Martinelli-Nelson correlation

This heat-transfer region has been more widely studied than either Region II or IV. However, the methods for evaluating the parameters have not been tested over a wide range of experimental conditions. Equations (71) and (72) must be coupled with a knowledge of the pressure drop, holdups, and other system parameters if the temperature and mass flow-rate profiles are to be determined. As mentioned earlier in this chapter, the pressure drop and holdups in phase change systems can be estimated by using the Martinelli-Nelson Correlation. 

Equations 7.81 and 7.83 are not easy to evaluate. In the following sections the Lockhart-Martinelli and Martinelli-Nelson correlations will be considered. The Lockhart-Martinelli correlation is valid when there is no change of phase, so dw/dx=0 in equation 7.81 and the second term in the numerator vanishes. In the Martinelli-Nelson correlation, values are given for the quantities in square brackets in equation 7.83. 

Over the range of Martinelli parameter of practical importance (0.1 frictional pressure gradient approximately twice that predicted by the homogeneous model. 

When these predictions are compared with measurements it is found that there is a significant dependence on the total mass flux G the Martinelli-Nelson correlation is accurate in the mass flux range 500-1000 kg/(m2s) while the homogeneous model gives good agreement when the mass flux is greater than 2000 kg/(m2s). 

The original Martinelli-Nelson correlation was based on relatively limited data. Thom (1964) has derived revised values of the quantities shown in Figures 7.14 to 7.17 from extensive measurements. 

Both Baroczy (1965) and Chisholm (1968) have modified the Martinelli-Nelson correlation to take into account the influence of the mass flux. Chisholm s modification is recommended by Collier (1972). Subsequently,... 

The following discussion indicates that the deviations are due to shortcomings in the Martinelli-Nelson correlation. 

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