Increase In Wall Temperature Research Articles

Investigation of Dynamic Characteristics of Liquid Nitrogen Droplet Impact on Solid Surface

Liquid nitrogen spray cooling technology exhibits excellent heat transfer efficiency and environmental protection performance. The promotion of this technology plays an important role in improving the sustainable development of the refrigeration industry. In order to clarify its complex microscale behavior, the coupled Level Set-VOF method was adopted to study the dynamic characteristics of liquid nitrogen droplet impact on solid surface in this paper. The spreading behaviors under various factors (initial velocity, initial diameter, wall temperature, and We number) were systematically analyzed. The results show that the spreading behaviors of liquid nitrogen droplet share the same process with the normal medium, which are rebound, retraction, and splashing. For the droplet with smaller velocity and diameter, Rebound is the common phenomenon due to the smaller kinetic energy. With the increase of droplet diameter (0.2 mm to 0.5 mm) and velocity (0.1 m/s to 5 m/s), the spreading factor increases rapidly and the spreading behaviors evolve into retraction and splashing. The increase of wall temperature accelerates the droplets spreading, and the spreading factor increases accordingly. For the liquid nitrogen droplets hit the wall, the dynamic behaviors of rebound (We < 0.2), retraction (0.2 < We < 4.9), and splashing (We > 4.9) will occur with the droplet weber number increased, which are consistent with the common medium. However, due to liquid nitrogen having lower viscosity and surface tension, the conditions of morphological transformations are different from the common media. The maximum spreading diameter has a power correlation with We, the power index of We is 0.306 for liquid nitrogen, lager than common medium (0.25). The reasons are: (1) the better wettability of liquid nitrogen, and (2) the vapor generated by the violent phase change ejects along the axial direction. The article will provide a certain theoretical basis for liquid nitrogen spray cooling technology, and can also enrich the flow dynamics of cryogenic fluids.

Temperature Distribution Analysis of Pulse Detonation Engines

In pulse detonation engines (PDE), combustion temperatures can rise as high as 3000 K across the detonation wave. The continuous exposure to such elevated temperature may risk the integrity of the structural components of the engines. In order to be able to estimate the heat load accurately. Hence, numerical and experimental studies of the temperature distribution on a pulse detonation engine model was conducted to quantify the heat load. Navier-Stokes conservation equations with viscosity and chemical reaction for deflagration-to-detonation transition (DDT) in detonation engines were solved through computational fluid dynamics. Reactive flow field of premixed mixtures (propane-oxygen) was modeled for detonation process. In the simulation, short-term detonation combustion (ms) and long-term wall heating process(s) are carried out together. Both single detonation and multiple continuous detonations were simulated and tested, and the simulation results are consistent with the experimental results. The results show that there is a correlation between heat flux and detonation wave structure and the instantaneous maximum heat flux appears in the detonation wave region of the detonation tube wall. The distribution of transient heat flux in time and space is very uneven, and the difference between transient heat flux and average heat flux is large. The position of detonation wave formation is the turning point of PDE wall temperature, and the temperature at the front end of the turning point is lower than that at the back end. The results show that the fresh mixtures have cooling effect on the detonation tube wall, which leads to the increase of the inner wall temperature with oscillation and the continuous increase of the outside wall temperature. The maximum wall temperature and the speed of temperature rise are positively correlated with detonation frequency. The results also show that the heat transfer coefficient of detonation tube has an effect on the initiation of detonation wave. When the heat transfer coefficient is large, detonation wave can not initiate in the studied engine. The focus of thermal protection is different between single detonation and multiple continuous detonations. Heat management of the detonation engines highlights an important part on the engine construction.

