Transfer Intensity Research Articles

Numerical and experimental study on temperature and heat transfer characteristics in centrifugal compressor diffuser

Lubrication oil aerosol deposit and coking in the compressor diffuser is a typical issue for the high power density internal combustion engine (ICE) using the closed crankcase ventilation (CCV) system. The aerosol coking significantly negatively influences the compressor's performance, leading to a penalty on ICE performance. The severity of the coking effect is highly dependent on temperature. In order to predict occurrence of coking and to clarify how to avoid aerosol coking in the compressor, the temperature distribution and heat transfer characteristics are investigated in this study. An experimental investigation on the diffuser temperature distribution at shroud side was carried out first. Numerical simulations that consider the heat transfer between the solid domain and the fluid domain are conducted, aiming at analyzing the temperature distribution of inner surface. The detailed simulation model of small high-pressure-ratio compressor for predicting coking risk is established. Furthermore, the simulation model is validated by the experimental results. The results indicate that the shroud side of the diffuser sees the highest temperature level in the diffuser. Under typical operation conditions, the temperature at the diffuser wall exceeds the threshold coking temperature of lubrication oil aerosol, this location most likely to have severe coking issues. Thus, the location of the shroud plate is the primary region that needs to be cooled down to mitigate the coking issue. Meanwhile, the intensity of heat transfer between the fluid and solid domain in the diffuser region degrades significantly along the flow direction and sees an 80% drop from diffuser inlet to outlet, indicating the requirements for further enhancement of heat transfer in diffuser shroud side along streamwise.

MODELING THE DYNAMICS OF HEAT AND MASS TRANSFER PROCESSES IN A TUBULAR HEAT EXCHANGER UNDER PULSED INFLUENCES

The paper discusses the results of experimental studies of the influence of the degree of inhomogeneity of a liquid flow on the dynamics of heat and mass transfer processes under pulsed impacts. High-voltage electric discharges in a liquid medium were used as impulse actions, through which an electro-hydraulic effect is realized, accompanied by the appearance of shock waves. The dynamics ofthe occurring nonlinear, rapidly changing heat and mass transfer processes at high hydraulic pressures cannot be described using differential equations. The simulation was carried out on the basis of the method of group consideration of arguments, the advantage of which is the construction of polynomial dependencies using a small amount of experimental data. The results of constructing polynomial dependences made it possible to reveal the synergistic effect of the influence of flow parameters on the dynamics of the impulse pressure amplitude and the intensity of heat transfer.

INTENSIFICATION OF HEAT TRANSFER IN HEAT EXCHANGE EQUIPMENT DURING CONDENSATION OF WATER VAPOR AFTER STEAM TURBINE INSTALLATIONS IN NUCLEAR POWER.

The determining parameter that characterizes the intensity of heat transfer in heat exchange equipment is the heat transfer coefficient, the value of which depends on the thermal resistances occurring in the corresponding equipment. Thus, in the heat exchanger-condenser of a steam turbine installation of a nuclear power station, this is the thermal resistance during heat transfer of cooling water in heat exchange tubes and during heat transfer of water vapor condensing in the intertube space. The value of the heat transfer coefficient also depends on the geometric and thermophysical characteristics of the heat heat exchange tubes, on the contamination of the cooling water, on the presence of air in the condensing vapors. According to the proposed scheme of the experimental setup of the "pipe in a pipe" type, calculations of the heat transfer coefficient were performed when using an external transparent glass pipe and an internal metal pipe, which was treated from the outside with a water-repellent coating that provides dropwise condensation of water vapor, as well as without treatment for film condensation. Contamination of the cooling water and the presence of air in the water vapor in both cases of condensation should be the same and as minimal as possible. The analysis of the results of the calculations allows us to draw the following conclusions: the change in the state of the outer surface of the heat exchange tubes increases the heat transfer coefficient during condensation of water vapor almost three times, which ensures an increase in the efficiency of heat transfer (more than 10%), and accordingly allows to reduce the working surface of the heat exchange equipment, which is especially relevant in modern conditions of operation of power equipment, when there is a need for emergency reconstruction of partially destroyed heat exchange equipment. Bibl. 11, Fig. 2.

