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This study aims to obtain aqueous extracts of valuable phytochemicals, in particular anthocyanins, from winemaking residues by using grape skins as natural electrical conductors allowing internal heat dissipation through Ohmic Heating (OH) effect. Two different electric pretreatments were evaluated: i) using mild temperatures at 40°C during 20min; ii) flash heating from 40 to 100°C in less than 20 seconds (no holding time). These pretreatments were followed by aqueous extraction in water at room temperature. Independently of the temperature applied, OH allowed to boost extraction levels increasing concentration of total phenolic compounds, as well as conductivity, soluble solids and red color intensity of the obtained extracts, as shown through principal component analysis (PCA). OH pretreatments at high-temperature short-time (HTST) due to the fast internal heating of grape skin structure allowed increase total concentration of anthocyanins from 756 to 1349g/g, with malvidin-3-O-glucoside being the main compound identified and quantified in the aqueous extracts through HPLC analysis (corresponding to about 60 % of the total). These results showed that OH bring potential to be an efficient and environmentally friendly technology towards sustainable food processes., This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UIDB/04469/2020 and BioTecNorte operation(NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020-Programa Operacional Regional do Norte. We would also like to thank the scientific collaboration under the FCT project UID/Multi/50016/2019. The author Marta Coelho would like to acknowledge FCT for your PhD grant with the reference SFRH/BD/1118842015. The authors want to thank to Adega Cooperativa de Ponte da Barca for the provided wine waste material., info:eu-repo/semantics/publishedVersion

Harvesting clean water from seawater is widely studied in thermal-driven vacuum membrane distillation (VMD) application. Although the conventional VMD promotes excellent flux due to the deaeration by means of vacuum, the external heat supply of the system suffers the heat loss during pumping high feed volume. The batch submerged VMD (S-VMD) which has internal heat supply was introduced in this work to provide uniform feed temperature in the feed tank. This simple and space-saving design makes it particularly suitable to supply water for small community with space limitation. To evaluate the energy efficiency of the S-VMD in desalinating seawater, the performance of the system had been simulated and verified with the experimental results. The effects of main operating parameters including feed temperature and its circulation rate, heat transfer coefficient, vacuum degree on permeate side, packing density of membrane and temperature polarization on the membrane permeation flux using saline water feed had been experimentally investigated. Energy efficiency in terms of gained output ratio (GOR) and thermal loss of the heat supply had also been examined. The simulated results showed that the flux enhanced with the increase of feed temperature, circulation rate, vacuum degree and packing density of membrane. The combination of feed temperature with circulation flow and packing density of membrane played dominant role to improve permeate flux and GOR of the system. This finding is important for the future implementation of S-VMD system in space-constraint remote area. The simulation results were in good agreement with experimental results, recording less than 5% error.

The stability of a layer of moist air above a heated surface of land or ocean is studied under the sudden influence of internal sources of heat release, which depend on the pressure and density. A dispersion equation is obtained for small 3D perturbations in a rotating atmosphere. It contains the previously known waves (acoustic, internal waves, and Brunt–​​Vaisala waves) and makes it possible to obtain a modified criterion for the onset of convective instability. This dispersion equation also makes it possible to study the effect of internal heat release on the dynamics of perturbation in these waves, including the conditions for the occurrence of instability generated by an atmospheric electric discharge. Taking into account new considered effects can lead to the identification of new instabilities and the modification of the previously known ones. The proposed system of equations allows numerical calculations of vortex flows in moist air in the near-surface layer and a more detailed study of the mechanisms of the beginning of hurricanes and tornadoes.

The nonlinear stability analysis of a ferrofluid layer system is formulated mathematically. This system considered the upper and lower free isothermal boundary with the system heated from below. A mathematical formulation is produced to study the behaviour of the chaotic convection in a ferrofluid layer system using Galerkin truncated expansion. The Boussinesq approximation is opted with the existence of internal heating and the magnetic number. It is found that the transition to chaos in this present study is identical to the Lorenz attractor and thus validate the method and analysis of this study. The impact of elevating the internal heat generation is found to hasten the instability of the system and as for the magnetic number, at M1 = 2.5 the homoclinic bifurcation occurs and thus accelerates the convection process.

The construction of water conservancy projects in cold regions experiences freezing-thawing cycles, which can greatly change the engineering properties of soil and have a significant impact on the construction of projects. Lianghekou Hydropower Station (LHS), is a controlling station with the largest installed capacity among the 7 middle reach projects in the Yalong River, the secondary tributary of the Yangtze River. LHS is located in a seasonally frozen soil area. Based on the measured data of air and ground temperature in winter in the dam core wall, the freezing-thawing variation of gravelly soil and contact clay during the filling process of the core wall are compared and analyzed, then the main impact factors of the freezing-thawing variation of soils are discussed. The results show that under the influence of air temperature, soil freezes unidirectionally from ground surface downward and deepens gradually, and the thawing processes are different at the aspects of thawing direction and rate. Air temperature and physical properties of soil including soil type, moisture content and dry density affect the freezing-thawing processes of soils. And the impact of engineering construction is more remarkable than natural factors. The engineering construction affects soil temperature and freezing-thawing process by controlling the initial temperature of soil, the speed and duration of the technological conversion of paving, compaction, and the length of placed duration at night. Due to the long placed duration of soil with the slow construction method, the initial temperature of soil gradually reduces, the heat transfer process inside soil is fast. Then the internal heat of soil releases, the decreasing rate of ground temperature of soil at different depths is fast and the frozen depth deepens. While due to the short placed duration of soil with the rapid construction process, the initial temperature of soil is high, high internal heat of soil is supplied every day, and the heat transfer process inside soil is slow. Then the decreasing rate of temperature of soil at different depths is slow, and the variation amplitude of frozen depth is small. This study provides useful guidance for the freezing-thawing prevention during the construction process of core wall dams located at high altitude region in winter.

