Inlet Gas Temperature Research Articles

Mathematical modeling and experimental study of a two-stage fixed-bed heat storage system for heat recovery of flue gases

This paper presents the results of experimental study and mathematical modeling of thermal energy recovery from the flue gases in a packed bed using phase change materials (PCMs). Air and water were used as the heat transfer fluids (HTFs) in the heating and cooling periods, respectively. Paraffin wax was used as the PCM which was encapsulated within polyethylene spheres of 40 mm diameter. The effect of temperature and velocity of the entering air to the bed on the system performance was investigated. In addition, mathematical modeling was conducted, and its numerical results were compared with experimental data. Moreover, two dimensionless parameters (i.e. efficiency and yield) were defined to evaluate the system performance under various operating conditions. The results of this study showed that the efficiency of energy recovery in the considered system could be increased by increasing the inlet gas temperature and decreasing the inlet gas velocity. A 40% increase in inlet gas temperature at constant gas velocity increases the system efficiency by up to 44%. Besides, the mathematical modeling results showed a good agreement with the experimental data.

Summary of a Numeric Method for Calculating Heat Transfer in the Rotary Air Preheater

Due to the introduction and implementation of new standards and new specifications, the structure of the heat transfer elements inside the air preheater has undergone relatively large changes. The thermal calculation method of the rotary air preheater is based on the Soviet 1973“Standard Method for Thermal Calculation of Boiler Units” It has been impossible to directly establish the heat transfer formula. According to the actual operating conditions of the rotary air preheater, the boundary conditions of the calculated heat transfer model can be obtained, including: the inlet temperature and inlet flow rate of the flue gas and air of the preheater; the heat transfer element of the regenerator is repeated Rotation, there are continuous conditions of the temperature of the heat storage element heat transfer element between the different air flow sub-bins. And a method for solving discrete equations is proposed.

Analyzing the thermodynamic performance of a hybrid system consisting of a gas turbine and two Stirling engines in series and parallel configurations

This paper aims to analyze the thermodynamic performance of a gas turbine–Stirling engine hybrid system with series and parallel configurations. The proposed hybrid systems include two separate cycles. In the first configuration, a gas turbine is combined with two Stirling engines in series formation, and in the second configuration, this combination is implemented in parallel formation. By conducting a parametric study of the introduced hybrid systems, the effects of the compressor pressure ratio, temperature of turbine inlet gases, type of fluid used in the Stirling engine, number of heater tubes, number of meshes and the matrix porosity of regenerator on the hybrid system’s efficiency and power output are investigated. The findings indicate that by raising the compressor pressure ratio and turbine inlet gas temperature, the system’s efficiency and power generation capacity are increased more in the parallel configuration than in the series configuration. Based on the results of comparison, the power generated by the hybrid system in parallel configuration and series configuration is 2.18 times and 1.8 times the power generated by a simple gas turbine cycle, respectively. The obtained results reveal that the electrical efficiency of the hybrid system in parallel configuration and series configuration is 56% and 49%, respectively, while the efficiency of a gas turbine hybrid system with just one Stirling engine is 42% and that of a simple gas turbine cycle is 30%.

Experimental Study on a Thermoelectric Generator for Industrial Waste Heat Recovery Based on a Hexagonal Heat Exchanger

