Thermodynamics Week 2 PDF

Thermodynamics Week 2: Thermodynamics System, States, and Properties Systems, Boundary, and Surroundings Surroundings - The environment outside of the system. Boundary - An imaginary/real line that...

Thermodynamics Week 2: Thermodynamics System, States, and Properties Systems, Boundary, and Surroundings Surroundings - The environment outside of the system. Boundary - An imaginary/real line that separates the system from the surroundings System - Boundary Types: -The object/body being studied 1. Fixed Boundary – a boundary that does not change. 2. Movable Boundary – a boundary that may change Closed System (Control Mass) Surroundin gs System Energy may Energy may freely enter freely exit Mass cannot flow in/out of the boundaries In this system, fixed mass is being observed. Energy flows in/out of the system either in the form of Work or Heat The volume of the system may change, depending on the type of boundary. Isolated System Surroundin gs System Mass, Energy Energy and mass can not pass the boundary. The system cannot interact with the environment. The volume and boundary is fixed. Open System (Control Volume) Surroundin gs Energy may Energy may freely enter freely exit System Mass may freely Mass may freely enter exit In this system, a fixed space is being studied. Mass and Energy can freely move across boundary. The volume of the system is fixed. Thermodynamic Properties Thermodynamic Properties Extensive Property Intensive Property Properties that depend on the Properties that are independent amount of matter in the system from the amount of matter in the  system Mass (m)  Temperature (T)  Volume (V)  Density ()  Pressure (P)  Specific Volume ()  Energy (E)  Specific Energy () Mass and Force  Mass is the amount of matter in a substance, and correlates to an object’s resistance to change in motion.  Force is the push/pull on an object that causes acceleration.  According to Newton’s 2nd Law of Motion:  If the units of the equation are not unified (same system of units), then the equation can be modified to: where k = constant of proportionality/ conversion factor. Non-standard Units of mass and force  Kilogram-force – when 1 kilogram-mass is accelerated by , it is equivalent to 1 From: Non-standard Units of mass and force  Pound-mass – is equal to 1 when accelerated at a rate of 32.174 From: Example  An athlete weighing is running at a velocity of 10 ft/s. Determine the mass () of the athlete if  An astronaut weighs on mars where the gravity if 38% that of earth. Determine the mass of the astronaut in if g = 9.7 m/s2. Pressure  The Force per unit area. It can be the force dn in all directions (static pressure) or in one direction (dynamic) by a fluid, or just distribution on an area.  ` Pressure  The Force per unit area. It can be the force dn in all directions (static pressure) or in one direction (dynamic) by a fluid, or just distribution on an area. Barometric Devices  Pressure is commonly measured using a barometer, U-tube manometer, etc that compares the pressure of two points—one of which is normally the atmospheric pressure.  Absolute Pressure – the pressure measured relative to perfect vacuum.  Gauge Pressure – the difference between two pressures.  Vacuum Pressure – Pressure lower than the atmospheric pressure. Barometric Devices  If  If U-Tube Manometer  A U-Tube manometer is a barometric device that measures the difference in pressure between its two ends.  It is composed of a U-shaped tube filled with mercury.  As the pressure of one end becomes greater, the greater pressure pushes the mercury downward, creating a height difference that is directly related to the gage pressure. Pressure in mmHg and inHg  When the pressure is expressed in mmHg or inHg, it means that the pressure is equivalent to: Where: Mercury Density () , but use Example  An bottle of water weighing of 1.5 has a weight that acts on a circular area on a table with a radius of 1”. Determine the pressure in a) and b) exerted by the bottle on the table. Assume g = a) 1.0529 psi b) 151.6197 psf  A Barometer has a gage pressure of 5 psi. If the atmospheric pressure is 15 psi, what is the absolute pressure in atm? ans. 1.3605 atm  A barometer has an absolute pressure of 2000 psf. If the atmospheric pressure is at SSLC, what is the gage pressure in psi? ans.  A wind tunnel has a U-Manometer of which one end is connected to the inlet while the other is at the test section. If the gage pressure is 20 mmHg, and the inlet pressure is at SSLC, what is the Test Section pressure in psf? Assume , ans. 2059.9760 psf Relative Density  Also called specific gravity, is a dimensionless quantity that expresses the ratio between two substances.  For water: Volume vs Specific Volume  Volume is the space occupied by a given mass  Specific Volume is the space occupied by a unit mass.  Specific Volume is an intensive property, while Volume is an extensive property Example  A fluid has a relative density of 0.7 to mercury. Determine the density, and the specific volume of the fluid. ans. 9520  A tank has a volume of 3L, inside is a gas that has a relative density of 0.5 compared to water. Determine the mass in and the specific volume of the gas in inside.. ans. 3.3069 x103 lbm , 1781.0686 Exercise:  An astronaut found a meteorite in Mars and when weighed it measured in Mars. The meteorite was then put on a piston connected to a manometer of which the other end was exposed to the atmosphere of which the measurement showed 10 mmHg. Determine the Atmospheric pressure if the Martian gravity is 38% that of Earth’s standard gravity. ,. Assume  Answer on the next slide Exercise: Given Solution: m = =0.3108 slugs 694.5854 psf