Internal heating effect with stability convection in a couple stress fluid saturated in an anisotropic porous medium has been studied numerically using linear stability analysis. The presence of internal heating on couple stress fluid in an anisotropic porous medium heated from below has been verified. The momentum equation and Boussinesq approximation is used for the density variation in the porous medium. By using Chebyshev Tau method numerically, the eigenvalue problems of the perturbed state were obtained from a normal mode analysis. The effect of the Rayleigh number, internal heat source and anisotropy parameter has been shown graphically. The critical Rayleigh number also has been obtained and plotted on the system. From the result, it is found that the mechanical anisotropy parameter and internal heating effect destabilized the system while couple stress fluid and thermal anisotropy parameter help in stabilizing the system.

Five identical cylindrical salinity-gradient solar ponds (SGSPs) with internal heat exchanger were constructed and operated. In order to optimize the performance of the SGSPs, mixtures of NaCl and Na2SO4 were used. Radiation flux, temperature of the zones, ambient temperature, inlet, and outlet temperature of the internal heat exchangers were measured. It was shown a controlled amount of Na2SO4 improves the thermal and salinity stability of the pond in the normal operation and heat extraction and lowers the pond temperature drop ratio to the water outlet temperature drop during the heat extraction, which means an improvement in the energy storage capacity. The pond with higher percentage of Na2SO4 requires less time to stabilize. Higher percentage Na2SO4 reduces the density gradient between the upper and lower convective zones of the pond and leads to rapid destruction of the upper layer. Maximum ability of heat extraction corresponds to the pond with 0.75% Na2SO4. In addition, to prevent the algae growth at higher percentage Na2SO4, spraying of HCl on the pond surface was used.

The current exploration focuses on the ethylene glycol (EG) based nanoliquid flow in a microchannel. The effectiveness of the internal heat source and linear radiation is reflected in the present investigation. The estimation of suitable thermal conductivity model has affirmative impact on the convective heat transfer phenomenon. The examination is conceded with the nanoparticle aggregation demonstrated by the Maxwell-Bruggeman and Krieger-Dougherty models which tackle the formation of nanolayer. These models effectively describe the thermal conductivity and viscosity correspondingly. The dimensionless mathematical expressions are solved numerically by the Runge Kutta Fehlberg approach. A higher thermal field is attained for the Bruggeman model due to the formation of thermal bridge. A second law analysis is carried out to predict the sources of irreversibility associated with the thermal system. It is remarked that lesser entropy generation is obtained for the aggregation model. The entropy generation rate declines with the slip flow and the thermal heat flux. A notable enhancement in the Bejan number is attained by increasing the Biot number. It is established that the nanoparticle aggragation model exhibits a higher Bejan number in comparision with the usual flow model.

In transcritical CO2 heat pump water heater, the pinch point in gas cooler and the utilization of internal heat exchanger (IHX) both have a significant impact on the optimal discharge pressure and system performance. A theoretical model was developed to investigate the effects, and the results demonstrated that when the water inlet temperature was low, the pinch point prevented the gas cooler outlet temperature from approaching the water inlet temperature at low discharge pressure, which impaired the coefficient of performance (COP). The application of IHX could reduce the gas cooler outlet temperature by 4.9 °C when the water inlet temperature was 10 °C and the discharge pressure was 8.5 MPa. In this condition, combining with the subcooling effect of IHX, the COP was accordingly improved by 26.3%. Regardless of the working condition, using IHX lowered the optimal discharge pressure and enhanced corresponding optimal COP. In addition, parametric analyses were conducted, and the results indicated that the augment of water outlet temperature and ambient temperature resulted in the rise of optimal discharge pressure. The increase of water inlet temperature mostly enlarged the optimal discharge pressure as well. Overall, the optimal discharge pressure varied within a range of 8.53 MPa to 13.38 MPa. The reduction of optimal discharge pressure caused by using IHX intensified with the increase of water inlet and outlet temperature. Nevertheless, the effect of ambient temperature was various depending on the working condition. The reduction of optimal discharge could be up to 1.18 MPa when the effectiveness of IHX was 0.6.

This study uses an optimization approach representation of the numerical solution for the variable viscosity, the uniform blowing/suction and the internal heat source effects on the free convection flow over a vertical permeable plate in porous media with a non-linear Boussinesq approximation. The internal heat source is of an exponential decaying form. The partial differential equations are transformed into non-similar equations and solved by Keller box method (KBM). Compared with the previously published articles, the results are considered to be very consistent. Numerical results for the local Nusselt number with the four parameters: 1) the blowing/suction parameter , 2) the viscosity-variation parameter , 3) internal heat source coefficient , 4) the non-linear temperature parameter are expressed in tables. Through the Taguchi method to predict the best point of the maximum of local Nusselt number is , , , .

