A flow microcalorimeter with rapid response (20 sec) and high sensitivity (10−8 μcal/sec detectability) is described. The design of the instrument permits easy construction. The operating temperature is determined by a liquid thermostat bath that can be set as desired. Typical test results are described.

Rapid Response Flow Microcalorimeter

An isothermal displacement calorimeter for positive excess enthalpies

REVIEW ARTICLE: Differential microcalorimeters

A modification of a calorimetric technique for heat capacity measurements on small samples of low thermal conductivity is described. The sample is connected to a sink of large heat capacity by a finite thermal resistance. Step-wise electrical heating of the sample gives rise to an increase in temperature as a function of time. Accurate evaluation of specific heat capacity is possible from the recorded curve. Theoretical analysis has been made using an electrical analogy. The influence of parasitic capacities as well as of the sample geometry on the response of the sample is considered in detail. The method has been used for high-precision measurements of the specific heat anomaly in the vicinity of the nematic-smectic-A phase transition in liquid crystals.

http://iopscience.iop.org/article/10.1088/0022-3735/10/4/014/pdf

Heat capacity measurements on samples of low thermal diffusivity

Instrumentation for heat measurement in differential microcalorimetry is described in sufficient detail so the electronic apparatus can be built and used reliably with various calorimeters. Theory and calibration techniques are explained for calculating endothermic and exothermic heats from indicated digital data for reaction calorimetry and temperature scan calorimetry (including DTA). The cooler of twin calorimeter cells is heated electrically to counteract thermal effects of the system being measured. This heating is by pulses of current, all identical, whose rate of occurrence is controlled proportionally to the small residual intercell temperature gradient; counting pulses gives heat indication directly as numbers. The heat per pulse is known accurately, and the pulsed (indicated) heat is related to effects of the system under study; the relation is by a constant, near unity factor (such as 1.010) which can be calculated using easily measured calorimeter parameters. The factor is constant because hea...

Harrison B. Albert

Papers

Pulsed‐Current Control and Measurement System for Precision Microcalorimetry