Centerline Temperature Research Articles

Experimental Characterization of Circumferentially Arranged Fuel Port Inverse Jet Diffusion Flame Burner

ABSTRACT This paper presents experimental studies on flame height, thermal and emission characteristics of Inverse Jet Diffusion Flame (IJDF) using a circumferentially arranged fuel port (CAFP) burner by following two different protocols, namely, Protocol I and Protocol II. Experiments are carried out to investigate the effect of momentum flux ratio (MFR) on flame height and base flame height characteristics for a fixed air jet velocity, by varying fuel jet velocity (Protocol I) and by varying air jet velocity for a fixed fuel jet velocity (Protocol II). For both Protocols, there is a decrease in flame height with MFR due to the deterioration of fuel-air mixing process. Two separate semi-empirical correlations between normalized flame height and MFR are proposed for Protocol I and II, respectively. The center-line temperature characteristics indicate a faster air-fuel mixing at higher MFR for both Protocols. Moreover, Froude number is used to delineate the buoyancy and momentum-controlled regimes in IJDF. A constant temperature plateau is defined to identify the suitability of burner for industrial heating applications and is found to be higher for 32-port burner than that of the 12- port inverse jet diffusion flame burner due to enhanced air-fuel mixing along the jet central axis. Moreover, at lower MFR, emission index (EI) of NO remains independent of both the Protocols, whereas at higher MFR, the variation depends on the type of Protocol due to a larger variation of Froude number. On the other hand, the variation of CO emission index is almost independent of Protocol I and II. The experimental results show that the present 32 port burner design outperforms the emission characteristics of 12-port burner for an overall equivalence ratio less than 1.63. Two semi-empirical correlations for EINO and EICO, respectively, are developed as a function of overall equivalence ratio and MFR, which can be used for design and development of CAFP IJDF burner.

Experimental Investigation on Large Scale Diesel Pool Fire in a Vertically Ventilated Compartment

An experiment was performed for pool diameter 1 m located at the center of a compartment which has a size of 4 m x 4 m x 4 m (l x w x h). The door size was 2 m x 1 m (Height x Width) which was fully open during the experiment. The purpose of experiment was to obtain a data of burning characteristic of diesel fuel within the compartment. The large scale heat release calorimeter measure the heat release rate (HRR) and concentration of O2, CO2& CO. The thermocouple arrays are installed at different places to measure the ceiling temperatures; centerline temperatures above the pool, doorway temperatures.The maximum HRR has found 1 MW and during steady period average hot gas layer temperature reaches to 400 0C. The average mass burning rate was maintained to 0.037 kg/m2s, which was compared with other previous conducted experiments for diesel pool fire.

Application of Boron Carbide as Burnable Poison in Sodium Fast Reactors

Generation IV reactors are expected to exhibit significant safety improvements compared to current ones. In sodium-cooled fast reactors (SFRs), fuel melting during transient over power (TOP) should be avoided as this is identified as a relatively frequent accident. Among these TOP accidents, a control rod withdrawal (CRW) accident is the most likely to happen and its impact depends on the magnitude of the inserted reactivity. This paper presents the required excess reactivity for different core designs and the way to reduce the reactivity inserted during a CRW transient through the use of burnable poisons (BPs).After evaluating various candidate materials, it appears that a low-enrichment boron carbide combined with a zirconium hydride moderator is the most promising BP for use in sodium fast spectrum reactors. Burnable poisons are located in pins of particular assemblies, which are in fixed positions in the core over the entire fuel cycle.Four core designs with different loading schemes and BPs are investigated. Core designs with BPs display low reactivity loss over the fuel cycle and thus limit the required initial excess reactivity of the core to compensate with control rods.Another constraint comes from the core power distribution, which should remain almost stable through the fuel cycle. This core power distribution can be modified by a suitable loading of BP assemblies. However, as their positions are fixed over the fuel cycle, they can compensate only part of the local flux tilt. These BP core designs slightly improve the reactivity feedback coefficients as they contain light materials slowing down neutrons. It is finally shown that a CRW transient with BPs reduces significantly the maximal fuel centerline temperature compared to a design without BPs and that a fuel melting during a CRW transient is avoided in the large SFR core.

