1	Thermodynamics I Asst.Prof.Dr.Denpong Soodphakdee Department of Mechanical Engineering
2	Heat Transfer Heat :- the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference.
3	Heat Transfer Heat has energy unit kJ (or Btu) Heat transferred between state 1 and 2 is denoted by Q₁₂ or just Q. Heat transfer per unit mass of a system is denoted by q.
4	Heat Transfer Heat transfer rate :- amount of heat transferred per unit time, denoted by . Amount of heat transferred during process determined by
5	Energy Transfer by Work Work :- the energy transfer associated with a force acting through a distance. Work is also a form of energy transferred like heat, therefore has unit of energy such as kJ. Work done during a process between state 1 and 2 is denoted by W₁₂ or just W. Work done per unit mass
6	Energy Transfer Formal sign convention Heat transfer to a system and work done by a system are positive Heat transfer from a system and work done on a system are negative
7	Energy Transfer Heat and Work are energy transfer mechanisms between system and its surroundings Both are recognized at boundaries of a system that is both heat and work are boundary phenomena System posses energy, but not heat and work Both are associated with process, not a state. Unlike properties, heat and work has no meaning at a state Both are path function (i.e. their magnitudes depend on the path followed during a process as well as the end states (start and end).)
8	Energy Transfer Heat and work are path function. Path functions have inexact differential designed by symbol d. Differential amounts of heat and work are dQ and dW, respectively. Properties are point functions. Point functions have exact differential designed by symbol d. Example of differential of volume is dV.
9	Energy Transfer Total volume change during a process between states 1 and 2 is Total work done during process 1—2 is
10	Electrical Work Electrical power is the rate of work done by electrical charge. Electrical work done during a time interval can expressed in terms of current I and potential difference V.
11	Mechanical Forms of Work The work done is proportional to the force applied (F) and the distance traveled (s).
12	Moving Boundary Work The expansion and compression work is often called moving boundary work or simply boundary work.
13	Moving Boundary Work
14	Boundary Work The net work done during a cycle is the difference between the work done by the system and the work done on the system.
15	Constant Volume Process During a process where volume of the system is kept constant, the boundary work is then equal to zero (dV = 0)
16	Isobaric Process A constant pressure process is called isobaric process.
17	Isothermal Process A constant temperature process is called isothermal process.
18	Polytropic Process During actual expansion and compression processes of gases, pressure and volume are often related by PVⁿ = C, where n and C are constants. A process of this kind is called a polytropic process.
19	Polytropic Process
20	Polytropic Process For the special case of n = 1 the boundary work becomes
21	Example
22	Gravitational Work Potential energy change equation is derived from
23	Acceleration Work Kinetic energy change equation is derived
24	Shaft Work
25	Spring Work
26	Example A piston-cylinder device contains 0.05 m³ of a gas initially at 200 kPa. At this state a linear spring which has a spring constant of 150 kN/m is touching the piston but exerting no force on it. Now heat is transferred to the gas, causing the piston to rise and to compress the spring until the volume inside the cylinder doubles. If the cross-sectional area of the piston is 0.25 m², determine (a) the final pressure inside the cylinder, (b) the total work done by the gas, and (c) the fraction of this work done against the spring to compress it.
27	Conservation of Mass Principle Net mass transfer to or from a system during a process is equal to the net change (increase or decrease) in the total mass of the system during that process
28	Conservation of Mass Principle Mass balance for a control volume Can be written in rate form
29	Conservation of Mass Principle Mass balance for steady-flow processes
30	Flow Work and The Energy of A Flowing Fluid
31	Total Energy of a Flowing Fluid Total energy of simple compressible system per unit mass
32	Total Energy of a Flowing Fluid Total energy of a flowing fluid per unit mass
33	Total Energy of a Flowing Fluid