Inlet Gas Temperature Research Articles

Reaction engineering approach for modeling single wood particle drying at elevated air temperature

In this paper, a semi-empirical drying model for convective drying of a single wood particle at elevated temperature is developed based on the reaction engineering approach (REA). The parameter of this model is determined and verified against both experimental and numerical data. The method proposed to identify the REA model parameter operates as follows: the evolution of the moisture content of a single wood particle over time is measured accurately by using a magnetic suspension balance. A continuum-scale model that takes into account major transport mechanisms relevant to wood particle drying is developed within the frame of volume averaging approach. Continuum model predictions are successfully assessed against the measurements conducted at four different inlet gas temperatures. A set of numerical simulation results obtained at 120 °C is used to deduce the REA model parameter. The fact that the REA model can fairly well reflect the experimental data at higher drying temperatures, i.e. 140 °C, 160 °C and 180 °C, is used to evaluate the accuracy of the REA model parameter. The REA model is also assessed using the continuum model simulations which are obtained for particles of different dimeters (2–20 mm) in a wide range of drying conditions (initial moisture content varies between 0.3 kg water/kg dry solid and 0.6 kg water/kg dry solid and air velocity between 0.005 m/s and 5 m/s). The results indicate that the REA model parameter is insensitive to variations of the drying conditions with an exception of inlet air velocity. The developed REA model can thus be considered as a simple predictive tool for drying of wood particles in a wide range of process conditions.

Simulation on gas-molten salt heat transfer in bubble column for solar thermal storage

The charging and discharging of molten salt thermal storage is of great importance to the operation and maintenance of the solar power plant. The molten salt bubble column is proposed for solar thermal storage, which is regarded as direct contact heat exchanger. The gas from the solar field is directly injected into the molten salt bubble column. High heat transfer rates can be achieved between the gas and the molten salt due to the direct contact. Numeric study on the hydrodynamics and heat transfer characteristic of the gas molten salt bubble column is carried out based on the two fluid model. The effect of the superficial gas velocity, gas inlet temperature and static liquid height are discussed. It is found that the volumetric heat transfer coefficient increases by increasing the superficial gas velocity and decreases by increasing the static liquid height. The distribution of the gas volume fraction varies from uniform flow to non-uniform flow and the heat rate become large as the gas superficial velocity increases.

Simulation study on the performance of direct expansion geothermal refrigeration system using carbon dioxide transcritical cycle

In the direct expansion geothermal refrigeration system using carbon dioxide transcritical cycle, the refrigerant loops are buried underground, and directly exchange heat with the soil. It can avoid polluting the underground water and soil even if the loops have the danger of corrosion and leakage, since carbon dioxide is a kind of safe natural substances. In this paper, the performance of this system is studied through simulation. The mathematic models of each component are established using the Static Distribution Parameter Method and the Lumped Parameter Method according to the characteristic of each thermodynamic process. Then, the simulation model of the direct expansion geothermal refrigeration system using carbon dioxide transcritical cycle is established. Based on the models, the performance of the transcritical refrigeration system is simulated. The simulation results manifest that the optimum high side pressure is 14.6 MPa and the maximum COP is 0.966 under the simulating conditions. The increases of gas cooler pressure, flow rate and inlet temperature of the chilled water all lead to a certain increase of the refrigeration capacity, the power consumption and COP. However, with the initial soil temperature rising, both the refrigeration capacity and COP tend to descend, but the power consumption rises on the contrary.

Investigation of Thermal Effect on Bypass Transition on a High-Pressure Turbine Guide Vane

The role of gas-to-wall temperature ratio on bypass transition along a highly loaded turbine guide vane is investigated through time-resolved heat flux measurements for different flow conditions. The tests are conducted in the von Karman Institute (VKI) isentropic compression tube (CT-2) facility. High response thin films mounted on the vane (VKI LS89 airfoil) coupled with analog circuits are used for the heat flux measurements. The first detectable wall heat flux fluctuations denote the onset of transition which is also evaluated by both the heat transfer coefficient and the intermittency factor distributions along the suction side. The exit Mach number is kept constant during each test by means of a downstream sonic throat while the gas-to-wall temperature ratio is varied from 1.14 to 1.51 by changing the inlet gas temperature. Four test cases are considered for different exit Mach numbers (0.52 and 0.86) and freestream turbulence intensity levels (0.8% and 5.3%) while the isentropic exit chord Reynolds number is maintained at 106. In the present test campaign, the length and the evolution of the phenomenon indicate a measurable effect of the gas-to-wall temperature ratio for test cases with mild pressure gradients.

