Natural Convection Conditions Research Articles

An electrical analogy model for performance evaluation of natural air-cooled TEG modules considering nonlinear effect of heat convection

With the outstanding merits of the simple principle and low computational cost, the electrical analogy model of thermoelectric generator (TEG) modules plays an important role in evaluating the performance of thermoelectric energy harvesting systems. However, owing to the simplification of the heat dissipation structure and difficulty in determining the heat dissipation parameters, it is difficult to accurately describe the nonlinear influence of thermal convection on the heat dissipation performance of the TEG module under natural air-cooled conditions, thereby reducing the estimation accuracy of the module temperature and output. A new nonlinear electrical analogy model to evaluate the performance of natural air-cooled TEG modules was proposed in this study. The proposed model more accurately describes the nonlinear influence of thermal convection on the thermal dynamic characteristics of the TEG module by introducing a heat transfer branch between the cold and hot side surfaces of the TEG module and the environment. A parameter extraction method based on multi-objective optimization and the non-dominated sorting genetic algorithm II (NSGA-II) was proposed to overcome the problem of the heat dissipation parameters of natural air-cooled TEG modules. The experimental results show that under natural convection conditions, the maximum estimation errors of the temperature and output voltage evaluated by the proposed model and parameter identification method are less than 6.18 % and 9.14 %, respectively. Under forced convection, the maximum estimation errors of the temperature and output voltage were less than 7.36 % and 8.71 %, respectively. The above estimation errors are significantly lower than the traditional model.

Steam Condensation Heat Transfer in the Presence of Noncondensable Gases (NCGs) in Nuclear Power Plants (NPPs): A Comprehensive Review of Fundamentals, Current Status, and Prospects for Future Research

Efficient steam condensation is crucial for safe nuclear power plant (NPP) operations, preventing pressure buildup, overheating, and the release of radioactive materials. However, the presence of noncondensable gases (NCGs), such as air, nitrogen, hydrogen, or helium, can hinder the condensation process by creating a thermal resistance layer that impedes steam diffusion and condensation on the system’s surface. Maximizing the efficiency of steam condensation requires a thorough grasp of the fundamental processes, theories, advancements, and technical hurdles. Therefore, this work thoroughly addresses these needs, with a particular emphasis on addressing the challenges posed by NCGs by dividing the work into four thematic areas. The first theme relates to a comprehensive examination of pure steam condensation phenomena, which includes an exploration of familiar condensation scenarios and various film condensation types. The second theme examines condensation in the presence of NCGs, their mixture properties, and related theories and modelling of heat and mass transfer. The third theme investigates condensation in NPP by exploring passive cooling systems and condensation phenomena under both natural and forced convection conditions during nuclear accidents, the origin of NCGs in NPP and their transportation aspects. This is followed by experimental work related to condensation scenarios and scale. Finally, the last theme looks upon the recent advancements in computational fluid dynamics (CFD) modelling of wall condensation, system analysis codes coupling with CFD, and the implementation of machine learning (ML) for predicting the condensation HTC. By bridging the gap between fundamental knowledge and practical applications, the four thematic areas presented in this work are aimed at providing a comprehensive foundation for researchers and experts in the field of steam condensation when NCGs are involved. The ultimate objective is to bolster the safety and efficacy of NPP operations by understanding the heat and mass transfer mechanisms while mitigating the risk of catastrophic events.

Experimental comparison of finned tube heat exchangers for heat rejection under natural convection conditions

