Chemical Engineering Thermodynamics Intro

Chemical Engineering Thermodynamics - Introduction

• Thermodynamics governs the relationships between heat and energy forms.
• Chemical Engineering Thermodynamics applies these principles to chemical and physical processes.

Dimensions and Units

• Dimensions are fundamental concepts like mass (M), length (L), time (t), and temperature (T).
• Units express dimensions, such as grams (g) for mass and centimeters (cm) for length.
• The SI System uses meter, kilogram, second, ampere, Kelvin, candela, and mole.
• Derived Units come from basic units, like Newton ($N = kg \cdot m/s^2$) and Pascal ($Pa = N/m^2$).

Measures of Amount or Size

• Mass (m) is the quantity of matter.
• Volume (V) is the space occupied.
• A mole (mol) is the amount of substance with as many elementary entities as atoms in 0.012 kg of carbon-12.

Force

• From Newton's Second Law: $F = ma$, where F is force, m is mass, and a is acceleration.
• Weight is the force exerted on an object due to gravity ($g \approx 9.8 m/s^2$).

Temperature

• Celsius scale uses water's freezing (0°C) and boiling (100°C) points.
• Kelvin scale: Absolute with 0 K as absolute zero; $T(K) = t(°C) + 273.15$.
• Rankine scale: Absolute in the English system; $T(°R) = t(°F) + 459.67$.
• Fahrenheit scale: $T(°F) = 1.8t(°C) + 32$.

Pressure

• Defined as force per unit area, or $P = F/A$.
• Units include Pascals (Pa), bars, atmospheres (atm), psi.
• Atmospheric Pressure: Pressure exerted by the atmosphere.
• Gauge Pressure: Pressure relative to atmospheric pressure.
• Absolute Pressure: Total pressure, including atmospheric pressure.

Work

• Energy transferred when a force acts through a distance.
• Mechanical Work: $W = F \cdot d$, where F is force and d is distance.
• PV Work: Work done by expansion or compression of a system; $W = \int P dV$.

Energy

• Kinetic Energy (KE): Energy due to motion; $KE = \frac{1}{2}mv^2$.
• Potential Energy (PE): Energy due to position; $PE = mgh$.
• Internal Energy (U): Energy associated with the molecular structure and activity of a system.
• Total Energy (E): Sum of kinetic, potential, and internal energies; $E = KE + PE + U$.

Heat

• Energy transferred due to temperature difference.
• Units are Joules (J), calories (cal).
• Specific Heat Capacity (c): Heat required to raise the temperature of a unit mass by one degree.
• Heat Transfer: Energy in transit due to a temperature difference.

State Postulate

• Simple Compressible System: Completely specified by two independent, intensive properties.
• The state of a simple compressible system is completely defined by two independent, intensive properties.

Equilibrium

• Thermodynamic Equilibrium: Uniform properties that do not change with time; thermal, mechanical, phase, and chemical equilibrium.

Phase Rule

• Gibbs Phase Rule: $F = 2 - \pi + N$, where F is the degrees of freedom, $\pi$ is the number of phases, and N is the number of chemical species.
• Degrees of Freedom: Number of intensive variables that can be independently varied without changing the number of phases.

Reversible Process

• Can be reversed without leaving any trace on the surroundings.
• Infinitesimally slow, involving a series of equilibrium states.
• Serves as an idealization for thermodynamic analysis.

Constant Processes

• Constant-Volume Process (Isochoric): Volume remains constant; $W = 0$.
• Constant-Pressure Process (Isobaric): Pressure remains constant; $W = P\Delta V$.

Enthalpy

• Thermodynamic property defined as $H = U + PV$.
• Useful for analyzing constant-pressure processes.
• Units are Joules (J).

Heat Capacity

• The amount of heat required to change a substance's temperature by one degree.
• Specific Heat at Constant Volume ($C_v$): $(\frac{\partial U}{\partial T})_v$
• Specific Heat at Constant Pressure ($C_p$): $(\frac{\partial H}{\partial T})_p$
• Relationship: $C_p = C_v + R$ (for ideal gases).

Process Equipment

• Facilitates chemical and physical processes.
• Examples of equipment: Heat exchangers, reactors, distillation columns, pumps, compressors, turbines.

