Heat Exchange Processes Research Articles

Повышение качества городской среды за счет использования трансформатора теплоты сезонного действия в системах теплоснабжения

The urban economy includes a large number of construction sites for various purposes that need reliable and efficient heat supply, and improvement of infrastructure. And at the same time, they must create a safe and comfortable urban environment. The most important state task of rational use of energy resources can be solved using secondary energy resources and renewable energy sources. Therefore, the development of new modern technologies for the secondary use of energy resources in the urban environment is an urgent task. The purpose of the study is to evaluate the energy and economic efficiency of the proposed seasonal heat transformer, designed to maintain road surfaces of various structures during the cold season without ice and snow cover, as well as to produce hot water in hot water supply systems by utilizing the heat of heating the road surface during the warm season. The method of balance calculations of heat exchange processes in technological power plants is used in the study. A device based on heat transformation processes has been proposed to improve the quality of the urban environment. The efficiency of the proposed device and the operating costs of its operation are determined. The proposed technical solution ensures a reduction in energy costs for buildings and energy savings, and also improves the operational parameters, convenience and safety of the adjacent territories.

Computational Fluid Dynamics Analysis of Solidification in Baffled Molten Salt-Air-Cooled Heat Exchangers

Abstract Due to their high freezing point, molten salt heat exchangers face the problem of salt freezing during cyclic operation. As a result, it is critical to detect the onset of salt solidification and anticipate the phase change behavior in high-temperature heat exchange processes, since these parameters influence heat exchanger design and operation. This study presents a three-dimensional transient computational fluid dynamics analysis of a pilot-scale exchanger with molten salt on the tube side and air on the shell side. The investigation focuses on the effects of the baffle arrangement and initial molten salt temperature on the air outlet temperature, pressure drop, and the onset of salt solidification. The pressure–velocity field coupling and turbulence parameters were solved by employing a segregated solver algorithm and a realizable k−ε turbulence model. Verification of the numerical model involved prior findings from a shell-and-tube heat exchanger using pure water as the shell-side fluid. The novel contribution of this work is to predict the time required for the molten salt to begin solidification within the tube bundle when air is used as the working fluid on the shell side of a single-segmented baffled shell-and-tube heat exchanger. The study concludes that, in the absence of a flow diverter, different baffle arrangements have minimal effect on the air outlet temperature or the start of salt solidification. A flow diverter, on the other hand, successfully slows solidification by distributing the flow, even when recirculation zones cause one-third of the heat exchanger length to remain ineffective. These findings provide a standard for future dynamic operation heat transfer assessments of molten salt-air-cooled heat exchangers.

Numerical study on the waste heat recovery from multi-sized copper slag particles by the moving bed

ABSTRACT Copper slag contains abundant waste heat resources but have not been effectively utilized, and the Moving Bed Heat Exchanger (MBHE) has great potential for recovering high-temperature particle waste heat. Therefore, in this research, we simulate the flow and heat exchange processes of multi-sized copper slag particles inside a moving bed heat exchanger, employing the Discrete Element Method (DEM), and introduce the thermophysical parameters of copper slag that varied with temperature in order to improve the modeling accuracy. The contact number, average temperature, and heat transfer coefficients of the particle streams are analyzed in detail for variations with flow rate with the aim of exploring the effect of key parameters on the waste heat recovery process. It is observed that the contact numbers in different heat exchanger tube layers decreases by 13.1%, 11.1%, 12.3%, 10.6%, and 16.8% as the particle flow rate increases from 1 mm·s−1 to 5 mm·s−1, respectively. The effective heat transfer coefficients of each layer increased by 15.0%, 21.7%, 33.9%, 58.7%, and 57.8%, respectively. Additionally, the temperature distribution of particle flow is more uniform.

Computer modeling of the non-stationary temperature distribution in bodies of spherical geometry

The processes of non-stationary heat exchange in bodies of spherical geometry are re-searched in this study. The mathematical model of thermal conductivity in a sphere and itsanalytical solution are presented and analyzed. The stability criterion for the analytical so-lution is determined under typical boundary and initial conditions. Numerical method forthe mathematical model with nonlinear and non-stationary boundary and initial conditionsis developed. The numerical method is based on functional programming using built-infunctions of the Maple software. The typical temperature distributions inside a sphere de-pending on time and radius were obtained. Developed approach significantly minimizestime of calculation for heat exchange problems in bodies of spherical geometry and showscapabilities of the system computer algebra Maple in terms of solving non-stationary non-linear problems of mathematical physics.

