Heat exchanger model development

The standard basic RadFrac model in Aspen simulations does not accurately predict the rapid pressure changes during emergency situations because the default heat-exchanger models do not account for heat-exchanger dynamics (condenser and reboiler). Simulations can be developed that include external heat exchangers whose dynamics can be incorporated with the model of the column vessel. 

In Figure 1 are shown the closed loop results for the proposed measurement-driven calorimetric controller (Eq. 46) (continuous plots) and for its exact model-based nonlinear SF counterpart (discontinuous plots) (Eq. 43). As it can be seen, the difference in behavior between the two controllers is almost imperceptible. The small differences are due to the estimation error dynamics. In other words, as expected from the theoretical developments, the calorimetric controller basically recovers the behavior of its exact model-based nonlinear SF controller (Eq. 43) counterpart, without needing the kinetics and heat exchange models. As... 

Therefore, the average heat transfer coefficient over the boundary layer build-up region is equivalent to twice the local heat transfer coefficient in the fully developed region. The solution of the Polhausen equation clearly bounds the 13 percent increase in Nusselt number for compact heat exchanger modeling. In fact, increasing the Sellars solution (Nu=4.36) by a factor of two would also bound the proposed Nusselt number. 

Nature as model for micro-reactor development general advantages of micro flow onset of industrial interest micro heat exchanger vision of mefhanol-fuel reforming costs stiU too prohibitive [231],... 

The high filament temperature used causes additional radiative heating of the substrate [530, 531]. Feenstra et al. [531, 548] have developed a heat transport model of their setup (Figure 68). All heat exchange is assumed to occur via ra-... 

The Geothermal Response Test as developed by us and others has proven important to obtain accurate information on ground thermal properties for Borehole Heat Exchanger design. In addition to the classical line source approach used for the analysis of the response data, parameter estimation techniques employing a numerical model to calculate the temperature response of the borehole have been developed. The main use of these models has been to obtain estimates in the case of non-constant heat flux. Also, the parameter estimation approach allows the inclusion of additional parameters such as heat capacity or shank spacing, to be estimated as well. 

For the heating and cooling of a semi-infinite PCM layer the model shown in Figure 134 has been developed. It consists of a heat exchanger made from a copper block and an acrylic glass container for the PCM. 

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 this chapter, we focus on the characteristics of the ideal-flow models themselves, without regard to the type of process equipment in which they occur, whether a chemical reactor, a heat exchanger, a packed tower, or some other type. In the following five chapters, we consider the design and performance of reactors in which ideal flow occurs. In addition, in this chapter, we introduce the segregated-flow model for a reactor as one application of the flow characteristics developed. 

EXAMPLE 2.4 APPLICATION OF LEAST SQUARES TO DEVELOP A COST MODEL FOR THE COST OF HEAT EXCHANGERS... 

In the introduction we mentioned that it is sometimes necessary to develop a model for the objective function using cost data. Curve fitting of the costs of fabrication of heat exchangers can be used to predict the cost of a new exchanger of the same class with different design variables. Let the cost be expressed as a linear equation... 

In a series of papers, Derby and Brown (144, 149-152) developed a detailed TCM that included the calculation of the temperature field in the melt, crystal, and crucible the location of the melt-crystal and melt-ambient surfaces and the crystal shape. The analysis is based on a finite-ele-ment-Newton method, which has been described in detail (152). The heat-transfer model included conduction in each of the phases and an idealized model for radiation from the crystal, melt, and crucible surfaces without a systematic calculation of view factors and difiuse-gray radiative exchange (153). 

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