Calculation of ultraviolet fluence rate distributions in an annular reactor: significance of refraction and reflection

A model, utilizing the multiple point source summation approximation for a linear lamp, is presented for the calculation of the fluence rate distribution and the average fluence rate in an ultraviolet (UV) reactor. The model is sophisticated, in that it accounts for both reflection and refraction as a beam of UV radiation passes through an air/quartz/water interface. When the effects of reflection and refraction are “turned off” (by setting the refractive indices to 1.000), there is only a small increase ( 6.5% arising from reflection) in the calculated average fluence rate for 10 mm path length transmittance (T′10) values less than 70%. Thus, under these conditions, the effects of reflection and refraction can be safely neglected (with a 6.5% correction for reflection). In many practical applications, such as drinking water treatment, the T′10 is usually much larger than 70%, where the error of neglecting refraction and reflection can be as large as 25%, and thus the more sophisticated model should be used.