9. state
second law of thermodynamics. Distinguish
between heat engine and refrigerato
Answers
Answer
The total entropy of an isolated system can never decrease on time and is constant if and only if all processes are reversible
Q. 1.
The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant if and only if all processes are reversible. Isolated systems spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy.
Also:
Energy is the ability to bring about change or to do work. The Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy.
The second law of thermodynamics, says that when energy changes from one form to another form, or matter moves freely, entropy (disorder) in a closed system increases. Differences in temperature, pressure, and density tend to even out horizontally after a while.
The Second Law of Thermodynamics, states that entropy within an isolated system always increases. This iron-clad law has remained true for a very long time. It predicted that there are certain conditions where entropy might actually decrease in the short term.
Some examples for the law:
(a) Heat transfer occurs spontaneously from hot to cold and not from cold to hot. (b) The brakes of this car convert its kinetic energy to heat transfer to the environment. The reverse process is impossible. (c) The burst of gas let into this vacuum chamber quickly expands to uniformly fill every part of the chamber.
- No process is possible whose result is the absorption of heat from a reservoir and the complete conversion of the heat into work.
- The Second Law of Thermodynamics is universal and valid without exceptions.
Q. 2.
A refrigerator is a reversed heat engine. Heat is transferred from the lower temperature level to higher temperature by applying external work to maintain the temperature below atmospheric temperature.Overall, heat is been extracted from the room and delivered to the outside air. The compressor consumes electric energy during this process and that energy also becomes thermal energy in the outside air.
Heat engine makes use of the properties of thermodynamics to transform heat into work. A heat pump is a similar device exept the condenser temperature is controlled to provide a heat source in a building. The condenser is inside the building and the evaporator is outside. Fans are required to move the air as it is a system in an open environment.
A heat engine is not a temperature control system, it is a system that uses Heat to convert it into Kinetic energy, which is the energy of movement.
A refrigerator has a compressor pump, an evaporator, a condenser, probes and controller, pipework connecting all of these and refrigerant such as CO2 or R114a. The evaporator is inside the refrigerator and any warm air in the inside of the fridge causes the refrigerant to evaporate, this causes a cooling effect as the energy to change the liquid to a gas is provided by the heat transfer. So the heat energy inside the refrigerator is used up. This occurs constantly as the refrigerant is pumped around the circuit. The cooling causes the temperature inside to fall. When it reaches around 3 degrees C, the eev which is an expansion valve, is closed by the controller via the sensing the temperature probe inside the refrigerator. This is openned again once the temperature reaches 5 degrees C for example. So an average temperature of 4 degrees C is maintained at the cost of the power supplied to the compressor pump,lights and controller power supply.
Heat pump and refrigerator are devices which transfer the heat from colder region to hotter region. And you need some kind of work input to do that as it is not a spontaneous process (2nd law of thermodynamics).
They both work on the same thermodynamic cycle. The difference in heat pump and the refrigerator is that when it comes to heat pump, we are concerned with the hotter region and when it comes to refrigerator, we are concerned with the colder region.
Pic up the points as to make your answer the best.
HOPE THIS HELPS.