1. 1st Law of Thermodynamics

2. CO3:
Ability to design using concepts and principles of First Law and Second Law of Thermodynamics.
OBJECTIVE
State and Explain the First Law of Thermodynamics,
Examine the moving boundary work or PdV work
Develop the general energy balance
Calculate energy balance problems for closed systems, steady-flow systems and Engineering devices

3. Content Energy Change of a System, Esystem
The First Law of Thermodynamics
Energy Balance
Energy Change of a System, Esystem
Energy Balance For Closed Systems
Energy Balance of Steady-flow Systems
Engineering Devices

4. THE FIRST LAW OF THERMODYNAMICS
The first law of thermodynamics (the conservation of energy principle) provides a sound basis for studying the relationships among the various forms of energy and energy interactions.
The first law states that energy can be neither created nor destroyed during a process; it can only change forms.
The First Law: For all adiabatic processes between two specified states of a closed system, the net work done is the same regardless of the nature of the closed system and the details of the process.
Energy cannot be created or destroyed; it can only change forms.
The increase in the energy of a potato in an oven is equal to the amount of heat transferred to it.

5. Polytropic, Isothermal, and Isobaric processes
Constant pressure process (isobaric process)
Constant volume process (V=constant)
Constant temperature process (Isothermal process)
dV = 0
So, boundary work:
Wb = 0

6. Energy Balance
The net change (increase or decrease) in the total energy of the system during a process is equal to the difference between the total energy entering and the total energy leaving the system during that process.
The work (boundary) done on an adiabatic system is equal to the increase in the energy of the system.
The energy change of a system during a process is equal to the net work and heat transfer between the system and its surroundings.

7. Energy Change of a System, EsystemOR
Internal, kinetic, and potential energy changes

8. (1). ENERGY BALANCE FOR CLOSED SYSTEMS
Heat transfer
Work transfer
Mass flow
Energy balance for any system undergoing any process
Energy balance in the rate form
The total quantities are related to the quantities per unit time is
Energy balance per unit mass basis
Energy balance in differential form

9. Energy balance for a cycle
For a cycle E = 0, thus Q = W.
Various forms of the first-law relation for closed systems when sign convention is used.

10. Example 1 (Shaft)
A rigid tank contains a hot fluid that is cooled while being stirred by a paddle wheel. Initially, the internal energy of the fluid is 800kJ. During the cooling process, the fluid losses 500kJ of heat and the paddle wheel does 100kJ of work on the fluid. Determine the final internal energy of the fluid. Neglect the energy stored in the paddle wheel.

11. Solution
The tank is stationary and thus the kinetic and potential energy changes are zero, ∆KE=∆PE=0. Therefore, ∆E=∆U and internal energy is the only form of the system’s energy that may change during this process.
Applying the energy balance on the system gives:
Therefore, the final internal energy of the system is 400 kJ.

12. Example 2: Electric Heating of a Gas at Constant Pressure (Resistance)
A piston-cylinder device contains 25 g of saturated water vapor that is maintained at a constant pressure of 300 kPa. A resistance heater within the cylinder is turned on and passes a current of 0.2 A for 5 min from a 120-V source. At the same time, a heat loss of 3.7 kJ occurs.
Show that for a closed system the boundary work Wb and the change in internal energy U in the first-law relation can be combined into one term, H, for a constant-pressure process.
(b) Determine the final temperature of the steam.

13. (a)

14. P0=P2=P1→Q-Wother=(U2+P2V2)-(U1+P1V1) Also H=U+PV, and thus
For a constant-pressure process, the boundary work is given as Wb=P0(V2-V1). Substituting this into the preceding relation gives
Q-Wother- P0(V2-V1) =U2-U1
However,
P0=P2=P1→Q-Wother=(U2+P2V2)-(U1+P1V1)
Also H=U+PV, and thus
Q-Wother=H2-H1 (kJ)
For a constant-pressure expansion or compression process:

16. (2). ENERGY BALANCE OF STEADY-FLOW SYSTEMS
Under steady-flow conditions, the mass and energy contents of a control volume remain constant.
Many engineering systems such as power plants operate under steady conditions.
Under steady-flow conditions, the fluid properties at an inlet or exit remain constant (do not change with time).

