A non-tubular Stirling engine heater for a micro solar power unit

This paper presents a non-tubular heat exchanger for use in a Stirling solar engine micro co-generation unit that is being developed by the University of Oviedo and the technological research centre Tekniker Foundation. The engine has been designed using scaling criteria, which imply a case of relaxed dynamic similarity, that is to say, without preserving the equality among all of the prototype’s and the derivative’s dimensionless groups. The geometrical characteristics of the heater are described and the variables that can influence the pressure drop and heat transfer in the heater are identified. The correlations for the friction factor and Stanton number have been measured under steady flow conditions to analyse the feasibility of the experimental heater. The Reynolds analogy is not fulfilled, and the compressibility effects are negligible. The comparison between the correlation predictions for the non-tubular heater and slotted or tubular heaters of well-known prototypes shows possible applications for heaters that reach high Reynolds numbers and that encounter practical problems associated with the use of bundles of tubes.