Relationship between the Intensity of Secondary Flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

Relationship between the Intensity of Secondary Flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

Multi-objective evolutionary multitasking algorithm based on cross-task transfer solution matching strategy

The superior performance of evolutionary multitasking (EMT) algorithms is largely owing to the potential synergy between tasks. Current EMT algorithms only involve a unidirectional process of transferring individuals from the source task to the target task. This method does not consider the search preference of the target task in the process of finding transferred individuals; therefore, the potential synergy between tasks is not fully utilized. Herein, we propose a bidirectional knowledge transfer method, which refers to the search preference of the target task in the process of finding transferred individuals. These transferred individuals fit the search process well for the target task. In addition, an adaptive strategy for adjusting the intensity of the knowledge transfer is proposed. This method enables the algorithm to adjust the intensity of knowledge transfer independently according to the living conditions of the individuals to be transferred to balance the convergence of the population with the computational intensity of the algorithm. The proposed algorithm is compared with comparison algorithms on 38 multi-objective multitasking optimization benchmarks. Experimental results show that the proposed algorithm is not only outperforming other comparison algorithms in more than 30 benchmarks, but also has considerable convergence efficiency.

Алгоритм газодинамического расчета асимметричных конусов методом локальных клиньев и конусов

Studies related to alteration in the shape of a body moving in the dense layers of the Earth’s atmosphere at high speed are associated with the need to consider an entire set of problems having no strict physical and mathematical description. To solve problems of this kind, it becomes necessary to use semi-empirical approaches tested on fundamental experimental data obtained in a fairly wide range of determining factors on the models characterized, as a rule, by an extremely simple pattern of the gas flow. Introduction of this mathematical description in real operating conditions is characterized by the need to study the processes of gas dynamics and heat transfer in the three-dimensional formulation combined with the complex nature of their course. These processes determine alteration in the shape of a body causing serious problems associated with rigorous solution of this complex mutually conjugate problem. As a result, there appeared a large number of publications devoted to approximate methods for calculating the spatial flow around bodies by the gas flow used to calculate intensity of the convective heat transfer. This article describes in detail the algorithm for solving the problem of spatial flow around blunt cones by the method of local wedges and cones

Finite Amplitude Oscillatory Convection of Binary Mixture Kept in a Porous Medium

In the present study, the double-diffusive oscillatory convection of binary mixture, 3He–4He, in porous medium heated from below and cooled from above was investigated with stress-free boundary conditions. The Darcy model was employed in the governing system of perturbed equations. An attempt was made, for the first time, to solve these equations by using the nonlinear analysis-based truncated Fourier series. The influence of the Rayleigh number (R), the separation ratio (ψ) due to the Soret effect, the Lewis number (Le), and the porosity number (χ) on the field variables were investigated using the finite amplitudes. From the linear stability analysis, expressions for the parameters, namely, R and wavenumbers, were obtained, corresponding to the bifurcations such as pitchfork bifurcation, Hopf bifurcation, Takens–Bogdnanov bifurcation and co-dimension two bifurcation. The results reveal that the local Nusselt number (NL) increases with R. The total energy is enhanced for all increasing values of R. The deformation in the basic cylindrical rolls and the flow rate are enhanced with R. The trajectory of heat flow was studied using the heatlines concept. The influence of R on the flow topology is depicted graphically. It is observed that the intensity of heat transfer and the local entropy generation are increased as R increases.

Current and future characteristics of land use based on intensity analysis and PLUS model : a case study of Foshan city, China

Land use change drives urban pattern change. The development of urbanization will result in the diminution of ecological land and the extinction of ecological defense. Foshan is a highly typical city. Identifying the characteristics of dynamic land use changes and predicting the future land use pattern are crucial components of land use planning. Land use transfer matrix and intensity analysis model were utilized in this study. Three representative years, 2010, 2015, and 2020, were used to analyze the interval, category, and transition level characteristics for Foshan City. Then, based on the PLUS model and the Markov model, multiple scenarios for the land use of Foshan City in 2030 were developed. The results indicate the following: (i) According to the interval level intensity analysis, the general trend of land use intensity between 2010 and 2020 is first rapid and then gradual. At the category level, construction land demonstrates stable activity with increasing intensity, whereas dike-ponds demonstrate continuous activity with decreasing intensity. (ii) From 2020 to 2030, there is a slowing in the intensity of site conversion. The natural development scenario is more in line with the city's development. (iii) In simulations of future urban scenarios, the dike-pond has a decreasing trend over the scenario. At the future transition level, three possible land use conversion systems exist: "forestland—dike-pond," "water—dike-pond," and "dike-pond—construction land." With this study, Foshan City can serve as a case study for sustainable development and rational planning.Article HighlightsLand use change components, quantity, exchange and shift were estimated.The largest net change occurred in 2010–2015 due to human activities.Spatial reallocation were characterized by exchange and shift.The largest exchange occurred in 2010–2020 due to the dike-pond eroded.The dike-pond has a decreasing trend over the simulated scenario.

