This paper describes two measurement methods for particle size distribution in gas-particle flow. One, which is called backward sampling method, utilizes "classification effect" during the backward sampling and the other, which is called the combined method, uses both backward sampling and anisokinetic sampling. We investigated the advanced procedure in which the Twomey algorithm is adapted as a data reduction method. The two methods were evaluated with numerically generated data and then

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... d to the measurement for fly ash from pulverized coal combustion. It was shown that the backward sampling method accurately estimates the particle size distribution for the particle. The combined method enables us to estimate complicated particle size distributions such as bimodal distribution. The size distributions of fly ash measured by both the backward sampling method and the combined method, are in agreement with the result obtained by the conventional method.