Heat Exchange Processes Research Articles

Study of the intensification of the heat exchange process in the MO-2 turbine oil cooler during the modification of tubes in tube grids.

Study of the intensification of the heat exchange process in the MO-2 turbine oil cooler during the modification of tubes in tube grids.

Study on the effect of ground stratification on heat transfer of vertical ground heat exchangers in lateritic clay areas

The potential effect of ground stratification on the efficiency of ground heat exchangers (GHEs) in lateritic clay regions remains unclear. Model experiments were conducted to investigate the effects of soil dry density, water content, and ground stratification on the heat exchange between GHEs and the surrounding lateritic clay. A 3D numerical model accounting for ground stratification was proposed and validated using experimental data. The model further examined the influence of soil moisture on the dynamic heat exchange process. The findings of the model experiments indicate that the heat from buried pipes increase soil temperature by 12.8 % when the initial water content of lateritic clay (with dry density of 1.1 g/cm3) rises from 5 % to 28 %. Raising the dry density from 1.1 to 1.3 g/cm3 at 28 % water content results in a 7.5 % temperature increase. The initial soil moisture and density have negligible effects on the temperature gradient within 18 cm of the geothermal pipes. The temperature increased faster in the sand layer than in the lateritic clay layer owing to the difference in thermal properties. The impact of heat produced by GHEs on the temperature field in homogeneous soil layers differs considerably from that in stratified soil layers. The 3D numerical model provided a good fit for the measured soil temperature in the stratified soil layer, including the soil temperature variation at the layered interface. The simulation results showed that for dry and saturated strata, the temperature of the lateritic clay around the GHEs increased with increasing initial stratum moisture. For unsaturated lateritic clay strata, because of the possible impacts of moisture and heat coupling migration, the temperature of the stratum around the GHEs first increased and subsequently decreased as the initial stratum moisture was enhanced.

Evaluation of influence of thermoplastic slurry flow conditions on heat transfer coefficient during beryllium ceramic formation

The article presents the results of calculation of the influence of thermoplastic slurry flow conditions on the total heat transfer coefficient when forming ceramic products. Methods of detailed description of casting processes and thermal calculations have been developed to ensure reliable correspondence of calculated data and experimental results implemented on the basis of calculational experiment. The modeling of physical processes occurring during the formation of products allows you to discover new opportunities for improving the quality of castings by allowing you to more closely track the change in the temperature-phase fields of the process and clearly present the solidification kinetics depending on the casting modes. The speed of heat removal from the casting during the solidification period determines the rate of movement of the slurry, along with the temperature field on which the width of the transition region depends. These factors have a direct influence on the formation of the structure of beryllium ceramics. The study of the heat exchange process in the formation of ceramic products depending on temperature, heat at phase transition is the main task, since they largely determine the technological and operational characteristics of beryllium ceramics. The design data allows to determine the optimal conditions of the ceramic casting process and to obtain a solidified product with a uniform structure at the outlet.

Про фундаментальну підготовку фахівців авіаційної та аерокосмічної галузей

The subject of the study is the state of the fundamental training of specialists in aviation, rocket, and space technology. Recently, the processes of expanding and deepening the fundamental training of specialists in the specialized areas of specific higher education institutions have been intensified. Unfortunately, experience of recent years has shown, the priorities rightfully belong to the aviation and aerospace industries, both in the scientific/creative and design/production spheres. Training of the specialists in the field of aerohydrodynamics of aircraft and their components; gas dynamics of the modern aircraft engines of various types, is currently the priority. In addition, both – the problems in aeroelasticity and research in the field of aerodynamic acoustics related to the environmental safety of the operation of aviation equipment are important for the design of the modern aircraft. Moreover, the design of aircraft that overcomes trans- and supersonic flight speed, requires in-depth study of the processes of heat and mass exchange determining physico-chemical transformations, which are also present in the internal gas-dynamic processes of gas-turbodynamic and rocket engines of aircraft. Structure and comparative analysis study of programs and courses for fundamental training of specialists in the aerospace industry at the universities of USA, Canada, Germany, China, as well as in KhAI, Ukraine, are presented. This study provides comparative information about scientific and experimental bases of aerodynamic complexes available in Ukraine and in leading organizations of North America and Western Europe. This study demonstrates the real unification of deep fundamental theoretical knowledge and practical skills with experimental research based on existing modern research laboratories. Conclusion. Analysis and comparative indicators presented in paper allow us to state that based on today’s needs, the National Aerospace University "Kharkiv Aviation Institute" is capable of significant increase of the quality of training for specialists of all levels for the developed aviation and rocket-space industries of Ukraine.

