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Thermo cht 2
| Term | Definition |
|---|---|
| Energy (E) | an extensive property E = KE + PE +U |
| kinetic energy | KE = 1/2 mV^2 |
| (gravitational) potential energy | PE = mgh |
| (molecular) internal energy | U=m(u2-u1) |
| Two forms of energy transfer in closed systems | Work & Heat |
| Work (W) | A form of energy transfer of which the sole effect “could have been” the raising of a weight Units : J = N∙m or ft∙lbf , Btu |
| path function | depends not only on the properties of the two end states but also on the path of the process. |
| inexact differential | example: work |
| exact differential | example: temperature |
| point function | the integral depends only on the two end states example: temperature |
| polytropic process: | for both closed systems and open systems: pv^n=c for closed systems: pV^n=c |
| Heat (Q) | A form of energy transfer that occurs due to temperature difference -path function -not a property - inexact differential |
| Power (W) | the rate of energy transfer by work Units = J/sec =W (→ Watt) or ft∙lbf/sec , Btu/h , hp |
| Rate of Heat transfer (Q) | the rate of energy transfer by heat |
| Three types of heat transfer defined in this course: | Conduction Convection Radiation |
| Conduction | heat transfer through direct contact in solids, liquids, and gases |
| Convection | heat transfer between the solid surface and the moving fluids |
| Radiation | heat transfer due to electromagnetic waves (or photons) without direct contact or intervening medium |
| forced convection | Newton's Law of cooling Q DOT = -hA(Tb-Tf) |
| Heat transfer can be neglected if: | 1) a good insulator is used 2) the temperature difference is very small 3) the surface area is too small to allow significant heat transfer 4) there is not enough time for heat transfer. |
| Heat Flux (qDOT) | QDOT per unit area |
| Specific Energy (e) | energy per unit mass |
| Specific Internal Energy (u) | internal energy per unit mass |
| The 1st Law of Thermodynamics | the conservation of energy For closed systems, E = Q −W |
Created by:
thermosucks
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