Heat Removal Process Research Articles

Efficiency of intensification of heat removement of a closedcircuit marine power plant cooling systems

The paper considers a method for increasing the efficiency of closedloop cooling systems of ship power plants that exclude the consumption of seawater. It is noted that currently widespread openloop cooling systems that provide for the consumption of seawater are subject to clogging, especially in polluted waters, which can lead to a shutdown of the power plant. Attention is drawn to the fact that, especially when operating a vessel in areas of intensive fishing, significant damage is caused to fish resources, and plankton as the basis of the food chain is intensively destroyed. An intensification of heat removal processes is proposed, which allows reducing the weight and size indicators of closed systems, thereby ensuring their wider implementation in shipbuilding. The objective of the study is to determine the most effective methods of such intensification. Using a ship casing heat exchanger as an example, the possibility of using gasliquid jets for this purpose was studied. Visual and thermal engineering studies were carried out on models of casing devices. The worst conditions of their operation (heat transfer under free convection) were simulated, when the outside water is motionless relative to the vessel hull. Visual studies showed that the emerging air bubbles have transverse pulsations that destroy the wall boundary layer formed along the heat transfer surface, which impedes the heat removal process. Thermal engineering studies confirmed a significant (ten times or more) increase in heat transfer. Moreover, this effect increases as the temperature difference between the heattransfer surface and the outside water decreases. This is important when the vessel is in equatorial waters. This method of process intensification is compared with the case of creating (for example, by means of a pump) a local flow of intake water along the surface of such a heat exchanger. It was determined that the latter is inferior in efficiency to gasliquid jets. It is concluded that the use of this fairly simple method of intensifying heat removal of closed cooling systems will ensure their wider implementation in shipbuilding practice.

Investigation of the Influence of Including or Omitting the Oxide Layer on the Result of Identifying the Local Boundary Condition during Water Spray Cooling

In the case of products made of steel, the presence of an oxide layer, which is formed during the steel production process as a result of high temperature, has a significant impact on the process of heat removal from the surface of the cooled material. For this reason, it is necessary to take into account the presence of the oxide layer in mathematical and numerical models used to simulate the distribution of the temperature field in cooled steel products. These models are based on the boundary conditions identified for given production conditions. This paper presents a comparison of the results of the identification of the boundary condition during water spray cooling of Armco iron with the use of the inverse solution. Numerical calculations were carried out using two models of heat conduction. In the first model, the presence of an oxide layer with different thermophysical properties than the base material (Armco iron) was taken into account. The second model assumed no oxide layer on the cooled Armco iron surface. It was found that the inverse solution obtained in the case of the heat conduction model taking into account the thickness of the oxide layer is correct in time and as a function of temperature. Thus, the boundary condition model obtained as a function of temperature is universal. However, this model requires an additional layer of oxides with different thermophysical properties than the base material to be included in the finite element model (FEM). Based on the conducted uncertainty tests of the inverse solution, it was found that the results of the determined boundary condition in the absence of the oxide layer on the cooled surface are subject to an error higher than 10% in comparison to the maximum reference value of the heat transfer coefficient.

Effect of forward and reverse cutting on tool wear behavior in ultrasonic vibration-assisted milling of 3D needle-punched C/SiC composites

C/SiC composites have excellent mechanical properties such as high specific strength and high temperature resistance, and are widely used in aerospace fields. However, due to its special structure and material properties, the tool wear is severe when machining with conventional methods, and the processing quality is poor. The purpose of this paper is to reveal the progressive wear behavior, wear mechanism of the tool, and its effect on machining performance in conventional milling (CM) and ultrasonic vibration-assisted milling (UVM) of C/SiC composites under forward fiber cutting (FC) and reverse fiber cutting (RC). The material removal and heat transfer models were established, and the stress distribution characteristics of cutting -edge were analyzed by finite element method (FEM). Combined with the wear morphology, cutting heat, and cutting force, the tool wear behavior and mechanism in UVM and CM under FC and RC were studied, and their effects on machining quality were analyzed. The results show that there are great differences in heat transfer and removal process between FC and RC. In UVM, the introduction of ultrasonic vibration reduces the adhesion of fine chips, weakens the strong friction and scratching between the hard chips and the cutting -edge, and alleviates the tool wear. The flank wear VB and cutting -edge wear area WA in RC are larger than those in FC, the abrasive wear is intensified, the material even peeling under mechanical shock, and the adhesive wear is more serious. When the tool wear intensifies to a certain extent, the difference of the cutting process caused by mechanical anisotropy of C/SiC composites is weakened, and the surface micro-defects and surface roughness Sa change little under FC and RC. This research contributes to the realization of high-quality and low-cost processing of C/SiC composites.