This article presents experimental analysis of heat removal capabilities of a wavy finned tube heat exchanger operating under natural convection conditions Two types of heat exchangers are considered in this work: standard construction exchangers, most often found in waste heat rejection devices and exchangers based on a novel geometry, which supports intensification of heat transfer processes under natural convection. The aim of the research was to experimentally verify the novel conception and to determine the thermal efficiency of heat exchangers under the influence of selected design parameters. The factors analyzed in the research include: temperature difference between the heat transfer surface and the surrounding air, different angles of the units transferring heat and the height of the exchanger casing. Four variants of the casing height were considered in this work. The conducted research also allowed to determine the influence of the fin spacing on the performance of the heat exchangers under natural convection conditions. The test results obtained show that the novel geometry allows for significance improvement of heat transfer efficiency. The proposed solution allowed to increase the density of the heat flux from 12% in (fin spacing of 2.8 mm) up to 24% (fin spacing of 5.6 mm). It was also observed that the height of the casing has significant impact on the heat transfer efficiency. For each of the analyzed cases, the heat exchanger without a casing was characterized by the lowest thermal efficiency, while the highest heat flux was removed from the exchanger with the highest casing (up to four times higher heat transfer rate). It was determined that the largest amount of heat was removed from exchangers located horizontally, while the exchanger with an angle of 60°, was characterized by the lowest rate of heat removal. Another factor which was determined to have significant impact on the performance of the heat exchangers is the spacing between the fins. The research results obtained shows that increasing the spacing of the finned surface from 2.8 mm to 5.6 mm resulted in an average twofold increase in thermal efficiency in the case of four-row exchangers and an almost threefold increase in the case of two-row exchangers. The obtained results can be used as basic guide for the development of finned tube heat exchangers operating under natural convection conditions.

Analysis of the Cooling Modes of the Lining of a Ferroalloy-Casting Ladle

Analysis of the Cooling Modes of the Lining of a Ferroalloy-Casting Ladle

Numerical study on heat dissipation and structure optimization of immersed liquid cooling mode used in 280Ah LiFePO4 batteries

Efficient thermal management can ensure the lithium-ion batteries to operate steadily and long-term, among which immersion liquid cooling with higher cooling power and battery module temperature consistency presents great potential. According to the different heat transfer methods, three forms of immersion liquid cooling can be distinguished: static flow immersion cooling (SFIC), forced flow immersion cooling (FFIC), and immersion coupled direct cooling (ICDC). In this study, the numerical model is first established to comprehensively compare the cooling characteristics of the three modes, and the effects of the battery spacing, inlet relative locations and thermal characteristics of the coolant on the FFIC mode were further investigated. The results show that the maximum temperatures of SFIC, FFIC, and ICDC are reduced by 4.23%, 5.70% and 13.29%, respectively, compared to natural convection conditions. The FFIC mode has highest sensitivity to the flow parameters of the coolant, indicating that the heat dissipation capability could be moderated by proper temperature control strategies. The UTTB structure is more efficient at dissipating heat as coolant enters from the upper section of the batteries and exits from both sides. It is also revealed that increasing the thermal conductivity and specific heat capacity of the coolant to 0.6 W/(m∙K) and 1500 J/(kg∙K), respectively, at a flow rate of 0.03 m/s enables the battery module maximum temperature to reduce by 2.78% and 6.20%. However, given the challenge of attaining effective coolant thermal characteristics, the combination of active control methods, such as regulating the flow parameters of the coolant, will be a more economically feasible method in the future.

Influence of convective heat transfer coefficients on thermal behaviour of a lithium-ion cell: a numerical study.

In the current study, the impact of C-ratio, convective heat transfer coefficient, and free stream temperature on the maximal cell temperature and temperature uniformity was computationally and statistically examined. Results revealed that the free stream temperature was the main influential factor for the maximal cell temperature for both natural and forced convection conditions while the C-ratio was the most effective parameter for the temperature uniformity for both natural and forced convections. On the other hand, the contribution of the free stream temperature to the maximum battery temperature increased from 63% to 94% when the conditions were changed from natural convection to forced convection. Moreover, the contribution of the C-rate to the temperature uniformity decreased from 89% to 79% when the conditions were changed from natural convection to forced convection. The results obtained from this study are significant in terms of determining which factor should be given more importance under natural and forced convection conditions.

