Free Convection Heat Transfer on Annular-Finned Tubes and Bundles Thereof

The use of air-cooled heat exchangers in various industries has increasingly become wide-spread due to their environmental friendliness and the absence of the need for cooling water. Air-cooled heat exchangers made of annular-finned tubes are widely used in chemical, petrochemical, oil-refining, gas, and food industries, and also at automobile CNG filling stations, in heat power and electric power engineering, refrigeration technology, and at nuclear power plants.The heat power of air-cooled heat exchangers is largely determined by the characteristics of the motion of the flow of cooling air through it, which can be organized with consumption of electric power by means of a ventilator or in an energy-saving regime, i.e., by free convection. Unfortunately, the region of ambient air temperatures, at which it is possible to use air-cooled heat exchangers under the conditions of free convection, is limited. Low intensity of heat transfer compared to forced convection is the main disadvantage of a free convective regime, which is usually compensated by an increase in the heat-transfer area, namely, by finning the heat-transfer area. In the case of equipping air-cooled heat exchangers with additional devices that make it possible to intensify free convection the heating capacity of a heat exchanger can be significantly increased.The paper presents a review of experimental and numerical investigations of free convection heat transfer on air-cooled annular-finned tubes and bundles thereof.