Computer simulation of the reliability of the heat exchange surface of the steam turbine condenser

The aim of the article is to demonstrate the relationship between the adaptive regulation of the heat exchange surface to specific operating conditions of a steam turbine condenser and the reliability and availability of this surface in a specific period of time. The article exemplifies the relationship between the settings of the condenser heat exchange surface and the resulting changes in the reliability structures of this surface. The method of creating a mathematical model of reliability estimation, which is characterized by the variability of the reliability structures of the heat exchange surface in relation to specific operating conditions in a specific period of time, was indicated. Then, exemplary simulations of the adaptation of reliability structures of specific pipe systems constituting the condenser’s heat exchange surface to specific processes of operation of this condenser are presented. The simulations refer to the time-varying thermal loads of the condenser, the time-varying mean thickness of the sediments, and changes in the temperature of the cooling water at the point of its intake over time. The adaptation of certain reliability structures consists in the adaptation of specific systems of pipes through which the cooling water flows to the currently existing operating conditions of the condenser in order to maintain the desired reliability of the heat exchange surface for a specified time. This is done by enabling or disabling the flow of cooling water through a given number of pipes in specific systems under given operating conditions. On the basis of computer simulations, the reliability functions, and the availability functions of the subsystem under consideration were estimated.

Study heat exchange in porous structures

This paper shows the problem with heat exchange depending on units of thermal power plant equipment. The type of structures is determined and the heat flow for different pressures is proposed. Studies are developed for the condition of the heat exchange surface. Devices with porous coatings eliminate the development of cracks in the components and units of TPP equipment have been suggested. The research is applicable to gas turbine units of TPP. Comparable capillary-porous and flow systems have high reliability, but the former allowed the reduction of coolant consumption dozens up to 80 times. The results show that at higher heat loads it is suitable to use in porous surfaces to control the cooling surface. Evaluation of capillary-porous structures has shown their advantages over traditional cooling systems.

Improving the unit for melting cheese masses

This paper reports the improved model of the unit for melting cheese masses. The device differs in the technique of heat supply to working tanks through the replacement of a steam jacket with heating by a flexible film resistive electric heater of radiative type (FFREhRT). The heat exchange surface of the working container was increased through heating the mixing device by FFREhRT. In addition, the unit is distinguished by utilizing secondary thermal energy of melting cheese masses (35...95 °C) by converting it with Peltier elements into a low-voltage power supply to autonomous fans (3.5...12 W) in order to cool the control unit. Such a solution would improve the efficiency of the proposed structure, which is explained by reducing the dimensional and weight parameters of the cheese melting unit by replacing the steam heating technique with an electric one. A decrease in the time to enter a stationary mode (85 °C) when melting cheese masses was experimentally confirmed: for the bowl of the examined unit ‒ 575 s, compared to the analog ‒ 725 s. That confirms the reduction in the time to enter a stationary mode by 21 % compared to the base unit B6-OPE-400. The estimation has established a 1.2-time decrease in the main indicator of resource efficiency of the specific energy consumption for heating the volume of a unit of product in the improved plant for melting cheese masses – 3,037.2 kJ/kg, compared to the base B6-OPE-400 – 3,672.5 kJ/kg. The results confirm an increase in resource efficiency that is achieved by the elimination of steam heat networks; the increased heat exchange surface of working bowls by heating the stirrer with the help of FFREhRT. The heat transfer that employs FFREhRT simplifies the operational indicators of the temperature stabilization system in the bowl of the cheese mass melting unit. The results reported here may prove useful when designing thermal equipment with electric heating while using secondary thermal energy.

Heat transfer in laser passive and deformable mirrors

In work, the possibilities of using uncooled and cooled optical elements (including laser passive and deformable mirrors) with an increase in the power of laser facilities are analyzed. To increase the permissible light loads acting on the optical elements, the use of highly efficient cooling systems with minichannels (coplanar and multi-tiered), providing a high compactness of the heat exchange surface and the intensification of heat transfer, is considered. The advantages and efficiency of the proposed cooling systems for reducing the displacement of the optical surface of the mirror due to bending are estimated.

