سنتز شبکه مبدل حرارتی درهم با استفاده از نانوسیم ها برای مبدل حرارتی درهم Interplant heat exchanger network synthesis using nanofluids for interplant heat exchange

1. Introduction One way of improving energy efficiency in industrial processes is by increasing heat integration. Typically different processes or process parts have their own specific processing tasks. These processes can be heat integrated in order to improve the energy efficiency of the entire system and to increase the overall economic efficiency of the total system and the individual processes. In heat integration between processes the process streams existing in an overall system are grouped into their own processes and heat integration between streams in the same group can be prioritized against heat integration between streams in different groups. This type of heat integration is called inter-plant heat integration. Otherwise heat integration between processes is similar to normal heat integration where the objective is to develop heat exchanger networks that minimize the annual energy and investment costs. The heat integration between processes can be accomplished directly or indirectly. The streams that transfer heat between process streams are called intermediate streams. Because intermediate streams are used purely as a heat transfer media, these should transfer heat as efficiently as possible. For this reason fluids that have high heat transfer coefficients and low viscosity in order to decrease the pressure-drop are optimal as intermediate streams. Naturally these properties are hard to find in a single fluid, and thus the choice of the optimal fluid is a compromise between the properties. Nanofluids have been an active research area because they provide increased heat transfer coefficients. Unfortunately they also typically increase pressure drop. Nanofluids are a new type of heat transfer fluids, in which particles with size of 1- 100 nm are suspended in a liquid. Most typically the particles are solid (Gupta et al. (2014) and Yu et al. (2012)), however recently also liquid phase nanoparticles (nanoemulsions) (Saarinen et al., 2015) as well as phase changing nanoparticles (Xu et al. (2015), Puupponen et al. (2015), Mikkola et al. (2017) and Trinh and Xu (2017)) have been investigated. Many studies have demonstrated that the addition of the nanosized particles can cause considerable enhancement in convective heat transfer performance of the base fluid. However, an adverse effect of the particles is that they increase the viscosity of the fluid, thus enhancing the needed pumping power (Mikkola et al., 2018). In most of the nanofluid studies the overall benefit, accounting for both heat transfer and the pressure loss enhancement, has not been properly investigated. For the purpose of the present study, we have chosen from literature five different type of water-based nanofluids, of which structure, heat transfer and pressure loss characteristics are well documented.