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Protrusions can be used to improve the transport processes involved, but the causes of the phenomena are still incompletely understood. Computational fluid dynamics analyses are performed under different sets of circumstances to gain insights into the physics of heat and mass transfer processes in a protruded millisecond microchannel reactor, wherein a steam reforming reaction is proceeding and protrusions are used to improve the transport processes involved. Recommendations are made on how to optimize design for better reactor performance. Particular emphasis is placed on delineating the role of methanol-air equivalence ratio and channel length in reactor performance. The results indicate that the equivalence ratio and channel length must be adjusted as needed to minimize pressure drops and maximize production of hydrogen. Necessary adjustments to the equivalence ratio of methanol to air can be made to control the maximum reactor temperature within certain needed limits. The short-channel design may be preferred over the long-channel design in order to simultaneously achieve low pressure drops and sufficiently high conversions in the reactor. Expectable compromises have to be made between hydrogen productivity and pressure drop.

To study the problem of predicting and preventing high-temperature heat damage in deep mining of mines. The heat exchange and mass exchange algorithms of the ventilation network parting wind and surrounding rock are applied, and the model of the heat exchange coefficient of the wind flow in the drenching tunnel is adopted. TF1M3D simulation platform is developed by the College of Safety Science and Engineering of Liaoning Technical University. It is a dynamic disaster simulation software that visually and dynamically reflects the disaster spread and evolution in the ventilation system during the occurrence of major disasters in mines. Based on the theory of mass-energy active wind network, TF1M3D simulation platform can solve the problems of heat and humidity exchange, heat and mass transfer numerical calculation and so on.@Combined with the engineering example of Daqiang Mine, the algorithm is incorporated into the mine network domain system, and TF1M3D is used on the MATLAB platform to simulate and solve the temperature of the wind flow of the whole mine network domain system, and predict the temperature of the 0306 working face of Daqiang Coal Mine and put forward the simulation program of refrigeration cooling. The simulation results show that the maximum temperature of the future 3106 working face of Daqiang coal mine reaches 34.6°C, and the heat damage problem is serious. In the adopted cooling program, two refrigeration units are preferred to four refrigeration units, and the effective temperature control range of the two 250 kW refrigeration units is from 25 to 305 m, while the cooling meets the temperature of the working face airflow below 30°C. The results show that the method can accurately predict the temperature of the wind flow after cooling and the location of the cooling source, which provides a basis for the scientific development of the cooling program. [ABSTRACT FROM AUTHOR]

A nanofluid is a solution of nanoparticles with diameters fewer than 100 nanometers suspended in a base fluid such as water, ethylene glycol, or oil. In the nanofluid, these nanoparticles are suspended. The goal of this research is to look at the functioning of a twin-pipe heat exchanger that uses counter flow arrangements and two different nanofluids as cooling fluids. Alkaline water is a basic fluid made up of silicon carbide (SiC) and carbon nanotubes (CNT). The goal of this research was to see how different compositions of SiC and CNT nanoparticles dispersed in water affected the heat transfer capacities of a twin pipe heat exchanger developed with a counterflow arrangement. The flow rate of the nanofluid and the particle volume concentration of alkaline water were (0.02) and (0.04), respectively. Fluids with constant intake temperatures of 60°C for water and 30°C for nanofluid flow at the same input velocity via a heat exchanger. Both fluids are traveling at the same rate. According to the findings, nanofluid absorbs more heat than water at a range of flow speeds. Because of the improved thermal properties of nanoscale fluids, this results in increased thermal efficiency in heat exchangers. [ABSTRACT FROM AUTHOR]

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This paper is devoted to improve the design solution of combined thermo-photovoltaic systems which works in concentrated solar radiation. The main problem is ensuring the efficient heat removing from the photoreceiving surface of such systems and transferring this heat energy to liquid heat carrier. In case of using concentrated solar radiation with high density of energy onto the photoreceiving surface the problem of intensifying the heat exchange processes is critical for ensuring the efficient and long-term work of combined thermo-photovoltaic systems. Based on the analysis of thermal processes, the design of a heat exchange unit for a combined photovoltaic plant is proposed. The main design feature of proposed solution is microchannels made on the back plate of photoreceiving surface. It is shown that this design creates a transient regime of coolant flow, which allows efficient cooling of solar cells under conditions of concentrated solar radiation and potentially will allow to receive record values of heat exchange coefficient between the coolant and the upper plate of the radiator. An analysis technique using criterial hydrodynamic equations and numerical modeling were used; the results obtained in both cases are in good agreement. The efficiency, thermal and electrical characteristics of a combined photovoltaic system with solar radiation concentration have been assessed. Preliminary estimations have been made for the specific parameters of installed energy characteristics of a heat-electric power plant, which under AM1 conditions and 400 times the concentration of solar radiation for solar cells with an efficiency of 30 % have the following values: electrical power 650 W, thermal power 2370 W, total installed net power 3020 W, overall efficiency 87 % which are significantly higher than parameters achieved for existing solar power plants. [ABSTRACT FROM AUTHOR]