Economic Analysis of Organic Rankine Cycle Using R123 and R245fa as Working Fluids and a Demonstration Project Report

The organic Rankine cycle (ORC) is a popular technology used in waste heat recovery and low-grade heat utilization, which are two important measures to solve the problems brought by the energy crisis. The economic performance of ORC system is an important factor affecting its application and development. Therefore, the economic analysis of ORC is of great significance. In this study, R123 and R245fa, two frequently-used working fluids during the transition period, were selected for calculating and analyzing the economic performance of an ORC used for recovery of waste heat with a low flow rate and medium-low temperature. Five traditional economic indicators, namely total cost, net earnings, payback period, return on investment, levelized energy cost, and present value of total profit in system service life, which is a relatively new indicator, were used to establish the economic analysis model of ORC. The variation effects of evaporation temperature, condensation temperature of working fluid, flue gas inlet temperature, and mass flow rate of flue gas on the above six economic indicators were analyzed. The results show that the optimal evaporation temperature of R123 is 125 °C, the optimal condensation temperature is 33 °C, and the optimal heat source temperature is 217 °C. For R245fa, the optimal evaporation temperature is 122 °C, the optimal condensation temperature is 27 °C, and the optimal heat source temperature is 177 °C. The economic performance of an ORC demonstration project was reported and used for comparison with the estimation and analysis. It was found that the single screw expander has an excellent economy performance, which greatly reduces the proportion of expander cost in the ORC system.

Biomass drying in a vibrating fluidized bed dryer with a Lagrangian-Eulerian approach

The objective of this study is drying analysis of biomass in a vibrating fluidized bed dryer with employing a DEM-CFD simulation tool as a multi-physics and multi-scale platform. In this approach, the particles are resolved as discrete elements coupled via heat, mass and momentum transfer to the surrounding gas phase leading to Lagrangian-Eulerian coupling approach. This tool predicts the motion of particles as discrete elements based on the Newtonian equations of motion; and the thermodynamic state of each particle is extended according to the related algorithms. The thermodynamic state stands for estimating the temperature and species distributions through the particle due to external heat sources and chemical reactions. The required experiments are carried out in the industrial-scale vibrating grate dryer. The intention of experimental works is estimating the moisture content, density and size distribution of materials as well as residence time to evaluate the simulation results. The aim is optimizing the operation and efficiency of vibrating fluidized bed dryer by investigating the influence of effective parameters as temperature and velocity of inlet gas, initial dryer temperature, initial moisture content of particles and grate intensity on drying process. At the end, the effect of size distribution is shown by temperature distribution of particles during interaction with the superheated steam in the system.

The Gas Flow Characteristics of A Helicopter Engine Exhaust Duct Using CFD Analysis

In this project is the gas flow characteristic of a helicopter engine exhaust and to derive an optimized geometry for the exhaust duct with minimum pressure loss using CFD analysis. In this project, the variables to be analyzed are the inlet static pressure, velocity and temperature of the exhaust gas at the exit of the exhaust duct. Cylindrical exhaust ducts of various dimensions are modeled by changing the primary and secondary inlet area and the exhaust geometry is optimized based on the CFD results. For the same optimized area of primary and secondary inlet, divergent exhaust duct is modeled and analyzed for various divergent angles. Parametric studies were carried out for a better comparison between cylindrical and divergent ducts for the better thermal efficiency.

