Transferência de Calor

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Conduction

Heat transfer through direct contact between particles of matter without bulk movement of the material.

Convection

Heat transfer by the bulk movement of fluids driven by temperature and density differences.

Thermal Radiation

Heat transfer via electromagnetic waves emitted by a body due to its temperature, requiring no medium.

Fourier's Law of Heat Conduction

q = -k * A * (dT/dx), stating heat flux is proportional to the negative temperature gradient and area.

Thermal Conductivity (k)

A property measuring a material's ability to conduct heat, expressed in W/(m·K).

Newton's Law of Cooling

q = h * A * (T_s - T_infinity), describing convective heat transfer rate from a surface to a fluid.

Convective Heat Transfer Coefficient (h)

A parameter measuring the rate of heat transfer between a solid surface and a fluid, in W/(m²·K).

Stefan-Boltzmann Law

E = emissivity * sigma * A * T^4, calculating the total radiant energy emitted by a blackbody or real surface.

Stefan-Boltzmann Constant (sigma)

A fundamental physical constant equal to approximately 5.67 x 10^-8 W/(m²·K^4).

Emissivity (epsilon)

The ratio of energy radiated by a material surface to energy radiated by a blackbody at the same temperature.

Blackbody

An idealized physical body that absorbs all incident electromagnetic radiation and emits maximum possible thermal radiation.

Thermal Resistance (R)

The resistance of a medium to heat flow, calculated as L/(k*A) for conduction or 1/(h*A) for convection.

Thermal Diffusivity (alpha)

alpha = k / (rho * C_p), measuring the rate at which heat diffuses through a material.

Specific Heat Capacity (C_p)

The amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius/Kelvin.

Nusselt Number (Nu)

A dimensionless ratio of convective to conductive heat transfer across a boundary: Nu = h * L / k.

Prandtl Number (Pr)

A dimensionless ratio of momentum diffusivity to thermal diffusivity: Pr = nu / alpha.

Reynolds Number (Re)

A dimensionless ratio of inertial forces to viscous forces in a fluid: Re = (rho * V * L) / mu.

Grashof Number (Gr)

A dimensionless ratio of buoyant forces to viscous forces in natural convection.

Rayleigh Number (Ra)

The product of Grashof and Prandtl numbers (Ra = Gr * Pr), used to characterize natural convection regimes.

Overall Heat Transfer Coefficient (U)

A measure of the total ability of a series of conductive and convective barriers to transfer heat.

Log Mean Temperature Difference (LMTD)

A logarithmic average of the temperature difference between hot and cold streams in heat exchangers.

Heat Exchanger Effectiveness (epsilon)

The ratio of actual heat transfer rate to the maximum possible heat transfer rate in a heat exchanger.

Biot Number (Bi)

A dimensionless ratio of internal conductive resistance to external convective resistance: Bi = h * L_c / k.

Lumped Capacitance Method

A transient conduction analysis assumption valid when Biot number is less than 0.1, treating internal temp as uniform.

Fourier Number (Fo)

A dimensionless measure of time in transient conduction: Fo = alpha * t / L^2.

Wien's Displacement Law

lambda_max * T = b, stating the peak emission wavelength of a blackbody is inversely proportional to its absolute temperature.

Planck's Law

Describes the spectral density of electromagnetic radiation emitted by a blackbody in thermal equilibrium at a given temperature.

View Factor (Shape Factor)

The fraction of radiation leaving surface i that directly strikes surface j.

Natural (Free) Convection

Fluid motion caused entirely by buoyancy forces arising from density variations due to temperature gradients.

Forced Convection

Fluid motion generated by an external source such as a pump, fan, or wind.

Phase Change Heat Transfer

Heat transfer accompanied by a change in physical state, such as boiling or condensation, involving latent heat.

Latent Heat of Vaporization

The energy required to change a unit mass of a substance from a liquid to a gas at constant temperature.

Critical Heat Flux (CHF)

The thermal limit in boiling where the heat transfer regime shifts to film boiling, resulting in a sudden surface temperature jump.

Film Boiling

Boiling regime where a continuous vapor blanket coats the heating surface, significantly reducing the heat transfer rate.

Thermal Contact Resistance

Temperature drop across an interface caused by surface roughness and air gaps between touching solid materials.