EFFECTS OF WALL TEMPERATURE ON THERMOPHYSICAL CHARACTERISTICS OF SPRAY-WALL IMPINGEMENT

For small- and medium-bore diesel engines, the phenomenon of spray-wall impingement is unavoidable, which affects the evaporation of the fuel, thermal efficiency, and emissions. Wall temperature is an important parameter in this process because it has an important influence on fuel evaporation. In this paper, the thermophysical characteristics of spray-wall impingement at different wall temperatures were studied. The results showed that with increase of the initial wall temperature, the impingement spray radius increased, but its rate of increase decreased, while the impingement spray height first increased and then decreased. During this process, the surface heat flux first increased and then decreased with the increase of initial wall temperature, which was due to the change of heat transfer regime on the wall. The transient heat transfer process at different initial wall temperatures was characterized by the Biot and Fourier numbers and the dimensionless surface heat fluxes were highly similar. A dimensionless correlation was developed to quantify the transient heat transfer process, which showed that the ratio of the internal thermal resistance of heat conduction in the wall to the wall surface convective heat transfer resistance changes almost linearly during the process of spray-wall impingement.

Determining pipeline parameters during the formation of arched ejection

Consideration is given to the mutual effect of pipeline bending, internal and external pressures, compression force effect, fluid flow along the pipeline with pre-assigned density, axisymmetric expansion of the pipe and its longitudinal contraction, change in the pipe wall temperature, and formation of arched ejections. An elastic pipeline is fixed on clamped sliding supports which do not hinder the fluid flow inside the pipeline along its axis. On the supports, both the deflection and the rotation angle are equal to zero. The pipeline is subjected to longitudinal compression. Compression force, pressures inside and outside the pipeline and velocity of fluid flow along the pipeline change independently of each other. This research treats the static interaction of instabilities depending on compression force, internal and external pressures, velocity of fluid flow, axisymmetric expansion of the pipe, and change in the pipe wall temperature. Flexural stiffness, tensile forces and external hydrostatic pressure stabilize the pipeline, while compression forces, internal hydrostatic pressure, fluid motion at any velocity inside the pipeline and an increase in the pipe wall temperature destabilize it. With an increase in the yield point of the pipeline material and the distance between the supports, the acceptable amplitude of arched ejection increases as well. With an increase in the internal pressure of the pipeline, the acceptable amplitude of arched ejection tends to be reduced. The obtained results enable analyzing the stability of pipeline systems. These results can be applied to analyzing static stability of pipelines at the stage of design, performance and elimination of arched ejections.

CFD study of the reactive gas-solid hydrodynamics in a large-scale catalytic methanol-to-olefin fluidized bed reactor

Lacking the understanding of multiphase flow in the fluidized bed methanol-to-olefin (MTO) process hinders the reactor design, operation, and optimization. Accordingly, a three-dimensional multiphase particle-in-cell model is established to study hydrodynamics and thermochemical characteristics during the MTO process in a fluidized bed reactor. After model validation, the influences of several critical operating parameters on reactor performance are discussed. The results show that particles in the medium part and freeboard of the reactor have heterogeneous velocity, temperature, and heat transfer coefficient (HTC) distributions. Thermal quantities of gas and solid phases are uniformly distributed in the medium part and freeboard of the reactor. The particle-averaged HTC under ranges from 60 to 120 W/(m2·K). Increasing wall temperature enlarges the particle HTC due to the enhanced exothermic reactions. Decreasing the particle diameter gives rise to a larger particle HTC. The vertical particle dispersion coefficient (Dz) is in the range of 0.01 m2/s to 0.03 m2/s. Methanol converts into olefin in a short period. Increasing methanol to catalyst ratio and wall temperature increases olefin including C2H4, C3H6, C4H8, and C5H10, and promotes the gas thermal properties. Particles with multi-sizes show a better MTO conversion performance than those with mono-sizes regarding the particle HTC and gas products.