The problem of cross diffusion (Soret/Dufour) and internal heat generation effects on combined convection flow of non-Newtonian fluids flow over the vertical wedge in a saturated porous medium with the entire regime is solved numerically. The internal heat generation is assumed to be an exponential decaying form. The power law model of Ostwald-de-Waele for non-Newtonian fluids is considered here. The entire regime of the combined convection is included, as the combined convection parameter varies from 0 (pure free convection) to 1 (pure forced convection). The transformed equations are obtained by using a suitable coordinate transformation and then Keller box method (KBM) is utilized to solve the non-similar equations for the variable heat flux and variable mass flux (VHF/VMF) conditions. Comparisons with the previously published article are performed and the good agreement is achieved. The main numerical results for the dimensionless temperature and concentration distributions, the local Nusselt and Sherwood numbers are obtained.

Objectives. Determination of the effectiveness of using various types of heat pumps in the extractive distillation of an isobutyl alcohol–isobutyl acetate mixture with n-butyl propionate as the entrainer.Methods. As the main research method, mathematical modeling was performed using the Aspen Plus V. 9 software package. As a model for describing the vapor–liquid equilibrium, the local composition equation-based UNIQUAC model was employed, and the Redlich–Kwong model was adopted to examine the non-ideal vapor phase. When modeling the conventional scheme of extractive distillation, parametric optimization was carried out according to the criterion of total energy costs in the reboilers of the columns. For economical evaluation, Aspen Process Economic Analyzer V10.1 tools were employed. Results. In comparison with the conventional extractive distillation scheme, three variants of schemes with vapor-recompression heat pumps were considered: with a heat pump placed on an extractive distillation column, on an extractive agent regeneration column, and with two heat pumps placed on both columns of the scheme. A scheme with an internal heat pump was also proposed, in which the heat pump compressor is located between sections of extractive columns that operate at different pressures: 506.6 kPa in the top sections and 101.3 in the bottom section. An economic analysis was conducted for all the considered schemes to calculate the total annual costs. It was shown that schemes with vapor-recompression heat pumps can significantly reduce the energy costs of extractive distillation by up to 39.6%; however, a significant reduction in the total annual costs is achieved only with sufficiently long operation periods of the plants. The reduction in the energy costs in the scheme with an internal heat pump was 44%, and the total annual costs were in the range of 20.2–30.1%, depending on the operating time of the plant. Conclusions. It was shown that using heat pumps in the extractive distillation of the mixture of isobutyl alcohol–isobutyl acetate with n-butyl propionate as the entrainer can significantly reduce energy costs. The scheme with an internal heat pump is the most economical of all the considered schemes.

It was established that the completion degree of the processes that accompany the iron ore pellets annealing on conveyor machines depends largely on the layer’s internal heat source distribution over separate zones. And the most significant role is played by the magnetite oxidation and carbonate dissociation. During the industrial research conducted on one of the Kachkanarsk’s mining and processing plant (KMPP) conveyor machines, the influence of the original batch composition on the thermal technical indicators of the machine was studied. The consistent pattern obtained for the heat source distribution in the pellet layer along the annealing conveyor machine allows one to optimize separate zone sizes, thermal parameters of the pellets annealing and to find the heat share from the external source for optimal fuel consumption.

A ferrofluid saturated porous layer convection problem is studied in the variable gravitational field for a local thermal nonequilibrium (LTNE) model. Internal heating and variation (increasing or decreasing) in gravity with distance through the layer affected the stability of the convective system. The Darcy model is employed for the momentum equation and the LTNE model for the energy equation. The boundaries are considered to be rigid-isothermal and paramagnetic. For the linear stability analysis of the three-dimensional problem, the normal mode has been applied and the eigenvalue problem is solved numerically using Chebyshev pseudospectral method, while weakly nonlinear analysis is carried out with a truncated Fourier series. The effect of different dimensionless parameters on the Rayleigh number has also been studied. We found that the system becomes unstable on the increasing value of nonlinearity index of magnetization ( $$M_3$$ ), porosity-modified conductivity ratio ( $$\beta $$ ), and internal heat parameter ( $$\xi $$ ). It is observed that the system is stabilized by increasing the value of the Langevin parameter ( $$\alpha _\mathrm{{L}}$$ ), variable gravity coefficient ( $$\delta $$ ), and effective heat transfer parameter ( $$H_1$$ ). Runge–Kutta–Gill method has been used for solving the finite-amplitude equations to study the transient behavior of the Nusselt number. Streamlines and isotherms patterns are determined for the steady case and are presented graphically.

Energy recovery, evaporative cooling and multiple evaporator are regarded as the effective and energy-efficient techniques to improve the energy efficiency of air conditioning system and reduce building energy consumption. In this paper, a parametric analysis and energy-saving potential evaluation for a new hybrid air conditioning system (HAC) under hot-humid climates are carried out theoretically based on detailed models. The proposed HAC incorporates into a dual-evaporator air conditioning system with an independent fresh air conditioner for both total and sensible energy recovery. One evaporator is installed between the total and sensible energy recovery loop of the fresh air conditioner to deeply dehumidify the fresh air for indoor humidity control. The other evaporator is installed inside the conditioned room to handle the indoor return air for temperature and humidity independent control. The parametric analysis mainly for the effect of air-to-water heat capacity ratio, ambient temperature, enthalpy-humidity ratio of the air-conditioned room and the number of heat/mass transfer units of the internal heat exchangers. The energy-saving potential of the HAC is also evaluated for applications in four typical cities (Changsha, Guangzhou, Fuzhou and Hangzhou) located in southern China over the summer period (June–August). The results show that, for the same air supply requirement, the HAC has an average energy-saving rate of 48.87% compared to conventional system with electric heater, and its power saving per hour is 24.85 W m−2.

