Convection In Tube Research Articles

Numerical investigation on liquid cooling of batteries in phase change materials

The primary focus of this study centres on managing the thermal conditions of the battery systems, addressing the various concerns related to external climatic factors on the vehicle’s performance and heat generation during the battery operation. The major objective of this study is to implement a passive thermal management system using the phase-change materials to model and control the temperature of the rechargeable batteries which are influenced mostly by critical temperature rise and external climatic influences. A numerical simulation involving a three-dimensional, single module model of a rechargeable lithium-manganese dioxide battery is involved. The control mechanism involves the application of the phase change materials within a parallelopiped structure with the battery positioned in the central location and cooled by the surrounding convective tubes through which liquid flows. The module is considered an adiabatic medium in nature. The numerical investigation involves three different C-rates for two different phase change materials RT27 and RT31, which are employed using the Finite volume method using the Ansys-Fluent. The detailed analysis of the surface temperature of the battery, liquid fraction fields and the average temperature attained by the battery module is involved using the two PCM materials.

A numerical study on thermal control of batteries by phase change materials with liquid cooling

The thermal control of the battery system concerns about reduction in heat generation during the operation of battery and the limitations of the vehicles due to the external climatic factors. This study focuses on the attempt to control the battery from external climatic factors and temperature peaks during its operation by the principle of passive thermal management system using phase-change material. A numerical investigation of a three-dimensional model for a cylindrical lithium-polymer battery as a single module is done. The thermal control is realized by a phase-change material for a battery placed inside a parallelopiped and cooled by convective tubes placed at constant temperature and the surface of the module is considered as adiabatic. The governing equations are solved using the Finite Volume method using Ansys-Fluent. The investigation involves 3 different C-rates for two different phase change materials. The results analyse the maximum temperature, temperature distribution and liquid fraction fields for the different cases. The obtained results indicated that for the two different PCM materials namely RT25HC and RT35HC used for the cooling of the batteries the maximum temperature reached by battery and the average temperature of the PCM materials used was observed to be higher in RT35HC.

Failure analysis of convection section tube in an ethylene cracking furnace due to metal dusting

To study the failure in the convection section tubes of an ethylene cracking furnace, macroscopic inspections, chemical composition analysis, metallographic microscopy, hardness testing, Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis are performed. The experiments confirmed the reason for metal dusting occurrence of 304H austenitic stainless steel that the inner wall Cr2O3 protective film was destroyed by overheating. There were dense circular corrosion pits on the fire side inside the furnace tubes, loose metal oxides and carbide particles were filled in the corrosive pits. Severe carburization occurred on the surface of the pits, the furnace tube experienced metal dusting. The metal dusting resulted in the decomposition of the surface layer of the metal alloy into metal particles and graphite to thin the wall thickness. Then the furnace tube cracked because of the stress concentration appeared in the furnace tube with reduced wall thickness. Finally, some suggestions and countermeasures on the failure of metal dusting of the furnace tube were proposed.

Optimization of Dimensions of Smooth and Twisted-Tape-Inserted Tubes for Heat Transfer with NaCl/KCl/MgCl2 Molten Salts by Principle of Entropy Generation Minimization

Abstract The entropy generation minimization principle is used as the criterion to optimize the flow and heat transfer of solar collectors and heat exchangers that use molten salts NaCl–KCl–MgCl2 and KCl–MgCl2. The Gnielinski correlation for the Nusselt number versus Reynolds number, as well as the Moody friction factor given by Petukhov, was used for the calculation of the convective heat transfer coefficient and pressure loss due to friction in smooth tubes. For twisted-tap-inserted tube, equations of Nu and friction factor provided by Manglik and Bergles were used. The objective function, the entropy generation rate of the heat transfer system, was expressed as the function of Reynolds number, Prandtl number, heating flux, tube diameter, etc. As a result of the analysis, the optimum Reynolds number was determined and thereby to determine the optimum Nusselt number, convective heat transfer coefficient, friction factor, and tube diameter, which also allows the calculation of optimum flow velocity. The analysis was conducted in the fluid temperature range of 500–700 °C, which covers the operation temperature for supercritical CO2 power cycles in concentrated solar power (CSP) system. Optimized results from the smooth tube and twisted-tap-inserted tube are compared, which is important to the design of solar receivers for CSP systems.

