Chapter 2: A Review of Thermal Sciences (40 Slides)

Chapter 2

Slide 1: Introduction to Thermal Sciences

  • Overview: Importance in analyzing renewable energy systems.
  • Key Areas: Thermodynamics, heat transfer, fluid mechanics.

Slide 2: Thermodynamics Basics

  • Definition: Study of energy transformations.
  • Key Concepts: System, surroundings, and boundary.

Slide 3: Forms of Energy

  • Types: Kinetic, potential, internal, thermal, and chemical energy.
  • Energy Conversion: Examples in renewable energy systems.

Slide 4: First Law of Thermodynamics

  • Statement: Energy cannot be created or destroyed.
  • Equation: (\Delta U = Q - W).
  • Example: Energy balance in a solar collector.

Slide 5: Energy Balance for Closed Systems

  • Closed System: No mass transfer.
  • Energy Balance Equation: Detailed breakdown.

Slide 6: Energy Balance for Open Systems

  • Open System: Allows mass transfer.
  • Examples: Wind turbines, geothermal power plants.

Slide 7: Specific Heat and Heat Capacity

  • Definition: Amount of heat required to change temperature.
  • Applications: Design of solar thermal systems.

Slide 8: Second Law of Thermodynamics

  • Concept of Entropy: Measure of disorder.
  • Applications: Efficiency limits of heat engines.

Slide 9: Heat Transfer Overview

  • Methods: Conduction, convection, and radiation.
  • Examples in Renewable Systems.

Slide 10: Conduction Heat Transfer

  • Fourier’s Law: ( q = -k \frac{\Delta T}{\Delta x} ).
  • Example: Insulation in solar panels.

Slide 11: Convection Heat Transfer

  • Newton’s Law of Cooling: ( q = h A \Delta T ).
  • Applications: Heat dissipation in wind turbine blades.

Slide 12: Radiation Heat Transfer

  • Stefan-Boltzmann Law: ( q = \sigma \epsilon A (T^4 - T_s^4) ).
  • Example: Solar radiation absorption by PV cells.

Slide 13: Fluid Mechanics in Renewable Energy

  • Overview: Study of fluid flow in energy systems.
  • Key Parameters: Velocity, pressure, and viscosity.

Slide 14: Bernoulli’s Equation

  • Equation: ( P + \frac{1}{2} \rho v^2 + \rho gh = \text{constant} ).
  • Example: Airflow analysis in wind turbines.

Slide 15: Viscosity and Flow Types

  • Laminar vs. Turbulent Flow: Characteristics and examples.
  • Impact on Efficiency: Fluid flow in geothermal systems.

Slide 16: Pressure Drop in Pipes

  • Darcy-Weisbach Equation: ( \Delta P = f \frac{L}{D} \frac{\rho v^2}{2} ).
  • Applications: Design of hydropower plants.

Slide 17: Heat Exchangers in Renewable Systems

  • Types: Counter-flow, parallel flow.
  • Application: Geothermal heat exchangers.

Slide 18: Heat Transfer in Solar Collectors

  • Flat-Plate Collectors: Mechanisms of heat transfer.
  • Design Considerations: Maximizing efficiency.

Slide 19: Thermal Efficiency of Power Plants

  • Definition: Ratio of work output to heat input.
  • Example: Efficiency calculation of a geothermal power plant.

Slide 20: Heat Engines and Cycles

  • Carnot Cycle: Idealized heat engine cycle.
  • Real-World Applications: Steam turbines in biomass plants.

Slide 21: Heat Transfer in Photovoltaic Cells

  • Heat Generation in PV Cells: Efficiency drops with temperature.
  • Cooling Techniques: Passive cooling and active cooling methods.
  • Impact on Efficiency: Importance of maintaining optimal operating temperature.

Slide 22: Energy Transfer in Wind Turbines

  • Betz Limit: Maximum theoretical efficiency of wind turbines.
  • Equation: ( Cp = \frac{P{out}}{0.5 \rho A v^3} ).
  • Example Calculation: Power output for a given wind speed.

Slide 23: Fluid Flow Around Wind Turbine Blades

  • Airfoil Design: Importance of lift-to-drag ratio.
  • Reynolds Number: Effect on laminar and turbulent flow.
  • Visualization: Diagram showing flow patterns around blades.

Slide 24: Thermodynamics of Biomass Combustion

  • Combustion Reaction: ( \text{C}6\text{H}{10}\text{O}_5 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{Heat} ).
  • Enthalpy of Combustion: Calculation using enthalpy tables.
  • Applications: Heat generation in biomass power plants.

