Lecture_3

# Lecture_3 - ME 2322 Engineering Thermodynamics I Lecture 03...

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ME 2322 Engineering Thermodynamics I Lecture 03, 1/20/11 Prof. Zhaoming He

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Chapter 1 Introduction and Basic concepts • Concepts – Dimension and units – System and surroundings – Closed system (control mass) and open system (control volume) – properties and state – state equilibrium and postulate – process and cycle • Review concepts of temperature and Pressure • Introduce a systematic problem-solving technique.
Static Fluid Pressure Calculation Choose reference point O (known pressure P 1 ) Measure distance Δ z from reference point to the point of interest of pressure Apply formula (regardless of x,y) Δ z is “+” if in gravitational direction Δ z is “–” if against gravitational direction) z g P P + = ρ 1 2 Z is gravitational direction O

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Pascal’s Law • The pressure applied to a confined fluid increases the pressure throughout by the same amount • Two hydraulic cylinders of different areas could be connected to exert a greater force 2 1 2 1 F F P P =
Multiple Fluids For the multiple immiscible fluids of different densities, the pressure at interfaces between the fluids is continuous (no discontinuous jump) Pressure at 1 (bottom of fluid 1) can be calculated by multiple steps of accumulation of multiple fluid region (starting from position with known pressure) P1 P2 P3 3 3 3 2 2 1 1 P gh gh gh P atm = + + + ρ ρ 1 1 1 gh P P atm + = 2 2 1 2 gh P P + = 3 3 2 3 gh P P + =

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1-87 A multifluid container is connected to a U-tube, as shown in the figure. For the given specific gravities and fluid column heights, determine the gage pressure at A. Also determine the height of a mercury column that would create the same pressure at A. Glycerin
Barometer Atmospheric pressure is measured by inverting a liquid-filled tube in a container that is open to atmosphere P atm = ρ gh h=760 mmHg Stardard P atm =101325 kPa at sea level and 0°C at standard g – P atm changes with elevation

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1. Problem statement: collect key information, understand problem and objective 2. Schematic: sketch physical system, list key features, relationship: properties, process, energy and mass interaction 3. Assumptions and approximations : simplify the problem by assume reasonable necessary values, relationship 4. Physical laws, properties: conservation of mass, energy 5. Analysis, calculations: determine unknowns, pay attention to unit 6. Reasoning, verification, and discussion: check the results
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Lecture_3 - ME 2322 Engineering Thermodynamics I Lecture 03...

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