A line of mono-sized and periodically spaced droplets is moving in the diffusion flame sustained by the droplet fuel evaporation. The temperature field within the droplets is measured using the two-color laser induced fluorescence technique. Experiments are undertaken on droplets made of different fuels including acetone, ethanol, 3-pentanone, n-heptane, n-decane and n-dodecane which have very different volatility and viscosity. A simplified model of the heat transfer within the droplet is developed, taking into account both heat conduction and heat advection by the droplet internal fluid circulation. Streamlines are assumed to follow those of a spherical Hill vortex, the intensity of which can be related to the friction coefficient. Comparisons between the measurements and the simulations reveal that the heat convection within interacting droplets is strongly reduced compared to the model of the isolated droplet.

An analysis of the flow that depends of the fuel composition (natural gas) in the combustor-transition piece system, applying Computational Fluid Dynamics, is presented. The study defines the velocity and temperature profiles at the exit of the transition piece and the hot streak along the system. The variation of the composition in the fuel depends of the amount of N 2 contained in the fuel, and the hot track influences on the temperature distribution at the input of the first stage of vanes and blades of the gas turbine. The study takes place in a three-dimensional model in steady state using FLUENT ® 6.3.26, applying the k-ε turbulence model and chemical equilibrium to the combustion process. The results show the influence of the transition piece geometry over the velocity and temperature profiles, principally, in the radial direction. The velocity profiles on the radial direction can be represented by six order polynomial and the temperature profile by third order polynomial. The temperature and velocity profiles keep a symmetry profile and they can be represented by six order polynomial at the circumferential direction. Knowing these profiles, it is possible to compute a more exact study of the heat transfer at vanes and blades of the first stage of the turbine to evaluate the performance and life of them. On the other hand, considering from 5% to 10% of N 2 in the fuel composition, the maximum temperature is reduced in the combustion process and consequently the NOx emissions too.

On the way to a new era of our society which will be based on hydrogen energy, it is needed to develop on-site hydrogen production systems to cover current insufficient infrastructures of hydrogen supply network systems. For this, a highly efficient compact reformer can be one of the most suitable solutions for on-site production of hydrogen which is supplied to distributed electric power-generation systems. But, the local and overall energy balance in the reformer should be precisely controlled since the reforming reaction processes of hydrocarbon fuels are very sensitive to reaction temperature in the reformer. For smaller reformers, in particular, the amount of heat loss through the outer surfaces is large enough to dominate the reactions. An appropriate way for thermal energy management, therefore, is necessary to accomplish highly efficient reformers. For these backgrounds, a compact tubular-typed fuel reformer was fabricated in this study, and was applied to produce hydrogen from methanol, focusing on the partial oxidation reaction (POR). The reformer was composed of a stainless steel pipe as the reactor exterior and ceramic honeycomb blocks inserted in two locations of the reactor. The honeycomb blocks are expected to assist the reforming reactions and transfer the thermal energy of the exhaust gas to the reaction region, acting as a heat regenerator. The upstream-side honeycomb block was aimed to perform an effective heat exchange from the reactor wall to the reactant gas. By inserting the block, the reforming reaction became stable at right after the block. The maximum hydrogen production was achieved in the condition of equivalence ratio, around 3.5. The other honeycomb block was inserted in the downstream of the reaction zone to convert the thermal energy of exhaust gas to radiation energy which can be transferred to the upstream reaction region. Comparing to the case without the downstream-side block, the temperature of the reaction region became higher. Gas temperatures in the downstream region, on the other hand, became lower. Methanol conversion ratio and hydrogen production ratio enhanced due to the higher temperature at the reaction region. These results indicate that the thermal energy possessed by the exhaust gas was regenerated in the reaction region by the downstream-side honeycomb block and contributes to enhance the efficiency of the fuel reformer.