In this research, three aspects of modeling, analyzing, and optimizing spiral plate heat exchangers (SPHEs) are studied. The main objective of this work is to pave the way for comparing manufacturers’ designed SPHEs with theoretical designed SPHEs without involving designers in using computational methods. To begin, with assumption of constant overall heat transfer coefficient and specific heat capacities, a mathematical modeling of SPHE based on energy balance equations is developed to model the SPHE as a network of series-connected equivalent internal heat exchangers to determine the temperature distribution in spiral turns. This modeling can facilitate the usage of temperature-enthalpy diagram in SPHEs’ analysis and design. Furthermore, a new algorithm for thermal design optimization of SPHEs has been proposed. The proposed algorithm is based on maximizing pressure drops at channels, considering geometric proportion of SPHE and minimizing the total cost simultaneously. To show the proposed method applicability in analyzing thermal and hydraulic design parameters, a single-phase counter-current SPHE is assessed and optimized for different design cases with temperature approach variations. Results of comparing manufacturers’/standard designed SPHEs and research/theoretical designed SPHEs by defining appropriate geometric proportion ranges confirmed that temperature approach variations can improve SPHE performance to a higher extent, such as finding temperature approach ranges for optimized SPHEs with higher compactness to reduce the manufacturing cost. This fact is revealed by introducing compactness-temperature approach diagram which depicts the geometric optimization of SPHEs and the effects of temperature differences in SPHE’s optimization.

Motorized spindle is a component with complex thermal properties. Its thermal boundary conditions change with operating conditions, and thus, the variations of spindle temperature field under different conditions are not exactly the same. Models with fixed structures and fixed coefficients have difficulty in predicting the spindle thermal error with high accuracy and stability. To solve this problem, study of the variation rules of the spindle temperature field is conducted in this paper. The variation process is divided into two stages: the non-uniform variation stage and the uniform variation stage. The variation characteristics are concluded into two parts: the overall variation tendency and the variation of temperature distribution from the inside to outside of the spindle. These conclusions provide a new perspective for temperature variable selection and coefficients adjustment. Based on the variation characteristics of the spindle temperature field, a new modeling method for spindle thermal errors is proposed. The basic temperature, the difference between temperature near the internal heat source and the basic temperature, and the ambient temperature are applied as input variables. The coefficient of the second input variable is set to adjust adaptively according to the spindle status. This method puts more emphasis on the variation rules of the spindle temperature field and can significantly increase the accuracy and the robustness of the prediction model. The model coefficients are optimized by PSO (particle swarm optimization). According to the experimental verification, the variation ranges of residual errors are reduced by at least 62% when predicting the thermal error in X-direction with the proposed model.

The low flux and high energy consumption problems of the conventional three-stage air-gap membrane distillation (AG-AG-AG)MD system caused by the low temperature difference between hot and cold feed at both sides of the membrane and high boundary layer thickness were solved successfully by replacing one of the three stages of air gaps by a water gap. The novel three-stage air-gap–water-gap membrane distillation (AG-AG-WG)MD system reduced energy consumption and increased flux due to efficient internal heat recycling by virtue of a water-gap module. Heat and mass transfer in novel and conventional three-stage systems were analyzed theoretically. Under a feed temperature of 45 °C, flow rate of 20 l/h, cooling temperature of 20 °C, and concentration of 340 ppm, the (AG-AG-WG)MD promoted flux by 17.59% and 211.69%, and gained output ratio (GOR) by 60.57% and 204.33% compared with two-stage (AG-WG)MD and one-stage AGMD, respectively. This work demonstrated the important role of a water gap in changing the heat and mass transfer where convection heat transfer across the water gap is faster by 24.17 times than conduction heat transfer through the air gap. The increase in flux and GOR economized the heating energy and decreased waste heat input into the system. Additionally, the number of MD stages could increase the achieving of a high flux with operation stability.

A parametric analysis and energy-saving potential evaluation for a new hybrid air conditioning system (HAC) under hot-dry climate are carried out theoretically based on developed models. The HAC incorporates into a conventional air conditioning system with an independent fresh air conditioner which is actually composed of a network of heat exchangers, including a packed bed and three air-to-water cooling coils. The fresh air conditioner can switch its work mode by changing the network connecting relations so as to adapt to different climate conditions. Under hot-dry climate conditions, the network can work like an external dew-point evaporative cooler (DPEC) using the exhaust air as the working gas, which is precooled in one of the three cooling coils. The other two coils are used for fresh air cooling and can be arranged in either parallel mode (HAC-P) or series mode (HAC-S). A sprayer is also designed for appropriate fresh air humidification before DPEC process. For parametric analysis, five independent affecting parameters are included: the air-to-water heat capacity ratio, the ambient temperature and humidity, the characteristic number of heat transfer units of the internal heat exchangers, and the fresh air flowrate. In this article, the energy-saving potential in the HAC-P mode is evaluated for applications in five northwest China cities—Karamay, Urumqi, Hami, Jiuquan and Lanzhou over the summer period (from June to August). The results show that the energy-saving rates are between 42.5% and 64.0% when it is compared with the conventional system.