Assessment of the Efficiency of Thermal Waste Regeneration in the Blown Impassable Channels of Heating Mains

To solve the problem of increasing the energy efficiency of thermal networks with heat pipelines located in impassable channels, a schematic and structural solution for the rational utilization of thermal waste generated during the transport of thermal energy has been developed. Due to the complexity of creating a full-scale experimental installation, a virtual experimental installation created by means of the Ansys software package was used in the study, on which an active numerical experiment was performed. Regression equations have been obtained for calculating the intensity of heat transfer from pipelines and channel enclosing structures with a given change in the size, length of channels and pipelines for various outdoor and ground temperatures characteristic of the heating and inter-heating periods. Statistical analysis, verification and validation of the obtained regression correlations were carried out, two-dimensional hypersurface crossections were obtained in the studied range of controlled factors. The results of numerical simulation of the operating modes of forced ventilation of impassable channels of heating mains with determination of the density of heat flows from the ground and mains water pipelines, air flow and the corresponding exhaust fan capacities have been presented. The following conditions in this case were accepted: the air flow rate is not higher than 8 m/s, the length of the heat pipeline section ensures the air temperature at the outlet of the channel at which there is no increase in heat losses from mains water pipelines to the ground under normal operating conditions of heating networks. The energy efficiency of heat utilization dissipated by mains water pipelines as well as ground cooling in impassable heating mains channels was investigated by intensifying their ventilation and using heat pump equipment at the end points of the channels for heating mains water, depending on the geometric characteristics of the heating mains section, air temperature, soil and mains water installations at central heating points or directly at heat sources. The potential of energy saving for district heating systems with various types of heat sources and the combined power system during the utilization of heat flows from the ground and heat pipelines laid in impassable channels has been identified. On the basis of the energy-saving potential, a technical and economic assessment was carried out and the conditions for the economic feasibility of implementing the proposed technical solution were determined.

Novel Insights on the Metal-Support Interactions of Pd/ZrO2 Catalysts on CH4 Oxidation.

With the environmental harm of unburnt CH4 in natural gas vehicle exhaust, oxidizing CH4 to CO2 over catalysts at low temperatures becomes an exigent issue. Supported Pd catalysts possess higher CH4 activity than other noble metal catalysts. A series of Pd/ZrO2 catalysts were synthesized to research the potential relationship among Pd particle morphology, electron transfer, CH4 oxidation mechanism, and catalytic activity. Characterizations show that the ratio of PdOx facets to edge/corner sites on four catalysts increases in the order of PZ85 ≈ PZ40 < PZ55 < PZ70 because of the difference in content of surface -OH groups, and this order turns out to be the same as that of electron transfer intensity, revealing the degree of metal-support interactions. This kind of metal-support interaction in PZ70 can be helpful to accelerate CH4 combustion via promoting the break of the C-H bond and dissociation of CO3* according to density functional theory studies. T90 of the PZ70 catalyst with optimum catalytic activity reaches 331 °C.

