BOILING HEAT TRANSFER IN TWO IN-LINE INDEPENDENTLY HEATED FINNED TUBES IN A CROSS FLOW

Abstract

• Nucleate pool boiling heat transfer is of common occurrence in many industrially important vapour generating equipment like, vaporisers, evaporators, reboilers etc. In most of the cases, this liquid boils on the outside of the tubes. Efficient design of such equipment requires accurate knowledge of the boiling characteristics of saturated liquids and their dependence on flow field. Comparatively few studies of cross flow boiling of water, as it occurs in devices such as fire tube boilers, are available in the literature. The present study has been undertaken to investigate the effect of 'cross flow in boiling across twin stainless steel finned tubes placed one above other in a vertical plane. Both the tubes are heated independently by supplying high current through these tubes with the help of two step down transformers.. The fins in the form of,metric threads (24 TPI) are cut on both tubes and a fixed distance is maintained between the tubes. The experiments were performed for the following operating conditions. Effective lengththe • tube = 19.5 mm Tube outside diameter = 19.15 mm Tube inside diameter = 17.11 mm Tube pitch diameter = 18.03 mm Tube material = stainless steel (AISI 304) Distance between tubes = 4.41 Heat flux = 10.92, 19.98, 27.54, 41.14, 53.6 kw m mass flux = 0, 5.33, 8.89, 12.45, 14.82, 17.31 kg/m2 sec working fluid = distilled water Bulk fluid temperature = 100° C, NOMENCLATURE A ' Heat transfer area (