A Numerical Analysis of the Effect of Corrugated Surface Profile on Heat Transfer in Turbulent Flow Through a Rectangular Mini-Channel

Technical Note Heat transfer in turbulent pipe flow revisited: similarity law for heat and momentum transport in low-Prandtl-number fluids

A nuclear power reactor's primary use is to generate thermal energy, which in turn produces electricity. The primary heat source is a nuclear fission event occurring inside the fuel rod. The convection heat is transmitted through the coolant by the heat energy generated at the fuel rod wall boundary. Better heat transfer is produced in the flow area by turbulence and irregularity. As a result, turbulent flow heat transfer may present a significant challenge when predicting and assessing the thermal performance of nuclear power reactors. Computational techniques in convective heat transfer have become indispensable for solving challenging issues in the fields of science and engineering thanks to the development of current sophisticated numerical methods and high-performance computer hardware. The development of novel computational techniques and models for complicated transport and multi-physical phenomena is constantly in demand throughout applicable disciplines. This chapter's objective is to provide some recent developments in computational techniques for convective heat transfer, taking into account research interests in the community of mass and heat transfer, and to showcase relevant applications in nuclear power plant engineering domains including future directions. This study describes the most recent advancements in nuclear reactor convective heat transfer research utilizing the computational fluid dynamics (CFD) method, particularly at Ansys Fluent. This work examines the convective heat transfer and fluid dynamics fluid dynamics for turbulent flows across three rod bundle sub-channels that are typical of those employed in the PWR-based VVER type reactor. In this paper, CFD analysis is carried out using the software tool Ansys Fluent. Temperature distribution profile, velocity profile, pressure drop, and turbulence properties were investigated in this study. Boundary conditions i.e. temperature, velocity, pressure, heat flux, and heat generation rate were applied in the sub-channel domain. The main obstacles and bright spots for the CFD methods in nuclear reactor engineering are discussed, which helps to further its further uses. We intend to research a full-length fuel bundle model for VVER-1200 in the future to gather specific fluid characteristic data and use the findings to analyze safety and operate nuclear power facilities in Bangladesh. This paper presents a thorough analysis of the sub-channel thermal hydraulic codes used in nuclear reactor core analysis. This review discusses several facets of previous experimental, analytical, and computational work on rod bundles and identifies potential future directions based on those earlier studies.

Purpose This study aims to introduce a metal porous burner design. Literature is surveyed in a comprehensive manner to relate the current design with ongoing research. A demonstrative computational fluid dynamics (CFD) analysis is presented with projected flow conditions by means of a common commercial CFD code and turbulence model to show the flow-related features of the proposed burner. The porous metal burner has a novel design, and it is not commercially available. Design/methodology/approach Based on the field experience about porous burners, a metal, cylindrical, two-staged, homogenous porous burner was designed. Literature was surveyed to lay out research aspects for the porous burners and porous media. Three dimensional solid computer model of the burner was created. The flow domain was extracted from the solid model to use in CFD analysis. A commercial computational fluid dynamics code was utilized to analyze the flow domain. Projected flow conditions for the burner were applied to the CFD code. Results were evaluated in terms of homogenous flow distribution at the outer surface and flow mixing. Quantitative results are gathered and are presented in the present report by means of contour maps. Findings There aren’t any flow sourced anomalies in the flow domain which would cause an inefficient combustion for the application. An accumulation of gas is evident around the top flange of the burner leading to higher static pressure. Generally, very low pressure drop throughout the proposed burner geometry is found which is regarded as an advantage for burners. About 0.63 Pa static pressure increase is realized on the flange surface due to the accumulation of the gas. The passage between inner and outer volumes has a high impact on the total pressure and leads to about 0.5 Pa pressure drop. About 0.03 J/kg turbulent kinetic energy can be viewed as the highest amount. Together with the increase in total enthalpy, total amount of energy drawn from the flow is 0.05 J/kg. More than half of it spent through turbulence and remaining is dissipated as heat. Outflow from burner surface can be regarded homogenous though the top part has slightly higher outflow. This can be changed by gradually increasing pore sizes toward inlet direction. Research limitations/implications Combustion via a porous medium is a complex phenomenon since it involves multiple phases, combustion chemistry, complex pore geometries and fast transient responses. Therefore, experimentation is used mostly. To do a precise computational analysis, strong computational power, parallelizing, elaborate solid modeling, very fine meshes and small time steps and multiple models are required. Practical implications Findings in the present work imply that a homogenous gas outflow can be attained through the burner surfaces while very small pressure drop occurs leading to less pumping power requirement which is regarded as an advantage. Flow mixing is realizable since turbulent kinetic energy is distinguished at the interface surface between inner and outer volumes. The porous metal matrix burner offers fluid mixing and therefore better combustion efficiency. The proposed dimensions are found appropriate for real-world application. Originality/value Conducted analysis is for a novel burner design. There are opportunities both for scientific and commercial fields.

