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differences between various parts of the solid. Thermal energy is
transferred from hotter to lower regions via vibrations of adjacent
molecules or the movement of free electrons through the material.
Metals, with many free electrons, are good conductors of heat. Convective heat transfer takes place in a fluid (gas or liquid) through
molecular motion and the circulation of currents. It can be divided
into natural convection and forced convection. Natural convection
is driven by the temperature gradients that cause density gradients
in gases or fluids, and as a result of these phenomena, buoyancy
forces occur and cause fluid movements. Forced convection is
caused by the some external force (e.g., a fan or pump). Radiation is
a flow of thermal energy from one source to another in the form of
electromagnetic waves and does not depend on a specific medium
of transfer.
Each of these heat-transfer means is in turn dependent on the
physical properties of the materials themselves, including their
heat capacity, expansion coefficient, conductivity, phase change, or
melting points. As discussed in detail in Section 4.4, these properties are reflected in various specific measures or coefficients useful
with a design context. Important measures for a material discussed
in Section 4.4 include the following: the melting temperature, T m ,
and the glass transition temperature, T g —both of which are important measures when the material dramatically changes its structure
and characteristics; the maximum and minimum service temperatures that bound the useful design range, T max and T min ; the specific
heat capacity, C p ; the linear thermal; and the expansion coefficient,
thermal diffusivity, and emissivity. Many other properties, such as
the creep rate (deformation over time) of materials, are also directly
affected by temperature changes.
Many of these properties can be potentially altered by the use of
nanomaterials (see chapter 7). These and related topics are discussed in the following sections after a brief review of how spaces
and products are designed with respect to thermal issues.
thermal Environments in products
Many common products contain components that generate, transfer, store, dissipate, exchange, buffer, or otherwise manage heat.
Some components, such as lighting devices, generate heat as a
consequence of their use rather than as an intention per se. Heat
is invariably generated in the conversion of one energy type to
another, and any device that does this, such as a common electric motor, becomes a heat source. Other components might have
The Thermal Environment
differences between various parts of the solid. Thermal energy is
transferred from hotter to lower regions via vibrations of adjacent
molecules or the movement of free electrons through the material.
Metals, with many free electrons, are good conductors of heat. Convective heat transfer takes place in a fluid (gas or liquid) through
molecular motion and the circulation of currents. It can be divided
into natural convection and forced convection. Natural convection
is driven by the temperature gradients that cause density gradients
in gases or fluids, and as a result of these phenomena, buoyancy
forces occur and cause fluid movements. Forced convection is
caused by the some external force (e.g., a fan or pump). Radiation is
a flow of thermal energy from one source to another in the form of
electromagnetic waves and does not depend on a specific medium
of transfer.
Each of these heat-transfer means is in turn dependent on the
physical properties of the materials themselves, including their
heat capacity, expansion coefficient, conductivity, phase change, or
melting points. As discussed in detail in Section 4.4, these properties are reflected in various specific measures or coefficients useful
with a design context. Important measures for a material discussed
in Section 4.4 include the following: the melting temperature, T m ,
and the glass transition temperature, T g —both of which are important measures when the material dramatically changes its structure
and characteristics; the maximum and minimum service temperatures that bound the useful design range, T max and T min ; the specific
heat capacity, C p ; the linear thermal; and the expansion coefficient,
thermal diffusivity, and emissivity. Many other properties, such as
the creep rate (deformation over time) of materials, are also directly
affected by temperature changes.
Many of these properties can be potentially altered by the use of
nanomaterials (see chapter 7). These and related topics are discussed in the following sections after a brief review of how spaces
and products are designed with respect to thermal issues.
thermal Environments in products
Many common products contain components that generate, transfer, store, dissipate, exchange, buffer, or otherwise manage heat.
Some components, such as lighting devices, generate heat as a
consequence of their use rather than as an intention per se. Heat
is invariably generated in the conversion of one energy type to
another, and any device that does this, such as a common electric motor, becomes a heat source. Other components might have
The Thermal Environment