Thermal hydraulic analysis of accident tolerant fuels for Reactivity-Initiated-Accident in PWR with different coolant channel geometries

This paper describes use of sub-channel analysis code COBRA-EN to assess the thermal hydraulic performance and influence of different coolant channel geometries on several accident tolerant fuel (ATF) materials. The results show that FeCrAl-based alloy (AMPT) cladding could reduce peak cladding temperature (PCT) and peak fuel centerline temperature (PFCT), but irradiated SiC/SiC composite (SA3/PyC50-A) cladding raised them. Significant PFCT reduction could be achieved by using ATF fuels, but higher PCT with heat transfer deterioration. In order to analyze the potential impact of coolant channel geometry size, four geometry models were subjected to sensitivity analysis. The results show that previous coolant channel geometry size was the best design for UO2. Heat transfer deterioration on cladding surface of ATF fuel/cladding systems could be sufficiently improved with 10% increase of coolant channel geometry size. So, 10% increase of coolant channel geometry size for ATF fuel/cladding systems possible is a better design.

Full-core analysis for FeCrAl enhanced accident tolerant fuel in boiling water reactors

The impact of replacing Zircaloy with FeCrAl, a candidate enhanced accident-tolerant fuel cladding material, was evaluated for 10 × 10 boiling water reactor fuel bundles. Results from a series of full-core parametric studies estimated that replacing UO2/Zircaloy with UO2/FeCrAl would require an average enrichment increase of 0.6% 235U throughout the fuel lattice with the cladding and channel box thicknesses halved and fuel pellet diameter increased. Full-core results indicated that UO2/FeCrAl models with these geometric/enrichment specifications matched the base UO2/Zircaloy cycle length of 527 effective full power days. Optimization studies of the full-core design established loading and control blade patterns for both Zircaloy and FeCrAl models. A side study was conducted modeling a hybrid fuel bundle consisting of FeCrAl cladding and a SiC/Ni/Cr channel box. By halving the cladding thickness, the enrichment level required was less than that of the Zircaloy base case design after performing loading pattern optimization of the hybrid bundle core. Lastly, the thermomechanical performance of a Zircaloy-cladded fuel rod was compared to that of a FeCrAl system. Results from this analysis show that, if starting from the same fuel-cladding gap thickness, a FeCrAl-clad fuel rod operates with a greater average fuel centerline temperature, comparable axial elongation and radial displacement, and longer time to gap closure compared to a Zircaloy-clad fuel rod. This fuel performance analysis was primarily based on the commercial Kanthal APMT FeCrAl alloy but also used available data for the C35M FeCrAl alloy developed at Oak Ridge National Laboratory.

Research on thermal behaviors of several accident tolerant fuels based on 5 × 5 bundle subchannel model

Accident tolerant fuel (ATF) materials need to be studied by subchannel analysis under a variety of transient conditions before being applied to Light-Water-Reactors (LWRs). The present study assesses the thermal behaviors of various ATF claddings and fuels under four different transient conditions which will give rise to the occurrence of Departure from Nucleate Boiling (DNB) phenomenon. A 5 × 5 rod bundle model is built to conduct the subchannel analysis, and maximum cladding temperature (MCT) and maximum fuel centerline temperature (MFCT) of different ATF cladding and fuel groups are obtained. The simulation results show that both MCT and MFCT are reduced with the utilization of FeCrAl cladding, superior to HNLS/ML-A and SA3/PyC150-A claddings that only reduce MCT but increase MFCT. Significant MFCT reduction but slight MCT increase are achieved in most transient cases with the application of UO2 + BeO/SiC fuel pellets. Due to the different safety limit of various ATF materials, safety margin analysis is performed as well. The results show FeCrAl possibly is the best alternative cladding material among claddings studied, because both cladding safety margin (CSM) and fuel pellet safety margin (FPSM) are improved. Compared to single UO2 fuel, a larger fuel pellet safety margin is still provided by UO2 + BeO/SiC fuel pellets.

