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Section 7. Machinery construction
Tretiak Oleksii, candidate of technical sciences (Ph. D.), SE "Plant "Electrotyazhmash", Deputy Head of Department on Mechanical Calculations, Senior Lecturer of Aerospace Thermal Engineering Department, National Aerospace University named after N. Ye. Zhukovsky "KhAI"
E-mail: alex3tretjak@ukr.net Kobzar Kostyantin candidate of technical sciences (Ph. D.), SE "Plant" Electrotyazhmash", Cheef Designer on Turbogenerators Deputy Head of Department on Hydrogenerators and LDCM
E-mail: kk7@ukr.net Repetenko Myhaylo, candidate of technical sciences (Ph. D.), assistant professor of Aerospace Thermal Engineering Department, Aerospace University named after N. Ye. Zhukovsky "KhAI"
E-mail: d15hnumg@i.ua
THE METHODOLOGY FOR CALCULATING OF GAS COOLERS FOR TURBOGENERATORS IN THREE-DIMENSIONAL SETTING
Abstract: the methodology for calculating the thermal state of gas coolers of Turbogenerators with hydrogen and water cooling is presented in the paper. The method for estimation of the reliability determination of carried out calculation is shown.
Keywords: Turbogenerator, Gas Cooler, Thermal State, Finning.
Introduction
The world market of Turbogenerators is very extensive. Its segmentation is made by the type of fuel of power plants that can work on coal, natural gas, nuclear fuel and other sources (biomass, geothermal sources, joint generation, combined: thermal and energy ones). In addition, the classification of the market is based on Turbogenerators rated from 10 MW up to 175 MW, from 175 MW up to 550 MW, 550 MW and over, as well as the type of cooling in these generators: air, hydrogen and water.
At the turn of the 50 s of the 20th century the greatest development was given to power plants based on steam turbines and Turbogenerators rated from 200 MW to 300 MW. These systems had sufficient reliability, and the possibility of modular arrangement let significantly save considerable time for the design and commissioning of new powers.
The important peculiar characteristics of Turbogenerators market is its segmentation based on such regions as the Asian-Pacific region, Europe, the Middle East and Africa,
North America and South America, which are in belts with a tropical and subtropical climate. In the Asia-Pacific region, there will be a high demand for Turbogenerators and the global market for these machines will reach 10 billion US Dollars by 2019, the average annual growth rate will increase by 0.7% from 2014 to 2019. At that at a period between 2014 and 2019, power increasing is expected and by 2019 it will reach 6.62 billion US Dollars.
According to the source Marketsand Markets Analysis, the share of the Turbogenerator market by geographic region for 2013 is shown in (Figure 1).
It is necessary to pay special attention to the fact that the design and operation features of the Turbogenerator are determined by its cooling system.
For today, almost all operating units have been designed on the basis of the methods using the empirical dependencies proposed in the last century, and excess heat and strength margins permit the extension of the design life resource without taking
into account the effect on reliability indices, which is a significant advantage for existing ones and a disadvantage for the newly developed designs, as having a low specific power per unit mass.
Figure 1. Turbogenerators Market Purpose of the Work:
- to develop a methodology for calculating of gas coolers, allowing to take into account the actual state of the cooling gas by the CFD method in a three-dimensional setting.
Description of Ventilation System Design of Turbogenerator rated 220 MW
In Turbogenerators with hydrogen-water and air cooling, two head elements (Fig. 2) namely are an axial fan and a centrifugal compressor. The axial fan detects the movement of
the cooling gas through the gas cooler and then the cooling of the stator core. The stator iron is cooled by an entire system of radial channels. In order to more evenly cool the stator, 8 compartments are arranged along its length, in 7 of which gas is directed by an axial fan, and in the 8th located on the drive side, the cooling gas is directed by the compressor. Cooling of the rotor winding is gas. The required flow rate is provided by a compressor whose characteristics are shown in Fig. 3. All gas enters the gap between the stator and the rotor and leaves the gap in the gas coolers from the side of the contact rings.
The axial fan determines the cooling gas flow through the gas cooler and then the cooling of the stator core. The stator iron is cooled by an entire system of radial channels. In order to provide more even cooling of the stator, 8 compartments are arranged along its length, in 7 of which gas is directed by an axial fan, and in the 8-th located on the drive side, cooling gas is directed by the compressor. Cooling of the rotor winding is gas. The required flow rate is provided by a compressor characteristics of which are shown in Fig. 3. All gas enters the gap between the stator and rotor and leaves the gap in to the gas coolers from the side of the slip rings.
At that, the existing compressor shall provide the necessary air flow to maintain the heat balance at all elements of the design in accordance with the requirements of GOST 535-2005 Turbogenerators.
gas cooler
Figure 2. Ventilation Diagram for Turbogenerator Rated 220 MW
Determination of Thermal State of Gas Cooler in Three-Dimensional Setting
According to the chosen diagram of the ventilation system of Turbogenerator (see Figure 2), the cooling gas temperature inside the gas coolers was calculated in a three-dimensional setting, taking into account the effect on the thermal state of all the elements of the unit.
In the limits of the proposed method, the turbulent flow of gas is described by a system of averaged Navier-Stokes equations written in generalized curve-linear coordinates, with the Jacobian of transformation J.
