|
|
|
Jet - A stream of fluid issuing from a nozzle or orifice, and having free boundaries. An example is the exhust stream from a jet engine.
Jet engine - A gas turbine used to provide a propulsive jet for aircraft, consisting of compressor, combustion system, and turbine. See also: Rocket.
Jet, Pulse - A jet propulsion engine using a pulsating flow of atmospheric air into which fuel is injected and burned to produce a pressure build-up. Such an engine was used in the German V-I . bomb.
|
Jet, Ram - The simplest form of jet propulsion engine, using a steady flow of atmospheric air with ram (i.e. piston) compressions. It consists of intake diffuser, combustion chamber, and propelling nozzle, and is of particular value for flight at supersonic speeds but produces no static thrust.
Jet stream - A variable region of strong westerly wind occurring in the upper troposphere with maximum speeds of 50 or 100 m/s (or 100 200 mph).
Jigs and Fixtures - Appliances used in engineering production for holding work on a machine tool so that the appropriate machining operations may be carried out quickly and correctly. Generally speaking a jig incorporates means for guiding the cutting tools, whereas a fixture locates and holds the work in position but contains no specific guides.
|
Joule Equivalent: Mechanical Equivalent Of Heat - The mechanical energy equivalent to unit quanitiy of heat. It is about 4.185 x 107 ergs/cal. Where the quantity of heat is expressed in terms of energy (as in MKS and SI units) the need for the concept no longer exists.
Joule Heat - See: Joule effect.
Joule, Interational - The work done per second when a current of one international ampere is passed through a conductor whose resistance is one international ohm. It has now been superseded by the joule.
|
|
Joule Law of Electric Heating - States that the heat produced by an electric current I, flowing through a resistance R, for a time, t, is proportional to I2 Rt.
Joule Law of Energy Content - For a perfect gas: states that the internal energy of a given mass of a perfect gas is a function of temperature only. This is also known as Mayer's hypothesis.
Joule- Thomson Coefficient - For the Joule- Thomson effect: the ratio of the change in temperature to the change in pressure.
Joule-Thomson Effect. See. Joule effect.
Joule-Thomson Inversion Temperature - The temperature at which the Joule-Thomson coefficient changes its sign for a given gas.
|
|
|
Joule-Thomson Valve - A throttling device used for the expansion of the working fluid in refrigerators employing the Joule- Thomson effect.
Jupiter - The largest planet in the solar system and fifth in order of distance from the Sun. Its diameter is about 11 times that of the Earth and its mass about 318 times, and its period of rotation is about 10 h. It has 12 satellites, of which four (10, Europa, Ganymede and Callisto) are named, the rest being referred to by number.
|
Johnson Noise - Random fluctuations in a conductor which arise from the thermal agitation of the electrons. It is sometimes called thermal noise but is not to be confused with temperature fluctuation. See also: Electrical noise.
Josephson Effect - An effect concerning the behaviour of two superconductors separated by such a short gap (say in the form of an oxide layer junction of thickness some
10-6mm) that their wave functions could overlap.
Joshi Effect - The change in the current passing through an ozonizer tube when the gas or vapour in the tube is irradiated with visible light.
Joule - The unit of work and energy in MKS and SI units. It is the work done (i.e. the energy transferred) when the point of application of 1N is displaced, a distance of 1 m in the direction of the force, and is equal to 107 erg.
Joule Cycle - A reversible sequence of operations of a heat engine in which air is used as the working fluid. It consists of adiabatic compression, heating at constant pressure, adiabatic expansion, and cooling at constant pressure to the initial state.
Joule Effect - (1) The heating effect of an electric current flowing through a resistance. It is also known as Joule heat. (2) The intial slight increase in length of a ferromagnetic rod subjected to a gradually increasing longitudinal magnetic field. This is also known as the joule magnetostriction effect. (3) The change in temperature of a compressed gas when it undergoes adiabatic throttled expansion, usually known as the Joule-Thomson effect.
|
|
