Dynamic object-oriented heat exchanger models for simulation of fluid property transitions

Abstract

Object-oriented heat-exchanger models were developed to simulate the dynamic thermal effects of dynamic changes in fluid composition and thus of fluid properties in a type of liquid typical for food products. The models were written in the object-oriented language Modelica as objects in a library structure being developed to simulate complex liquid food process lines and their control systems. The models were based on moderate discretization of the heat exchanger into control volumes, and the fluid dispersion was modelled either as ideal mixing or as transport delay in each control volume. The transport delay model exhibited the best computational performance as well as affording flexibility in fluid dispersion modelling. KeywordsAxial spatial coordinate (along the fluid channel), m or exponent in Equation (2) y Spatial coordinate perpendicular to x and z, m or exponent in Equation (2) z Vertical spatial coordinate, m or exponent in Equation (2) Greek lettersDispersive thermal conductivity due to flow dispersion defined by

A dynamic object-oriented model for efficient simulation of microbial reduction in dispersed turbulent flow

“…The basis for simulations is dynamic models. We are engaged in developing such models (Skoglund, 2003;Skoglund, Årzén & Dejmek, 2006;Skoglund & Dejmek, 2007) in the language Modelica (Modelica Association, -; Tiller, 2001). The Modelica language is noncausal, object-oriented, and suitable for physical modelling.…”

Theoretical analysis of a method for segmented heat exchanger design

“…T h,i is the inlet temperature of the hot fluid, T c,i is the inlet temperature of the cold fluid, T c,o is the specified outlet temperature of the cold fluid, C h (1) and C c (1) are the thermal capacities of the hot and the cold fluids of the first segment, U 1 is the overall heat transfer coefficient of the first segment, and C h (2) , C c (2) and U 2 are the corresponding parameters of the second segment. Assuming that the cold fluid absorbs all the heat released by the hot fluid, we obtain…”

“…The assumption that the heat released from the hot fluid can be completely absorbed by the cold fluid on each segment leads to where T c,o (1) and T h,o (1) are the outlet temperatures of the cold and hot fluids of the first segment, and are also the inlet temperatures of the cold and hot fluids of the second segment. The above equation can be rewritten as follows:…”

“…In these cases, to make the physical parameters take their mean values gives rise to inaccurate design results. Moreover, in some low temperature heat exchangers, there are relatively large temperature differences between their inlets and outlets, so the variation of fluid properties cannot be ignored [1]. To improve the design of heat exchangers, especially the shell-tube heat exchangers, some new ideas were proposed in [2].…”

“…Later, based on the ε-NTU method, Shah and Sekulić improved this method and put forward a numerical method for checking heat exchanger design which considered the non-uniformity of fluid velocity and variation of fluid properties with temperature [8,9]. Skoglund et al applied the finite volume method to the numerical analysis of the flow and heat transfer in heat exchangers with variable fluid properties [1].…”