Methods & Means for Property Measurement & Need For A Law P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Be Cautious, while Numerically Describing a Macroscopic Property… …

Temperature Scales Significance of Temperature FahrenheitCelsiusKelvin 9,944.45°F5,506.92°C5, K Black body temperature of visible surface of Sun 6,169.76°F3,409.87°C3, KFreezing point of tungsten 3,034.26°F1,667.92°C1, KFreezing point of titanium 1,984.32°F1,084.62°C1, KStandard freezing point of copper 1,947.53°F1,064.18°C1, KStandard freezing point of gold 1,763.20°F961.78°C1, KStandard freezing point of silver 1,220.58°F660.32°C KStandard freezing point of aluminum °F419.53°C KStandard freezing point of zinc °F231.93°C KStandard freezing point of tin °F156.60°C KStandard freezing point of indium 212°F.00100°C KStandard boiling point of water 136°F °C KWorld record high air temperature

Multiple Options :Temperature Measuring Devices  Liquid in glass  Bimetallic  Thermocouple  Resistance Temperature Detectors  Radiation and optical pyrometers  Gas thermometers

Liquid in Glass Thermometer

MaterialCoefficient of Volumetric Thermal Expansion  in /K Mercury180 Ethyl Alcohol1120 petrol950 Water0 to 695 (4 to 90 0 C) Glass9.9

Bimetallic Expansion Thermometer Free End At Reference Temperature At Higher Temperature A Measure of Temperature Material  in /K Chromium4.9 Copper16.5 lead28.9 Zinc30.2

The Problem of Quantification of Temperature Numerical description of temperature demands a zero temperature point. Each temperature scale identified one such zero temperature point. Most popular zero was freezing point of water. Knowing the true zero was felt to be a scientific challenge.

Ideal Gas Temperature Scale This is the most important empirical scale. An ideal gas is defined to be one which obeys Boyle’s Law. Boyle’s Law: At constant temperature, the volume of a gas varies inversely with pressure. Mathematically: T is the empirical temperature, a (primitive) property….

Gas Thermometers

Further Experiments on Gas Thermometers T ( 0 C) P, kPa

Further Experiments on Gas Thermometers : Unit mass of Gas at a fixed volume T ( 0 C) p, kPa Gas A Gas B Gas C Absolute Zero!

Further Experiments on Gas Thermometers : Unit mole of gas T ( 0 C) p, kPa Gas A Gas BGas C Absolute Zero!

Further Experiments on Gas Thermometers : Unit mole of gas T ( 0 C) p, kPa Absolute Zero!

98.60°F37°C KHuman body temperature reference 85.58°F29.76°C KStandard melting point of gallium 68°F.0020°C KRoom temperature reference 39.15°F3.97°C KTemperature of maximum water density 32.02°F0.01°C KTriple point of water 32°F.000°C KStandard freezing point of water 0°F °C KFahrenheit's zero °F-38.83°C KTriple point of mercury °F-89.20°C KWorld record low air temperature °F °C83.81 KTriple point of argon °F °C54.36 KTriple point of molecular oxygen °F °C24.56 KTriple point of neon °F °C13.80 KTriple point of molecular hydrogen °F °C0 K.00Thermodynamic absolute zero

Thermodynamic Temperature There is a naturally-defined zero on this scale. It is the point at which the pressure of an ideal gas is zero, by making the temperature also zero Thermodynamic temperature is the fundamental empirical temperature; its unit is the Kelvin which is defined as the fraction 1/ of the thermodynamic temperature of the triple point of water. How to use these quantified macroscopic properties to identify a Thermodynamic System ?

State of A Thermodynamic System The collection of all properties for a thermodynamic system at a certain condition is defined as the state of the system. These properties are not independent. It was observed that any of them can be expressed as a function of some of the others. The first three as internal properties of state. While the others as called state-functions. Internal and external properties of state are generically mentioned as variables of state. If the variables of state can take arbitrary values, they are defined as independent variables; in the opposite case, they are called dependent variables.

What is the beginning of Happening …… What is the culmination of Happening ……

Scottish physicist Joseph Black On returning to Glasgow as professor in 1756, Black met up with James Watt ("mathematical instrument maker to the University"). This meeting stimulated the next phase of his work involving the concept of latent heat, and the first steps in calorimetry. Here again, it was the quantitative aspects of his work which led to his discoveries, particularly in the careful measurement of heat. "He waited with impatience for the winter" in Glasgow so that he could do experiments on the freezing and melting of water and water/alcohol mixtures that led to the concept of latent heat of fusion.

Scottish physicist Joseph Black in his (1786) Lectures on Chemistry, as such: “[There exists] a tendency of heat to diffuse itself from any hotter body to the cooler around, until it be distributed among them, in such a manner that none of them are disposed to take any more heat from the rest. The heat is thus brought into a state of equilibrium. This equilibrium is somewhat curious. We find that when all mutual action is ended, a thermometer, applied to any one of the bodies, acquires the same degree of expansion: therefore the temperature of them all is the same, and the equilibrium is universal.”

Equilibrium Frequently we will refer not only to the properties of a substance but to the properties of a system. It is necessarily imply that the value of the property has significance for the entire system. This implies equilibrium. Every system in this universe spontaneously move towards equilibrium.

Thermal Equilibrium It is observed that a higher temperature object which is in contact with a lower temperature object will spontaneously transfer heat to the lower temperature object. The objects will approach the same temperature, and in the absence of loss to other objects, they will then maintain a equal temperature. They are then said to be in thermal equilibrium. Thermal equilibrium refers to equality of temperatures. Thermal equilibrium is the subject of the Temperature measurement.

Zeroth Law of Thermodynamics An Universal Law for Measurement …

Zeroth Law of Thermodynamics The "zeroth law" states that two thermodynamic systems in thermal equilibrium with the same environment are in thermal equilibrium with each other. If A and C are in thermal equilibrium with B, then A is in thermal equilibrium with C. Maxwell [1872] Practically this means that all three are at the same temperature. A basis for comparison of effect of temperatures.

Demonstration of Zeroth Law When Two bodies have equality of temperature with a third body, they in turn have equality of temperature with each other. BRASS Copper If the substance that composes the system is in thermal equilibrium, the temperature will be the same throughout the entire system, and we may speak of the temperature as a property of the system