ME200 01-02

013 bars 147 psi 37 temperature 0th law of

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Unformatted text preview: e SI pressure units 1 Pa = 1 N/m2 1 bar = 105 Pa = 100 kPa 1 atm = 1.013 bars = 14.7 psi 37 Temperature • 0th law of thermodynamics If objects A and B are separately in contact with a third object C, then A and B are in thermal equilibrium with each other if placed in thermal contact 38 Temperature • • • Two objects in thermal equilibrium with each other are at the same temperature Temperature is the property that determines whether or not an object is in equilibrium with other objects A device that is used to measure the temperature of a system is a thermometer, which makes use of the temperature dependence of some physical property, e.g. volume, length, pressure, electrical resistance, color etc. 39 Examples of Thermometers Thermometer Physical Property Measured • Ideal gas Pressure and volume of dilute gas • Mercury bulb Expansion or contraction of fluid • Bimetallic strip Difference in expansion of two solid • Thermocouple Voltage across dissimilar metals • Optical Pyrometer Color of emitted light 40 Constant-Volume Gas Thermometer This is the standard thermometer • Temperature is proportional to pressure T=a+bp • 41 Temperature • Celsius scale: We assign 0oC => freezing point of water at 1 atm 100oC => boiling point of water at 1 atm 42 Temperature • Lowest possible temperature: • 0o Kelvin temperature 43 Temperature, Problem Solving 44 45 Temperature • Kelvin scale: • Rankine scale • Conversion: T(oC) = 5/9 (T(oF) - 32)T(oC) = 5/9 (T(oF) + 40) - 40 T(oF) = 9/5 T(oC) + 32 T(oF) = 9/5 (T(oC) + 40) - 40 46 Example 2-2 At 3:25 am on January 7, 2014, the air temperature in West Lafayette was -14oF. Most household freezers maintain a temperature around −20°C. Which temperature was higher? 47...
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