Effects of mixing ozone on combustion characteristics of premixed methane/oxygen in meso-scale channels

To investigate the effect of ozone on the combustion characteristics of premixed methane/oxygen in meso-scale channels, the flammability limits of the mixture with ozone are obtained experimentally, and the influence of ozone concentration on the near-limit combustion process is analyzed from the perspective of thermal effect and chemical kinetics effect by numerical simulation. Moreover, the changes of OH radicals, outer wall temperature and wall heat loss in mixture mixing ozone are compared. The results show that mixing ozone can significantly broaden the flammability limit of premixed methane/oxygen, increase the reaction temperature, and make the combustion zone move towards the inlet. Also, the chemical effect of ozone is more significant than its thermal effect. The concentration of OH and other free radicals are increased significantly by the interaction between the O atom produced by ozone decomposition and fuel molecules, which further accelerates the chain branching reaction, and enhances the whole combustion process. However, the total heat loss is increased by 4%–8% due to the sharp raising of radiation heat. Additionally, it is found that under non-stoichiometric conditions and low inlet flow rate, the increase of OH radical and outer wall temperature is more obvious, and the wall heat loss is also larger.

Numerical prediction of the operating point for the cryogenic twin-screw hydrogen extruder system

An extruder-type cryogenic pellet injector system for plasma fuelling is under research at Institute for Plasma Research (IPR), India. A twin-screw extruder is a most stable device in the form of closed volumes of hydrogen between screw threads and promising process due to continuous production of hydrogen pellet for plasma reactor. In the present investigation, a non-Newtonian, non-isothermal CFD model was developed which modeled the shear rate and temperature-dependent viscosity in the Herschel Bulkley model. Brinkman number (Br) varies from 0.15 to 0.46 at 5 and 15 rpm respectively. Due to increasing the screw rotation speed for a given throughput, the shear rate increases (therefore, also the Br) and results in larger viscous dissipation. Solid hydrogen temperature is predicted at the location of the flight gap and intermeshing zone for the different barrel temperatures under varying screw rotation speeds (5–15 rpm). Prediction of hydrogen temperature at the intermeshing zone of the extruder system plays a vital role to decide the barrel temperature. Due to more number of moving surfaces at the intermeshing zone of the extruder system, the temperature of solid hydrogen is higher and increases above the melting point temperature. The effect of barrel wall temperature and screw rotation speeds (5–15 rpm) on the viscous dissipation rate and pressure development at required throughput was also examined for an extruder system. It is important to estimate the barrel wall temperature to get an operating point and corresponding viscous dissipation rate, which determines the cooling load required for extruder-die set-up. The results show that as the die wall temperature increases, the viscous dissipation, as well as the pressure drop decreases in the die. The investigation showed that the die’s wall temperature and screw rotation speed affect the operating point of the extruder-die system.

Quenching experiments of vertical Inconel and Zircaloy tubes in internal water flow

In this study, quenching experiments of vertical Inconel and Zircaloy tubes in internal water flow were conducted. The effects of the initial tube wall temperature, liquid subcooling, and liquid injection velocity on the quench temperature, the reaching time to quench temperature, and the quench front velocity were examined. For the experimental conditions, the initial tube wall temperatures were 700 and 1000 °C, the liquid subcoolings were 10, 50, and 75 °C, and the liquid injection velocities were 0.05 and 0.1 m/s. An increase in the initial tube wall temperature increased the quench temperature and prolonged the reaching time to quench temperature with the decrease of the quench front velocity. An increase in liquid subcooling shortened the reaching time to quench temperature and increased the quench temperature and quench front velocity. In addition, an increase in the liquid injection velocity reduced the reaching time to quench temperature, and increased the quench temperature and quench front velocity. For all cases, the Inconel tube exhibited a longer reaching time to quench temperature with lower quench temperature and quench front velocity than those of the Zircaloy tube. Based on the present experimental data for the quench temperatures of Inconel and Zircaloy tubes, the previous correlations were compared and assessed. The correlation of Kim and Lee (1979) predicted the quench temperature data with reasonable accuracy.

