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Opis: The plate heat exchanger (PHE) is a component that provides heat to be transferred from hot water to domestic cold water without mixing them with high efficiency. Over the lifetime of the PHE, cyclic pressures act on the brazing points and the plates, and this may lead to fatigue failure. The fatigue behaviour of the PHE, designed using copper-brazed 316L stainless steel, was investigated in this study. First, the fatigue tests under the load ratio R = 0.1 were performed on the Vibrophore 100 testing machine to obtain the S-N curve of the analysed brazed joint. Based on the obtained experimental results, an appropriate material model of the analysed brazed joint has been created, which was validated with numerical calculation in the framework of a program code Ansys. A validated material model was then used for the subsequent numerical analysis of PHE. In order to carry out a numerical calculation using the finite element method (FEM), a three-dimensional model of the heat exchanger was created based on the previous scanning of PHE-geometry. Thereafter, the geometry was parameterised, which allowed us to perform parametric simulations (monitoring different responses depending on the input geometry). Numerical simulations were carried out in the framework of the Ansys 2023-R1 software, whereby the obtained results were analysed, and the responses were appropriately characterised according to previously determined load cases.
Ključne besede: brazed joint, fatigue, experimental testing, computational analyses, heat exchanger
Objavljeno v DKUM: 31.01.2024; Ogledov: 316; Prenosov: 58
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Opis: This paper presents an application of the improved pinch methodology by performing a simplified exergy analysis in a real-size ammonia plant. Besides the well known pinch technics like composite curves and grand composite curve, the improved approach with the extended grand composite curve was implemented. The latter presents the most energy intensive units in the process separated from the process background as well as the direct transfer of enthalpy from hot utilities to cold utilities. Based on this presentation the synthesis of modified heat exchanger network was performed which results in considerable decrease of utilities demand.
Ključne besede: chemical engineering, process design, exergy analysis, ammonia plant, pinch methodology, extended hrand composite curve method, enthalpy exchange, distillation column, heat exchanger network
Objavljeno v DKUM: 10.07.2015; Ogledov: 1830; Prenosov: 110
Celotno besedilo (182,17 KB)
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Opis: Economically viable process designs should be, in addition to other criteria, profitable over their entire process lifetimes not only at the present time. An improved process design can be achieved by establishing an appropriate trade-off between product income, raw material, operating costs, and investment. The full lifetime of the processes and future prices have to be considered rather than optimising them on a yearly basis using current prices. Single-period optimisation and synthesis models for processes reflects current prices only. The prices can fluctuate rather quickly and the optimal solution may be very different from one year to the another. Therefore, the traditional superstructural synthesis approach applying a mixed-integer nonlinear programming model was upgraded: i) over time, by considering an entire lifetime, which can be described by a multi-period model and ii) the whole field of variation regarding uncertain future prices. A stochastic approach considering the statistical distribution of price projections over an entire lifetime was used on different case studies instead of the traditional deterministic approach accounting for nominal future price projection. The objective was the maximisation of the expected net present value of a process or the expected incremental net present value of different process subsystem. The heat exchanger network has been one of the subsystem, which can significantly contribute to operating costs due to savings of external utility consumption. For this subsystem a deterministic and stochastic multi-period mixed-integer nonlinear programming (MINLP) synthesis models have been developed in order to account for future price projections. Considering higher energy prices gives rise to larger initial investments compared to solutions obtained with current prices. However, due to the uncertainties of utility prices' forecasts, retrofitting using an extension of HEN during future years of the lifespan might be a better strategy. The objective is to identify a design that is the most suitable for effective future extensions and preferably with the lowest sensitivity to energy price fluctuations, as there can be various designs featuring similar initial investment. The results supports that it is economically beneficial to consider future utility prices as the incremental investment is not only paid-off but additional savings are achieved. Process-to-process Heat Integration can also significantly affect the trade-off between investment and operating cost. The aim of Total Site (TS) HEN synthesis was to develop a model synthesis for the TS that, besides many other important features, would also consider future utility prices. Two strategies for TS synthesis have been developed: i) sequential, when HI is performed within a process during the first step and then after a process-to-process HI has been performed, and ii) simultaneous, where the HI is performed within and between processes simultaneously. The second strategy can reveal additional opportunities for heat recovery that might not be identified when applying the first strategy. Comparison of the results obtained at consideration of current utility prices and forecasted utility prices indicates that is worth to account for future utility prices. The separation processes also consume a significant amount of energy. The synthesis of a distillation column sequence integrated within its heat exchanger network was used as a case study for the separation of a multi-component stream into pure component products by considering future utility prices. This analysis has been performed in order to evaluate the magnitude of the influence of forecasted utility prices. It can be concluded that forecasted utility prices can be beneficial, however, the technical limits of the systems should be carefully observed. The price fluctuation can also be observed for other prices not only utility prices, e.g. raw material cost, product price, etc
Ključne besede: future prices, forecasted prices, stochastic optimisation, mathematical programming, Heat Exchanger Network, Total Site, distillation column sequence, methanol production
Objavljeno v DKUM: 04.05.2015; Ogledov: 2190; Prenosov: 177
Celotno besedilo (4,74 MB)

Opis: Ground coupled heat pump (GCHP) utilizes the immense renewable storage capacity of the ground as a heat source or sink to provide space heating, cooling, and domestic hot water. GCHP systems are generally comprised of watersource heat pumps and ground heat exchangers (GHEs). Consisting of closedloop of pipes buried in boreholes, ground heat exchangers (GHEs) are devised for extraction or injection of thermal energy from/into the ground. Despite the low energy and lower maintenance benefits of ground-source heat pump systems, little work has been undertaken in detailed analysis. Many models, either numerical or analytical, have been proposed to analyze the thermal response of vertical heat exchangers that are used in ground coupled heat pump systems (GCHP). In both approaches, most of the models are valid after few hours of operation since they neglect the heat capacity of the borehole. In this paper, we present for three various multiple borehole configurations a comparison between g-functions, which will be calculated after an analytical model of final line source and g-functions, obtain with numerical model derived from the work of Eskilson. A case study is presented to show how the ground temperature changes with time for various multiple borehole configurations.
Ključne besede: geothermal heat exchanger, heat transfer, heat conduction, thermal influence
Objavljeno v DKUM: 31.05.2012; Ogledov: 2006; Prenosov: 47
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