Determination of global absorptivity and emissivity of some opaque bulk materials using an integrating sphere calorimeter without ports

A design of a calorimeter based on the principle of an integrating sphere for the determination of thermal absorptance, α, and emittance, ε, of opaque bulk materials is presented. A transient technique based on the sample heating and cooling histories is employed in this work. Arrays of four thermocouples used as temperature sensors on the sample within the integrating sphere are interfaced to a thermal card on a Fluke-2286/5 data logger. Two of the thermocouples measure the average ambient temperature inside the sphere, whereas the other two thermocouples are used to obtain an average value of the temperature of the sample. The use of an 'integrating sphere calorimeter' configuration results in much simpler heat balance equations within the enclosure as opposed to other methods which take into consideration convective and radiative heat coefficients (Kola et al 1995 Meas. Sci. Technol. 6 888-92, Otieno et al 1997 Meas. Sci. Technol. 8 239-44). When solved analytically, the equations return thermophysical values which are in good agreement with values obtained using other methods and calorimeter configurations. The experimental results obtained from our 'integrating sphere' calorimeter show that the absorptance for aluminium is α ≤ 0.100 and its emittance is ε ≤ 0.176. For copper α ≤ 0.325, ε ≤ 0.240. These values compare well with other known experimental values of α ≤ 0.099 and ε ≤ 0.174 for aluminium and α ≤ 0.349 and ε ≤ 0.246 for copper respectively (Kola et al 1995 Meas. Sci. Technol. 6 888-92, Otieno et al 1997 Meas. Sci. Technol. 8 239-44). Our values are much closer to values obtained using standard techniques (Jaworske 1994 Thin Solid Films 253 233-7, http://www.sheldahl.com).