Heat Exchange Processes Research Articles

Perfection of an Energy-Economic and Environmental Parameters of the Ground Source Heat Pump Systems with Preventing Freezing of the Soil around Ground Pipes

This article is devoted to the methods for perfection of energy, economic factors, environ-mental factors and work modes of the ground source heat pump systems with the account of climate conditions. The purpose of the work is to predict and prevent freezing of the soil during long term of exploitation of the low-power and high-power ground source heat pump systems for justifying rational conditions of implementation GSHP in Ukraine and South-East Regions of Europe. This goal is achieved by solving the following problems: determining the energy-economic and environmental factors based on considering the work modes of the ground source heat pumps; evaluation of the operating efficiency of ground source heat pump systems based on minimizing fuel consumption and green-house gas emissions; perfection of solutions enable implementation of ground source heat pumps friendly to the environment and justifying rational conditions of implementation the ground source heat pumps for residential sector. The important results of the work are the obtained and analyzed data on the influence of energy and economic factors both environmental criteria on the work modes and scheme-constructive solutions of ground source heat pumps. Modeling of heat exchange processes in the soil around the soil tube shows that in order to avoid freezing of the soil, the minimum permissible specific number of vertical tubes should be at least 0.12–0.15 pieces/m2 of heated area. The significance of the results consists in the possibility of using the results of numerical simulation for preventing freezing of the soil around ground pipes of the ground source heat pump systems.

Electric field simulation in the electrochemical machining of a thin-walled part cavity

The article is aimed at simulating an electric field in the interelectrode gap during the electrochemical machining of a thin-walled part cavity for aerospace equipment. The study involved simulating the process of electrochemical cavity machining at a constant voltage in a steady-state mode in the COMSOL Multiphysics environment. The simulation was carried out for the scheme of electrochemical machining with a movable cathode and vertical and horizontal feeding to the workpiece surface undergoing machining while maintaining a constant interelectrode gap. The following simulation conditions were adopted: 12Cr18Ni10Ti stainless steel as the material of the cathode tube; AlMg6 aluminum alloy as the material of the thin-walled part; NaNO3 solution as the electrolyte. When simulating the electric field in the interelectrode gap, the heat exchange process was taken into account. The simulation of the electric field in the electrochemical cavity machining of a thin-walled part yielded a macro that allows the process simulation to be adapted to different input process conditions. As a result of the simulation, the following distribution patterns were obtained: current density in the cathode, potentials, electric field in the interelectrode gap and adjacent area, and process temperature of electrochemical machining. The simulation results show that the electric field lines are directed toward the cathode from the workpiece periphery. This means that anodic dissolution of material occurs in a given region, which characterizes the law concerning the distribution of potentials in an electrochemical cell. The temperature distribution pattern obtained in the simulation revealed that a temperature increase in the machining zone is insignificant. An increase in electrolyte temperature is shown to result in a proportional increase in wall temperature. Thus, the conducted study provides a theoretical insight into the examined process.

Перспективные конструкторские решения для сушки жидких пищевых систем

An assessment of promising alternative design solutions for drying liquid food systems is given. Drying technology and techniques for removing moisture from liquid materials in a dispersed state have found widespread use in the food industry. The almost instantaneous drying of the sprayed particles in the coolant flow causes the formation of a developed phase interaction surface and acceleration of heat and mass transfer procedures, as well as the exclusion of overheating of the material due to intensive volumetric evaporation of moisture. A number of dryer designs have been developed to eliminate disadvantages (such as the large size of the dryers and their relatively high energy consumption and complexity of structural elements) or to reduce their impact on the course of the dehydration operation. The design specifics of devices for dewatering in the atomized state are due to the methods of supplying thermal energy, technological conditions and limitations, parameters of the dried product and the final powder substance, as well as its specific yield, peculiarities of the spraying operation, etc. The justification of the method of spray drying of liquid food material and the constructive use of the apparatus should be based on the study of a set of parameters and characteristics of the dehydration object, as well as on the construction and solution of a mathematical model of heat and mass transfer and exchange processes at the boundary of the phase section, as well as their mechanism in the development of a rational method of moisture removal to ensure the quality of finished products and energy- and resource saving. The proposed plant designs are recommended for organizing the drying process of liquid products, in particular for drying broths in fish production technologies.