Development of the hydrodynamic and thermal boundary layers of forced convective laminar flow through a horizontal tube with a constant heat flux

The development of the thermal and hydrodynamic boundary layers of laminar flow through a smooth horizontal tube was investigated for forced convective conditions. The tube was heated at a constant heat flux and had an inner diameter of 4 mm and a length of 6 m. Numerical simulations were conducted using ANSYS Fluent 19.3 with a highly structured mesh and accurate temperature-dependent thermophysical properties. Laminar flow of air, water, and a mixture of 75% ethylene glycol (by weight fraction) in water was simulated, which covered a Reynolds number range of 630 to 2000 and Prandtl number range of 0.7–70. Theoretical methods were also used to obtain the relevant boundary layer growth parameters, such as velocity profiles, velocity gradient, vorticity, temperature profiles, Nusselt numbers, as well as hydrodynamic and thermal boundary layer thicknesses. Subsequently, methods were proposed to determine the development of both boundary layers in the entrance region, the locations at which the boundary layers merged, and the location at which the flow became fully developed. By analysing the velocity and temperature profiles, it was found that our conventional understanding of the merging of the boundary layers in internal tube flows had to be modified. Three distinct regions were identified in the hydrodynamic entrance region of laminar forced convective tube flow: (1) hydrodynamic inlet region, (2) shear stress developing region, and (3) vorticity adjustment region. Furthermore, three distinct regions were identified in the thermal entrance region: (1) thermal inlet region, (2) convective diffusion region, and (3) conductive diffusion region.

Dynamic Simulation and Modeling of Water Tube Boiler Systems: A Comprehensive Review

Water tube boilers (WTBs) are well renowned for their great efficiency, quick steam production, and capacity to withstand high pressures and temperatures. They are widely employed in a variety of industrial applications as well as in power production. The ongoing review considered the situation of bubbling intensity move to immersed, normal liquids in convective stream with expectations of laying out a system for gauging heat move coefficients. The goal of this examination is to make a coordinated intensity move and hydrodynamic model for concentrating on kettle elements under shifting burden circumstances. To calculate water surface heat transfer, a model for transient heat transfer has been created and connects directly with the hydrodynamic simulation. Heat transmission is ordered into a few strategies, including heat conduction, convection, warm radiation, and energy move through stage shifts. The transient intensity move model decides by and large intensity move from the gas side, the gas temperature profile, and intensity move from the water side in the heater water wall (FWW) and a convection tube bank (CTB) by determining the heat transfer and water wall temperature in various locations. Using the expected worth of waterside heat move from the transient force move model, mass energy and energy protection conditions are determined for both normal course circuits. It enhanced to include boiler control characteristics such as load management and water flow control. In the future, examine real-time monitoring technologies that are able to anticipate and avoid possible problems, increasing the boiler's overall safety.

Dynamic modeling of a water tube boiler

AbstractThe present work aims to develop an integrated heat transfer and hydrodynamic model for the study of boiler dynamics in fluctuating load conditions. A transient heat transfer model has been developed to estimate water side heat transfer and it is directly integrated with the hydrodynamic model. Two independent natural circulation circuits for furnace water wall and convection tube bank have been considered due to differences in heat transfer, dryness fraction, and void fraction. The transient heat transfer model calculates the heat transfer and water wall temperature of the various sections to calculate total gas side heat transfer, gas temperature profile, and waterside heat transfer in the furnace water wall and convection tube bank. Mass momentum and energy conservation equations are generated for both natural circulation circuits using the estimated value of waterside heat transfer of the transient heat transfer model. These equations are integrated with mass and energy conservation equations for the drum below water level and drum above water level to generate a system of equations to estimate drum pressure and water level fluctuation. This model has been extended for boiler feedback control systems, including the load management and the water level control system.

