Design software simulates battery operation

 

CD-Adapco has partnered with Battery Design LLC, a company with more than 10 years experience with the development of lithium-ion (Li-ion) battery analysis software and cell design consulting. The two firms have developed a way to design and analyze Li-ion battery cells, modules, and pack installations. This new battery design software lets users migrate from short length scale simulations, such as studies of a detailed single cell, to complex battery modules, packs or complete installations, including multiple hundreds of battery cells and their surrounding structure and cooling system. The same battery performance model, currently a range of three, can be used in any of the different length scale models. This removes need for duplicating or simplifying the engineering tasks, thereby facilitating the division of labor:

one engineer, probably part of the cell team, creates a battery cell model and begins running cell level simulations. This model can then be passed to another analyst, maybe working in the application team, who uses it to create complex simulations of battery modules or packs. This process ensures that there is no duplication in the two engineers’ time while providing a high fidelity numerical model and coupled flow, thermal, and electrochemical solution.

The software can compute the thermal and electrical or electrochemical solution within one code and ensure that all phenomena are included to achieve a correct overall performance.

The Battery Simulation Module (BSM) combines an electrochemical solver with flow and thermal solvers. These can calculate the 3D thermal, fluid, and electrochemical properties of lithium-ion battery cells on several length scales, starting from each finite volume/e-cell within a battery cell, to the entire pack, including thermally-conducting parts such as metallic connectors at high discharge/charge rate. This is achieved through a closely coupled 3D simulation which returns the electrochemical and thermal properties as complex distributions over the electrodes and battery cells. The internal construction of each cell is taken into account without need to resolve all layers independently, balancing computation effort with appropriate detail.

Battery Design Studio (BDS) was developed to provide a simulation environment for the analysis and design of the electrochemical system and detailed geometry of a single battery cell. A choice of three battery performance models is offered to users, enhanced with significant developments relevant to contemporary cell design, such as multiple active materials or particle sizes.

The software provides a complete battery definition including all geometric details of the cell, details of the collector technology, number of electrodes, and a relevant numerical model of the battery’s performance under load. The model is then tested under appropriate discharge and thermal conditions. This rapidly confirms the correct behaviour of the electrical model which can then be used to study the cell response to load and to understand its limiting factors.

CD Adapco
www.cd-adapco.com

Shouded Wind Turbines Accelerate Output

Our objective while developing wind technology is to reduce costs and increase the power output of wind turbines. The principle behind our studies is to use the effect of static wing or sail structures, which convert energy more efficiently, to increase the efficiency of turbines. Many attempts have already been made during the last decades to use external shrouded systems, but with success only in wind tunnel studies, not in ambient air. The reasons become clear from our use of STAR-CD.

Based on a patent of the Grumman Corporation, a private company built a prototype at considerable expense, which failed to meet the expected success. CD Adapco’s STAR-CD studies of wind turbines with and without shrouds immediately showed the relationship between the force exerted by the flow on the turbine and transfer of both energy and linear momentum. Given a certain force, the energy transfer does not depend on the velocity of the flow, but the momentum transfer does. As a consequence, it is not possible to increase the power of a conventionally shrouded wind turbine beyond the theoretical limit for the same turbine without shroud (the so called Betz limit). With this realization, millions of dollars could have been saved before the prototype stage, with obvious benefits to the project profitability and overall success.

But the success did not stop there. STAR-CD was able to assist in finding a solution. Past shrouded systems closely fitted the propeller to minimize tip-vortex drag. If instead, one leaves a larger space between the propeller tips and the shroud, it has a beneficial effect over a wider radius of the propeller.

Figure 1 shows one of CD Adapco’s wind turbine models, surrounded by a shroud, which is curved like a sail. The surface area of the shroud is about 3 times larger than the area covered by the rotating propeller. Figure 2 shows the velocity in a cross section through the model in the flow direction. Contrary to the conventional system, the air accelerates as it approaches the turbine, and the static shroud plays an active part in the energy extraction of the system, hence the name “partially
static turbine”.

Figure 3 compares the mean total pressure in the flow tube, which passes through the propeller for the bare wind turbine and the shrouded one. The large pressure drop for the shrouded wind turbine could in principle also be achieved in an unshrouded system, but only for small wind velocities. In the shrouded system this large pressure drop occurs while the air is moving through the propeller at a mean axial velocity of 7.2 m/sec (while the ambient wind only has a velocity of 5 m/sec) –

in an unshrouded system, or in a shrouded system, which does not interact with an additional flow of air, this situation would constitute a severe violation of energy and momentum conservation.

Figure 4 compares the power of the shrouded wind turbine compared to the unshrouded design. The increase in peak power is a factor of 4.
The same principle can also be applied to water. For a given flow rate, one can significantly reduce size of a Kaplan wind turbine. Or for a given turbine size, one can produce the same power at a lower flow rate. We expect this not only to reduce the price of hydro-power, but it should also open new applications, since the partially static turbine allows for hydro power construction in places where large dams are not feasible.

STAR-CD has taught us a lot about partially static systems. Still more can be learnt in the optimization of shrouded designs and prototype builds.

We are actively searching for partners and collaborators in industry and other research institutes to take these studies to the next stage.

REFERENCES:
Bet F. and Grassmann H., ‘Upgrading conventional wind turbines’, Renewable Energy, January 2003, Elsevier Press, www.elsevier.com/locate/renene

Grassmann H., Bet F., Cabras G. Ceschia M>, Cobai D> and DelPapa C. ‘A partially static turbine – first experimental results’, Renewable Energy, to be published, ElsevierPress, www.elsevier.com/locate/renene

Ganis M., “CFD analysis of the characteristics of a shrouded turbine” www.diplom.de