Numerical analysis of convective heat loss from a cylindrical–hemispherical receiver using a glass cover and an air curtain

AbstractIt is imperative to mitigate the convective heat loss from the receiver to improve the overall efficiency of the parabolic dish concentrator. In this study, the reductions of convective heat loss from the cylindrical‐hemispherical receiver are numerically analyzed and the model was validated by the experimental data from literature. In the first case, the impact of the glass cover on convective heat loss is examined under conditions of both natural and forced convections at various receiver orientations (γ = 0°, 30°, 60°, and 90°). Numerical results clearly demonstrate that the use of a glass cover significantly reduces the intrusion of surrounding air into the receiver cavity which leads to an enhancement of the stagnation zone inside the cavity and, as a consequence, a noticeable reduction in convective heat loss is observed. To perform analysis of the receiver with glass cover under forced convective condition, the wind velocities over the receiver are considered in the range of 1–6 m/s. The maximum reduction of convective heat loss using the glass cover is achieved to be 58.44% with wind velocity of 5 m/s at γ = 60°. In the second case, the influence of air curtain at the receiver aperture under natural convective heat loss conditions is analyzed. The analysis incorporates three variables: receiver orientation (γ = 0°–60°), nozzle width ( = 0.002–0.004 m), and nozzle outlet velocity ( = 0.5–3.5 m/s). The results show that the air curtain minimizes the outflow of receiver inside air and results in an improvement in the stagnation zone inside the cavity. The maximum effectiveness of the air curtain is found to be 43.2% at nozzle width of = 0.004 m and nozzle velocity of = 1.5 m/s at receiver orientation of 60°. It is also noteworthy that the optimal nozzle velocity decreases with the increase of nozzle widths.

GPU parallel computing based on PF-LBM method for simulating dendrites growth under natural convection conditions

This study introduces a GPU-based parallel computing approach that combines the phase-field model (PF) and the lattice Boltzmann model (LBM). By establishing a coupled multiphase field model incorporating physical external fields such as flow field, temperature field, and solute field, the research simulates the growth of single grains and multiple grains under the influence of natural convection. The variations in dendritic morphology, flow field, and solute field during dendritic solidification processes are observed. Initially, the study analyzes the morphology of equiaxed dendrites and the growth patterns of primary dendrites arms under natural convection conditions. The evolution of equiaxed dendrites in single grains and multiple grains under various conditions is investigated. Furthermore, the study explores the impact of different anisotropy strengths on the growth of single grains and multiple grains under natural convection. Notably, a distinct “necking” phenomenon is observed when the anisotropy strength of a single grain is 0.05. In the case of multiple grains, where competition between dendrites is present in addition to the influence of natural convection, a pronounced “necking” phenomenon is evident at an anisotropy strength of 0.03. Moreover, OpenCL parallel technology is designed on the GPU platform to accelerate the solution of the model. The parallelization of the phase-field model coupled with the LBM model on the GPU demonstrates a clear advantage. The parallel computation based on GPU not only exhibits absolute superiority but also shows more significant acceleration effects as the computational domain increases.

Mechanism of interaction between zirconium dioxide and fluoride melts

In this work, the mechanism of interaction between zirconium dioxide and fluoride melts was studied. Dissolution rates and maximum permissible oxide contents in the KF-AlF3 and NaF-AlF3 melts were determined under natural convection conditions at a temperature of 750 °C. The results of solubility measurement show that the limiting content of ZrO2 in the KF-AlF3 melt ([KF]/[AlF3] = 1.3) is 0.69 ± 0.10 mol. %, and in the NaF-AlF3 melt ([NaF]/[AlF3] = 1.3) at 800 °C it is 0.54 ± 0.04 mol. %. The calculated dissolution rate of zirconium oxide under these conditions in melts based on potassium fluoride and sodium fluoride is 0.022 mol/min and 0.017 mol/min, respectively. The influence of the cationic composition of the medium and the concentrations of additives on the liquidus temperatures of the melts was studied. It has been established that the increase in liquidus and solidus temperatures is facilitated by the addition of zirconium and aluminium oxides, as well as by the replacement of potassium fluoride with sodium fluoride while maintaining the molar ratio of the replaced cations. Analysis of thermal effects by differential scanning calorimetry (DSC) shows that, regardless of the molar ratio of the components, the onset of the thermal effect in melts based on potassium fluoride occurs at a temperature of 542 °C and in the systems with sodium fluoride additives at a temperature of 597 °C. Presumably, this dependence is associated with the melting of the KAlF4 and K2NaAl3F12 phases formed in the melts based on KF-AlF3 and KF-NaF-AlF3, respectively. It has been established that the melting of the KF-AlF3 mixture is accompanied with a mass loss of up to 1.3 wt. %, which is associated with partial evaporation of KAlF4.