To study on the thermoelectric power generation for industrial waste heat recovery applied in a hot-air blower, an experimental thermoelectric generator (TEG) bench with the hexagonal heat exchanger and commercially available Bi2Te3 thermoelectric modules (TEMs) was established, and its performance was analyzed. The influences of several important influencing factors such as heat exchanger material, inlet gas temperature, backpressure, coolant temperature, clamping pressure and external load current on the output power and voltage of the TEG were comparatively tested. Experimental results show that the heat exchanger material, inlet gas temperature, clamping pressure and hot gas backpressure significantly affect the temperature distribution of the hexagonal heat exchanger, the brass hexagonal heat exchanger with lower backpressure and coolant temperature using ice water mixture enhance the temperature difference of TEMs and the overall output performance of TEG. Furthermore, compared with the flat-plate heat exchanger, the designed hexagonal heat exchanger has obvious advantages in temperature uniformity and low backpressure. When the maximum inlet gas temperature is 360 °C, the maximum hot side temperature of TEMs is 269.2 °C, the maximum clamping pressure of TEMs is 360 kg/m2, the generated maximum output power of TEG is approximately 11.5 W and the corresponding system efficiency is close to 1.0%. The meaningful results provide a good guide for the system optimization of low backpressure and temperature-uniform TEG, and especially demonstrate the promising potential of using brass hexagonal heat exchanger in the automotive exhaust heat recovery without degrading the original performance of internal combustion engine.

Deposition Mechanism Analysis of Cold-Sprayed Fluoropolymer Coatings and Its Wettability Evaluation

Polymer coating by cold spray presents interesting features such as the possibility of protecting metallic substrates or adding functionalities to a structure. However, it is characterized by a low deposition efficiency and a weak interface between the substrate and the coating. In this study, we performed fluoropolymer coatings by the cold-spray process. Analysis of the particle deposition during cold spray highlighted the importance of the particle size, substrate temperature and inlet gas temperature and pressure on the adhesion polymer/substrate. The addition of hydrophobized fumed nano-ceramics (FNC) to the polymer feedstock enhances the deposition efficiency and polymer adhesion on the substrate. The addition of fumed nano-alumina (FNA) to the polymer feedstock tends to give better results than fumed nano-silica in terms of deposition efficiency thanks to (1) the difference in surface charge leading to the attractive force between the polymer and the FNA during the powder preparation stage and (2) a homogeneous repartition of the FNA on the polymer particle surface. In addition, the hydrophobization of the FNC maintains and enhances the hydrophobicity and water repellency properties of the fluoropolymer coating.

Selective CO Methanation in H2-Rich Gas for Household Fuel Cell Applications

Polymer electrolyte membrane fuel cells (PEMFCs) are often used for household applications, utilizing hydrogen produced from natural gas from the gas grid. The hydrogen is thereby produced by steam reforming of natural gas followed by a water gas shift (WGS) unit. The H2-rich gas contains besides CO2 small amounts of CO, which deactivates the catalyst used in the PEMFCs. Preferential oxidation has so far been a reliable process to reduce this concentration but valuable H2 is also partly converted. Selective CO methanation considered as an attractive alternative. However, CO2 methanation consuming the valuable H2 has to be minimized. The modelling of selective CO methanation in a household fuel cell system is presented. The simulation was conducted for single and two-stage adiabatic fixed bed reactors (in the latter case with intermediate cooling), and the best operating conditions to achieve the required residual CO content (100 ppm) were calculated. This was done by varying the gas inlet temperature as well as the mass of the catalyst. The feed gas represented a reformate gas downstream of a typical WGS reaction unit (0.5%–1% CO, 10%–25% CO2, and 5%–20% H2O (rest H2)).

O2, H2O or CO2 side-feeding policy in methane tri-reforming reactor: The role of influencing parameters

Methane tri-reforming is an efficient route to produce syngas. Distributing one component through a micro-porous membrane, namely side-feeding procedure, is an effective method for controlling reactions pathway and achieving the higher performance in membrane reactors. More recently, Alipour-Dehkordi and Khademi (2019) suggested a feasible and beneficial membrane multi-tubular reactor with O2, H2O or CO2 side-feeding policy to describe the methane tri-reforming for producing a suitable syngas for the methanol and dimethyl ether direct synthesis processes. To complete the previous research, a theoretical study was presented to detect the role of effective parameters, including molar flow rate of feed components, membrane thickness, shell-side pressure, and inlet gas temperature on the H2/CO ratio, CH4 conversion, H2 yield, and CO2 conversion. Several results were observed, however one of the most attractive results was to achieve CO2 conversion up to 40% in these configurations by controlling the influencing parameters (compared to CO2 conversion in the conventional tri-reformer (i.e., 11.5%)); that would be favorable for the environment.

