Woodceramic Heating Elements for Low Temperature Heating

摘要

Woodceramics are carbon-carbon composites produced by impregnating plant-origin lignocellulosic materials with phenolic resin and by carbonizing the resulting precursor at temperatures higher than 650 deg C. Since the electric resistance of the woodceramics changes as a function of the carbonizing temperature, heating elements for use in biological incubator systems can be prepared by controlling the electric resistance to obtain optimal Joule heat. Woodceramic heating blocks carbonized at temperatures lower than 800 deg C were found preferable from the viewpoint of lower water absorptivity. Then, woodceramic test specimens (310 x 52 x 18 mm~3) were produced from medium density fiberboard (MDF) at carbonizing temperatures of 650, 700, 750, and 800 deg C (which are simply denoted as 650, 700, 750, and 800, respectively). The electric resistance of the test specimens 650, 700, 750, and 800 at applied voltage of 10 V was 50, 10, 8, and 4 OMEGA, respectively. Thus, single test piece of 650, 3 serially connected 700, 7 serially connected 750, and 10 serially connected 800 were used to obtain the temperature profile. Temperature rise of each test specimen was measured under applied voltages of 10, 20, 30. and 40 V. For 650, fair temperature stability was obtained at 22 C (10 V) and 27-3 PC (20 V). The advantages of the woodceramic heaters as compared with the conventional ceramic heaters are: (1) quick rise in temperature; (2) high stability at designated temperature; (3) lower power consumption; and (4) free of air convection (heats the sample directly and homogeneously).