A Graph-Based Technique for the Automated Control-Oriented Modeling of District Heating Networks

Advanced control strategies for delivering heat to users in a district heating network have the potential to improve performance and reduce wasted energy. To enable the design of such controllers, this paper proposes an automated plant modeling framework that captures the relevant system dynamics, while being adaptable to any network configuration. Starting from the network topology and system parameters, the developed algorithm generates a state-space model of the system, relying on a graph-based technique to facilitate the combination of component models into a full network model. The accuracy of the approach is validated against experimental data collected from a laboratory-scale district heating network. The verification shows an average normalized root mean square error of 0.39 in the mass flow rates delivered to the buildings, and 0.15 in the network return temperature. Furthermore, the ability of the proposed modeling technique to rapidly generate models characterizing different network configurations is demonstrated through its application to topology optimization. The optimal design, obtained via a branch and bound algorithm, reduces network heat losses by 15% as compared to the conventional length-minimized topology.Comment: Manuscript submitted 16 August 2023 to the ASME Journal of Dynamic Systems, Measurement and Contro

Geometrically Complex Planar Heat Exchangers

In this study, geometrically complex planar heat exchangers, designed in line with the Constructal Law and operating at steady-state, are investigated numerically. The work is divided into two parts, one focusing on diffusion heat transfer in a rectangular plane and another on conjugate diffusion-convection heat transfer in a circular plane heat exchanger. In the first part, a heat generating rectangular solid volume made of a low conductivity material is cooled through a small, isothermal side-section of the domain. The diffusion cooling process is improved by distributing within the heat generating material a fixed amount of a high conductivity material. The question of how to best distribute the high conductivity material to cool the domain and at the same time optimize the decrease in its maximum temperature is answered via geometric optimization based on Constructal Law. The result is a T-shaped network type distribution for the high conductivity material embedded in the heat generating volume. However, this embedded approach, called here the “in-plane” distribution, is of very limited practical use for being too intrusive to the domain. An alternative proposed and investigated here is the “out-of-plane” distribution, in which the high conductivity material network is placed on top of the heat generating plane. Three different network distributions with increased complexity and same specifications (i.e., same uniform heat generation rate, planar aspect ratio and thickness of generating volume, and same volumes of base material and high conductivity material) are investigated numerically for both, in-plane and out-of-plane configurations. The main objective is to compare the heat transfer effectiveness achieved by each configuration. This aspect is very important because, if the effectiveness are comparable, the option of using the out-of-plane distribution could alleviate the practical limitations of the in-plane (embedded) configuration. An additional effort in this first part of the project is to extend the analysis to a non-dimensional parametric study, where the number of different networks is increased to six and different amounts of low and high thermal conductivity materials are investigated. This part if not only to establish if in-plane and out-of-plane yield similar results, but also to understand how the high/low thermal conductivity volume ratio influences the removal of heat out of the heat generating volume. The results, obtained numerically, show the two networks, i.e., in-plane and out-of-plane, yield nearly identical temperature distributions and heat transfer effectiveness (to within the numerical uncertainty achieved by the simulations) for all configurations tested. Hence, one can confidently use the out-of-plane networks instead of the in-plane networks in practical applications of T-shaped network cooling cold plates. The results also confirm the robustness of the thermal design and extend previous work, showing an increase in network complexity (e.g., by increasing the number of assemblies in each network) indeed yields better cooling performance, even when some of the stringent assumptions imposed in the analysis of building the networks are not fully satisfied. In the second part of the work, a heat generating material in a circular planar domain (a disk) is now cooled via convection through circular channels from the center to the periphery of the domain. The optimum distribution of the fixed volume convection channels in the domain, again following Constructal Law, yields a tree-shaped network starting with one inlet at the center of the disk, and flowing through bifurcating channels toward a set number of outlets distributed uniformly at the periphery of the disk. Here the thermal-hydraulic performance of the resulting tree-shaped flow networks is obtained numerically and compared to the simpler, radial flow networks (feeding the same number of peripheric outlets) for cooling the disc. The flow entering at the center of the disc is assumed isothermal and fully developed. Two tree-shaped flow networks are considered, having either six (one bifurcation level) or twelve (two bifurcation levels) outlets, conceived for maximizing the cooling and minimizing the flow resistance. Both, tree-shaped and radial flow configurations are set with the same disc solid and fluid (channels) volumes, and same uniformly distributed volumetric heat generation rate in the solid region. The results show the best performance flow distribution depends on factors that go beyond the channels being either radial or bifurcating, highlighting the very complex heat transfer interaction in this conjugated convection-diffusion system. Moreover, the flow separation effect intrinsic to the channel bifurcations and neglected in previous studies, is essential to the thermal design as it affect not only the overall pressure loss but also the overall heat transfer performance, particularly when the flow channel Reynolds number is high, as one would expect

Volumetric heat transfer via constructal theory, and its applications in permafrost and hydrogen energy storage