The SolidWorks software package contains a Flow Simulation application module that allows numerical modeling of internal and external flows of liquids or gases. The sufficient
accuracy of this module makes it possible to apply it to solve the most engineering problems. The basic methods and description of the mathematical apparatus used in SolidWorks FlowSimulation are presented in [1].
Long-term operation of Turbogenerator is ensured with the following parameters of hydrogen and water:
a) parameters of hydrogen: over-pressure in the housing is 3.5-105 Pa; purity by volume is not less than 97%; the temperature at the outlet of the gas coolers is 50 °C;
b) water parameters, coming in to the gas coolers: flow rate is 111.1 l/s; the temperature at inlet is 42°C;
c) parameters of water entering the first circuit of the heat-exchanger: flow rate is about 56 l/s; the temperature at inlet is 42 °C.
Three-dimensional model, the initial and boundary conditions necessary for a three-dimensional calculation are shown in (Figure 4). Three-dimensional grid of a gas cooler is shown in (Figure 5).
H, I link HjO
m tm w w m m m m m m m
V
fl 1 „ J
Figure 3. Characteristics of the Compressor
3 m/s 6013^5 Pa lOWs
Figure 4. Three-Dimensional Model, Initial and Boundary Conditions
Figure 5. Three-Dimensional Grid of the Gas Cooler
Figure 6. Plugging of Tubes
At that it shall be taken in to consideration that according to the works of Samorodov Yu. A. [2], the tubes of gas coolers
of Turbogenerators are subjected to clogging and plugging during operation (see Figure 6).
In order to take into consideration this circumstance, it is supposed to take into account the change in the water pressure in the tube for both a sharp jump and a change in the effective area of the working cross section, according to the work of Ber-man S. S. [3]. In this case, the values of the parameter P shall decrease according to decreasing in the area of cross-section F.
As a condition for the convergence of the solution, the following criteria were chosen for the volume: minimum, average and maximum values of solid and fluid temperatures, minimum, average and maximum speed, and average temperature and speed flow rate values. The calculation was carried out until the convergence criterion was reached and at least three purges of the calculation area were executed.
An additional condition is the condition of symmetric repetition along the width of the gas cooler.
The results of a three-dimensional calculation of the thermal state of the gas cooler in accordance with specified initial and boundary conditions are shown in (Figure 7).
Figure 7. Calculated Field of Temperatures
Analyzing the obtained results it can be concluded that the values of the obtained temperatures are at the level of admissible ones and satisfy the requirements of GOST 5352005 for the cooling medium of Turbogenerators.
Comparison of Calculated and Experimental Data In order to calculate the coolers of Turbogenerators, in which cooled coolant by its physical properties differs from that used in experiments, it is necessary to present the experimental data in similarity criteria.
Criterion equations for the intensity of heat transfer and hydraulic resistances have the following relationships:
Nu =f (Re; Pr) and Eu = f(m; Re) where Re - Reynolds criterion;
Nu - Nusselt criterion;
Pr - Prandtl criterion;
Eu - Euler criterion;
m - number of rows of tubes along the depth of the bundle.
When processing of the experimental data in the criterial form, the values of the physical constants of air are determined depending on the average air temperature. For the defining geometric dimension, for example, for tubes with loop-wire finning, the wire diameter of the loop is accepted equal to 0.69 mm.
In the similarity criteria for Reynolds and Euler, the airflow speed in the live section was determined in the same way as in the processing of experimental data used in the form of graphical dependences an = f(Wj and AP = f(W^).
In Nusselt similarity criteria, a convective heat transfer coefficient shall be introduced that does not take into account the thermal resistance of the ribs and reflects only the intensity of the heat transfer process.
The existing graphical dependence Eu = f(Re) (see Fig. 8), obtained earlier at the stand of SE "PLANT "ELECTRO-TYAZHMASH", can be represented by an equation in the criterial form on one transverse row of finned tubes, namely: E = 6400 • Re-20
u
Or for "m" rows: E = 6400 • m • Re-2'0.
Figure 8. Dependence Eu from Re
The obtained equations in the criterial form can be used in heat-engineering calculations of heat-exchangers only for surfaces having the same geometric characteristics as the investigated surface within Re from 150 up to 500.
In order to measure the temperature, control devices with a working range of 0^100 °C were used, with a division rate of 0.1 °C.
In the course of the carried out analysis it was determined that the error of the proposed method is at the level of errors of the measured instruments.
Conclusions
1. The method for calculating of gas coolers of Turbogenerators in a three-dimensional setting, taking into account the geometric characteristics of the cooling system design of the whole unit, is developed.
2. For the first time the influence of the head elements of the rotor and contamination of the water supply system to the thermal state of cooling gas is taken into consideration.
3. The analysis of the comparison of the experimental data with the results obtained with the help of proposed method is carried out. It is shown that the calculated values are in the range of the measured errors of temperature control devices of Turbogenerator.
References:
1. Alyamovskyi A. A. Engineering Calculations in Solid Works Simulation / Alyamovskyi A. A.- M.: DMK Press, 2010.- 464 p.
2. Samorodov Yu. N. Defects and Faults of Generators / Y. N. Samorodov.- M.: CJSC "STF "Energoprogress", 2005.- 100 p.
3. Berman S. S. Heat-Exchangers and Condensing Devices of Turbine Plants. - M.: MASHGIZ, 1959.- 423 p.
