Research in thermal energy

The section has expertise in numerical modelling of systems and components and the development of simulation tools for these. This involves disciplines such as mechanics, fluid dynamics, heat transmission, emission formation and surface phenomena, as well as the use of modern methods as pinch analysis, exergy analysis and thermoeconomics. Experimental research includes facilities for testing of performance and emissions from internal combustion engines and road vehicles. The section is also active in experimental research of heat transfer in refrigeration and heat pump systems as well as small-scale power cycles. The group is active in the education of students on DTU’s MSc programmes in Sustainable Energy and in Engineering Design and Applied Mechanics.

Alternative power plants
Alternative power plants based on fuel cells are under study. The power generation varies from 5kW to large MW classes for different purpose; small power generators for houses need and large plants for decentralized/centralized stations. In such plants Solid Oxide Fuel Cells are mostly used in combination with traditional plants. Gasifiers using wood pellets, biogases and municipal wastes are also considered. Contact: mr@mek.dtu.dk

Biorefineries
The research within biorefineries aims at generating novel designs for plants producing fuel, electricity and heat by using thermodynamic simulation tools. The plants investigated are mainly thermo-chemical plants based on gasification of biomass followed by chemical synthesis – biological plants based on fermentation are however also investigated. The plants are optimized with respect to energy/exergy efficiency. A focus area is lowering the CO₂ emission from the plants by using carbon capture and storage (CCS), which enables the plants to have a negative net CO₂ emission. The integration of electrolysis of water based on renewable electricity is also investigated. Contact: lrc@mek.dtu.dk

Heat pumps, combined heat and power and optimal heat supply
Heat pumps may be applicable for high-efficient heat supply in an energy system based on renewable energy sources as solar and wind with minimal use of thermal power stations based on fossil fuels or biomass. But in the current, modern energy system state-of-the-art heat pumps are not competitive with optimized combined heat and power production. Focus of the research is the best possible heat supply system in current and future energy systems, including working media, heat products and storage of thermal energy. Contact: be@mek.dtu.dk

Heat transfer
Turbulent models for analysis of complicated flow geometries are developed to estimate heat and flow distribution inside industrial components. An in-house code is developed to account for different transport equations when modeling turbulence heat and fluid flow such as RANS (Reynolds Average Navier Stocks) and k–epsilon models with linear and non-linear eddy viscosity models. For the temperature field, SED (Simple Eddy Diffusivity), GGDH (Generalized Gradient Diffusion Hypothesis), WET (Wealth Earning Times), NLSF (Non-Linear Scalar Flux) and NLED (Non-Linear Eddy Diffusivity) models are considered. Contact: mr@mek.dtu.dk

Hydrogen refueling stations
The focus is to model a system which can refuel a hydrogen car or lift truck within 2-3 minutes. Such short time demands an effective refrigeration system since extracting hydrogen from a high pressure source to a car tank (at considerably lower pressure) provides heat that must be removed. Different refueling strategies as well as modeling are studied. Contact: mr@mek.dtu.dk

Industrial energy systems
The research is focused on the optimization of industrial energy systems by application of thermodynamic models and exergy analysis in combination with thermoeconomics. Focus is on the extension of process integration to not only cover heat exchanger networks. Applications are e.g., brewing, pulp and paper and dairy industry. Contact: be@mek.dtu.dk

Integration of biomass processes
Several biomass processes can benefit by integration of energy and/or mass. The biomass processes considered are mainly drying, pelletization, torrefaction, gasification, biogas production. These processes may also be integrated with downstream conversion of the gas/biogas to electricity/heat/fuel. The aim with the research within this field is design of optimal biomass conversion routes (all the way from drying/pretreatment to production of electricity/heat/fuel) with respect to energy/exergy efficiency. This includes determining whether a specific process should be placed decentralized (close to the biomass resource) or centralized. Thermodynamic simulation tools are used to estimate the performance of the designed biomass conversion routes. A very important focus area is recycling of the biomass nutrients to the soil and making sure the recycled nutrients are plant available. This could be achieved by using a low-temperature gasifier that produces a nutrient rich ash with an adjustable carbon-content. Contact: lrc@mek.dtu.dk