Linear stability of convective motion in a tall vertical annulus was analysed in the paper. The base flow was generated by a non-uniform distribution of heat sources in the radial direction. The base flow velocity and temperature were obtained analytically solving the system of Navier-Stokes equations under the Boussinesq approximation. The linear stability problem was solved for axi-symmetric and asymmetric perturbations by a collocation method based on the Chebyshev polynomials. Numerical results showed that there were three destabilising factors: (1) increase of the gap between the cylinders, (2) increase of the density of internal heat sources towards to the outer boundary of the annulus and (3) increase of the Prandtl number.

Existing heat balancing and energy targeting model in Pinch Analysis rely on use of interpolated values of specific heat capacities and global values of minimum temperature difference ∆Tmin, respectively. Even though this model is useful in estimation of the maximum internally recoverable heat recoverable in processing plants, it does not adequately represent the actual state properties of industrial processes. Specific heat capacities of fluids are polynomial functions of temperature of material under processing. The values of ∆Tmin also vary depending on the nature of the process stream under analysis. In this study, improvement to the heat balancing and energy targeting processes of pinch analysis was proposed. The study combined the use of stream specific values of ∆Tmin and polynomial temperature functions of specific heat capacities for heat targeting model. This was coded and executed using a PHP program. The model performance was tested using data from three thermochemical plants, Plant A, B and C, which process linear alkyl benzene sulphonic acid, dairy products and ethanol, respectively. The proposed method for heat balancing computed more heating requirements for plant A, B and C by 0.37%, 0.65% and 0.72% respectively, compared to the traditional method of heat balancing. The cooling loads for Plant A and B were less by 2.23% and 32.52% respectively, while for Plant C, they were more by 0.64%. The computed internally recoverable heat targets were more by 1.5%, 4.5% and 2.2% for Plants A, B and C. Simulations of the proposed model were carried out over a range of temperature targets, for different process streams. For gaseous process streams, heating and cooling load requirements were less. Reverse behavior was observed in liquid and steam containing streams, where the heating and cooling load requirements were more.

The formulation and method of solution of the problem of time-optimal control of induction heating process of an unlimited plate with two control actions on the value of internal heat sources with technological constraint in relation to a one-dimensional model of the temperature field are proposed. The problem is solved under the conditions of a given accuracy of uniform approximation of the final temperature distribution over the thickness of the plate to the required. The method of finite integral transformations is used to search for the input-output characteristics of an object with distributed parameters with two control actions. The preliminary parameterization of control actions based on analytical optimality conditions in the form of the Pontryagin maximum principle is used. At the next stage reduction is performed to the problem of semi-infinite optimization, the solution of which is found using the alternance method. The alternance properties of the final resulting temperature state at the end of the optimal process lead to a basic system of relations, which, if there is additional information about the shape of the temperature distribution curve, is reduced to a system of equations that can be solved. An example of solving the problem of time-optimal control of temperature field of an unlimited plate with two offices is carried out in two stages. At first stage the case of induction heating without maximum temperature constraints is considered, at the second stage is carried out on the basis of the results of the first stage to obtain the solution subject to the limitation on the maximum temperature of the heated billet.

Thermodynamic analysis including energetic and exergetic analysis is carried out employing Engineering Equation Solver for the five modified cycles: dual expansion cycle, internal heat exchanger cycle, work recovery cycle, work recovery with internal heat exchanger cycle and vortex tube expansion cycle. Contours are developed to study the effect of gas cooler temperatures and evaporator temperatures on the system performance and optimum gas cooler pressure. The modified cycle with work recovery turbine offers relatively higher COP and higher exergetic efficiency with lower compressor discharge pressure. The exergy loss in compressor, gas cooler, throttle valve and vortex tube (VT) are considerably higher than that in internal heat exchanger (IHX), evaporator and turbine. It is observed that COP of modified cycle with VT is slightly less than that with IHX, whereas the cycle with work recovery turbine brings the highest COP with the improvement of 25% at the gas cooler exit temperature of 305 K and evaporator temperature of 248 K.

Purpose This paper aims to present thermal and mechanical stresses in solid and hollow thick-walled cylinders and spheres made of functionally graded materials (FGMs) under the effect of heat generation. Design/methodology/approach Constant internal temperature and convective external conditions in hollow bodies along with internal heat generation with a combination of outer convective conditions in solid bodies are investigated individually. The effect of the heat convection coefficient on solid bodies is additionally discussed. The variation of the FGM properties in the radial direction is adapted to the Mori–Tanaka homogenization schemes, which produces irregular and two-point linear boundary value problems that are numerically solved by the pseudospectral Chebyshev method. Findings It has been shown that the selection of the mixtures of FGMs has to be made correctly to keep the thermal and mechanical loads acting on objects at low levels. Originality/value In this study, both solid and hollow functionally graded cylinders and spheres for different boundary conditions that are as their engineering applications are examined with the proposed method. The results have demonstrated that the pseudospectral Chebyshev method has high accuracy, low calculation costs and ease of application and can be easily adapted to such engineering problems.

