H4SV-22-C re based on trust responsibility and traditional Helical gear reducers H4

Flender/Flender Gear Units/Helical gear reducers H4

finnedtubeswithspecificmodificationsintendedtoimprove heat transfer during pool boiling. These modifications involved - additional grooves at the base of the fins on both tubes and - partial flattening of the fins on both tubes, this resulting in -sha ed fins with very narrow gap of 0.2 mm at the outer edge in one case and to -shaped ffns with somewhat wider gap of 0.3 mm in the other. plain tube was also studied, so that the heat transfer performance could be compared not only among the finned tubes. The experimental substances used were the propane derivative R2, which is open to consid- eration as an alternative to R1 and R1 in certain ran es, and the ethane derivatives R1a and R1a, as well as an equimolar mixture of the two & admixture of combustible R1a is being considered in order to reduce the relatively great direct contribution of R1a to global warming). 2 3. Results The heat transfer during pool boiling of the new refrigerants R1a (CH, .CF, R1a (CH, . CHFJand R2(CF3~CHF~CF,aswellasofaroughlyequimolarmixtureofR1aandR1 5a, was measuredovera large rangeof boiling pressuresand heat fluxdensities using three finned tubes with different fin geometries. One of the tubes was conventional finned tube, butwith closer fin spacing than up to now, while the other two were so-called enhanced tubes, modi- fied at the fin tip ( or shape) and fin base (,, grooves) in order to improve heat transfer The test results show that, if used for evaporating new refri erants, the two enhanced tubes, in particular, promise substantial improvements over plain tu%es at boiling pressures up toabout 1 bar The greatest improvement was abtarned with the YX tube and R1a as the refrig- erant, meaning that, if this tube is used, energy consumption can be reduced as result of the smaller temperature gradient and, at the same time, the quantity of refrigerant required and the amount of material for the evaporators can be reduced as result of the higher heat