Plume rise measurements at industrial chimneys

Atmospheric Environment Pergamon Press 1969. Vol. 3, p. 316. Printed in Great Britain. IT is cheering to read a paper describing work in which the plume rise from a large number of industrial chimneys has been measured. It is good to note that a fair range of rates of heat emission has been covered, and that the necessary atmospheric measurements were also made so as to give a clear picture of the situation for each experiment. I wish that some photographs could have been included in the paper to give some concept of the quality of photograph which was obtained and to show just how the measurements of height were made, when using the stack itself as a type of yard-stick. The idea of using the peculiarities of the plume itself to obtain a measure of wind speed is an intriguing one but here again a sample pair of photographs would have been very helpful. One would imagine that the shape of the plume outline would change as the plume drifts with the shape of the plume outline would change as the plume drifts with the wind and that there would be difficulties in identification. Some work on this is being done in South Africa to see if, in any way, there could be ambiguity about the resultant value for the wind speed. Comment on FIG. 1 of Bringfelt’s paper When the graph (for 500 m distance of measurement) is studied, it is apparent that the values which have been obtained by other writers, for stacks with emissions in the range 20-50 MW play a large part in the determination of the position of the regression line. Because of the nature of a log-log graph, the points for the high energy emissions cluster more closely together than do the points for the lower energy emissions. Thus, if it is accepted that an exponential equation accurately represents the plume rises for the whole of the energy range from 1 MW to 50 MW, the value of the exponent will be heavily influenced by the high energy values on the graph. Now there has been considerable discussion (in two issues of Atmospheric Environment-Vol. 1, No. 4 and Vol. 2, No. 3) on this subject during which it was suggested that the exponential equation cannot cover avery large range of energies. It is thereforeinteresting to seewhat theresults of Bringfelt’s measurements for the energy range 1 to 10 MW will give for a in a. When a regression line is drawn for the 26 observations, at 500 M, which were made during periods of neutral or unstable atmosphere, the equation which results is ux H = 145 Q”‘45 It is not intended to claim that this is a true representation of plume rise for low energy emission rates but it is suggested that when more measurements at low energy emission rates have been made it may well be found that a single exponential equation will be inadequate for a wide range of energies. Those of us who have the task of prescribing working heights for industrial stacks need an equation which will encourage us to think that we are not penalising the small stacks, by making them too high, and are not making serious mistakes by allowing large stacks with high energy emissions, to be too low. At the moment it seems wise to use two equations with an arbitrary division at 20 MW, using one exponent for the smaller stacks and another for the larger stacks. The paper under review gives information which is a step towards the achievement of such an object, but more experimental information is needed and it is hoped that others will be able to add to what has been given in the paper. E.C. HALLIDAY

National Physical Research Laboratory (C.S.Z.R.),

P.O. Box 395, Pretoria, South Africa.

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