The problem of steady-state laminar two-dimensional rarefied gaseous flow by natural convection heat transmission in a partly heated square two-sided wavy cavity with an internal heat generation is numerically studied employing the finite volume procedure. The Boussinesq approximation is adopted to account for buoyancy effects. A favorable comparison for validation purposes with previously published work is obtained. The study is performed with distinct values of the external Rayleigh number (104 ≤ RaE ≤ 106), Knudsen number (0.01 ≤ Kn ≤ 0.1), inclination angle (ϕ = 0°, 30°, 60°, and 90°), three non-dimensional heater lengths (L/H = 0.175, 0.35, and 0.52), while the Prandtl number (Pr) is fixed at 0.7. The outcomes of this research yield that the average Nusselt number (Nuavg) relies inversely on Kn and directly on RaE. Moreover, it is revealed that increasing L/H value decreases Nuavg values at the lower partially heated cavity wall. Additionally, the study reveals that as the heat generation term (Qgen) increases, the Nuavg increases as well. Finally, a correlation between Nuavg and the parameters inspected in this research is suggested.

Methods for determination of thermal properties of various materials, including iron ore, are adequately covered in the relevant literature. They rely, as a rule, on certain solutions to the problem of heat conductivity without consideration of internal heat sources that occur in the body of sample under study if the heating (cooling) process is accompanied by various thermochemical and phase transformations, which is typical of iron ore materials. Therefore, such methods allow determination of only effective or apparent values of thermal properties, which adequately reflect properties of the material only in specific heat treatment conditions. The point is that in the presence of internal heat sources, parameters to find substantially depend on the heating rate and sample shape and size. This paper considers a new technique, which allows finding (at known calculated values of heat capacity and material density) how five thermal parameters (temperature and heat conductivity coefficients, power of internal heat sources, as well as effective values of heat and temperature conductivity) depend on the heating (cooling) temperature. Improvement of methods of processing iron ore materials at elevated temperatures in various heat aggregates requires knowledge of thermal properties of the materials and variation of these parameters during heat treatment in a wide temperature range. This is due to the fact that heating of such materials is usually accompanied by development of complex physical and chemical processes such as oxidation and reduction of iron oxides, decomposition of carbonates, porosity and strength change, formation of new chemical compounds, and others, many accompanied by release or absorption of heat [1–12]. The degree of completion of these processes depends on the temperature conditions and composition of the material and coolant. Consideration of the effect of these conditions on the temperature distribution in the treated layer of material and consequently on the duration of the heat treatment it is possible only having reliable data on the thermal constants [13]. Methods of determination of thermal properties of iron ore materials are widely discussed in the literature [14–20]. However, all they address the heat conductivity problem without consideration of internal heat sources, and thus can determine only the effective values of thermal parameters, valid for specific conditions of heating. The effect of internal heat sources on thermal properties to find can be taken into account only by using respective solutions to the heat conductivity problem. The below method to determine the complex of thermal properties of iron ore materials relies on the solution to the heat conductivity problem with internal heat sources under symmetric heating conditions of the first kind, which is valid for objects of simplest shape (infinite plate, infinite cylinder, ball).

A phenomenological model of the kinetics of austenite decomposition of low-carbon low-alloy high-strength steels is presented. The model is based on experimentally obtained empirical dependences linking the transformation rates with the specific power of the heat flux from the metal volume and with the temperature of this volume. This model was used to implement the finite-difference scheme to solve the problem of heat conduction in a medium with internal heat release sources. The digital twin of the cooling process, which includes the specified calculation procedure, is integrated into the TLS 5000 automation system of PAO Magnitogorsk Iron and Steel Works. The determined mass fractions of austenite decomposition products are used for both the design certification of the structural state of rolled products and the construction of statistical models to predict mechanical properties.

The paper addresses a mixed convection boundary layer flowing on a horizontal surface embedded in porous medium with exponentially decaying internal heat generation (IHG) and internal mass generation (IMG) from a specific component with chemical reaction in order to investigate the heat and mass transfer characteristics. Corresponding similarity solutions are used to reduce the governing partial nonlinear differential equations to three ordinary differential equations for the dimensionless stream function, temperature, and concentration with the following parameters: mixed convection parameter $$\varepsilon$$ , chemical reaction parameter $$\gamma_1$$ , and Lewis number $$Le$$ . The influences of these parameters on the velocity, temperature and concentration profiles, and Sherwood and Nusselt numbers are thoroughly compared and graphically illustrated. Computations are performed with a system of parameters using built-in codes in Maple. Media with and without IHG and IMG are compared with available open literature using graphs and tables and are found to be in excellent agreement.

The dc in a power system may be caused by geomagnetic disturbances that are the result of solar storms and high-altitude nuclear detonations. Increased inverter-based generation is also contributing to small dc injection into the power systems. The resultant dc could have serious consequences for the power systems as it may drive power transformers into saturation, cause transformer internal heating, cause large draw of reactive power, and misoperation of protective relays. This letter proposes a novel power electronics-based dc mitigation approach that involves a transformerless series active filter integrated between the neutral point and ground of power transformers serving multiple purposes. The first objective is to surpass the effect of dc injection, the second goal is voltage regulation, and the third is to provide harmonic isolation or impedance balancing. The proposed device is currently being developed on a 7.2-kV/240-V single-phase transformer; however, the solution is also relevant for 24–500-kV networks. The system circuitry, operation, and control are implemented and verified for this letter in a controller hardware-in-the-loop (C-HIL) test setup using a Typhoon HIL-402 simulator. Results indicate that our approach is a promising alternative to traditional neutral capacitor-blocking strategies.

