This study investigates evaporation heat transfer performance of refrigerant R-134a falling film on three horizontal copper tubes in a vertical column. Experiments were performed at saturation temperatures of 10 and 26.7°C. The liquid flows through a liquid feeder with a row of circular holes at a rate of 0.0075 ∼ 0.0363kg/ms, while heat fluxes varied from 4.5 to 48.5kW/m2. A smooth tube, a fin tube of 0.4mm fin height, 60FPI (Fins Per Inch), and a new boiling enhanced tube (mesh tube) were tested. The test results show that heat transfer coefficient of the smooth tube increases with increasing heat flux and fluid temperature, and increases slightly with increasing flow rate before dry-out occurs. At low flow rates (less than 0.015kg/ms) or when Ref (≤ 255), the fin tube is in thin film evaporation mode and results in a large heat transfer coefficient. At high flow rates (0.0225, 0.03, and 0.0375kg/ms) the falling film evaporation curves are similar to those in pool boiling. For all tubes, the fluid temperature and the flow rate have only minor influences on heat transfer coefficient before dry-out occurs. The 60 FPI tube and the mesh tube enhance the falling film evaporation heat transfer coefficient 6.3 ∼ 8.29 fold and 1.9 ∼ 5.0 fold, respectively, as compared with the smooth tube. A new correlation of falling film evaporation, accounting for contributions of nucleate boiling and spray convection, is proposed. It predicts h-values of the falling film evaporation data of the smooth surface within ±30%.

La technique d'évaporation présentée dans ce travail consiste à faire ruisseler un liquide à évaporer à la surface d'ailettes enroulées en spirale autour d'un tube vertical, chauffé intérieurement par un fluide caloporteur. Le tube et les ailettes sont usinés dans un monobloc massif en graphite imprégné. Compte tenu de la grande complexité de la géométrie de cet échangeur et de l'écoulement sur ses ailettes, la détermination du coefficient de transfert thermique par convection externe est difficile à obtenir par un calcul direct. Il est déterminé ici par voie indirecte en suivant la méthode de Wilson basée sur deux étapes : une expérimentale et l'autre théorique. On détermine dans cet article la quantité de chaleur échangée et la conductance globale au transfert thermique de cet échangeur/évaporateur lors de l'échauffement. On détermine également les différentes résistances partielles ainsi que le coefficient de convection entre la paroi externe de l'ailette et le film de la solution à chauffer. La démarche proposée dans cet article a permis de valider la méthode indirecte.

Two different modes are utilised by vertebrate species to generate the appendicular muscle present within fins and limbs. Primitive Chondricthyan or cartilaginous fishes use a primitive mode of muscle formation to generate the muscle of the fins. Direct epithelial myotomal extensions invade the fin and generate the fin muscles while remaining in contact with the myotome. Embryos of amniotes such as chick and mouse use a similar mechanism to that deployed in the bony teleost species, zebrafish. Migratory mesenchymal myoblasts delaminate from fin/limb level somites, migrate to the fin/limb field and differentiate entirely within the context of the fin/limb bud. Migratory fin and limb myoblasts express identical genes suggesting that they possess both morphogenetic and molecular identity. We conclude that the mechanisms controlling tetrapod limb muscle formation arose prior to the Sarcopterygian or tetrapod radiation.