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Abstract The mathematical model of heating substation, which is an important part of district heating system, is presented in this paper. The main components of district heating substation system, from the automatic control perspective, that are observed in this paper are heat exchanger and three-way valve. Presented mathematical model is developed so it could operate in real-time, since the crucial aspect of development, deployment and testing of new control techniques and optimization algorithms is their accurate validation on the real system. However, the accessibility to a real system is often not possible. Corresponding to this, an alternative is the existence of the correct mathematical model of a process, with the ability to operate in real-time. First, the presented mathematical model of district heating substation is decomposed to the simpler models of its main elements, in order to provide the analysis of the various parameters on the model performance through numerical simulation. Second, a real-time model is developed in LabVIEW software package and deployed on the embedded controller with a real-time processor as a three-layer application which enables data acquisition and communication with a programmable controller. [ABSTRACT FROM AUTHOR]

Abstract: The formation of particulate deposits on flue gas heat exchanger surfaces will reduce heat transfer efficiency, increase the instability of equipment operation and introduce a major uncertainty into the heat exchanger design. In this paper, a numerical model was developed to predict the flue-ash particle deposition rate by considering particles transport, sticking and rebound behaviors based on the software FLUENT, extended by user-defined functions (UDFs). The numerical model was applied to cross-flow tube bundle heat exchangers with a 6-row tube arrangement. The effects of six parameters (particle diameter, flow velocity, spanwise tube pitch, longitudinal tube pitch, tube geometry shape, and arrangement) on fouling rate, as well as on the heat transfer and hydrodynamics performance, were examined. It was found that particle deposits accumulated primarily in the flow stagnation region, recirculation region, the vortex separation and reattachment regions. Increasing particle diameter moved the deposition zones towards the windward side of tubes. Using both oval tubes and staggered arrangements can reduce the fouling rate. With the increase in longitudinal tube pitch, both the particulate deposit rate and the heat transfer performance increased. To account for fouling and heat transfer performance, a tube spacing value of 2 was recommended. [Copyright &y& Elsevier]

Abstract: This paper proposes a new method for fouling detection in a heat exchanger. It is based on the modeling of the system in a fuzzy Takagi–Sugeno representation derived from a physical model. With this representation, the design of a fuzzy observer with unknown inputs of polynomial types is obtained via a LMI formulation. Main advantages of the proposed method are that neither specific sensor, excepted standard ones, nor special operating conditions such as steady state regime are required. Some realistic simulations show the efficiency of the proposed technique. [Copyright &y& Elsevier]

Abstract: The work presented in this paper investigates the degradation effect of flow maldistribution on the thermal and hydraulic performance of a heat exchanger. A new mathematical model is derived based on Taylor series expansion to describe the contribution of each of the four statistical moments of distribution on the degradation problem. It is found that the first two moments, i.e. mean and standard deviation, have the highest effect on the performance degradation. Subsequent higher moments will give declining degradation effects until the fourth moment, kurtosis, which has no significant effect. Maldistribution with low standard deviation and high positive skew will give low thermal deteriorations, though a distribution with negative skew is preferred for low hydraulic performance losses. The design of the heat exchanger could be modified to give these favourable moments which would minimize the degradation effects of the maldistribution. Consequently, any effort to modify the flow distribution profile should be focused on optimizing the first three moments. [ABSTRACT FROM AUTHOR]

Abstract: This article analyzes parallel flow microchannel heat exchangers with non-adiabatic thermal condition imposed on the wall separating the fluids and the ambient. For purposes of analysis, a thermal model comprising of two governing equations, one for each of the fluids, is developed and analytically solved to obtain equations for calculating the axial temperature and thereby the effectiveness of both fluids. Provision is provided in these equations for the temperature of the ambient interacting with the hot fluid to be different from that associated with the cold fluid. Analytical equations for determining the heat transfer between the individual fluids and the respective ambient as well as that between the fluids are also developed in this paper. The temperatures/effectiveness of the fluids depend on parameters such as NTU, fluid heat capacities, thermal resistance between the individual fluid and the respective ambient and ambient temperatures. In addition, under certain operating conditions the phenomenon of temperature-cross is observed. Depending on the ambient temperatures, increase in NTU will continuously improve the effectiveness of one the fluids; the effectiveness of the other fluid over the same NTU range increases before peaking and subsequent decrease. Equations for determining the NTU at which this peak value in effectiveness occurs are also provided. An unbalanced flow microchannel heat exchanger with the hot fluid having the lowest heat capacity has better effectiveness than when the cold fluid has the lowest heat capacity. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents the geometry of infinite regular polyhedrons that can be used to construct the heat exchange units. The basic structural component of the infinite solid consists of six hexagons, which meet in the common vertex. The mathematical model of heat and mass transfer inside the labyrinth heat exchanger is shown. The first and the second Kirchhoff’s laws are used to simulate fluid flow distribution at hydraulic network created with connected basic solids. Heat balance equations are adopted to describe forced convection heat transfer inside developed heat exchanger. Good accordance among the experimental data and calculation results over whole simulation range is obtained. The efficiency and thermal characteristic of the labyrinth heat exchanger is presented in the form of graphs. [Copyright &y& Elsevier]

Abstract: In this paper, an intelligent controller is applied to govern the dynamics of electrically heated micro-heat exchanger plant. First, the dynamics of the micro-heat exchanger, which acts as a nonlinear plant, is identified using a neurofuzzy network. To build the neurofuzzy model, a locally linear learning algorithm, namely, locally linear mode tree (LoLiMoT) is used. Then, an intelligent controller based on brain emotional learning algorithm is applied to the identified model. The intelligent controller is based on a computational model of limbic system in the mammalian brain. The brain emotional learning based intelligent controller (BELBIC) based on PID control is adopted for the micro-heat exchanger plant. The contribution of BELBIC in improving the control system performance is shown by comparison with results obtained from classic PID controller without BELBIC. The results demonstrate excellent improvements of control action, without any considerable increase in control effort for PID+BELBIC. [Copyright &y& Elsevier]

This paper deals with the application of adaptive fading Kalman filtering (AFKF) to the design of an observer used to predict the state of an counter-current heat exchanger. In order to implement the AFKF, an accurate mathematical model, based on the approximation of temperatures along the process by first order dynamic model, is considered. This method could be applied when the heat exchanger is solicited by the flow rate changes. Experimental validation of this method is illustrated by an example. [Copyright &y& Elsevier]