Generation characteristics of thermal NOx in a double-swirler annular combustor under various inlet conditions

The NOx emission of gas turbine is a key factor of air pollution. It is still a challenge to realize low-NOx generation for all the gas turbines with diverse types of combustors and operation schemes. In this study, a three-dimensional simulation of the internal flow and combustion in a double-swirler annular combustor of a heavy-duty gas turbine was carried out. The realizable k-ε turbulent model and finite rate/eddy dissipation combustion model were employed for the numerical calculation. The effects of the swirl number and temperature of the inlet premixed gas flow on the thermal performance and the relationship between the velocity-temperature field synergy and the thermal NOx formation were investigated on the basis of field synergy principle. The results indicated that the change of the outer swirl number had a greater impact on thermal NOx generation than the change of the inner swirl number. The velocity-temperature field synergy in the combustor became better as the inlet swirl number or the inlet gas temperature increased. This synergy had a correlation with the thermal NOx generation. The formation rate of thermal NOx in the combustor should be controlled with the optimized velocity-temperature field synergy rather than the sole reduction of inlet gas temperature by considering the required thermal uniformity and capacity. The adopted field synergy is a promising concept to evaluate the thermal related performance of combustor. The obtained results on the generation characteristics under various inlet conditions may guide the design and operation of gas turbine combustors.

Numerical study on operating characteristics of self-driven total heat recovery system for wet-hot flue gas

This paper proposes a self-driven wet-hot flue gas total heat recovery system according to the characteristics of the heat transfer process of flue gas condensation, which uses the sensible heat in the high-temperature section to drive the system and complete the deep waste heat recovery of flue gas. The effect of flue gas and secondary water flow rate, flue gas and secondary water inlet temperature, and flue gas moisture on system performance were investigated and analyzed. Besides, the applicability analysis of technology and economic analysis are also performed. The results show that under the rated working conditions, the flue gas outlet temperature and relative humidity are 41.39 °C and 61.25%, respectively, and the maximum heat recovery rate of the system can reach 11.6%. When the flue gas inlet temperature is increased from 350 °C to 550 °C, the heat exchange capacity of the system is increased by 46%. Besides, when the flue gas inlet parameter is 550 °C/ and 120 g/kg (a), if the expected heat recovery rate of the known project is 10%, the maximum temperature of the secondary water that can be prepared by the self-driving system is 63 °C and the payback time is 2.53 years. When the flue gas inlet temperature and the moisture content is high, the system can provide hot water with higher temperature and is more energy-efficient than the traditional scheme.

Thermal effects in H2O and CO2 assisted direct carbon solid oxide fuel cells

Thermal effects in a H2O and CO2 assisted tubular direct carbon solid oxide fuel cell (DC-SOFC) are numerically investigated. Parametric simulations are further conducted to study the effects of operating potential, the distance between carbon and anode, inlet gas temperature, and anode inlet gas flow rate on the thermal behaviors of the fuel cell. It is found that the fuel cell with H2O as gasification agent performs considerably better than the cell with CO2 as gasification agent in all cases. It is also found that the temperature field of the fuel cell is highly uneven. The breakdown of the heat sources in the fuel cell shows that the H2O assisted DC-SOFC has much higher heat generation and consumption than the CO2 assisted cell. Interestingly, a thermal neutral voltage is observed, at which no heating or cooling of the cell is needed. In addition, the distance between the anode and the carbon layer is required to be as small as possible, which improves the temperature uniformity of the fuel cell. The results of this study demonstrates the importance of thermal effects in DC-SOFCs and form a solid foundation for DC-SOFC thermal management.

