Simulation of helically wrapped, compact heat exchangers

A new category of heat exchanger has been invented which fulfills the dual requirements of compactness and high thermal efficiency. The underlying principle of the exchanger is the helical intertwining of the tubes which carry the participating fluids. To ensure a thermal bridge of high conductivity between the tubes, silver braze was introduced into the interstitial space. Numerical simulation was used to characterize the performance of this category of heat exchanger. The simulation model is three-dimensional for both fluid flow and heat transfer and is also conjugate in that it encompasses two flow passages, their walls, and the interconnecting silver braze. A fabrication means was also developed. Numerical results were obtained for two general classes of heat exchange situations, one of which dealt with single-phase flows while the other related to two-phase flows. The single-phase situation investigated here is a water-water heat exchanger. The heat exchange effectivenesses evaluated from the numerical simulations demonstrated a level of enhancement of 84 compared to a baseline case consisting of straight flow passages. This level of enhancement is substantially higher than that achieved by other modes of augmentation. The results also showed that further enhancements can be achieved by increasing the number of helical turns per unit length. Experimentation was used to validate the basic computational model. For a given physical situation, the measured relationship between volumetric fluid flow and pressure drop was compared with that predicted by the numerical simulation. The excellence of the agreement lends strong support to the physical principles that underlie the simulation model