Natural gas is transported from production areas using high-pressure pipelines to pass through pressure reducing stations and then to the consumer. When temperatures drop, the problem of freezing of natural gas and ice appears. To protect against this phenomenon, we use a water bath to improve the temperature of the gas before reducing its pressure. One of the essential elements in the design of a low thermal efficiency water bath heater is the gas coil that runs inside the heater. In this study, the analysis of heat transfers and gas flow velocity inside the corrugated coil was performed with varying wave amplitude (10 mm, 15 mm, and 20 mm). The three-dimensional unsteady Reynolds-Navier-Stokes equations are solved using both the realizable k-ε turbulent model and the finite volume method to obtain the flow field. The results of this study showed that using corrugated coils with a larger capacity leads to an increase in the Nusselt number and friction factor, respectively, by about 6.57% and 114%. In general, the heat exchange inside the corrugated twisted gas coil can be enhanced by increasing the wave amplitude. [ABSTRACT FROM AUTHOR]

In this research, a dual heat source heat pump evaporator (AWSHP) with low-temperature hot water and air energy as the heat source is presented for the frosting problem of an air-source heat pump (ASHP) in low-temperature operating conditions. The critical frost region of the AWSHP system was also mapped using air temperature and water spray temperature as variables. The heat transfer characteristics as well as the anti-frost performance of AWSHP under different operating conditions were analyzed through experiments and simulations. According to the study's findings, the AWSHP system's refrigerant evaporation temperature was higher at the same ambient temperature than that of the ASHP. With AWSHP spray water volume of 8L/min and heat pump condenser circulating water volume of 15L/min, the average refrigerant heat exchanger and COP of AWSHP increased by 14.8% and 11.1%, respectively, compared with the ASHP system. At the same time, the AWSHP anti-frost operation strategy is proposed for low-temperature operating conditions. When the water spray volume was adjusted to 0.25 and 1.75 m³/h, respectively, under varying hourly meteorological conditions, the frost-free operation time was 61.21% and 89.24%, respectively. This was an improvement of 18.17% and 46.20%, respectively, compared to the ASHP. [ABSTRACT FROM AUTHOR]

The issue of creating a criteria base for the Hartmann–Sprenger pipe workflow based on a closed mathematical model is considered. On the basis of a closed mathematical model, the main parameters affecting the increase in the total temperature of the gas at the end of the dead-end cavity above the deceleration temperature of the incoming flow are recorded. Parameters with the same dimension are combined into one group so that only one dimensionless complex is obtained for all these quantities. Finding dimensionless complexes based on the modeling theory allowed us to determine the criteria base of the Hartmann–Sprenger pipe workflow.

Wetted wires are a unique column internal with several advantages compared to spray and packed columns. These include near-perfect liquid distribution, extremely low pressure drops, and better heat or mass transfer due to droplet circulation. Currently, wetted-wire columns remain within the laboratory prototyping stage. The primary goal of this review is to present the current research on wetted-wire columns and to highlight the gaps that impede scale-up and commercialization. Initially, wetted-wire columns were proposed as an alternative to spray towers. However, wetted-wire columns occupy a space in between spray towers and packed columns. Therefore, wetted-wire columns should also be analyzed more like packed columns to increase the speed of technological translation. Wetted-wire column literature is presented by defining features (wire diameter, nozzle diameter, pitch, and material) and by performance indicators (operating range, pressure drop, hold-up, and separation efficiency). In addition, adjacent literature on wire-like structures is discussed. [ABSTRACT FROM AUTHOR]

Heat exchangers make it possible to utilize energy efficiently, reducing the cost of energy production or consumption. For example, they can be used to improve the efficiency of gas turbines. Improving the efficiency of a heat exchanger directly affects the efficiency of the device for which it is used. One of the most effective ways to intensify heat exchange in a heat exchanger without a significant increase in mass-dimensional characteristics and changes in the input parameters of the flows is the introduction of turbulators into the heat exchangers. This article investigates the increase in efficiency of heat exchanger apparatuses by introducing turbulent lattice structures manufactured with the use of additive technologies into their design. The study is carried out by numerical modeling of the heat transfer process for two sections of the heat exchanger: with and without the lattice structure inside. It was found that lattice structures intensify the heat exchange by creating vortex flow structures, as well as by increasing the heat exchange area. Thus, the ratio of convection in thermal conductivity increases to 3.03 times. Also in the article, a comparative analysis of the results obtained with the results of heat transfer intensification using classical flow turbulators is carried out. According to the results of the analysis, it was determined that the investigated turbulators are more effective than classical ones, however, the pressure losses in the investigated turbulators are much higher. [ABSTRACT FROM AUTHOR]

The Darcy–Forchheimer model for a two‐dimensional hydromagnetic flow in a horizontal channel, including the dynamic interaction of porous and nonporous media, is investigated in this study due to the importance of the consequences of heat exchange in porous materials. The novelty of the current investigation is to study the hydrodynamics of fluid flowing through a channel with free and non‐Darcy porous media linked next to one another influenced by the potent Lorentz force. The prime objective of this investigation is to analyze the influence of critical nondimensional parameters on the rate of heat transfer and shear forces exerted on the walls of the channel. Numerical simulations are carried out using the finite element method within the COMSOL Multiphysics program, which offers a versatile framework to explore the behavior of velocity and isothermal contours. The essential optimal stability of this adopted model is achieved for specific scenarios employing a finely meshed grid and grid‐independent analysis. It is noteworthy that larger Prandtl numbers enhance heat transmission rates from surfaces at high temperatures, whereas greater Eckert numbers are correlated with lower Nusselt numbers. On the lower surface, the Forchheimer and magnetic drag forces reduce skin friction, whereas the top surface displays a different pattern. The aforesaid findings have a variety of engineering applications by improving the flow dynamics in porous and nonporous materials. This study can be beneficial in designing heat exchanger devices. [ABSTRACT FROM AUTHOR]