Numerical Verifications on Heat Transfer to Supercritical Water Flowing Upward in a 4-m Long Bare Vertical Tube

Abstract Thermal efficiency and safety of generation-IV nuclear-power-reactor concept supercritical water-cooled reactor (SCWR) are largely dependent on the coupled supercritical water (SCW) thermophysical properties and heat transfer performance in the supercritical region. This paper presents the numerical investigation of the heat-transfer characteristics of SCW flow in a 4-m long circular tube (ID = 10 mm) based on computational fluid dynamics. Numerical model for SCW was established in this analysis and forced-convection heat transfer was studied at different operating conditions. The data were collected at pressure of about 24 MPa, inlet temperatures from 320 to 350 °C, mass flux from 1000 to 1500 kg/m2·s, and heat flux up to 1500 kW/m2. Results of numerical simulation predict the experimental data with reasonable accuracy. A dimensional analysis was conducted to derive the general form of an empirical supercritical water heat-transfer correlation. The decrease of turbulent viscosity due to the decrease of density leads to a lower turbulent diffusion and turbulent kinetic energy, which inhibits heat transfer. The increased wall temperature and localized heat transfer deterioration (HTD) would occur as the liquid in the core of the tube is isolated for the low-density fluid adheres to the near-wall region, which is characterized by low thermal capacity.

Wall Temperature Effects on Ignition Characteristics of Liquid-phase Spray Impingement for Heavy-duty Diesel Engine at Low Temperatures

ABSTRACT The effect of wall temperature on the ignition of vapor-phase spray impingement has been studied extensively, but the mechanism of the liquid-phase case is not clear. Thus, the visualization experiment was conducted at wall temperatures of 363–673 K using Mie-scattering, shadowgraph, and direct photography methods in a constant volume combustion vessel. The results reveal that, compared with the vapor-phase wetting-wall, when the liquid fuel impinges on the cold wall, the threshold temperature of the autoignition increases greatly to 363 K. Furthermore, the wall temperature strongly affects the evaporation and fuel-air mixing under the liquid impingement case. As the wall temperature increases from 423 K to 573 K, the enhanced evaporation results in a significant reduction in the spray radius, height, and area. However, the evaporation is inhibited and the spray parameters increase when the wall temperature further rises to 623–673 K. This characteristic may be caused by the Leidenfrost effect, which is the main difference from the vapor-phase impingement. Too low wall temperature (below 520 K) easily leads to misfire and unstable ignition, and the threshold temperature of the autoignition is greatly increased, while a higher wall temperature exceeding the Leidenfrost temperature is also not conducive to rapid and stable ignition. With the increase of wall temperature, the ignition delay first shortens from 4.1 ms to 3.2 ms gradually and then prolongs to 3.6 ms again, while the flame area and intensity first increase and then decrease, and the transition temperature is 573 K. When liquid wetting-wall inevitably appears in a heavy-duty diesel engine operating at low temperatures, it is necessary to raise the wall temperature moderately to ensure stable ignition. However, it should not exceed the Leidenfrost temperature, otherwise, evaporation will slow down and ignition will worsen due to the Leidenfrost effect.

Solidification and melting model of phase change material with volumetric shrinkage/expansion void in an annulus

A one dimensional analytical model is proposed to analyze the solidification/melting of phase change materials (PCMs) incorporating the shrinkage/expansion void in an annulus. An air-PCM system is considered in this study. Paraffin wax is considered as PCM and filled inside the annulus, while air is considered inside the void. Separation of Variable method involving Bessel’s function is employed to obtain temperature distribution for air, solid and liquid domains and to locate interface positions. Stefan condition and mass conservation equation are used at the interfaces. Results obtained from the present model are found to be in good agreement with the existing test results. Effect of various parameters such as density ratio, end wall temperature, and radius ratio on the solidification/melting of PCM have been investigated. The solid-liquid interface moves 76.53% and 70.88% during solidification and 34.26% and 35.32% during melting for density ratio of 1 and 1.16, respectively during a time period of 1400 s. Shrinkage as well as solidification rate increases with decrease in cold wall temperature, increase of radius ratio and increase in Stefan number; while expansion as well as melting rate increases with increase in hot wall temperature, increase of radius ratio and increase in Stefan number.

