Process is defined as the changing or refining of raw materials that pass through or remain in a liquid, gaseous, or slurry state to create end products. The methods used to control process variables while manufacturing a product is referred as process control. oil and gas, cement, power e.t.c are examples of process industries. Process variable is a condition of process fluid (liquid or gas) that can change the manufacturing process in some way. Common process variables are listed below
2. Flow
3. Level
4. Temperature
5. Density
6. PH
Pressure : It is defined as force applied per unit area. P= F/A where, F = force and A = area. Units of pressure are bar, pascal, psi, tor, atm, kg / cm2, lb / in2.
1 Pa = 1N/ m2
1 psi = 1 lb/in2 (English unit) = 6,894 Pascal
1 Torr = 133.322 pascal
1 bar= 100000 pascal
1 atm= 101325 pascal
Flow : it is defined as volume per unit of time at specified temperature and pressure. Units of flow are kg / hr, litter / min, gallon / min, m3 / hr, Nm3 / hr.
Level : The height of a liquid or powder represented in meter ,mm, cm or percentage.
Temperature : It is an objective comparative measure of hot or cold. Units are Degree Centigrade, Degree Fahrenheit, Degree Kelvin, Degree Rankin.
Fahrenheit [°F] = [°C] × 9⁄5 + 32
Kelvin [K] = [°C] + 273.15
Rankine [°R] = ([°C] + 273.15) × 9⁄5
Delisle [°De] = (100 − [°C]) × 3⁄2
Newton [°N] = [°C] × 33⁄100
Reaumur [°Re] = [°C] × 4⁄5
Density : It is mass per unit volume. unit of density is kg/m3
PH : is a numeric scale used to specify the acidity or alkalinity of an aqueous solution. It is the negative of the logarithm to base 10 of the activity of the hydrogen ion. Solutions with a pH less than 7 are acidic and solutions with a pH greater than seven are alkaline or basic.
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