Applied Thermodynamics
Applied thermodynamics is the science of the relationship between heat, work, and systems that analyze energy processes. The energy processes that convert heat energy from available sources such as chemical fuels into mechanical work are the major concern of this science. Thermodynamics consists of a number of analytical and theoretical methods which may be applied to machines for energy conversion.
Laws of TD..
The zeroth law of thermodynamics
The first law of thermodynamics
The second law of thermodynamics
Definition of: Heat engines, Turbines , Steam turbine, Gas turbine, Compressor, Thermodynamic cycle, Working fluid, Ideal gas, System
Definition of processes: Isobaric, Isothermal, Isentropic, Isometric, Adiabatic, Adiabatic mixing, Throttling, Free expansion, Polytropic
Heat transfer:Heat transfer, Heat exchangers, Heat flow through a pipe, Heat flow through a wall
Air Conditioning:Air conditioning, Humidifiers, Direct Steam Injection, Contact factor of a nozzle, Contact factor of a coil, Psychrometric chart, Hygrometer
Definition and/or units of: Energy, Exergy, Power, Enthalpy, Entropy, Temperature, Pressure, Specific volume, Density, Specific heat capacity, Sensible heat, Latent heat, Thermal conductivity, Molar mass, Mass flow
Heat is a form of energy that is transferred from one body (system) to another body (system or surroundings). Heat transfer can occur when there is a temperature difference. Assume two bodies with different temperatures are brought into contact with each other. The heat transfers from the hotter body to the colder one. This will continue until the temperature of the bodies are the same (thermal equilibrium).
The SI unit of heat is joule (J).
Other units are:
1 cal (calorie)= 4.1868 J
1 Btu (British thermal unit)= 1055.05 J
thermie= 4.184E6 J
ft.lbf= 1.35582 J
kJ= 1000 J
MJ= 1E6 J
hp.h (horsepower.hour)= 2.6845E6 J
kWh= 3.6E6 JMWh= 3.6E9.
Work is defined as the scalar product of a force, F, and a distance,L. This is equivalent to the product of the force and the distance moved in the direction of the force. For instance, when a boundary of a system moves in the direction of the force acting on it, the surroundings do work on the system. If the direction of the movement is reversed, then the work is done by the system on its surroundings. The SI unit of work is joule (J) that is the same unit as energy.
1 J= 1 N.
m= 1 W.s
Other units are:
1 kpm= 9.80665 J
1 ft.lbf= 1.35582 J.
Work
thermie= 4.184E6 J
ft.lbf= 1.35582 J
kJ= 1000 J
MJ= 1E6 J
hp.h (horsepower.hour)= 2.6845E6 J
kWh= 3.6E6 J
MWh= 3.6E9
Work is defined as the scalar product of a force, F, and a distance,L. This is equivalent to the product of the force and the distance moved in the direction of the force. For instance, when a boundary of a system moves in the direction of the force acting on it, the surroundings do work on the system. If the direction of the movement is reversed, then the work is done by the system on its surroundings.
The SI unit of work is joule (J) that is the same unit as energy.
1 J= 1 N.m= 1 W.s
Other units are:
1 kpm= 9.80665 J
1 ft.lbf= 1.35582 J
The Second Law of Thermodynamics
The second law of thermodynamics states that no heat engine can be more efficient than a reversible heat engine working between two fixed temperature limits (Carnot cycle) i.e. the maximum thermal efficiency is equal to the thermal efficiency of the Carnot cycle: or in other words If the heat input to a heat engine is Q, then the work output of the engine, W will be restricted to an upper limit Wmax i.e. It should be noted that real cycles are far less efficient than the Carnot cycle due to mechanical friction and other irreversibility.
Steam turbines
Steam turbines are devices which convert the energy stored in steam into rotational mechanical energy. These machines are widely used for the generation of electricity in a number of different cycles, such as:
Rankine cycle
Reheat cycle
Regenerative cycle
Combined cycle
The steam turbine may consists of several stages. Each stage can be described by analyzing the expansion of steam from a higher pressure to a lower pressure. The steam may be wet, dry saturated or superheated. Consider the steam turbine shown in the cycle above. The output power of the turbine at steady flow condition is:
P = m (h1-h2)
where m is the mass flow of the steam through the turbine and h1 and h2 are specific enthalpy of the steam at inlet respective outlet of the turbine. The efficiency of the steam turbines are often described by the isentropic efficiency for expansion process. The presence of water droplets in the steam will reduce the efficiency of the turbine and cause physical erosion of the blades. Therefore the dryness fraction of the steam at the outlet of the turbine should not be less than 0.9.