Energy efficiency potential determination for an oil treatment and stabilization unit at the field

Relevance. The desire to increase the energy efficiency of industrial enterprises and reduce greenhouse gas emissions from their activities. Reducing specific energy consumption at large oil refineries and petrochemical plants is not new and is quite widely used. Dozens of monographs and thousands of articles are devoted to these areas. But it should be taken into account that in the oil refining industry, all crude oil, even that which does not reach the refinery, necessarily passes through oil preparation and stabilization units at the fields. Therefore, in order to create energy-efficient and environmentally friendly processes throughout the entire oil refining chain, it is necessary to increase the energy efficiency of the oil preparation and stabilization units located at the fields. There are very few research works on thermal energy integration of oil preparation and stabilization units. Aim. Determination of target design and energy values for an energy-efficient retrofit project of the heat exchange network for the surveyed oil preparation and stabilization units and of its energy efficiency potential. Methods. Pinch analysis methods are used to determine the target values of an energy-efficient retrofit project. Mathematical modeling of heat exchange processes in the heat exchange network and economic analysis were performed using the Pinch 2.02 software; the Aspen HYSYS software package was used to create a simulation engineering model of the oil preparation and stabilization units. Results. When determining the target values of the heat exchange network retrofit project, the cost of energy and heat exchange equipment, the cost of collectors for splitting process streams, and technical restrictions on the placement of heat exchanger sections were taken into account. The inclusion of fuel gas in the process stream table has allowed the definition of target parameters for the optimal unit heat exchange network design to evolve. In the process of evolution of target values, the energy efficiency potential of the surveyed oil preparation and stabilization units was determined, which shows the possibility of reducing specific energy consumption by 77%. Upon implementation of the heat exchange network retrofit project and achievement of target parameters, the following economic results will be obtained: IRR=42%, NPV=7425780 USD, DPP 4 years. Also, CO2 emissions can be reduced by 30 thousand tons per year. It should be noted that the evolution of target designation and all target values for the reconstruction project were obtained before the implementation of the heat exchange network oil preparation and stabilization units project itself.

Experimental Studies of Fluid Flow Resistance in a Heat Exchanger Based on the Triply Periodic Minimal Surface

This study describes experimental data on 3D-printed compact heat exchangers. The heat exchanger is a prototype designed and manufactured additively using 3D printing in metal—AISI 316L steel. The device’s design is based on the triply periodic minimal surface (TPMS) geometry called gyroid, which can only be obtained by incremental manufacturing. This innovative heat exchange surface structure enables these devices to provide higher thermal performance while reducing their weight by up to 50%. Few publications describe thermal or flow tests in this type of device. They mainly concern computer simulations that have yet to be experimentally verified. The authors of this study conducted innovative flow tests to determine pressure drops during the flow of working fluids under conditions of variable temperature, mass flow rate and thermal load. Water was used as a heat transfer fluid during the tests. The range of parameters for the entire experiment was ṁ = 1–24 kg/h; Δp/Δl = 0.05–2 kPa; tcold = 20 °C; thot = 50 °C. Flow characteristics during the single-phase heat exchange process were determined, including Δp/Δl = f(ṁ), Δp/Δl = f(Re), Δp/Δl = f(f). The experimental data will be used to determine the relationships describing flow resistance in structures based on a triply periodic minimal surface, and it also enables one to specify the energy consumption of these devices and compare the profitability of their use to conventional designs, i.e., shell-and-tube or plate heat exchangers.