Numerical evaluations on enhanced steam–air condensation outside S-type tubes under natural convection conditions

Steam-air condensation is extensively utilized in various industrial fields. In pursuit of better efficiency in applications, this study promoted a novel structure of heat transfer enhancing tube named S-type tube. It combines the superior heat transfer performance of short tubes and inclined tubes, demonstrating a high potential for enhanced condensate heat transfer. To evaluate the heat transfer property and obtain the optimized S-type tube structure, three-dimensional CFD methods were used, coupled with the liquid film model in STAR-CCM + software. The effcts of wall sub-cooling, pressure, air mass fraction and downward forced velocity, bend radius, horizontal section length on the steam–air condensation heat transfer characteristics outside S-type tubes were investigated. It was identified that S-type tubes can enhance the steam–air condensation heat transfer capability, and the enhanced heat transfer ability increases with the increase of pressure and the decrease of air mass fraction, and remains basically unchanged with changes in sub-cooling. The condensation heat transfer coefficients outside S-type tubes are 0.9 ∼ 1.71 times that of vertical tube range 0.2 MPa to 0.8 MPa. The main mechanisms affecting the condensation heat transfer are summarized: the scouring effect between tube segments to enhance heat transfer and the air layer pileup effect to inhibit heat transfer. The heat transfer enhancement capacity for the S-type tube is determined by the relative magnitude between the scouring effect and the pileup effect. Both effects increase as bend radius decreases; therefore, selecting an appropriate bend radius is crucial.

Analyzing battery thermal management systems: A comparative study of hydrogel and various PCMs in different configurations and convection conditions

No comprehensive analysis has been conducted to compare the performance of hydrogel- and phase change materials (PCMs)-based approaches for cooling lithium-ion batteries in the literature. The present study addresses this gap by comparing the effectiveness of hydrogel and various PCMs in two pack configurations: a fully-filled pack (Pack I) and a partially-filled pack (Pack II) in different convection conditions. While PCM-filled packs show no significant decrease in the cell temperature as a function of the distance between the cells, hydrogel-based cooling results in a significant decrease of 5.27 °C in the maximum temperature of the pack (Tmax) with increasing the distance from the cell radius to twice the cell radius. The study also finds that the effectiveness of latent heat in reducing the cell temperature decreases at higher melting temperatures. Among Packs I with small cell distances, n-Octadecane with the melting temperature of 28°C performs best with Tmax of 45.1 °C at the end of the cycles. However, for large cell distances (twice the cell radius), the hydrogel pack outperforms other cooling methods with a Tmax of 36.1 °C. In Packs II, at all cell distances, n-Octadecane is preferred. For hydrogel, at the end of the cycles, Tmax of Pack I is 3.0°C lower than that of Pack II under natural convection conditions. The study also reveals that Packs II with forced convection conditions are more effective than Packs I. Finally, the research shows that dispersing graphene nano-plates in n-Octadecane has an insignificant effect on the thermal behavior of the battery packs.

