The document provides an overview of heat transfer, detailing its modes: conduction, convection, and radiation, along with the governing laws such as Fourier's law and Newton's law of cooling. It also explains the concepts of thermal contact resistance and critical radius of insulation, emphasizing their significance in designing effective heat transfer systems. Applications in HVAC systems, power generation, and electronic cooling illustrate the importance of heat transfer principles in various fields.

1. Heat Transfer
PREPARED BY MRS SOUMYA HUBLIKAR

2. Introduction
Heat transfer is the fundamental process by which thermal energy is
exchanged between different materials or systems. This introduction
explores the key concepts that govern the movement of heat, setting
the stage for a deeper understanding of thermal systems and their
applications.

3. Modes of Heat Transfer
•Conduction
•Convection
•Radiation

4. Conduction
Atomic Vibrations
In conduction, heat is transferred through the vibration of atoms and molecules within a
material
Temperature Gradient
Conduction occurs due to a temperature gradient, where heat flows from the hotter region
to the cooler region.
Thermal Conductivity
The rate of conduction depends on the material's thermal conductivity, which varies
based on the atomic structure.

5. Convection
•Fluid Motion
Heat is transferred by the movement of a fluid, such as air or water, over a surface
•Natural Convection
Heat is transferred by the movement of a fluid, such as air or water, over a surface.
•Forced Convection
Fluid motion is driven by an external force, such as a fan or pump.

6. Radiation
•Electromagnetic Waves
Heat is transferred through the emission and absorption of electromagnetic waves, even
in a vacuum.
•No Medium Required
Radiation can transfer heat even in a vacuum, unlike conduction and convection.
•Emissive Power
The rate of radiation heat transfer depends on the emissive power of the surface.

7. Laws of Heat Transfer
Fourier's Law
Heat conduction is proportional to the temperature gradient and the material's thermal
conductivity.
Newton's Law of Cooling
The rate of convective heat transfer is proportional to the temperature difference
between the surface and the fluid.
Stefan-Boltzmann Law
The rate of radiative heat transfer is proportional to the fourth power of the absolute
temperature.

8. Thermal Contact Resistance
•Thermal contact resistance is the resistance to heat flow at the interface
between two materials in contact. It arises due to surface irregularities
and imperfect mating of the surfaces.
•Accounting for thermal contact resistance is crucial in the design of
efficient heat transfer systems, such as heat exchangers and electronic
cooling applications
•Contact pressure, surface roughness, and the presence of interfacial
materials (e.g., thermal grease) can all influence the thermal contact
resistance.

9. Critical Radius of Insulation
•The critical radius of insulation is the thickness of insulation at
which the heat loss from an insulated pipe or cylinder is
minimized.
•Knowing the critical radius is important for optimizing the
insulation design to achieve maximum efficiency and cost-
effectiveness.
•The critical radius depends on the thermal conductivity of the
insulation and the surrounding medium.

10. Electrical Analogy and Overall Heat
Transfer Coefficient
•Heat transfer can be analogous to electrical circuits, with
temperatures and heat fluxes corresponding to voltages and
currents, respectively. This analogy helps in the analysis and
design of thermal systems.
•The overall heat transfer coefficient (U) is a measure of the
overall effectiveness of heat transfer between a fluid and a
solid surface. It accounts for various modes of heat transfer,
such as conduction, convection, and radiation.

11. Applications of Heat Transfer
•HVAC Systems
Heating, ventilation, and air conditioning rely on heat transfer principles to regulate indoor
temperatures
•Power Generation
Heat transfer is crucial in power plants, where thermal energy is converted into electricity
•Electronics Cooling
Efficient heat dissipation is necessary to prevent overheating in electronic devices and
components.

12. THANK YOU