Influence of Cooling Medium Flow Character on the Operation of Heat Exchangers with Steam Condensation Inside Tubes
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Journal of Engineering Physics and Thermophysics, Vol. 93, No. 5, September, 2020
INFLUENCE OF COOLING MEDIUM FLOW CHARACTER ON THE OPERATION OF HEAT EXCHANGERS WITH STEAM CONDENSATION INSIDE TUBES O. O. Mil′man, S. A. Isaev, A. V. Ptakhin, A. V. Kondrat′ev, A. Yu. Kartuesova, and V. S. Krylov
UDC 621.175
The influence of the character of cooling medium motion in a heat exchanging apparatus on the process of steam condensation in the latter is considered in the cases of cross flow past a tube bank in the apparatus, longitudinal flow past tubes in the bank in the regimes of forward flow and countercurrent flow, superheated steam condensation, and of nonuniform distribution of the cooling medium in different zones of the apparatus. It has been established that in the case of cross flow past the first rows of the tube bank, cooling medium zones with reduced heat transfer efficiency appear in the apparatus. The dependence of the pressure losses by the steam, which condenses in a heat exchanger in regimes of countercurrent flow, forward flow, and cross flow, is investigated. Experimental data on the superheated steam temperature have been obtained and generalized. The positive influence of the throttle on the line of removal of the steam–air mixture to a steam–jet ejector in nonuniform cooling of the parallel channels of the condenser has been established experimentally, and the presence of the optimal size of the throttle on the line of removal of noncondensing gases has been confirmed. Keywords: tube bank, steam condensation, superheated steam, nonuniform cooling, countercurrent flow, forward flow, throttle, noncondensing gases. Introduction. Heat-exchange apparatuses with steam condensation constitute an important part of thermal-power engineering equipment. Investigation of such apparatuses and search for the methods of their perfection is an important task of the modern power engineering. The materials presented generalize a considerable volume of computational-experimental data on the operation of heat exchangers with steam condensation inside tubes and channels. The results of these investigations will be helpful in designing condensation equipment and development of the means of increasing its efficiency and reliability. Heat Exchange in the Parallel Channels of the Heat Exchanger with Cross Flow past the Tube Bank in It. Figure 1 shows a qualitative picture of the change in the mean temperature of a cooling medium as it moves in the heat exchanger–condenser. Neglecting the dependence of the steam saturation temperature tsat on the change of steam pressure, we can see that the tube-bank temperature head, which determines the heat removal from a tube, decreases from the first tube (Δt1 = tsat – t1 ) to the last one (Δt4 = tsat – t4 ). Consequently, the steam flow rate and steam velocity in the fourth tube must be smaller than in the first one. This leads to the following paradox: the steam pressure drop in the first tube must be larger than in the fourth one, but in reality the stem pressure drop p1 – p2 is th
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