Low-temperature heat to power conversion
The research activities within this field cover a range of applications, with the common feature that power is obtained from low-temperature heat sources. Examples of applications include power production form geothermal heat sources, industrial waste heat and exhaust gases from marine diesel engines. When considering low-temperature heat sources it is recognized that it is possible to obtain more power from a cycle featuring an organic working fluid, i.e. an Organic Rankine Cycle (ORC), or a working fluid consisting of a mixture of water/ammonia, i.e. a Kalina cycle. The research activities within this field are aimed at deriving more efficient cycles for low-temperature heat to power conversion. Novel cycle configurations and working fluids are studied. Using numerical simulations tools both steady-state and transient performances are modelled. The research includes advanced thermodynamic methods based on energy and exergy analysis. Contact: frh@mek.dtu.dk

Machinery systems for ships
Within the shipping industry progressive reductions in maximum allowable fuel sulphur content and NO_x emissions are imposed and a regulatory framework for CO₂ emissions is expected to be put into force within a near future. The research activities within the marine field at the section are aimed at designing and optimizing two-stroke diesel engines with waste heat recovery systems. Moreover, machinery systems based on gas turbines and waste heat recovery systems for high-speed ferries are investigated. A large focus area is to derive a zero-dimensional two-stroke diesel engine model that predicts with reasonable accuracy the effects on performance and emissions of changed engine design and operating parameters and emission abatement technologies. Unconventional design solutions for waste heat recovery systems are studied. Systems including water/steam as well as unconventional working fluids are considered. Contact: frh@mek.dtu.dk

Power plant Engineering
The research within power plant engineering is aimed at designing, modelling and optimizing power plants that reduce the fuel consumption and pollutant emissions. Novel design and operational strategies for large solid-fuelled steam power plants are considered. Using numerical simulations tools both steady-state and transient performances are modelled. An example is the design and modelling of power plants with integrated bio-ethanol production. Furthermore, power plants based on gas turbines and bottoming cycles used for off-shore platforms are studied. In this work, gas turbines with waste heat recovery systems are designed and subsequently their load control strategies are optimised, considering part-load and dynamic performances. One of the challenges within this work is to derive methodologies for predicting the part-load performance of turbomachinery. The research area also includes the modelling and optimisation of concentrated solar thermal power plants. Contact: frh@mek.dtu.dk

Refrigeration systems
Refrigeration for food conservation, comfort cooling and other applications is a significant consumer of electricity. Research focuses on minimization of consumption and integration with other energy consumptions. Contact: be@mek.dtu.dk, wb@mek.dtu.dk

Stirling engines
Optimization of engine performance; operation on natural gas and renewable fuels such as wood chips and biogas are studied. Contact: hc@mek.dtu.dk 

Two-phase flow in heat exchangers
The research primarily focuses on evaporating two-phase flows in heat exchangers for heat pumps or refrigeration systems. Compactness and charge minimization are significant issues in the development of refrigeration systems and optimal performance of the heat exchangers is therefore crucial. Optimal flow distribution in heat exchangers with parallel runs help decreasing the necessary heat exchanger area. One dimensional, discretized numerical models of the evaporating flow in heat exchangers are used as a tool in order to investigate, which phenomena are governing the flow distribution. Heat transfer and pressure drop is investigated locally throughout the evaporator. Contact: wb@mek.dtu.dk

Major experimental facilities
Approximately 600 m2 of laboratory space is available for experimental set-ups. The Thermal Energy Systems Section has a wide range of test facilities and instrumentation at its disposal, including a 12 m3 low temperature chamber for tests down to -70°C. A second test chamber operates in the temperature range 0 - +40°C with full humidity control. Refrigeration systems with capacities up to 50 kW, using carbon dioxide, ammonia, and hydrocarbons, are also available. Test facilities exist also in the fields of gasification of biomass, and small-scale power generation. The biomass facility includes three different types of gasifier of our own design and macro TGA equipment for basic reactivity measurements.