Measurement and prediction of evaporator shell-side pressure drop

The pressure drop across a heat exchanger is an important parameter, along with the heat transfer capacity. In fact, the operating cost throughout the life of the exchanger depends on the pressure losses. Therefore, it is important to be able to predict pressure drop accurately as it is to predict heat transfer. A new data set of shell-side pressure drop measurements taken during isothermal flow of brines in shell and tube evaporators was collected in the Alfa Laval laboratory. It covers several different configurations of industrial shell and tube evaporators and a wide range of operating conditions, with cross flow Reynolds number ranging from 170 to 33,000. The database is compared against two predictive procedures available in the literature for computing shell-side pressure drop, showing that no method is accurate enough for design purpose. As a further step, a new suggested procedure is presented, which extends the Wills and Johnston [Wills MJN, Johnston D. A new and accurate hand calculation method for shellside pressure drop and flow distribution. 22nd National Heat Transfer Conference, HTD N. 36. New York: ASME; 1984, p. 67–79] method to the low Reynolds number range and improve its capability to predict experimental data.