Gas turbine shaft is generally exposed to high temperature gases and may seriously be affected and overheated due to temperature fluctuations in the combustion chamber. Considering vortex flow in the combustion chamber, it may increase the heat release rate and combustion efficiency and also control location of energy release. However, this may result in excess temperature on the combustor equipments and gas turbine shaft. Vortex flow in the vortex engine which is created by the geometry of combustion chamber and conditions of flow field is a bidirectional swirl flow that maintains the chamber wall cool. In this study a new gas turbine combustion chamber implementing a liner around the shaft and liquid fuel feeding system is designed and fabricated. Influence of parameters such as axial position in the combustor direction and equivalence ratio are studied. Experimental results are compared with the numerical simulation by the existing commercial software. Swirl number i.e. ratio of angular flux of angular momentum to angular flux of linear momentum multiplied by nozzle radius, in this study is assumed to be constant. In order to measure the temperature along the liner, K type thermocouples are used. Results show that the heat transfer to the liner at the inlet of combustion chamber is enough high and at the outlet of combustion chamber is relatively low. The effect of parameters such as equivalence ratio and the mass flow rate of oxidizer on the temperature of the liner is investigated and compared with the numerical solution. This type of combustion chambers can be used in gas turbine engines due to their low weight and short length of combustion chamber.

This paper presents experimental and numerical studies on the fuel reforming process on an Ni/YSZ catalyst. Nickel is widely known as a catalyst material for Solid Oxide Fuel Cells. Because of its prices and catalytic properties, Ni is used in both electrodes and internal reforming reactors. However, using Ni as a catalyst carries some disadvantages. Carbon formation is a major problem during a methane/steam reforming reaction based on Ni catalysis. Carbon formation occurs between nickel and metal-support, creating fibers which damage the catalytic property of the reactor. To prevent carbon deposition, the steam-to-carbon ratio is kept between 3 and 5 throughout the entire process. To optimize the reforming reactors, detailed data about the entire reforming process is required. In the present paper kinetics of methane/steam reforming on the Ni/YSZ catalyst was experimentally investigated. Measurements including different thermal boundary conditions, the fuel flow rate and the steam-to-methane ratios were performed. The reforming rate equation derived from experimental data was used in the numerical model to predict synthetic gas composition at the outlet of the reformer.

This study shows a procedure to optimize polymer exchange membrane (PEM) fuel cell gas channels in the systems bipolar plates with the aim of globally optimizing the overall system net power performance. Two geometrical gas flow channel configuration are considered, parallel channel and serpentine. Geometric optimization is carried out to determine the configuration which offers minimum pressure drop within the system and the maximum heat and mass transfer for optimal system performance. The systems are subjected to the constraints of total fixed volume and materials. The systems total and net power, efficiency and polarization curves are presented as a function of system temperature, pressure, geometry and operating parameters. Predicted results are compared successfully against past data involving channel flow profiles in gas channels. The configurations obtained from the geometric optimization reduce the overall pumping power requirement and subsequently cost for the supply of required fuel and oxidants to the fuel cell through the channels.

A numerical simulation tool to predict the performance of a tubular SOFC is developed. For the convenience of the infrastructure, it has become more important to consider feeding hydrocarbon fuels like methane, which would be widely used, rather than hydrogen. Although it is well known that the performance of an SOFC drops largely when methane is fed compared with hydrogen, the reason for this is not yet well explained and thus prevents efficiently constructing an optimized SOFC system. Therefore, the present investigation is carried out to clarify how an SOFC performs when different fuels are fed. The calculation based on one-dimensional computation is carried out by introducing the parameters of actual electrode microstructures, obtained from the images taken by the focused ion beam scanning electron microscope (FIB-SEM). Values are adapted in calculating the ohmic, activation and concentration overpotentials. Proper experiments were also carried out to verify the validity of the numerical simulation. Although slight errors are found in the calculation results for fuels with high steam concentration, performances of hydrogen and methane fed cells were well predicted. Temperature distribution within the cell is also clearly shown. Through the present investigation, the performance drop, when the fuel is changed from hydrogen to methane, is found mainly caused by the temperature distribution of the cell that gives a concrete guide to construct an SOFC system.