Performance analysis of double-stage heat pump and refrigeration cycles

Multistage refrigeration systems are investigated to/enhance the performance of vapor compression refrigeration cycles based on our previous work on multistage low-grade thermal energy conversion. A double-stage heat pump and refrigeration cycles (D-S) is expected to reduce the irreversible loss in the heat exchange process. However, certain characteristics of independently configured systems, namely, compressor power and coefficients of performance (COPs), have not been sufficiently clarified. This study aims to elucidate highly advanced heat pump and refrigeration systems by comparing D-S, a basic single-stage heat pump and refrigeration cycles, and a two-stage compression cycle. D-S shows higher COPs for both the refrigeration and heat pump cycles compared with the other cycles, especially at high thermal conductances. The reduction of the irreversible loss in the heat exchange process is confirmed via the entropy generation rate; in particular, the COP increases with a decrease in the entropy generation rate. The evaporation and condensation temperatures of the refrigerant approach the temperature of the heat source when the thermal conductance exceeds 150 kW/K for the refrigeration cycle. The heat exchangers exergy destruction of D-S is 169 kW, S-S is 189 kW, the two-stage cycle is 184 kW/K when the thermal conductance is 100 kW/K.

Identification of heat exchanger process through Hammerstein and polynomial models

Process industries extensively use heat exchangers in their operations, playing a crucial role in various sectors by facilitating efficient heat transfer, conserving energy, and reducing operational costs. This paper focuses on identifying and validating the system model, with the primary task of designing the controller involving the determination of the mathematical representation of the system. The First Order Plus Dead Time (FODT) model, derived from basic principles, is used to represent the system. To analyze the system’s behavior and construct a suitable controller, model development is essential, achieved by constructing principles models using energy balance equations to identify the heat exchanger process. Data collected from the model are utilized in the identification process, with the temperature at the outlet of the hot air blower being the controlled variable in this investigation. The research aims to determine the mathematical model based on time versus temperature data acquired from the Heat Exchanger. Various system identification methods, such as Hammerstein Wiener (HW), Auto Regressive with Exogenous Input (ARX), Box-Jenkins (BJ), Output-Error (OE), and Auto Regressive Moving Average with Exogenous Input (ARMAX) models, are implemented for the heat exchanger. The models obtained undergo validation, and the best-fit model closest to the physical system is considered for controller design. After conducting the analysis, it was found that the Output-Error (OE) model outperforms other models in terms of achieving the best fit.

Combined Gas Tungsten Arc Welding and Shielded Metal Arc Welding Processes for Joining Tube to Tubesheet in Shell and Tube Heat Exchangers

Abstract Flawless tube and tubesheet joints are necessary for shell and tube heat exchanger with high leakproof ability and durability. The consequence of mixing of transfer fluids due to the defective welded or expanded tube-to-tubesheet joint results in complete malfunctioning of the heat exchange process. In this case, there is a high demand for quality assessment of the fabricated tube-to-tubesheet joints (TTS) based on the international standards. Additionally, the literature on assessing the mechanical and metallurgical characteristics of tube-to-tubesheet joints using any one welding technique is available; however, articles dealing with the use of multiple welding techniques are scanty. In the current work, the quality assessment of strength welded and light expanded (3%) tube-to-tubesheet joints followed by light expansion was performed whereas for welding, combined gas tungsten arc welding (GTAW) and shielded metal arc welding (SMAW) as root pass and cap pass were adopted in the fabrication stage. Quality and sound tube-to-tubesheet joints were produced using welding and tube expansion process. Linear and circular indications representing the cracks were absent on the developer in the liquid penetration test. The minimum leak path (MLP) was greater than the two-third of tube wall thickness. The results strongly qualify the use of combined gas tungsten inert gas and shielded metal arc welding process for manufacturing of tube-to-tubesheet joints. The methodology and results in the current article are beneficial for researchers and industrialists working close to shell and tube heat exchangers and boilers.

Simulation of the heat exchange processes of an absorber and a generator with NH3/LiNO3

A mathematical model is the representation, through equations, of the phenomenon that you want to model. In the context of control systems, models are used to analyze and design control systems. A system is dynamic when its variables change depending on another variable, which is generally time. In this article, an absorption refrigeration system is considered, a model and simulation of it is carried out and the results are compared with the available experimental data, where the existence and uniqueness of the solution in a certain space of finite smoothness is demonstrated, and the certain properties of the solution to the problem.

