time required is more.

  6. Not suitable for thermolabile substances.

Commonly Asked Questions.

  1. With a well labelled diagram describe construction and working of Tray Dryers.

  2. Write a short note on the Tray Dryer.
Labels:

Popular posts from this blog

Rate of Drying Curve.

  Definition Drying is defined as the removal of liquid from a product usually with application of heat. Rate of Drying Curve. Drying process can be divided into three periods Initial Adjustment Period. Constant drying rate period. First falling drying rate period. Second falling rate period. Initial Adjustment Period (A-B): Also called the “ Heating up” period . In this period the substance gets heat and increases in temperature. Drying has not yet started. Constant drying rate period (B-C): During this period the temperature of the solid and the rate of drying remain constant. The moisture evaporating from the surface is replaced by water diffusing from the interior of the solid at a rate equal t o the rate of evaporation.  The moisture content at the end of constant rate (point C) is referred to as the critical moisture content (CMC).  At CMC, dry spots start appearing and drying rate starts falling . First falling drying rate period (C-D): This period is also called the period of
Read more

Heat Exchangers and Heat Interchangers.

  In pharmaceutical industries many types of equipments are used for transfer of heat, they can be classified as follows, Heat Exchangers. Heat Interchangers. Heat Exchangers: These devices are used for transferring heat from a fluid (Hot Gas or Steam) to another fluid (Liquid) through a metal wall. Heat Interchangers: These devices are used for transferring heat from a One liquid to another liquid or one gas to another gas through a metal wall. HEAT EXCHANGERS; The equipment used for heat transferring are known as heat exchangers. Some of the processes that involves heat transfer in pharmaceutical industries are: Preparation of starch paste (in steam jacketed kettle). Crystallization. Evaporation. Distillation.  Classification of heat exchangers On the basis of transfer of heat, heat exchangers are classified as: Direct transfer type:  The hot and cold fluids are separated by a metal wall through which the heat is transferred from hot fluid to cold fluid. E.g. shell and tube heater, 
Read more

Flash Distillation.

  Principle: When a hot mixture is allowed to enter from a high-pressure zone into a low pressure zone, the entire liquid mixture is suddenly vaporized. This process is known as flash vaporization .  During this process, the chamber is cooled.  The less volatile fraction is condensed and the more volatile component remains in the vapor phase .  This process requires time, hence liquid and vapor are kept in intimate contact until equilibrium is achieved. Flash distillation is also called equilibrium distillation because separation of two liquids takes place when liquid and vapor phases are at equilibrium. Equipment used for Flash Distillation: Construction: It consists of a pump, which is connected to a feed reservoir.  Pumps help in pumping the feed into the heating chamber.  The heating chamber is heat supplied by steam.  The other end of the pipe is directly introduced into the vapor-liquid separator through a reducing valve.  The vapor outlet is provided at the top of the separato
Read more