Coupled Heat and Flow Analysis Inside a Diversion-Type Gas Heater With Vertical Guide Plate Structure

In the natural gas heating process, the cylinder-type heater using water as an intermediate heating medium is the most extensively used. The heat exchange rate between the heating medium water and the fire and gas tubes in the great-capacity cylinder appears to be the most important element affecting a gas heater’s thermal efficiency. The water heat flow field within a new diversion-type gas heater with vertical guide plate design is described in this paper. In contrast to prior research that concentrated on natural convection heat transfer in medium water, the radiation impact is included. The discrete-ordinate model was utilized to build a 2-D combined natural convection and participating medium radiation heat transfer model, which was solved using the finite volume technique with unstructured body-fitted grids. First, experimental data were used to validate the numerical model. The coupled heat flow fields with vertical guide plates of various heights were then analyzed. The numerical findings reveal that utilizing a vertical guide plate structure, the proportion of radiation heat transfer in the total heat transfer rate reaches 25.1%, indicating that water radiation cannot be ignored. The vertical guide plate structure might help to create a well-organized flow pattern in the cylinder, which would improve natural convection heat transfer while having no influence on water radiation. Installing a vertical guide plate with a height of 550 mm and a thickness of 5 mm can lower the overall heat transfer rate in the convective tube bundle by 2.04%. In China, this technique has been given a patent.

Analysis and Prediction of Flow-Induced Vibration of Convection Pipe for 200 t/h D Type Gas Boiler

This paper is aimed at the analysis and prediction of the fluid-induced vibration phenomenon in the convection tube bundle area caused by Karman vortex street shedding in the background of a 200 t/h large-capacity D-type gas boiler. Based on the numerical simulation of flue heat state flow field and fast Fourier transform, the lift coefficient curve of different monitoring areas and the corresponding Karman vortex street shedding frequency are obtained. The accuracy of the analysis model is validated by comparing Karman vortex shedding frequency with acoustic equipment standing wave frequency. In order to meet the design requirements of the 200 t/h D-type gas boiler for reliable and stable operation, the vibration characteristics and variation rules of a convection tube bundle in a D-type boiler under different working conditions are predicted.

Three-Dimensional CFD Model Development and Validation for Once-Through Steam Generator (OTSG): Coupling Combustion, Heat Transfer and Steam Generation

The current research studies the coupled combustion inside the furnace and the steam generation inside the radiant and convection tubes through a typical Once-Through Steam Generator (OTSG). A 3-D CFD model coupling the combustion and the two-phase flow was developed to model the entire system of OTSG. Once the combustion simulation was converged, the results were compared to field data showing a convincing agreement. The CFD analysis provides the detailed flow behavior inside the combustion chamber and the stack, as well as the two-phase flow steam generation process in the radiant and convective sections. The flame shape and orientation, the velocity, the species, and the temperature distribution at the various parts of the furnace, as well as the steam generation and the steam distribution inside the pipes were investigated using the developed CFD model

НАНОЖИДКОСТИ: ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ В ИСТОЧНИКАХ ТЕПЛОТЫ

The application of nanofluids in thermal systems has great prospects, since the addition of nanoparticles gives a significant increase in the coefficient of thermal conductivity. The nanofluids thermal conductivity depends on the thermal conductivity coefficient of the base liquid and the volume nanoparticles fraction. It is assumed that the heat transfer coefficients and thermal conductivity are in direct correlation. Computational studies show that the increase in the heat transfer coefficient on the coolant side by adding nanoparticles in the coolant volume concentration of up to 10% is up to 23 % in the convective tube bundle. The increase in the heat transfer coefficient on the coolant side in the fire tube is up to 23 % when changing the volume concentration of nanoparticles in the range up to 10 %.