Heat Transfer Modeling of a High-Temperature Porous-Medium Filled Solar Thermochemical Reactor for Hydrogen and Synthesis Gas Production

In this paper, heat transfer modeling of a high-temperature porous-medium filled solar thermochemical reactor for hydrogen and synthesis gas production is investigated. The numerical simulation is performed using a three-dimensional (3D) numerical model and surface-to-surface radiation model coupled to Rosseland approximation for radiation heat transfer. The effects of operating conditions and the porous structural parameters on the reactor thermal performance were investigated significantly. It was found that large axial temperature gradient and high-temperature distribution throughout the reactor were strongly dependent on the operating conditions. The inlet gas temperature has remarkable effects on the temperature distribution. The thermal performance of porous-medium filled solar thermochemical reactor could be improved by preheating the inlet gas up to 393.15 K. Moreover, a correlation was established between the protective gas inlet velocity and the porosity of porous media. The temperature difference decreased with the increase in the porosity of the inner cavity of the reactor. In contrast to the front and back parts of the inner cavity of the reactor, higher temperature distribution could be obtained in the porous region by increasing the average cell diameters of porous media.

Preparation and thermophysical properties of Ti4+ doped zirconia matrix thermal barrier coatings

There is an upper limited temperature of about 1200 °C for yttrium oxide partially stabilized zirconia coatings. With the increasing temperature of inlet gas (>1200 °C), new thermal barrier coatings are urgently needed to replace traditional yttrium oxide partially stabilized zirconia. Ti4+ ion doping has been recognized as an effective method to achieve this. In this work, a novel ceramic coating with low thermal conductivity at 1600 °C is synthesized, and the microstructure, chemical components, phase structures are analyzed. The thermal diffusivity and thermal conductivity of the as-sprayed coatings initially exhibited low values up to 1600 °C. The mechanism of low thermal conductivity is analyzed. The oxygen vacancies effectively reduce thermal conductivity, which can be proved by the ablation experiment (at 1600 °C). The effect of lattice defects caused by differences in the masses and radii of Ti4+ and Zr4+ ions on the phonon scattering coefficient is analyzed quantitatively. These results indicate that this coating is a promising candidate for thermal barrier coatings at high temperatures.

Heat recovery from an autothermal ammonia synthesis reactor for solar thermochemical energy storage

The previously proposed ammonia synthesis system for ammonia based solar thermochemical energy storage is complex with two catalyst-filled reactors, i.e., a heat recovery reator to heat the working fluid and an autothermal synthesis reactor to preheat the feed gas. In this paper, an autothermal heat recovery reactor (AHRR) is proposed, which cannot only heat the working fluid but preheat the feed gas simultaneously with ammonia synthesis. A model is proposed to simulate heating of the working fluid, e.g., sCO2, and the feed gas in an AHRR. Based on the model results, the AHRR not only requires less catalyst volume but has the potential for lower heat losses to the environment than the previous system. A sensitivity analysis is performed to analyze the potential model error. The analysis shows the model is most sensitive to the activation energy of the catalyst Ea. A parametric study has been performed to investigate the effects of diameters, mass flow rates, and inlet gas temperature for reaction on the reactor wall volume of the AHRR. The results show that smaller diameters of center tube and outer annulus are preferred for reducing the reactor size due to enhanced heat transfer for the secondary flows. But smaller catalyst bed thickness is not preferred because of larger pressure drop. Increasing sCO2 mass flow rate also reduces the reactor size by enhancing heat transfer. Although increasing inlet gas temperature for reaction decreases the reactor size as well as the required pumping power, there is a trade-off between reducing the reactor size and increasing the size of the heat exchanger for preheating the feed gas from the storage. The study provides a baseline for a further optimization including economic analysis.

Analysis of the dynamics of paste drying in a spouted bed

Although there are some models available in the literature for paste drying in spouted beds, few of them have focused on transient analysis of dynamical systems. Our objective was to integrate experiments and simulations of a dynamic model to investigate the transient response to disturbances and interruptions in the feed flow during paste drying in a spouted bed with inert particles. The spouted bed consisted of a cylindrical column with 50.0 cm of height and 20.0 cm of diameter. Drying tests were performed at inlet gas temperatures of 70 °C and 100 °C and inlet air flow 30% above the minimum spouting velocity. A 5% w/w suspension of calcium carbonate was used as paste material, and glass spheres of 2.2 mm were used as inert materials. Different patterns of step function changes were tested in the paste feed flow rate. A lumped parameter model was used to predict mass and heat transfer during the drying. Experiments and simulations were in good agreement.