Influence of Operating Parameters on Plasma-Assisted Dry Reforming of Methane in a Rotating Gliding Arc Reactor

The environmental impact of greenhouse gases such as carbon dioxide and methane can be reduced if they are used as feedstock to synthesize chemical building blocks such as syngas (CO, H2) via dry reforming. Methane dry reforming is investigated using an Ar/CO2/CH4 rotating gliding arc (RGA) reactor powered by a dual-stage pulsed DC power supply. Tangential gas injection combined with a static magnetic field enabled the rotation and upward displacement of the arc along the conical cathode and the grounded anode, yielding to a larger plasma volume. Different parameters such as peak arc current (0.74 and 1.50 A), total gas flow rate (3.7, 4.7 and 6.7 SLPM), CO2/CH4 ratio (1.0, 1.5, 2.0) and gas inlet preheating (room temperature, 200 °C) were studied to determine the most efficient parameter combination. Gas conversion was measured online using a calibrated mass spectrometer and offline using a gas chromatograph. Noticeable increases in CO2 and CH4 conversions, as well as H2 and CO yields, were obtained when doubling the peak arc current. For the larger peak current, higher H2 yields were obtained at a CO2/CH4 = 1.0, and the best energy efficiencies were obtained at the lowest specific energy input values. No significant effect of the gas inlet temperature on the conversions or yields was found. Trace amounts of acetylene and ethylene, as well as some carbon deposits were observed as by-products of syngas generation. The low amount of by-products obtained implies a good selectivity for CO and H2, i.e., a cleaner syngas when produced with RGA discharge.

A computational fluid dynamics (CFD) approach of thermoelectric generator (TEG) for power generation

To harvest waste heat from flue gas in the industry, this study develops an advanced simulation technology by integrating computational fluid dynamics (CFD) and a thermoelectric module (TEM) where the TEM is modeled as a heat sink to absorb waste heat from flue gases. The influences of Reynolds number, convection heat transfer coefficient at the cold surface, flue gas inlet temperature, dual TEM, and channel geometry on the performance of the TEM system are evaluated. The results clearly provide a measure in increasing the performance of TEM with rising the Reynolds number, flue gas inlet temperature, and convection heat transfer coefficient at the cold surface. In the dual TEM system, the performance of the leading TEM is very close to that of the single TEM, and the dual TEM can produce an additional 43% power when compared with the single TEM. However, this also implies that the output power of the trailing TEM drops 57% when compared to the leading one, stemming for its impact upon the downstream TEM. When the channel geometry is modified to raise the flue gas velocity at Re = 1,000, the output power and efficiency increase by 53.5% and 25.2%, respectively.

Plugin energy penalty model and gypsum production for flue gas desulfurization prediction

The present paper presents two process functions for the estimation of the energy demand for $$\hbox {SO}_{2}$$ filtering from coal flue gas streams and the gypsum production by wet flue gas desulfurization (WFGD) systems. Functions are prepared to be used as plugins on conceptual design procedures of industrial processes based on coal combustion with some sulfur content without the need of modeling the complete WFGD system. An energy penalty function (EPF) is proposed as the ratio of demanded work to operate the filtering process with respect to the input flue gas volumetric flow rate, called the work ratio. Dihydrate calcium sulfate is a value product estimated by a gypsum slurry production function (GPF) based on the ratio of gypsum production to the input flue gas volumetric flow rate. Mass, energy and species balances are solved to simulate WFGD operation based on the inlet and outlet flue gas temperature, $$\hbox {SO}_{2}$$ content and cleaning efficiency, and results are compared to data from coal-fired power plants, from now on called the reference model. Design of experiment (Box–Behnken method) is used to identify main parameter weighting and cross-dependencies to finally build the EPF and GPF plugin functions. Relative deviations with respect to the reference model are of 1.41% and 0.05% for EPF and GPF, respectively. Both equations can be coupled to any kind of combustion system to quantify the energy penalty related to flue gas $$\hbox {SO}_{2}$$ removal and to predict the corresponding amount of gypsum as a by-product and to predict optimal operational conditions.

