A. Yu. Ryabchikov

Experience gained from development of modernized oil coolers for the oil supply system used in 800-MW turbines

Problems encountered during retrofitting of oil coolers in operating steam turbine units are discussed. Results obtained from numerical simulation of oil leaks occurring in the gaps between the tube bundles of oil coolers are presented. Different design versions of a modernized MB-270–330 oil cooler are calculated, and the effect of different design parameters on the performance characteristics of such apparatuses is analyzed. The adopted technical solutions made it possible to develop the oil cooler that has been installed in 13 of the 15 800-MW turbine units that are currently in operation in Russia.

Investigation of the effect of pressure increasing in condensing heat-exchanger

The effect of pressure increase was observed in steam condensation in the intermediate coolers of multistage steam ejector. Steam pressure increase for ejector cooler amounts up to 1.5 kPa in the first ejector stage, 5 kPa in the second and 7 kPa in the third one. Pressure ratios are equal to 2.0, 1.3 and 1.1 respectively. As a rule steam velocities at the cooler inlets do not exceed 40...100 m/s and are subsonic in all regimes.The report presents a computational model that describes the effect of pressure increase in the cooler. The steam entering the heat exchanger tears the drops from the condensate film flowing down vertical tubes. At the inlet of heat exchanger the steam flow capturing condensate droplets forms a steam-water mixture in which the sound velocity is significantly reduced. If the flow rate of steam-water mixture in heat exchanger is greater than the sound velocity, there occurs a pressure shock in the wet steam.On the basis of the equations of mass, momentum and energy conservation the authors derived the expressions for calculation of steam flow dryness degree before and after the shock. The model assumes that droplet velocity is close to the velocity of the steam phase (slipping is absent); drops do not come into thermal interaction with the steam phase; liquid phase specific volume compared to the volume of steam is neglected; pressure shock is calculated taking into account the gas-dynamic flow resistance of the tube bundle. It is also assumed that the temperature of steam after the shock is equal to the saturation temperature.The calculations have shown that the rise of steam pressure and temperature in the shock results in dryness degree increase. For calculated flow parameters the velocity value before the shock is greater than the sound velocity. Thus, on the basis of generally accepted physics knowledge the computational model has been formulated for the effect of steam pressure rise in the condensing heat exchanger.

Gas Dynamics And Heat-and-mass Transfer In Multistage Steam Jet Pumps With Intermediate Condensers

To specify the gas dynamics physical model and the design methods for ejectors, as well as the intermediate coolers functioning features, a range of complications has been formulated. It has been proven that the coefficient defining the critical section position of the secondary stream and characterizing the entrainment ratio of the ejector first stage depends on the characteristics of “a sound pipe” zone. Within this zone the velocity of the secondary stream can exceed sonic speed while the shock waves in the primary stream decrease. The optimum axial dimensions of the ejector are determined by the characteristics of “a sound pipe”. The experimental investigations results reveal that the flow rate portion of steam condensed in the first stage cooler is about 70–80% of the full flow rate of steam entering the cooler and virtually doesn’t depend on the air content in steam. The cooler efficiency depends on steam pressure, which is determined by the performance of the subsequent stage ejector and also by the cooling water temperature and flow rate.

Heat Transfer Augmentation During WaterSteam Condensation On Twisted Profile Tubes

Some results are presented of experimental and theoretical research of hydrodynamics and heat transfer during condensation of water steam (both stationary and slowly moving) on twisted profile tubes (TPT). For a heat transfer coefficient during condensation of stationary steam on TPT two characteristic areas were observed. At small values of condensate film Reynolds numbers a TPT heat transfer coefficient can be 10–15% below that of the plain tubes depending on profile parameters. With the rise of both condensate film Reynolds number and profile parameter h/s heat transfer coefficient increases up to 50% in comparison to a plain tube. During slowly moving steam condensation the TPT heat transfer coefficient increases up to 70% as compared to a plain tube. Conducted research and industrial tests results showed that the assured effect of a heat transfer coefficient increase in TPT heat exchangers could reach for turbine condensers 15%, for low cycle heaters 35–40%. The heat exchangers hydraulic resistance increases by 40–70%.

Single-phase media hydrodynamics and heat transfer in heat exchangers with twisted profile tubes

A profiled heat exchanger tube is the one in which some features have been incorporated into the tube geometry for heat transfer enhancement. They offer a perspective method of steam turbine shell-and-tube heat exchangers improvement. Twisted profile tubes (TPT) are widely used in power engineering. This paper presents some results of experimental and theoretical research of hydrodynamics and heat transfer in TPTs. It is revealed that the heat transfer coefficient for water flow in a TPT increases up to 80% compared to that of a plain tube. With a rise of media Reynolds number, the heat transfer rate in a TPT decreases in comparison to that of a plain tube, but for air flow in a TPT the heat transfer coefficients ratio does not depend on the Reynolds number value. Water flow hydraulic losses in TPTs increase from 15 to 100% depending on the tube profile parameters.

Statistical simulation of failures of heat exchangers in developing a comprehensive system for monitoring the state of steam-turbine units

Results from statistical simulation of damages to the tube systems of the condensers and high-pressure heaters used in steam-turbine units are presented. The flow of failures of high-pressure heaters is described, using which their failure rates are estimated, and data are given that allow measures to be recommended on improving the system of maintenance activities for these apparatuses.