EXECUTIVE SUMARRY Energy storage to reduce peak-load demands on utilities is emerging as an important way to address the intermittency of renewable energy resources. Wind energy produced in the middle of the night may be wasted unless it can be stored, and conversely, solar energy production could be used after the sun goes down if we had an efficient way to store it. It is uses an electrochemical process to convert hydrogen gas into electricity. The role of fuel cells in energy storage is a very important criteria and it is compared with regular batteries for the advantages of fuel cells over the latter. For this reason fuel cells can be employed. PEM fuel cells can be effectively used for this reason. But the performance and durability of PEM fuel cells are significantly affected by the various components used in a PEM cell. Several parameters affect the performance and durability of fuel cells. They are water management, degradation of components, cell contamination, reactant starvation and thermal management. Water management is the parameter which plays a major role in the performance of a fuel cell. Based on the reviews, improvement of condensation on the cathode side of a fuel cell ismore » expected to improve the performance of the fuel cell by reducing cathode flooding. Microchannels and minichannels can enhance condensation on the cathode side of a fuel cell. Computational fluid dynamics (CFD) analysis was performed to evaluate and compare the condensation of steam in mini and microchannels with hydraulic diameter of 2mm, 2.66mm, 200µm and 266µm respectively. The simulation was run at various mass flux values ranging from 0.5 kg/m2s and 4 kg/m2s. The length of the mini and microchannels were in the range of 20 mm to 100 mm. CFD software’s GAMBIT and FLUENT were used for simulating the condensation process through the mini and microchannels. Steam flowed through the channels, whose walls were cooled by natural convection of air at room temperature. The outlet temperature of the condensate was in the range of 25oC to 90oC. The condensation process in minichannels was observed to be different from that in microchannels. It was found that the outlet temperature of the condensate decreased as the diameter of the channel decreased. It was also evident that the increase in length of the channel further decreased the outlet temperature of the condensate and subsequently the condensation heat flux. The investigation also showed that the pressure drop along the channel length increased with decreasing hydraulic diameter and length of the mini and micro channel. Conversely, the pressure drop along the channel increased with increasing inlet velocity of the stream. It was then suggested to use microchannels on the cathode section of a fuel cell for improved condensation.« less

This study presents a computational fluid dynamics (CFD) analysis of heat transfer and pressure drop in a straight slot impingement jet, utilizing nanofluid within a square duct. The working fluid comprises nanoparticles (diameter dp = 25 nm) suspended in water at a volume fraction (ϕ) of 2.5%. The investigation of different values of Reynolds numbers (Re) from 8,000 to 17,000, with variations in different geometrical parameters such as slot jet height ratio (: 0.3–0.6), spanwise pitch ratio (: 0.18–0.45), and streamwise pitch ratio (: 0.88–1.30). Three-dimensional numerical simulations are conducted using the ANSYS CFD module, incorporating the RNG k-ε turbulence model to solve governing equations in a turbulent regime. The CFD results show strong agreement with both the experimental results and empirical correlations results with similar geometrical configurations and flow conditions for a plain-wall square duct. The deviations are around 6% for the Nusselt number () and 3% for the friction factor (), demonstrating the reliability of the CFD model. The nanofluid exhibits a notable enhancement in heat transfer performance compared to pure water. Variations in , and significantly influence , with the optimal configuration ( = 0.5, = 0.3, = 0.97) yielding the highest heat transfer enhancement across most Reynolds numbers. The thermohydraulic performance parameter (THPP) ranges from 0.97 to 1.04, reaching its peak at Re = 8,000 for = 0.5, = 0.3, = 0.97. These findings highlight the potential of impingement jet cooling with nanofluids for thermal management in industrial applications, offering enhanced heat transfer efficiency through direct fluid impact on target surfaces.

Mass and heat transfer in a circular tube with biofouling

Experimental investigation aimed at characterizing fluid flow and heat transfer in mini channels is presented in this paper. Forced convection flow of water through rectangular mini channels with hydraulic diameters in the range 0.28–3.67 mm and aspect ratio (H/W) 0.33–2.5 was investigated, for different flow regimes, and correlations were proposed for the flow friction and heat transfer characteristics. Fully turbulent convective heat transfer was achieved in mini channels at lower Reynolds numbers compared to conventional sized channels. Critical Reynolds number for flow transition was found to decrease with the hydraulic diameter. A comparison of the results in mini channels and microchannels indicate common trends, especially in the dependence of flow transition on the hydraulic diameter. Experimental results were compared with predictions for flow and convective heat transfer in conventional sized channels. Based on the finding that the frictional and heat transfer characteristics of the mini channels deviated from the predictions, a few new correlations are proposed for the laminar and turbulent flow regimes.

Enhancement of natural and forced convection heat transfer has been the subject of numerous academic and industrial studies. Stationary inserts can be efficiently employed as enhancement devices for heat transfer and temperature blending in the heat convection systems. Generally, a stationary heat transfer enhancement insert consists of a number of equal (or similar) motionless segments, placed inside of a pipe in order to control flowing fluid streams. An ideal insert, for temperature blending in compressible flow applications, provides a smaller standard deviation of temperature with minimized pressure drop and required space. The ratio of temperature uniformity to the pressure drop can be used to determine the efficiency of an insert design. It is possible to use different segment lengths for a given insert design to maximize this ratio. Numerical simulation for heat transfer in turbulent flow is employed to simulate the flow and thermal fields for streams of cold and hot gases flowing across stationary inserts with variable segment length and to study the impact of the segment length on the performance of the insert. It is shown that the insert with variable segment length is more effective in temperature blending for two compressible streams.