The transient temperature of the wellbore plays an important role in the selection of downhole tools during the drilling of deep shale gas horizontal wells. This study established a transient temperature field model of horizontal wells based on the convection heat transfer between wellbore and formation and the principle of energy conservation. The model verification shows that the root mean squared error (RMSE) between the measured annular temperature neat bit and the predicted value is 0.54 °C, indicating high accuracy. A well in Chongqing, China, is taken as an example to study the effects of bottom hole assembly (BHA), drill pipe size, drilling fluid density, flow rate, inlet temperature of drilling fluid, and drilling fluid circulation time on the temperature distribution in wellbore annulus. It is found that the increase in annular temperature is about 1 °C/100 m in the horizontal section when a positive displacement motor (PDM) is used. A Φ139.7 mm drill pipe is more favorable for cooling than Φ139.7 mm + Φ127 mm drill pipe. Reducing drilling fluid density and flow rate and inlet temperature is beneficial to reduce bottom hole temperature. Bit-breaking rock, bit hydraulic horsepower, and drill pipe rotation will increase the bottom hole temperature. The research results can provide theoretical guidance for temperature prediction, selection of proper drill tools, and adjustment of relevant parameters in deep shale gas horizontal wells. [ABSTRACT FROM AUTHOR]

Methods for enhancing fluid dynamics and thermal mixing in 3D open flow were performed and evaluated numerically in the current study. The impacts of a grouping of active and passive techniques of enhancement, namely: nonuniform magnetic field, complex geometry and nanofluids, on hydrodynamic and thermal behaviors were assessed. Flow characteristics such as degree of mixing, Nusselt number, and secondary flow structure indices were evaluated for various enhancement protocols being considered. An external magnetic field was applied in this project in two ways: over the entire channel or on specific stretches of the complex duct. In addition, mentioned flow features are examined along the channel with the number of Hartmann (Ha) ranging between 0 and 50 and three angles of orientation of the magnetic field (0, π/4 and π/2). The results show that the optimal protocol to achieve good thermal mixing between hot and cold fluids with a degree of mixing exceeds the 90% is for a nonuniform use of magnetic force oriented by π/2 or π/4. Moreover, it was observed that by applying the same optimized protocol, the parietal heat transfer represented by the Nusselt number was increased by more than 45%. [ABSTRACT FROM AUTHOR]

This paper presents a technique for measuring the temperature of an inhomogeneous underlying surface using unmanned aerial vehicles (UAVs). To test the proposed technique, measurements over various landscapes are presented: dunes in an arid zone, a temperate swamp, a subarctic city, and a combination of natural and anthropogenic landscapes in the Arctic. A measuring complex based on a DJI Mavic 2 Zoom quadrocopter with a Flir TAU 2R thermal camera is used. Methods for correcting emerging hardware errors and artefacts have been developed. To obtain detailed data on the spatial distribution of the surface brightness temperature, the orthomosaic construction method is used. Thermal maps of surfaces with surface height inhomogeneities (dunes), moisture inhomogeneity (swamps), and urban areas in polar and subpolar conditions are obtained at different times of the day. It is shown that thermal contrasts can reach the first tens of degrees Celsius within an area of 10–20 ha, both under the background of daytime heating and nighttime cooling of the surface, and could have a significant effect on the spatial distribution of the heat transfer characteristics of the atmosphere and the underlying surface. These methods are recommended for constructing surface thermal maps using thermal imaging technology. [ABSTRACT FROM AUTHOR]

In addition to providing general constraints on probability distributions, fluctuation theorems allow us to infer essential information on the role played by temperature in heat exchange phenomena. In this numerical study, we measure the temperature of an out-of-equilibrium active bath using a fluctuation theorem that relates the fluctuations in the heat exchanged between two baths to their temperatures. Our setup consists of a single particle moving between two wells of a quartic potential accommodating two different baths. The heat exchanged between the two baths is monitored according to two definitions: as the kinetic energy carried by the particle whenever it jumps from one well to the other and as the work performed by the particle on one of the two baths when immersed in it. First, we consider two equilibrium baths at two different temperatures and verify that a fluctuation theorem featuring the baths temperatures holds for both heat definitions. Then, we introduce an additional Gaussian coloured noise in one of the baths, so as to make it effectively an active (out-of-equilibrium) bath. We find that a fluctuation theorem is still satisfied with both heat definitions. Interestingly, in this case the temperature obtained through the fluctuation theorem for the active bath corresponds to the kinetic temperature when considering the first heat definition, while it is larger with the second one. We interpret these results by looking at the particle jump phenomenology. [ABSTRACT FROM AUTHOR]