Performance Deterioration of Pitot Tubes Caused by In-Flight Ice Accretion: A Numerical Investigation

In-flight ice accretion on typical pitot-static systems is numerically investigated to reveal their performance deterioration under both rime and glaze icing. Coupled with the open source computational fluid dynamics (CFD) platform, OpenFOAM, the numerical strategy integrates the airflow determination by the Reynolds-averaged Navier-Stokes equations, droplet collection evaluation by Eulerian representation, and ice accumulation by mass and energy conservation. Under varying inflow conditions and wall temperatures, the calculated ice accretion performance indicates that the ambient temperature has the most significant effect on the icing-induced failure time, leading to an almost exponential growth. Meanwhile, the blocking time is found to be linearly proportional to the increase in wall temperature. With the increase in inflow velocity, the failure time follows a parabolic variation with glaze ice accretion while shows a monotonic reduction under rime icing conditions. In addition, when the angle of attack increases, failure accelerates under both the glaze and rime icing scenarios. These findings provide guidance for the protection design of pitot tubes. A nonlinear regression analysis is further conducted to estimate the failure performance. The predicated failure times show reliable consistency with numerical results, demonstrating the capability of the obtained empirical functions for convenient predictions of failure times within the applicable range.

Experimental investigation on minimum film boiling temperature during reflooding in multi-rectangular narrow channels

Determination of minimum film boiling temperature (Tmin) is significant in the nuclear reactor safety analysis. Tmin represents the start of quenching which is vital to mitigate the severity of the accident. In this paper, a bottom reflooding experiment is carried out to investigate Tmin and quench velocity in multi-rectangular narrow channels. Effects of working conditions, including inlet subcooling, reflooding velocity, initial wall temperature, and system pressure on Tmin and quench velocity, are analyzed in detail. It is found that Tmin and quench velocity distinctly increases with the increase of subcooling, system pressure, and reflooding velocity. However, the effect of reflooding velocity on Tmin and quench velocity is mild when the reflooding velocity is relatively high. Tmin increases with the increase of initial wall temperature, while quench velocity drops. Tmin at the upper position of the heating wall is lower than that at the lower position because the water subcooling changes when flowing along the heating channel. A prediction model of Tmin during reflooding in rectangular narrow channel is proposed, and very good agreement is achieved comparing with experimental data with ±10% uncertainty.

Heat transfer and entropy production evaluation on premixed hydrogen/air-fuelled micro-combustors with internal threads

A micro-combustor with a tailored internal thread is proposed to uniform the wall temperature and improve the second law efficiency of a micro thermophotovoltaic (MTPV) system. The influences of 1) the thread form, 2) the inlet velocity and 3) the nominal diameter on the system’s thermal performances are investigated by performing computational fluid dynamics simulations. Results indicate that the application of the proposed corrugated thread structures can reduce the flame temperature and enhance heat transfer remarkably. The recirculation zone formed in the spiral grooves is conducive to obtaining uniform temperature on the outer combustor surface. Especially when the inlet velocity increases to 5 m/s, the standard deviation of the wall temperature can be maintained below 20 K. In addition, the mean wall temperature and the standard deviation of the wall temperature both increase distinctively with the increase of the nominal diameter. Entropy production is the analysed for the tested combustors with different thread forms. Moreover, the second law efficiency of a triangular thread is above 65%, while the entropy production from the chemical reaction and heat conduction proceses contribute more than 90%. The present work provides a new design of the internal structure for optimizing micro-combustors performances.

