A simple analytical model to predict the onset of Ledinegg instability
in vertical channels under downflow conditions has been developed and
evaluated. The model divides the flow field into three regions based
upon the fluid temperature. The pressure drop is then found by solving
an appropriate set of equations for each region. The theoretical resu
lts are compared to an extensive set of experimental data covering a r
ange of channel diameters and operating conditions. Agreement is excel
lent, and the prediction of the velocity at which the minimum point in
the demand curve occurs is within 12 percent over the range of experi
mental results. A parameter, the ratio between the surface heat flux a
nd the heat flux required to achieve saturation at the channel exit fo
r a given flow rate, is found to be a very accurate indicator of the m
inimum point velocity.