# ORIFICE DISCHARGE COEFFICIENT (Cd)

The ratio of the actual flow through an orifice to that of the theoretical or isentropic flow through an orifice. Basically this parameter is a measure of the orifice efficiency. Valves are dimensionless and range from 0.61 for a thin-plate orifice to 0.85 for thick plate square-edged orifices, and up top 0.90

## Related Terms

### DIELECTRIC STRENGTH

A measure of the ability of an insulating material to withstand electric stress (voltage) without failure. Fluids with high dielectric strength (usually expressed in volts or kilovolts) are good electrical insulators. (ASTM Designation D 877.)

### COPPER STRIP CORROSION

A qualitative measure of the tendency of a petroleum product to corrode pure copper.

### SALINITY

A measure of the concentration of dissolved mineral substances in water.

### ASH

A measure of the amount of inorganic material in lubricating oil. Determined by burning the oil and weighing the residue. Results expressed as percent by weight.

### ASPIRATING PSYCHROMETER

A device which draws sample of air through it to measure humidity.

### POISE

A measure of viscosity (absolute viscosity) numerically equal to the force required to move a plane surface of one square centimeter per second when the surfaces are separated by a layer of fluid one centimeter in thickness. It is the ratio of the shearing stress to the shear rate of a fluid and is expressed in dyne seconds per square centimeter (DYNE SEC/CM2); 1 centipoise equals .01 poise.

### NEUTRALIZATION NUMBER

A measure of the total acidity or basicity of an oil; this includes organic or inorganic acids or bases or a combination thereof (ASTM DesignationD974-58T) .

### VAPOR PRESSURE-REID (RVP)

Measure of the pressure of vapor accumulated above a sample of gasoline or other volatile fuel in a standard bomb at 100°F (37.8°C). Used to predict the vapor locking tendencies of the fuel in a vehicle's fuel system. Controlled by law in some areas to limit air pollution from hydrocarbon evaporation while dispensing.

### VISCOSITY INDEX (VI)

A commonly used measure of a fluid's change of viscosity with temperature. The higher the viscosity index, the smaller the relative change in viscosity with temperature.

### CONDUCTIVITY METER

An electric instrument used to measure the conductivity of water to determine its content of dissolved solids.