BRIEF COMMUNICATION AN EXPERIMENTAL APPROACH FOR THE DETERMINATION OF DEVELOPMENT LENGTH IN PARTICULATE FLOWS MELDA OZDINC CARPINLIOGLU and MEHMET YASAR GUNDOGDU Department of Mechanical Engineering, Gaziantep University, Gaziantep 27310, Turkey (Received 9 March 1997; in revised form 25 June 1997) 1. INTRODUCTION Since Boothroyd (1966), there has been continuing research on the modelling of two-phase particulate ¯ows with special emphasis paid to the associated pressure drop and drag reduction due to the practical importance of the manner. However, complete understanding has not been reached yet, and as Coughran (1988) has suggested in his paper there is need for more exper- imental information on gas±solid ¯ow systems. Some of the theoretical and experimental investi- gations conducted up to now are given in the papers of Rossetti and Pfeer (1972); Pfeer and Kane (1974); Radin et al. (1975); Yang (1978); Garner and Kerekes (1980); Michaelides and Roy (1987); Rizk and Elghobashi (1989); Kennedy and Kollmann (1993). Furthermore, the hand- books by Govier and Aziz (1977) and Hetsroni (1982) should be cited here as direct references to consult for the ¯ow of multiphase systems. A survey of the related literature has pointed out that the basic parameters in¯uencing the particulate ¯ows are the size and shape of the particle, particle loading ratio, Reynolds number, Re, of ¯ow, and ¯ow direction. An experimental investigation conducted on the determination of development length of two- phase particulate ¯ows is presented in this Brief Communication. Solid particles of considerably greater size than those referred to in the cited literature were used, directed also towards the simulation of pneumatic conveying of solids in pipelines. Irregular shaped granular solid par- ticles were loaded into air ¯owing through a horizontal pipe by means of a particle feeder. The development length of a two-phase ¯ow ®eld can be determined either using the velocity pro®les (Lodes and Mierka, 1990) or wall static pressure gradients (Obot et al. 1993). In this study, the development length, which was treated as the necessary distance downstream of the particle fee- der for the attainment of homogeneous particle distribution in air, was estimated by evaluating the variation of local friction factors; f p+a calculated from the measurements of local static pressure gradients; dP/dx. The measurements were conducted in air¯ow Re, based on mean air velocity, U, and inner pipe diameter, D, in the range 51,500 RRe R109,000 at particle loading ratios, M p /M a , of 5% RM p /M a R 30% to determine the in¯uence of M p /M a and Re on the development length. 2. EXPERIMENTAL SET-UP AND MEASUREMENTS The measurements were conducted in an open circuit blower type horizontal ¯ow test set-up shown in ®gure 1. The set-up consisted of a blower unit, a particle feeder and a pipe system Int. J. Multiphase Flow Vol. 24, No. 2, pp. 347±353, 1998 # 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0301-9322/98 $19.00 + 0.00 PII: S0301-9322(97)00051-7 347