The Thermophysical Aspects of the Transformation of Porous Structures in Versatile Nanostructured Materials

The technology of obtaining porous nanostructures is based on ecological organosilicon materials and their uses in some spheres of human life, for example, for medical preparations, for thermal insulation of building structures and industrial equipment, and for cleaning. The purpose of this study was to establish correlations between various experimental parameters (shear stress, speed pulsations, temperature, viscosity, and processing time) and the rheological characteristics of suspensions obtained by the method of liquid-phase dispersion; it was a study of hydrodynamic effects and the processes of heat and mass exchange in liquid systems during the liquid-phase dispersion of hydrogel monoliths by means of discrete-pulse activation in a special rotary apparatus. The dehydration of hydrogels was carried out by two methods: convective drying in a layer and spraying in the coolant flow. Experiments have shown that the key parameters for obtaining stable homogeneous suspensions are a synergistic combination of concentration factors and processing time. To obtain adsorbents in the form of pastes with specified adsorption properties and a monolith size of up to 300 μm, the optimal parameters were a hydrogel concentration of 70% and a processing time in the double-recirculation mode. Xerogels obtained by convective drying are a polydisperse mixture of strong monoliths and fragile aggregates. In contrast, xerogel monoliths obtained by spray drying show great homogeneity in terms of dispersion and strength characteristics. The rheological parameters of the hydrogel dispersions, which depend on the concentration and hydrodynamic treatment modes, are the dominant factors affecting the moisture extraction during drying. This study marks the first investigation into the resilience of porous organosilicon structures against the influence of intense turbulence fields and mechanical stresses experienced within the rotor apparatus during suspension production.

Numerical study of CO2 trans-critical process inside micromodel based porous structures under supercritical pressures

Understanding the flow, heat transfer, and trans-critical process of carbon dioxide in porous media is crucial for various applications, including CO2 sequestration, soil remediation and oil and gas recovery, due to its unique physical properties in the critical region. In this study, a porous media model on a microfluidic chip structure was simulated to emphasize the heat transfer and trans-critical process of CO2 under supercritical pressure in porous media. The study aims to observe the behaviors of CO2 during its transition from subcritical to supercritical temperature under supercritical pressure. The main objective is to observe the temperature distribution and pressure change of CO2 in a porous media model under the influence of bottom heating. At the same time, we observe the changes in the position of the critical temperature point of CO2 in porous media and analyze its heat exchange process in porous media. After the flow reaches a steady state, the temperature span near the grains is 1.6 K, and the pressure drop per unit length is 1480.3 Pa/mm. As the flow time progresses, the critical temperature line migrates from outlet region to inlet region, the range of sCO2 narrows from 81.7 % to 84.7 % in the porous media region. Finally, the influence of different working conditions on the trans-critical region is studied. It is hoped that this study will contribute to the understanding of the trans-critical process of CO2 in porous media.

Modified efficiency-NTU method (m-ε-NTU) for calculating air coolers in dehumidifying or frost conditions. Part IV

