Keynote Speakers
(not complete list)
Developing and Validating Multiphase Heat Transfer Modelling
Understanding how multiphase flow can be modelled, where heat and reactions are present, requires differing levels of fidelity depending on the end use, i.e. for developing designs or defining new control approaches or whether to provide an understanding of the underlying phenomena. Therefore at Nottingham we have developed a range of techniques that allow us to investigate at the appropriate level depending on the context of the physics/
chemistry/biology that we are modelling and the application. To validate these modelling approaches we have developed experimental facilities, testing approaches, visualisation and measurement techniques. The approaches, and how these work together to extend engineering science and methodology, will be explored within this talk.
Modeling of Irradiated Particle-Laden Turbulence Subject to Uncertainty
The study of thermal radiation interacting with particle-laden turbulence is of great importance in a wide range of scientific and engineering applications. In a recent project at Stanford University, we focused on numerical simulations of volumetric solar energy receivers in which small size particles interact with turbulent air flow to transfer energy from a radiation source to the fluid. The computational study of such systems is challenging because of the complex coupling of thermo-fluid mechanisms governing the underlying physics at different scales. I will describe the main physical models and computational tools built during the project, their validation against a dedicated experimental campaign and some of the most interesting results related to particle clustering. To build confidence and improve the prediction accuracy of the numerical simulations, the impact of uncertainties on the quantities of interest was an important driver of the project. This, however, requires a computational budget that is typically a large multiple of the cost of a single calculation, and thus may become infeasible for expensive simulation models featuring many uncertain inputs and highly non-linear behavior. In this regard, multifidelity methods have become increasingly popular in the past years as acceleration strategies to reduce the computational cost. These methods are based on a hierarchy of generalized numerical resolutions, or model fidelities, and attempt to leverage the correlation between high- and low-fidelity models to obtain a more accurate statistical estimator with a relatively small number of high-fidelity calculations. We will present the development and the performance of two different multifidelity strategies for uncertainty quantification. The final part of the presentation I will present more recent results regarding the use of dimensional reduction techniques combined with the Buckingham Pi theorem to obtain scaling laws for the observed results.
Simulation and Modelling of Nano-Particle Formation in Flames
Nanoparticles have gained enormous economic importance, as they can often replace classic materials with far inferior properties. The use of nanoparticles ranges from simple fillers (like soot in tyres) to pigments in the cosmetics industry (sunscreen) to optical coatings or electrode materials for performance-enhanced lithium-ion batteries. Nanoparticles can be produced in the gas phase or wet phase, or alternatively by energy-intensive crushing of large particles. A very cost-effective way is to decompose a precursor at high temperature, followed by cooling and condensation of the desired (primary) particles. This process can be implemented particularly efficiently in flames. Here, both the reaction kinetics of precursor and fuels must be taken into account, as well as the aerosol dynamics (condensation, evaporation, surface growth, agglomeration), and the transport processes in the flow. Nanoparticle-laden flow with an Eulerian description is characterised by extremely high Schmidt numbers, i.e. the diffusion rates are low, so that the Batchelor scales (the smallest scales in the scalar field) are often smaller by orders of magnitude than the already tiny Kolmogorov scales of the turbulent flow. Since both aerosol dynamics and reaction kinetics depend strongly nonlinearly on concentration, there is a great need for appropriate fine structure or source term models. The talk will present some application examples of nanoparticle synthesis simulations, complemented by basic research topics on the development of aerosol dynamics, reaction and transport models.
Evolution of Heat Flow Architectures, a Constructal Approach
In this talk we will discuss how the constructal law of evolutionary design allows to predict how heat flow structures evolve towards better efficiency. When most of today designs are based on trial and error, the constructal law empowers us with the ability to predict what the configuration of the energy system should be. We will cover the case of thermochemical storage as an example of thermal energy storage, and will show how the storage reactors can be designed to increase the heat exchanges while maintaining their compactness. Next, we will discuss the thermal management of EV batteries. The work will highlight the superiority of designs based on tree-shaped configurations for improving the heat transfer while decreasing the friction losses of the heat transfer fluid. We will also exemplify how to discover effective fluid networks to pump water by capillary action for evapotranspiration. In all those examples, the theoretical framework relies on the search for maximum flow access by evolving the shape and morphology of the flow networks.
Improving the Flexibility of Power Steam Boilers by Optimizing the Heating and Cooling of Critical Pressure Components
Jan Taler, Dawid Taler, Piotr Dzierwa, Karol Kaczmarski, Marcin Trojan
The start-up and shut-down times of a steam boiler and, thus, the entire power unit can be significantly reduced by optimising the heating and cooling times of a critical pressure element in the boiler. The paper proposes a new method for determining the optimum fluid temperature changes for optimising the start-up and shut-down of the steam boiler. The total stress from pressure and thermal load, at the edge of the hole in a thick-walled component, does not exceed the allowable stresses during optimum heating. The stress concentration factors at the edges of the holes were determined using the Finite Element Method (FEM) to represent the real construction of the junction between the pressure component and the connector. The application of the developed method was illustrated using the example of optimal heating and cooling of a steam boiler drum. Three-dimensional FEM analysis for determining the transient temperature and stress distributions was carried out for the junction of the drum and downcomer. It was demonstrated that the total circumferential stress from pressure and thermal load at the hole edge does not exceed the allowable stress if the optimum fluid temperature variations were applied. The method proposed in this paper was compared with the European standard EN 12952-3, which makes it possible to determine allowable heating and cooling rates of boiler pressure components as a function of pressure. The resulting comparisons show that using the developed method, the boiler start-up and shut-down times can be reduced by about one and a half times compared to the equivalent times determined using the methods in standard EN 12952-3.
Target-Controlling Principle of Local Thermal Resistance for Energy Saving and Storage Processes
Ting Wang, Wei Cui, Hongliang Chang, Ting Ma, Min Zeng, Qiuwang Wang
Energy saving and storage technologies are widely used in the fields of energy, power, petrochemical industry, metallurgy, refrigeration, aerospace and so on. Developing advanced and efficient energy saving and storage technologies is urgent to achieve carbon neutrality. One of the key factors affecting the performance of energy saving and storage technologies is the momentum, heat and mass transfer in the energy saving and storage processes. This report presents a target-controlling principle of local thermal resistance for energy saving and storage processes. In the process of single-phase heat transfer enhancement, a directional plug flow control method of single-side thermal resistance is proposed to achieve a reasonable match between thermal resistance and flow resistance. The corresponding technologies of continuous helical baffled shell-and-tube heat exchanger, longitudinal corrugated internally finned tube and grate-particle composite stacking bed are developed. In the process of two-side heat transfer enhancement, a local target-controlling method of two-side thermal resistances is established. Considering the difference between the spanwise and streamwise thermal resistances, the high-temperature gas-gas heat exchanger and moving bed heat exchanger are developed. In the process of phase change energy storage, the space-time evolution mechanism of thermal resistance is revealed. Two hybrid regulation methods of thermal resistances for energy storage technologies are developed, including the combined enhancement technology of applying ultrasonic and nano-particle phase change materials, and the power generation technology based on multi-temperature zone phase-change materials and thermoelectric device. The proposed target-controlling principle of local thermal resistance is of great significance to guide the precise design of energy saving and storage equipment.
Keywords:
Energy saving and storage processes, Local thermal resistance, Target-controlling principle, Directional plug flow, Hybrid regulation.