Refrigerators appear to violate the Second Law of Thermodynamics, but the key reason they do not is because of the work needed as input to the system. They are essentially heat pumps, but work to cool a region instead of heat it.
Note that the COP of a heat pump depends on its duty. The heat rejected to the hot sink is greater than the heat absorbed from the cold source, so the heating COP is 1 greater than the cooling COP. applies to heat pumps and applies to air conditioners or refrigerators. For heat engines, see Efficiency.
An air conditioner works using a thermodynamic cycle called the refrigeration cycle. It does this by changing the pressure and state of the refrigerant to absorb or release heat. The refrigerant (aka coolant) absorbs heat from inside of your home and then pumps it outside.
Typically the thermodynamic system in a refrigerator analysis will be a working fluid, a refrigerant, that circulates around a loop, as shown in Figure 3.7. Then a pump or compressor is used to do work on the refrigerant, adding additional energy to it and thus further raising its internal energy.
A heat pump is similar to a refrigerator. The only point of difference between the two is of the operating temperatures. The working temperatures in a refrigerator are of the colder level and atmosphere, whereas working temperatures in heat pump are of hotter level and atmosphere.
All the refrigerators, deep freezers, industrial refrigeration systems, all types of air-conditioning systems, heat pumps, etc work on the basis of the second law of thermodynamics. All types of air and gas compressors, blowers, fans, run on various thermodynamic cycles.
In thermodynamics, heat means energy which is moved between two things when one of them is hotter than the other. That is, heat is defined as a spontaneous flow of energy (energy in transit) from one object to another, caused by a difference in temperature between two objects; therefore, objects do not possess heat.
Often the exit kinetic energy is neglected (if in a problem, the flow velocities are specified, the kinetic energy term should be included). Normally, the process in the turbine is adiabatic and the work output reduces to decrease in enthalpy from the inlet to exit states.
Turbine efficiency is the ratio of actual work output of the turbine to the net input energy supplied in the form of fuel. For stand-alone gas turbines, without any heat recovery system the efficiency will be as low as 35 to 40 per cent.
Adiabatic process is defined as. The thermodynamic process in which there is no exchange of heat from the system to its surrounding neither during expansion nor during compression. Adiabatic process can be either reversible or irreversible.
For an adiabatic turbine which undergoes a steady-flow process, its inlet and exit pressures are fixed. Hence, the idealized process for turbine is an isentropic process between the inlet and exit pressures. The desired output from a turbine is the work output.
Turbine. A turbine is a rotary steady state steady flow machine whose purpose is the production of shaft power at the expense of the pressure of the working fluid. Normally, the process in the turbine is adiabatic and the work output reduces to decrease in enthalpy from the inlet to exit states.
Rapid compression is a very quick process, so we can assume that there is no heat transfer between the air in the pump and its surroundings. In such case we say that it is an adiabatic process, which can be described by Poisson's equation.
Isentropic (or adiabatic) Compression/Expansion Processes
If compression or expansion of gas takes place with no flow of heat energy either into or out of the gas - the process is said to be isentropic or adiabatic. The isentropic (adiabatic) process can be expressed with the Ideal Gas Law as. p / ρk = constant (2)The isentropic process is a special case of a more general process known as a polytropic process where → Pvn = constant and n is any number.
- Special Cases. n = 1.
- Pv = RT = constant ⇒ isothermal process. n = 0.
- Pv0 = constant = P ⇒ isobaric process (constant pressure) n = k.
- Pvk = constant ⇒ isentropic process (k = cp/cv)
In thermodynamics, an isentropic process is an idealized thermodynamic process that is both adiabatic and reversible. The work transfers of the system are frictionless, and there is no transfer of heat or matter. In this occasional reading, it means a process in which the entropy of the system remains unchanged.
Large Francis turbines are individually designed for each site to operate with the given water supply and water head at the highest possible efficiency, typically over 90%. In contrast to the Pelton turbine, the Francis turbine operates at its best completely filled with water at all times.