Slide 25: Energy Balance in Geothermal Heat Pumps

  • Heat Transfer Equation: ( Q = m \dot{c}_p \Delta T ).
  • Coefficient of Performance (COP):
    • Heating Mode: ( \text{COP}{heating} = \frac{Q{out}}{W_{in}} ).
    • Cooling Mode: ( \text{COP}{cooling} = \frac{Q{in}}{W_{in}} ).
  • Example: COP calculation for a ground-source heat pump.

Slide 26: Analyzing Solar Thermal Power Systems

  • Working Fluid: Role of heat transfer fluids (e.g., molten salts).
  • Parabolic Trough Collector: Concentration of solar energy.
  • Energy Efficiency: Factors affecting the performance.

Slide 27: Understanding Heat Exchanger Design

  • Log Mean Temperature Difference (LMTD):
    • Equation: ( \Delta T_{lm} = \frac{\Delta T_1 - \Delta T_2}{\ln(\Delta T_1 / \Delta T_2)} ).
  • Application: Geothermal heat exchangers.
  • Example Calculation: Heat transfer rate.

Slide 28: Heat Transfer in Solar Ponds

  • Definition: Solar ponds use salt gradient to store thermal energy.
  • Heat Transfer Mechanism: Conduction and convection.
  • Efficiency Considerations: Design for maximum heat retention.

Slide 29: Specific Heat Capacities of Renewable Fuels

  • Definition: Heat required to raise the temperature of a substance.
  • Examples: Specific heat values for water, ethanol, and biodiesel.
  • Importance: Role in designing energy storage systems.

Slide 30: Fluid Dynamics in Hydropower Systems

  • Continuity Equation: ( A_1v_1 = A_2v_2 ).
  • Bernoulli's Principle: Energy conservation in fluid flow.
  • Application: Water flow through turbines.

Slide 31: Convection Heat Transfer in Solar Water Heaters

  • Free vs. Forced Convection: Differences and applications.
  • Nusselt Number: ( \text{Nu} = \frac{hL}{k} ).
  • Example: Heat transfer in a solar water heater.

Slide 32: Thermal Conductivity of Insulation Materials

  • Importance: Reducing heat losses in renewable energy systems.
  • Equation: ( q = \frac{kA \Delta T}{d} ).
  • Example: Selecting insulation for geothermal pipes.

Slide 33: Radiation Losses in Solar Energy Systems

  • Emissivity: Surface property affecting radiation.
  • Equation: ( q_{rad} = \sigma \epsilon A (T^4 - T_s^4) ).
  • Example: Radiative losses from a solar panel.

Slide 34: Thermodynamic Cycles in Renewable Energy

  • Rankine Cycle: Common in biomass and geothermal plants.
  • Brayton Cycle: Applications in concentrated solar power (CSP).
  • Efficiency Calculations: Comparing different cycles.

Slide 35: Heat Transfer Optimization in Heat Exchangers

  • Effectiveness-NTU Method:
    • Effectiveness: ( \epsilon = \frac{Q{actual}}{Q{max}} ).
  • Example: Sizing a heat exchanger for a geothermal system.

Slide 36: Energy Storage in Renewable Systems

  • Thermal Energy Storage (TES): Storing heat in molten salts, water.
  • Phase Change Materials (PCMs): Using latent heat for energy storage.
  • Example: Solar energy storage using molten salt.

Slide 37: Calculating Work in Renewable Systems

  • Work Done by Turbines: ( W = \dot{m} \cdot (h_1 - h_2) ).
  • Applications: Wind turbines, hydroelectric generators.
  • Example: Calculating work output of a wind turbine.

Slide 38: Heat Losses in Renewable Systems

  • Sources of Losses: Conduction, convection, and radiation.
  • Minimizing Losses: Design considerations.
  • Example: Reducing heat loss in solar thermal systems.

Slide 39: Overview of Geothermal Power Plant Efficiency

  • Energy Extraction: Use of heat exchangers and turbines.
  • Efficiency Calculations: Comparison with other renewable sources.
  • Example: Calculating overall efficiency of a geothermal power plant.

Slide 40: Summary and Review of Chapter 2

  • Key Concepts: Thermodynamics, heat transfer, fluid mechanics.
  • Applications in Renewable Energy: Solar, wind, geothermal, and more.
  • Preparation for Next Chapter: Fundamentals of Solar Energy.