Extensive analysis of SOFC fed by direct syngas at different anodic compositions by using two numerical approaches

The paper presents an extensive analysis of the techno-energy performance of SOFC, when directly fed by syngas of different compositions. An ad hoc numerical modeling is developed and then run in a Matlab calculation environment. The model considers coupled site chemical reactions and multi-species gas diffusion in gases and electrodes, and considers the concurrent electroreactions of hydrogen and carbon monoxide, as well as the kinetics of the internal thermochemical processes. The numerical modeling deals with two approaches: the WGS_SOFC_Model and the DIR_SOFC model, suitable for predicting SOFC behavior with the absence and presence of methane respectively. The analyses are based on the assessment of the main output variables of the fuel cell, voltage, power density, electric efficiency vs the current density simulated, and by varying the input parameters, fuel composition, inlet gas temperature and SOFC excercise pressure, while calculating the composition of the output gas. A wide-ranging carbon deposition analysis completes the overall assessment. It is based on pressure, temperature and additional steam to carbon ratio as control parameters, and is aimed at finding the thermodynamic conditions and so the operative region that staves off the undesired phenomenon.Temperature increase affects SOFC energy performance as well as pressure positively. Electric efficiency is about 45–50% for high quality syngases, while about 30% for lower quality ones. The parallel carbon deposition analysis reveals that a working region of compromise must be detected, since increasing a control variable does not ensure an overall improvement. This evidence is more noticeable in syngases with significant methane content meaning the cracking carbon deposition is difficult to control.The numerical modeling presented, and so the overall analysis performed, is aimed to set a valid tool to come to the comprehension of the conditions of feeding and of excercise of SOFC, and to find the solution to excercise the electrochemical device efficiently and safely.

Design and Testing of a Gas-Helium Conduction Cooled REBCO Magnet for a 300 kvar HTS Synchronous Condenser Prototype

A 300 kvar high temperature superconducting synchronous condenser is under construction. In this work, a test superconducting magnet consisting of two double-pancake coils was designed, fabricated and tested. The coils had an effective length of 300 mm. They were wound by 5 mm wide REBCO tapes and vacuum impregnated by paraffin. The test magnet was cooled by a distributed-tubes-inside-pancakes conduction cooling structure. In this structure, 20 K helium gas was forced to flow in the tubes which were embedded in stainless-steel cover plates of coils. The magnet was installed in a vacuum chamber for cooling and transport tests. The results showed that the magnet was effectively cooled to about 22 K and operated stably at 281 A. The magnet steady-state temperatures at different operation current were recorded, approximately 2 K higher than the helium gas. Moreover, the thermal stability of the magnet was evaluated by adjusting inlet gas temperature from around 20 K to 25 K, and no magnet quench was observed. It was concluded that the cooling structure of the test magnet could fulfill the requirements of the 300 kvar HTS synchronous condenser.

Design and Test Verification of Acceleration Control for the Auxiliary Power Unit Based on N-Dot Acceleration Control Law

The acceleration control law based on the rotor acceleration N-Dot has been widely applied in the design of aero-engine control systems, especially in the design of transient control law. Its advantage lies in the fact that it can guarantee the consistency of the acceleration performance of engine, not affected by engine manufacturing error, component performance degradation, and so on so forth. During the development of full authority electronic control system (FADEC) for an auxiliary power unit (APU), an acceleration control law is designed based on N-Dot and corrected with turbine inlet gas temperature for APU. The modified N-Dot acceleration control law is verified through rig test and the results show that the designed control system by integrating the modified N-Dot acceleration control law with the limit protection control can effectively prevent the engine from surge and over-speed during the acceleration process, and fully take advantage of the acceleration performance of the engine.

