Netsu Bussei

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The gaseous diffusion coefficients of HFC134a (CH₂FCF₃) and HFO1234yf (CH₂ = CFCF₃) into dry air, nitrogen and oxygen have been measured in the temperature range 303.2-453.2 K and at atmospheric pressure by the use of the Taylor dispersion method. The diffusion coefficients into oxygen only could be measured correctly in the entire temperature range and the measurements for dry air and nitrogen in the temperature range 423.2-453.2 K, having abnormally small temperature coefficients, were judged to be too small. At temperatures up to 393.2 K where all the measurements are considered to be correct, the diffusion coefficients do not vary in practice on substituting pure nitrogen or oxygen for dry air. The diffusion coefficients increase with decreasing molecular weight and those for HFO1234yf and HFC134a are systematically higher than those for CFC12 (previously reported) by about 4% and 6%, respectively. The present results with reasonable temperature coefficients can be reproduced well by the functional form D = AT^B, where D (cm²s^-1) is the diffusion coefficient at 101.325 kPa (1atm) and T(K) is the absolute temperature. The constants A and B are as follows: HFC134a- (air, nitrogen, oxygen), A = 5.04×10^-6, B = 1.75; HFO1234yf- (air, nitrogen, oxygen), A = 4.93×10^-6, B = 1.75.

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