Master's Project (M.S.) University of Alaska Fairbanks, 2016Constructal theory is widely used as a powerful tool in designing of engineering systems (flow configurations, patterns, geometry). This theory is observed in nature and its principles are applicable to general engineering. Constructal theory encompasses a wide range of space in the "design", drawing from each and every field from engineering to biology. The universal design of nature and the constructal law unify all animate schemata such as human blood circulatory systems, and inanimate systems, such as urban traffic and river basins. The proceeding research applies the overlying theories of constructal theory to the two different systems in order to achieve best thermal performance phenomena. The first is stabilization of roadway embankments in the permafrost regions with design modifications in existing thermosyphon evaporators with tree structure designs, and defining the optimal spacing between two neighboring thermosyphons based on thermal cooling phenomena. This research utilizes constructal law to the generation of tree-shaped layouts for fluid flow, so that the flow structures use the available space in optimally. The intention here is the optimization of geometry of the flow system. This begins with the most simple cases of tree-shaped flows: T- and Y-shaped constructs, the purpose of which is to create a flow connection between one point (defined as a "source" or "sink") to an infinity of points (via a line/area/volume). Empirically speaking, tree-shaped flows are natural examples of selforganization and optimization. By contrast, constructal law is theory which states that flow architectures such as these are the evolutionary results of nature which tend toward greater global flow access. Tree-shaped flows can be derived from this constructal law. The mathematical simulation revealed that there exists an optimal spacing between two neighboring thermosyphons, and the tree structures perform better than the existing configuration in terms of thermal cooling. The second part of the research is to find an effective way to reject heat released from the metal hydride powder to the outer environment during the hydrogen absorption process. The main objective of this investigation is to minimize the time required for the absorption process, and to reduce the hotspot temperature by determining the optimal aspect ratio of rectangular fins, while the total volume of fins used is kept constant. The intension of using constructal theory in this part of research is to find the optimal geometrical parameters (length, width) of the fin structure for better thermal performance of the metal hydride reactor system. The simulations revealed that there exists an optimum aspect ratio of rectangular fins for accelerating heat rejection and lowering the hotspot temperature in a cylindrical metal hydride reactor. Constructal theory is supremely adapted for use in 2-dimensional and 3-dimensional design for heat transfer structures, as it allows for incorporation of minute analysis of the interior structure with the goal of optimizing for heat transfer. In its application in the realm of engineering, every multidimensional solid structure that is to be cooled, heated or serviced by fluid streams must be vascularized. By this definition, 'vascularization' includes, however is not limited to, structures such as trees, geometrical spacing, and solid walls. Here, every geometric detail will be sized and positioned to achieve maximum efficacy from an engineering design point of view. Furthermore, via design morphing we can achieve low resistances in flow structures which are applicable in cooling and heating applications. An example is that of a ground-source heat pump design where the piping design is morphed by constructal law and spaced in an optimal way to achieve maximum thermal efficiency when extracting heat from the ground

Research Proposal for an Experiment to Search for the Decay {\mu} -> eee

We propose an experiment (Mu3e) to search for the lepton flavour violating decay mu+ -> e+e-e+. We aim for an ultimate sensitivity of one in 10^16 mu-decays, four orders of magnitude better than previous searches. This sensitivity is made possible by exploiting modern silicon pixel detectors providing high spatial resolution and hodoscopes using scintillating fibres and tiles providing precise timing information at high particle rates.Comment: Research proposal submitted to the Paul Scherrer Institute Research Committee for Particle Physics at the Ring Cyclotron, 104 page

Multi-split configuration design for fluid-based thermal management systems

High power density systems require efficient cooling to maintain their thermal performance. Despite this, as systems get larger and more complex, human practice and insight may not suffice to determine the desired thermal management system designs. To this end, a framework for automatic architecture exploration is presented in this article for a class of single-phase, multi-split cooling systems. For this class of systems, heat generation devices are clustered based on their spatial information, and flow-split are added only when required and at the location of heat devices. To generate different architectures, candidate architectures are represented as graphs. From these graphs, dynamic physics models are created automatically using a graph-based thermal modeling framework. Then, an optimal fluid flow distribution problem is solved by addressing temperature constraints in the presence of exogenous heat loads to achieve optimal performance. The focus in this work is on the design of general multi-split heat management systems. The architectures discussed here can be used for various applications in the domain of configuration design. The multi-split algorithm can produce configurations where splitting can occur at any of the vertices. The results presented include 3 categories of cases and are discussed in detail.Comment: 11 pages, 18 figure

Optimisation of Balçova-Narlıdere geothermal district heating system

Thesis (Master)--Izmir Institute of Technology, Mechanical Engineering, Izmir, 2003Includes bibliographical references (leaves: 118-121)Text in English; Abstract: Turkish and Englishxiv, 121 leavesThe main goal of this study is to determine optimum control strategy of Balçova-Narlıdere geothermal district heating system to minimise the energy consumption. First heat demand model of the system was constructed by using statistical method called time series analysis. This model provides the heat demand forecast of next day, by considering ambient temperature forecast of the next day. Then geothermal pipeline system and city distribution system have been modelled in the PIPELAB district heating simulation program. To model the system close to the actual case, database of Balçova geothermal company was used as an input, and the code of PIPELAB program was adapted to be used in geothermal pipeline system. Once the sysem was modelled in PIPELAB, it would be possible to obtain pressure and temperature distribution along the pipe networks in the system. To determine the optimum operation strategy of the wells according to the changing heat demand first the energy consumption of each well pump was defined as a function of their heat production rate. Then these functions were inserted into dynamic programming algorithm which selects the optimum well operation strategy among thousands of options. Also power consumption models of circulation pumps were built and calibrated with actual values. Finally optimum control strategy for the system was determined and the system model was operated by using optimum control strategy according to ambient temperature data of 2001 and 2002. The acual energy consumption values were compared with the optimum energy consumption values and decisive factors in efficient control and operation of the system have been defined