In this paper, a novel concept of a finned piston system is presented and analyzed in which the compression heat is continuously extracted from the compression chamber. The resulting compression characteristic moves in the direction of an isothermal process, reducing the temperature of the compressed fluid in the compression chamber and reducing the necessary mechanical work required to carry out the process. The finned piston concept consists in an integrated heat exchanger inside of the chamber that is constituted of imbricated flat fins placed on the stator part and on the mobile piston. The internal heat exchange on the surface is strongly increased in comparison with a classical piston/cylinder. The energetic performance of the new system is evaluated with the help of simulation. The pressures, forces, and temperature of the compressed gas are simulated as well as the mechanical work needed. The different curves are compared with the system's adiabatic and isothermal characteristics. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the non-isothermal laminar flow and heat transfer of oil with Newtonian and viscoplastic rheologies. Heat exchange with the surrounding environment leads to the formation of a near-wall zone of viscoplastic fluid. As the flow proceeds, the transformation of a Newtonian fluid to a viscoplastic state occurs. The rheology of the Shvedoff–Bingham fluid as a function of temperature is represented by the effective molecular viscosity apparatus. A numerical solution to the system of equations of motion and heat transfer was obtained using the Semi-Implicit Method for Pressure-Linked Equations (SIMPLE) algorithm. The calculated data are obtained at Reynolds number Re from 523 to 1046, Bingham number Bn from 8.51 to 411.16, and Prandl number Pr = 45. The calculations' novelty lies in the appearance of a "stagnation zone" in the near-wall zone and the pipe cross-section narrowing. The near-wall "stagnation zone" is along the pipe's radius from r/R = 0.475 to r/R = 1 at Re = 523, Bn = 411.16, Pr = 45, u1 = 0.10 m/s, t1 = 25 °C, and tw = 0 °C. The influence of the heat of phase transition of paraffinic oil on the development of flow and heat transfer characteristics along the pipe length is demonstrated. [ABSTRACT FROM AUTHOR]

The article presents the results of studies of the parameters of a new flat aluminum thermosyphon, the evaporator of which contains two identical parallely operating panels, each of which has 8 minichannels. The panels are united by single vapor and liquid collectors. The working fluid is acetone. A study was carried out to investigate the influence of a thermal load and the degree of thermosyphon filling with working fluid on the heat exchange coefficients of the evaporator and condenser, as well as on the thermal resistance of the thermosyphon. [ABSTRACT FROM AUTHOR]

With the use of the asymptotic method, it is shown that the three-layer problem on the conjugate heat exchange in an anisotropic medium with counterflows of liquid, formulated in the zero approximation, is equivalent to the analogous problem formulated using the Newton law. It was established that in the case where the counterflows of liquid in such a medium have equal strengths, the summary convective heat transfer in the medium is suppressed, and the medium takes new properties consisting in the appearance of heat flow mixed in nature, whose value is determined by the relation similar to the Fourier heat conduction law. By this meant that in the case where a temperature gradient is superimposed on a three-layer system of equivalent counterflows of liquid, in it there arises a heat flow having a value proportional to the temperature gradient in the medium and propagating in the direction opposite to the direction of this gradient. The effective coefficient of heat conductivity of medium, generated in it by the counterflows of liquid, separated by an immovable layer, is proportional to the square of the velocity of these flows. An immovable layer in a medium, separating the counterflows of liquid, increases the generation of heat in the medium, and the heat flow generated exceeds substantially the molecular one even in the case where it has a low velocity. Such processes provide the mass exchange in living organisms and their heat exchange with the environment. [ABSTRACT FROM AUTHOR]

The urban environment represents one of the main contexts in which natural resources are exploited to support intensive human activities, especially from an energy perspective. In this context, there is still a lack of general methodologies/tools which can be used to understand the behavior of buildings and to prove their sustainability under real operating conditions, depending on their location, construction characteristics and materials, plants, external conditions, and conduction. In this research, the Buckingham theorem is applied to the thermophysics of buildings, describing the heat transfer of opaque surfaces in a transient regime. The abstraction of dimensionless numbers merges the main phenomena of interest, such as thermal conduction, convection, and radiation, enhanced by consideration of the surface sun–air temperature and the external air temperature. The parameters themselves were mutually matched through a proper equation, whose coefficients were determined by a regression analysis of the measurements from an intensive experimental campaign investigating a building in Florence for 3 years. The resulting correlation shows a good agreement with the available dataset and a determination coefficient of over 70%. Therefore, the proposed approach, owing to the generalization of the dimensionless numbers, suggests the possibility of sustainability estimates, from an energy point of view, of envelope/plant/user systems, including assessments at a higher scale than that of a single building. [ABSTRACT FROM AUTHOR]