In the fourth part of the article, the algorithm for applying the newly developed the m-ε-NTU method for calculating air coolers in dehumidifying or frost conditions is described step by step, and its comparison with the method of segmented division of the heat exchanger is also given. This comparison showed good convergence of the calculation results with a multiple reduction in their execution time. The value of the deviation of the calculated value of thermal power calculated using the newly developed method from the same value calculated using the method of segmented division averaged 3.23% modulo and does not exceed 4.5% modulo. When the heat exchanger is divided into 40 segments, the execution time of the calculation programs increases approximately 18 times compared to using the newly developed method, which can be called a significant advantage of the latter. Considering the above, the newly developed method can be widely used for the selection of air coolers, their verification and design calculations.
 BACKGROUND: A universal method for calculating air coolers that is applicable to design and verification calculations is necessary. The method should consider the effect of dehumidification and frosting on the heat exchange process and allow the quick performance of many calculations to simulate the operation of refrigeration and air conditioning systems without significant loss of accuracy. However, this example of calculation method that addresses all the above-mentioned criteria is unavailable in the domestic and foreign literature.
 AIM: This study develops a universal method for calculating air coolers that is applicable to design and verification calculations. This method considers the influence of dehumidification and frosting on the heat exchange process and allows the quick performance of many calculations to simulate the operation of refrigeration and air conditioning systems without significant loss of accuracy.
 MATERIALS: The developed method for calculating air coolers is based on the classical approach of ε-NTU (efficiency– the number of heat transfer units) and is its adaptation, allowing consideration of the influence of dehumidification and frosting on the heat exchange process and performing the calculation (including the combined operating mode of the air cooler) without dividing the heat exchanger into separate segments. The estimation of the error of calculations performed using the developed method was conducted by comparing the calculated values of the thermal power of the device with those using the segmented division method for various operating modes (including combined).
 RESULTS: Comparison with the segmented division method of the heat exchanger showed good convergence of the calculation results with multiple reductions in execution time. The deviation value of the calculated value of the thermal power computed using the developed method from that using the segmented division method averaged 3.23% modulo and did not exceed 4.5% modulo. When the heat exchanger was divided into 40 segments, the execution time of the calculation programs increased approximately 18 times compared to using the developed method, which can be called a significant advantage of the latter.
 CONCLUSION: The division of the heat exchanger into segments for calculation does not result in a significant increase in accuracy compared with the new method. Thus, the developed m-ε-NTU method can be widely used for the selection of air coolers, their verification, and design calculations.

Tube Blockage Solutions for Industrial Heat Exchangers

This study investigates the root causes of blockages in heat exchanger tubes and proposes effective mitigation strategies. Industrial heat exchangers face recurrent challenges from tube blockages, impairing operational efficiency. Through a combination of experimental analysis, computational modeling, and data-driven approaches, the research identifies the role of contaminants in causing pressure drops and outlines targeted maintenance protocols. Findings underscore the significance of proactive measures in optimizing heat exchange processes, offering valuable insights for enhancing system performance across diverse industrial applications. Highlights: Tube blockages disrupt production efficiency. Pressure drop due to blockages affects system performance. Analysis needed for prevention measures. Keywords: Production Process, Blockage, Exchangere

The influence of geometry on the heat exchange potential of embedded planar retaining walls with seasonally-balanced thermal load

A number of operational cases exist where embedded retaining walls, used in the construction of underground spaces such as basements and shallow tunnels, have also been utilised as ground-heat exchangers in shallow geothermal energy systems. These are complex structures in terms of their geometry, the surrounding temperature field and boundary conditions, and there are currently no methods to assess their heat exchange capacity in a simple and expedient manner. This contribution uses the finite element method to validate the use of the method in predicting heat flow for this application and then, to assess the influence of wall and excavation geometry in the heat exchange process. The influence of the soil and wall thermal conductivity is shown to be quasi-linear with the latter showing the greatest influence on peak heat exchange. The work identifies a geometric parameter - the ratio of excavation depth to total wall panel depth, H/L which in combination with the wall thickness (D), provide a consistent and simple means by which the heat exchange potential can be estimated, for a given set of wall and soil thermal properties and boundary conditions.

Design and Simulation of a Multi-Channel Biomass Hot Air Furnace with an Intelligent Temperature Control System

Timely and effective drying of agricultural products is crucial for ensuring the quality and yield of grains. Biomass drying enhances energy utilization and reduces energy pressure. To this end, a novel multi-channel circulating biomass hot air furnace was designed to provide precise control of the heat source for grain drying, thereby improving the efficiency and quality of the drying process. The combustion process utilizes a multi-channel combined air supply to ensure complete combustion of biomass pellet fuel. During the heat exchange process, heat exchange plates isolate hot and cold areas, discharging combustion exhaust, while ensuring a pure air output. Using rapeseed as the drying subject, a temperature controller based on adaptive fuzzy PID was designed, targeting the biomass hot air furnace’s heat exchange system for modeling and verifying the model with the step response method. Model simulations were conducted in Matlab’s Simulink module using both adaptive fuzzy PID and traditional PID controllers, for a given signal. The settling times for the conventional PID and fuzzy PID were 445 s and 364 s, respectively, with overshoots of 20.1% and 6.3%, showing that the fuzzy PID controller performed better in terms of control performance. The validation tests showed that both control methods could maintain the temperature within ±5 °C. Compared to traditional PID control, the adaptive fuzzy PID control achieved a precision of ±3 °C. At the target temperature of 90 °C, the error was reduced to 3.7%, with a stabilization time of 1014 s. The use of fuzzy PID control exhibited better dynamic response characteristics, meeting the drying needs of rapeseed. This study provides a theoretical basis for the structural design and control system design of biomass hot air furnaces.