Study on the vertical oscillatory gas-liquid two-phase flow and heat transfer characteristics

Exploring the flow and heat transfer characteristics of oscillations will help to evaluate the dynamic behavior and safety of thermal management systems (TMS) in automobiles, ships, and aircraft. Faraday waves is a phenomenon that standing waves oscillate with half of the driving frequency under specific oscillation conditions. The current work combines both, studying the influence of oscillation parameters of Faraday waves on heat transfer since the oscillatory liquid surface and the shaking of the liquid-filled container frequently occurs in practical engineering applications. A numerical simulation on heat transfer characteristics under different vibration parameters was carried out in this study. The results demonstrate that oscillation has a promotion effect on the heat transfer coefficient. The influence of the driving frequency on heat transfer will be affected by the driving amplitude. When the driving amplitude is greater than 0.83 mm or the driving frequency is greater than 22 Hz, the waveform will change from periodic and regular to disorder and turbulence, and the heat transfer between the two-phase flow will be significantly enhanced. In the range of oscillation parameters covered in this study, increasing the driving amplitude is more effective than increasing the driving frequency for enhancing heat transfer. And when the driving amplitude is big enough, such as A = 1.03 mm, the heat transfer intensity increases to about 1.5–2 times as against A = 0.43 mm. Therefore, when considering the design of TMS, the dynamic empirical correlations proposed by this study can offer some useful guidance.

Spray and dynamic heat transfer induced by 2-methylfuran transient spray impingement on piston surface

In the face of increasing air pollution and stricter emission requirements, it is very important to reduce particulate matter emissions in engine exhaust. The presence of the attached liquid film in gasoline direct injection engines produced by spray impingement is an important reason for the increase in engine particulate emissions. The dynamic heat transfer induced by the spray impingement is a key factor affecting the evaporation and existence time of liquid film. In this paper, a single-hole injector was used to carry out 2-methylfuran (MF) spray impingement experiments. The macroscopic morphological characteristics and the dynamic heat transfer of transient spray impingement under different conditions were systematically studied. Spray particle size distribution and spray impact force were also measured to assist in explaining the underlying mechanism responsible for the dynamic heat transfer. The results show that the surface heat flux increases with the rise of initial piston surface temperature. Increasing the injection pressure makes the droplets have a stronger impact force and smaller average diameter, which enhances the heat flux and also produces more bounce and splash of droplets on piston surface. Both the number of small-size droplets and impact force are reduced by the intense evaporation caused by increasing the injection temperature, resulting in the decrease of heat flux and surface temperature reduction. Increasing the distance decreases the droplet diameter and impacting force, as a result, the heat transfer intensity is weakened.

Numerical simulation on heat transfer characteristics of unstable steam jet condensation under rolling condition

Direct contact condensation technology has been widely used in nuclear power, aerospace, chemical industry, and other fields due to efficient mass and heat transfer characteristics between two phases. Rolling motion applied to offshore cases typically significantly affects dynamic flow and heat transfer characteristics. Thus, investigating the heat transfer characteristics of unstable steam jet condensation is necessary. The present study numerically explored the heat transfer coefficient of main and detached bubbles under rolling and static conditions. The relationship between pressure and heat transfer coefficient was assessed to reveal the pressure generation mechanism. The peak value of pressure oscillation was mainly caused by the rapid collapse induced by intense condensation of detached bubble instead of main bubble. The heat and mass transfer intensity could be fortified under rolling conditions. It would increase as the maximum rolling amplitude rise and the rolling period decrease, while the maximum improvement was up to 30%.

Sediment and Particulate 137Cs Budget Studies in Upa River Basin: History, Results, and Prospects

The intensive pollution of vast areas after the Chernobyl accident, especially in the territories of Ukraine, Russia, and Belarus, has not only become a serious environmental issue, but also presents wide methodological opportunities for studying the functioning of natural systems. The proposed work is a generalization of the results of studies on the migration of 137Cs in the runoff of river sediments, which were carried out in the basin of the Upa River for over 30 years after the accident. This basin is one of the most radioactively contaminated and studied in Central Russia. Over the past three decades, under the conditions of the decreasing snowmelt runoff in the spring and reduced share of cultivated land over the post-Soviet period, the intensity of the 137Cs transfer has decreased. The 137Cs deposit losses associated with erosion activities do not exceed a few percent. Most of the mobilized sediments and sediment-associated radionuclides accumulate in dry valleys or artificial reservoirs. With a general reduction in the durations of floods, rivers have become the predominant channels for the transfer of sediment yield and particulate pollutants. The exploration of the vertical distribution of the 137Cs in the accumulative strata makes it possible to identify the changes in the sediment budgets of the rivers and their radioecological consequences.