Thermovision study of a residential building under climatic conditions of South Kazakhstan in a cold period

In this study, a nine-storey residential building was examined for thermal protection, located in Shymkent, Republic of Kazakhstan. Two two-room flats were considered with the possibility to inspect the exterior envelopes in four orientations. The examination was carried out at different times of the day according to three criteria: exterior envelope in the form of corner joints, translucent envelope in the form of window openings and the exterior façade of the building. The study found that the temperature at the surface of the room joints at lunchtime increased from 0.8% to 12% depending on the orientation of the exterior envelope. At the same time, it was found that in the morning and evening hours the temperature inside the living rooms is maintained at 25.8 - 26.5ºC due to excessive consumption of heat energy by increasing the heating power up to 15.6% relative to lunchtime, which leads to an excessive increase in air temperature by 7 - 18%. The value of humidity of living rooms also showed non-compliance with the optimal value by 3 - 15% relative to the current norms. As a result of the analysis of thermograms of translucent openings it was found that the surface temperature of the envelope at lunchtime increased by 9.9 - 23.2% in all cases of orientations, and the surface temperature of translucent openings of southern orientation is on average 18.2% higher relative to other orientations, which also indicates the influence of solar radiation on the thermal values of translucent openings. The analysis of thermograms and temperature of characteristic points of the external façade with regard to orientations showed a temperature difference from 7.5ºC to 21ºC depending on the orientation of the building, where the most exposed to solar radiation façade of southern orientation, which showed an increase in surface temperature by 3 times. Thus, the obtained results of the study will further contribute to the development of energy-efficient designs of external enclosures, considering the influence of all factors on the process of heat exchange, which is the main objective of the authors’ comprehensive study.

Simulation of a Heat Transfer Mechanism in a Shell and Tube Coil Heat Exchanger

Statement of the problem. The mechanism of heat exchange between counterflow circuits in a shell-and-tube coil heat exchanger, inside which heating and heated coolants flow, is discussed. It is required to build computer models of the movement of coolants in different operating conditions, to simulate the mechanism of heat exchange in the countercurrent mode of movement of coolants in a shell-and-tube coil heat exchanger. This problem was solved in the Solidworks Flow Simulation software package. Results. A mathematical model of the heat exchange process in a shell-and-tube coil heat exchanger was obtained with visualization of the mechanisms of coolant movement inside the heating and heated circuits. Conclusions. Based on the simulation results, a comparison was made of various computer models of the apparatus obtained. The optimal design has been determined.

Augmentation of Pool Boiling Heat Transfer Using the Laser Treatment Technology

The paper discusses applying the laser technique to modify the copper heater surface. The interaction of the laser beam with the base material leads to its melting, and various shapes can be obtained during the process. The study is focused on the boiling heat transfer analyses of the specimen in the form of a disc with longitudinal microfins of a height of 0.5 mm. The optical microscope was used to determine the morphology of the surface. The laser beam generated significant roughness, which benefitted the overall thermal performance. Considerable heat transfer augmentation was recorded for the laser–made surface in relation to the untreated sample, which served as a reference. The heat flux was several times higher, while the laser–treated sample's boiling curves were shifted to the area of smaller temperature differences. Two boiling models proved unsuccessful in predicting the heat exchange process occurring during pool boiling of distilled water and ethyl alcohol. According to the Smirnov, Xin and Chao models, the average differences between the experimental data and calculation results were ca. 93 kW/m2 and 116 kW/m2 for water, 78 kW/m2 and 68 kW/m2 for ethanol.

Sustainable heating and cooling for residential buildings: coaxial ground heat exchangers

As the world fights climate change challenges and the soaring demand for energy-efficient solutions, the need for sustainable heating and cooling systems in residential buildings has become paramount. Traditional systems rely on fossil fuels and contribute significantly to greenhouse gas emissions. Ground source heat pumps (GSHPs) have emerged as a promising technology, offering a sustainable alternative to conventional space conditioning systems. Central to the success of GSHPs is the efficient and reliable operation of their ground heat exchangers, with lower installation costs, as a prospective solution for future residential applications. This paper presents a numerical axisymmetric (r-z) finite volume method solution of the thermal performance of coaxial ground heat exchangers (CGHE) that incorporate phase change material (PCM) in the ground for GSHP applications. An analysis of the CGHE with PCM grout is presented, highlighting the advantages of heat exchange performance over normal grouts. The temperature comparison on three different points in the grout with different grouting materials was carried out to analyse the behaviour of different grouting materials during the heat exchange process. The investigation from a temperature point of view showed that the inclusion of PCM in the grouting material improves the thermal performance of the CGHE.