The influence of internal heat sources on temperature distribution during the operation of thermoelectric generators (TEG) is investigated. Taking into account various factors affecting the temperature regime, including internal heat sources, a multilevel model of a two-stream TEG has been developed, which allows one to calculate the temperature distribution and the integral characteristics of the generator. The calculations were carried out using the PHOENICS program package; as a result, the dependences of the electrical characteristics and the temperature drop on the junctions on the load resistance, speed, and coolant temperature were obtained. A comparison is made with the corresponding indicators in the absence of internal heat sources. It is concluded that the influence of internal heat sources on the temperature drop and electric power increases with decreasing load resistance. Thus, in the maximum power mode, which corresponds to the ratio of the load resistance to the internal resistance of the module m = 1.15, the temperature drop decreases by 3.5–4.0%, while that at m = 0.01 is by 7.5–8.5%. TEG power in maximum power mode decreases by 7.5–8.0%. Studies have shown that the influence of internal heat sources on the characteristics of the TEG is more substantial when the flow rate in the heat exchangers is lower. The greatest decrease in the values of indicators due to the influence of internal sources was observed at v = 0.2 m/s and amounted in maximum power mode to 5.5–6.0% for the temperature difference and 12–13% for power. The results obtained indicate that the influence of internal sources on the characteristics of TEGs is significant enough, which implies that the most accurate estimates of the thermal and electrical performance of TEGs can be made only by taking into account the effect of internal heat sources on the temperature distribution in TEGs.

The objectives of the research are to explored the heat and mass transport over a paraboloid surface of revolution by taking the effects of Lorentz force, resistive heating and internal heat source. The dimensionless version of the model was attained via similarity transformations. Then, for solution purpose, RK scheme is utilized and performed computations for the flow fields. The influence of different physical quantities on the flow characteristics described comprehensively via graphs. It is examined that the stretching index parameter m opposes the fluid velocity and the temperature enhances for Eckert number. Moreover, significant impacts of the Schmidt number are observed for mass transfer gradient.

Improvement of product performance, efficiency, and reliability is a major concern of experts, scientists, and technologists dealing with the dynamics of water conveying nanoparticles on objects with nonuniform thickness either coated or sprayed with the catalyst. However, little is known on the significance of quartic autocatalysis as it affects the dynamics of water conveying alumina and cupric nanoparticles. In this study, comparative analysis between the dynamics of water conveying 29 nm CuO and 47 nm $$\hbox {Al}_2\hbox {O}_3$$ on an upper horizontal surface of a paraboloid of revolution is modeled and presented. In the transport phenomena, migration of nanoparticles due to temperature gradient, the haphazard motion of nanoparticles, and diffusion of motile microorganisms were incorporated into the mathematical models. Due to the inherent nature of the thermophysical properties of the two nanofluids, viscosity, density, thermal radiation, and heat capacity of the two nanofluids were incorporated in the mathematical model. The nonlinear partial differential equations that model the transport phenomenon were transformed, non-dimensionalized and parameterized. The corresponding boundary value problems were converted to an initial value problem using the method of superposition and solved numerically. The concentration of the catalyst increases significantly with buoyancy at a larger magnitude of space-dependent internal heat source in the flow of 29 nm CuO–water nanofluid. Negligible migration of nanoparticles due to temperature gradient decreases the concentration of the fluid throughout the domain.

The numerical examination of radiation and natural convection in a porous radial fin along with varying internal heat generation with respect to temperature is carried out in the current study. The aim of this study is to scrutinize the heat transfer phenomenon in fin wetted with water-based carbon nanotubes like single-walled carbon nanotubes and multiwalled carbon nanotubes. In the proposed work, the Darcy’s model is employed for the analysis. The modeled equations are nondimensionalized and solved by utilizing Runge–Kutta–Fehlberg method. The impact of relevant parameters on the heat transfer rate is comprehensively explored with an aid of graphs. Here, multiwalled carbon nanotube–water shows better heat transfer from surface of fin compared to single-walled carbon nanotube–water.

The stability of natural convection in a vertical layer of heat-generating Darcy porous medium saturated with an Oldroyd-B fluid using a local thermal non-equilibrium (LTNE) model has been investigated numerically. The impermeable vertical walls of the porous layer are maintained at different uniform temperatures. As a consequence of LTNE model, two temperature equations representing the fluid and solid phases separately are used for the heat transport equation. A uniform volumetric heating in both fluid and solid phases is considered and the transfer of heat between the phases is considered in the basic state. The internal heating introduced asymmetry in the basic flow which led to the existence of competing modes. The intricacies of internal heat source strength in the fluid and the solid phases are clearly discerned on the stability of the system. The stress relaxation parameter $$\Lambda_{1}$$ , fluid-heat generation parameter $$Q_{f}$$ , solid-heat generation parameter $$Q_{s}$$ and the porosity-modified conductivities ratio $$\gamma$$ were found to exhibit destabilizing effect on the system, while the strain retardation parameter $$\Lambda_{2}$$ shows an opposite trend even in the presence of internal heating.

