Heat And Work Flashcards
Thermodynamics
Relationship between the properties of a substance and the quantities of work and heat- cause a change in the thermodynamic state.
Thermodynamics in context: piston engine, jet engine, compressors, boilers, turbines, cooling towers and heat exchangers. Deal with the transfer of heat and work.
Uppercase- absolute quantities, lowercase- specific quantities,
Describing processes
Fluids can be compressed. Expanded, heated, cooled. Described in terms of systems, states with boundaries and surroundings. Systems are closed/ open, steady/ unsteady.
Thermodynamics system
Any defined region where we study the energy and matter interactions with its surroundings. Systems are classified with how they exchange matter with the environment around them (surroundings).
Systems
An isolated system, should have no exchange of matter and heat.
A closed system, has no exchange of matter but CAN exchange heat.
Open system can exchange heat and matter.
Open steady system has continuous exchange of both energy and matter with its surroundings, constant properties.
Open unsteady allows the exchange of matter and heat, properties change over time.
Closed unsteady allows energy transfer but does not allow matter to enter/ leave.
Flow and non flow processes
Flow- on a fluid, open system
Non flow- on a fluid, closed system
Thermodynamics state
Determined by values of its properties at that moment (temp, enthalpy). Properties are the characteristics of a system which can be used to describe the state of a system. State can be determined by only two independent properties. State of system changes when heat/ work travel across a boundary.
More work for the same pressure and volume for repairing a piece of equipment.
State
Thermodynamic state depends on properties. Change in property= final- initial value. Value of properties are irrespective of intermediate states.
Thermodynamic equilibrium
Achieved in a system when no further changes take place if it were isolated from its surrounding.
Reversible and non reversible process
When a fluid is in thermal equilibrium. When a fluid changes state, it undergoes a process.
If fluid is not in thermal equilibrium, it is non reversible.
Zeroth law
If two bodies are at equal temp to a third body, they are also equal to temp to each other.
Define work
Height can be defined as a property of a system. Work done when a force moves object through a distance. If a part of a system boundary undergoes a displacement under the action of pressure, work done= force*distance.
Change of state; work
W+ work appears at the boundary when a system changes its state due to the movement BY the system
W- work done ON the system when work is transferred at system boundary. Example is chipurning, since paddle is moving against the resisting force of the fluid.
When work is being done by a system it is W-. Any energy that is in that fluid, it is going to go down., we have lost some of it as work. When heat is added, it is Q+.
Work Wand heat Q
W is + when transferred outwards.
Q is + when transferred inwards.
