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SFEE for liquid nozzles, pumps and water turbine: toward the Bernoulli equation

SFEE for liquid nozzles, pumps and water turbine: toward the Bernoulli equation. Assumptions: Incompressible substance, B. Negligible heat transfer C. negligible friction despite “the rubbing liquid layers” D. B and C leading to near isothermal operation. SFEE applied to heat exchangers.

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SFEE for liquid nozzles, pumps and water turbine: toward the Bernoulli equation

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  1. SFEE for liquid nozzles, pumps and water turbine: toward the Bernoulli equation Assumptions: Incompressible substance, B. Negligible heat transfer C. negligible friction despite “the rubbing liquid layers” D. B and C leading to near isothermal operation.

  2. SFEE applied to heat exchangers hot (h) cold (c) Take CV enclosing the stream that is hot at inlet Take CV enclosing the stream that is cold at inlet

  3. Mixing chambers or “direct contact heat exchangers” 3 2 1 Conservation of mass Conservation of energy

  4. Throttling devices Flow restriction A device that causes a drop in pressure by restricting the flow passage can be termed a throttling device.

  5. Throttling devices • Slow flows, DKE effects can be • neglected Flow restriction Capillary tube expansion valve used to drop refrigerant pressure and temperature Throttling is an isenthalpicprocess. Negligible heat transfer (small devices) Fundamentally, non-quasiequilibrium.

  6. Physical effects in throttling From upstream to downstream section: Pressure (P) drops (due to fluid-solid friction) Velocity increases slightly Specific volume increases Temperature of fluid may increase or decrease or remain same (Joule Thomson effect). The fluids for which temperature decreases are candidates for use in refrigerators. Ideal gas temperature remains same. Incompressible substance  temperature increases Throttling of a refrigerant on T-v / P-v diagram (on board).

  7. Throttling calorimeter to measure steam quality P-v diagram? Board!

  8. Reading assignment • Cyclic processes in engineering: “Power cycles” and “Refrigeration cycles”. (Moran Section 2.6, next slide) • System integration of steady flow devices to execute composite processes and power/refrigeration cycles (Subsectiontitled “System Integration” of Section 4.3, next slide) • Special topics (not in book, may be covered in lecture) • Differential form of the steady flow energy equation • The quasi-equilibrium steady flow heat transfer.

  9. First law analysis of a simple power cycle For the closed system shown: Do steady state open system analysis of all components. Boilers/condensers are heat exchangers where one fluid undergoes (here the working fluid of the power plant, usually steam) undergoes vaporization/ condensation Thermal efficiency of a power plant

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