A.S. Nafey

Maximum entropy generation of in‐series connected heat exchangers

Theoretical analysis of entropy generation and availability destruction of “n” similar cocurrent or counter-current heat exchangers connected in series are presented. A criterion for comparing the relative performance of any number of in-series connected similar heat exchangers is developed. The effect of different influencing parameters such as the number of connected heat exchangers, the individual effectiveness of each unit, the heat capacity rate ratio and flow arrangement on the quality of heat exchange are presented. It is found that, the maximum of availability destruction (maximum entropy generation) for in-series-connected similar cocurrent heat exchangers is obtained at ϵ*=1/(1+δ). However, for counter-current heat exchangers connected in-series; ϵ=1/(∑δi/n). This analysis might be useful for a proper choice of the number of heat exchangers to be connected together and the choice for the best operating conditions. Copyright

New anti-scalant performance evaluation for MSF technology

Abstract The desalination industries are looking for the reduction in the unit cost of desalinated water through developments in the technologies, process optimization, etc.; multi stage flash (MSF) technology has a proven track record for high reliability in the tough seawater condition. One of the technical barriers to improve the MSF system performance is the scale formation phenomena. This phenomenon can be manipulated by nanofiltration or by chemical treatment (anti-scalant). A pilot plant was constructed to evaluate the performance of a novel anti-scalant, under high top brine temperature (TBT) condition. Techniques such as atomic absorption spectroscopy and X-ray diffraction are used to measure the scale deposition in the test sections. Different operation parameters such as TBT, salinity, dosing rate, and operation with/without ball cleaning are considered. The experimental results indicate that the scale inhibition shows good performance after 72 h even for a low dosing rate of 2.5 ppm.