Liquid breakup mechanism utilization is prevalent in numerous applications. One of the most common uses of this phenomenon is in fuel injection systems. Liquid fuel is injected into an ambient air, to prepare a combustible mixture. Generally, evenly spread tiny fuel droplets are desirable. This is usually achieved through multiple liquid breaking mechanisms: Primary breakup of liquid jet, Secondary breakup of travelling liquid droplets, and Secondary breakup of wall-impinging liquid droplets. Indeed, many studies are devoted to the modelling of those phenomena. However, the absolute majority of those studies are limitedly focused on the isothermal case, where liquid is assumed to be of ambient gas’ temperature. Conversely, practical conditions, under which rather cold fuel is normally injected into hot ambient air, suggest the real case to be non-isothermal. Moreover, the non-isothermal nature of that process seems to have its effect at the most relevant to breakup regions, i.e. the breaking interfacial surfaces. It is shown that as these surfaces can be in instant contact with a hot ambient, breakup can be greatly altered by the extent of this sudden thermal exposure, through its mostly transient and even spatial effect on physical properties of breaking interfaces. This is shown to be of significant effect on all breakup mechanisms: primary and secondary. New models are suggested for these non-isothermal phenomena, which combine transient heat-transfer with inter-phase hydrodynamic breakup, through physical properties’ dependency on temperature. Results are discussed in terms of effect on spray breakup products, and a careful comparison with the trend of a limited number of so-far available experimental results is presented.

A study has been carried out by experimental simulation of the loss of coolant accident (LOCA) in an Indian pressurized heavy water reactor (IPHWR). The experiment has been carried out taking a completely voided fuel channel of Indian PHWR at 40 bar inside pressure as test-section. In order to simulate the rate of heat generation during LOCA, the pressure tube (PT) was electrically heated with a 12VDC/3500A rectifier. Initially the set-up was maintained at 300 °C temperature by resistance heating of PT. After attaining nearly steady state a step input of 21 kW electrical heating was given to the test-section which resulted in the temperature rise of PT with a gross rate of 2.8 °C/s. The ballooning deformation of test-section tube i.e. PT initiated at 575 °C temperature. With the progress of ballooning the rate of temperature rise was reduced due to high heat transmission to CT and subsequently to water in the tank surrounding CT. The pressure tube (PT) and calendria tube (CT) contact established at the average PT temperature of 680 °C. The contact was also confirmed from the average temperature profile of CT.

Dye sensitized solar cells (DSC) are an attractive alternative to the conventional photovoltaic cell because of their low cost electricity production from solar radiation. The advantages of a DSC include the ability to generate power without emitting pollutants and requiring no fuel. While modeling of the physical and transport phenomena in DSC has been widely reported in the literature, a thorough analysis to quantitatively determine the optimal design and operating configuration in installation is lacking. The present study incorporates a model of the DSC coupled with a model to predict global irradiance on a terrestrial surface to analyze the hourly, daily, monthly and annual performance of a DSC installation over a wide range of design and operating parameters. Optimum design and operating parameters are derived from the analysis.

Hydrogen can be produced from water splitting with relatively high efficiency using high-temperature electrolysis. This technology makes use of solid-oxide cells, running in the electrolysis mode to produce hydrogen from steam, while consuming electricity and high-temperature process heat. When coupled to an advanced high temperature nuclear reactor, the overall thermal-to-hydrogen efficiency for high-temperature electrolysis can be as high as 50%, which is about double the overall efficiency of conventional low-temperature electrolysis. Current large-scale hydrogen production is based almost exclusively on steam reforming of methane, a method that consumes a precious fossil fuel while emitting carbon dioxide to the atmosphere. Demand for hydrogen is increasing rapidly for refining of increasingly low-grade petroleum resources, such as the Athabasca oil sands and for ammonia-based fertilizer production. Large quantities of hydrogen are also required for carbon-efficient conversion of biomass to liquid fuels. With supplemental nuclear hydrogen, almost all of the carbon in the biomass can be converted to liquid fuels in a nearly carbon-neutral fashion. Ultimately, hydrogen may be employed as a direct transportation fuel in a “hydrogen economy.” The large quantity of hydrogen that would be required for this concept should be produced without consuming fossil fuels or emitting greenhouse gases. An overview of the high-temperature electrolysis technology will be presented, including basic theory, modeling, and experimental activities. Modeling activities include both computational fluid dynamics and large-scale systems analysis. We have also demonstrated high-temperature electrolysis in our laboratory at the 15 kW scale, achieving a hydrogen production rate in excess of 5500 L/hr.