Study Outlines Challenges of Repurposing Oil and Gas Wells for Geothermal Applications

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 215751, “Challenges for Repurposing Oil and Gas Wells for Geothermal Applications,” by Livio Santos, SPE, and Arash Dahi Taleghani, SPE, The Pennsylvania State University. The paper has not been peer reviewed. _ This work provides insights into the technical and economic viability of repurposing oil and gas wells for geothermal energy production for direct heating. The potential benefits—especially for areas that are highly dependent on fossil fuels for heating—and challenges of this approach are assessed, while technical, market, and policy barriers for future development are identified. Repurposing oil and gas wells for geothermal energy requires a multidisciplinary approach that involves expertise in geology, engineering, and regulatory affairs. Introduction Repurposing abandoned wells for power generation in geothermal energy projects can present challenges because of the low temperatures associated with these wells. The low temperature gradients and thermal energy available in such wells have been found to limit overall power-generation potential. The same low-temperature geothermal resources can still be used effectively, however, for community heating applications. Community heating systems have lower temperature requirements compared with those necessary for power generation and are compatible with available heat from low-temperature geothermal sources. In particular, closed-loop geothermal systems, specifically designed for community heating, offer several advantageous features. The closed-loop design ensures that the fluid remains contained within the system. These systems are environmentally compatible because they do not extract or discharge water from natural sources. Additionally, with better control over the working fluid and heat-exchange process, closed-loop systems deliver optimized system performance, energy efficiency, and cost savings. They also require less maintenance and feature lower operational risks because of the closed circuit. Closed-loop systems offer fluid-selection flexibility and streamlined regulatory compliance. Not all abandoned wells are suitable for repurposing, however. Thorough feasibility assessments and well-integrity evaluations are necessary to ensure that the abandoned well is structurally sound, has the appropriate depth and geological characteristics, and can extract geothermal heat effectively. The condition of the well casing, cementing, and any potential wellbore damage also must be evaluated. An economic analysis is performed to assess the financial viability and cost-effectiveness of the geothermal community heating system. Finally, an environmental impact assessment evaluates the environmental consequences of the geothermal community heating system.

The Robin boundary condition for modelling heat transfer

The heat exchange between a rigid body and a fluid is usually modelled by the Robin boundary condition saying that the heat flux through the interface is proportional to the difference between their temperatures. Such interface law describes only the unilateral heat exchange. The goal of this paper is to compare the Robin boundary condition starting with the transmission condition (the temperature and the flux continuity) using rigorous mathematical analysis. Our main results are the following. We first show that a generalized version of the Robin boundary condition can be justified. Second, we prove that replacing the generalized by the standard Robin condition can be justified for high convection velocity if the conductivity of the surrounding liquid is much lower than that of the body. On the other hand, if the fluid conducts much better than the body, then the effective boundary condition is shown not to be the Robin one, but it involves second-order derivatives. We strongly believe that those findings bring new insights to the physics of the heat exchange processes and, thus, could prove useful in engineering practice.