Small-Scale Power Plants Based on Organic Rankine cycle (ORC) using Low-Boiling Fluorocarbon Working Fluids when Operating at High Initial Cycle Conditions

The purpose of the work is to develop and analyze the operation of a thermal circuit based on the organic Rankine cycle (ORC) using low-boiling working substances of the fluorocarbon class when operating at high initial cycle parameters. This goal is achieved by energy analysis of single- and multi-stage thermal circuits of power plants with a turbine circuit operating on low-boiling fluorocarbon work-ing substances, such as octafluoropropane C3F8 and decafluorobutane C4F10. It is proposed to integrate the ORC thermal circuit as an extension to a small-capacity gas turbine power plant (GTU), operating on synthesis gas after a biomass gasifier. The most important results of the work are the possibility of implementing a cycle with a low condensation temperature of the medium, which allows, when using low-boiling working fluids, to significantly reduce the temperature of the heat removal process and, consequently, increase the efficiency of the cycle. The possibility of using the listed working substances in power plants with a turbine circuit, which until now have been used mainly as refrigerants for refrig-eration and heat pump systems, has been shown. The significance of the results of the work lies in the fact that, based on the analysis of the energy complex, a circuit solution has been proposed and justified that can increase the energy efficiency of the power supply complex, increasing the volume of generated electrical power and providing a number of technological and environmental advantages.

Energy-technological complex of Kalina cycle for seawater desalination

A scheme has been developed for the use of low-potential energy for heating water, including for the purpose of desalination of sea water. An assessment of the effectiveness of the Kalina cycle is given. It is proposed to use heated water in the water treatment cycle. This cycle can be implemented on geothermal sources near the ocean. Installations based on renewable energy sources fit into the country’s economy in an environmentally friendly way, and also increase energy security. Thus, the cycle is integrated into the seawater desalination system. However, there are some disadvantages to using geothermal energy. First, it is only available in certain parts of the world, since geologically active areas are required to access heat. In addition, installing the necessary equipment and infrastructure can be costly, making it difficult for some people to access this form of energy. Finally, the heat removal process can also lead to environmental degradation as it can harm sensitive ecosystems and water sources in the area.

Analysis of steady-state operation of high temperature heat pipe and optimization of the working medium

High temperature heat pipes exhibit excellent heat transfer performance and can operate stably under high temperature conditions above 750K. They are widely used in heat recovery and heat removal processes. In this paper, a flow and heat transfer model is established to calculate the temperature, pressure, and velocity distribution of the high temperature heat pipe, and the results are similar to the experimental data. In addition, the working medium of the high temperature heat pipe is optimized through a novel optimization method based on probability, and it is concluded that sodium has better heat transfer performance than lithium and potassium under 800K-1000K operating conditions. The optimal result is consistent with the simulation result, which provides a reference for the optimization of working medium in high temperature heat pipes under other operating conditions.

Study of the effect of refrigeration treatment modes on the duration of the poultry meat cooling process

Currently, more and more attention is paid to the quality of food products and especially products that are sold in a chilled state. This is due to the fact that these products have a limited shelf life and to a greater extent must retain all quality characteristics. At the same time, refrigeration processes bear the main burden in terms of energy consumption, and therefore directly affect the cost and quality of the product. In this regard, reasonable refrigeration regimes are an integral part of production. This paper presents a study of various ways of cooling chicken meat, with the simulation of various parameters of the process of heat removal in the refrigerator. The studies were carried out on an operating experimental facility at various temperatures and air speeds, both simple air cooling and air-drop cooling were carried out. In the course of the study, the duration and dependences of the temperature of the cooled sample and the drying of the product on the mode of refrigeration were established. As a result of mathematical processing for the most optimal mode, analytical dependences of the shrinkage value of the test sample were obtained.As a result of the research, the most appropriate mode of refrigeration treatment of chicken meat was recommended, which allows to reduce the weight loss of products during the cooling process.