Heat Exchanger for a Sustainable Thermal Process

Heat Exchanger for a Sustainable Thermal Process

Thermal design calculation method of the whole coil closed cooling tower with condensation inside the tube

In this paper, the heat exchange process of a closed cooling tower with condensation inside the tube is analyzed. Combined with the calculation method of a traditional closed cooling tower, the thermal model and mathematical model of the whole coil closed cooling tower with condensation inside the tube are established. The fourth-order Runge-Kutta (RK4) method is used to write a program to solve the differential equation. A case is calculated to solve the heat exchange area and spray water temperature. Its feasibility for design reference is verified.

Матричное моделирование и диагностика состояния регенеративных подогревателей высокого давления

Increasing the efficiency of heat exchangers is a promising area of energy saving, which is one of the priority areas of the development of science, engineering, and technology in the Russian Federation. Improvement of heat and mass transfer in regenerative heaters and condensers of turbine units of thermal power plants can significantly increase the operating efficiency of power equipment. Diagnostics of the condition and improvement of operating modes of the high-pressure regenerative heater which are an integral part of regenerative heating systems for feedwater of turbine units, are urgent scientific and practical tasks. To develop a model of a high-pressure regenerative heater, the methodology of matrix formalization of the description of heat and mass transfer processes has been used. To solve problems of diagnosing the state of heating surfaces of heat exchange equipment, mathematical programming methods have been applied. Within the framework of the matrix formalization methodology, an approach to modeling and solving diagnostic problems of multi-stage heat exchangers considering the phase transition in coolants has been developed. The sensitivity of the resulting model to input signals has been studied. Solutions of the problem of diagnosing the state of a high-pressure regenerative heater have been obtained and analyzed. Analysis of the obtained calculated results has shown an adequate description using the model of the real heat exchange process for the analyzed heater and the possibility to use the proposed model for monitoring and operational diagnostics of power equipment. The proposed approach allows us to formulate and solve inverse problems of diagnosing the state of equipment of heat exchange installations for various purposes.

Thermal and aerodynamic characteristics of air cooled condenserfor steam turbine power unit

THE PURPOSE. Increased water consumption at power plants leads to a deterioration of the environmental situation not only in countries with limited water supply sources, but also in countries with significant reserves of fresh water. There is a need to consider the possibility of using an air condenser as an alternative use in industrial water supply systems at a power plant. To present a methodology for calculating the main characteristics of a condenser (condensation and reflux sections), to estimate the aerodynamic resistance and fan power for an air-cooled condenser as part of a steam turbine power unit. Determine the influence of air temperature and pressure in the condenser on the calculation of the air condenser. To develop recommendations for the selection of parameters of air condensers operating as part of steam turbine power units. METHODS. Methods for designing heat exchangers, modeling and intensifying heat exchange processes were used in the course of calculating an air condenser unit. RESULTS. A method for calculating an air-cooled condenser for a 110 MW condensing turbine has been developed. The analysis of the calculation of the heat transfer coefficient is given. The analysis of the values of the heat exchange area of the condensing unit is presented. The effect of pressure in the condenser on the main calculated characteristics of the condenser is shown. Recommendations for the selection of the fan capacity in the condenser and the design temperature of the cooling air have been developed. CONCLUSION. The issue of using air coolers in the power industry is still poorly covered in the literature, however, environmental problems and the shortage of fresh water are becoming more and more urgent all over the world. The development of air-cooling systems is a very topical issue for modern power engineering. It is shown that for stationary installations of condensation of water vapor, the most suitable is the hipped-roof arrangement of the heat-exchange sections with the lower arrangement of the fans. Quantitative estimates of the change in the heat transfer coefficient and the area of the heat-exchange surface are given for the pressure range of 8…20 kPa. The power consumption of the fan depends significantly on the temperature of the cooling air and the vacuum in the condenser.

