Short-hot-wire method for the measurement of total hemispherical emissivity of a fine fibre
Seiji Fujiwara, Xing Zhang, Motoo Fujii
A new short-hot-wire method for the measurement of total hemispherical emissivity of a fine fibre is proposed. This method uses two short hot wires and is based on the analytical solution of one-dimensional steady-state heat conduction along the hot wires and fibre. Two hot wires are arranged parallel to each other. Both the hot wires are supplied with a constant direct current to generate heat and maintain the same average temperature. A test fibre bridges the wires and its ends are attached to the centre position of each hot wire to form an H-type probe. By the use of this two hot wires technique, the total heat transmitted from the hot wires to the fibre is completely radiated from the fibre to the surroundings under vacuum conditions. Therefore, the average temperature rise of the hot wire depends on the emissivity of a fibre. The steady-state heat conduction for the H-type probe is analytically solved to obtain the accurate relationship between the temperature rise of the hot wires and the fibre emissivity. Based on this relationship, the emissivity of the fibre can be estimated when the average temperature and the heat rate of the hot wires with known thermal properties are measured. The theoretical analysis has confirmed that the present method can obtain emissivity in the range of 0.1 – 1.0 within an error of ±1% for the fibre with its diameter around 10 mm.