CHOICE OF THE PARAMETERS OF TWISTED TAPES FOR HEAT TRANSFER INTENSIFICATION IN THE CHANNELS OF THE POWER EQUIPMENT COOLING SYSTEM

The paper presents the results of analyzing the efficiency of heat removal processes in the channels of the power equipment cooling system. The processes of heat transfer in the ventilation ducts of the cooling system for traction motors of diesel locomotive power plants are considered. The feasibility of using artificial intensification of heat transfer processes in the ducts with the help of spiral tapes is analyzed. Convective heat transfer intensifiers of this type are characterized by a significant increase in heat transfer coefficients, ease of manufacture, and low material consumption. Such devices can be used both in the design of new units and in the modernization of existing heat exchange equipment. The efficiency of intensification of heat transfer processes was evaluated by the level of reduction in the power of cooling system fans. The estimates were made assuming the same heat transfer coefficients in the channels with spiral strip inserts and in the channels without inserts. The length of the spiral tapes and the channel is the same. The effect of finning of the channel surface by the inserts was not taken into account. Known criterion equations were used to calculate the convective heat transfer coefficients and hydraulic resistance. It is shown that, despite the increase in hydraulic resistance coefficients and pressure losses in the channels of the air cooling system, the use of spiral tapes due to a noticeable decrease in the speed and, consequently, the cooling air consumption provides a reduction in fan power in a wide range of geometric parameters of spiral tapes while ensuring the required temperatures of equipment elements. The influence of the temperature of the walls of the cooling system channel on the required fan power when using artificial heat transfer intensifiers in the form of spiral tapes is estimated. Recommendations for the selection of geometric characteristics of spiral tapes are proposed, at which, taking into account the values of the channel wall temperature, a decrease in the power of the cooling system fans should be expected.

Design of continuous-duty high-power converter for multi-purpose welding applications

One large-current high-power full-bridge DC-DC converter is often used to cater several multi-characteristic welding loads. The load could be a welding arc or a conductive molten flux. The contour of operating point (voltage-current) of each load type is different. The converter often operates under complex light-load conditions. The design of such high power continuous-duty converter needs to meet three objectives – desired control performance, high across-the-load efficiency, and superior thermal management. To address the thermal issues, this article proposes to use parallel-connected converter modules. It helps distribute the power loss over larger component base; increased surface area would assist the heat removal process. For high operating efficiency, this article proposes superior component engineering in each module. And, for high across the load efficiency, this article proposes to enable or disable an efficient converter module based on the current demand. It means each converter module is equipped to feed the connected load in stand-alone mode. For reduction of power loss, this article elaborates the role of each critical component. The distribution of heat loss would be optimally shared if the current sharing by converter modules is equal, but it needs to be compatible to the dynamic behavior of multi-input process loads. This research proposes and practically validates that single PWM-controller driven parallel-connected converter-modules are not only compatible to process dynamics, the idea would achieve proper current sharing among similar components.

Autonomous Thermosiphon System of Passive Residual Heat Removal from the Primary Circuit of the Reactor Plant: Features of Operation, Characteristics and Basic Advantages

An autonomous system of passive removal of residual heat (PRRHS) of a reactor installation with VVER designed to ensure the safety of nuclear power plants in an accident with complete long-term blackout is considered. The system provides for the removal of heat directly from the first circuit of the reactor plant (PRRHS R). In order to increase the reliability and safety of the emergency heat sink, heat exchange equipment based on closed-type evaporation and condensation devices – two-phase thermosyphons – has been used in the system. The main feature of such heat exchangers is that their thermosiphon assemblies structurally separate the primary circuit and the auxiliary circuit of the PRRHS, which is removed outside the reactor compartment, and provide safe and efficient heat removal, reduce the risk of radioactive contamination spreading beyond safety barriers. Such autonomous passive systems will provide effective heat removal directly from the primary circuit by changing the chain of successive heat transfer sites from nuclear fuel to the final absorber and excluding from it such elements, as for example steam generators, the condition and operability of which in the emergency process of heat removal have a major impact on the safety of the reactor core. The article presents a diagram of an autonomous heat sink system; also, a description of its operation is given. The main characteristics of the course of the emergency process of removal of residual heat by the autonomous thermosiphon PRRHS R obtained by computational modeling have been considered. The advantages of an autonomous thermosiphon passive system in comparison with a passive heat removal system of a reactor installation with VVER through the second circuit are analyzed. The obtained results are proposed to solve the problems of diversification of passive safety systems of evolutionary reactor plants of nuclear power plants with VVER type reactors.