Inner thermal layout optimization for nanofluid-filled horizontal annular pipes

This paper investigates the optimization of the inner thermal layout in nanofluid-filled horizontal annular pipes under natural convection conditions. Two-dimensional models of annular pipes are established using a numerical simulation approach. Then, using this as the simulation tool, the layouts of single-, triple-, and quadruple-heat-source annular pipes are optimized. The coordinates of the inner cylinders are defined as the decision variables, and the average Nusselt number (Nu) on the cold wall surface as the objective function. For the single-cylinder model, both the Bayesian optimization algorithm (BOA) and the genetic algorithm (GA) derive the same results: an axisymmetric layout where the single heat source is positioned slightly above the axis of the annulus. However, the BOA takes much less computational time than the GA and, consequently, is chosen for cases with more complex geometry. The optimization layout of the three-cylinder model also shows an axisymmetric distribution, while the result for the four-cylinder model presents a centrally symmetric distribution. Compared to the original average Nu, the optimized ones are enhanced by 17.83%, 8.36%, and 6.18% for single-, triple-, and quadruple-heat-source annular pipes, respectively. The results of this study can be used for guiding the layout design and optimization of the nanofluid-filled exchangers with multi-inner heat sources.

Effect of Citrate Electrolyte Temperature on the Properties of Co-W Coatings

The influence of temperature on the properties of nanocrystalline Co-W coatings obtained from a citrate electrolyte at pH 6.7 and deposited under natural convection conditions was studied. The influence of the electrolyte temperature on the morphology, composition, structure and roughness of coatings, as well as their corrosion and tribological properties, is demonstrated. It is shown that the structure of the coating can change from the X-ray amorphous to the crystalline one when the deposition temperature of the coating is increased to 90 ºС. The average value of the mass wear of Cо-W coatings formed at 80 ºС and measured under the linear friction condition of 0.08 mg, and 62 times lower than that of a Cr coating (4.95 mg) and 84 times lower that at the surface of steel SK-5 (6.71 mg). When testing by the reciprocating wear method, the value of the volumetric wear of Co-W coatings obtained in the temperature range 50–70 ºС was 0.00109 mm3, which is 55 times lower than the wear value of a Cr coating (0.0596 mm3) and 41 times lower than that of the steel SK-5 surface (0.0449 mm3). The paper also shows a slight decrease in the currents of corrosion coatings and a decrease in the dispersion values of the corrosion potentials obtained after mechanical polishing of the surface of the coatings at temperatures in the range of 20–90 ºС. It is shown that under the corrosive effect of 3.5% sodium chloride, an increase in the deposition temperature of the coating is accompanied by a slight in-crease in the corrosion current.

Modified correlations for the Nusselt numbers at the boundaries of a bottom-heated molten metal layer in a stratified corium melt pool and an assessment of heat transfer conditions during a severe accident

The paper discusses new correlations for the Nusselt numbers at the side and bottom surfaces of a bottom-heated molten steel layer under the conditions of mixed natural convection of the melt at Rayleigh (Ra) numbers from ∼ 106 to 1012. The melt layer under consideration is characterized by radial non-uniformity of the temperature distribution, when the averaged temperatures of the top and side surfaces of the layer show a difference in value. This thermal pattern of the molten metal layer is typical when a stratified corium molten pool forms during a severe accident (SA). Upper metallic melt layer goes above the oxide phase of corium pool, and it is heated along its bottom surface. For an adequate prediction of heat transfer at the side and bottom surfaces of a layer in a SA, we developed special correlations for the Nu numbers. They take into account Rayleigh number and additional factors that determine geometric parameters of the layer and the temperature conditions at the bottom, side and top surfaces of the layer. Parameters in the developed correlations for the Nu numbers were determined via CFD simulation and mathematical processing of the simulation results. CFD simulations by means of the ANES code were completed in accordance with a specially developed experiments matrix. Two-parameter k-ω turbulence model by Wilcox, which includes Menter’s improved near wall functions, has been implemented in the CFD code and applied accordingly. To evaluate the accuracy and predictability of the developed correlations we ran a comparative analysis of the Nu numbers at the sidewall and bottom surfaces of the melt layer, as defined on the basis of the developed correlations for the Nu numbers and as defined in CFD simulation. The comparison showed a strong correspondence of the results within a wide range of Rayleigh number values of ∼ 106 < Ra < 1012. The analysis of the developed correlations allowed shaping a number of critical arguments that define heat transfer conditions at the melt layer boundaries. It was found that the Nu numbers at the side and bottom surfaces are largely dependent on the difference in the temperatures of the top and side surfaces of the layer. As the difference between the these temperatures widens, the Nu numbers increase drastically (by tens of percent or more) in comparison to similar Nu numbers defined on the basis of the well-known correlations. It is specified that when the temperatures at the top and side surfaces of the layer are equal, the heat transfer conditions at the side surface are defined by “Globe and Dropkin” correlation used for the horizontal surfaces of the layer. We also evaluated the significance of the geometric parameters on the Nu values for the sidewall and bottom surfaces of the melt layer. Multiplicative effect of this parameter and of the parameter for temperature conditions at the boundaries of the layer mentioned above may lead to a significant (by times) increase of the Nu values. That must be considered in the thermal analysis of the corium pool and the processes of the SA.