Approach to automating numerical calculation of the state of heat transfer processes in closed devices

In recent decades, changes in temperature and humidity have been used in many fields of technology: chemical technology, metallurgy, oil refining, mechanical engineering, biology and space research. One of the important issues in space exploration is the creation of closed facilities for the study of underwater processes. For large-scale systems, it is necessary to maintain a certain temperature and humidity regime that allows people inside the apparatus to live and work. The work examines heat exchange processes occurring in closed-loop hardware systems. It is assumed that the considered network is filled with refrigerant (liquid, gas, air, etc.) and consists of flow line, structural elements, volumes, valve, regulator and mixer - distributor. In such networks, systems of differential equations (ordinary and special derivatives), as well as an algorithm for automatic construction of mathematical models of heat transfer described by numerical schemes have been developed. A special methodology and algorithm have been developed for solving this type of problems. During the solution, two methods were used and the obtained results were compared. During the solution, obvious and non-obvious schemes were used, and the most stable scheme was chosen among them.

A REVIEW ON MOISTURE TRANSMISSION PROPERTIES THROUGH TEXTILE CLOTHING

Thermo-physiological comfort is one of the important aspects of clothing which enable to maintain a constant body temperature through the thermal balance of the heat generated by a persons body and to transfer it to the atmospheric environment. The thermo-physiological comfort of the clothing is mainly influenced by its moisture transmission ability and thermal resistance. This is due to the clothing comfort sensation is mainly determined by a balance process of moisture and heat exchange between the human body and the environment through the clothing system. The current paper aims to enhance the understanding of mechanism involved, various influencing parameters, current research regarding moisture transmission properties of fabric.

ANALYSIS OF THE BURNING ENVIRONMENT OF A BOILER UNIT DURING THE COMBUSTION OF NON-DESIGN COAL

This paper presents the results of a study of the temperature fields of combustion products of nondesign coal from the Karazhyra open pit in the combustion space of a boiler unit. The purpose of the work is to establish operating conditions for the combustion chamber of the KV-T-116.3-150 boiler unit, ensuring the absence of slagging of radiation heating surfaces, reliable circulation in the boiler and minimal heat loss when burning off-design fuel.Experimental studies were carried out to determine the temperature of combustion products of nondesign fuel, which made it possible to construct gas isotherms and evaluate the operation of the boiler combustion chamber. Laboratory tests were also carried out on samples of non-design fuel, and its qualitative composition was determined. Heat losses during combustion of non-design fuel have been determined. Data on the efficiency of the boiler installation with variable heating output were obtained, and the optimal operating mode of the boiler unit was established.The subject of this work is of particular interest due to the need to control and reduce the intensity of slagging and contamination of heating surfaces, reduce the level of harmful emissions, and intensify heat exchange processes in the flues of boiler plants when burning modern fuels.To examine the heat exchange processes in the boiler, the method of pyrometric study of the combustion space was used at different heat outputs.

КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ ПРОЦЕССОВ ТЕПЛООБМЕНА

The article considers mathematical models of calculation of thermal conductivity in a constant cross-section rod, change of a liquid temperature along the length of the pipe and calculation of two-dimensional temperature field of liquid under the flow in the pipe. The mathematical model of fluid flow in the tube is realized in the form of a program for computers. The results of modeling of processes of heat conduction and heat exchange are presented. The task of simulation of heat exchange processes using numerical method of solving the Cauchy problem in the form of finite differences is considered in detail. This approach makes it possible to calculate the value of the studied parameter at any point of the object under investigation. The numerical method involves obtaining a system of algebraic equations for unknown variables and an algorithm for solving these equations. The main dependencies describing the process of thermal conductivity in the rod of the final length are given. The results of the calculation of the temperature change by the length of the rod are presented in a graphical presentation. The main dependencies describing the process of temperature change of the liquid flowing through the pipe are given. The results of the calculation of temperature pressure change over the length of the pipe are presented in a graphical presentation. The problem statement and mathematical model of the process of flow of incompressible liquid in the pipe are considered in detail. On the basis of the developed mathematical model, a computer model, implemented in the form of a program for computers, was created. The results of calculation, using the method of running, of two-dimensional temperature field of liquid along the pipe length are presented. The temperature dependence of the liquid in the various nodal points of the pipe section along the length of the pipe is presented in a graphical form.

