J. Phys. IVFrance 109 (2003) 99 t) EDP Sciences, Les Ulis DOI: 10.1051/jp4:20030657 Determination of thermal effusivity of liquids by use of open photoacoustic cell and front excitation configuration A. Sikorska and B. Linde Institute of Experimental Physics, University of Gdansk, Ul. Wita Stwosza 57, 80-952 Gdansk, Poland Abstract : The applied procedure of thermal effusivity determination for liquid samples taking advantage of photoacoustic signal amplitude measurement with microphone registration is presented. The experimental results obtained for distilled water and ethyl alcohol are shown to illustrate the sensitivity of the applied procedure. The results are in reasonable agreement with the data obtained from the literature. 1. INTRODUCTION 1/2 Thermal effusivity, es, is a thermophysical parameter defined as es= (pkC) s @ where where is density, k is thermal conductivity and C is specific heat of the sample. It determines the sample's ability to exchange heat with environment and therefore plays an important role in investigation of quenching processes by use of photoacoustic technique. On the other hand, photothermal methods have been successfully applied to study thermal parameters of solids and the results were presented in many publications, as for example [t,2,3]. Much less attempts have been made with liquid samples, probably because of spurious effects which are present in this case. Among them one should mention periodic evaporation and condensation or periodic thermal expansion of liquid placed in a sealed cell which can substantially change the pressure in the cell and contribute to a total signal. To avoid these difficulties one can apply the open cell configuration. In this case the measured liquid is placed outside the working volume of the cell behind thermally thin metal foil which closes the cell. Investigations of thermal effusivity of transparent liquids by use of an open photoacoustic (PA) cell with rear excitation were reported in the work [4]. Also the idea of front excitation have been applied for determination of this parameter [5,6]. In this work we present our approach to determination of thermal effusivity using open photoacoustic cell with front excitation of a metal foil and the results obtained for test liquids. 2. THEORETICAL BACKGROUND The idea of an open cell method with a front configuration is illustrated in Fig. 1. The thermally thick layer of liquid under research is placed behind a thin metal foil which closes the PA cell from the top. The metal opaque absorber is illuminated with modulated light via transparent window in the bottom of the cell. Adapting Rosencwaig and Gersho general formula (21) given in the work [7] for the case of thermally thin and optically thick metal foil (ases «<1, exp[±CY,!,] B, » as, exp[-pjs] 0) and thermaHy thick liquid layer behind thé foi! (oblb»l, exp[-0),!b]0) and