Heat transfer characteristics of the air-oil heat exchanger with spiral tube

The cooling problem of hot-end components has become an important factor restricting the aero-engine performance, life and reliability. In order to improve the cooling quality of the cooling air, the supercritical aviation kerosene was used as a heat sink to cool the cooling air in a spiral heat exchanger. The flow and heat transfer process of the air-oil heat exchanger with spiral tube were numerically simulated using Fluent software. The flow and heat transfer situation of air and aviation kerosene were analyzed in detail. The optimized spiral heat exchanger with the diaphragm was presented to enhance the heat transfer capacity of the air side. It is found that the heat transfer performance of the air-oil heat exchanger is greatly enhanced by the spiral tube due to the secondary flow effect. With the increase in the turning angle of the spiral tube, the effect of the secondary flow for the heat transfer enhancement is strengthened. The PEC index of the spiral heat exchanger increases with the increase in the air flow rate. The spiral heat exchanger with the diaphragm can effectively improve the heat transfer performance of the heat exchanger, and increase the PEC index of the air side by more than 20%.

The influence of the probiotic “Bioseven” on indicators of survival and growth of calves in the early postnatal period

Dairy cattle breeding is one of the promising areas of agriculture. With a systematic approach and modern technologies, it is a highly profitable agrarian business that is dynamically developing. According to experts, the competitiveness and profitability of the industry can be increased due to the use of natural feed additives and preparations to obtain ecologically safe products for humans. Among them, preparations of microbiological origin are increasingly used, in particular, probiotics, which contain living microorganisms useful for the macroorganism. These drugs are used for prophylactic or therapeutic purposes. It is known that most microorganisms inhabiting the intestines are safe and do not cause diseases, but there is a constant competition between bacteria of different species for space and nutrients. The inconsistency of the microclimate parameters in the calf pens had a direct negative effect on the calf's body, especially in the early postnatal period. In particular, the deviation from the temperature balance, increased air humidity, and the presence of drafts caused a violation of the heat exchange processes of the calves' body with hypothermia and overheating of the body, and, as a result, provoked the frequent occurrence of respiratory diseases. In addition, increased air humidity and high microbial pollution caused the emergence of diseases with functional disorders in the digestive tract due to an imbalance of normal flora and increased activity of the development of transit microbes from the external environment, which negatively affected the homeostasis of the calves' body, weakened the natural resistance of calves, their growth, preservation and often led to the death of animals. Oral use of the probiotic “Bioseven” in a dose of 5.0 g (1.5·109 CFU/cm3) based on 10 kg of live weight ensured the complete preservation of the herd of young calves, accelerated their growth energy, as evidenced by exterior indicators of the animals of the experimental group against the control and probable (P < 0.05) average daily gains in live weight – 1.236 ± 0.37 kg/day versus 1.002 ± 0.41 kg/day in the control group of calves. In further studies, we used a dose of the probiotic “Bioseven” – 5.0 g (1.5·109 CFU/cm3) based on 10 kg of live weight, as the optimal dose of the experimental drug, established by the results of research. Comparative results of studies of growth indicators in the calves of the experimental group showed a significant advantage in the actual probable (Р < 0.01) increase in their live weight during the experimental period, which exceeded the similar indicators of the control by 23.6 %. The results of studies of indicators of average daily live weight gain were significantly (Р < 0.05) higher than those of control calves by 28.5 % (Р < 0.01), which testified to the effectiveness of the use of the probiotic “Bioseven” in young calves. Taking into account the obtained results, it becomes clear that the components of the probiotic drug “Bioseven” have a positive effect on the formation of cicatricial digestion in calves.

Mathematical modeling and prediction of values of partial indicators of heat-exchange processes at underwater wet welding

At computer modeling of heat-exchange processes there arises a necessity of parametric forecasting of values of partial indicators of multifactor systems of underwater wet welding. Ensuring the reliability of such a prediction makes it possible to use the obtained models for engineering calculations in the design of technological welding processes. On the example of experimental data on the estimation of gas formation in the process of arc combustion the methodology – approved in shipbuilding production – is proposed. Mathematical dependences providing the minimum error of estimation at changing the values of influencing parameters, are obtained. The formation of gas bubbles significantly affects the heat-exchange processes in underwater welding, which determines the cooling rate of the welded joint and affects the formation of hardening structures.

