An Easier Approach to Introduce Entropy in Undergraduate Thermodynamics Classes

The common tutorial method of teaching entropy is far twisted and complicated. The convention is to first present Carnot corollaries followed by a “rational argument” to justify the corollaries. In the next step, the efficiency of Carnot engine is argued to be solely dependent on the thermal reservoirs temperatures. Then, thermodynamic temperature scale is introduced to show QL/QH equals TL/TH followed by the Clausius inequality, and finally introducing entropy S. It is not surprising why entropy has been one of the most difficult concepts to teach or learn. The way it is taught in textbooks is not straight unlike many other properties and concepts that are comparably much less cumbersome to understand. Interesting to note is that the inventor of entropy; Clausius, derived the famous Carnot efficiency by simply using the p-V diagram of a Carnot cycle operating with an ideal gas. The objective of this article is to shed light to the original method of Clausius and to present a simple and easy-to-digest approach, so students can better understand where entropy is originated from. Furthermore, we will show that the proof of Carnot corollaries is not concrete and certain objections can be raised.

Calorimetric determination of the deviation between the International Practical Temperature Scale 1968 and the Thermodynamic Temperature Scale

A flow calorimeter was constructed to measure the isobaric heat capacity cp for dilute fluids for pressure [Formula: see text] and for temperature [Formula: see text]. The special design features of the calorimeter facilitate measurements at extremely high accuracy. In this paper the measurements have been used to explore the metrology of the temperature. Measured values of cp were compared with corresponding theoretical values calculated via statistical mechanics. From the comparison, the deviation between the International Practical Temperature Scale of 1968 and the (theoretical) Thermodynamic Temperature Scale has been obtained. The results of this metrology are in good agreement with those obtained with the PVT gas thermometer and those obtained by radiometry. The comparison establishes the accuracy of the calorimeter and, more important, the feasibility of cp metrology, especially for probing local stretching or contraction of the International Practical Temperature Scale. The integration of this distortion, starting from the triple point of water, yields the deviation between the scales. It is, e.g., between 30 mK and 40 mK at the boiling point of water, according to our results.

Temperature, Strain, and Magnetic Field Measurements

This chapter discusses three measurements parameters: temperature, strain, and magnetic field strength. It stresses the measurement of temperature because it is the primary variable in nearly all low-temperature material properties. The chapter contains information on methods and auxiliary materials. Areas of frequent concern, such as thermal contact, heat leak, thermal anchoring, thermal conductivity of greases, insulators, lead wires, ground loops, and feedthroughs are also reviewed. The chapter provides an overview and historical development of temperature scales because the practical use of all thermometers is associated with some approximation of the thermodynamic temperature scale. A short section is devoted to types of temperature measuring devices. The characteristics of commercially available resistance-type strain gauges at low temperatures are stressed.