Heat Transfer in Mechanical Engineering

Study Notes

Depends on:
- Temperature difference
- Material properties (thermal conductivity, specific heat capacity)
- Distance between particles
Fourier's Law: Q = -k \* A \* (dT/dx)
- Q: heat transfer rate
- k: thermal conductivity
- A: cross-sectional area
- dT/dx: temperature gradient

Types:
- Natural Convection: buoyancy-driven fluid motion
- Forced Convection: fluid motion driven by external means (e.g., pumps, fans)
Depends on:
- Fluid properties (density, viscosity, specific heat capacity)
- Flow characteristics (velocity, turbulence)
- Surface roughness and orientation
Newton's Law of Cooling: Q = h \* A \* (T_s - T_f)
- h: convection heat transfer coefficient
- A: surface area
- T_s: surface temperature
- T_f: fluid temperature

Depends on:
- Temperature of emitting body
- Emissivity of emitting body
- View factor (geometry of emitting and receiving bodies)
Stefan-Boltzmann Law: E = ε \* σ \* T^4
- E: radiative heat flux
- ε: emissivity
- σ: Stefan-Boltzmann constant
- T: temperature of emitting body

Heat transfer occurs through three primary modes: conduction, convection, and radiation

Heat conduction occurs between particles in physical contact
Factors affecting conduction:
- Temperature difference between particles
- Material properties: thermal conductivity and specific heat capacity
- Distance between particles
Fourier's Law of Heat Conduction: Q = -k \* A \* (dT/dx)
- Heat transfer rate (Q) is proportional to thermal conductivity (k), cross-sectional area (A), and temperature gradient (dT/dx)

Convection is the transfer of heat through fluid motion
Types of convection:
- Natural Convection: buoyancy-driven fluid motion
- Forced Convection: fluid motion driven by external means (e.g., pumps, fans)
Factors affecting convection:
- Fluid properties: density, viscosity, and specific heat capacity
- Flow characteristics: velocity and turbulence
- Surface roughness and orientation
Newton's Law of Cooling: Q = h \* A \* (T_s - T_f)
- Heat transfer rate (Q) is proportional to convection heat transfer coefficient (h), surface area (A), and temperature difference (T_s - T_f)

Radiation is the transfer of heat through electromagnetic waves
Factors affecting radiation:
- Temperature of the emitting body
- Emissivity of the emitting body
- View factor: geometry of emitting and receiving bodies
Stefan-Boltzmann Law: E = ε \* σ \* T^4
- Radiative heat flux (E) is proportional to emissivity (ε), Stefan-Boltzmann constant (σ), and temperature (T) of the emitting body

Immunology is the study of the immune system and its functions, focusing on defense against pathogens and disease-causing microorganisms.

Innate Immunity: Provides non-specific, immediate defense against infection, using physical barriers (skin, mucous membranes) and cellular responses (neutrophils, macrophages).
Adaptive Immunity: Offers specific, acquired immunity against specific pathogens, comprising cell-mediated immunity (T cells) and humoral immunity (B cells and antibodies).

Recognition: Pathogen recognition occurs through pattern recognition receptors (PRRs).
Activation: Immune cells (e.g., dendritic cells, T cells) are activated in response to pathogen recognition.
Effector Response: Pathogens are eliminated by immune cells and molecules (e.g., cytokines, antibodies).
Memory Response: Long-term immunity against future infections is established.

T Cells (T Lymphocytes):
- CD4+ (Helper T cells): Activate immune responses.
- CD8+ (Cytotoxic T cells): Directly kill infected cells.
B Cells (B Lymphocytes): Produce antibodies against pathogens.
Antigen-Presenting Cells (APCs): Dendritic cells, macrophages, and B cells present antigens to T cells.

Antibodies (Immunoglobulins): Proteins produced by B cells to neutralize pathogens.
Cytokines: Signaling molecules that coordinate immune responses (e.g., IL-2, IFN-γ).
Complement System: A group of proteins that work together to help eliminate pathogens.

Immunodeficiency: Weakened immune system (e.g., HIV/AIDS).
Autoimmune Disorders: Immune system attacks self-antigens (e.g., rheumatoid arthritis, lupus).
Hypersensitivity Reactions: Overactive immune response to harmless substances (e.g., allergies).