Failure investigation of a 304 stainless steel geothermal tube

The investigation of this paper aimed at finding the failure cause of a heavily cracked geothermal water convection tube, utilizing electron backscattered diffraction, double loop potentiodynamic polarization test, and energy-dispersive X-ray spectroscopy. Results show the failure was attributed to stress corrosion cracking (SCC). Chloride in the service environment has induced the initiation of SCC cracks. The sensitization of matrix increased the susceptibility to intergranular cracking, which may result from improper heat treatment before service. The residual stress arising from the manufacturing process promoted the failure process. The SCC cracks originated from the internal tube. In the early stage, the cracks propagated along austenite grain boundaries. Thereafter, they transformed into a coexisting mode of intergranular cracking and transgranular cracking. The failure was attributed to the synthetical effect of sensitization, chloride, and residual stress.

Performance Analysis on Combustion and Heat Transfer of the Ship Power Plant

Study results on the supercharged boiler numerical simulation are on the boiler, convection tube bundle or the super-heater. These study subjects in a single model, and simplified the boundary condition to a certain extent. This paper takes the boiler as a whole research object. On the furnace chamber for combustion simulation, using the profile boundary information file boundary condition setting, faithfully transmitting boundary parameter spatial distribution. Followed by the simulation of heat transfer between the convection tube bundle and super-heater modules, we can get a real fluid flow and heat transfer condition, thus reacting to the complex heat transfer and flow inside of boiler, knowing the distribution of temperature, speed, pressure and other parameters. We can also see the change rule of the combustion and heat transfer processes in that supercharged boiler. Then we discuss the impact of the not uniform heat load on the convection heating surfaces, and preliminary analyzes the mechanism of combustion and heat transfer in supercharged boiler.

Calculation studies of the heat supply system operating mode influence on the gas tube boiler heating surfaces temperatures

The paper considers the influence of the heat carrier temperature variation in supply and return pipelines on the efficiency of the gas tube hot water boiler operating in the heat supply system and on its surfaces temperatures. The temperature dependence graphs of the convective bundle tube wall and flame tube on the ambient temperature have been constructed. The basic calculation formulas used for the calculation as well as the temperature graph of the heat supply system operation depending on the ambient temperature and the temperature of the heat carriers are presented. The heat supply system operation modes, under which the convective bundle surfaces are subjected to the low-temperature corrosion, have been determined.

Cause analysis of corrosion leakage in convection section of ethylene cracking furnace

Convection tubes of an ethylene cracking furnace at a petrochemical plant had multiple leaking points along longitudinal directions after a fraction of the anticipated tube life span. To study the cause of the failure, the failed tubes were investigated with macro inspections, chemical composition analysis, metallographic microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Through analysis of the failed tube samples, we found no evidence of scaling corrosion caused by S and Cl and no significant corrosion contributed by carburisation of the inner wall. By combining cavitation characteristics observed from the leaking tube inner wall and the feed composition changed by the plant recently, we highly suspected that cavitation was the main reason causing the tube to leak. A simulation model was built to illustrate the possibility of liquid cavitation at the leaking region of the tube. After the plant controlled the heavy component in the light hydrocarbon suspected of causing the liquid cavitation, the investigated tube section did not show any similar leaking problem.

Cracking failure analysis of convection tube of heat recovery steam generator

The failure causes of cracks on a convection tube of heat recovery steam generator were analyzed by the optical microscope and scanning electron microscope analysis. The results show that the circumferential crack of the convection tube belongs to fatigue fracture. The micro-crack defect on the surface of fracture promotes the fatigue crack propagation.