Enhancing heat transfer performance analyses of a hydrogen-fueled meso-combustor with staggered bluff-bodies

To improve the energy conversion efficiency of a thermo-photo-voltaic system, there is a need to optimize the combustor performance. This work considers applying staggered bluff-bodies to enhance thermal performance in a hydrogen-fueled meso-combustor. Effects of the equivalence ratio ϕ, the staggered bluff-bodies dimensionless height h, and the pitch ratio PR are numerically assessed and analyzed. To characterize the heat transfer intensity inside the channel, an average Nusselt number is introduced. Results show that the implementation of staggered bluff-bodies can generate longitudinal vortices, thus promoting mixing and enhancing the heat transfer performance significantly. Up to 73 K increase in the mean wall temperature (MWT) can be achieved. Meanwhile, MWT shows a non-monotonic dependence on ϕ, but the Nusselt number is found to vary monotonically with ϕ. Furthermore, increasing h is shown to be accompanied by a high Nusselt number, leading to a more uniform and higher MWT. Finally, it is shown that the PR of the staggered bluff-bodies plays a critical role in optimizing the system's thermal performance, and a low PR is more favorable but associated with a high pressure loss. The insights gained from this study may be of assistance to design a high-efficiency power system.

Comparative studies of shock-wave boundary-layer interactions in Earth and Mars atmospheres

Investigations of ramp-induced shock-wave boundary-layer interaction have been carried out for real gas flows of air and carbon dioxide through hypersonic laminar flow simulations corresponding to Earth and Mars atmospheres. An in-house-developed solver, which accounts for the real gas effects, has been employed for these studies. Effects of various parameters like wall temperature, freestream stagnation enthalpy, freestream Mach number, and blunt leading edge are explored on the intensity of shock-wave boundary-layer interaction (SWBLI). In either case, an increase in separation length is observed with an increase in wall temperature and a decrease in Mach number as well as freestream stagnation enthalpy. Here, the intensity of alteration is always noted to have a higher percentage for the Mars gas model. Further, separation length is found to be almost equal for the same wall to total temperature ratio in both of the flow mediums. The present study also affirms the fact that the leading edge bluntness can be used as a tool to reduce the size of the separation region in these planetary atmospheres. Revised correlations have been proposed for hypersonic Earth atmospheric flow with real gas effects to predict the extent of upstream influence and separation bubble size. The outcomes of simulations have also helped to device new correlations for these flow features of SWBLI for Mars atmospheric conditions. In all, the need for consideration of real gas effects and an exclusive real gas flow solver for the Mars atmosphere are the prominent recommendations of current studies.

Numerical Simulation of Heat Transfer in Laminar Natural Convection of Mixed Newtonian-Non-Newtonian and Pure Non-Newtonian Nanofluids in a Square Enclosure

Abstract This paper presents a steady-state heat transfer model for the natural convection of mixed Newtonian-Non-Newtonian (Alumina-water) and pure non-Newtonian (Alumina-0.5 wt% Carboxymethyl Cellulose (CMC)/water) nanofluids in a square enclosure with adiabatic horizontal walls and isothermal vertical walls, the left wall being hot and the right wall cold. In the first case, the nanofluid changes its Newtonian character to non-Newtonian past 2.78% volume fraction of the nanoparticles. In the second case, the base fluid itself is non-Newtonian and the nanofluid behaves as a pure non-Newtonian fluid. The power-law viscosity model has been adopted for the non-Newtonian nanofluids. A finite-difference based numerical study with the Stream function-Vorticity-Temperature formulation has been carried out. The homogeneous flow model has been used for modeling the nanofluids. The present results have been extensively validated with earlier works. In Case I, the results indicate that Alumina-water nanofluid shows 4% enhancement in heat transfer at 2.78% nanoparticle concentration. Following that there is a sharp decline in heat transfer with respect to that in base fluid for nanoparticle volume fractions equal to and greater than 3%. In Case II, Alumina-CMC/water nanofluid shows 17% deterioration in heat transfer with respect to that in base fluid at 1.5% nanoparticle concentration. An enhancement in heat transfer is observed for increase in hot wall temperature at a fixed volume fraction of nanoparticles, for both types of nanofluid.