Experimental Investigation of a Regenerative Kalina Cycle for Electrical Power Generation Using Waste Heat

Kalina cycle is a thermodynamic power cycle uses any waste heat source (low temperature source) to generate electrical power or cooling. Many versions of Kalina cycle exist. In this paper a regenerative Kalina version is designed and constructed. The cycle consists of the following main components: heat recovery vapor generator (HRVG), separator, turbine, condenser, throttling valve, mixer (absorber), heat exchanger and pump. The heat exchanger is used to heat the working fluid coming from the pump before entering the HRVG by the hot saturated liquid (weak solution) coming from the separator. The cycle uses aqua ammonia mixture as the working fluid with different ammonia concentrations. The effect of many operating conditions on cycle performance is studied such as ammonia (NH3) mass fraction (range from 0.85-0.89), low pressure (range from 2-4 bar), and maximum pressure (range from 20-40 bar). The dryness fraction (DF) at separator entrance is kept at 0.3. The results show that the highest thermal efficiency obtained is 12.9% at Pmax=35 bar, Pmin=2 bar, and x=0.85. The highest value of the net power is 0.367 kW at x=0.89 at turbine inlet pressure of Pmax=20 bar. The highest value of exergy efficiency is 28.5% at Pmax=35 bar, Pmin=2 bar. It is noticed that the highest exergy destruction is in the heat recovery vapor generator (HRVG) which is about 48% due to high temperature heat exchange process and low mass flow rate. The exergy destruction is larger at Pmax=35 and x=0.89 than the exergy destruction at Pmax=20 bar and x=0.89.

INTEGRATION OF HIGH-TEMPERATURE SURFACE HEAT EXCHANGE

Despite the discrete nature of the interaction of droplets of sprayed liquid with a high-temperature surface, the inevitable formation of a liquid film leads to the fact that the main qualitative laws of the heat exchange that occurs in this case are characteristic of the known process of heat exchange during boiling. At the same time, the presence of extensive theoretical and experimental studies of “large-volume boiling” and the process of steam generation in channels does not allow us to establish the conditions of heat exchange during the thermal interaction of a dispersed liquid - water with different concentrations of surfactants with a high-temperature surface. We did not find any materials about this process in the scientific literature. With a number of features common to the above two cases of heat exchange (the presence of boiling crises, film and bubble modes, etc.), cooling a high-temperature surface with a droplet medium containing various concentrations of surfactants has significant distinctive features due to the hydrodynamics of the process, which is the subject of further study. To fully explore the above task, the following must be done: Develop a methodology for experimental study of local conditions of non-stationary heat exchange of sprayed water with different concentrations of surfactants. Develop and manufacture an experimental setup on which to conduct research on the effects of irrigation density, surface temperature, degree of liquid underheating, its speed and angle of impingement on the surface. Develop a mathematical model for calculations of heat flows, heat transfer coefficients, dynamics of hydraulic methods of liquid dispersion – water with different concentrations of surfactants, critical heat flows and surface temperatures in the transition region from film to bubble boiling as a function of determining factors. Establish the independent influence of the degree of non-stationarity of the process on the heat exchange conditions.

THE INFLUENCE OF INCLINATION ANGLE ON THE HEAT TRANSFER CHARACTERISTICS OF MINIATURE TWO-PHASE THERMOSYPHONS WITH NANOFLUIDS

