The loading of adhesive layers in the uncured state is a problem in many adhesive bonding applications. Normal stresses lead to a constriction of the bonded surface and impair its strength. One example of this is the heat curing process of adhesive layers in hybrid-joined mixed structures. If the joined materials have different coefficients of thermal expansion, this can lead to a widening of the adhesive gap during heat curing and thus to normal stress on the liquid adhesive layer. This can significantly reduce the original bonding surface, giving it a meandering structure. In the subsequent production process, this structure is cured, which can lead to increased stress build-up in the cured joint due to the reduced bonding surface and the notch effect that occurs. An important, but still largely unconsidered influence on the reduction of the adhesive surface is the heat input into the adhesive layer and the associated change in viscosity and degree of curing. The aim of the project is to experimentally characterise and numerically describe the influence of different temperature profiles and degrees of curing on the problem known as viscous fingering. The focus is on the "bonding of steel-intensive structures". For this purpose, fluid dynamic simulations are carried out, taking viscoelastic adhesive behaviour into account, in order to predict the reduction of the bonding area. Based on the results, a meta-model is extended to predict the effective bonding area without simulation. This provides engineering offices and users of point joining technology - especially SMEs - with a tool for optimising the design of joined structures while taking the manufacturing process into account. Furthermore, the metamodel is integrated into FE simulation software in order to be able to evaluate the influence of viscous fingering on the mechanical properties.

Start: 05/2024

Funding: Federal Ministry for Economic Affairs and Climate Protection/AiF-IGF

Funding reference: 01IF23212N

The project is the first to pursue a holistic approach for the modular and gradual energy-efficient refurbishment of apartment blocks and neighbourhoods. This includes an easy-to-use, manufacturer-independent digital renovation assistant for specific planning and commissioning, a standardised, efficient integration of heat pumps with innovative PVT and PCM technology and a self-learning energy management system with integrated operational monitoring. The main innovations of the solution approach presented lie in the following points: - Digital support during planning, implementation and commissioning through innovative, data-based methods - Integration of PVT heat pump-PCM storage heating systems in heterogeneous building stock - Implementation and demonstration of a self-learning, predictive energy manager as a network of local building energy managers and a central neighbourhood energy manager - Development, modelling and use of PCM storage systems also enables time-flexible, The validation and demonstration includes the conceptual design, implementation and monitoring of refurbishment measures for 20 multi-storey buildings and is carried out iteratively for the practical development and testing of the digital refurbishment assistant and the technical system solution modules for CO2-minimised heat and power supply. The two-level energy management system is being investigated in practice in an apartment building and tested virtually in a neighbourhood using hardware-in-the-loop simulation.

Start: 01/2024

Funding: Federal Ministry for Economic Affairs and Climate Protection

Funding reference: 03EN6024A

The decarbonisation of industrial process heat is a challenge of the energy transition. In the predominantly fossil-fuelled temperature range up to 200 °C, which accounts for around 40 % of process heat requirements, there is a barely tapped potential for reducing greenhouse gas emissions in waste heat utilisation through heat recovery and heat pumps. A lack of expertise regarding sensible applications and optimum integration points for complex processes and variable infrastructures, a lack of technological solutions for converting and storing heat above 100°C, the high cost of data collection and concerns regarding process reliability are the main reasons for the lack of implementation. The aim of the research project is therefore to develop a digital decision support system as a central anchor for the planning and configuration of heat pump storage systems (HSS) for the resilient and efficient conversion and storage of heat. In order to reduce the high transaction costs associated with the necessary data collection, the plan is to utilise methods from process mining. On this data basis, the design, integration and layout of WSS can be optimised for decision support, taking into account the possible combinations of heat sources and sinks as well as process-related, temporal, spatial, ecological and economic restrictions. Another aim is to develop and build a modular and configurable high-temperature storage system on a laboratory scale in order to ensure a robust and uninterrupted supply. The developed systems will be tested in a company-specific and sensitive manner in a virtual production environment. Both the storage system and the prototype increments of the decision support system will be implemented in a demonstrator for dissemination, further development and multiplication.

Start: 01/2024

Funding: Federal Ministry of Economics and Climate Protection

Funding reference: 03EN2109A

Compared to conventional structured packings, sandwich packings allow for intensified mass transfer and reduced liquid maldistribution. This is achieved by combining structured packing segments with different geometric surfaces. The lower accumulation layer has a higher specific geometric surface area and therefore a lower capacity limit compared to the upper separation layer. Accumulation packings are preferably operated with a flooded accumulation layer. This results in the desired intensified phase contact in this layer and the bubbling layer above it. As part of the first funding phase, a rate-based mass transfer model was developed that can be used to calculate the separation performance of accumulation packings, taking into account the complex fluid dynamics over the entire operating range. The fluid dynamics were analysed using ultrafast X-ray tomography, which was established for this purpose and for which extensive algorithms are now available. The overall model validation was carried out using experiments on the CO2 absorption option with aqueous MEA solutions. The extensive experimental and numerical studies also indicate a need to extend the model. The determination of the flooding points is to be improved on the basis of a mechanistic fluid dynamics model. In addition, the fluid flow has so far been considered as an ideal piston flow without capturing backmixing effects. However, dispersion flows are to be expected, particularly in the accumulation layer and the bubbling layer above. With the help of regime-specific dispersion coefficients in the extended rate-based model, a more differentiated view of mass transport and reactions is possible. In addition, the previously unknown mass transport parameters in the bubbling layer are determined and the model is extended to the application for rectification processes.

Start: 02/2022

Funding: German Research Foundation (DFG)

Funding reference number: KE 837/26-3

Co-operation partner: TU Dresden

The progressive miniaturisation of devices has led to the development of microchannel heat exchangers, which are characterised not only by small geometric dimensions but also by intensified transport processes. These efficient micro-scale heat exchangers are used in particular for innovative applications with limited installation space, such as in microelectronics. Various optimisation approaches are being used to further increase the heat transfer performance of these devices. One approach to reducing thermal resistance is the use of microstructured channel walls. However, in addition to the improved thermal properties, the structuring of the surface results in an increased pressure loss. Consequently, the main challenge in the design of structured microchannels is to reconcile these conflicting influences. As part of the project, the influence of surface roughness on fluid dynamics and heat transfer is therefore investigated using numerical methods. For this purpose, geometries with different surface roughness are produced using additive manufacturing and converted into CAD models. These serve as the basis for the computational fluid dynamics (CFD) model, which is used to model the transport processes on the rough surface. Finally, concepts for the design of additively manufactured microchannel heat exchangers with microstructured surfaces are to be derived from the results obtained.

Start: 09/2021

Funding: Budget funds