Numerical and Experimental Investigation of Melting of Paraffin in a Hemicylindrical Capsule

Abstract Phase change of paraffin in a hemicylindrical storage unit is investigated numerically and experimentally. The predicted findings are confirmed by comparison with the experimental results of the present work. Good agreements are achieved between the two approaches. The influence of the hot wall temperatures of 80, 85, and 90 °C is examined. The conduction mechanism is dominant only during the initial periods of the charging process, while buoyancy-driven convection is prevalent at later stages. The charging rate and stored energy both increased, whereas the melting time is reduced as the wall temperature increases. The Nusselt number increases sharply at the initial period of the fusion process, followed by a decaying trend with time until it stabilizes when the charging process is terminated. Increasing the cell diameter from 20 to 40 cm will raise the melting time by 300% for the wall temperature of 90 °C. In addition, under the same operating conditions, the melting of the phase change material (PCM) inside the hemicylindrical cell is faster than that observed in a rectangular one with equivalent volume. Savings in melting time due to using hemicylindrical container instead of a rectangular one of equivalent PCM volume are about 7.1%, 8.3%, and 11.7% for hot wall temperatures of 65, 75, and 85 °C, respectively.

Investigating the Performance of CO Boiler Burners in the RFCC Unit with CFD Simulation

The combustion chamber's internal refractory in Imam Khomeini Oil Refinery Company (IKORC) was damaged in several parts, requiring operating conditions and re-inspecting the design of the combustion chamber using CFD. Simplify the combustion chamber 3D simulation, decrease in the number of calculations, the symmetry principle was applied in the simulation. The results, independent of the mesh network, were investigated via increasing the mesh nodes. The one-stage, two-stage, multi-stage and overall mechanisms, which were designated, were examined and compared to actual measured data and a calculation error of less than 8% was obtained. Ultimately, selecting overall mechanisms, the simulation results, streams mixing and length of the chamber were scrutinized, and as a result, the current design was approved. The temperature and velocity of the flows in the combustion chamber were investigated. In the combustion chamber, the farther we are from the burners, the more uniform the velocity and temperature profiles also become as the wall temperature increases. The rate of combustion reaction was evaluated with the temperature of different points in the combustion chamber. The results showed that the combustion chamber wall's temperature is in the appropriate range and has not suffered any thermal damage. Unlike the combustion chamber wall, the burner wall (at the mixing point) has an unauthorized temperature; there is the possibility of thermal damage that can be eliminated by changing the number of currents. Unsuitable thermal profiles also showed large amounts of oxygen in the exhaust gas indicated that the steam boiler performance is far from the optimal condition and specific changes would be required in the air streams. Streamline demonstrated that the primary air stream was more effective for decreasing CO and NOX amounts in the outlet stream. The secondary air stream was also significant to prevent thermal damage to the internal coating and reduce safety hazards.

Numerical study of the boil-off gas (BOG) generation characteristics in a type C independent liquefied natural gas (LNG) tank under sloshing excitation

In this paper, a numerical model considering phase change and external heat leakage is established to study the thermodynamic and hydrodynamic of a type C LNG tank under sinusoidal sloshing excitation. The volume of fluid (VOF) method, coupled with the mesh motion treatment, is adopted to predict the movement of the vapor-liquid interface. The sinusoidal sloshing excitation is realized by a user-defined function (UDF). Compared with related fluid sloshing experiments, the feasibility of the numerical model is verified. The numerical results show that the sloshing excitation has great influences on the thermophysical process and the BOG generation of the LNG tank. The effects of different sloshing frequencies and amplitudes on the thermodynamic characteristics of the LNG tank are studied. In addition, the partial damage of the insulation system is also studied, and it is found that the sloshing has little effect on the critical superheat of the tank wall where the insulation layer is partial damaged, but it will delay the increase of the tank wall temperature. This study is significant to deeply understand the thermal behavior of the LNG sloshing and the characteristics of the BOG generation under sloshing condition during the actual marine transportation of LNG ships.