Steam Generator Strength Computation for Nuclear Electric Power Plants of a Low Power

Today, the world oversees an explosive development of the nuclear power stations (NPS) of a low power. Most projects deal with pressurized water reactors and as a matter of fact with steam generators (SG). Ukraine has a well-developed engineering industry backbone that can be used for the production of the equipment required for the nuclear power plants of a low power. This scientific paper delves into the computations of the strength of elements used for the monotube steam generator with cylindrical coils that is the most presentable of all the projects in question in IAEA materials. Appropriate methods were developed to perform structural computations and steam generator strength computations. The mathematical model was developed that allows us to perform strength computations of the SG elements making use of the analytical method with reference to the Regulations and do simulations using the ANSYS software code. The specified elements include the body elements, in particular the cylindrical part, the flange, the bottom and the cover, including the heat carrier branch pipe and heat exchange tubes. The comparison of the data obtained by both methods showed their similarity and accordingly, the accuracy of the data that are indicative of the need for an increase in the wall thickness of the cylindrical part of the external branch pipe intended for the heat carrier. The body bottom strain for calculated dimensions exceeds the permissible value by 1.56 %. Since this value is 5 % lower than permissible values it is deemed that the strength condition is passed through. The simulation proved that the strength conditions are met for heat exchange tubes, for the body, the body cover, the body flange, the conical part of the external branch pipe intended for the heat carrier. Based on the analysis done, we would like to recommend performing strength computations using the normative method with the subsequent check out by the simulation using the computer code.

MATHEMATICAL SIMULATION OF THE HEATING SYSTEM RADIATOR OF AS A CONTROL OBJECT

The problem of mathematical modeling of a heating system radiator as a control object is considered. The purpose of its development is to create a generalized mathematical model of thermal processes in a room heated by means of water radiators. A calculation scheme of heat transfer processes between the heat carrier of the radiator and the air of the room has been developed, on the basis of which the heat balance equations are writt en. This takes into account both steady and unsteady heat transfer processes between the coolant, radiator and room air. A block diagram of the mathematical model of a heating radiator has been developed. After the introduction of assumptions and transformation of the structural diagram of the nonlinear model, the structural diagram of the linear mathematical model of the heating radiator was obtained. On its basis, the transfer function of the heating radiator is derived, the output coordinate of which is the thermal power. The resulting transfer function can be used in a generalized mathematical model of a heated room. The analysis of the transfer function of the heating radiator is carried out and it is shown that its dynamics is determined not only by geometric parameters, but also by the fl ow rate of the heat carrier.

Determination of the Temperature Graph of Heat Supply With Minimal Heat Losses

Heat losses by pipelines of heat supply systems are calculated for the average temperature of the heat carrier per year or for the heating period for the conditions of a qualitative method of regulating the heat load. The presence of cuts of the temperature graph, the use of other methods of central regulation, are not reflected in the regulatory documents and require special research, which determines the relevance of the work. Heat losses through thermal insulation structures of pipelines have been determined for various graphs of central regulation. Heat losses were determined for each external temperature, taking into account its duration. It is shown that the average linear annual heat losses for most of the graphs correspond to a lower external temperature than the average external temperature for the heating period. Therefore, the calculation must be performed for a higher temperature of the heat carrier than is accepted according to regulatory documents.

INFLUENCE OF APARTMENTS’ MODERNIZATION ON THE TEMPERATURES OF HEATING SYSTEM IN THE BUILDING

When modernizing apartment buildings, heating appliances are replaced or old ones are left, high thermal temperatures are usually maintained, thus limiting the increase in the DH system’s efficiency. In the article, in order to evaluate the impact of the reduced thermal temperature of the building on space heating when the radiator area remains constant, 3 alternatives have been analyzed. They include cases when after the building modernization old heating appliances are left, but the temperature of the heat carrier is reduced up to 60/40/20 °C in one case or even up to 45/25/20 in another alternative. There has also been examined the possibility of reducing the heat carrier temperature of the heating system without modernization of the building. An hourly data analysis of the heating system model for two typical months of the heating season has been performed. The analysis shows that after the modernization of the building, when heating device areas are left the same, the existing heating temperature can be reduced to 60/40/2020 °C.

Nanofluid suspensions as heat carrier fluids in single U-tube borehole heat exchangers

The borehole heat exchanger (BHE) is a critical component to improve energy efficiency and decreasing environmental impact of ground-source heat pump systems. The lower thermal resistance of the BHE results in the better thermal performance and/or in the lower required borehole length. In the present study, effects of employing a nanofluid suspension as a heat carrier fluid on the borehole thermal resistance are examined. A 3D transient finite element code is adopted to evaluate thermal comportment of nanofluids with various concentrations in single U-tube borehole heat exchangers and to compare their performance with the conventional circuit fluid. The results show, in presence of nanoparticles, the borehole thermal resistance is reduced to some extent and the BHE renders a better thermal performance. It is also revealed that employing nanoparticle fractions between 0.5% and 2 % are advantageous in order to have an optimal decrement percentage of the thermal resistance.

Numerical study of combustion and heat transfer in a composite heat carrier generator

To investigate the operational problems of the composite heat carrier generator (CHCG) in actual industrial applications such as overheating and poor safety performance, an integrated analytical model was established. For this model, the commercial software Fluent was first applied to simulate the gas-liquid turbulent flow, diesel vaporization and combustion, and the mixing process between the flue gas and the preheated water. Taking the parameters obtained from the Fluent model as the boundary condition, an indirect contact heat transfer model considering the heat transfer between the hot flue gas and the cold water has been solved. Based on this model, the areas where the phenomena of overheating and high thermal stress are prone to occur have been determined, and the size of the water sleeve has been redesigned.

CASE ANALYSIS OF HEAT PUMP INTEGRATION IN DISTRICT HEATING SYSTEM

The installation of heat pumps in district heating (DH) systems is one of the most promising technologies to increase the efficiency of heat supply by using renewable energy sources and reducing heat carrier temperatures in the networks. The possibilities of installing heat pumps in DH systems are very wide, but most often the main purpose of their application is to increase the temperature of the supplied heat carrier at the heat substations of individual consumers or their groups. This paper describes a study that analyzed the possibilities of integrating an individual heat pump at a heat substation in a building to reduce the temperature of the heat carrier in the return line. The results of the study revealed the dependences of the reduction of the heat demand of the building from the DH network, the power of the heat pump, the coefficient of performance (COP), and the reduction of the return temperature.