Physics Performance Report for PANDA Strong Interaction Studies with Antiprotons

To study fundamental questions of hadron and nuclear physics in interactions of antiprotons with nucleons and nuclei, the universal PANDA detector will be build. Gluonic excitations, the physics of strange and charm quarks and nucleon structure studies will be performed with unprecedented accuracy thereby allowing high-precision tests of the strong interaction. The proposed PANDA detector is a state-of-the-art internal target detector at the HESR at FAIR allowing the detection and identifcation of neutral and charged particles generated within the relevant angular and energy range. This report presents a summary of the physics accessible at PANDA and what performance can be expected

Geometric optimization of complex thermal-fluid dynamic system by means of constructal design

In this work the Constructal Theory is exposed in its generality, trying to approach it through examples mostly of a physical-engineering nature. Constructal Theory proposes to see living bodies as elements subject to constraints, which are built with a goal, an objective, which is to obtain maximum efficiency. Constructal Theory is characterized by Constructal Law, which states that if a system has the freedom to morph it develops over time a flow architecture that provides easier access to the currents that pass through it. The Constructal Law is as general as the First and Second Laws of Thermodynamics, but it has a very different purpose which makes it unique and complementary to those laws. While the First Law points to the conservation of energy, both the Constructal Law and the Second Law point to change, that is, to a direction in time. Contrary to the Second Law, the Constructal Law applies to systems that are out of balance, that is, to systems that evolve over time. While the second law deals with state variables, the Constructal Law combines flows and design. The thesis continues with the application of the Constructal Theory for a cardiac bypass shape optimization. Through the Constructal Theory the constraints under which the system is free to morph are defined and, through the classical engineering optimization processes (numerical simulations and optimization algorithms) the optimum conditions are defined, i.e., those conditions that guarantee the minimum resistance to the passage of the fluid. The characterization of the blood flow was an important step in the study of this system, as the heartbeat induces a pulsed regime inside the veins. Therefore, the simulations conducted in transient regime consider the deformed velocity profile according to the conditions dictated by the pressure gradient established by the heartbeat

Algorithmic generation of vascular network models for additive manufacturing

Fabrication of functional vascularised three-dimensional tissue constructs has been a long-standing objective in the field of tissue engineering. Currently, the main limitation in this field is the inability to produce fully vascularised tissue with an internal mass transport system (vascular network) that can provide cells with nutrients and oxygen while removing waste, to imitate the functions of human living tissue. Achieving such a system would allow the development of large-scale tissue constructs and increase the potential for in vivo integration. There are different approaches to attempt vascularisation, which use a diversity of techniques. Among these, one of the most promising is additive manufacturing due to its versatility, reproducibility, and compatibility with suitable materials. With the aim of contributing towards the efforts in this field, the present work presents a method for the automatic generation of physiologically-based vascular network structures as solid 3D models suitable for additive manufacturing technologies. Considering the natural hierarchical branching vasculature as an ideal solution, an algorithm was developed to generate branching tree structures connected at the ends to form vascular networks. The implementation is based on previous work in the field of computational bio-simulation of arterial tree growth. It consists of a space-filling algorithm that connects all given points to a growing tree within a defined three-dimensional volume, while fulfilling constraints associated with the physiological laws of circulation. The networks are generated using a CAD environment and thus can be used in additive manufacturing processes. An investigation was carried out on the effect of three input parameters (namely volumetric flow rate, pressure difference across the tree, and number of terminal points) in order to find a suitable combination of parameters that would produce networks with diameters above the fabrication threshold. In order to demonstrate feasibility and functionality of the networks fabricated using this proposed method, two network models were produced by 3D printing and subsequently used as a sacrificial structure to produce PDMS blocks with the hollow vascular networks embedded in it. Particle tracking was used to measure the flow velocity in the channels at two different inlet flow rates. Comparisons were made with theoretical values obtained from computational fluid dynamics simulations and show a good agreement between experiment and theory. From the measurements of maximum velocity, it was observed that at a lower flow rate, the experimental values were closer to the theoretical values than at a higher flow rate. This might be due to the challenges that higher flow rates represent, such as less accurate particle tracking. Given the overall agreement, it is concluded that computational fluid dynamics simulations are a fast and effective way to analyse flow in vascular network models produced by the method here proposed.The Cambridge Trust, CONACyT (Consejo Nacional de Ciencia y Tecnologia), EPSRC Cambridge & Cranfield Doctoral Training Centre in Ultra Precisio