Compact heat exchangers

Background

Compact heat exchangers are used in a great variety of applications. They allow for an increased heat transfer rate, require less volume and weigh less compared to other heat exchanger types. The disadvantage is the higher pressure drop. They are clearly the preferred choice for applications which require a high heat transfer rate in a limited volume such as air conditioning devices, heat pumps, automotive radiators, etc. In these applications the main thermal resistance is located on the airside. To improve the heat transfer rate different strategies are used such as the addition of fins at the airside (e.g. plain fins, louvered fins, slit fins, offset strip fins, ...), the use of vortex generators or the application of novel materials (e.g. metal foams, polymer heat exchangers, …). Only a limited number of fin designs or configurations with novel materials have been studied and described in open literature, as a large set of experiments is required to acquire sufficient data and the parameter space considered is very large. Currently these experiments are performed on actual heat exchangers or scaled versions. However, as the computational power and accuracy of simulation codes increase, more and more research is being done through 'numerical experiments', i.e. computational fluid dynamics (CFD). Careful benchmarking remains very important, especially when performing heat exchanger optimization.

Scope of research

This research aims to investigate the interaction between the flow behaviour and the resulting thermodynamics within compact heat exchangers (fin structures) in order to optimize and design better units for specific applications. Both experimental and numerical studies are performed, seeking a strong synergy between these disciplines. The experimental data (water tunnel and wind tunnel experiments, hotwire measurements, Laser Doppler Anemometry (LDA), infrared (IR) thermography, ...) are used to develop heat transfer and pressure drop correlations. They also provide reliable benchmarking data for numerical codes (cycle simulations, full scale heat exchanger simulations or CFD flow field and thermal hydraulic computations). The numerical results provide a more detailed look into the flow physics. This combined approach is currently used to study junction flows and the use of vortex generators in compact heat exchangers (H. Huisseune), the use of metal foams for heat exchanger applications (P. De Jaeger) and the performance characteristics of different enhancement techniques (B. Ameel).

Wind tunnel for heat transfer and pressure drop measurements.
Wind tunnel for heat transfer and pressure drop measurements.
Water tunnel for flow visualization experiments.
Water tunnel for flow visualization experiments.