A Study on the Failure of AISI 304 Stainless Steel Tubes in a Gas Heater Unit

This paper investigates a failure in convection section tubes of a gas heater unit in a petrochemical plant. Tubes are made of AISI 304 stainless steel. The failure is reported after 5 years of service at working temperature 500 °C. The failure is in the form of circumferential cracks in the vicinity of the weld. Various characterization techniques, including optical and electron microscopes as well as energy-dispersive X-ray spectroscopy (EDS), were used to study the failure. Results showed that that the damage has initiated in the heat affected zone (HAZ) area parallel to the weld/base metal interface. Cracks have propagated alongside grain boundaries, resulting in an intergranular fracture. The main cause of failure was concluded to be attributable to the grain boundary sensitization and intergranular grain boundary attack due to improper welding and long time exposure of tubes to high temperature. Possible mitigation strategies to minimize similar failures will be discussed.

Failure analysis of 304H stainless steel convection tube serviced in an ethylene cracking furnace

Abstract The failure of a convection tube used in an ethylene cracking furnace after service for >6 years was analyzed by various characterizing techniques. Cracks were found on the second convection tube located under the straight tube section. Severe bulging deformation was found around the cracking area. Stereoscopic inspection revealed that the main crack has penetrated through the tube wall, while a circumferential crack network was formed on the failed tube surface. Chemical composition analysis confirmed that the failed tube material belong to the 304H stainless steel family. SEM analysis on the fractured surface showed that the cracking mechanism was mainly intergranular brittle fracture. Microstructure observation found that grains within the cracked area experienced severe growing compared with intact area. Besides, more coarsened chromium carbides distributed within grains and along grain boundaries around cracked area, where voids were also occurred at grain boundaries. Based on the above inspection and analysis, the crack of the convection tube were confirmed to be caused by the localized overheating. The root cause for such localized overheating may due to inadequate steam flow and uneven heat distribution within the convection tube during service.

Numerical investigation of saturated upward flow boiling of water in a vertical tube using VOF model: effect of different boundary conditions

In this paper a numerical simulation of upward two-phase flow evaporation in a vertical tube has been studied by considering water as working fluid. To this end, the computational fluid dynamic simulations of this system are performed with heat and mass transfer mechanisms due to energy transfer during the phase change interaction near the heat transfer surface. The volume of fluid model in an available Eulerian-Eulerian approach based on finite volume method is utilized and the mass source term in conservation of mass equation is implemented using a user defined function. The characteristics of water flow boiling such as void fraction and heat transfer coefficient distribution are investigated. The main cause of fluctuations on heat transfer coefficient and volume fraction is velocity increment in the vapor phase rather than the liquid phase. The case study of this research including convective heat transfer coefficient and tube diameter are considered as a parametric study. The operating conditions are considered at high pressure in saturation temperature and the physical properties of water are determined by considering system’s inlet temperature and pressure in saturation conditions. Good agreement is achieved between the numerical and the experimental values of heat transfer coefficients.

Modelling of ash deposition in biomass boilers: a review

The ash deposition process in biomass boilers can induce many ash-related problems. It will reduce the heat transfer in the furnace walls and convective pass tubes and decrease the boiler efficiency and capacity. Previous review work and experience about the ash deposition process was almost focusing on coal-fired utility boiler, providing an extensive summary of knowledge and current developments about ash deposition processes, but few was concentrating on the biomass fuel-derived boiler. Numeral empirical and traditional methods, such as ash fusibility, ash viscosity, and slagging and fouling indices, which are based on the temperature and the chemical compositions, cannot fully predict the complicated ash deposition processes. To understand the nature of ash deposition in biomass boilers, full attention should be paid to the ash deposition processes, including the transformation process of mineral matter in biomass fuels and deposition characteristics. To predict the ash deposition process, some ash deposition models, such as the ash transportation model, the ash formation model, the ash impacting model, the ash sticking model and the ash growth model, should be developed. This paper will give a brief introduction to the traditional methods about the ash deposition. In additional, an extensive state-of-the-art review of the ash deposition in biomass fuel-derived boiler will be presented. Lastly, the comprehensive ash deposition models including the mechanistic models and CFD modelling will be built to address the ash-related issues, which can guide further investigation.