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On the Construction and Calibration of Dual-Probe Heat Capacity Sensors

Dep. of Agronomy, Kansas State University, Manhattan, KS 66506

View larger version (19K): [in a new window]   Fig. 1. Diagram of a dual-probe heat capacity sensor. For some sensors, the length of the temperature probe was reduced to 18 mm.

View larger version (33K): [in a new window]   Fig. 2. Effect of calibration media on the estimate of rapp. Shown are data from sensors with (a) full-length, 28 mm, temperature probes and (b) shortened, 18 mm, temperature probes. Comparisons are made among sensors constructed from 1.27- and 1.67-mm diam. stainless steel needles mounted in bodies fabricated from high thermal conductivity (HTC) RBC4300 epoxy and low thermal conductivity (LTC) urethane epoxy. Different letters indicate rapp is statistically different within a given media type (P < 0.10).

View larger version (16K): [in a new window]   Fig. 3. Temperature increase at the temperature probe following an 8-s, 858-J m–1 heat pulse in water-saturated and dry glass beads. Data are from an experimental sensor (1.27-mm probes, urethane body) with fine-wire thermocouples attached 4 and 14 mm from the sensor body. Arrows depict the time of maximum temperature increase.

View larger version (22K): [in a new window]   Fig. 4. Effect of pulse length on the estimate of rapp. Shown are data from sensors with (a) full-length, 28 mm, temperature probes and (b) shortened, 18 mm, temperature probes. Comparisons are made among sensors constructed from 1.27- and 1.67-mm diam. stainless steel needles mounted in bodies fabricated from high thermal conductivity (HTC) RBC4300 epoxy and low thermal conductivity (LTC) urethane epoxy. Results from the instantaneous pulse (Eq. [1]) and finite pulse (Eq. [2]) models are shown.

View larger version (14K): [in a new window]   Fig. 5. Effect of interval between repeated measurements on the determination of rapp.