Modeling of Heat Transfer in Composite Bodies Reinforced with Tubes with Swirlers Through Which a Twisted Liquid Heat Carrier Moves in the Turbulent Mode. II. Model Problem

For a model problem, we compute the velocity form-parameters of the flows of heat carrier in tubes and the temperature fields in concrete cylindrical shells longitudinally and spirally reinforced with steel tubes filled with air pumped through these tubes. We compared the results obtained in the cases of reinforcement of these structures with smooth tubes and tubes with swirlers. It is shown that the application of tubes with swirlers significantly intensifies the process of heat removal from the structure as compared with the tubes with smooth inner surfaces if all other conditions are identical. It was discovered that, for some types of thermal boundary conditions, the efficiency of heat removal from the structure strongly depends on the direction of pumping of the heat carrier through the tubes. We also studied the influence of the parameters of reinforcement, the cross-sectional sizes of the tubes, and the velocity of motion of the heat carrier in the tubes on the temperature field formed in the shell. It was shown that the variations of these parameters make it possible to control, to a significant degree, the intensity of heat removal from the composite body. It is also demonstrated that some well-pronounced temperature edge effects may appear in the vicinities of edges of the reinforced-concrete shell.

Enhancing Monocrystalline Solar Module Efficiency through Front-Surface Cooling with 96% Alcohol

Electrical energy generation in solar modules is mainly limited by the increase in their temperature, and a heat removal process plays an important role. The main goal of the experiment was to keep the temperature of the cooled module below 47 °C through a series of the five short cooling and heating cycles and to determine the changes in the solar module output power during the cooling process with 96% ethyl alcohol. The optimal duration of the cooling cycles was determined to be between 3–6 min and for the heating process, it was 4–5 min. During the heating and cooling cycles the temperature of the cooled module did not exceed 42.1 °C. At the end of five active cooling cycles the temperature difference of 22.6 °C was achieved. The biggest difference in power between the cooled and uncooled module was 4.9%. The solar module efficiency was increased by 3.2%. It was concluded that alcohol, due to its evaporative losses, is not a viable cooling agent for solar modules. Nevertheless, it can serve as a potent additive in both active and passive cooling systems to augment the output power of solar modules.

3D Numerical Analysis of a Phase Change Material Solidification Process Applied to a Latent Thermal Energy Storage System

The techniques for releasing thermal energy accumulated in periods of high availability to meet the demand in periods of low energy supply contribute to the continuity of the cycles involved in thermodynamic processes. In this context, phase change materials are capable of absorbing and releasing large amounts of energy in relatively short periods of time and under specific operating conditions. However, phase change materials have low thermal conductivity and need to be coupled with high-thermal-conductivity materials so that the heat flux can be intensified and the energy absorption and release times can be controlled. This work aims to numerically study the solidification process of a phase change material inserted into a triplex tube heat exchanger with finned copper walls to intensify the thermal exchange between the phase change material and the cooling heat transfer fluid, water, that will receive the energy accumulated in the material. This work proposes the 3D numerical modeling of the triplex tube heat exchanger with finned walls and meets the need for numerical models that allow for the analysis of the full geometry of the latent heat thermal energy storage system and the thermal and fluid dynamic phenomena that are influenced by this geometry. Results of the temperature, liquid fractions and velocity fields during phase transformations are presented, analyzed and validated with experimental data, presenting average errors of below 5%. The total material discharge time was approximately 168 min, necessary for the complete solidification of the phase change material, with water injected into the triplex tube heat exchanger at a flow rate of 8.3 L/min and a temperature of 68 °C. The solidification process occurred more slowly in the same direction as the length of the triplex tube heat exchanger, and from 80% of the material in the solid state, the difference between the solidification time for z = 0 and z = 480 mm was 30 min. The fluid dynamic conditions developed in the latent heat thermal energy storage system promoted a maximum negative heat flux of −6423 w/m2 to the annular internal surface and −742 w/m2 to the annular external surface, representing a heat removal process nine times less intense on the external surface. The total energy released to the cooling heat transfer fluid was 239.56 kJ/kg.