FEATURES OF CALCULATION OF ON-BOARD HEAT EXCHANGERS

Aspects of designing an onboard heat exchangers for the cooling system of the ship's power plant are considered. Such heat exchangers must be designed in accordance with the classical foundations of the theory and calculation of heat exchangers. At the same time, the key design points are considered by well-known sources in a separate setting related to the peculiarities of their consideration as specific elements of the theory. In this regard, they are not united by a single system necessary for their use in specific design problems. Accordingly, the paper highlights, concretizes and refines the parameters of the formulas used in the computational problem. In particular, the calculation of the heat transfer coefficient from the seawater side is performed according to the formula that gives the average value of the coefficient for the vessel. The heat transfer coefficients from the side of the coolant of the inner loop are calculated according to the well-known formulas recommended for calculating heat transfer in channels of any shape. Attention is drawn to the fact that heat transfer from the hold side goes to the finned wall. In this regard, the heat transfer coefficients determined by the indicated formulas should be considered convective. The transition to the given values of the heat transfer coefficients should be carried out considering the efficiency of the finned heat exchange surface, which considers the uneven temperature of various sections of the heat exchange surface. The calculation of heat transfer was carried out considering possible surface contamination. The procedure for performing the calculation steps is proposed, as a result of which the dimensions and heat engineering parameters of the heat exchanger can be determined. It was found that the use of the considered proposals leads to results close to those recommended by authoritative sources. The above proposals do not contradict the experience of creating and designing such structures. The recommendations can be used for educational and practical purposes by those who design heat exchangers of similar designs.

Optimization of geometric parameters and analysis of exergy efficiency of heat recovery units glass furnaces

The paper presents the results of optimization of the geometric parameters of the heat exchange surface of water and air-heating heat exchangers of glass-making furnaces and an analysis of their exergy efficiency. Ensuring the efficient operation of heat recovery units in various thermal circuits is an urgent problem of heat power engineering. The aim of the work is to establish the optimal areas of the geometric parameters of the heat exchange surface of heat recovery units of glass-melting furnaces and to analyze their exergy efficiency. The paper presents the results of solving the tasks necessary to achieve the goal: - using statistical methods for planning the experiment, determine the levels of variation of the parameters of the geometric surface of heat transfer for the heat recovery units under study and calculate the values of the criteria for evaluating the efficiency at the points of the central orthogonal compositional plan; - to obtain the regression equations for the investigated heat exchangers, to determine the optimal areas of change in the geometric parameters of the heat exchange surface and the corresponding exergy efficiency criteria. To determine the optimal areas of geometric parameters of the heat exchange surface, a complex methodology is used based on the methods of exergy analysis and statistical methods of the theory of experiment planning. It has been established that when designing heat recovery schemes for heating water in heat supply systems and for heating blast air, heat recovery units with the following values of the areas of variation of the geometric parameters of the heat exchange surface can be used: - the values of the area of variation of the distance between the panels for heat recovery units with a staggered and corridor arrangement of pipes in a bundle s1 = 58.0-62.0 mm. - the values of the areas of change in the diameter of pipes for a hot water heat exchanger with a corridor arrangement of pipes d = 41.0-43.0 mm and for an air heating heat exchanger with a staggered and corridor arrangement of pipes d = 29.0-31.0 mm. - the use of the values of the ranges of change of other parameters is carried out taking into account additional technological factors. It has been established that the exergy efficiency of hot water heat recovery units is in all cases higher than the exergy efficiency of air heating units. For hot water heat exchangers, the values of exergy criteria are lower than for air heating ones: k – 2.0 times, ε – by 7.5%, m0 – 1.9 times. The expediency of using the investigated heat recovery units in heat recovery circuits of glass melting furnaces has been established, taking into account the results obtained and in the presence of certain technological factors. The results obtained and further developments in the field of optimization of the operating parameters of heat recovery units for glass-melting furnaces will provide an increase in the efficiency of heat recovery equipment for power plants.

