Simple Pharmanotes

  Principle: Vacuum drying is generally used for the drying of substances which are hygroscopic and heat sensitive, and is based on the principle of creating a vacuum to decrease the chamber pressure below the vapor pressure of the water, causing it to boil.  Hence, water evaporates faster, and the rate of drying increases. Construction: The oven is divided into hollow trays which increases the surface area for heat conduction. The oven door is locked airtight and is connected to a vacuum pump to reduce the pressure. The materials to be dried are kept on the trays inside the vacuum dryer and pressure is reduced by means of vacuum pump. The enclosed space ( approximately 1.5 meter cube ) is divided in to a number of portions by means of 20 hollow shelves, which are part of the jacket.  These shelves provide a larger surface area ( about 45 to 50 meter square ) for conduction of heat.  Over the shelves, metal trays are placed for keeping the material.  The oven door can be locked tightly

  Principle: Silverson mixer emulsifiers produce intense shearing force and turbulence by the use of high-speed rotors.  This turbulence causes the liquids to pass through fine space formed by closely placed perforated metal sheets.  Circulation of material takes place through the head by the suction produced in the inlet at the bottom of the head.  Circulation of the material ensures the rapid breakdown of the dispersed liquid into smaller globules. Construction:   It consists of long supporting columns connected to a motor that gives support to the head.  The central portion contains a shaft, one end of which is connected to the motor and the other end is connected to the head.  The head carries turbine blades.  The blades are surrounded by a mesh, which is further enclosed by a cover having openings. Working: The emulsifier head is placed in the vessel containing immiscible liquids (or coarse emulsion) in such a way that it should get completely dipped in the liquid.  When the mot

  Principle of FBD: The equipment works on a principle of fluidization of the feed materials.  In the fluidization process, hot air is introduced at high pressure through a perforated bed of moist solid particulate.  The wet solids are lifted from the bottom and suspended in a stream of air (fluidized state) Construction of FBD: The dryer is made up of stainless steel or plastic. A detachable bowel is placed at the bottom of the dryer, which is used for charging and discharging. The bowel has a perforated bottom with a wire mesh support for placing materials to be dried. A fan is mounted in the upper part for circulating hot air. Fresh air inlet, prefilter and heat exchanger are connected serially to heat the air to the required temperature. The temperature of hot air and exit air are monitored. Bag filters are placed above the drying bowl for the recovery of fines. Working: The wet granules to be dried are placed in a detachable bowl. The bowl is inserted in the drier. Fresh air can p

  Meta Filter: Principle: Mechanism is surface filtration. In this, metal rings contain semicircular projections, which are arranged as a nest to form channels on the edges. This channel offers resistance (strainer) to the flow of solids (coarse particles). The clear liquid is collected into the receiver from the top.  Construction: Metafilter consists of a series of metal rings. These are threaded so that a channel is formed on the edges. It contains a grooved drainage column on which a series of metal rings are packed. These rings are usually made up of stainless steel and have dimensions of about 15.0 mm internal diameter and 22.0 mm external diameter . Each metal ring has a number of semicircular projections (0.8 mm in thickness) on one side of the surface. The projections are arranged as a nest to form channels on the edges. These rings are tightened on the drainage column with a nut. Meta Filters are also known as edge filters .  Working: Filters are placed in a vessel Slurry is

  Filter Leaf: Principle: It is an apparatus consisting of a longitudinal drainage screen covered with a filter cloth. The mechanism is surface filtration and acts as a sieve or strainer. Vacuum or pressure can be applied to increase the rate of filtration Construction: The leaf filter consists of a frame enclosing a drainage screen or grooved plate. The frame may be any shape circular, square or rectangular. The whole unit is covered with filter cloth. The outlet for the filtrate connects to the inside of the frame through suction.  Working: The filter leaf is immersed in the slurry. Vacuum system is connected to the outlet. The slurry passes through the filter cloth. Finally filtrate enters the drainage canal and goes through the outlet into the receiver. Air is passed to flow in reverse direction which facilitates removal of cake  Advantages of filter leaf: Simplest form of filter used for batch process. A number of units can be connected in parallel to increase the surface area of