Unit Operations and Powder Technology 2023 PDF

Unit Operations and Powder Technology Pharmaceutics IV PH 311 Dr. Alaa Elnima 2023  content Unite processes: Powder Technology: – Fluid mechanics. – Particle size reduction – Heat trans...

Unit Operations and Powder Technology Pharmaceutics IV PH 311 Dr. Alaa Elnima 2023  content Unite processes: Powder Technology: – Fluid mechanics. – Particle size reduction – Heat transfer. and importance. – Mass transfer. – Characteristics of – Evaporation. powders. – Drying. – Fluidization of powder. – Separation techniques. – Mixing of powders. – Mixing. – Powder as a dosage form. – Centrifugation. – Polymerization.  Fluid Mechanics Introduction Study the behaviour of fluids (i.e. liquids & gases). Why it matters in pharmacy? – Manufacture of drug formulations. – Designing of drug delivery systems (IV & inhalers). – Drug dissolution. – Quality control. – Pharmacokinetics of drugs.  Fluid flow concept A fluid is a substance, that continuously deforms (flow) under an applied shear stress. Include liquids or gases. Fluid flow refer to the continuous and directed motion of a fluid, inside either a restricted or an unrestricted area. Usually from high to low pressure.  Types of fluid flow A B Gas ǀ PA = Patm PB ǁǀ ꓦ Velocity, µ µ ǁ ǀ Liquid ǁ ǀ Pressure difference, PA - PB  Fluid flow patterns 1. Laminar incompressible flow; flow velocity is proportional to pressure drop. 2. Turbulent incompressible flow; pressure drop to 50% of initial pressure. 3. Compressible flow; the pressure change is large, the volume and density of the fluid is changing as it flows. For gases only. 4. Choking flow; gases flowing at speed of sound, flow velocity independent of pressure difference.  Laminar Flow Streamline flow or viscous flow. Is characterised by the smooth, orderly movement of fluid in parallel layers. Fluid particles move in layers with one layer sliding with other. No exchange of fluid particles between layers. Low velocity and high viscosity.  Turbulent Flow Is wild and complex. Paths of individual fluid particles are erratic and inter- crossing. Velocity vectors at different directions, the average motion in one direction. Characterised by high velocity and low viscosity.  Reylond's number In 1880s by Osborne Reynolds. At low flow rate, the dye filament remained unbroken as it flowed along with the water, indicating laminar flow. At higher flow rates, the flow became turbulent such that the dye filament began to oscillate and eventually broke up into eddies which dispersed the dye right across the tube.  The nature of flow depends on: – The density ρ – The viscosity µ – The pipe Diameter D – average velocity through the pipe ū Larger pipes, faster velocities and greater densities tend to give more inertia to the flow and make it turbulent, while small pipes, slow flow and high viscosities tend to give laminar flows. Arranged those factors in a relation; – Re = Dūρ/ µ – Reynolds number , Re, is a dimensionless number.  Based on his study, found that Reynolds number is: – the ratio between inertial forces (ρ), and viscous forces (µ). – Re < 2100 is laminar flow, the viscous forces dominate leading to highly organised and predictable fluid motion. – 2100 < Re < 10000, the flow is transitional between laminar and turbulent, – Re > 10, 000 is turbulent flow, the inertial forces dominate, leading to unsteady, chaotic fluid motion. Fluid Mechanics PART 2  Velocity profiles The overall average velocity is constant. The velocity along the centre of the pipe is likely to be higher than that near the walls of the pipe. So velocity depends on the radial position within the pipe, and across the pipe there is a velocity profile. The shear experienced by the fluid at the wall is transmitted through the fluid, resulting in formation of a velocity gradient, with fluid in the centre moving at the highest velocity, then continuously decrease towards the wall.  Re number is proportional to fluid velocity. Moving towards the wall, Re decrease, the flow changes from turbulent to transitional to laminar to ultimately stationary at the wall. Boundary layer is a layer of more or less stationary fluid immediately surrounding an immersed object in relative motion with the fluid. Within this layer, the fluid velocity increases from zero at the wall to the free stream velocity away from the wall.  Boundary layer Reynolds number provides a crucial mathematical tip- off about the expected boundary layer nature. The free stream velocity, kinematic viscosity and the length from the leading edge of the body to the point of interest affect the Re for the boundary layer. Also, mathematical calculation to predict the thickness. Major role in computational fluid dynamics (CFD), that enables the numerical prediction of fluid flow and heat transfer.  In laminar flow, the velocity profile is the same at any cross section of the pipe. The laminar flow average velocity ū is: – directly proportional to the pressure drop. – inversely proportional to the viscosity. – inversely to the pipe length. – proportional to the pipe diameter to the fourth power.  Laminar flow applications Laminar flow equipment such as laminar flow hoods, bio- safety cabinets, and chemical fume hoods minimize the risk of contamination to the worker and the products such as a hazardous drug, infectious particles, bacteria, viruses or cellular organisms.  Turbulent flow applications Turbulent mixers. Bioanalytical separation; Turbulent flow chromatography (TFC) is a widely used on-line sample preparation technique for the LC–MS analysis of biological samples. Depend on mass separation as a consequence of the turbulent flow. Purified water system, minimise the formation of biofilm.  Summary Laminar flow refers to the smooth and orderly flow of a fluid. Turbulent flow, in contrast, is chaotic and disordered. Is influenced by the Reynolds number - a dimensionless parameter that predicts changes in fluid behaviour. For a Reynolds number (Re) < 2000, the viscous forces dominate. The turbulent flow occurs at higher Reynolds numbers, specifically > 4000. Laminar flow the velocity is constant across the pipe while in turbulent flow, a velocity gradient developed across the pipe. QUIZ QUESTIONS  What is the difference between laminar flow and turbulent flow? a) Laminar Flow is characterized by chaotic movement of fluid particles, while Turbulent Flow describes layers of fluid gliding smoothly past each other. b) Laminar Flow, often referred to as streamline flow, is characterized by layered fluid motion, with each layer gliding smoothly past its neighbouring layers without mixing. On the other hand, Turbulent Flow denotes chaotic and haphazard movement of fluid particles in all directions, making the flow highly unpredictable. c) Laminar Flow refers to the speed of the fluid, while Turbulent Flow describes the direction in which the fluid is moving  Laminar or Turbulent flow? 1. pouring honey or thick syrup from a jar. 2. fast-moving rivers and streams. 3. blood flow in larger arteries. 4. Air flow in operating theatres. 5. Mixing of chemical substances to obtain homogenous mixture.  Discuss What is the best type of flow in pharmaceutical industry? Laminar or Turbulent? Why?