4. Updated_Heat_Transfer_Presentation.pptx

HMT

1. Heat Conduction, Thermal Resistance, Overall Heat Transfer Coefficient, and Mass Transfer An Overview Presented by: Md. Helal Hossain Department: Mechanical Engineering, World University of Bangladesh

2. Heat Conduction Concepts - Definition: Heat conduction is the transfer of thermal energy within a body due to temperature gradient. - Fourier’s Law: q = -kA dT/dx - q = Heat transfer rate (W) - k = Thermal conductivity (W/m·K) - A = Cross-sectional area (m²) - dT/dx = Temperature gradient (K/m) - Examples: - Conduction in metals - Heat transfer in building materials

3. Thermal Resistance - Definition: Opposition to heat flow through a material. - Thermal Resistance Formula: - Conduction: R_cond = L/kA - L = Thickness of the material (m) - Convection: R_conv = 1/hA - h = Convective heat transfer coefficient (W/m²·K) - Radiation: R_rad involves emissivity and other complex factors. - Composite Systems: Series and parallel thermal resistances.

4. Overall Heat Transfer Coefficient - Definition: Combined effect of conduction, convection, and radiation in heat transfer. - Formula: - 1/U = 1/hi + L/k + 1/ho - U = Overall heat transfer coefficient (W/m²·K) - hi and ho = Internal and external convective heat transfer coefficients - L = Thickness of the material - k = Thermal conductivity - Applications: - Heat exchangers - Building insulation

5. Mass Transfer - Definition: Movement of mass from one location to another, often occurring in gases or liquids. - Driving Forces: Concentration gradients, pressure gradients, temperature gradients. - Modes of Mass Transfer: - Diffusion: Movement from high to low concentration. - Fick’s Law: J = -D dC/dx - J = Diffusion flux (kg/m²·s) - D = Diffusion coefficient (m²/s) - dC/dx = Concentration gradient - Convection: Mass transfer due to bulk motion of fluid. - Advection: Transport with a moving fluid. - Examples: - Drying of clothes - Perfume scent spreading in air

6. Applications and Examples - Heat Conduction: - Thermal insulation in buildings - Cooling of electronic devices - Thermal Resistance: - Design of thermal insulators - Heat sinks in electronics - Overall Heat Transfer Coefficient: - Designing efficient heat exchangers - Thermal management in automotive radiators - Mass Transfer: - Separation processes (distillation, absorption) - Environmental engineering (pollutant dispersion)

7. Summary - Key Concepts: - Heat conduction is driven by temperature gradients. - Thermal resistance is the opposition to heat flow. - Overall heat transfer coefficient accounts for combined modes of heat transfer. - Mass transfer involves movement due to concentration gradients and fluid motion. - Importance: Understanding these concepts is crucial for designing efficient thermal and mass transfer systems in engineering.

8. Q&A - Questions and Discussion - Encourage audience to ask questions and discuss real-world applications. - Provide further explanations on complex topics as needed.

9. References - Books and Articles: - Incropera, F.P., DeWitt, D.P., "Fundamentals of Heat and Mass Transfer" - Cengel, Y.A., "Heat and Mass Transfer: Fundamentals and Applications" - Relevant research papers and articles

10. Heat Exchanger Design - Definition: A device used to transfer heat between two or more fluids. - Types of Heat Exchangers: - Shell and Tube - Plate - Air Cooled - Double Pipe - Key Design Considerations: - Thermal Performance: Effectiveness, NTU (Number of Transfer Units) - Pressure Drop: Fluid flow resistance - Material Selection: Corrosion resistance, thermal conductivity - Design Equations: - Log Mean Temperature Difference (LMTD) method - Effectiveness-NTU method

11. Analysis of Heat Conduction - Definition: Study of heat transfer through solid materials. - Governing Equation: Fourier’s Law of Heat Conduction - \( q = -kA _x000C_rac{dT}{dx} \) - One-dimensional Heat Conduction: - Steady-state: Temperature distribution does not change with time. - Transient: Temperature distribution changes with time. - Analytical Methods: - Separation of Variables - Method of Images - Numerical Methods: - Finite Difference Method - Finite Element Method