Study on airflow field and fiber motion with new melt blowing die

In this study, a new melt‐blowing die was studied with the computational fluid dynamic approach. A bead‐viscoelastic element fiber model was established to model three‐dimensional paths of the fiber motion with the standard linear solid (SLS) constitutive equation in different airflow fields. The effects of this newly designed die on the velocity field, temperature field, and turbulence fluctuation field at the centerline were studied and compared with the traditional melt blowing die. The fiber motion was simulated and compared with the airflow field of different dies. The simulations results demonstrated that the new die was able to reduce the velocity fluctuations of the air flow near the outlet of the polymer capillary and generate the higher centerline air velocity and temperature. The fiber attenuation and motion were related to the centerline air velocity, temperature, and turbulent fluctuation in the melt blowing process. POLYM. ENG. SCI., 59:1182–1189 2019. © 2019 Society of Plastics Engineers

Effect of burners configuration on performance of heat treatment furnaces

In order to obtain the most uniform temperature of the load, heat transfer in heat treatment furnaces used in the steel industry was studied. Different two-equation turbulence models were compared with experimental results. The Realizable k-ε model, predicts the load center line temperature better than the other two models, and it agrees closer to the experimental data. Also, by considering the radiation effect in the numerical simulation, the results were improved by 33% compared with experimental data. Finally, from different configurations of the burners studied and the results showed that the best temperature uniformity would be achieved for the configuration when the burners were located in a three down-three up arrangement.

Performance analysis of UO2 fuel rod for low-power research reactor application

A concept of low-power research reactor (LPRR) with innovative design features is recently proposed by Korea Atomic Energy Research Institute (KAERI) in South Korea. A conventional UO2-Zircaloy 4 fuel rod is proposed to be used as a driver fuel for the operation since it is advantageous to employ the conventional fuel rod in terms of sustainable long-term operation and cost-efficiency of the LPRR. The fuel rod for the given core specification was designed in detail.The performance analysis for UO2-Zircaloy 4 fuel rod was conducted to show its irradiation behaviors with the modification of FRAPCON code which is utilized for the commercial UO2 fuel performance analysis. Temperature distribution from fuel pellet centerline to bulk coolant was estimated, in which fuel centerline temperature at the axial peak power location was much lower than fuel melting temperature. The design analysis for the fuel safety in terms of rod internal pressure and cladding hoop stress was addressed to confirm the applicability of the fuel rod in the LPRR.

Investigation of the effect of using graded porosity on the thermal performance of the encapsulated ice thermal energy storage tank

AbstractThe storage tank has great impact on the performance of ice thermal energy storage (ITES) system. Previous researches show that enhanced temperature gradient in the tank improves the thermal performance of system. This study deals with the investigation for determining the effect of using graded porosity in the storage tank of encapsulated ITES system. In this study, it was researched that the effects of uniform, two‐graded, and three‐graded porosities inside the storage tank. Energy equation in porous medium was solved analytically to determine the centerline temperature changing in the tank. At the end of study, it was found that the lower porosity supplied higher thermal performance. However, lower porosity requires higher tank volume. Graded porosity provided the almost equal thermal performance with lower uniformly distributed porosity, although it had a higher porosity. Energy efficiency values were very high and changed between 95.23% and 99.98% in all porosity structure and working conditions. On the contrary to the energy efficiency values, exergy efficiency values were changed over a wider range between 35.80% and 88.71%. The highest exergy efficiency of 88% was seen in ε = 0.4 uniform porosity. Also, (ε1 = 0.4, ε2 = 0.5) two‐graded porosity and (ε1 = 0.4, ε2 = 0.5, ε3 = 0.6) three‐graded porosity provided higher exergy efficiency. While exergy efficiency increased with increasing heat transfer fluid (HTF) flow rate, decreased with decreasing HTF inlet temperature.

