The pressure difference is calculated from values at nodes P and E, ( actually for a control volume constructed around the “e”-location, for a staggered variable arrangement), as indicated in Fig. 41.1:

Fig. 41.1: Interpolation of velocity components for mass flux calculation: control volume around “e”-face

	(41.2)

The overbar in Eqs. (41.2) denotes linear interpolation from values at nodes on either side of the cell face. For computing convenience, Equations (41.2) can be rewritten as following equation( Eqs. (41.1)):

	(41.3)

Thus, the cell face velocities are made dependent on the pressure at neighbouring nodes, employing the basic idea of staggered grids which is successfully used for orthogonal grids (see Patankar, 1980). The velocity components at the other cell faces are calculated in a similar manner.