17. Mass balances for a steady-flow process
A water heater in steady operation.
Where;
p is density,
V is the average flow velocity in the flow direction.
A is the cross-sectional area normal to the flow direction.

18. Energy balances for a steady-flow process

19. Energy balance relations with sign conventions (i. e
Energy balance relations with sign conventions (i.e., heat input and work output are positive)
when kinetic and potential energy changes are negligible
Some energy unit equivalents

20. ENGINEERING DEVICES
Many engineering devices operate essentially under the same conditions
for long periods of time.
The components of a steam power plant (turbines, compressors, heat exchangers, and pumps), for example, operate nonstop for months before the system is shut down for maintenance.
Therefore, these devices can be conveniently analyzed as steady-flow devices.
A modern land-based gas turbine used for electric power production. This is a General Electric LM5000 turbine. It has a length of 6.2 m, it weighs 12.5 tons, and produces 55.2 MW at 3600 rpm with steam injection.

21. Nozzles and Diffusers
Nozzles and diffusers are commonly utilized in jet engines, rockets, spacecraft, and even garden hoses.
A nozzle is a device that increases the velocity of a fluid at the expense of pressure.
A diffuser is a device that increases the pressure of a fluid by slowing it down.
The cross-sectional area of a nozzle decreases in the flow direction for subsonic flows and increases for supersonic flows. The reverse is true for diffusers.
Energy balance for a nozzle or diffuser:
Nozzles and diffusers are shaped so that they cause large changes in fluid velocities and thus kinetic energies.

22. Turbines and Compressors
Turbine drives the electric generator In steam, gas, or hydroelectric power plants.
As the fluid passes through the turbine, work is done against the blades, which are attached to the shaft (Wout, work transfer from fluid). As a result, the shaft rotates, and the turbine produces work.
Compressors, as well as pumps and fans, are devices used to increase the pressure of a fluid. Work is supplied to these devices from an external source through a rotating shaft (Win, work transfer to devices).
A fan increases the pressure of a gas slightly and is mainly used to mobilize a gas.
A compressor is capable of compressing the gas to very high pressures.
Pumps work very much like compressors except that they handle liquids instead of gases.
Energy balance for the compressor in this figure:

27. Throttling valves Energy balance
Throttling valves are any kind of flow-restricting devices that cause a significant pressure drop in the fluid.
What is the difference between a turbine and a throttling valve?
The pressure drop in the fluid is often accompanied by a large drop in temperature, and for that reason throttling devices are commonly used in refrigeration and air-conditioning applications.
Energy balance
The temperature of an ideal gas does not change during a throttling (h = constant) process since h = h(T).
During a throttling process, the enthalpy of a fluid remains constant. But internal and flow energies may be converted to each other.

28. Mixing chambers 10C 60C 43C 140 kPa
In engineering applications, the section where the mixing process takes place is commonly referred to as a mixing chamber.
Energy balance for the adiabatic mixing chamber in the figure is:
The T-elbow of an ordinary shower serves as the mixing chamber for the hot- and the cold-water streams.

29. Heat exchangers
Heat exchangers are devices where two moving fluid streams exchange heat without mixing. Heat exchangers are widely used in various industries, and they come in various designs.
The heat transfer associated with a heat exchanger may be zero or nonzero depending on how the control volume is selected.
Mass and energy balances for the adiabatic heat exchanger in the figure is:
A heat exchanger can be as simple as two concentric pipes.

30. Pipe and duct flow
The transport of liquids or gases in pipes and ducts is of great importance in many engineering applications. Flow through a pipe or a duct usually satisfies
the steady-flow conditions.
Pipe or duct flow may involve more than one form of work at the same time.
Energy balance for the pipe flow shown in the figure is
Heat losses from a hot fluid flowing through an uninsulated pipe or duct to the cooler environment may be very significant.