Law Of Conservation Of Energy In Energy Balance

University:
Elon University
Course:
PHY 2010 : General Physics I
Academic year:

2023
Views:

415

Pages:

3
Author:

Gebrakan B

Energy Conservation Law: Fundamentals and Implications in Total Energy Systems Concept of the Law of Conservation of Energy The total energy of the system and environment cannot be created or destroyed. 2.1 Energy Balance for Closed and Unsteady-state Systems Macroscopic mass balance for closed, unsteady-state systems (Accumulated mass in the system) = (mass in) - (mass out) M system m Go to -m (2.1) out Analogously, the macroscopic energy balance for a closed system, Unsteadystate can be written (Accumulated energy in the system) = (energy in) - (energy out) (U EP EK ) system E Q W (2.2) Work (W) done to the system System energy (U+ EP + EK)=E (E can changes over time) Heat (Q) enters the system Figure 2.1 Closed, unsteady-state system with heat (Q) and work (W). lOMoARcPSD|26370826 Example 2.1. Closed system energy balance application Alkaloids are nitrogen-containing chemical compounds that can be produced by plant cells. In a study, a closed tank as shown in figure C2.1, the cylinder has a volume of 1.673 m3 filled with water containing two alkaloids, ajmalisin, and serpentine. The temperature of the solution is 10 o C, to get dry alkaloids, 1 kg of water in the tank will be evaporated. The assumed properties of water can be used to replace the properties of the solution. How much heat must be transferred to the tank if 1 kg of saturated liquid water at 10o C is completely vaporized with an end state of 100 o C at 1 atm Figure C2.1 Completion: The displayed data can be used to find other properties in the steam table Initial condition data, p = 1 atm, T = 10o C, and Ȗ = 41.99 kJ/kg, final condition data, p = 1 atm, T = 100o C, and Ȗ = 2506 kJ/kg Closed system. Unsteady state so can use pers. 2.1 (U EP EK ) system EK 0 E Q W ,because water is at rest EP 0 ,because the water in the center changes very little lOMoARcPSD|26370826 water flow in the tube is maintained by using a regulator. In boiler systems, simplify the general energy balance equation as much as possible by considering the assumptions used. 2. Calculate Q for the system in figure S2.1 below Figure S2.1 3. A 13 MW steam turbine operates under steady state conditions using 20 kg/s of steam. Steam inlet conditions are pressure 3000 kPa and temperature 450o C. Outlet conditions are 500 kPa, saturatred vapor. Inlet steam velocity is 250 m/s and outlet steam velocity is 40 m/s. What is the heat transfer in kW for the turbine as a system?