ENHANCEMENT TO CONDENSING HEAT-TRANSFER - NEW DEVELOPMENTS

Most effective fin shapes for enhancing the heat transfer in in-tube, shell-and-tube and plate-fin condensers of refrigerants are discussed using dimensionless expressions for heat transfer coefficients. As for in-tube condensation, micro-fin tubes with trapezoid fins improve the heat transfer coefficient by twice or more as compared with smooth tu bes. The enhancement factor of the local heat transfer coefficient and the penalty factor of the frictional resistance are also discussed. O ptimally designed low-fin tubes in shell-and-tube condensers ensure te n times or more enhancement of heat transfer coefficients. The local a nd average Nusselt numbers for a vertical plate-fin condenser with ser rated-fins are also presented. The Nusselt numbers are larger than tho se for plane plate condensers by about ten times.