Physical characteristics of maize seeds and their technological significance in processing and storage of sowing material

Topicality. The research on the preparation of high-quality seed of maize hybrids based on the consideration of their technical and technological properties at the stages of harvesting, processing and storage is relevant today. Purpose. To study and determine the essential physical parameters that characterise technical and technological characteristics and affect the seed quality of maize hybrids. Methods. The research includes theoretical and practical calculations with a review of literature sources, laboratory and model experiments and the laying out of field trials, mathematical and statistical evaluation of the data obtained. The experiments were carried out according to standardised methods of DSTU and agrotechnical recommendations, and the source material was hybrids bred by the State Enterprise Institute of Grain Crops of the National Academy of Agrarian Sciences of Ukraine. Results. The most significant physical characteristics of seeds are evaluated: shape, linear size, volume and geometric surface of seeds, their weight and specific weight, mechanical strength of maize hybrids and self-pollinated lines, and differences between them are determined. Experiments on seed separation, drying and storage were carried out, and certain physical characteristics were identified that have a special impact on the technology of these processes and form the seed quality. Conclusions. The dry seed quality during the separation process is most affected by the linear size of the seed, in particular, seed width, depending on which the fractions with the highest germination and yield are separated (tailing through round holes of 8 mm and more in diameter). Drying is influenced by the coefficient that characterises the ratio of the geometric area to the volume of the seed; at a coefficient of more than 1.0 (in experiments – 1.14–1.22), the intensity of moisture transfer and the drying rate increase by 8.3–15.7 % compared to a coefficient of 1.0. During storage, especially long-term storage, the quality and resistance of seeds is affected by the equilibrium moisture content, which should be at the level of 12 %, depending on the environmental conditions. Key words: maize seed, harvesting, drying, storage, physical characteristics, germination, yield

Influence of heater size on critical heat flux in flat microchannels with intense localized heating

Experiments were carried out on flow boiling in mini- and micro- channels under local heating for different heater size. It was found that with an increase in the channel height in the range of 0.2–3.7 mm, the intensity of heat transfer and the critical heat flux increase significantly. For a given flow rate and channel height, the critical heat flux on the 3x3 mm2 heater exceeds the heat flux on the 10x10 mm2 heater, and the difference increases with increasing channel height. Boiling curves were also obtained.

A Transition Transfer Mechanism in Payment Network

People’s economic activities constitute a payment network for money transfer. The existing studies on the transfer law of money in payment networks are relatively few and cannot explain the money transfer mechanism in those in detail. In order to quantitatively describe the transfer law of funds in payment networks, this paper constructs a payment network energy model for in-depth study. In order to quantitatively describe the transfer distance, probability and intensity of funds in the payment network nodes, this paper first constructs a model describing the transfer of funds in the payment network based on quantum financial algorithms, and a transfer matrix describing the evolution of funds in it is constructed in the model. Then we make an analogy between the transfer of funds in the payment network and the quantum wandering of microscopic particles, and find that the intensity of payment in the network and the quantum wandering on the microscopic network have similar properties. Finally, an empirical strategy is constructed with real data for empirical evidence, which supports the theory in the model of this paper. For the empirical evidence, considering that the exchange rate corresponds to a complex payment network behind the rate, data of 49 countries’ exchange rates in the foreign exchange market from January 1, 2017-August 1, 2022 are selected. We construct a descriptive strategy for statistical funds leaping between nodes according to the model in this paper and empirically validate the data by a clustering algorithm. It is found that the leap distance and probability of funds in the payment network generally show a cardinal distribution with d.f. = 1, in which the intensity of funds transfer is a smooth asymptotic process from strong to weak, and some aggregation and non-uniform distribution phenomena are also found in it. This paper fully reveals the transfer mechanism of funds on the payment network, which is of some significance to the understanding of the payment law of economic activities.