Data presented in this paper were collected with the aim of describing the mean monthly temperature evolution of a lateritic soil in an equatorial zone during the dry season. The site is located in Cameroon and has the following geographical coordinates: latitude 3.879444° North and longitude 11.468333° East. Data collection involved measuring the water temperature and depth of existing wells at the site and determining their geographical coordinates. The data were collected manually. The temperatures of the various wells were measured daily throughout February 2022, and the average monthly temperatures were then calculated. These are presented in this paper, along with the other measured data. Several pieces of equipment were used for this purpose. An infrared laser thermometer was used to measure the temperatures of the various wells. A UTM GPS (Universal Transverse Mercator Global Positioning System) unit was used to determine the geographical position of each well in the study area. A plumb line was used to measure the depths of the various wells. The length of the plumb line inserted into the well was measured using an ankle brace. An infrared rangefinder was used to measure the distance, surface area, and volume of each well. The Coordinate Converter application was used to convert the east longitude and north latitude of each well in the study area into decimal degrees. Microsoft Excel was used to draw up tables of measured and converted data and to plot a graph. Surfer software was used to produce isothermal maps. The data collected provide information on changes in the average monthly temperature of the soil at the site as a function of its depth and geographical position. This information facilitates the installation of heat pumps and other heat exchangers to meet the heating and cooling needs of buildings in the area. Additionally, this data can be reused to identify suitable locations for the construction of new water wells and buildings at the site.

In this paper, a novel concept of a finned piston system is presented and analyzed in which the compression heat is continuously extracted from the compression chamber. The resulting compression characteristic moves in the direction of an isothermal process, reducing the temperature of the compressed fluid in the compression chamber and reducing the necessary mechanical work required to carry out the process. The finned piston concept consists in an integrated heat exchanger inside of the chamber that is constituted of imbricated flat fins placed on the stator part and on the mobile piston. The internal heat exchange on the surface is strongly increased in comparison with a classical piston/cylinder. The energetic performance of the new system is evaluated with the help of simulation. The pressures, forces, and temperature of the compressed gas are simulated as well as the mechanical work needed. The different curves are compared with the system’s adiabatic and isothermal characteristics.

This study investigated the impact of a cylindrical obstacle on convection in an inclined square cavity filled with water-Al2O3 nanofluid. Using the finite volume method, the problem was resolved by having the inner cylinder rotate adiabatically while other walls were thermally insulated. Additionally, the bottom wall was hotter than the top. The study examined the effects of cylindrical obstacle radius (0.1 ≤ R ≤ 0.2), rotation speed (-500 ≤ Ω ≤ 500), Richardson number (0.01 ≤ Ri ≤ 100), volumetric nanoparticle fraction (0.02), and Grashof number (Gr = 104 ) on heat transfer rate or Nusselt number. The results were compared with previous literature, and the influence of the cylindrical obstacle rotational speed on convection flow was evaluated. An increase in the counterclockwise angular rotating speed resulted in higher nanofluid flux. The heat transmission coefficient increased as the Richardson number decreased. The use of nanofluid in the enclosure increased the coefficient of heat flow through mixed convection. Finally, the study showed that the convection heat exchange is enhanced with the increase in the radius. Moreover, an enhancement of the Nusselt number around 46% was reported for the cylinder, under Gr=10000, ∅=0.02, =45° and Ri= 10.

The present analysis shows that the most crucial parameter for a correct representation of the observed temperature behavior are the heat exchange coefficient and the wind. The different approaches tested all have limitations, but they can reproduce reservoir temperature trends at different depths with a maximum standard deviation ranging from 3 °C to 8 °C. HIGHLIGHTS Tropical reservoir's water temperature is strongly influenced by air–water heat exchanges, but the fast exchanges of temperature in tropical zones made traditional formulations of exchange coefficients to be insufficient.; The parameter that mainly affects the heat transfer and thermal stratification process is the transfer coefficient A and can be used as an approximation for estimating the exchange rate of the reservoir.;

The paper gives a systems analysis in the field of heat transfer and temperature distribution (TD) along the length of oil production wells (OPW). The analysis shows that the existing mathematical models are suitable only for determining TD along the length of casing string (CS) and are not suitable for determining TD along the length of the tubing run, since the existence of the interfacial (between the CS and the tubing) annulus of the fluid and gas layers with heat capacity and thermal conductivity that differ significantly from the heat capacity and thermal conductivity of rocks surrounding the CS. Given the above, mathematical models taking into account the impact of the fluid and gas layers in the annulus on the heat transfer from the upward fluid flow to the tubing wall and from the wall to the interfacial annulus are developed. To ensure the technological effectiveness of the obtained model, formulas for quantitative estimation of the heat transfer of the fluid flow into the surrounding environment are given. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper presents examples from the practice of operating arc steel-smelting furnaces (EAFs), verifying the hypothesis on the complex heat exchange of arcs in spherical segments in the bath. The thermal radiation of arcs in spherical segments is converted into convective and thermal conduction flows, heating the entire volume of metal and slag. No more than 3%–4% of the arc power is spent on evaporation of the metal under the arcs, while 76–78% of the arc power is converted into convective and thermal conduction flows that heat the bath. The metal waste under the arcs is 8–9%, in which 91–92% of the metal waste is accounted for in the zones of exposure to the bath with oxygen. With an oxygen consumption of 10–15 m3/t in the EAF, metal waste is 3%; with an increase in oxygen consumption to 50 m3/t, metal waste increases by 2.5–4 times to 7.5–12%. With an increase in the absorption coefficient of the gaseous atmosphere of the DSP-100 furnace, the maximum density of thermal radiation fluxes from the arcs to the walls decreases proportionally. With an increase in the height of the slag layer by 3.7 times, the maximum density of thermal radiation fluxes of the arcs on the water-cooled wall panels decreases by 2.6 times. [ABSTRACT FROM AUTHOR]