Numerical investigation on the effect of gas parameters on ozone generation in pulsed dielectric barrier discharge

Pulsed dielectric barrier discharge is a promising technology for ozone generation and is drawing increasing interest. To overcome the drawback of experimental investigation, a kinetic model is applied to numerically investigate the effect of gas parameters including inlet gas temperature, gas pressure, and gas flow rate on ozone generation using pulsed dielectric barrier discharge. The results show that ozone concentration and ozone yield increase with decreasing inlet gas temperature, gas pressure, and gas flow rate. The highest ozone concentration and ozone yield in oxygen are about 1.8 and 2.5 times higher than those in air, respectively. A very interesting phenomenon is observed: the peak ozone yield occurs at a lower ozone concentration when the inlet gas temperature and gas pressure are higher because of the increasing average gas temperature in the discharge gap as well as the decreasing reduced electric field and electron density in the microdischarge channel. Furthermore, the sensitivity and rate of production analysis based on the specific input energy (SIE) for the four most important species O3, O, O(1D), and O2(b1∑) are executed to quantitatively understand the effects of every reaction on them, and to determine the contribution of individual reactions to their net production or destruction rates. A reasonable increase in SIE is beneficial to ozone generation. However, excessively high SIE is not favorable for ozone production.

Modeling of Chemical Vapor Deposition of Silane for Silicon Production in a Spouted Bed via Discrete Element Method Coupled with Eulerian Model

A CFD–DEM coupling model was applied to the silicon production by silane chemical vapor deposition in a spouted bed to investigate local phase movements, mass transfer, heat transfer, and the deposition rate of silicon. Silicon particle growth by heterogeneous deposition on the seed particle and fines formation in the gas phase were included. In addition, the scavenging effect was also considered in the particle growth mechanism. The spouted bed has advantages to promote heterogeneous deposition time due to a larger solid holdup and higher gas residence time in the annulus region. Furthermore, the effects of operating conditions, i.e., inlet gas temperature, silane composition, and gas velocity, on the reactor performance were investigated in detail, and some guidelines are provided for the choice of operating conditions. Verification of solid movement results with the experimental data and correlations show good agreement. In addition, the axial profile of bed voidage agrees well with correlation.

Innovative thermodynamic parametric investigation of gas and steam bottoming cycles with heat exchanger and heat recovery steam generator: Energy and exergy analysis

In this study, gas and steam bottoming cycles, driven by the exhaust gas of Gas turbine cycle, are analyzed thermodynamically. The waste heat of the Gas turbine topping cycle (GT) exhaust gas is used partially to heat the air in the air bottoming cycle and partially to generate steam by passing it through HRSG in the steam bottoming cycle. The topping Gas turbine and air bottoming cycles are coupled with the heat exchanger, whereas the topping and steam bottoming cycles are coupled with Heat Recovery Steam Generator (HRSG). The effects of turbine inlet temperature (1100 K ⩽ TIT ⩽ 1500 K), pressure ratio (6⩽rpt⩽12) and flow rate of exhaust gas on the Net work and combined thermal efficiency and exergy loss of exhaust gas are investigated. It is observed that the Net work of steam bottoming cycle is higher than the Net work of gas bottoming cycle and for higher values of turbine inlet temperature TIT = 1500 K, 90% of power is recovered through the bottoming cycle at lower pressure ratio. The combined thermal efficiency increases by 10% with an increase in the turbine inlet temperature from 1100 to 1500 K. It is found that the combined thermal efficiency increases with all pertinent parameters.

A computational fluid dynamics model of a rotary regenerative heat exchanger in a flue gas desulfurization system

Rotary regenerative heat exchangers (RHEX) are commonly used in flue gas desulfurization (FGD) systems to improve the dispersion of pollutants, reduce the visible plume, avoid liquid droplet rainout from the stack and avoid corrosion problems on the system materials. In this study, transient behaviors of heating and cooling cycles of a rotary regenerative heat exchanger in an FGD system were investigated via a 3-D computational fluid dynamics (CFD) model. For this purpose, the rotary regenerative heat exchanger was modelled using porous media approach for the heat transfer surfaces (i.e. matrix) inside the heat exchanger. A standalone channel model as used to obtain porous media parameters and heat transfer coefficient. Numerical results confirmed by published literature. Effects of different operating conditions on the performance of the heat exchanger have been investigated. In conclusion treated gas outlet temperature increases with increasing angular velocity and treated gas inlet temperature while it decreases with decreasing load. Consequently, untreated gas outlet temperature decreases with increasing angular velocity and decreases with the decreasing treated gas inlet temperature and load. By means of overall system performance it is observed that overall system performance increases with decreasing angular velocity and treated gas inlet temperature while it increases with decreasing load.

