Optimal Fin-Side Design of Compact Tube-in-Fin Heat Exchangers with Rippled Fins

The optimal design of rippled fins found in the common compact heat exchanger is addressed to maximize the heat transferred per unit pressure drop (pumping power). Ripples are common for structural integrity and to facilitate handling and manufacture. Typical designs operate at Reynolds numbers below about 1200. Because a complex flow with heat transfer-process is involved, the optimal design synthesis approach—modeling, objective function definition and optimization—coupled with the desire to efficiently verify the results leads to a highly effective hybrid design technique and substantially less experimentation than might be expected. The model uses a finite difference marching procedure and variable fluid properties. General results for ripple designs and spacings are obtained and corroborated experimentally. In general a short ripple of about 25 deg and height/fin spacing of 0.25 are optimum. Distance between ripples is shown to be a simple function of Reynolds numbers. The final discussion addresses aspects of this approach, its strengths and limitations.