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In the present investigation, a non-linear mathematical model is developed for the analysis of Septuple effect flat falling film evaporator (SEFFFE) system used for concentrating black liquor in a nearby paper mill. This model is capable of simulating process of evaporation considering variations in boiling point rise (τ), overall heat transfer coefficient (U), heat loss (Q loss), flow sequences, liquor/steam splitting, feed, product and condensate flashing, vapor bleeding and physico-thermal properties of the liquor. Based on mass and energy balance around an effect a cubic polynomial is developed and solved repeatedly in a predetermined sequence using generalized cascade algorithm. For development of empirical correlations for τ, U and Q loss, plant data have been collected from SEFFFE system. These correlations compute τ, U and Q loss within average absolute errors of 2.4%, 10% and 33%, respectively, when their results are compared with the plant data. [Copyright &y& Elsevier]

In this paper, a novel model is presented for predicting thermophysical properties of superheated steam (SHS) in offshore superheated steam injection wells (OSSIW). Firstly, a mathematical model comprised of mass, energy and momentum balance equations is proposed for OSSIW. Secondly, the distribution of temperature, pressure and superheat degree along the wellbores are obtained by finite difference method on space and solved by using the iteration technique. Then, model validation and sensitivity analysis are conducted. The results show that (1). The superheat degree increases at first but then turns to decrease with the increase of injection rate. (3). The superheat degree increases with the increase of injection temperature. (4). The superheat degree at well bottom increases at first but then turns to decrease with the increase of injection pressure. (5). The superheat degree in the wellbore has a drop when seawater starts to flow. [ABSTRACT FROM AUTHOR]

Abstract: This paper discusses two practical aspects of reduced-order models (ROMs) based on proper orthogonal decomposition (POD) and presents the derivation and implementation of a ROM for non-isothermal multiphase flow. The POD method calculates basis functions for a reduced-order representation of two-phase flow by calculating the eigenvectors of an autocorrelation matrix composed of snapshots of the flow. The flow is divided into transient and quasi-steady regions and two methods are shown for clustering snapshots in the transient region. Both methods reduce error as compared to the constant sampling case. The ROM for non-isothermal flow was developed using numerical results from a full-order computational fluid dynamics model for a two-dimensional non-isothermal fluidized bed. Excellent agreement is shown between the reduced- and full-order models. The composition of the autocorrelation matrix is also considered for an isothermal case. An approach treating field variables separately is shown to produce less error than a coupled approach. [Copyright &y& Elsevier]

Abstract: Heat transfer intensification is an effective technique for improving energy recovery in heat exchanger networks (HEN) by enhancing heat transfer without any network topology modifications. In this paper, a novel optimization method has been developed for the synthesis of intensified heat exchanger networks with a simple mixed integer linear programming (MILP) model under retrofit scenario, and a robust solution strategy based on two iteration loops has been proposed. The new method has distinctive advantages over existing design methods, as the new MILP model can effectively and significantly reduce computational difficulties associated with nonlinear formulation in existing HEN retrofit formulations. Three cases have been tested to demonstrate the validity and efficiency of the proposed approach, which requires very short computational times to obtain optimal solutions when energy saving or profit is to be maximised through retrofit. [Copyright &y& Elsevier]

Abstract: Dynamic simulations of distillation columns are widely used to develop effective control structures. The normal distillation models assume instantaneous heat transfer in the condenser and reboiler. However, when dynamic simulations are used in the analysis of safety problems in the event of emergency situations, the basic model does not accurately represent the dynamic response. Accurate response times are essential in the design of safety systems for the column. For example, a failure of the supply of cooling water will lead to rapid increases in pressures and temperatures that occur in seconds. Accurately determining the rates of increase in these important variables and the time period to reach critical limits (safety response time) permits the engineer to quantitatively design effective safety systems. This paper illustrates how rigorous condenser and reboiler models can be developed in Aspen Plus and their dynamics evaluated in Aspen Dynamics. [Copyright &y& Elsevier]

Abstract: It has been well established that heat transfer in a helical coil is higher than that in a corresponding straight pipe. However, the detailed characteristics of fluid flow and heat transfer inside helical coil is not available from the present literature. This paper brings out clearly the variation of local Nusselt number along the length and circumference at the wall of a helical pipe. Movement of fluid particles in a helical pipe has been traced. CFD simulations are carried out for vertically oriented helical coils by varying coil parameters such as (i) pitch circle diameter, (ii) tube pitch and (iii) pipe diameter and their influence on heat transfer has been studied. After establishing influence of these parameters, correlations for prediction of Nusselt number has been developed. A correlation to predict the local values of Nusselt number as a function of angular location of the point is also presented. [Copyright &y& Elsevier]

Abstract: In this paper, a rigorous MILP formulation for grass-root design of heat exchanger networks is developed. The methodology does not rely on traditional supertargeting followed by network design steps typical of the Pinch Design Method, nor is a non-linear model based on superstructures, but rather gives cost-optimal solutions in one step. Unlike most models, it considers splitting, non-isothermal mixing and it counts shells/units. The model relies on transportation/transshipment concepts that are complemented with constraints that allow keeping track of flow rate consistency when splitting takes place and with mechanisms to count heat exchanger shells and units. Several examples from the literature were tested, finding that the model usually obtains better solutions. In some cases, the model produced unknown solutions that were not found using superstructure optimization methods, even when the same pattern of matches is used. [Copyright &y& Elsevier]