Longitudinal Heat Flow Calorimetry: A Method for Measuring the Heat Capacity of Rock Specimens Using a Divided Bar

Abstract

Abstract We present a method for measuring the heat capacity of a rock specimen using a divided bar apparatus in a “transient” mode. The specific heat capacity can be derived if the mass of the specimen is known. Thermal conductivity can be measured during a steady-state phase of the measurement process, and longitudinal thermal diffusivity can also be derived if the specimen volume (and hence density) is measured. A divided bar delivers a longitudinal flow of heat through a rock specimen and is conventionally used only in a steady-state mode for thermal conductivity measurements. Our method employs a time-series record of temperature changes at four points along the divided bar assembly to compare the net thermal energy absorbed by a specimen to its change in temperature during thermal re-equilibration from one steady-state temperature to another. The technique is calibrated using a set of analytical standards of known heat capacity. Our method yields mean values of specific heat capacity within ±1 % of published values for cultured quartz. Repeated measurements on the same specimens also give consistent results within approximately ±1 %. A combined thermal conductivity and heat capacity measurement takes less than one hour per specimen. Our method can be replicated with any divided bar apparatus employing a precise electronic temperature control system capable of switching between two steady-state mean temperatures, along with a digital data-logging system capable of recording and displaying data at a rate of one record per second.