This paper reports the development of a computer simulation programme
for an orbiting screw, or Nauta mixer, in which convection is dominant
. It is based on a volume-element model and a priori knowledge of the
process, and yields a complicated higher order linear differential equ
ation representing this continuous dynamic system. The equation was so
lved numerically using a computer simulation programme. The reliabilit
y of the model has been verified by means of a radiotracer response su
rvey. The results indicate the validity of the programme and demonstra
te that it can be used to predict mixing time, analyse the mixing proc
ess and improve mixer design. In principle, the programme in its prese
nt form is useful for scaling-up.