A novel comprehensive evaluation methodology of organic Rankine cycle for parameters design and working fluid selection

In order to improve the overall performance of organic Rankine cycle (ORC) systems, a novel evaluation method using the combination of grey relational method and entropy theory was presented. Based on a comprehensive evaluation indicator, which is constituted by 4 indicators in terms of thermodynamics, economy and environment, system performance was evaluated under different turbine inlet pressure and pinch point temperature difference. Besides, a performance comparison of six different working fluids was conducted. The results show that ORC system can achieve a better comprehensive performance at lower pinch point temperature difference in the evaporator. And there is an optimal turbine inlet pressure, which is significantly influenced by the inlet temperature of exhaust gas, to minimize the value of comprehensive evaluation index (CEI). As a low global warming potential (GWP) working fluid, butane produces the best comprehensive performance for exhaust temperature range of 443–483 K, and R1233zd(E) gives the highest value of CEI in exhaust temperature range of 483–513 K. Additionally, R1234yf is recommended for exhaust temperature lower than 443 K.

Simulation and Visualization of Cell Performance Distribution of SOFCs

Introduction It has been reported for SOFC systems that high electrical efficiency beyond 70% could be achieved theoretically in a recent study[1]. It is important to understand the internal characteristics to design highly efficient SOFC. However, it is difficult to visualize internal reactions experimentally. From these reasons, it is desired to develop a simulation technique for visualizing various phenomena within fuel cell stacks. Here, we focus on numerical analysis on electrode kinetics. Exchange current density is an important phenomenological parameter in considering electrochemical reaction kinetics at SOFC electrodes and in simulating cell performance. Here, the exchange current density of fully pre-reformed methane-fueled SOFC anodes is measured and phenomenological equations of anode exchange current density are derived. Furthermore, we combine numerical analysis with the phenomenological relations to simulate the spatial distribution of anode overvoltages. Experimental conditions In this study, electrolyte-supported cells were used to measure the anode exchange current density. The electrolyte material was ScSZ (ScSZ:10mol% Sc2O3–1mol% CeO2–89mol% ZrO2) and the electrode prepared using NiO-ScSZ was applied to the anode. The electrode prepared using LSM（LSM: (La0.8Sr0.2)0.98MnO3）and LSM-ScSZ was applied to the cathode. By changing operation temperature, fuel utilization (Uf), and steam-to-carbon ratio (S/C), anode overvoltage was measured at each current density (0.25, 0.3, 0.35, and 0.4 cm2) for methane-fueled pre-reformed SOFCs by the current interrupt method. The anode exchange current density was then derived from the current density and anode overvoltage values. In simulation, three-dimensional cell model was created using a numerical analysis software. A parallel co-flow model was considered. The inlet gas temperature was 800°C and the anode gas composition was fixed with the S/C of 2.5. Results and discussion The equation of anode exchange current density based on hydrogen-fueled model[2] was revised to consider the equilibrium reforming reaction, the water gas shift reaction, and the conservation law of anode gas partial pressure. It has been reported that the electrochemical reaction, where the adsorbed hydrogen atom (Had) in hydrogen-based fuels is rate-limiting[2], an Arrhenius-type equation shown in Eq. 1 has been proposed based on the assumption that the electrochemical reaction of Had is rate- limiting: i 0,a = a·exp(b/RT)·PH2(A) 0.5·PH2O(A) 0.5 (1) The partial pressure terms were modified considering the equilibrium reforming reaction and the water gas shift reaction. Pre-exponential factor a and activation energy b were fixed using the experimental results. Fig. 1 shows the experimental results of anode exchange current density. The phenomenological values derived from Eq. 1 are shown in Fig. 1. As the fuel utilization varied, the exchange current density increased and reached the maximum at around 40% of Uf. The experimental results could be well fitted by Eq.1. The SOFC cell performance simulation was performed using the three-dimensional SOFC model. Fig. 2 shows the anode overvoltage distribution along the fuel flow direction from the left side to the right side. The overvoltage decreased from the inlet towards the outlet. This is partly because oxygen partial pressure on the anode increased to the outlet and the electromotive force and the exchange current decreased.