The electrical, geometric, and thermophysical parameters of the arcs of arc steel-melting furnaces change with a frequency of 50 Hz, i.e., 50 times/s. Under vertical electromagnetic force directed along the electrode axis, the arc squeezes out the liquid metal and slag, forming a depression in the form of a spherical segment in the bath. Under horizontal electromagnetic force directed perpendicular to the arc axis, the arc moves along the electrode and the metal bath at a velocity of 30–100 m/s, capturing and throwing the liquid metal from the spherical segment and slag onto the bath surface far to the slopes. Under Archimedean force, new layers of metal and slag are formed in the spherical segments, and the process of moving layers of metal and slag from the spherical segments at a velocity of 30–100 m/s is repeated 50 times/s. Powerful heat flows of radiation from arc columns in spherical segments in the bath are transformed into powerful convective heat flows during the turbulent movement of metal, slag, and thermal conductivity flows, which heat the entire volume of the bath of metal and slag. The hypothesis of the transformation of heat radiation flows in spherical segments into heat conduction and convective flows during turbulent movement and displacement of liquid metal and slag is verified by experiments and operation of arc steel-smelting furnaces. [ABSTRACT FROM AUTHOR]

Heat exchange plays an important role in hydrodynamical systems, which is an interesting topic in theory and application. In this paper, the authors consider the global stability of steady supersonic Rayleigh flows for the one-dimensional compressible Euler equations with heat exchange, under the small perturbations of initial and boundary conditions in a finite rectilinear duct. [ABSTRACT FROM AUTHOR]

This study investigated the impact of a cylindrical obstacle on convection in an inclined square cavity filled with water-Al2O3 nanofluid. Using the finite volume method, the problem was resolved by having the inner cylinder rotate adiabatically while other walls were thermally insulated. Additionally, the bottom wall was hotter than the top. The study examined the effects of cylindrical obstacle radius (0.1 ≤ R ≤ 0.2), rotation speed (-500 ≤ Ω ≤ 500), Richardson number (0.01 ≤ Ri ≤ 100), volumetric nanoparticle fraction (0.02), and Grashof number (Gr = 104) on heat transfer rate or Nusselt number. The results were compared with previous literature, and the influence of the cylindrical obstacle rotational speed on convection flow was evaluated. An increase in the counterclockwise angular rotating speed resulted in higher nanofluid flux. The heat transmission coefficient increased as the Richardson number decreased. The use of nanofluid in the enclosure increased the coefficient of heat flow through mixed convection. Finally, the study showed that the convection heat exchange is enhanced with the increase in the radius. Moreover, an enhancement of the Nusselt number around 46% was reported for the cylinder, under Gr=10000, Φ=0.02, γ=45° and Ri= 10. [ABSTRACT FROM AUTHOR]

Tailoring the properties of hot-stamped components offers the potential to enhance crash performance while simultaneously improving downstream joining processes. In recent years, an innovative technology suited for achieving tailored properties involving the utilization of a specialized furnace chamber, known as the TemperBox®, has been introduced. Within this chamber, a cooled aluminum mask shields specific areas of the blank from incoming heat radiation and concurrently absorbs the blank's own radiation. The duration of the heat radiation exchange can influence the diffusion-dependent phase transformation and, consequently, the resulting mechanical properties. Hence, the intermediate cooling duration assumes a pivotal role as a parameter, as is investigated in this study. To examine the effects, specimens of the steel 22MnB5 AS150 are subjected to intermediate cooling of varying durations, followed by forming and partial quenching. The temperature profile of the blank during intermediate cooling prior to forming and quenching is analyzed. Subsequently, the tailored hot-stamped components are assessed for hardness, strength, ductility, and thickness strain. The study reveals that with increasing duration of partial intermediate cooling and targeted radiation exchange, a homogeneous ferritic–pearlitic structure is formed from an austenitic structure. This uniform structure of ferrite and pearlite is reflected in lower hardness and strength values, along with improved ductility. Additionally, this paper introduces a simulation methodology designed to calculate the dynamics of thermal radiation and the kinetics of phase transformation. [ABSTRACT FROM AUTHOR]

The article analyses the thermodynamic conditions for long-term storage of hydrates and proposes a methodology for calculating the main thermodynamic parameters that ensure long-term stability of the structure of gas hydrates. A criterion for optimizing thermodynamic parameters and heat and mass transfer parameters for effective introduction of new technology

This article considers a nonlinear system of partial differential equations describing the boundary layer. Such a system is commonly solved by numerical methods. Here, the Dorodnitsyn–Lees variables were used to carry out an analysis and derive the formulas for calculating the body temperatures and the heat fluxes to the body generated by the reacting compressible gradient boundary layer.

