Chemical Engineering

Full Answer Section

• Laminar flow is characterized by fluid particles moving along smooth, parallel layers with minimal mixing between them. It typically occurs at lower velocities. Turbulent flow, on the other hand, is characterized by chaotic and random movement of fluid particles, leading to significant mixing. It typically occurs at higher velocities. The Reynolds number is used to predict whether a flow will be laminar or turbulent.

• Raoult's Law is used to determine the vapor pressure of an ideal solution. Specifically, it states that the partial pressure of a component in the vapor phase above an ideal solution is equal to the mole fraction of that component in the solution multiplied by the vapor pressure of the pure component at the same temperature. Mathematically: Pi​=xi​Pi∗​ where:  

  • Pi​ is the partial pressure of component $i$ in the vapor phase
  • xi​ is the mole fraction of component $i$ in the liquid phase
  • Pi∗​ is the vapor pressure of pure component $i$ at the given temperature

• A commonly used unit to measure viscosity is the Pascal-second (Pa·s) in the SI system. Another common unit, particularly in older literature and some industries, is the centipoise (cP), where 1 cP = 0.001 Pa·s.

• The primary purpose of a distillation column is to separate components of a liquid mixture based on their differences in boiling points (volatility). By repeatedly vaporizing and condensing the mixture along the height of the column, the more volatile components are concentrated in the vapor phase at the top, while the less volatile components are concentrated in the liquid phase at the bottom.

• One example of a unit operation in chemical engineering is distillation. Other examples include filtration, evaporation, mixing, reaction, and heat exchange.

• A heat exchanger is used for the transfer of thermal energy (heat) between two or more fluids at different temperatures. This can be for the purpose of heating one fluid and cooling another, or for recovering heat from a process stream.

• Residence time in a reactor refers to the average amount of time a fluid element spends inside the reactor. It is an important parameter for determining the extent of reaction that occurs within the reactor. For a continuous flow reactor, it is often defined as the volume of the reactor divided by the volumetric flow rate of the fluid entering the reactor.

• The term enthalpy ($H$) refers to a thermodynamic property of a system that represents the total heat content of the system at constant pressure. It is defined as the sum of the internal energy ($U$) of the system and the product of its pressure ($P$) and volume ($V$): $$H=U+PV$$ Changes in enthalpy ($\Delta H$) are particularly important in chemical reactions as they indicate the heat absorbed or released at constant pressure.

• The role of a catalyst in a chemical reaction is to increase the rate of the reaction without being consumed in the overall process. Catalysts achieve this by providing an alternative reaction pathway with a lower activation energy.

• One common method for separating solid particles from a liquid is filtration. This involves passing the liquid through a porous medium that retains the solid particles while allowing the liquid to pass through.

• The main function of a packed bed reactor is to facilitate chemical reactions by passing a fluid (gas or liquid) through a stationary bed of solid catalyst particles. The large surface area of the catalyst packing promotes contact between the reactants and the catalyst, leading to higher reaction rates.

• The compressibility factor ($Z$) in the context of real gases is a dimensionless quantity that quantifies the deviation of a real gas from ideal gas behavior. It is defined as the ratio of the actual molar volume of a gas to the molar volume predicted by the ideal gas law at the same temperature and pressure: Z=nRTPV​ For an ideal gas, $Z=1$. Deviations from unity indicate non-ideal behavior due to intermolecular forces and the finite volume of gas molecules.  

• Batch processing involves carrying out a process in discrete steps or batches. A fixed amount of reactants is loaded into a vessel, the reaction or separation occurs, and then the products are removed before the next batch is processed. Continuous processing, on the other hand, involves a continuous flow of materials through the system. Reactants are continuously fed into the system, and products are continuously withdrawn, allowing for steady-state operation and often higher production rates.

Sample Answer

Here are the answers to your chemical engineering questions:

1. The ideal gas law equation is: PV=nRT​ where:

   • $P$ is the pressure
   • $V$ is the volume
   • $n$ is the number of moles
   • $R$ is the ideal gas constant
   • $T$ is the absolute temperature

2. Mass transfer is the net movement of mass from one location, usually meaning a stream, phase, fraction or component, to another. Mass transfer occurs when there is a concentration gradient of a species within a system.