Full-Field Dependence on Inlet Modeling of Non-Isothermal Turbulent Jets Using Validated Large Eddy Simulations

Inlet conditions for a turbulent jet are known to affect the near field behavior but eventually lose their significance downstream. Metrics of importance are often derived from mean and fluctuating velocity components, but little has been done to explore inlet effects on transport of a scalar quantity (e.g., temperature). This paper aims to provide fundamental understanding in this regard and employs large eddy simulations (LES) of a nonisothermal round turbulent jet (Reynolds number of 16,000) with geometry and boundary conditions mimicked after a well-known experimental study. The jet inlet is first modeled with a standard Blasius profile and next by performing a simulation of the upstream flow modeled with either detached eddy simulations (DES) or LES for the second and third approaches, respectively. Only the model employing LES for both upstream nozzle and downstream jet is found to completely capture the root-mean-square (RMS) temperature behavior, namely, a distinct hump when normalized by the local mean centerline temperature at roughly five diameters downstream. Regarding the far field conditions, all three inlet conditions converge for the centerline values, but the radial distributions still portray non-negligible differences. Not surprisingly, the complete LES modeling approach agrees the best with experimental data for mean and RMS distributions, suggesting that the inlet condition plays a vital role in both the near and far field of the jet. The current effort is the very first LES study to successfully capture flow physics for a nonisothermal round turbulent jet in near and far field locations.

Application of the Transient Heat Transfer Measurement Technique Using Thermochromic Liquid Crystals in a Network Configuration With Intersecting Circular Passages

The present study deals with the application of the transient thermochromic liquid crystal (TLC) technique in a flow network of intersecting circular passages as a potential internal turbine component cooling geometry. The investigated network consists of six circular passages with a diameter d = 20 mm that intersect coplanar at an angle θ = 40 deg, the innermost in three, the outermost in one intersection level. Two additional nonintersecting passages serve as references. Such a flow network entails specific characteristics associated with the transient TLC method that have to be accounted for in the evaluation process: the strongly curved surfaces, the mixing and mass flow redistribution at each intersection point, and the resulting gradients between the wall and passage centerline temperatures. All this impedes the choice of a representative fluid reference temperature, which results in deviations using established evaluation methods. An alternative evaluation approach is introduced, which is supported by computational results obtained from steady-state three-dimensional (3D) Reynolds-averaged Navier–Stokes equations (RANS) simulations using the shear-stress transport (SST) turbulence model. The presented analysis uncouples local heat transfer (HT) coefficients from actually measured local temperatures but uses the time information of the thermocouples (TC) instead that represents the fluid temperature step change and evolution along the passages. This experimental time information is transferred to the steady-state numerical bulk temperatures, which are finally used as local references to evaluate the transient TLC experiments. As effective local mass flow rates in the passage sections are considered, the approach eventually allows for a conclusion whether HT is locally enhanced due to higher mass flow rates or the intersection effects.

Effects of static pressure, pressurization, and depressurization on n‐heptane pool fires in an airplane cargo compartment

SummaryThe cargo compartment of an airplane in flight is a complex environment with dynamic pressure (pressurization and depressurization), nonconservative oxygen, and unidirectional ventilation. In this study, n‐heptane pool fires were performed under static pressure, pressurization, and depressurization in a full‐scale airplane cargo compartment. The static pressure included 30 and 90 kPa, the pressurization was from 30 to 90 kPa at rates of 6, 12, 19, and 25 kPa/min, while the depressurization was from 90 to 30 kPa at rates of 6, 12, 17, and 20 kPa/min. The effects of pressure, oxygen concentration, and ventilation on pool fire characteristics including fuel mass loss rate (MLR), flame centerline temperature, and flame shape under each condition were concluded. The results show that the predominant factor of MLR was different in three conditions. The flame is divided into four regimes, in which the fuel vapor regime is used to emphasize the influence of fuel vapor on flame temperature above the fuel surface. The concept of average flame shape is put forward to reflect the flame occurrence probability. And its bottom, which named average flame root, presents the negative correlation with compartment pressure.