In this way, compressors increase pressure and compress gases using their blades. In contrast, turbines reduce the pressure of flow media such as steam or gases in order to convert the expansion of these media into power that makes the blades rotate.
Pressure is highest either at the end of the compressor, or right before the power turbine section. Temperature is going to be the highest in the combustion section. If it's a turboprop, then the highest velocity is probably going to be at the diffuser.
In impulse turbine all hydraulic energy is converted into kinetic energy by a nozzle and it is is the jet so produced which strikes the runner blades. In reaction turbine only some amount of the available energy is converted into kinetic energy before the fluid enters the runner.
In aeronautical engineering, overall pressure ratio, or overall compression ratio, is the ratio of the stagnation pressure as measured at the front and rear of the compressor of a gas turbine engine. The terms compression ratio and pressure ratio are used interchangeably.
Turbine is a rotary mechanical device which extracts energy from fluid flow converts it into useful work. It work on simple principle the energy from fluid flow turns the three propeller like blade around the rotor which is connected to the main shaft that spin the generator which produces electricity.
The first turbine stage, however, is often an impulse stage for controlling the steam flow and for rapidly reducing the pressure in stationary nozzles from its high steam generator value, thereby lowering the pressure that the casing has to withstand.
There are 3 main
types of impulse
turbine in use: the Pelton, the Turgo, and the Crossflow
turbine.
Turbines are also divided by their principle of operation and can be:
- An Impulse turbine, which is driven by a high-velocity jet (or multiple jets) of water.
- A Reaction turbine.
The high pressure turbine is designed to efficiently extract work out of the high pressure steam as it initially enters the main propulsion turbines. The low pressure turbine is designed to efficiently extract work out of steam which is exhausting out of the high pressure turbine at a lower pressure.
If you have water flowing through your property, you might consider building a small hydropower system to generate electricity. But a 10-kilowatt microhydropower system generally can provide enough power for a large home, a small resort, or a hobby farm.
A standard micro hydro system (where water is channelled in a pipe) should have at least 50% overall efficiency, after all losses. A small low-head turbine could generate about 1 kilowatt (1000 watts) from a flow of 100 litres per second dropping through 2 metres.
With the average person using 100 gallons of water per day for direct use, the average household of four uses 400 gallons in indirect use. Figure 2 shows that the average household can indirectly use from 600 to 1,800 gallons of water to meet their electricity needs.
The average wind turbine employed to generate electricity is a 1.5 MW wind turbine. Assuming it is constantly spinning and generating power it is on average generating enough power for 332 average size homes over the course of a single year.
A turbine is a device that harnesses the kinetic energy of some fluid - such as water, steam, air, or combustion gases - and turns this into the rotational motion of the device itself. Turbines are used in wind power, hydropower, in heat engines, and for propulsion.
Hydropower is the most efficient way to generate electricity. Modern hydro turbines can convert as much as 90% of the available energy into electricity. The best fossil fuel plants are only about 50% efficient. In the U.S., hydropower is produced for an average of 0.85 cents per kilowatt-hour (kwh).
If you don't mind equations the easiest way to explain how much power you could generate is to look at the equation for calculating hydropower:
- P = m x g x Hnet x η
- Hnet = Hgross x 0.9 = 2.5 x 0.9 = 2.25 m.
- 3 m3/s = 3,000 litres per second.
- Power (W) = m x g x Hnet x η = 3,000 x 9.81 x 2.25 x 0.751 = 49,729 W = 49.7 kW.
A typical home uses approximately 10,932 kilowatt-hours (kWh) of electricity per year (about 911 kWh per month). Depending on the average wind speed in the area, a wind turbine rated in the range of 5 to 15 kW would be required to make a significant contribution to this demand.
The output of a wind turbine depends on the turbine's size and the wind's speed through the rotor. An average onshore wind turbine with a capacity of 2.5–3 MW can produce more than 6 million kWh in a year – enough to supply 1,500 average EU households with electricity.