Heat transfer characteristics in turbulent flow and flow patterns of PCM slurry using super-hydrophobic gel particles

The accurate modelling of heat transfer to turbulent flow and the prediction of the temperature distribution in the flow remain one of the problem areas of numerical simulations. Traditional turbulence closure models, like the k–ε model, effectively only increase the viscosity of the fluid and introduce wall functions close to boundaries to obtain the correct velocity distribution. These turbulence models do not model the small‐scale mixing that occurs in turbulent flow. When solving the energy equation these small‐scale mixings dominate the heat transfer rate at the boundaries as well as the temperature distribution in the flow. This paper outlines a revised method, based on the k–ε turbulence model, that can be used to predict heat transfer in turbulent flow. A single turbulent conductivity term is introduced that can be used over the complete flow field including the boundaries. A detailed description of the mathematical model and boundary conditions used for the turbulence model are included in the paper. The effective turbulent conductivity method was evaluated in several finite difference simulations of water flowing through a smooth pipe while being heated. Simulation and verification were performed over a range of Reynolds numbers. Verification of the model is accomplished by comparing the numerically predicted centre temperature of the fluid as well as the heat flux to the fluid to measured temperatures in a similar pipe. From these results it is concluded that the revised turbulent conductivity model holds great potential to obtain accurate simulated heat transfer rates for general applications.

Field synergy equation for turbulent heat transfer and its application

Vortex formation and heat transfer in turbulent flow past a transverse cavity with inclined frontal and rear walls

Air conditioner system is made up of a condenser that removes unwanted heat in an enclosure through the refrigerant and transfers the heat outside. Improving the heat transfer of air conditioning condenser is still a difficult task because of the broader set of materials and various parametric designs involved. Due to this high cost, the experimental set-up cost cannot be modified, instead, simulation analysis was introduced in the optimization process in order to achieve a near-optimal solution. The aim of this research is to improve the heat transfer rate for air conditioning condenser by material and parametric design optimization. The system was designed based on one basic parameter optimization: varying the condenser tube diameter. This variable was changed in order to improve the heat transfer of the condenser. Simulations using Computational Fluid Dynamic (CFD) analysis and thermal analysis were carried out to have a better understanding and distinct visualization of the fluid flow and materials used, and to compare the results. The materials that were used for CFD analysis are R32 and R290, and for thermal analysis are copper (C12200) and aluminum. The analysis was done using Analysis System (ANSYS) software. Different parameters were calculated from the results that were obtained and graphs were plotted between various parameters such as heat flux, static pressure, velocity, mass flow rate and total heat transfer. From the CFD analysis, the result shows that R32 has more static pressure, velocity, mass flow rate and total heat transfer than R290 at a condenser tube diameter of 7mm. In thermal analysis, the heat flux is more for copper (C12200) material at a condenser tube diameter of 7mm than aluminum.

This paper describes the prediction method of the bottom temperature of power Si MOSFET by using CFD (Computational Fluid Dynamics) analysis. For accurate thermal design of electronics, nano-micro scale hot spot temperature in semiconductor devices should be considered in thermal design. CFD analysis is widely used in thermal design of electronics. However, it is difficult to detect accurate temperature of nanomicro scale hot spots using CFD analysis. Then, the method to detect nano-micro scale hot spot temperature in semiconductor device is required. Electro-Thermal Analysis is attractive method to calculate temperature distribution of semiconductor devices. In Electro-Thermal Analysis, boundary conditions are important to calculate temperature distribution of semiconductor devices. Considering power Si MOSFET, which is widely used in semiconductor devices, the device is cooled from the bottom of the device. Therefore, the bottom boundary temperature of power Si MOSFET is dependent on cooling performance of cooling system. And temperature of the bottom surface is important for nano-micro scale hot spot estimation in Electro-Thermal Analysis. Then, in this paper, appropriate CFD modeling of power Si MOSFET is discussed for detecting the bottom temperature of power Si MOSFET. To verify the appropriate CFD modeling, the results of CFD analysis are compared with the experimental results, and the suitable assumption of heat generation in CFD analysis is discussed. From the result, the assumption of surface heat generation at the top of the power Si MOSFET is suitable assumption in CFD analysis. Therefore, it can be said, to calculate accurate nano-micro scale hot spot temperature in power Si MOSFET using Electro- Thermal Analysis, the bottom temperature as the important boundary condition in Electro-Thermal Analysis can be obtained by the CFD modeling. Further, it can be found that it is important to consider the heat transfer from the electrodes to the outside through the electrical wires in CFD modeling.

Thermal performance of a novel heat transfer fluid containing multiwalled carbon nanotubes and microencapsulated phase change materials