At present, the issue of modern heat-loaded electronic devices cooling is becoming increasingly relevant, given the clear trend towards miniaturization. A potential solution is the use of highly efficient cooling systems based on the evaporation-condensation cycle, with nanofluids serving as the heat carriers. These nanofluids are colloidal dispersions of nanoparticles in a base fluid (distilled water). Miniature thermosyphons (gravity heat pipes) can serve as the main element in such systems. This work presents and analyzes the experimentally obtained main heat transfer characteristics of miniature thermosyphons with nanofluids, namely: maximum heat fluxes that the system can transfer, and minimum total thermal resistance. During the development and design of the system, there is not always complete information regarding the scenarios of electronic device usage and their spatial arrangement, which can significantly influence the operation modes of the thermosyphons. Therefore, considerable attention in the work is paid to spatial arrangement (inclination angle relative to the horizontal level). The geometric parameters of the investigated thermosyphons were as follows: total length 700 mm, internal diameter 5 mm, and the filling ratio varied by changing the length of the heating zone in the range of 0.44–1.66. The condensation zone length for all experiments was 200 mm. Water-based nanofluids with added carbon black DG-100 nanoparticles (mass concentration 0.3 %) were used as the heat carrier. A similar miniature thermosyphon with deaerated distilled water as the heat carrier was used for comparison. Special attention was paid to determining the effect of adding nanoparticles to the base heat carrier and studying the influence of the filling coefficient and inclination angle on the heat transfer characteristics of the system. A significant influence of the filling ratio (length of the heating zone) on the heat transfer capacity of the system was observed. An increase in maximum heat fluxes of up to 21 % was recorded with the addition of nanoparticles to the heat carrier, while the total thermal resistance of the miniature thermosyphons remained at the same level (no deterioration was observed). The optimal range of inclination angles was determined to be 40–70°, with a critical angle at 30°, which is observed for water-based thermosyphons as well. A dependence was proposed to calculate the maximum heat flux that the system can transfer with a similar to the studied miniature thermosyphon for the angle range of 20–60°, assuming that heat transfer characteristics for vertical placement are known. Existing potential mechanisms for intensifying heat exchange processes in thermosyphons with nanofluids are analyzed. Bibl. 27, Fig. 10.

On the quantitative assessment of the thermal effect of heat transfer

Due to the constant rise in the cost of energy resources, as well as the tightening of rules for enterprises on environmental indicators, a thorough analysis of the operation of not only heat engines, but also auxiliary power equipment, including heat exchangers, is necessary. One of the criteria for the perfection of thermal processes in a heat exchanger can be the value of the irretrievably lost quality of energy [2]. The objective of this article is to estimate the maximum transferred thermal power, with known available thermal powers of heat carriers, using various methods: 1. arithmetic, using the logarithmic mean value of the difference in heat-exchanging media, 2. graphical arithmetic, using hyperbolas of constant power of heat-exchanging media, 3. calculating the minimum value of the total entropy loss as a result of irreversible heat exchange processes from a hot heat carrier to a wall, through a wall and from a wall to a cold heat carrier. The listed methods were developed by the authors and do not contradict similar developments by domestic and foreign authors [1- 4].

Research on the Correlation between the Barrel Temperature and the Parameters of Interior Ballistic and Charge

Abstract Aiming at the problem that the barrel life of a large calibre artillery is obviously lower than the international advanced level, and the thermal erosion inside the barrel is serious, based on modern interior ballistic theory and heat transfer theory, a simulation of one-dimensional two-phase flow interior ballistic, heat exchange process between gas-solid two-phase flow and the barrel is carried out. The influence of maximum pressure in bore, charge, propellant explosion temperature, barrel structure and other parameters on the barrel temperature is obtained, and the correlation between the barrel temperature and parameters of interior ballistic and charge is analyzed, providing direction for the design of low-ablation interior ballistic and charge.

A numerical study of the effect of different geometrical parameters on the cooling processes in electrical transformer

Proper thermal control is one of the most important aspects that should be considered when utilizing electrical transformers. This research work offers a numerical analysis of the effect of changing the shape of transformer fins on the heat exchange process. Based on the results of CFD simulations, several types of fin shapes such as rectangular, triangular and wavy are discussed to describe the improvements of heat transfer. The study examines the shape of an electrical transformer, determining the optimal distance between fins, fin shapes, transformer shape, rib type, and rib number. The results are then applied to a special case, representing the best of all variables on the transformer. The study also considers the effect of increasing the surface area of the ribs on the fins, and the number of ribs used on the fins. The temperature gradient of a coil, oil, and transformer varies depending on the distance between fins, fin shape, rib type, and number of ribs. The coil temperature is 383 K when the fins are 7 cm apart, 381 K when the fins are 5 cm apart, and 381 K when the fins are 3cm apart. The temperature gradient also varies depending on the rib type, with triangular ribs increasing the surface area for heat energy transfer and reducing the temperature value. The oil temperature gradient varies depending on the fins, ribs type, and number of ribs. The heat transfer coefficient gradient of the transformer surface varies depending on the fins, ribs type, and number of ribs. The surface heat transfer coefficient reaches 1.5 W/m2. K when the fins are l shape, 1.6 W/m2. K when the fins are c shape, 1.7 W/m2. K when the fins are z shape, 1.4 W/m2. K when the ribs are rectangular, 1.6 W/m2. K when the ribs are triangular, and 1.4 W/m2. K when the ribs are 9 ribs.

