Heat transfer and pressure drop enhancement techniques

There is an urgent need from all industrial partners to investigate and develop traditional heat transfer enhancements, whilst limiting the pressure drop. Examples of heat transfer enhancement technologies are Additive Manufacturing (AM) printed materials with integrated microchannels, meta-materials with exceptional heat-transfer, macro- and microchannels, ribs, dimples, surface roughness, acoustic effects, and porous media. Basic research on heat transfer with focus on insulation and decreasing thermal emissions is also promoted. Minimizing thermal emissions will decrease energy consumption, increase efficiency, reduce heat pollution, and improve operator’s working environment. The aim is to develop methodologies that estimate the energy improvements in relation to cost. For some applications thermal mixing in confined environments is of importance (e.g., cooling in power stations) and accurate models are needed to assess the impact of turbulent mixing on heat transfer. The work package includes three PhD projects, one at each partner University. Read more about the individual sub-projects below.

Task 1. Flow turbulence and thermal mixing control for unconfined and confined flows

Higher fidelity computational fluid dynamics simulations will be carried out to understand the behavior of flow separation and possible secondary flows on aerodynamic performance and heat transfer for flat and curved surfaces and complex geometrical configurations. The sensitivities to the operating and boundary conditions will be assessed (including impact of non-isentropic temperature fluctuations). Adjoint based topology optimization for heat transfer problems will be deployed enabling novel designs using optimization algorithms. Optimization of heat sinks (heat capacity, thermal conductivity) with the objective function being the heat flux through the adjacent solid structure will be carried out. Optimization of passive flow control devices (roughness elements; micro vortex generators; fins) using topology optimization with the purpose to enhance the heat transfer flux between the hot wall and the fluid flow.

Task Leader: Mihai Mihaescu, KTH. PhD student: Romain Seppey, KTH

Task 2: Optimal heat transfer and heat recovery considering detailed geometry, surfaces texture and wall treatment

Heat transfer models based on e.g. Physics-Informed Neural Networks (PINNs) will be developed to correctly represent the heat transfer and its sensitivity to the incoming flow conditions. The models will be implemented, verified and validated using higher fidelity simulation data and experiments carried out on benchmark cases. In a second stage focus is set on heat transfer for different surface textures including anisotropic surfaces and the induction of secondary flows. Here the impact of the misalignment between the flow direction and the preferred direction of the surface texture on the heat transfer mechanisms at the wall will be assessed. In a third stage the effect of surface treatment and fouling will be considered. Assessments of thermal efficiency and cost will be made for different topologies of interest.

Task Leader: Anna-Lena Ljung, LTU. PhD student: Yuvarajendra Anjaneya Reddy, LTU

Task 3: Optimal heat transfer with active flow and acoustic control

This task targets enhance understanding of the impact of infrasound on the cooling performance as well as the interaction between low-frequency acoustic waves and flow and thermal boundary layers. The influence on fluid flow and heat transfer will be assessed for different sonic frequencies, particle velocities, acoustic impedances of cooling medium. Knowledge will be built concerning the manner of generating standing waves for particular configurations of interest. Cooling process is unsteady and thus it is of importance to address the highly transient heat loads by smart flow and heat transfer control strategies. Theoretical analysis, especially dimensional analysis, will be performed to explore possible mechanisms of acoustic waves on flow and heat transfer. By performing a parametric study, using simplified simulation models, the optimum parameters can be assessed, which then will serve practical engineering applications. Experiments and numerical modeling with low-frequency acoustic treatment will be performed with the purpose to assess the impact on heat transfer. Besides acoustic control, other possibilities to actively control the flow and heat transfer for improved thermal efficiencies and to reduce fouling will be investigated.

Task Leader: Lei Wang, LTH. PhD student: Pierre De Rijcke, LTH