Fuel cells are electrochemical energy conversion devices that convert chemical energy in fuels directly into electrical energy, without the process of combustion. As a result, they are not constrained by the thermodynamic limitations of heat engines and therefore have the potential to achieve higher efficiencies. Various fuel cell types exist, operating from room temperature to over 1000 °C. This paper focuses on two of the leading fuel cell types, namely the lower temperature (80–120 °C) polymer electrolyte membrane fuel cell (PEMFC) and the higher temperature (500–1000 °C) solid oxide fuel cell (SOFC), with particular attention paid to the importance of thermal management and heat transfer in these systems, as it is thermal transients, and the appropriate design of the thermal management sub-system, that frequently limit fuel cell system performance and durability. Two examples of research from the authors’ laboratories are given; the first relates to the measurement and modelling of heat transfer in PEMFCs; the second to the thermal management of SOFCs.

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that are necessary to resolve for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been described for modeling the impact and subsequent liquid spread. Because the environment is difficult to instrument and costly to test, the existing validation data are of limited scope and quality. A comparatively well instrumented test involving a rocket propelled cylindrical tank of water was performed, the results of which are helpful to understand the adequacy of the modeling methods. Existing data include estimates of drop sizes at several locations, final liquid surface deposition mass integrated over surface area regions, and video evidence of liquid cloud spread distances. Comparisons are drawn between the experimental observations and the predicted results of the modeling methods to provide evidence regarding the accuracy of the methods.

Recently developed approaches to the hydrodynamic and kinetic modelling of fuel droplet heating and evaporation are reviewed. Two new solutions to the heat conduction equation, taking into account the effect of the moving boundary during transient heating of an evaporating droplet, are discussed. The first solution is the explicit analytical solution to this equation, while the second one reduces the solution of the differential transient heat conduction equation to the solution of the Volterra integral equation of the second kind. It has been pointed out that the new approach predicts lower droplet surface temperatures and slower evaporation rates compared with the traditional approach. A simplified model for multi-component droplet heating and evaporation, based on the analytical solution of the species diffusion equation inside droplets, is discussed. A new algorithm, based on simple approximations of the kinetic results for droplet radii and temperatures, suitable for engineering applications, is discussed.

Experimental study has been conducted to study the heat transfer characteristics of the hydrocarbons as the base fuel and water emulsions. The focus is mainly paid on the effect of the ambient emulsion temperature and alcohol additives on the boiling and its inception of fine water droplet dispersed in the emulsions. Heat transfer was measured using an electrically heated horizontal thin Pt wire. It is concluded that there is the transition point in the heat transfer coefficient, which is just above the boiling point of emulsified component of water. The heat transfer of water in fuel emulsions and effect of alcohol additives on it were also revealed.

Experimental and numerical study is performed on subsonic hydrogen jet diffusion flame formed from the vertical circular nozzle. Emphasis is placed on the effect of the cavity height formed at the fuel injection nozzle tip on suppression of the flame lift-off. It is found that (i) an increase in the cavity height triggers and enhances a vacuum pressure, (ii) the air from the surroundings is transported naturally into the cavity to replenish the air entrained and consumed by the jet flame, and (iii) the vacuum pressure results in the mitigation of flame lift-off propensity.

An experimental and numerical study of a laminar boundary layer with combustion has been carried out at hydrogen and nitrogen fuel mixture blow through a porous plate. At that main flow velocity ranged from 2 to 4 m/sec and the mass fraction of hydrogen in the fuel from 1 to 11%. The lower limit of stable combustion depending on the blow intensity and hydrogen content in the fuel mixture was obtained experimentally. Data on the temperature distribution in the boundary layer have been obtained and analyzed. The simulation results show that in this range of parameters combustion occurs in the kinetic mode.

