Marco Nesarajah

Component-Oriented Modeling of Thermoelectric Devices for Energy System Design

Thermoelectric (TE) devices are used in the form of Peltier coolers and as TE generators, with the latter producing electrical energy from waste heat, based on the Seebeck effect. In both cases, modeling of the TE device is a prerequisite for the design and control verification of the resulting overall energy system. To this end, the model has to be integrated seamlessly in an overall system model containing other electrical, thermodynamic, or even mechanical components. Following this premise, this paper presents a component-based model for TE devices described in the Modelica language. The model incorporates the temperature dependences of decisive material properties (Seebeck coefficient, thermal conductivity, and electrical resistivity) in 1-D spatial resolution. With the help of few additional geometrical parameters, e.g., the thickness of TE legs, the model is capable of describing the dynamic behavior of the TE device in accordance with the experimental results.

Modelica® Library for Dynamic Simulation of Thermoelectric Generators

The contribution presents a new modeling library for the dynamic simulation of thermoelectric generators (TEG) in 1D spatial resolution. The core of the library is a model of the thermoelectric legs (TEL), which has already been published by the authors. In the submitted work, this model is expanded to an overall Modelica® library for complete TEGs. The library is open source and can be extended. It is also usable by end users without deeper knowledge through a graphical user interface (GUI). The use of the library is illustrated by the example of an electronic thermostat valve powered by a TEG.

Modeling and simulation of a thermoelectric Energy Harvesting System for control design purposes

This contribution presents a simulation model of an Energy Harvesting System (EHS) based on Thermoelectric Generators (TEGs) using waste heat from the exhaust pipe of an oil-fired heating system. The overall system is modeled and simulated in the component-oriented environment Modelica®/Dymola®. The model is used to analyze and verify different control concepts to maximize the power output of the EHS. The TEGs used are devices consisting of thermoelectric material that exploit a temperature difference to generate electrical energy due to the Seebeck Effect. By means of TEGs, the overall energy efficiency of combustion processes can be improved by converting a portion of the remaining waste heat into electric power. For this purpose, TEG pairs (pTEGs) are installed on the exhaust pipe alongside the exhaust gas stream. However, with the exhaust gas losing heat in downstream direction, the final pTEG may lower the overall EHS performance due to their electrical resistance. With the help of the presented simulation model, it is possible to remove detrimental pTEGs from the EHS. This removal may happen either statically, i.e. in the design phase, or dynamically, i.e. by finding the ideal instant of time to disconnect and to revive them during operation.

Thermoelectric power generation: Peltier element versus thermoelectric generator

This paper presents a detailed comparison between Peltier elements (also called thermoelectric coolers (TEC)) and thermoelectric generators (TEG) for the usage as thermoelectric power generators. Whereas the former is normally known for cooling applications or heat pump uses, it can also be used as generator. Today, thermoelectric energy harvesting systems find more and more utilization, e.g. in wireless sensors or exhaust pipes. The efficiency of thermoelectric materials for the low temperature sector (between 0 °C and 200 °C) is actually not very high, but the costs for TEGs are. As TECs and TEGs consist of the same thermoelectric material for this temperature sector (Bi2Te3), the upcoming question is in which temperature range and under which conditions expensive TEGs can be replaced by cheap TECs. Therefore, in this contribution, TECs and TEGs are tested and compared under the same conditions.

Multiphysics Simulation in the Development of Thermoelectric Energy Harvesting Systems

This contribution presents a model-based development process for thermoelectric energy harvesting systems. Such systems convert thermal energy into electrical energy and produce enough energy to supply low-power devices. Realizations require three main challenges to be solved: to guarantee optimal thermal connection of the thermoelectric generators, to find a good design for the energy harvesting system, and to find an optimal electrical connection. Therefore, a development process is presented here. The process is divided into different steps and supports the developer in finding an optimal thermoelectric energy harvesting system for a given heat source and given objectives (technical and economical). During the process, several steps are supported by simulation models. Based on developed model libraries in Modelica®/Dymola®, thermal, thermoelectrical, electrical, and control components can be modeled, integrated into different variants, and verified step by step before the system is physically built and finally validated. The process is illustrated by an example through all the steps.

Energy Harvesting from Open Fireplaces

This contribution presents a green barbecue or fireplace, which recovers electrical energy from the heat of the fire by the use of thermoelectric generators (TEGs). TEGs use a temperature difference to generate electrical energy based on the Seebeck effect. To generate a sufficient temperature difference, the fireplace was designed to ensure a good heat transfer to the hot TEG sides. Furthermore, CPU cooling elements using heat pipes were mounted on the cold TEG sides. As a side effect, the recirculation of the preheated air from these coolers into the fire can improve the burning process. The gained energy is used to load a mobile device via an USB plug and to supply 12 V DC via a vehicle plug. Possible applications of the system are of course barbecues where the DC power may be used to support mobile devices or entertainment systems. A more serious application is found in rural areas without electrification where the electricity generated during cooking may replace expensive batteries or environmentally unfriendly diesel generators. Moreover, a simulation model for the green barbecue is created. The contribution will describe the construction of the green fireplace and the developed simulation model. Finally the simulation results are compared with real test readings and an outlook on further developments to a controlled fireplace is given.

Object-Oriented Modeling of an Energy Harvesting System Based on Thermoelectric Generators

This paper deals with the modeling of an energy harvesting system based on thermoelectric generators (TEG), and the validation of the model by means of a test bench. TEGs are capable to improve the overall energy efficiency of energy systems, e.g. combustion engines or heating systems, by using the remaining waste heat to generate electrical power. Previously, a component-oriented model of the TEG itself was developed in Modelica® language. With this model any TEG can be described and simulated given the material properties and the physical dimension. Now, this model was extended by the surrounding components to a complete model of a thermoelectric energy harvesting system. In addition to the TEG, the model contains the cooling system, the heat source, and the power electronics. To validate the simulation model, a test bench was built and installed on an oil-fired household heating system. The paper reports results of the measurements and discusses the validity of the developed simulation models. Furthermore, the efficiency of the proposed energy harvesting system is derived and possible improvements based on design variations tested in the simulation model are proposed.

Modeling of a Heat Pipe for Using in Thermoelectric Energy Harvesting Systems

Thermoelectric energy harvesting systems (EHS) consist of thermoelectric generators (TEG), which generate electrical power due to a temperature difference. Consequently, a main challenge to build up such an EHS is a good heat transfer to and from the TEG. On the one hand heat has to be send to the hot TEG side and on the other hand the waste heat from the cold TEG side has to be dissipated. For this heat transfer heat pipes are very reasonable. They have a 1000-fold better thermal conductivity than copper and so the existing heat quantity can be used more effectively. To model a heat pipe in a most general way, the modeling language Modelica® is used. Thereby, the model can be build based on its physics as well as its material properties. The dimensions of the pipe as well as the used working fluid or the used heat pipe material are parameters adjustable for specific cases. In this contribution, the theoretical aspects of a heat pipe will be described and the modeling with Modelica® for different modeling approaches in the simulation environment Dymola® will be shown. Finally, the model of the heat pipe will be validated with laboratory measurements.