Heat Transport

Efficient heat transport, or heat transfer, is a focus of numerous projects across a wide range of our research activities at Fraunhofer ISE. The applications are analyzed both experimentally and simulatively.

Heat transport processes are simulated differently depending on the type of transfer. The calculations are based in each case on spatially resolved partial differential equations. Pure heat conduction, e.g. in solids, is solved by a heat conduction equation (in simplified form Fourier's law); free or forced convection is calculated coupled with a flow simulation; heat radiation is calculated on the basis of surface properties and temperatures (e.g. Stefan-Boltzmann law). The investigated media exist in all classical aggregate states (solid, liquid, gaseous) and also undergo phase changes during the simulations due to the process.

The software Comsol Multiphysics®, OpenFOAM and Ansys Fluent / Ansys CFX are available for Fraunhofer ISE for the simulations.

R&D Services for Heat Transport

In our business areas we offer the following services in the field of heat transport:

• Calculation of temperature fields in PV modules and solar thermal collectors and their effect on e.g. mechanics.
• Combined simulation of flow and heat transport in heat exchangers
• Heat transport in thermal storages
• Validation of simulated heat transfer processes with experimental tests
• Optimization of air flow and heat exchanger geometry in air conditioning units
• Simulation of heat and cold transfer in adsorption and compression processes
• Heat transfer calculations for different material combinations

Coaxial Heat Exchanger for Decentralized Ventilation

A coaxial heat exchanger is a tube-in-tube heat exchanger. For use in a ventilation unit, the concept of the heat exchanger was rethought and the surface area between the two air streams (exhaust and supply air) was significantly increased by geometric modification in a center section of the tubes (see figure). In winter, the supply air flowing in from outside is heated on this large surface by the warm exhaust air and fed into the room. The essential task in the heat exchanger development was to design the geometry in such a way that an energy-efficient, compact and low-noise decentralized ventilation unit is possible. However, the geometric variations are innumerable (number of channels, length of transition areas, wall thicknesses, ...), so an iterative process of simulation of flow and heat transfer using FEM together with experimental work on the heat exchanger was performed. For this, it was necessary to vary the geometry under boundary conditions that allowed additive manufacturing of the component and easy installation of the device in the wall of the house.

Further information on this topic

Optimization of the Thermal Resilience of a Junction Box

Bypass diodes are located in the junction box of a PV module. When a bypass condition occurs, the high currents in the bypass diodes can cause severe heat generation. If the heat is not dissipated well, this leads to overheating of the junction boxes and thus to failure of the module.