Experimental study of the solid fouling effect on the air-cooled apparatus characteristics

External fouling on the heat exchange surface of air-cooled apparatus are formed during operation, which leads to a significant increase in energy consumption and deviations from the optimal operating mode of the entire system. This phenomenon is a problem for all energy conversion systems. This paper presents the experimental study results of a complex of a commercial cooled object with real fouling on the air condenser surface. To study the effect of fouling, an experimental bench was developed – a single-stage refrigerating machine that provides cold supply to a thermostatic chamber. Three types of fouling were used: sand, fluff and dust. Fouling were picked from the operating condensers and identical in the type of heat exchange surface to the experimental sample. With a change in the quantitative and qualitative composition of the fouling, the air condenser thermal and aerodynamic characteristics and the energy efficiency of the machine as a whole were determined. The experiment showed that at maximum fouling of the heat exchange surface with sand and fluff, air movement stops. This means that at a certain thickness of sand and fluff layer, an air impermeable dense structure is formed. Dust with the same form of filling the free space for the flow remains permeable to air. Experiments showed that the qualitative composition of the fouling is the main factor that determines the heat exchanger performance. It was found that from the experimental set of fouling, roadside dust has the greatest negative effect on the condenser characteristics and the machine as a whole. The aerodynamic properties of the heat exchanger depend to some extent on the qualitative composition of the fouling. As a conclusion, it was suggested that the process nature of air flow passing through the investigated fouling can be described as gas flows in porous media.

METHOD AND RESULTS OF HYDRAULIC CALCULATION OF THE HEAT EXCHANGE SURFACE OF THE ONCE-THROUGH STEAM GENERATOR

Ukraine with her developed machine-building potential can take the deserving place in the production of small modular reactors. One of basic elements of small modular reactors equipment is steam generator. Among different types a deserving place is occupied by once-through steam generator. small modular reactors can exemplify to transport nuclear installation, for example KLT-40S. The calculation of hydraulic resistance is included in designing of steam generators, that it is necessary for the choice of pumps and optimization of structural parameters. In the presented article methodology of hydraulic calculation of once-through steam generator is examined with the coiling surface of heating. As a result of analysis of literature formulas were selected for the calculation of hydraulic resistance for four modes of flow: transverse flow of the coolant over horizontal coils, movement in bent tubes of a single-phase working fluid, boiling water and superheated steam. Results over of calculation of steam generators are brought by power 45 МВт with different structural parameters: diameter of coils, horizontal and vertical pitches of coils location in a bunch, speed of feedwater and coolant. The got results were verified by comparing to data of calculation on the code of ASPEN-TECH. It was found out as a result of research that increase of diameter of coils, as well as the increase of pitches of coils location in a bunch does not reduce hydraulic resistances, as expected, but increases them as a result of worsening of heat exchange and, accordingly, increase of heat-exchange surface. The increase of speed of coolant results in the height of resistance on the side of coolant and does not influence on resistance of working body. The increase of speed of feedwater increases resistance on the side of working fluid and does not influence on resistance of coolant.

Geothermal heat use to eliminate hydrate formations in oil deposit injection wells

The article is devoted to an actual issue: the development of internal downhole heat exchangers technology to combat hydration in injection wells. Purpose: development of conceptual solutions for the use of geothermal coolant in the internal well heat exchanger of the injection well. A scheme of an internal downhole heat exchanger with a geothermal heat carrier has been developed, and includes a supply line of a geothermal carrier through the heat exchange surface of the injection well into the productive reservoir of the oil field. The scheme provides targeted utilization of thermobaric energy of a geothermal source to combat hydration in the injection well. A mathematical apparatus for describing the process of heat utilization and heat exchange in injection well is proposed. It is established that the capacity of one geothermal well discovered at the oil depths in the Dnipro-Donetsk basin is sufficient to eliminate hydration in 1-3 injection wells, and determines the feasibility of their joint work.

Improving the heat transfer efficiency of a direct-flow recycling boiler using organic fluid

This paper considers the problem of studying the heat transfer exchange during boiling in a direct-flow recycling boiler using an organic coolant. The study was conducted using numerical modelling in the ANSYS software package. Asaresultofthestudyavisual picture eofvaporphasedistributionwasobtained. This picture shows that the studied heat-exchange surface can be conditionally divided into two areas: the area of intense vaporization and the area in which the degree of dry vapor varies insignificantly. Analysis of changes in the heat transfer coefficient along the length of the heat-exchange surface led to the conclusion that heat transfer in the second area is inefficient. Based on the results of the study, it was concluded that intensification of heat transfer is necessary, for which it is proposed to install a separator at the boundary between the selected areas. The subject of the study is the dependence of the variationin the heat transfer coefficient along the length of the pipe and the determination of the boundary between the selected areas at various values of the defining parameters. Numerical simulation for therange of variationofthe defining parameters corresponding to the actual temperature regimeof power steam boilers and the conditions for the implementation of heat recovery in organic Rankine cycle unitswas performed.