The results of the analysis of practical experience in the development of potash seams using longwall mining systems at the mines of OAO “Belaruskali” are presented. Positive changes in the technical and economic indicators of mines and an increase in the safety of mining operations were noted with the introduction of resource-saving technologies without leaving the pillars between the excavation columns or with leaving the pillars between the columns with dimensions at which they are destroyed by mining pressure in the goaf. It is noted that the use of mechanized stoping complexes characterized by high energy capacity, combined with large depths of development, is the main reason for the temperature increase in longwalls to values exceeding the maximum permissible air temperature regulated by sanitary standards. Based on production studies, it was concluded that the temperature regime along the length of the longwall face is determined by the temperature of rocks in the developed longwall space, heat emissions from the equipment of the power train, and the temperature of the rock mass ahead of the longwall. The conclusion has been drawn about the feasibility of using developed technological schemes in deep mining conditions, which provide a reduction in longwall temperature by 6-9 °C or more through isolated ventilation of longwall and power trains, as well as heat exchange between the airflow entering the longwall and the rocks in the developed space.

The main purpose of the work is to present the possibility of using the finite element method implemented in the COMSOL 3.5a program in the heat transfer symmetry 2D module to determine thermal diffusivity by the classic and modified pulse methods. The method of determining the thermal diffusivity by means of measuring and recording the course of the temperature difference between the extreme surfaces of the tested sample and changes in the temperature increase on the back surface after a laser shot at its front surface, assuming that the sample is adiabatic for a representative experimental course at a given temperature, is discussed. This paper presents the basic metrological conditions for the implementation of the modified pulse method for testing the temperature characteristics of thermal diffusivity on the example of nickel. The heat pulse generated by the laser method at the extreme surface of the sample for a thermostatic temperature of 341.8 °C was simulated. Using the inverse problem in both the classic and modified methods, the thermal diffusivity of the material in question was determined and these results were compared with the experimentally obtained values. The values of thermal diffusivity differ from those obtained experimentally by 3.3% for the classic method and approximately 2.5% for the modified method. A preliminary analysis of the influence of the number of nodal points on the numerical results obtained was also carried out and the results for the number of nodes between 64 and 17,000 change by only 1.1%. The paper presents a combination of experimental and numerical studies which is useful in science and simplifies the process of time-consuming experimental studies.

The object of this study was the processes of heat and mass transfer in a column heat exchanger with direct phases contact. The investigated problem is related to the need to determine the estimates of the kinetic characteristics of heat exchange during the concentration of solutions in a contact heat exchanger equipped with dual-flow trays. In particular, it was assumed that the determination of the influence of the gas velocity in the apparatus and the density of liquid irrigation of the plates, as well as the geometry of the plates, on the kinetic coefficients would make it possible to reveal the patterns of heat and mass exchange between the liquid and the air in contact with it in the column apparatus. It was determined that to increase the intensity of mass transfer in the gas and heat transfer in the liquid, it is necessary to increase the gas velocity and irrigation density. Then the gas velocity and irrigation density have approximately the same effect on the intensity of mass transfer in the gas and heat transfer in the liquid. When studying the effect of the geometry of the plate on the kinetic coefficients of heat transfer in the liquid and mass transfer in the gas, it was established that the value of the portion of the free cross section of the plate has a decisive influence on the value of the considered kinetic coefficients. A generalized equation was built, which makes it possible not only to calculate the enthalpy transfer coefficient during the interaction of sodium chloride solution with air but also to determine the limiting stage of this process. The results could be used to design a unit for concentrating a hot solution of sodium chloride by evaporating water during blowing with air in a contact heat exchanger. This would make it possible to obtain crystalline sodium chloride using secondary energy resources and other non-traditional sources of thermal energy. [ABSTRACT FROM AUTHOR]

Particles less than 100 nanometers in size are suspended in a base fluid such as water, oil, and ethylene glycol. These nanoparticles are floating in the nanofluid. The purpose of this study is to research the operation of a counter-flowing, double-pipe heat exchanger using two distinct nanofluids as cooling media. Titanium carbide and carbon nanotubes combine to form alkaline water, a basic fluid. The purpose of this research was to assess the performance of a counterflow double-pipe heat exchanger using water with different concentrations of titanium carbide and carbon nanotubes. Alkaline water had a particle volume concentration of 0.06, and its nanofluid-flow rate was 0.03. Using a heat exchanger, water is heated to 65 °C while nanofluids are heated to 35 °C, both at a constant input velocity. The speed of both fluids is constant. The findings demonstrate that nanofluid outperforms water in heat absorption across a broad range of flow speeds. Heat exchangers benefit from the improved thermal characteristics of nanoscale fluids. [ABSTRACT FROM AUTHOR]

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain. [ABSTRACT FROM AUTHOR]