Numerical Analysis of Transfer of Heat by Forced Convection in a Wavy Channel

Convective heat transfer of laminar forced convection in a wavy channel is studied in this paper. Numerical simulations of the 3D steady flow of Newtonian fluid and heat transfer characteristics are obtained by the finite element method. The effects of the Reynolds number (10 ≤Re≤1000), number of oscillations (0 ≤N≤5) and amplitude of the wall (0.05 ≤A≤0.2) on the heat transfer have been analyzed. The results show that the average Nusselt number is elevated as the Reynolds number is raised, showing high intensity of heat transfer, as a result of the intensified effects of the inertial and zones of recirculation close to the hot wavy wall. The rate of heat transfer increases about 0.28% with the rise of the number of oscillations. In the transfer of heat along a wavy surface, the number of oscillations and the wave amplitude are important factors. With an increment in the number of oscillations, the maximal value of the average velocity is elevated, and its minimal value occurs when the channel walls are straight. The impact of the wall amplitude on the average Nusselt number and dimensionless temperature tends to be stronger compared to the impact of the number of oscillations. An increase of the wall amplitude improves the rate of heat transfer about 0.91% when the Reynolds number is equal 100. In addition, when the Reynolds number is equal 500, the rate of heat transfer grows about 1.1% with the rising of the wall amplitude.

Measurement of the thermal diffusivity of optical materials and products by a new thermographic express method that does not require cutting samples from bulk

Thermal diffusivity a and thermal conductivity λ are important for many building, structural and functional material applications. They determine the intensity of heat transfer, the quality of thermal insulation, the rate of heating / cooling, reaching a stationary mode, and the efficiency of power equipment. In laser technology, the radiation strength of the optical components of the system depends upon them, and in laser technologies with material removal they determine the speed and quality of processing. Most methods for measuring a and λ in solid materials require cutting out samples of a certain geometry, which makes them unsuitable for testing finished products. The paper proposes and describes an express method for determining a and λ in translucent materials, which does not require cutting a sample from a controlled object. It consists in the analysis of a non-stationary temperature field on the surface of the test object using a high-speed thermal imaging camera. The unsteady heating spot was created by a focused laser beam. It was switched on abruptly and operated in the mode of continuous irradiation with a constant intensity during the entire time of measurements. Heat propagated from this spot to the periphery, creating a non-stationary temperature field containing information about a and λ. The a value was extracted from the primary data using original algorithms and software. A thermal imager, as a recorder of a dynamic temperature field, provides a number of advantages – non-contact, high speed and a large amount of information (each of the many hundreds of thousands of pixels of a professional thermal imager matrix is a temperature sensor in a small surface area). Measurements of a and λ in semitransparent materials of laser optics have their own specifics. The low radiation absorption coefficient and the possible curvature of the surface (for example, in lenses) require special measures, which are described in the article. Due to the large amount of information contained in the dynamic patterns of the thermal field and the possibility of averaging over a large data array, the RMS of the thermal diffusivity measurement does not exceed 2 %.

Двумерное течение Пуазейля ньютоновской жидкости с вязкостью, зависящей от температуры

The problem of a two-dimensional Poiseuille flow of a Newtonian fluid with a viscosity exponen-tially dependent on temperature under the influence of longitudinal pressure and temperature gra-dients is reduced to a two-parameter boundary value problem for a third-order ordinary differential equation with respect to a dimensionless unknown characterizing the change in temperature across the channel. In the range of negative values of the dimensionless longitudinal temperature gradient, the solution has two branches. By closing, the branches form a boundary on the parameter plane beyond which Poiseuille-type flows do not exist. The solutions belonging to different branches dif-fer in the flow rate and intensity of heat transfer by the liquid through solid boundaries. The latter circumstance entails deceleration of the flow in the near-wall areas. In the region of positive values of the dimensionless longitudinal temperature gradient, the solution is unique. With an increase in the mentioned parameter, the heat flow to the liquid from the walls increases, which entails the formation of a more bulged velocity profile compared to the isothermal case. At sufficiently large values of the longitudinal temperature gradient, there appears a ‘stick’ flow with a uniform velocity distribution everywhere except for narrow layers near solid boundaries. It is shown that the rate is proportional to the ratio of the densities of the transverse and longitudinal heat flows. Explicit ex-pressions for the pressure and shear stress fields are given. The properties of monotonicity of the velocity and temperature profiles as functions of the transverse coordinate have been studied. It is shown that, regardless of the values of the dimensionless parameters of the problem, the velocity has a positive maximum on the central axis of the channel and monotonically decreases to zero at the solid boundary.