Unit Operations - Heat Transfer

increase

If the thermal conductivity of the fluid increases, the heat transfer coefficient will

Fourier's law equation

The equation (see picture) is called

decrease

If the viscosity of the fluid will increase, the heat transfer coefficient in a turbulent flow system will

forced convection

In a fluid, if the currents are set in motion by the action of a mechanical device, and the flow is independent of density gradients, the phenomena is called

decreases from pipe wall to the insulated surface

The heat transferred radially across an insulated pipe per unit area

convection

The transfer of heat from a point to another within a fluid, or between a fluid and a solid or another fluid, by the movement or mixing of the fluids involves

rating a heat exchanger

It is a method of developing the design for a heat exchanger wherein the engineer assures the existence of an exchanger and makes calculations to determine if the exchanger would handle the process requirements under reasonable conditions

natural convection

When water inside a beaker is being heated over a hot plate, the mechanism of heat transfer through the water is considered to be

temperature gradient

The driving force in heat transfer is

based on the inside area

In using the design equation of heat transfer, q = UA🔺Tln the U and A may either be based on the inside or outside area of the pipe. For a system where air is flowing inside a pipe while being heated by condensing steam outside the pipe, the proper U and A to be used is

one has a high thermal conductivity

If a man touches two metals which were kept together at room temperature, why would one metal feel colder than the other

Nusselt Number

The term (see picture) is known as

isotropic solids

In heat transfer by conduction, due to symmetry the heat flow at a point is perpendicular to the isothermal surface through the point. This mode of conduction is characteristic of

Biot Number

The ratio of the internal thermal resistance of a solid to the boundary layer thermal resistance is described by

Prandtl Number

The measure of the relative effectiveness of momentum and energy transport by diffusion in the velocity and thermal boundary layers is given by

thermal diffusivity

the property of the solid that provides a measure of the rate of heat transfer relative to the energy storage is referred to as

0.1 to 100 μm

The range of wavelengths of electromagnetic waves that is associated with thermal radiation is from

black body

An ideal surface that absorbs all incident radiation, regardless of wavelength and direction and is also considered to be a perfect emitter is referred to as a

Wien's Law

The spectral distribution of a perfect emitter has a maximum and that the corresponding wavelength depends on temperature. The maximum spectral emissive power is displaced to shorter wavelengths with increasing temperature. These statements refer to

Stefan-Boltzman Law

The amount of radiation emitted in all directions and over all wavelengths by a perfect emitter is proportional to the fourth power of the absolute temperature of the emitter. This is the statement of

Kirchoff's Law

The ratio of the emissive power of a body to its absorptivity is a constant and the same for all radiating bodies in a confined enclosure under thermal equilibrium. this is a statement of

gray body

A theoretical body where the absorptivity and emissivity are independent of the wavelength over the spectral region of the irradiation and the surface emission is called

the conductive resistance is very small compared with the convective resistance

Thermal lumped analysis may be applied if

decreases

Two parallel infinite walls at different temperatures are radiating energy to each other. If a sheet of negligible thermal resistance is placed midway between the walls, and the sheet is considered a black body, the heat transferred by radiation between the two walls is

oxygen

Which among the gases listed is transparent to gas radiation

nucleate boiling

In boiling, the stage when the rate of bubble formation increases so that the velocity of circulation increases and the heat flux, q and 🔺T also increase is referred to as

only the conduction on one side affects the temperature distribution

A semi-infinite solid in heat conduction is one where

2 baffles and 4 tubes

A 2-4 shell and tube heat exchanger means that there are

the outside area of the inner pipe

Air flowing inside the annular space of a double pipe heat exchanger is being heated by steam inside the inner pipe. For this case, the U in the heat transfer equation should be based on