Investigation of Wire Structures for Heat Transfer Enhancement in Compact Heat Exchangers

Enhanced heat transfer surfaces enable more energy-efficient, compact andlightweight heat exchangers. However, no single surface geometry exists thatsimultaneously optimizes all of these three objectives. With the presence oftrade-offs, many different enhancement designs have been developed and arestill being developed. Within this thesis, enhanced heat transfer surfaces basedon cylindrically shaped pin fins with wire diameters in the order of 100 μm areanalyzed for flat-tube heat exchangers.Very high convective heat transfer coefficients and material savings can beexpected. The objective of this thesis is to estimate the performance potentialof these wire structures.Four steps are taken to allow an estimation. Firstly, a performance evaluationmethod for comparing different types of enhancements is developed. Themethod’s objectives are defined as the energy, volume, and mass efficiencyof the enhancement. Secondly, computational thermal-fluid-dynamic simulationsof fluid flow through different wire structure geometries are performedand thermal-hydraulic correlations are developed. Thirdly, the technical feasibilityof manufacturing wire structure heat exchangers is analyzed and a selectionof samples is tested experimentally for their thermal-hydraulic performance.Lastly, the thermal-hydraulic correlations are used to optimize theenergy, volume, and mass efficiency of the wire structure enhancement withrespect to specified geometrical and operational constraints.The evaluation shows benefits for the wire structures when the volume andespecially the mass efficiency is taken into consideration. The potential isequivalent or higher when a combination of volume and energy efficiency isconsidered for air velocities up to approximately 2.5 m/s. For higher velocitiesiAbstractthe analyzed wire structure designs appear not to confer any advantages overstandard fins when evaluated for energy and volume efficiency