Experimental study on the effect of inverted aperture plate temperature on frosting characteristics under rising flow considering edge effect

To reduce the negative impact of frost formation on cold surfaces in low-temperature environments, metal wire mesh can be set in the air flow direction from the cold surface to reduce air humidity. To quantitatively determine the effectiveness of dehumidification after passing through a metal wire, the frosting process needs to be studied. To analyze the mechanism of frost formation under the horizontal wire mesh surface, the wire mesh was simplified as a flat plate with holes, or aperture plate, with plate temperature varying at a range of -15.0 °C to -5.0 °C. The results show that, as the plate temperature decreases, the droplet condensation and growth and droplet solidification stages gradually decrease, the average frost layer thickness and frost layer growth rate rise, and overall frost layer surface roughness increases. For a frosting duration of 1,800 s, compared to -5.0 °C, the average frost layer thickness from -7.5 °C to -15.0 °C inside the hole increased by 56.68 % and 156.41 %, while the plate edge region away from the hole increased by 40.76 % and 169.92 %, respectively. The reverse melting frequency gap between the inside hole region and the plate edge region away from the hole increases with the decreasing aperture plate temperature. At -15.0 °C, the reverse melting frequency inside the hole is 5.00 × 10−3 Hz lower than in the region of the plate edge away from the hole. The results of this article are beneficial for understanding the frosting process of wire mesh or perforated-fin heat exchanger.

Theoretical studies of the expedient radius of thin pipe insulation

Decentralized ventilation systems with exhaust heat recovery are an energy-efficient solution for organizing and maintaining comfortable microclimate parameters in apartments and individual residential buildings. Such supply and exhaust systems do not require additional space for the distribution network of air ducts and significant intervention in the interior of the premises. One such device is the Vents TwinFresh regenerative installation. Twin Fresh install in the structure of the outer wall. The task of follow-up is to increase the efficiency of its work. Studies of heat exchange processes in the thin channels of the heat regenerator carried out. Channels with different thermophysical properties are studied. Experimental uncertainty decreases with better thermal insulation of the investigational stand. It is confirmed by the decrease in overheating and the heat transfer coefficient of the external surface thermal insulation when its thickness increases. Overcoming the critical diameter of the insulation of the experimental installation allows to minimize the measurement error, which takes into account the influence of heat exchange processes of the outer surface of the insulation with the environment. It is necessary to determine not the critical but the expedient diameter of the insulation. When using the appropriate thickness of thermal insulation, the temperatures on the inner and outer surfaces of the pipe have practically the same value. Thus, it is possible to take temperature readings of thin tubes from the outside, not from the inside, with the same accuracy. Accordingly, the design of the test stands for experimental research is simplified. The scope of application of the appropriate diameter of thermal insulation is not limited only to studies of heat transfer. This concept can used in any systems, equipment, and techniques that require insulating materials.

Математичні моделі локального нагрівання елементів електронних пристроїв

Linear and non-linear mathematical models for the determination of the temperature field, and subsequently for the analysis of temperature regimes in isotropic spatial heat-active media sub-jected to internal and external local heat load, have been developed. In the case of nonlinear boundary-value problems, the Kirchhoff transformation was applied, using which the original nonlinear heat conduction equations and nonlinear boundary conditions were linearized, and as a result, linearized second-order differential equations with partial derivatives and a discontinu-ous right-hand side and partially linearized boundary conditions were obtained. For the final linearization of the partially linearized differential equation and boundary conditions, the ap-proximation of the temperature according to one of the spatial coordinates on the boundary sur-faces of the inclusion was performed by piecewise constant functions. To solve linear bounda-ry-value problems, as well as obtained linearized boundary-value problems with respect to the Kirchhoff transformation, the Henkel integral transformation method was used, as a result of which analytical solutions of these problems were obtained. For a heat-sensitive environment, as an example, a linear dependence of the coefficient of thermal conductivity of the structural material of the structure on temperature, which is often used in many practical problems, was chosen. As a result, analytical relations for determining the temperature distribution in this envi-ronment were obtained. Numerical analysis of temperature behavior as a function of spatial co-ordinates for given values of geometric and thermophysical parameters was performed. The in-fluence of the power of internal heat sources and environmental materials on the temperature distribution was studied. To determine the numerical values of the temperature in the given structure, as well as to analyze the heat exchange processes in the middle of these structures, caused by the internal and external heat load, software tools were developed, using which a ge-ometric image of the temperature distribution depending on the spatial coordinates was made.

