Thermodynamics All Definitions

Gas that changes volume changes when pressure is applied.

The measure of the mass of an object per unit volume.

The property of a working fluid that combines the flow energy (PV) and internal energy (U) into a single convenient term.

Is a measure of the available energy in a system. units Btu/°R, J/K

Thermal energy in transition.

The Energy a substance possesses to the rotation, vibration, translation, and interactions among the molecules of the substance.

Pressure applied to a confined fluid is transmitted undiminished throughout the confining vessel or system.

A description of the molecular structure of a substance. They include solids, liquids, vapors, gases, and plasmas.

Usually indicative of a change in molecular or atomic spacing.

The force per unit of area that a substance exerts on its surroundings.

Property of a substance that relates the volume occupied by a unit of mass. units ft3/lbm

A unique condition of a material,

Is a measure of the random motion of the molecules of a system. It is a fundamental measure of the object's thermal properties.

The process of heat transfer between interacting adjacent molecules of the material through which the heat is being transferred.

The process of heat transfer where there is a physical mixing of matter at different temperatures, and heat is transferred as a result of the contact between them. Heat transfer that is the result of the mixing and motion of fluids.

A measure of the amount of heat required to cause a one-degree change in the temperature of the object.

Heat that is transferred without producing a temperature change. Always associated with a phase change.

Heat that is added or removed from an object, which results in a change in the temperature of the object.

The heat capacity per lbm of a substance. It is a material property that describes the ability to store thermal energy.

A liquid existing to the left of the saturated liquid line. Infers that the pressure of the liquid is above the saturation pressure for its temperature.

The amount by which a liquid is subcooled, that is, cooled below its saturation temperature (°F).

The temperature difference between the saturation temperature for the existing condenser vacuum and the actual temperature of the condensate. It is expressed as the number of degrees subcooled.

The point is the highest temperature (critical temperature) and pressure (critical pressure) at which a gas and liquid can exist in equilibrium as distinguishable phases.

Represents values of pressure and temperature at which a substance can exist as both a liquid and solid in equilibrium.

The amount of heat that must be added to cause liquid to change phase to a gas or vapor.

The amount of liquid present in a wet vapor mixture.

An h-s (Specific Enthalpy – Specific Entropy) property diagram for steam.

The amount of vapor present in a wet vapor mixture.

Arrangement of the thermodynamic processes on a temperature versus specific entropy (T-s) property diagram.

A function of temperature and pressure. It arises from the consideration that the water is saturated with heat, and if any more heat is supplied, the water evaporates into steam.

The pressure at which liquid first begins to evaporate into steam, while at a given temperature.

The temperature at which liquid first begins to evaporate into steam, while under a given pressure.

Tabulations of values for pressure, temperature, specific volume, specific enthalpy, and specific entropy.

A liquid existing to the left of the saturated liquid line. Infers that the liquid exists at a temperature below saturation for its pressure.

Represents values of pressure and temperature at which a substance can exist as both a solid and gas in equilibrium.

Denotes a gas heated beyond its saturation temperature for a given pressure.

The single point at which the three phase lines (solid, liquid, gas) can exist in equilibrium.

Represents values of pressure and temperature at which a substance can exist as both a liquid and gas in equilibrium.

The unit of dynamic viscosity equal to 6.72 × 10−4 lbm/ft sec.

When the same mass flow exists everywhere in a pipe. This means the same mass of fluid flows past any two reference points along the pipe in any given time.

Represents the potential energy the fluid possesses due to its elevation above a reference level. It is expressed by the vertical distance, in feet, between the reference level and the level of the fluid.

Any substance that flows freely because its particles are not rigidly attached to one another.

It is the results of friction between the fluid and the pipe and between the fluid molecules.

Pressure drop associated with fluid friction.

Fluid with a constant density during the flow process. Liquids, water in particular, can be treated as such.

The dynamic (or absolute) viscosity (μ) divided by the density of the fluid (ρ).

A streamline flow. The flow is: 1) layers of water flow over one another at different speeds with virtually no mixing between layers, 2) fluid particles move in definite and observable paths or streamlines, and 3) characteristic of viscous (thick) fluid or is one in which viscosity of the fluid plays a significant part.

The amount of the fluid mass that passes a reference point per unit time.

Represents the specific PV energy the fluid possesses due to its pressure. It is expressed by the height, in feet, of a column of the fluid whose weight is equivalent to the pressure of the fluid. Commonly referred to as static pressure, and is the sum of gravity, applied forces, and atmospheric pressure.

Quantity used to measure the degree of pipe roughness that is equal the average height of surface irregularities (ε) divided by the pipe diameter (D).

A unitless value based on the average velocity, diameter of the pipe, density of the fluid and the viscosity of the fluid. Useful in predicting the type of fluid flow.

The summation of static pressure and dynamic pressure.

The movement of fluid through a system via cross currents that destroy the layers of fluid flow. The irregular movement of particles of the fluid. The particles travel in irregular paths with no observable pattern and no definite layers.

Represents the kinetic energy the fluid possesses due to its velocity. It is the height, in feet, to which the flowing fluid would rise in a column if all of its kinetic energy were converted to potential energy.

A fluid property that measures the resistance of the fluid to deforming due to a shear force. (lbf sec/ft2).

The volume of a fluid that passes a reference point per unit time.

The sudden conversion of kinetic energy to pressure or mechanical energy in the flow of fluid in a piping system.

Fouling from the growth of marine animals or plants.

The process of heat transfer between interacting adjacent molecules of the material through which the heat is being transferred.

Heat transfer by the process of bulk motion and mixing of macroscopic portions of a fluid.

Heat exchanger where the tube side fluid and the shell side fluid both flow in opposite directions. The fluids enter the heat exchanger at opposite ends.

Heat exchanger where the tube side fluid flows perpendicular to the shell side fluid. That is, one fluid flows through tubes and the second fluid flows across the tubes at a 90° angle.

The accumulation of solid material in a heat exchanger, this includes scale, biologics, and sludge. This restricts the flow through the heat exchanger and increases the pressure drop across the exchanger and reduces effectiveness of the heat exchanger.

Accurate method for determining the effective temperature difference across a heat exchanger when the temperature difference varies across the length of the heat exchanger.

Term used arrived at experimentally, that represents a material or component’s ability to transfer heat. (Btu/ft2 hr °F)

Heat exchanger where the tube side fluid and the shell side fluid both flow in the same direction. The fluids enter at the same end of the heat exchanger.

Fouling from deposits occurring due to inorganic salts coming out of solution on the heat transfer surfaces.