Modeling and simulation of cooling water systems subjected to fouling

Abstract

Abstract This paper presents the modeling and simulation of cooling water systems, encompassing the cooling tower, the pump, the set of interconnected pipe sections, and the coolers. The model is composed of mass, energy, and mechanical energy balances, also contemplating the influence of the fouling rate in the heat exchangers. The simulation can determine the flow rates and temperatures along the network for each time instant during the investigated time period. The fouling rate evaluation considers its dependence with local temperature and velocity. Consequently, the heat exchanger equations are not represented by analytical solutions, but by differential energy and mechanical energy balances which allow the determination of the fouling rate at each point along the heat exchanger surface (i.e. the fouling thermal resistance and the corresponding deposit thickness are calculated at each point along the thermal surface of each cooler). The utilization of the proposed approach is demonstrated through three examples of cooling water systems. The first example contains one cooler and illustrates that the system behavior is the result of the hydraulic and thermal interactions among its elements (cooling tower, pump, pipe sections, and coolers), which indicates that analysis focusing on isolated elements may compromise the accuracy of the simulation results. The second example explores the inclusion of control loops in the proposed model. The third example is composed of three coolers and analyzes the interactions of multiple exchangers aligned in parallel, which shows that the behavior of each cooler in the network depends on the operation of the other exchangers in the system.