A process model for underground coal gasification – Part-III: Parametric studies and UCG process performance

Underground gas gasification (UCG) is a clean coal technology which involves in-situ gasification of deep-seated underground coal. The process can be divided in two phases based on state of coal seam and direction of cavity growth. In phase-I, cavity grows mainly in vertical direction while in phase-II it grows in horizontal direction. The in-house simulator developed for both the phases of UCG has been reported earlier Samdani et al. (2016a,b). It incorporates reaction kinetics, flow patterns, spalling, heat and mass transfer effects. In this work, we take further insight and perform parametric studies to examine the effects of different operating conditions, coal properties and design parameters on key performance indicators i.e. exit gas quality, energy generation rates etc. The investigation revealed that the exit gas quality and rate of coal consumption are strong functions of spalling rates and kinetics of reactions; the coal having very low spalling tendency or less reactivity may not be favorable for the UCG process. An important parameter called critical spalling rate has emerged through this analysis. It is the property of given coal above which UCG is sustainable. In addition, model performance is also sensitive to inlet gas temperature, pressure and composition. Optimum performance of UCG is obtained at a steam to oxygen ratio of 2.5 and at the highest possible inlet gas temperature, operating pressure, and oxygen content in the feed. Among the design parameters, the length of outflow channel is very important as it strongly affects both the exit gas calorific value and its fluctuations with time. The predicted effects of different parameters are in accord with the observations during lab-scale UCG experiments and different field trials. This study demonstrates the importance of a process model to determine the best conditions for UCG process and to evaluate feasibility of the process for a coal seam under consideration.

Experimental study on the heat transfer of gas with coagulative particles flowing through a packed granular bed filter

An experimental study was carried out on heat transfer of gas with coagulative particles flowing through a packed granular bed. A logarithmic mean temperature difference (LMTD) method was used to obtain the overall heat transfer coefficient. An empirical formula was used to compare with the experimental results. The results show that the heat quantity released by the concretion of coagulative particles has an improved influence on the heat transfer when the inlet gas temperature of packed bed is above the melting point of the coagulative particles and outlet gas temperature is below the melting point. However, the heat quantity absorbed by the melting of coagulative particles can weaken the heat transfer when both the inlet and outlet gas temperature of the packed bed are above the melting point of coagulative particles. Two modifiedcorrelations are proposed to give the Nusselt number.

Deep seawater intake for primary cooling in tropical offshore processing of natural gas with high carbon dioxide content: Energy, emissions and economic assessments

In deepwaters offshore oil-gas rigs, centrifugal compressor trains are major power consumers, requiring intercoolers conventionally designed assuming surface seawater for primary cooling, limiting compressor inlet gas temperatures to 40 °C at tropical sites. On the other hand, at tropical deepwaters the available deep seawater at 4 °C can be exploited to reduce compression power – nearly proportional to inlet gas absolute temperature – entailing energy, economic and environmental benefits. This work considers a new primary cooling for deepwaters offshore platforms based on deep seawater (DSW) intake at 4 °C from depths around 900 m, reducing the outlet temperature of intercoolers to 12 °C. DSW intake alternative is assessed in terms of power consumption, CO2 emissions and economy employing detailed equipment sizing and cost estimation. Depending on gas flow rate, it is shown that DSW intake lowers compressors power up to 9.2%, besides several indirect benefits: elimination of one CO2 compressor; 30% less heat transfer areas; 4.5% less fuel gas consumption; 4% less gas turbines power; 9.5% (15 MMUS$) less investment; 14.4% (226 t) less topside weight, while making refrigeration unnecessary for dew point adjustment. DSW intake also entails 5% more efficient energy usage and 9327 tCO2/y less emissions, boosting economic performance under carbon taxation.