Advantages and Disadvantages of Connect Anti Surge System Gas Pipe of Multistage Centrifugal Recycle Gas Compressor with Process Heat Exchanger in Power Former Unit in Daura Refinery

Advantages and Disadvantages of Connect Anti Surge System Gas Pipe of Multistage Centrifugal Recycle Gas Compressor with Process Heat Exchanger in Power Former Unit in Daura Refinery

Numerical investigation in effects of refrigerants’ thermodynamic properties on performance of supersonic ejector

ABSTRACT Using zeotropic mixtures with unique temperature glide characteristics as the working medium in heat-driven ejector refrigeration system will potentially reduce the irreversible losses in heat exchange process. However, the intrinsic link between the pure/mixture refrigerants’ thermophysical properties and the entrainment performance of supersonic ejector has not yet been elucidated. In this study, a novel ejector CFD model is established by coupling the real-gas thermodynamic equation and species transport equation, then the relationships between thermophysical properties of pure/mixture refrigerants and ejector’s dimensionless operational parameters were thoroughly investigated. The results indicated that the ejector expansion ratio rises as primary flow inlet temperature or refrigerant’s normal boiling point increases, while the dimensionless parameters of primary nozzle are relatively insensitive to the variation of primary flow inlet temperature and refrigerant’s boiling point, resulted in changes of supersonic jet expansion behaviour. Moreover, the specific volume and adiabatic index change characteristics resulted in minor fluctuations of primary nozzle’s dimensionless parameters. When the bubble point temperature is fixed at 30℃ in the condenser, the saturated vapor/liquid phase pressure glide characteristics of R600a/R1234ze mixture may lead to an increasement of ejector’s compression ratio.

Ferromagnetic and ohmic effects on nanofluid flow via permeability rotative disk: significant interparticle radial and nanoparticle radius

The significance of interparticle spacing and nanoparticle radius for the case of single-phase nanofluid flow has often been neglected. Tremendous applications of this phenomenon can be witnessed in different fields, especially in electron microscopes, heat exchange processes, and many others. This research highlights this vital aspect of Ohmic heating in nanofluid flow over a spinning disk. To ensure the novelty, a ferromagnetic nanoparticle (Manganese ferrite) has been incorporated to examine interparticle spacing and particle radius to explore the features of heat transfer. The ferromagnetic nanofluids are vital in carriers for drug delivery systems, in cancer treatment, design of systems for hyperthermia therapy, in microfluidic devices used for chemical synthesis, etc. The quantiles of dimensional equations are converted into dimensionless ones by adopting similarity transformations and to solve highly coupled nonlinear equations numerically, built-in bvp5c MATLAB tool is utilized. The effect of a few revealed factors, the velocity and temperature distributions, are examined via visualization. Furthermore, streamlined plots are also visualized. The outcomes produced showed excellent agreement with those made in the literature in the same direction by assuming some exceptional cases on different gradients. Further, the outstanding results are reported as; the permeability of the surface produces the suction velocity, and the enhanced suction velocity attenuates the fluid velocity in either of the case of pure and nanofluid. The increase in thermal radiation boosts up the heat transfer rate whereas the augmentation in the Eckert number retards it significantly.

Deepwater Renewal in a Large, Deep Lake (Lake Geneva): Identifying and Quantifying Winter Cooling Processes Using Heat Budget Decomposition

AbstractWintertime deepwater renewal, which is important for heat–oxygen–nutrient exchange in lakes, is traditionally considered to be mainly driven by 1D vertical convective cooling. However, differential cooling between shallow and deep waters can produce density currents that flow into deep layers. In order to determine the role that these two cooling processes play in deepwater renewal, field measurements and 3D numerical modeling were combined to investigate heat content dynamics in Lake Geneva's large basin, the Grand Lac (maximum depth 309 m), during an exceptionally cold air spell in early 2012 where complete overturning had been reported. In a novel approach, the heat budget of the lake was decomposed, which allowed the identification and quantification of the heat budget components. The heat budget decomposition revealed that vertical convective cooling only penetrated to 200 m and that lateral advection was not only caused by density currents being discharged from the shallow littoral zone of the Grand Lac, but also from the Lake's shallow Petit Lac basin (maximum depth 75 m); the latter was found to be the main driver of heat content decrease in the deep layers of the Grand Lac below ∼200‐m depth. These findings provide unique insight into heat exchange processes that cannot be obtained from field data or numerical simulations alone. Heat budget decomposition proved to be a powerful, universally applicable tool for quantifying the contribution of alternative deepwater renewal processes. This is important, since deepwater renewal by convective cooling is weakening due to persistent global warming.