THERMO-MECHANICAL INVESTIGATION OF PACKED BEDS FOR THE LARGE-SCALE STORAGE OF HIGH TEMPERATURE HEAT

ABSTRACT Thermal storage systems are central elements of various types of power plants operated from renewable and conventional energy sources. Where gaseous heat transfer media are used, a regenerator-type heat storage based on a packed bed inventory is a particularly cost-effective solution. However, suitable design tools that cover the thermo-mechanical aspects of such a design are still missing today. As a basis for such a tool, this contribution presents a novel approach to investigate the thermo-mechanical behaviour of such a storage under thermocyclic operation. The relevant relations are formulated on the basis of the discrete element method (DEM). Results of simulation runs determine the temporal and spatial displacements and acting forces for the individual bodies. Coupling the equations to a simplified thermal model allows to investigate the thermo-mechanical behaviour. Initial results for a thermocyclic operation using simplified assumptions are presented. BACKGROUND Thermal energy storages for the high temperature range are central components for power plants driven from renewable energy: Heat storage allows solar thermal power plants to continuously operate beyond sunshine duration. In fossil CHP power plants they increase the operational flexibility and thus improve the revenue situation. Industrial waste heat use and electricity storage based on Adiabatic Compressed Air Energy Storages (ACAES) are further examples. An increasing interest in these technologies calls for large-scale storage solutions in a temperature range between 500-1000°C with storage capacities up to 3GWh for discharge durations between 4 and 12h. In many applications the heat is transferred by gaseous heat transfer media, such as air or flue gas. Here, a direct contact between the heat transfer fluid and storage inventory is a particularly cost-effective design solution. Installations of these socalled regenerator-type heat storages have been used in the steel and glass industry for many decades. The storage inventory is stacked from ceramic bricks. To reach the cost targets for power plant applications, regenerators based on a packed bed inventory are a promising option. They offer a large specific heat transfer area and high heat transfer rates, as well as the potential to reduced investment costs, especially for natural stones as an inventory material

Study of Whey Protein Adsorption under Turbulent Flow

Reducing fouling in heat exchangers during treatment of milk products is one of the great challenges in the dairy industry. One approach to mitigate fouling is to alter the surface characteristics of the heat exchangers making them less prone to protein adsorption. On this background the European project MODSTEEL was established to study the use of new modified stainless steel surfaces to control fouling of milk components. This part of the project focuses on the adsorption of b-lactoglobulin (b-Lg) from a whey protein solution on unmodified and modified 316 2R stainless steel surfaces by in situ ellipsometry under well-defined flow conditions, in the turbulent regime. The effects of temperature, flow rate and surface modification, including SiF3+ and MoS2 ion implantation, DLC (Diamond-Like Carbon) sputtering, and DLC-PlasmaCVD (Chemical Vapour Deposition), were investigated. The amount of protein adsorbed is discussed in relation to the thermal stability of b-Lg, surface properties and hydrodynamic conditions

Theoretical and Experimental Study on Dropwise Condensation in Plate Heat Exchangers

This paper describes the outline of a simulation model for an oil-cooled flat-plate condenser and summarises the main results from its application. Mass and energy balances are solved for a specific Alfa Laval plate heat exchanger with three channels. Dropwise condensation on the corrugated plate surface is described using a modified model from the literature, and studied through high-speed imaging. Parameter variations show the most relevant parameters of the model. The influence of temperature difference, oil flow, pressure and some model parameters on the simulation results is analysed. The results of the simulations are compared to experimental data, showing that the model is useful over a certain range of parameters, but has to be improved for high heat fluxes to achieve a better fit to the experimental data