Skip to main content

Renin Angiotensin Mechanism.

Theory of Filtration.

 

  • The flow of any liquid through any porous medium offers a resistance to its flow. The rate of filtration in such cases is expressed as:

  • Filtration Rate= Driving force/Resistance by filter medium

  • Rate is expressed as the volume of filtrate per unit time (dv/dt) and gets affected by various factors,

  • It can be explained by,

    • Kozeny-Carman Equation.

    • Darcy's Equation.

    • Poisulle’s Equation.

  1. Poisulle’s Equation:

  • Poiseullie considered that filtration is similar to the streamline flow of liquid under pressure through capillaries.

  • Poiseullie's Equation is

  • Where, 

  • V = rate of flow, m³/s (l/s)

  • AP= Pressure difference across the filter, Pa

  • r = radius of capillary in the filter bed, m

  • L = thickness of filter cake (capillary length), m

  • n = viscosity of filtrate, Pa.s

  • If the cake is composed of a bulky mass of particles and the liquid flows through the interstice, then flow of liquids through these may be expressed by this equation.

  1. Darcy’s Equation:

  • Poiseullie's law assumes that the capillaries found in the filter are highly irregular and non-uniform.

  • Therefore, if the length of capillary is taken as the thickness of bed, a correction factor for radius is applied so that the rate is closely approximated and simplified.

  • The factors influencing the rate of filtration has been incorporated into an equation by Darcy, which is:

  • Where, K = permeability coefficient of cake, m² 

  • A= surface area of porous bed (filter medium), m² 

  • Other terms are same as the previous equation.

  • K depends on characteristics of cake, such as porosity, specific surface area and compressibility.

  • Other terms are same as previous equation

  • Permeability may be defined quantitatively as the flow rate of a liquid of unit viscosity across a unit area of cake having unit thickness under a pressure gradient of unity.

  • This equation is valid for liquids flowing through sand, glass beds and various porous media.

  • This model is applied to filter beds or cakes and other types of depth filter.

  • This equation is further modified by including characteristics of K by Kozeny-Carman.

  1. Kozeny-Carman Equation:

  • The Kozeny-Carman equation is widely used for filtration.

  • Where,

  • ε = porosity of cake (bed)

  • S = specific surface area of particles comprising the cake m²/m³

  • K = Kozeny constant (usually taken as 5) Other terms are same as previous equations

  • Limitations:

  • It does not consider the fact that depth of granular bed is lesser than the actual path traversed by the fluid.

  • The actual path is not the same throughout the bed, but it is sinuous or tortuous.

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 ...
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 ...
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...
Read more