MECH0005 Topic Notes: Fluid Mechanics and Thermodynamics

Flashcards covering key concepts in fluid mechanics and thermodynamics from the UCL lecture notes.

Fluid

A substance that deforms continuously when acted upon by a shear stress of any magnitude.

Viscosity (µ)

The measure of a fluid's resistance to deformation or flow; defined as the ratio of shear stress to shear rate.

Surface Tension (σ)

The effective tangential force per unit length exerted on an imaginary line through a liquid surface, resulting from intermolecular interactions.

Capillary Action

The ability of a liquid to flow in narrow spaces without the assistance of external forces, driven by adhesive and cohesive forces.

Pressure (P)

The force exerted by the weight of a fluid per unit area; it is constant in all directions in a fluid at rest.

Reynolds Number (Re)

A dimensionless number used to predict flow patterns in different fluid flow situations; it indicates whether the flow is laminar or turbulent.

Buoyancy

The upward force exerted by a fluid on an object immersed in it, equal to the weight of the displaced fluid.

Thermal Efficiency (η)

The ratio of useful work output to the heat input in a heat engine; it indicates the effectiveness of energy conversion.

Carnot Cycle

A theoretical thermodynamic cycle consisting of two isothermal and two adiabatic processes, it represents the most efficient cycle possible.

Clausius Inequality

An expression in thermodynamics that quantifies the change in entropy; it states that the cyclic integral of δQ/T is less than or equal to zero.

Entropy (S)

A measure of the disorder or randomness in a system; it quantifies the amount of energy in a physical system that is not available to do work.

Isentropic Process

A thermodynamic process that is both adiabatic (no heat transfer) and reversible.

Ideal Gas Law

A physical law that describes the relationship between pressure (P), volume (V), number of moles (n), and temperature (T) in an ideal gas, expressed as PV=nRT.

First Law of Thermodynamics

A statement of the conservation of energy principle, indicating that the change in internal energy of a system equals the heat added to the system minus the work done by the system.

Hagen-Poiseuille Law

A physical law that gives the pressure drop due to viscous fluid flow through a long cylindrical pipe.

Control Volume

A specified region in space through which mass and energy may flow; used in analyzing fluid flow systems.

Refrigeration Cycle

A thermodynamic cycle that transfers heat from a low temperature reservoir to a high temperature reservoir by means of work input.

Work Done by a System (W)

Energy transferred by a system during a process; in thermodynamics, it describes the work that a system does during its expansion or compression.

Specific Heat Capacity (c)

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

Material Derivative

A time derivative that accounts for both local and convective changes in a fluid property.

Non-Newtonian Fluid

A fluid whose viscosity changes with the applied shear stress or with the shear rate, as opposed to a Newtonian fluid.