Analysis of the influence of large-scale room circulation on the human microenvironment

In this study, the effects of indoor large-scale circulation on the human microenvironment under natural convection and air-conditioning conditions were investigated by experiments and numerical simulations in a climate chamber. The effect of human thermal plumes on airflow was studied by large-scale circulation period characteristics. The main influencing factors of the vortex structure distribution are analysed under two conditions. The results show that the thermal plume under natural convection condition is the main factor affecting the large-scale circulation, and the indoor large-scale circulation has a significant effect on the microenvironment around the human body. The supply air jet can significantly reduce the large-scale circulation period. Moreover, the air supply jet and the human thermal plume are coupled to form multiple small-scale circulations.

Thermal storage process of phase change materials under high humidity and laminar natural convection condition: Prediction model and sensitivity analysis

The application of phase change materials (PCMs) in renewable energy storage and building temperature regulation is considered an effective method to reduce the use of fossil fuels and carbon emissions. However, issues concerning the utilization of PCMs in high-humidity environments remain to be addressed to fill the gap in real-world applications. This paper establishes a simplified novel two-zone model, comprehensively considering the natural convection on the surface of the PCP in high-humidity environments, as well as the formation, movement, and evaporation of water films on the surface. Subsequently, numerical solutions and experimental validation are conducted, and the influence of high-humidity environments on the heat and moisture transfer is elucidated. The results indicate that a high-humidity environment can significantly suppress the sensible heat transfer with a ratio range of latent heat to sensible heat typically around 1–4. Furthermore, the increase in the height of PCP leads to an increase in the proportion of sensible heat transfer. On the contrary, increasing the thermal conductivity of the PCM can amplify the latent heat transfer. The results can help further study the thermal storage and the dehumidification potential of phase change units in application on a large scale under high humidity conditions.

Development and experimental study of a 3-dimensional enhanced heat pipe radiator for cooling high-power electronic devices

A 3-dimensional enhanced heat pipe radiator (HPR) is developed to meet the requirements of heat dissipation and temperature uniformity in the cooling of high-power electronic components. The radiator is composed of a conventional flat heat pipe base and roll-bond flat heat pipe fins, which can enhance heat transfer in three dimensions. By means of experiments, the heat transfer characteristic is firstly studied under different filling ratios for a single roll bond flat heat pipe. Then, a comparison is performed of the heat transfer performance between the HPR and the conventional aluminum fin radiator (CAFR) under different heating powers and wind speed conditions experimentally. In this research, HPR demonstrates obvious advantages in the heat transfer. Results show that the optimum filling ratio is 35% for the roll-bond flat heat pipe. The start-up time of HPR is shorter (25 mins), and the start-up performance is not affected by power variation. HPR has a low thermal resistance of less than 0.48 °C/W compared with CAFR, which can effectively control the heat source temperature difference is about 1.7 °C–1.8 °C. The maximum heat dissipation of HPR and CAFR is almost the same under natural convection condition. But when the wind speed is 4 m/s, the maximum heat dissipation of HPR increased by 58.2% compared to the maximum heat dissipation of CAFR.