A novel experimental based statistical study for water management in proton exchange membrane fuel cells

Water management is a key issue in low-temperature PEMFCs. For proper water management, processes leading to dehydration or flooding of cells should be clearly understood, hence prevented. Here, the effects of Anode Stoichiometry (AST), Cathode Stoichiometry (CST) and inlet gas temperature (T*) on the cell performance and water management in PEMFC are experimentally studied. Two methods, namely (i) direct- and (ii) indirect-method are employed to monitor water accumulation in cathode flow channels of a multi-path-parallel-serpentine PEMFC. Flow visualization served as direct method (item (i)), in which recorded videos of transparent channels were analyzed via an image-processing algorithm to monitor water coverage ratio (WCR). Simultaneously an inlet-to-exit pressure drop coefficient (Φ) was defined for indirect-method (item (ii)). AST, CST and T* were taken as input to provide three experimental based correlations for generated electrical power, WCR and Φ as a response. According to the results, an increase in AST reduces water-content in cathode channels; decreases performance also raises the sensitivity of generated power to variations in other operating-parameters. However, an increase in CST and T* reduces water contents in cathode channels also increases the cell power and lowers sensitivity of the power to the variation of other operating-parameters. It is observed that strong connectivity exists between WCR and Φ. This is verified by obtaining a high Pearson correlation coefficient of 0.887 between WCR and Φ. It is demonstrated that dehydration and flooding could be prevented when 3 ≤ WCR ≤ 4, from which appropriate operating-parameters AST, CST and T* could be retrieved.

Desorption of VOC from polymer adsorbent in multistage fluidized bed

Abstract The desorption process of volatile organic compounds (VOC) from a polymer adsorbent in counter-current multistage fluidized bed was studied. And a mathematical model considering the mass transfer dynamics was developed, which was validated from experiment data. The gaseous ethyl acetate mass transfer was discussed, and the limiting step is the intraparticle mass transfer of the desorption process. The value of intraparticle mass transfer coefficient is between 1.85 × 10−6 and 1.38 × 10−5 m·s−1 under temperature of 100–160 °C. Experiments under different operating conditions were carried out. The effects of operating conditions such as gas–solid flow ratio, gas inlet temperature and total stage number of multistage fluidized bed on outlet VOCs concentration and desorption efficiency were discussed. The maximum outlet VOCs concentration and corresponding desorption efficiency of the multistage fluidized bed desorber was calculated under different gas inlet temperatures and total stage numbers.

Eulerian-Eulerian Numerical Study of the Flue Gas Desulfurization Process in a Semidry Spouted Bed Reactor.

The Eulerian–Eulerian two-fluid model (TFM) in conjunction with kinetic theory of granular flows (KTGF) was used for analyzing water vaporization and the semidry flue gas desulfurization process in a two-dimensional powder–particle spouted bed (PPSB). In an environment with high-temperature gas, desulfurization slurry is wrapped on the surface of moving particles and evaporated, along with the application of the user defined function (UDF) method to accomplish water heat and mass transfer by considering evaporation in the simulation process. The simulation results revealed that the best mass- and heat-transfer effect of each phase can be found in the outer annulus and the near spout region, both of which are also the main areas where water vaporization occurs. The rate of desulfurization products decreases with the increase in inlet gas temperature as the water vaporization rate increases. The volume fraction of desulfurization reaction products decreases with the increase in inlet flue gas temperature. Compared with other working conditions, the highest desulfurization efficiency reaches 84% when the inlet flue gas temperature is 480 K. The change of the desulfurization product rate with the radial distance is the same under different superficial gas velocities, with the peak desulfurization efficiency appearing in the annulus. The optimal operating parameter for the desulfurization process is available in PPSB, and the desulfurization efficiency and gas handling capacity reach the best result when the superficial gas velocity equals 1.2 Ums.

CFD analysis on the effect of radiation and inlet gas temperature on porous media solar heater

The effect of porosity on flow and thermal characteristics is significant. Fluid flow through porous media has many practical relevance such as agriculture, engineering, bio-medical, etc. applications. In the present study, flow of gas and through solar heater is simulated and the heat transfer characteristics are studied. Two-dimensional numerical simulations are carried using ANSYS-Fluent. Velocity of gas at the inlet is varied from 0.005 to 0.5 m/s and passed through the porous media with porosity value of 0.7. Results are presented in the form of pressure variation, velocity variation and temperature variation.