Heat transfer is involved in all thermal processes and the efficiency of the heat transfer is of utmost importance for the efficiency of the process as a whole.
Energy transfer over a temperature difference always constitutes a thermodynamic loss, and the larger the difference, the larger the loss. For this reason, methods of enhancing heat transfer, i.e. reducing the temperature difference, are important to reach high thermal efficiency of the system.
Research at the Division of Applied thermodynamics and refrigeration started from design of heat pumping equipment involving heat exchange with the ambient and with the fluids or bodies to be cooled or heated. Within the systems, a refrigerant is circulating, changing phase from liquid to gas in the evaporator and back to liquid in the condenser. It is thus natural that the heat transfer research at the division has a focus on two-phase flow, but that enhanced heat transfer in single phase flow is also important.
The research conducted in this area covers:
Compact heat exchangers
Enhanced heat transfer
Cooling of electronics
Industrial processes, pinch
Projects
Projects related to heat transfer during the last ten years have for example been investigating:
Flow boiling in small channels
Condensation in vertical rectangular channels
Heat transfer of nanofluids
Porous surfaces for enhanced boiling heat transfer
3D-printing of heat exchangers
Compact Minichannel Latent Energy Storage for Air Related Cold Storage Applications
Cold storage using cold air in different applications can reduce the energy use and contribute to mitigation of greenhouse gas emissions significantly. Such applications are free cooling in HVAC systems, in automotive evaporators and in refrigeration systems running on floating condensing mode. Latent Thermal energy storage (LTES), employing Phase Change Materials (PCM) as energy storing medium, is a useful technology which can be used to reduce the energy consumption of energy systems. In the storage system, using air and PCM, a compact and robust heat exchanger in terms of energy density and power is highly in demand.
This project aimed to measure advantages and disadvantages of deep borehole heat exchangers as well as to propose design guidelines for multiple borehole fields with coaxial collectors.
Refrigeration and heat pump systems today use refrigerants with high global warming potential (GWP). Within the next ten years, these will be substituted by natural and synthetic fluids with low GWP. Such fluids are always flammable and to reduce the connected risks it is important to reduce the charge of refrigerant. To achieve this, heat exchangers with small internal volume are required. New designs of the heat exchangers for low charge can simultaneously give better heat transfer, if the design is done correctly, which will increase the COP.
