485Searching for efficient ways of enhancing heat transfer processes is the main line of efforts taken to improve heat exchangers. Solution of this problem becomes especially important in view of the acute need to modernize the Ukrainian gas transportation system for making it more efficient and for essentially reducing the consumption of "technological" gas in gas turbine driven gas pumping units (GPUs), which constitute the basis of the existing fleet of GPUs. Since the majority of such GPUs use gas turbine units oper ating in accordance with a simple regenerative cycle and a regeneration ratio not exceeding r = 0.70-0.75, increasing the regeneration ratio to r = 0.80-0.85 is the most realistic and relatively low cost approach to modernization under the present day conditions. This, for example, makes it possible to decrease the consumption of "technological gas" in GPK 10 gas pumping units by as much as 1500000 m 3 /year on the average. However, increasing the regeneration ratio to the above mentioned values entails an essential drop of temperature difference between heat exchanging media and, as a consequence, the need to use the heat transfer surface with a considerably larger area with the corresponding growth of the overall dimensions, weight, and cost of the regenerative air heater, as well as growth of pressure losses in the gas turbine unit's gas and air paths.To achieve the minimal cost of such moderniza tion, new generation regenerators must be developed, the designs of which should be based on solutions that will make it possible to obtain acceptable weight, dimensions, and cost. At the same time, the solutions implemented in the designs of such regenerators must make it possible to manufacture them using the exist ing technological equipment and to use the existing erection equipment and foundations in retrofitting concrete gas pumping stations.Taking into account the fact that no alternative to tubular regenerators is foreseen in the near future due to their highly reliable operation and simple design, researchers and developers should focus their efforts on improvement of the tubular elements of heating surfaces. In doing so, the following should be borne in mind:(i) A relatively small difference between the proper ties of combustion products at p ≈ 0.103 MPa and air at p ≈ 0.45-0.60 MPa, between which heat transfer takes place, results in that the heat transfer coefficients on the gas and air sides are of the same order.(ii) The best way in which the regenerator's heat transfer coefficient can be increased under such con ditions is to decrease the thermal resistances to heat transfer on each side; the use of one sided finning or heat transfer intensifiers cannot give a considerable improvement in the heat transfer coefficient.(iii) The proposed technical solutions must be pro duction friendly and should not cause the manufac ture of heating surfaces becoming essentially more labor consuming and costly.One approach that has frequently been proposed in recent years for solving the considered proble...

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There have been relatively few publications detailing heat transfer to supercritical water (SCW) flowing through a channel with a bundle or just with a single rod (annular channel) as compared to heat transfer to SCW in bare tubes. In the present paper, results of experimental heat transfer to SCW flowing upward in an annular channel with a heated rod equipped with four helical ribs and a 3-rod bundle (rods are also equipped with four helical ribs) are discussed. The experimental results include bulk-fluid-temperature, wall-temperature, and heat-transfer-coefficient (HTC) profiles along the heated length (485 mm) for these flow geometries. Data obtained from this study could be applicable as a reference estimation of heat transfer for future fuel-bundle designs.

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