Center for Emerging Energy Sciences

                     

Precision Metrology & Precision Measurement Science:

Vacuum Calorimeter

An open-system differential vacuum calorimeter was design and developed at our laboratory. A calorimeter is used to measure the heat output of a system contained within the calorimetric boundary. The calorimeter is contained within the vacuum vessel, and operated in the Knudsen regime, to eliminate nonlinear convective losses. Superinsulation has been used to reduce radiative transfer with-in the vacuum vessel. A differential calorimeter approach was used to improve the calorimetric response via common-mode rejection. 

A scroll pump (Edwards nXDS15i) and 6-inch turbomolecular pump (Varian Turbo-V 300HT) are used to achieve high vacuum (1E-7 torr). Commercially available thermoelectric modules (TEM) are used both as passive heat-flux sensors as well as active heat pumps. The heat pumps are utilized to control an isothermal reservoir to provide a reference temperature for the passive TEMs. A custom fabricated liquid cooled heat-sink has been utilized to remove waste heat generated by the heat pumps. The active TEMs are controlled via a bipolar proportional-integral-derivative (PID) controller (TE Technology TC-720); the control reference is a 15 kΩ thermistor embedded into isothermal reservoir. 

The calorimeter was designed to house two containers, an active container, and a control container. Two different container styles were also evaluated: a wet container used for electrochemical cells, and a dry container used for gaseous environments. Operating temperature is limited to 250 °C because of the heat pumping capability of the TEMs used to control the isothermal reservoir temperature. The calorimeter was designed for input powers ranging from 1 mW to 28 W; linear calibration up to 28 W yielded a Pearson's r exceeding 0.999.