Using of large eddy simulation model for a spatially developing turbulent natural convection boundary layer in water along a side-heated vertical wall with high Rayleigh number ([formula omitted

To further understand the turbulent natural convection in the residual heat removal process of a nuclear reactor in accidental condition, a spatially developing natural convection boundary layer along a side-heated vertical plane in water is simulated with Large Eddy Simulation (LES) strategy. The maximum modified Rayleigh number (Ra*=Ra×Nu) reaches 8×1014 with the uniform heat flux input (≈10000W/m2). In particular, the buoyancy driven flow is simulated by an incompressible flow solver with Boussinesq approximation. The Wall Adaptive Local Eddy (WALE) model is selected as the sub-grid scale model for the LES simulation. After comparing with available measurements, it is found that reasonable agreement has been achieved in wall temperature distribution along the heated wall, heat transfer rate as well as mean temperature, mean velocity and turbulent statistics in the boundary layer. The detailed vortex structure and velocity spectra in the boundary layer corresponding to different regime are clearly demonstrated. It is shown that the transition process in the boundary layer can be accurately presented with the refined mesh (x+≈0.1) in the near wall region. To be more specific, the appeared ordered vortex street in the transition stage and the estimated critical Rayleigh number for turbulence inception correspond well to previous experimental observations. The significant effect of early transformation of two-dimensional (2D) linear Tollmien–Schlichting waves on the heat transfer is also proved. It is expected that current study can enhance the understanding of turbulent boundary layer at high heat flux and high Rayleigh number.

Characteristic analysis of natural circulation residual heat removal in small reactor

In order to study the characteristics of small helium-xenon cooled nuclear reactor that only relies on natural circulation to remove residual heat after shutdown, this paper carries out geometric and physical modeling of helium-xenon cooled nuclear reactor, and uses CFD to simulate the process of natural circulation residual heat removal. Variation laws of the hot spot temperature on the surface of fuel cladding and the mass flow of helium-xenon mixed gas under different working conditions are calculated, and the transient characteristics of temperature, flow and other related parameters in the system loop are analyzed. The calculation results show that during the natural circulation residual heat removal process, the overall change trend of the hot spot temperature on the surface of the fuel cladding, the average temperature of the primary coolant and reactor outlet temperature first rises to the highest value and then decreases, and the mass flow of helium-xenon mixed gas shows an exponential decay trend; Increasing the initial mass flow of helium-xenon mixed gas and reducing the residual heat of the reactor core can reduce the maximum hot spot temperature on the surface of the fuel cladding. The relevant research results provide a useful reference for the optimal design of natural circulation residual heat removal of helium-xenon cooled nuclear reactor.

Determination of thermal properties (and their uncertainties) during the cooling of apples (Malus communis)

AbstractThe present study goal was to determine the thermal properties of apples during their cooling. Fuji apple was cooled in a domestic refrigerator by natural convection. Thermal properties were determined assuming the geometry of an equivalent sphere. An optimizer software (LS Optimizer) was used for the inverse problem. A new heat conduction software was developed to solve the direct problem, using the spherical geometry of the diffusion equation with the boundary condition of the third kind. Thus, thermal properties of apples and their uncertainties were calculated during cooling. The developed software for the direct problem was used to simulate the cooling kinetics for any previously specified point within the sphere. The fitting of the simulated curve to the experimental points showed coefficient of determination (R2) greater than 0.99 and low values of the chi‐square function (). Therefore, it can be concluded that the spherical geometry and the boundary condition of the third kind were adequate to describe the process of heat removal for apple. Determined values of thermal diffusivity and convective heat transfer coefficient wereα = (1.38 ± 0.07) × 10−7 m2 s−1andh = (1.360 ± 0.018) × 10−6 m s−1, respectively, with confidence intervals of 95.4%. Another confirmation of the developed model was the fact that the thermal diffusivity was similar to the estimate by Riedel correlation (α = 1.38 × 10−7 m2 s−1). The position of the thermocouple in the equivalent sphere calculated by numerical solution wasr = 6.6 mm.Practical ApplicationsOne of the main contributions of this paper is the calculation of thermal parameters along cooling with their uncertainties. This will result in very accurate simulation of the pasteurization and freezing processes. Furthermore, the values obtained in the study can be used to predict new cooling curves for the same product, but with different dimensions.

Simultaneous laser-induced fluorescence, particle image velocimetry and infrared thermography for the investigation of the flow and heat transfer characteristics of nucleating vapour bubbles

