Heat Transfer Mechanisms: Conduction, Convection, Radiation

Heat Current

Total heat flow through materials.

Thermal Conductivity

Material's ability to conduct heat.

Convection

Heat transfer via fluid motion.

Forced Convection

Fluid movement caused by external forces.

Natural Convection

Fluid movement due to density differences.

Cross-Sectional Area

Area through which heat flows.

Heat Flow

Transfer of thermal energy between objects.

Radiation

Heat transfer via electromagnetic waves.

Surface Area

Total area exposed to heat transfer.

Wind-Chill Factor

Increased cooling effect from wind.

Evaporative Cooling

Cooling through evaporation of sweat.

Allen's Rule

Shorter appendages in cold habitats.

Heat Loss Rate

Energy lost from the body, 100-200 W.

Convection in Atmosphere

Influences weather patterns globally.

Convective Currents

Movement of air affecting local breezes.

Viscosity

Fluid's resistance to flow.

Thermal Updrafts

Rising warm air aiding bird flight.

Heat Transfer Mechanisms

Methods: conduction, convection, radiation.

Cooling Fins

Increase surface area for heat dissipation.

Blood Convection

Forced convection mechanism in human body.

Temperature Difference

Driving force for heat transfer.

Electromagnetic Radiation

Energy emitted as waves.

Radiation from Cold Habitats

Adaptations to minimize heat loss.

Infrared Waves

Long wavelengths carrying energy at ordinary temperatures.

Self-luminous

Object emits visible radiation when heated.

White Hot

Appearance of an object emitting visible light.

Emissivity

Dimensionless number indicating surface radiation efficiency.

Stefan-Boltzmann Law

Rate of radiation proportional to T^4.

Stefan-Boltzmann Constant

Fundamental constant in radiation equations.

Heat Current

Energy transfer rate due to radiation.

Thermal Equilibrium

Condition where radiation rates are equal.

Rate of Radiation

Energy emitted per unit time from a surface.

Surface Area

Total area from which radiation occurs.

Temperature Increase Factor

Rate of radiation increases with T^4.

Dull Black Surface Emissivity

Nearly unity, high radiation efficiency.

Smooth Copper Surface Emissivity

Approximately 0.3, lower radiation efficiency.

Net Heat Flow

Positive value indicates heat loss from an object.

Radiative Energy Transfer

Energy exchange due to temperature differences.

Rate of Absorption

Energy absorbed from surroundings by an object.

Rate of Energy Radiation Equation

Describes energy emission based on temperature and area.

Rate of Energy Radiation Example

Comparison to small electric space heater output.

Temperature Conversion

Necessary for calculations in Kelvin scale.

Rate of Radiation Calculation

Uses surface area and emissivity in equations.

Human Body Radiation

Emits energy to maintain thermal balance.

Radiation from Surroundings

External energy impacting an object's heat loss.

Heat Production at Rest

Human body generates about 75 W of heat.

Evaporative Cooling

Heat removal through evaporation of moisture.

Net Heat Loss

Heat lost minus heat gained by an object.

Emissivity

Measure of an object's ability to emit radiation.

Blackbody

Ideal absorber and emitter of radiation.

Ideal Reflector

Absorbs no radiation, ineffective at radiating.

Vacuum Bottle

Insulated container minimizing heat transfer.

Dewar Flask

Container for storing cryogenic liquids.

Thermograph

Image capturing infrared radiation emitted by objects.

Thermography

Study of temperature distributions using infrared imaging.

Conduction

Heat transfer through direct contact of materials.

Convection

Heat transfer via mass motion of fluids.

Radiation

Heat transfer through electromagnetic waves.

Kinetic Energy

Energy of motion at the atomic level.

Copper Rod

Example of a good conductor of heat.

Temperature Distribution

Variation of temperature across a given area.

Infrared Radiation

Long-wavelength radiation not visible to the eye.

Pit Vipers

Snakes that detect infrared radiation for hunting.

Special Cameras

Devices capturing infrared images for analysis.

Energy Loss

Heat energy escaping from a system.

Local Temperature Variations

Temperature differences caused by tumors or disorders.

Conductors

Materials that facilitate heat transfer efficiently.

Insulators

Materials that resist heat transfer.

Electromagnetic Radiation

Energy transfer without the need for matter.

Free Electrons

Electrons that carry energy in metals.

Thermal Conductors

Materials that efficiently transfer heat.

Heat Flow Direction

From higher to lower temperature regions.

Heat Current (H)

Rate of heat transfer per unit time.

Cross-Sectional Area (A)

Area through which heat flows.

Temperature Gradient (ΔT/L)

Temperature difference per unit length.

Thermal Conductivity (k)

Material property affecting heat transfer rate.

Insulated Rod

Rod where heat flows only end to end.

Heat Transfer Equation

H = k A (ΔT/L)

Heat Flow Direction

Heat flows from hot to cold regions.

Heat Current (Q)

Rate of heat transfer through materials.

Steady-State Heat Flow

Constant heat flow with no accumulation.

Latent Heat of Fusion

Heat required to melt ice without temperature change.

Area (A)

Surface area perpendicular to heat flow direction.

Wall Thickness (d)

Distance heat must travel through material.

Temperature Interface (T_i)

Temperature at the boundary between two materials.

Heat Flow Rate

Heat current measured in watts (W).

Conduction Equation

Q = k A (T1 - T2) / d.

Heat Flow in Series

Equal heat current through connected materials.

Heat Flow in Parallel

Total heat flow is the sum of individual flows.

Thermal Conductivity (k)

Material's ability to conduct heat, measured in W/m·K.

Example of Heat Flow

Heat transfer through a Styrofoam cooler.

Time Conversion

1 day = 86,400 seconds.

Ice Melting Calculation

Mass of ice melted relates to heat absorbed.

Temperature Drop

Difference in temperature across a material.

Cross-Sectional Area

Area through which heat flows, affecting current.

Junction Temperature (T_j)

Temperature at the connection point of two bars.

Heat Transfer Mistake

Styrofoam should not conduct better than copper.

Practice Problem

Determine ice melting time in sunlight.

Heat Flow Example

Heat flow through steel and copper bars.

Effective Length

Length needed for specific junction temperature.