Thermodynamics and Conservation Laws

• Conservation of Mass: Mass is neither created nor destroyed.
• Conservation of Energy (First Law): Energy is neither created nor destroyed; it can only be converted; $\Delta U = Q - W$.
• Second Law: The total entropy of an isolated system can only increase or remain constant, reaching a maximum at equilibrium.
• Third Law: The entropy of a perfect crystal at absolute zero temperature is zero.

Engineering Problem Solving

• Steps: Define the problem, gather information, develop a plan, execute the plan, evaluate the solution.

Computer Programs

• Software for thermodynamic calculations and simulations.
• Examples: Aspen Plus, CHEMCAD, MATLAB.
• Applications: Process design, optimization, and analysis.

Pricing Strategies - Price

• Price: amount charged for a product/service.
• Customer gives up value to gain the benefits.
• Price = Value

Pricing Strategies - Factors to Consider

• Customer Perceptions of Value
  • Price ceiling: No demand above this price.
  • Value-based pricing.
• Product Costs
  • Price floor: No profits below this price.
  • Cost-based pricing.
• Other Internal and External Considerations
  • Marketing strategy, objectives, and mix.
  • Nature of the market and demand.
  • Competitors' strategies and prices.

Customer Value-Based Pricing

• Includes good-value pricing and value-added pricing.

Cost-Based Pricing

• Types of Costs: Fixed, variable, and total costs;
• Cost-Plus Pricing: Adding a standard markup to the cost of the product.
• Break-Even Pricing: setting price to break even on costs of making/marketing a product or to make a target profit.

Competition-Based Pricing

• Includes going-rate pricing and sealed-bid pricing.

Other Considerations

• Overall Marketing Strategy, Objectives, and Mix
  • Pricing plays a role in: survival, current profit maximization, market share/product quality leadership.
• Organizational Considerations
  • Small companies: Prices set by top management.
  • Large companies: Handle pricing by divisional or product managers.

The Market and Demand

• Pricing depends on market types such as: pure competition, monopolistic, oligopolistic, or pure monopoly.
• Analyze price-demand relationships via the demand curve and price elasticity of demand.

The Economy

• Economic conditions can impact a firm's pricing strategies.
• Relevant Factors: Boom/recession, inflation, interest rates

New Product Pricing Strategies

• Price skimming and market-penetration pricing.

Product Mix Pricing Strategies

• Includes product line pricing, optional-product, captive-product, by-product, and product bundle pricing.

Price Adjustment Strategies

• Discount/allowance pricing, segmented pricing, psychological pricing, promotional pricing, geographical pricing, dynamic pricing, and international pricing.

Price Changes

• Initiating Price Cuts: Excess capacity, falling demand, to dominate market.
• Initiating Price Increases: Cost inflation, excess demand.
• Consider buyer and competitor reactions to price changes.

Public Policy and Pricing

• Pricing within Channel Levels: price-fixing, predatory pricing.
• Pricing across Channel Levels: deceptive pricing, price discrimination, price maintenance.

Heat Transfer - Modes of Heat Transfer

• Conduction: Heat transfer in a solid or stationary fluid due to a temperature gradient.
  • Fourier's Law: $q'' = -k\frac{dT}{dx}$.
• Convection: Heat transfer between a surface and a moving fluid due to a temperature difference.
  • Newton's Law of Cooling: $q'' = h(T_s - T_{\infty})$.
• Radiation: Net heat transfer between two surfaces due to electromagnetic waves.
  • Stefan-Boltzmann Law: $q'' = \epsilon \sigma (T_s^4 - T_{surr}^4)$.

Heat Transfer - Thermal Resistance

• Conduction Resistance: $R_{cond} = \frac{L}{kA}$
• Convection Resistance: $R_{conv} = \frac{1}{hA}$
• Radiation Resistance: $R_{rad} = \frac{1}{h_{rad}A}$;
  • where $h_{rad} = \epsilon \sigma (T_s + T_{surr})(T_s^2 + T_{surr}^2)$
• Total Resistance:
  • For series resistances: $R_{total} = R_1 + R_2 + R_3 +...$
  • For parallel resistances: $\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} +...$

Heat Transfer Rate

• $q = \frac{T_1 - T_2}{R_{total}}$

Heat Transfer - Fin Efficiency

• $\eta_{fin} = \frac{q_{actual}}{q_{max}}$
  • $q_{max} = hA_{fin}(T_b - T_{\infty})$

Heat Transfer - Overall Heat Transfer Coefficient

• $U = \frac{1}{A R_{total}}$