Boiling is an effective heat removal process, used for heat exchange and thermal management purposes in many technological applications, from the scale of microelectronic devices to nuclear reactors. However, the physical mechanisms involved in this process are not fully understood yet due to the complexity that arises from the many interacting underlying sub-processes involved in the nucleation, growth and detachment of bubbles that occur during the process. Here, we present an advanced methodology based on combined, synchronized high-speed infrared (IR) thermometry, ratiometric two-colour laser-induced fluorescence (2cLIF) and particle image velocimetry (PIV), along with sample results of an experimental investigation conducted in deionized water, aimed at elucidating the mechanisms involved in the bubble lifecycle. IR thermometry is used to measure the time-dependent 2-D temperature and heat flux distributions over a boiling surface, and 2cLIF is used to measure the time-dependent temperature-field in a vertical plane, in the liquid phase around developing bubbles. Furthermore, PIV is used to measure the velocity fields around the bubbles, in the same plane as 2cLIF. The investigation reveals and allows us to quantify fundamental heat transfer aspects such as the contribution of triple contact line evaporation to the bubble growth process, the dynamics of the near-wall superheated liquid layer, the mixing effect produced by bubble growth and departure, convection effects around the bubble, and quenching heat transfer. Specifically, we observe that, in our experiment, with slowly growing bubbles, the microlayer does not form, and the evaporation at the solid-liquid-vapour contact line contributes to approximately one third of the total heat transferred to the bubble. We also observed that the fluid that rewets the dry spot at the bubble base, as the bubble departs from the boiling surface, comes from the near-wall superheated thermal boundary layer adjacent to the bubble, i.e., it is warmer than the fluid in the bulk. We confirm this finding by modelling this quenching heat transfer phase as a transient conduction process.

Comparative investigation and optimization of turning process parameters using Taguchi technique in turning of Inconel 718

In this work, sustainability in manufacturing is accomplished by introduction of a vortex tube. Vortex tube separates the hot compressed air and the cold air that flows through the tube and exits the cold air alone on to the work piece. Vortex tube are used for cooling the cutting tools in turning and milling operations. Modern CNC machine tools are embedded with the vortex tube for effective heat removal process from the cutting tool. By the implementation of vortex tube, the liquid coolant are totally eliminated. Sustainable manufacturing targets towards non-polluting means of manufacturing techniques and energy efficient method of manufacturing. The community, society and employees of sustainable manufacturing are economically sound and safe. Sustainable manufacturing is the innovative technique that do not compromises with the traditional method of manufacturing. In this work, sustainability in manufacturing is accomplished by introduction of a vortex tube. This invariantly reduces the use of cutting oil and thereby reduces the pollution and attains sustainability in manufacturing.

Sustainable manufacturing for turning of Inconel 718 using uncoated carbide inserts

In this work, sustainability in manufacturing is accomplished by introduction of a vortex tube. Vortex tube is a mechanical device that separates the hot compressed air and the cold air that flows through the tube and exits the cold air alone on to the work piece. The objective of the work is to implement sustainability in the manufacturing process for turning of Inconel 718 using coated carbide inserts. This is achieved by the implementation of vortex tube, which is used for cooling the cutting tools in turning and milling operations. Modern CNC machine tools are embedded with the vortex tube for effective heat removal process from the cutting tool. By the implementation of vortex tube, the liquid coolant is totally eliminated. The work piece considered in this work is Inconel 718. 38 mm diameter and 75 mm long cylindrical bar stock is used in this work as the test specimen for turning using uncoated carbide inserts. Design of experiments are used to conduct 27 set of experiments and for each set of experiments, the flank are measured and recorded. The flank wear is found to be decreased upto 7.2% with the implementation of the vortex tube in the turning process. The main effects plot for means for the flank wear with and without vortex tube is plotted and discussed.

Effect of Boric Acid Solubility in Steam on the Process of Mass Transfer during Emergency Cooling of VVER-1200 Nuclear Reactor

The mechanisms of boric acid mass transfer in a VVER-1200 reactor core are studied in this work in the event of a major circulatory pipeline rupture and loss of all AC power. The VVER-1200's passive core cooling technology is made up of two levels of hydro accumulators. They use boric acid solution with a concentration of 16 g H3BO3/kg H2O to control the reactivity. Because of the long duration of the accident process, the coolant with high boron content starts boiling and steam with low concentration of boric acid departs the core. So, conditions could arise in the reactor for possible accumulation and subsequent crystallization of boric acid, causing the core heat removal process to deteriorate. Calculations were carried out to estimate the likelihood of H3BO3 build-up and subsequent crystallization in the core of the VVER reactor. According to the calculations, during emergency the boric acid concentration in the reactor core is 0.153 kg/ kg and 0.158 kg/kg in both the events of solubility of steam and without solubility of steam respectively and it does not exceed the solubility limit which is about 0.415 kg/kg at water saturation temperature. No precipitation of boric acid occurs within this time during the whole emergency process. Therefore, findings of the study can be used to verify whether the process of decay heat removal is affected or not.