Classical and the statistical approaches to thermodynamics:
Classical thermodynamics is based on experimental observations whereas statistical thermodynamics is based on the average behaviour of large groups of particles.
The light-year:
In this unit, the word light refers to the speed of light. The light-year unit is then the product of a velocity and time. Hence, this product forms a distance dimension and unit.
kg-mass and kg force:
Kg-mass is the mass unit in the SI system whereas kg-force is a force unit. 1-kg-force is the force required to accelerate a 1-kg mass by 9.807 m/s2. In other words, the weight of 1-kg mass at sea level is 1 kg-force.
Intensive and extensive properties:
Intensive properties do not depend on the size (extent) of the system but extensive properties do.
Quasi-equilibrium process:
A process during which a system remains almost in equilibrium at all times is called a quasi-equilibrium process.
Isothermal, isobaric, and isochoric processes:
A process during which the temperature remains constant is called isothermal; a process during which the pressure remains constant is called isobaric; and a process during which the volume remains constant is called isochoric.
Specific gravity:
The specific gravity, or relative density, and is defined as the ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4°C, for which dH2O = 1000 kg/m3). That is, SG= d/ dH2O. When specific gravity is known, density is determined from d= SG x dH2O.
Pascal’s law:
Pascal’s principlestates that the pressure applied to a confined fluid increases the pressure throughout by the same amount. This is a consequence of the pressure in a fluid remaining constant in the horizontal direction. An example of Pascal’s principle is the operation of the hydraulic car jack.
Total Energy:
The sum of all forms of the energy a system possesses is called total energy. In the absence of magnetic, electrical and surface tension effects, the total energy of a system consists of the kinetic, potential, and internal energies.
Acid Rain :
Fossil fuels include small amounts of sulphur. The sulphur in the fuel reacts with oxygen to form sulphur dioxide (SO2), which is an air pollutant. The sulphur oxides and nitric oxides react with water vapor and other chemicals high in the atmosphere in the presence of sunlight to form sulfuric and nitric acids. The acids formed usually dissolve in the suspended water droplets in clouds or fog. These acid-laden droplets are washed from the air on to the soil by rain or snow. This is known as acid rain.
Greenhouse effect: Carbon dioxide (CO2), water vapor, and trace amounts of some other gases such as methane and nitrogen oxides act like a blanket and keep the earth warm at night by blocking the heat radiated from the earth. This is known as the greenhouse effect.
Smog:
Smog is the brown haze that builds up in a large stagnant air mass, and hangs over populated areas on calm hot summer days. Smog is made up mostly of ground-level ozone (O3), but it also contains numerous other chemicals, including carbon monoxide (CO), particulate matter such as soot and dust, volatile organic compounds (VOC) such as benzene, butane, and other hydrocarbons. Ground-level ozone is formed when hydrocarbons and nitrogen oxides react in thepresence of sunlight in hot calm days.
Blackbody:
A blackbody is an idealized body that emits the maximum amount of radiation at a given temperature, and that absorbs all the radiation incident on it. Real bodies emit and absorb less radiation than a blackbody at the same temperature.
Emissivity and absorptivity and Kirchhoff’s law of radiation:
Emissivity is the ratio of the radiation emitted by a surface to the radiation emitted by a blackbody at the same temperature. Absorptivity is the fraction of radiation incident on a surface that is absorbed by the surface. The Kirchhoff’s law of radiation states that the emissivity and the absorptivity of a surface are equal at the same temperature and wavelength.
Saturated vapor :
Saturated Vapor (Dry Saturated Vapor) is thevapor that exists at the saturation temperaturecorresponding to its pressure and is on the verge of condensation. Any removal of heat causes it to condense.
Superheated vapor:
Superheated Vapor is theVapor that has a temperature higher than the saturation temperature at the same pressure and is not about to condense. Heat can be removed without immediate condensation until it reaches the saturation state.
Critical point:
At critical point the saturated liquid and the saturated vapor states are identical.
Triple point:
Triple point is a temperature at which the three phases of a pure substance coexist in equilibrium.
Quality:
Quality is the fraction of vapor in a saturated liquid-vapor mixture. It has no meaning in the superheated vapor region.
R and Ru:
Ru is the universal gas constant that is the same for all gases whereas R is the specific gas constant that is different for different gases. These two are related to each other by R = Ru / M, where M is the molar mass of the gas.
Principle of corresponding states:
All gases have the same compressibility factor Zat the same reduced temperature and pressure.
Mass and volume flow rate:
Mass flow rate is the amount of mass flowing through a cross-section per unit time whereas the volume flow rate is the amount of volume flowing through a cross-section per unit time.
Flow energy:
Flow energy or flow work is the energy needed to push a fluid into or out of a control volume. Fluids at rest do not possess any flow energy.
Thermal energy reservoir:
A thermal-energy reservoir is a body that can supply or absorb finite quantities of heat isothermally. Some examples are the oceans, the lakes, and the atmosphere.
Kelvin–Planck expression of the second law:
It is expressed as “No heat engine can exchange heat with a single reservoir and produce an equivalent amount of work”.
COPRefrigerator :
The coefficient of performance of a refrigerator represents the amount of heat removed from the refrigerated space for each unit of work supplied. It can be greater than unity.
COPHeat Pump :
The coefficient of performance of a heat pump represents the amount of heat supplied to the heated space for each unit of work supplied. It can be greater than unity.