We have investigated the study of double diffusive stationary convection in the presence of applied magnetic field and internal heating. A weakly nonlinear stability analysis has been performed using the finite amplitude Ginzburg-Landau model. This finite amplitude of convection is obtained at third order of the system. It is assumed that the buoyancy term has two parts, steady and oscillatory parts. The second part is varying sinusoidally with time and vibrates the system with finite amplitude δ1 and frequency ω. The effects of δ1 and on heat/mass transports have been analysed and depicted graphically. The studies are established that the heat/mass transports can be controlled effectively by gravity modulation. Further, it is found that internal Rayleigh number Ri is to enhance heat transfer and reduces the mass transfer in the system.

A linear stability assessment was performed to study the impact of internal heating and variable gravity in an anisotropic porous medium of a ferrofluid layer system on the onset of Benard-Marangoni convection. The system is heated from below with both the lower and upper limits are considered as completely insulated to the disturbance of the temperature. The eigenvalue problem is solved by using regular perturbation technique to obtain the critical Marangoni number and also the critical thermal Rayleigh number. It is noted that the increase of value anisotropic permeability, Darcy number and also magnetic number will enhance the convection of the system while the increasing values of anisotropic thermal diffusivity will help to stabilize the system.

The technology, flow diagram, and results of combined cleaning of deposits from the internal heating surfaces (tubes) of high-pressure heaters are described. The technology makes it possible to substantially reduce the temperature drops in HPHs.

A transient numerical analysis of natural convection of near-freezing water in a cavity with lateral openings and internal heat sources is carried out to investigate the influence of the heat dissipation rate in the flow configuration. The heat sources were positioned to create buoyancy-opposing and buoyancy-assisted conditions simultaneously and the top and bottom walls are kept at 0◦C. The non-linear dependence of the physical properties with temperature is considered in the governing equations. Based on the heat dissipation rate, six different regimes were observed and classified through a qualitative analysis of the temporal evolution of the velocity and temperature fields. The characteristics of heat transfer for each regime are analyzed to define the most important mechanisms of heat removal. In the upper layer (heated from below), the buoyancy forces eventually overcome the viscous forces and unsteady thermal plumes are formed, in-creasing the heat removal through the openings, while the heat transfer with the top wall is not significant. In the lower layer, the development of wave-like instabilities leads to oscillatory regimes for intermediate heat dissipation rates, while for high dissipation rates a steady convective regime is observed. This behavior increases the heat transfer with the bottom wall, making it much more significant when compared with the upper layer.

Thermo-mechanical effects due to changes in the ambient temperature on the shop floor and internal heat sources caused by the manufacturing process significantly contribute to the geometric deviations of a machine tool and therefore, the geometric deviations of the manufactured workpiece. Minimizing these thermally induced geometric deviations is worthwhile since the requested tolerances of machined workpieces become continually smaller nowadays. To investigate the overall deformations of a machine tool structure due to variations in ambient temperature the geometric errors of a five-axis machine tool at different ambient temperatures by means of a portable climate simulation chamber are systematically mapped. While positioning and squareness errors of the linear axes are significantly influenced by the ambient temperature, straightness as well as rotational errors were less sensitive to temperature effects. For the investigated machine tool errors of the two rotational axes are negligible due to an active cooling of these axes. Through numerical error compensation of the linear axes, the geometric errors of the investigated machine tool can be reduced up to 80%. Finally, an outlook how a temperature-dependent compensation could be derived from previously measured compensation fields at discrete temperatures and afterwards applied on-the-fly during manufacturing is given.

Nonlinear convective flow and heat transfer characteristics are analyzed between stationary nonporous and porous rotating disks utilizing graphene nanoparticles in a water and ethylene glycol base fluid. Heat transfer characteristics are analyzed via incorporating thermal radiation and heat absorption/generation. The governing fluid equations are computed numerically using Runge–Kutta based shooting technique after employing appropriate transformations. Characteristics of sundry variables are elaborated graphically as well as through the construction of Table for water base and ethylene glycol based graphene nanoparticles. It is observed that improvements in nonlinear convection variable owing to temperature and heat generation variable improve wall friction in radial direction. Improvement in Hartman number decreased wall friction in radial and tangential directions along with Nusselt number in graphene/ethylene glycol and graphene/water nanofluid. Ethylene glycol based graphene nanofluid takes less time for execution as compared to water based nanofluid.

Exact and numerical solutions for steady heat conduction in the enclosure between two long isothermal elliptic tubes with uniform internal heat generation are obtained. The heat conduction process within the enclosure is mainly influenced by internal heat generation, axis ratio of inner tube and major axes ratio of the two tubes. The solutions are obtained in terms of the temperature and local heat flux distributions. The study has shown that the numerical results are in excellent agreement with the analytical results.

In this paper, the heat transfer in thin film flow on unsteady stretch plate of nanofluids is studied. The nanoparticles of copper Cu, alumina Al2O3 and titanium TiO2 with water-base fluid are considered. Similarity transformations simplify the governing equations. The resulting combined nonlinear differential equations were calculated by the homotopy analysis method (HAM). The solutions in form of series are extracted, and the numerical results are presented. An improvement in the volume of the nanoparticles fraction could boost the temperature profile, and related boundary layer thickness is observed. In addition, film thickness parameter $$\gamma$$ decreases with the increase in nanoparticle fraction $$\phi$$ and unsteadiness parameter S.