Comparison of thermal characteristics of three modifications of gravity heat pipe with threaded evaporator at different inclination angles

In this paper, the thermal characteristics of three modifications of a gravity heat pipe with a threaded evaporator (cylindrical, semi-flattened, and flattened) under natural convection conditions are experimentally investigated. That is considered to be of practical interest for the use in energy-efficient passive cooling systems of electronics for various purposes (LED lighting devices, batteries of electric vehicles, transmission modules of radars, etc.). The length of the gravity heat pipe was 230 mm, the primary diameter was 12 mm, the thickness of the flattened sections was 5.5 mm, and the working fluid was Freon 141b. The input power was varied from 5 W to 50 W (in 5 W increments) at tilt angles of 0°, 15°, 30°, 45°, 60°, and 90°. This paper presents the analysis of the flattening effect on various parameters, including the temperature in the heating zone, temperature distribution along the length of the gravity heat pipe, thermal resistance, and effective thermal conductivity. It is established that the semi-flattened heat pipe exhibits the best thermal characteristics. Moreover, this study reveals the influence of the orientation of the flattened part of the gravity heat pipe relative to the horizontal plane (parallel or perpendicular to it) on its thermal characteristics. The results obtained indicate the prospects of using semi-flattened and flattened gravitational heat pipes with a threaded evaporator in passive air-cooling systems for electronics with input power values up to 50 W, for example, in passive cooling systems for LED devices, power amplifiers for transmitting modules, etc.

Experimental Investigation and Modeling: Considerations of Simultaneous Surface Steel Droplets’ Evaporation and Corrosion

The present work focuses on the problem of steel surface corrosion as a kinetic expression when water droplets are repeatedly deposited and evaporated on/from its surface. This process, together with the rainwater film corrosion process, belongs to the theoretical foundations of the problem of atmospheric corrosion. It was considered that the formation of water droplets on surfaces is a random but repetitive process, as well as the fact that experimental and theoretical observations show that the droplet corrosion front of a metal surface is located in its zone circumference. We thus aimed to establish how the corrosion process evolves on a steel plate when many drops are deposited and removed repeatedly. An experimental setup and working procedure were used to obtain data characterizing the simultaneous process of steel surface corrosion and water droplet evaporation. For natural convection conditions with a variable relative humidity and temperature environment, an extensive data set consisting of the dynamics of individual droplet evaporation coupled simultaneously with the corrosion of the steel surface under the droplet was obtained. The mathematical models for evaporation and corrosion under the droplet have the same dynamic transfer surface for water evaporation and oxygen supply in the droplet. An approach for determining this surface depending on the momentary droplet mass was considered. Several simultaneous measurements of evaporation–corrosion dynamics were used to calibrate the coupled models, which were then used to show their compatibility with experimental data.

Performance assessment of compound parabolic concentrating photovoltaic system based on optical-thermal-electrical-environmental coupling

Based on established optical-thermal-electrical-environmental coupling model and proposed method for calculating electrical efficiency, the effects of tilt angle (θ) on the optical performance, thermal performance and electrical performance of compound parabolic concentrating photovoltaic (CPC-PV) system were numerically investigated by using the coupled Monte Carlo ray tracing (MCRT) and finite volume method (FVM). The results show that with the increase of θ, the peak irradiation flux on the PV panel surface increases sharply. When θ is larger than the critical angle, the shadow area appears and the distribution uniformity of irradiation flux decreases rapidly. Under natural convection condition, increasing θ reduces the distribution uniformity of temperature on the silicon elements with a maximum temperature difference of 120.93 °C at the same position. While, the air average flow velocity around PV panel and reflector surfaces decreases, and the maximum flow velocity appears on reflector surface. Radiative heat loss is dominant in CPC-PV system, and convective heat transfer on the glass surface has a greater impact on the combined heat transfer than that on the TPT surface. From the aspects of values and variation trends, the electrical efficiency calculated by using traditional empirical formula defies the facts. The regional discrete integral method proposed in this study accounts for the effects of shaded areas and non-uniform temperatures on electrical performance. The maximum difference between the electrical efficiency calculated by using the present method and the traditional empirical formula is 10.59 %.