ОБОСНОВАНИЕ ПРИМЕНЕНИЯ КОМПОЗИТНЫХ БАЛЛОНОВ В КОММУНАЛЬНО-БЫТОВОМ ОБЕСПЕЧЕНИИ ПОТРЕБИТЕЛЕЙ ГАЗОМ

The introduction of new advanced materials into gas supply practice leads to the creation of new products with improved qualities. For domestic use, along with traditional metal cylinders for liquefied petroleum gas, composite cylinders have recently been offered. Possessing a number of undeniable advantages, composite cylinders annually increase their share of presence in the field of bottled gas supply. However, the transition from traditional metal cylinders for the consumer should not be accompanied by a banal change of vessels, but requires a comprehensive, competent approach with justification for decisions made on the formation of a gas supply system for the consumer based on cylinders made of composite materials. Using the basic principles characterizing changes in the states of gas mixtures included in liquefied hydrocarbon gas, the characteristics of heat exchange, the vessels under study, the principles of operation of gas-using equipment for the consumer, parameters are determined that form the basis for the competent use of composite cylinders for the consumer using liquefied gases of various brands. As a result of the research, the mass of gas for filling cylinders was determined, taking into account the seasonality of operation and brands recommended for domestic consumption, the process of heat exchange between the cylinder and the environment was studied, taking into account its operating mode and the uneven generation of the vapor phase in the daily cycle of operation to ensure food preparation and hot water supply to consumers, the optimal periods of continuous operation of an individual cylinder installation with different capacities of a sin-gle composite cylinder and the number of cylinder replacements in the annual operating cycle were determined.

Experimental correlation of natural convection in low Rayleigh atmospheres for vertical plates and comparison between CFD and lumped parameter analysis

This paper offers a comprehensive exploration of thermal analysis for space systems operating in low Rayleigh atmospheres, with a primary focus on enhancing the accuracy and reliability of convective heat transfer modeling. The study centers around an analysis of a vertical heated plate experiment, where a lumped parameter model is employed to encompass conductive, radiative, and convective heat transfer mechanisms. To advance the accuracy of convective heat transfer coefficient calculations, this paper introduces a novel approach involving the utilization of Nusselt number correlations. These correlations are developed through an analytical solution derived from the Navier-Stokes equations, tailored specifically for the internal natural convection problem. This approach treats convection as a heat exchange process between the heated plate and the surrounding air, thereby improving the precision of modeling internal convection within a lumped parameter framework. A specific correlation (González-Bárcena et al.) is obtained for the proposed problem, derived from experimental tests conducted in a thermal vacuum chamber, under varying pressure conditions to control the Rayleigh number. Additionally, the findings are validated using Computational Fluid Dynamics (CFD) tools to calculate the velocity and temperature fields within the cavity. The González-Bárcena et al. correlation significantly enhances temperature predictions, demonstrating an improvement of up to 10∘C when compared to conventional literature correlations. The methodology presented in this paper holds promise for extension to more complex experiments in low Rayleigh atmospheres, including those conducted in the Earth's stratosphere or on the Martian surface, thereby contributing to the advancement of thermal analysis in challenging space environments.

Impact of inlet steam state on ejector internal flow and performance considering non-equilibrium condensation

Most of the numerical studies adopted dry gas model to predict transonic and supersonic flow in steam ejectors, but it cannot accurately reflect flow characteristics in ejectors, since the condensation and evaporation of wet steam is ignored. The current work develops and validates a CFD model describing spontaneous condensation to simulate complicated flow behaviors and phase transition inside an ejector, and illustrates the impact of initial state of primary fluid including wet, saturated and superheated state on flow characteristics, mass and heat exchange and ejector performance. It is found that the initial steam wetness obviously impacts the average liquid fraction in the ejector. Both the superheated and wet initial primary steam suppress the process of mass and heat exchange during nucleation, and the position and intensity of nucleation are influenced by the inlet steam state. Compared with the case of dry saturated inlet steam, the superheated inlet steam improves entrainment ratio by 3.7%, and decreases compression ratio by 2.5%.