Hydrogen-fuelled internal combustion engines are still investigated as an alternative for current drive trains because they have a high efficiency, near-zero noxious and zero tailpipe greenhouse gas emissions. A thermodynamic model of the engine cycle enables a cheap and fast optimization of engine settings for operation on hydrogen. The accuracy of the heat transfer sub model within the thermodynamic model is important to simulate accurately the emissions of oxides of nitrogen which are influenced by the maximum gas temperature. These emissions can occur in hydrogen internal combustion engines at high loads and they are an important constraint for power and efficiency optimization. The most common models in engine research are those from Annand and Woschni, but they are developed for fossil fuels and the heat transfer of hydrogen differs a lot from the classic fuels. We have measured the heat flux and the wall temperature in an engine that can run on hydrogen and methane and we have investigated the accuracy of simulations of the heat transfer models. This paper describes an evaluation of the models of Annand and Woschni with our heat flux measurements. Both models can be calibrated to account for the influence of the specific engine geometry on the heat transfer. But if they are calibrated for methane, they fail to calculate the heat transfer for hydrogen combustion. This demonstrates the models lack some gas or combustion properties which influence the heat transfer process in the case of hydrogen combustion.

This paper presents an analysis of heat-transfer to SuperCritical Water (SCW) in bare vertical tubes. A large set of experimental data, obtained in Russia, was analyzed and a new heat-transfer correlation for SCW was developed. This experimental dataset was obtained within conditions similar to those for proposed SuperCritical Water-cooled nuclear Reactor (SCWR) concepts. Thus, the new correlation presented in this paper can be used for preliminary heat-transfer calculations in SCWR fuel channels. The experimental dataset was obtained for SCW flowing upward in a 4-m-long vertical bare tube. The data was collected at pressures of about 24 MPa for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. The values ranged for mass flux from 200–1500 kg/m 2 s, for heat flux up to 1250 kW/m 2 and for inlet temperatures from 320 to 350°C. Previous studies have confirmed that there are three heat-transfer regimes for forced convective heat transfer to water flowing inside tubes at supercritical pressures: (1) Normal Heat-Transfer (NHT) regime; (2) Deteriorated Heat-Transfer (DHT) regime, characterized by lower than expected Heat Transfer Coefficients (HTCs) (i.e., higher than expected wall temperatures) than in the NHT regime; and (3) Improved Heat-Transfer (IHT) regime with higher-than-expected HTC values, and thus lower values of wall temperature within some part of a test section compared to those of the NHT regime. Also, previous studies have shown that the HTC values calculated with the Dittus-Boelter and Bishop et al. correlations deviate quite substantially from those obtained experimentally. In particular, the Dittus-Boelter correlation significantly over predicts the experimental data within the pseudocritical range. A new heat-transfer correlation for forced convective heat-transfer in the NHT regime to SCW in a bare vertical tube is presented in this paper. It has demonstrated a relatively good fit for HTC values (±25%) and for wall temperature calculations (±15%) for the analyzed dataset. This correlation can be used for supercritical water heat exchangers linked to indirect-cycle concepts and the co-generation of hydrogen, for future comparisons with other independent datasets, with bundle data, as the reference case, for the verification of computer codes for SCWR core thermalhydraulics and for the verification of scaling parameters between water and modeling fluids.

Fluid flow contributes much to fuel-air mixture formation in a micro-combustor, the RNG k-ε turbulence model was used to simulate the cold flow field of a falling fuel film microcombustor, and comparison was made between numerical result and experimental results. It is shown that the RNG k-ε turbulence model translated the flow field of a complex structure micro-combustor and the soot accumulation on the wall of combustion chamber. The experimental results showed that soot accumulation occurs in vortex backflow area near the wall of combustion chamber and the numerical methods is helpful for understanding the way of soot accumulation in the wall of combustion chamber. Therefore, modifications on the flow field with different diameters and entrance direction of the air flow into the primary combustion chamber were made. The numerical simulation of flow distribution showed that the flow field of micro-combustor could be ideal for eliminated soot accumulation.