کتاب English for the Students of HVAC-R ( Heating, Ventilation, Air-Conditioning ) pdf و چاپی

For an understanding of refrigeration, air conditioning and central heating, it is necessary to know some fundamentals, technical/scientific terms, defini-tions and measurements. Terms such as density, specific gravity, velocity, etc are frequently used in technical passages related to the subject.
The density of a material is the mass per unit volume of the material. Density is expressed as pounds per cubic foot or grams per cubic centimetre. The relative density or specific gravity of a substance is the ratio of the density of the substance to the density of water of 4ºC. The specific volume of a substance is the volume occupied by unit mass of the material. By definition it will be clear that specific volume is the reciprocal of density, i.e.