Heat exchanger network derivation

At the conceptual stage for heat exchanger network synthesis, the calculation of heat transfer coefficient and pressure drop should depend as little as possible on the detailed geometry. Simple models will be developed in which heat transfer coefficient and pressure drop are both related to velocity1. It is thus possible to derive a correlation between the heat transfer coefficient, pressure drop and the surface area by using velocity as a bridge between the two1. 

In the 1980s, there was a great deal of research into design methods for heat exchanger networks see Gundersen and Naess (1988). One of the most widely applied methods that emerged was a set of techniques termed pinch technology, developed by Bodo Linnhoff and his collaborators at ICI, Union Carbide, and the University of Manchester. The term derives from the fact that in a plot of the system temperatures... 

Remark 1 For (i) and (ii) we assumed a values of HRAT. For (iii) and (iv) we can have H RAT = TIAT since we decompose into subnetworks based on the location of the pinch point(s). We can also have in (iii) and (i v)EM AT = TIAT < HRAT for each subnetwork which may result in less units, less total area, and less investment cost. By relaxing EM AT — TIAT, that is, being strictly less than H RAT, more opportunities to make matches are introduced in the heat cascade. Note, however, that for the network derivation we may have EM AT < HRAT of EM AT = HRAT depending on which criterion of feasible heat exchange is considered. In principle, if EM AT < H RAT, EM AT can take any small value e close to zero. Also note that EM AT is not a true optimization variable but simply a requirement for feasible heat exchange that can even be relaxed (i.e., may be e from zero). If EM AT - TIAT = e > 0, then the only specification in the above problem statement is that of HRAT based upon which (i) and (ii) are obtained. We will discuss later on how such a specification can be overcome. 

In the present study, amorphous silica-alumina nanomaterials with controlled mesoporous distribution have been synthesized by two templateless approaches (1) vacuum-sol process, and (2) ultrasonic-sol process. It is found that the preparation method affects the precursor sol properties and the specific surface area and pore volume of the final materials. Ultrasonic-sol method favors the formation of monodispersed sol particles with narrow size distribution. Because of several base-exchange cycles and absence of drying process prior to heat treatment, the gel derived fiom ultrasonic-sol method may have enough stiffiiess to protect the network fiom pore collapse by capillary force, thus, leading to produce the materials with... 

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