Clausius expression of the second law:
No device can transfer heat from a cold medium to a warm medium without requiring a heat or work input from the surroundings.
Internal and external irreversibilities:
The irreversibilities that occur within the system boundaries are internal irreversibilities; those which occur outside the system boundaries are external irreversibilities.
Statement of the Carnot principles:
The thermal efficiency of an irreversible heat engine is lower than the efficiency of a reversible heat engine operating between the same two reservoirs, and
The thermal efficiency of all the reversible heat engines operating between the same two reservoirs are equal.
Entropy:
Entropy is a property of reversible processes and is an abstract property. It’s a function of quality of heat (i.e.,temperature), which leads the conversion of heat into work.
Second law efficiency:
The second-law efficiency is a measure of the performance of a device relative to its performance under reversible conditions. It differs from the first law efficiency in that it is not a conversion efficiency.
Compression ratio : It is the ratio of the maximum to minimum volumes in the cylinder.
Mean effective pressure:
The MEP is the fictitious pressure which, if acted on the piston during the entire power stroke, would produce the same amount of net work as that produced during the actual cycle.
Stroke: Stroke is the distance between the TDC and the BDC
Bore: Bore is the diameter of the cylinder.
Top dead center: TDC is the position of the piston when it forms the smallest volume in the cylinder
Clearance volume: Clearance volume is the minimum volume formed in the cylinder.
Propulsive power:
The power developed from the thrust of the engine is called the propulsive power. It is equal to thrust times the aircraft velocity.
Propulsive efficiency:
The ratio of the propulsive power developed and the rate of heat input is called the propulsive efficiency. It is determined by calculating these two quantities separately, and taking their ratio.
Utilization factor Pu for cogeneration εu plants:
The utilization factor of a cogeneration plant is the ratio of the energy utilized for a useful purpose to the total energy supplied. It could be unity for a plant that does not produce any power.
Binary power cycle:
Binary power cycle is a cycle which is actually a combination of two cycles; one in the high temperature region, and the other in the low temperature region. Its purpose is to increase thermal efficiency.
Water-source heat pump and it’s COP: A water-source heat pump extracts heat from water instead of air. Water-source heat pumps have higher COPs than the air-source systems because the temperature of water is higher than the temperature of air in winter
Thermoelectric circuit: The circuit that incorporates both thermal and electrical effects is called a thermoelectric circuit.
Seebeck and the Peltier effects:
When two wires made from different metals joined at both ends (junctions) forming a closed circuit and one of the joints is heated, a current flows continuously in the circuit. This is called the Seebeck effect. When a small current is passed through the junction of two dissimilar wires, the junction is cooled. This is called the Peltier effect.
Inversion line: The inversion line is the line on a Temperature-Pressure (T-P) diagram that separates the regions where a gas cools or heats during a throttling (Joule-Thomson) process.
Inversion temperature: The maximum inversion temperature is the highest temperature at which a gas can produce cooling during a throttling process.
Apparent molar mass : It is the average or the equivalent molar mass of the gas mixture.
Dalton’s law of additive pressures: The pressure of a gas mixture is equal to the sum of the pressures each gas would exert if existed alone at the mixture temperature and volume. This law holds exactly for ideal gas mixtures, but only approximately for real gas mixtures.
Amagat’s law of additive volumes: The volume of a gas mixture is equal to the sum of the volumes each gas would occupy if existed alone at the mixture temperature and pressure. This law holds exactly for ideal gas mixtures, but only approximately for real gas mixtures.
Ideal solution:
Mixtures or solutions in which the effects of molecules of different components on each other are negligible are called ideal solutions (or ideal mixtures).
Specific humidity:
Specific humidity is the amount of water vapor present in a unit mass of dry air.
Relative humidity:
Relative humidity is the ratio of the actual amount of vapor in the air at a given temperature to the maximum amount of vapor air can hold at that temperature.
Radiation effect: It is the direct heat exchange between the body and the surrounding surfaces. It can make a person feel chilly in winter, and hot in summer.
Humidification and dehumidification: Humidification is to add moisture into an environment, dehumidification is to remove it.
Sensible heat: Sensible heat is the heat added or removed from a substance that causes a change in temperature without changing its phase (state).
Latent heat of Vaporization:
It is defined as an amount of heat energy required to convert 1 kg of saturated water into dry and saturated steam keeping the temperature and pressure constant.
Latent Heat of Fusion:
The latent heat of fusion is defined as the quantity of heat, required to convert one kg of ice into water at constant temperature (0°C). Its value is taken as 334.5 kJ/kg.
Evaporative cooling: Evaporative cooling is the cooling achieved when water evaporates in dry air.
Spray pond: A spray pond cools the warm water by spraying it into the open atmosphere.
Air-fuel ratio:
Air-fuel ratio is the ratio of the mass of air to the mass of fuel during a combustion process.
Dew-point temperature of the product gases:
The dew-point temperature of the product gases is the temperature at which the water vapor in the product gases starts to condense as the gases are cooled at constant pressure. It is the saturation temperature corresponding to the vapor pressure of the product gases.
Higher Heating Value:
The higher heating value of a fuel is the total amount of heat released when the fuel is completely burned, and the water vapor formed is condensed back to liquid.
Lower Heating Value:
The lower heating value of a fuel is the heat released when the fuel is completely burned but the water formed remains in vapor form.
