Module 1 thermodynamics Thermodynamics → Thermo + dynamics ( Heat + motion) SYSTEM : is defined as a quantity of matter or region in space chosen for study. SURROUNDINGS: is the mass or region outside the system. BOUNDARY: is the real or imaginary surface that separates the system from its surroundings mathematically has no thickness, thus it can neither contain any mass nor occupy any volume in space. The BOUNDARY can be FIXED or MOVABLE. Two basic kinds of systems are: • CLOSED SYSTEMS (Control mass ) • OPEN SYSTEM (Control Volume) CLOSED SYSTEM (CONTROL MASS): consists of fixed amount of mass and no mass can cross its boundary. Energy ( heat or work) can cross the boundary the volume of a closed system does not have to be fixed ISOLATED SYSTEM : is a special case for a closed system where even the energy is not allowed to cross the boundary ( e.g. closed adiabatic system) OPEN SYSTEMS or CONTROL VOLUME is a properly selected region in space, which usually encloses a device that involves mass flow such as a compressor, turbine or nozzle. Both mass and energy can cross the boundary of a control volume CONTROL SURFACE: is the boundaries of control volume, and they can be real or imaginary. 1|Page Module 1 thermodynamics PROPERTIES OF A SYSTEM: 1- Intensive properties are those that are independent of the mass of a system, such as temperature, pressure, and density. 2- Extensive properties are those whose values depend on the size—or extent—of the system. Total mass, total volume, and total momentum 3- Specific properties are Extensive properties per unit mass Some examples of specific properties are specific volume Density: is defined as mass per unit volume 𝜌= 𝑚 𝑣 𝑘𝑔 ( ⁄ 3) 𝑚 specific volume (ν) which is defined as volume per unit mass 𝑣 1 𝑣= = 𝑚 𝜌 specific gravity, or relative density is defined as the ratio of the density of a substance to the density of some standard substance at a specified temperature. ρ (water) = 1000 (kg/m3). 𝑆𝐺 = specific weight 𝜌 𝜌𝑤𝑎𝑡𝑒𝑟 is the weight of a unit volume of a substance 𝛾𝑠 = 𝜌𝑔 (𝑁⁄ 3 𝑚 ) 2|Page Module 1 thermodynamics Describing a SYSTEM PROPERTIES of a fluid determine a STATE. When TWO (or more) INTENSIVE independent properties are known, the exact state of the substance is known. When a property changes, a change of STATE occurs. Thus, a state of a substance can be defined by its PRESSURE and TEMPERATURE. Process: is Any change that a system undergoes from one equilibrium state to another Cycle: is A system is said to have undergone a cycle if it returns to its initial state at the end of the process. Thermal equilibrium The zeroth law of thermodynamics : states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. 𝑇𝑅 = 𝑇𝐹 + 460° 𝑇𝐾 = 𝑇𝐶 + 273° 9 ℉ = ( × ℃) + 32° 5 5 ℃ = (℉ − 32° ) 9 Example : Convert 0F into degrees Celsius (C). 5 ℃ = (℉ − 32° ) 9 C 0F 3 2 9 5 C 3 2 9 5 C C = -17.78 3|Page Module 1 thermodynamics Pressure is defined as a normal force exerted by a fluid per unit area. Pascal (Pa) it has the unit of Newtons per square meter (N/m2) 𝑃𝐺𝑎𝑢𝑔𝑒 = 𝜌𝑔ℎ The basic manometer. The pressure in a fluid does not vary in the horizontal direction within a fluid, the pressure at point 2 is the same as the pressure at point 1. 𝑃𝐺𝑎𝑠 = 𝑃𝑎𝑡𝑚 + 𝜌𝑔ℎ 4|Page Module 1 thermodynamics 5|Page