GEOGRAPHICAL ANALYSIS OF THE FACTORS AFFECTING THERMAL COMFORT IN AL-MASHKHAB DISTRICT

The climate is one of the most important environmental factors that affect human comfort and health, as the human body responds to climatic elements involuntarily due to their effect on the heat exchange process between the human body and the thermal environment in which it lives. Several thermal comfort indicators were applied to determine the limits of thermal comfort in the study area (Ghom indicator and wind cooling indicator k), which depended on the most stable climate elements in the study area (temperature, relative humidity, and wind). As a result, the climatic seasons of the year were determined based on the cold winter months (December, January, and February). The spring season is represented by the months of (March and April), which are moderate, while the summer season represents The hot months (May, June, July, August, and September). The months (October and November) represent the fall season. The study concluded after comparing the results of the monthly distribution of climate indicators with the classification limits of human thermal comfort that the state of thermal extremism did not appear, represented by the great stress that threatens health during the months of the year, while the state of severe thermal discomfort appeared clearly, especially during the day of the summer months (severe hot discomfort) and the nights of the winter months (severe cold discomfort), so these two seasons are the least suitable for practicing most types of activities in open places, while the most suitable times for practicing various activities were represented by the spring and fall seasons, as the degree of influence of climate elements on the human feeling of comfort varied during the months of the year as in Tables (3, 5), and the study recommends the necessity of linking various human activities and events to human thermal comfort and linking vacations to the months of thermal discomfort.

Совершенствование работы скруббера для очистки выбросных газов с повышением эффективности за счет вторичного использования теплоты

The article is dedicated to the current problem of increasing energy efficiency by recycling heat emitted during the condensation of spent gaseous steam-water mixtures in various thermal plants. Special attention is paid to the application of contact heat exchangers withdrawing heat and moisture from escaping hot gases to be recycled in the production flow. Industrial facilities and enterprises of production synthetic fiber in particular are significant sources of emissions of anhydride, binary compounds of sulfur and nitrogen, including their solid micro-particles. Such emissions negatively affect the atmosphere, climate, and human health. Various types of gas purifying equipment are considered: i.e., scrubbers, DESP systems, and various types of dust collectors (mechanical, fabric, granular, etc.). A model has been provided to calculate the parameters of a scrubber designed to purify and recycle the heat waste of emission gases from various devices used by chemical fiber production enterprises. The model is based on the cell approach and considers the processes of heat and mass exchange between gaseous and liquid phases. Mathematical dependences describing heat and mass transfer processes in the scrubber are also provided, including recurrent matrix equations to analyze the kinetics of such processes. The author presents the methodology of model parameter calculation, including the determination of temperature, pressure, and moisture content in various locations of the device. The proposed methodology helps to determine both transition processes and the stationary state in the scrubber in question. Notably, the obtained calculations demonstrate the high efficiency of the device operation. The suggested calculation methodology can be implemented in any software designed for operations with matrices, which makes it a useful tool for engineering calculations and the optimization of systems of heat waste purification and recycling at industrial enterprises. The article is of interest to experts in the field of thermal energy.

Development of a combined drying plant for agricultural products

Abstract The paper presents the development materials for a combined drying unit for agricultural products with IR radiation, operating in a closed-loop mode. Due to the constant uniform movement along a closed loop, the entire mass of the product being dried is uniformly coated with a flow of drying agent and is subjected to intensive heat treatment. The superimposed effect of IR radiation in combination with convective heat exchange intensifies the process of heat and mass exchange and reduces the drying time.

Increase in the energy efficiency of the biogas production process through vibration activation of heat and mass exchange processes in the bioreactor

Increase in the energy efficiency of the biogas production process through vibration activation of heat and mass exchange processes in the bioreactor