SPARK-LS: A novel design of a compact liquid chloride salt cooled fast reactor based on tube-in-duct fuel concept

A novel design of a compact liquid chloride salt cooled fast reactor (SPARK-LS) was proposed in the present study as a distributed energy resource for easy transportation and convenient deployment in diverse applications, such as electricity generation and district heating. The SPARK-LS reactor with rated power of 40 MWth can operate for 10 effective full power years without refueling. An innovative tube-in-duct fuel concept with coolant inside the tubes and fuel outside was adopted to achieve higher fuel volume fraction and lower pressure drop when compared with traditional pin-type fuel. Neutronics and thermal-hydraulics design and preliminary safety analysis were accomplished to obtain an optimized core design by using the advanced reactor design and analysis code system SARAX. Titanium was adopted as the reflector material due to its low density, good corrosion resistance, large strength-to-density ratio and decreased albedo with the neutron spectrum hardening. The optimized core design featured with compact volume and light weight was proved to satisfy the design constraints of peak coolant temperature, peak fuel centerline temperature and coolant pressure drop. The negative coolant density reactivity coefficient in the full core was ensured during the whole core lifetime thanks to the compact core design and the adoption of the titanium reflector. Based on the quasi-static reactivity balance method, five anticipated transients without scram were analyzed to confirm the inherent safety feature of SPARK-LS. It was shown that passive shutdown could be achieved safely for all the transients and the residual decay heat after the shutdown could be removed automatically by the natural circulation of coolant.

Analysis of Neutronics and Thermal-Hydraulic Behavior in a Fuel Pin of Pressurized Water Reactor (PWR)

This paper presents a comparative analysis of different parameters such as enthalpy, moderator temperature, moderator density, flow velocity, pressure, and fuel temperature profile at the fuel pin cell level of PWR. Moreover, in this paper pitches to fuel pin radius ratio are varied from 2.3 to 4. The methods and implementation strategy are such that the coupled neutronic and thermal-hydraulic analysis is executed in a fully one dimensional (1D) manner. The thermal hydraulic is based on moderator/coolant mass and enthalpy equation together with one group diffusion equation for fuel pin. Modelling of fuel pin cell and subchannel is executed in two steps. First, the governing equations are derived assuming that all the parameters appearing in the equations are temperature independent. Fuel pin centerline temperature and radially averaged temperature equations are derived from Fourier laws of thermal conductivity. Finally, diffusion coefficient, fission cross-section and absorbing cross-section are evaluated with respect to the fuel pin temperature. The outcome will be helpful for further neutronics and thermal analysis of PWR. Thermal hydraulics parameter varies the maximum 30 percentage from the lowermost value.

Thermal radiation modelling of pool fire with consideration on the nonuniform temperature in flame volume

The accidental leakages of combustible fuel during storage and transportation cause the pool fires which impose hazardous heat on the nearby occupants and facilities mainly by thermal radiation. This paper presents a new semi-empirical radiation model, namely, the multi-layer cylindrical flame model to predict the radiant heat flux field of pool fires. As the centerline temperature of pool fire varies significantly with vertical height, a formula is proposed to characterize the vertical profile of flame surface emissive power with which the new model can predict the radiant heat flux. The reasonable layer number (the number of small cylinders used for model prediction) can be determined using sensitivity analysis. Comparisons with the experimental data of methanol, heptane, toluene and propane pool fires of different pool diameters indicate that the new radiation model can give a good prediction on the thermal radiation in both horizontal and vertical directions, in spite of fuel type and pool diameter. In comparison with the point source model and three typically single cylindrical flame models, the new radiation model seems to give encouraging results relative to the validity of model system. Sensitivity analysis is also conducted to rank the importance of model parameters.

