GPAT Pharmaceutical Engineering Flashcards

24 sample cards from the Pharmaceutical Engineering deck

Sampled from the end of the deck, so these are different cards from the ones shown on the syllabus page.

1. Distinguish Newtonian from non-Newtonian fluids with examples.

   Newtonian fluids have viscosity independent of shear rate (water, glycerin, dilute solutions). Non-Newtonian fluids have shear-dependent viscosity - e.g., pseudoplastic (shear-thinning, like methylcellulose gels), dilatant (shear-thickening), and Bingham plastic (toothpaste).

2. State Reynolds number, its formula, and the laminar/turbulent transition values for pipe flow.

   Re = D v rho / eta (diameter x velocity x density / viscosity); dimensionless ratio of inertial to viscous forces. In pipes: laminar Re < 2000, transitional 2000-4000, turbulent Re > 4000.

3. State Bernoulli's principle for fluid flow.

   For an ideal incompressible fluid in steady flow, the total mechanical energy is conserved: P/rho + v^2/2 + g*z = constant (pressure energy + kinetic energy + potential energy). Where velocity increases, pressure decreases.

4. Name two devices that measure fluid flow rate based on Bernoulli's principle.

   The venturi meter and the orifice meter - both create a constriction; the pressure drop across it is related to flow rate. (A rotameter is a variable-area flow meter; a pitot tube measures velocity.)

5. What are the three modes of heat transfer, and which dominates in a steam-jacketed kettle heating a liquid?

   Conduction, convection and radiation. In a steam-jacketed kettle, conduction through the vessel wall and convection within the liquid dominate (radiation is negligible).

6. State Fourier's law of heat conduction.

   Q = -k A (dT/dx): the rate of heat conduction is proportional to the thermal conductivity k, the area A, and the temperature gradient, and flows from hot to cold (negative sign).

7. Give the basic equation for heat transfer in an exchanger and define the overall coefficient.

   Q = U A delta-T_lm, where U is the overall heat-transfer coefficient, A the heat-transfer area, and delta-T_lm the log mean temperature difference between the two fluids.

8. Why are heat-sensitive pharmaceutical fluids often heated in plate or scraped-surface exchangers?

   They give high heat-transfer coefficients with short residence times and good temperature control; scraped-surface units also handle viscous/fouling products, minimising thermal damage to thermolabile materials.

9. Define filtration and the two main mechanisms by which a filter retains particles.

   Filtration separates suspended solids from a fluid by passing it through a porous medium. Mechanisms: surface (screen/sieve) filtration - particles larger than pores retained on surface; and depth filtration - particles trapped within the tortuous channels of a thick medium.

10. State the simplified Darcy/filtration principle relating flow rate to pressure.

    Filtration rate is directly proportional to the pressure difference and filter area, and inversely proportional to the fluid viscosity and the resistance of the cake plus medium (dV/dt = (delta-P x A) / (eta x R)).

11. What is centrifugation and the principle behind it?

    Centrifugation separates particles from a liquid (or two liquids) using centrifugal force generated by rapid rotation, which greatly increases the effective gravitational settling per Stokes' law, accelerating sedimentation by density difference.

12. Differentiate a sedimentation centrifuge from a filtration (perforated) centrifuge.

    A sedimentation centrifuge has a solid-walled bowl; solids settle against the wall and supernatant decants (for fine particles/clarification). A filtration centrifuge has a perforated basket lined with filter cloth; liquid passes through and solids are retained as a cake (for coarse crystals, e.g., centrifuge for crystal washing).

13. Define absolute humidity and relative humidity.

    Absolute humidity = mass of water vapour per unit mass of dry air. Relative humidity (RH) = ratio of actual water-vapour partial pressure to the saturation vapour pressure at that temperature, expressed as a percentage.

14. Why is humidity control critical in pharmaceutical manufacturing?

    Humidity affects powder flow and caking, tablet/capsule moisture uptake, drug stability (hydrolysis), microbial growth, electrostatic charge, and effervescent/hygroscopic product integrity; controlled RH ensures product quality and reproducibility.

15. What is dew point and what does it indicate?

    Dew point is the temperature to which air must be cooled (at constant pressure) for water vapour to begin condensing (saturation, 100% RH). A lower dew point indicates drier air; it is a key measure in cleanroom and drying-air control.

16. What instrument measures humidity, and name a method used in pharmaceutical area monitoring.

    A hygrometer measures humidity; the psychrometer (wet-and-dry bulb thermometer) determines RH from the wet-bulb depression using a psychrometric chart. Electronic capacitive/dew-point sensors are used for continuous HVAC monitoring.

17. What is the basic principle of the vapour-compression refrigeration cycle?

    A refrigerant is compressed (compressor), condensed releasing heat (condenser), expanded through a throttle valve (pressure/temperature drop), and evaporated absorbing heat from the load (evaporator). It transfers heat from a low- to a high-temperature region using latent heat of the refrigerant.

18. Define 'ton of refrigeration' and coefficient of performance (COP).

    One ton of refrigeration = rate of heat removal to freeze 1 short ton of water at 0 C in 24 h (about 3.517 kW). COP = useful refrigerating effect / work input; a higher COP means a more efficient system.

19. What are the main functions of an HVAC (air-conditioning) system in a pharmaceutical facility?

    It controls temperature, humidity, air cleanliness (filtration), room pressure differentials, and air-change rates to maintain cleanroom classification, prevent cross-contamination, and ensure product/personnel comfort and GMP compliance.

20. What type of filter is used in pharmaceutical HVAC to achieve cleanroom air quality, and what is its efficiency?

    HEPA (High Efficiency Particulate Air) filters, which remove >= 99.97% of particles of 0.3 micrometre, are used in the supply air to clean rooms (ULPA filters give even higher efficiency for critical zones).

21. How do positive and negative room pressure differentials protect pharmaceutical products?

    Positive pressure (room higher than surroundings) keeps contaminants out, protecting sterile/non-hazardous products. Negative pressure (room lower) contains hazardous/cytotoxic or sensitising materials, preventing their escape to adjacent areas.

22. What is the difference between batch and continuous operation, with a pharmaceutical example of each?

    Batch: a fixed quantity is processed through each step then discharged before the next batch (e.g., a fluidised bed dryer load, a reaction in a stirred kettle). Continuous: material flows in and product flows out steadily (e.g., continuous tablet manufacturing line, continuous distillation column).

23. Why is copper traditionally used for stills and tubing in some pharmaceutical/water systems despite stainless steel's dominance?

    Copper has excellent thermal conductivity (good heat transfer) and is easily fabricated; it was traditionally used for stills and heating coils. However, it can contaminate products with copper ions and corrodes, so stainless steel has largely replaced it for product contact.

24. What is the heat-transfer significance of the log mean temperature difference (LMTD) versus arithmetic mean in exchangers?

    Because the temperature difference between the two fluids varies along the exchanger, the LMTD = (delta-T1 - delta-T2)/ln(delta-T1/delta-T2) gives the correct driving force; using a simple arithmetic mean overestimates the driving force and undersizes the exchanger.

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