To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate whole body dry and evaporative heat exchange. These responses are modulated by the rise in body temperature (thermal factors), as well as several nonthermal factors implicated in the cardiovascular response to exercise (i.e., central command, mechanoreceptors, and metaboreceptors). However, the way these nonthermal factors interact with thermal factors to maintain heat balance remains poorly understood. We therefore used direct calorimetry to quantify the effects of dose-dependent increases in the activation of these nonthermal stimuli on whole body dry and evaporative heat exchange during dynamic exercise. In a randomized crossover design, eight participants performed 45-min cycling at a fixed metabolic heat production (200 W/m²) in warm, dry conditions (30°C, 20% relative humidity) on four separate occasions, differing only in the level of lower-limb compression applied via bilateral thigh cuffs pressurized to 0, 30, 60, or 90 mmHg. This model provoked increments in nonthermal activation while ensuring the heat loss required to balance heat production was matched across trials. At end-exercise, dry heat loss was 2 W/m² [1, 3] lower per 30-mmHg pressure increment (P = 0.006), whereas evaporative heat loss was elevated 5 W/m² [3, 7] with each pressure increment (P < 0.001). Body heat storage and esophageal temperature did not differ across conditions (both P ≤ 0.600). Our findings indicate that the nonthermal factors engaged during exercise exert dose-dependent, opposing effects on whole body dry and evaporative heat exchange, which do not significantly alter heat balance. NEW & NOTEWORTHY To maintain heat balance during exercise, humans rely on skin blood flow and sweating to facilitate dry and evaporative heat exchange. These responses are modulated by body temperatures (thermal factors) and several nonthermal factors (e.g., central command, metaboreceptors), although the way thermal and nonthermal factors interact to regulate body temperature is poorly understood. We demonstrate that nonthermal factors exert dose-dependent, opposing effects on dry and evaporative heat loss, without altering heat storage during dynamic exercise. [ABSTRACT FROM AUTHOR]

The hydrodynamic and thermal interaction of water with the high-temperature melt of a heavy metal was studied via the Volume-of-Fluid (VOF) method formulated for three immiscible phases (liquid melt, water, and water vapor), with account for phase changes. The VOF method relies on a first-principle description of phase interactions, including drag, heat transfer, and water evaporation, in contrast to multifluid models relying on empirical correlations. The verification of the VOF model implemented in OpenFOAM software was performed by solving one- and two-dimensional reference problems. Water jet penetration into a melt pool was first calculated in two-dimensional problem formulation, and the results were compared with analytical models and empirical correlations available, with emphasis on the effects of jet velocity and diameter. Three-dimensional simulations were performed in geometry, corresponding to known experiments performed in a narrow planar vessel with a semi-circular bottom. The VOF results obtained for water jet impact on molten heavy metal (lead–bismuth eutectic alloy at the temperature 820 K) are here presented for a water temperature of 298 K, jet diameter 6 mm, and jet velocity 6.2 m/s. Development of a cavity filled with a three-phase melt–water–vapor mixture is revealed, including its propagation down to the vessel bottom, with lateral displacement of melt, and subsequent detachment from the bottom due to gravitational settling of melt. The best agreement of predicted cavity depth, velocity, and aspect ratio with experiments (within 10%) was achieved at the stage of downward cavity propagation; at the later stages, the differences increased to about 30%. Adequacy of the numerical mesh containing about 5.6 million cells was demonstrated by comparing the penetration dynamics obtained on a sequence of meshes with the cell size ranging from 180 to 350 µm. [ABSTRACT FROM AUTHOR]

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The development of in-chamber elements of a tokamak thermonuclear reactor is associated with a large number of challenging engineering problems, one of which is the removal of heat flows with a specific density of 10–20 MW/m2. Results of an experimental study of cooling by a two-component dispersed coolant flow directed perpendicular to the cooled surface are discussed. The study is a continuation of the research on enhancing the heat removal efficiency. The efficiency of this cooling method is due to a decrease in the proportion of convective heat transfer and an increase in heat exchange during evaporation. It is shown that the use of a two-component dispersed coolant flow makes it possible to remove heat flux densities exceeding 10 MW/m2 at a pressure of the coolant components not exceeding 0.5 MPa; the effect of the ratio of components on the efficiency of heat removal is investigated. The experimental data obtained indicate the high efficiency of the proposed cooling method. The heat transfer coefficient was found to reach 200 kW/(m2 K), a value which is significantly higher than that for conventional cooling methods based on single-phase water flow. [ABSTRACT FROM AUTHOR]

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions. [ABSTRACT FROM AUTHOR]

In recent theoretical studies of the authors, some estimates of the atmospheric disturbances related to inhomogeneities of the gravity field (IGF) have been obtained. The main attention was paid to dynamic effects: disturbances of the wind field under the influence of IGF. In this paper, attention is drawn to the fact that noticeable thermal effects of IGF can also exist in the surface layer of the atmosphere. These inhomogeneities, deforming the fields of pressure, air density, and air temperature, affect the temperature regime of the boundary layer and the heat exchange of air with the underlying surface. An analytical model designed to estimate the magnitudes of these effects is considered. Based on the proposed model, an analytical solution is found for a linear stationary two-dimensional problem for perturbations caused by one horizontal harmonic of the IGF in a semi-infinite stably stratified medium rotating around a vertical axis. The temperature of the lower boundary (underlying surface) was assumed to be fixed. It was also assumed for this boundary that the no-slip and no-flow conditions are satisfied. The attenuation of all disturbances with height was also assumed. The essential similarity parameters in this problem are analogues of the Rayleigh and Taylor numbers, in which the given horizontal scale of IGF serves a spatial scale. Analytical expressions are obtained for the profiles of temperature perturbations and amplitudes of deviations of vertical heat fluxes on the surface. The latter, along with amplitudes of gravity field inhomogeneities, depend most strongly on the background stratification of the medium. In highly anomalous regions, the amplitudes of heat flux deviations, according to the estimates obtained, may reach and even exceed 1 W/m2, which gives grounds for taking into account the gravity field inhomogeneities in climatic calculations and numerical models of the atmosphere. [ABSTRACT FROM AUTHOR]