Coupled neutronic/thermal-hydraulic hot channel analysis of high power density civil marine SMR cores

Core average power density of standard small modular reactors (SMR) are generally limited to 60–65 MW/m3, which is 40% lower than for a standard civil PWR in order to accommodate better thermal margins. While designing a SMR core for civil marine propulsion systems, it is required to increase its power density to make more attractive for future deployment. However, there are obvious thermal-hydraulic (TH) concerns regarding a high power density (HPD) core, which needs to be satisfied in order to ensure safe operation through accurate prediction of the TH parameters.This paper presents a coupled neutronic/thermal-hydraulic (TH) hot channel analysis of a HPD 375 MWth soluble-boron-free PWR core using 19.25% 235U enriched micro–heterogeneous ThO2-UO2 duplex fuel and 16% 235U enriched homogeneously mixed all-UO2 fuel with a 15 effective full-power-years (EFPY) core life. To perform this analysis the hybrid Monte Carlo reactor physics code MONK is coupled with sub-channel analysis TH code COBRA-EN. This approach is used to investigate the feasibility of different HPD marine PWR concepts and to identify the main TH challenges characterising these designs. To design HPD cores of between 82 and 111 MW/m3, three cases were chosen by optimizing the fuel pin diameter, pin pitch and pitch-to-diameter ratio. These cases have been studied to determine whether TH safety limits are satisfied by evaluating key parameters, such as minimum departure from nucleate boiling ratio, surface heat flux, critical heat flux, cladding inner surface and fuel centreline temperatures, and pressure drop. The results show that it is possible to achieve a core power density of 100 MW/m3 for both the candidate fuels, a ∼50% improvement on the reference design (63 MW/m3), while meeting the target core lifetime of 15 EFPY and remaining within TH limits. The size of the pressure vessel can therefore be reduced substantially and the economic competitiveness of the proposed civil marine PWR reactor core significantly improved.

Effects of viscous dissipation on heat convection of viscoelastic flow inside isothermal channels and tubes

In the present paper, analytical solutions for thermal convection of the Finitely Extensible Nonlinear Elastic model with Peterlin’s closure (FENE-P) in isothermal slits and tubes are presented by considering the viscous dissipation effects for the first time. Temperature distributions are derived in closed form, namely the HeunT function, and Frobenius series solutions for the slit and the tube flows, respectively. The effects of fluid elasticity, the Brinkman number and the extensibility parameter on the thermal convection characteristics of FENE-P fluid flows are investigated in detail. Generally, the Brinkman number causes a fall in the Nusselt number, but a rise in the centerline temperature. The results reveal that during the cooling process the Nusselt number experiences a decrease with the Brinkman number, while the centerline temperature rises. However, during the heating process the former increases and the latter decreases. As the main innovation of this study, the results show a strong relation between the Nusselt number and the Brinkman number and also between the centerline temperature and the Brinkman number.

Irradiation testing of enhanced uranium oxide fuels

Enhanced uranium oxide fuel types are being tested in the Halden Research Reactor in Norway with the aim is to assess the effect that these enhancements have on fuel performance. Fuel temperatures, rod pressures and dimensional changes are being monitored online and an extensive post-irradiation examination programme is planned. Preliminary data show that fuel centerline temperatures can be lowered by addition of ThO2 to the fuel matrix, or by incorporating Cr or SiO2-TiO2 as a network structure within the fuel. In parallel, two types of cladding coatings are tested in order to investigate their in-core properties. No abnormal behaviour has been noted during the first 100 days of irradiation.

Pool fires of jatropha biodiesel and their blends with petroleum diesel

Combustion characteristics of pool fire of jatropha biodiesel (jatropha methyl ester – JME) and their blend with diesel were studied. Experiments were conducted in a compartment of size 4 m (L) × 4 m (W) × 4 m (H). Natural ventilation is applied by means of a door opening of size 1 m (W) × 2 m (H). Fuel was burned in pan size of 0.6 m and placed at the center of floor, initial fuel depth and lip height were 0.04 m and 0.08 m respectively. Blends of jatropha biodiesel with petroleum diesel were tested for biodiesel concentration of 20, 50 and 80% by volume. Various parameters including burning rate, heat release rate, exhaust emission (CO), flame centerline temperature etc. are measured. Radiative fraction is calculated from the measured heat flux data. Results show that with an increase in biodiesel concentration, combustion efficiency decreases. Plume centerline temperature is highest for B100 – JME pool fire, and the lowest for diesel pool fire. Also, the radiative fraction of fuels are comparable having lowest radiative fraction for jatropha biodiesel.