Gas Mass Flow Research Articles

Exergy Analysis of Organic Rankine Cycles with Zeotropic Working Fluids

Waste heat recovery is one of the possible solutions to improve the efficiency of internal combustion engines. Instead of wasting the exhaust stream of an energy conversion system into the environment, its residual energy content can be usefully recovered, for example in Organic Rankine Cycles (ORC). This technology has been largely consolidated in stationary power plants but not yet for mobile applications, such as road transport, due to the limitations in the layout and to the constraints on the size and weight of the ORC system. An ORC system installed on the exhaust line of a bus powered by a natural gas spark ignition engine has been investigated. The thermal power available at engine exhaust has been evaluated by measuring gas temperature and mass flow rate during real driving operation. The waste thermal power has been considered as heat input for the ORC plant simulation. A detailed heat exchanger model has been developed because it is a crucial component for the ORC performance. The exergy analysis of the ORC was performed comparing different working fluids: R601, R1233zd(E) and two zeotropic blends of the two organic pure fluids. The model allowed the evaluation of the ORC produced energy over the driving cycle and the potential benefit on the engine efficiency.

PERFORMANCE OPTIMIZATION OF SUPERCRITICAL CO2 GAS HEATER IN A BIOMASS-CO2 POWER GENERATION SYSTEM

A comprehensive computational fluid dynamics (CFD) simulation model was developed in the current research to simulate a shell-and-tube supercritical CO<sub>2</sub> gas heater used in a biomass-CO<sub>2</sub> power generation system. The model was based on the actual design of the heat exchanger and relevant operational parameters. The simulation model was validated using manufacturer operational data and empirical correlations before being utilized to evaluate the performance of the heat exchanger and its related system under various operating conditions and heat exchanger designs. The results of the simulation demonstrate that the heating capacity of the heat exchanger can be increased differently by increasing the flue gas temperature, flue gas mass flow rate, and CO<sub>2</sub> mass flow rate. Furthermore, there is an optimal CO<sub>2</sub> pressure ratio that can improve the system's thermal efficiency. Decreasing the distance between hot fluid pipe inlet and cold fluid outlet ports, as well as hot fluid pipe outlet and cold fluid inlet ports, can effectively enhance the heating capacity of the shell-and-tube heat exchanger and its associated system. In quantity, with the new heat exchanger design, the heating capacity exhibits maximumly 9.2% average improvement, while the associated system thermal efficiency can have an average 6% enhancement with varied flue gas mass flow rates. Based on the CFD simulation outcomes, recommendations for enhancing the heat exchanger designs and system controls have been identified.

Experimental study on 10-cm ECRIT neutralizer with nitrogen gas

Electron cyclotron resonance ion thruster (ECRIT) with a diameter of 10 cm can be operated in multiple types of gases and it is feasible to be applied to air-breathing electric propulsion systems. The study on the neutralizer of the ECRIT running in nitrogen gas is the basis for the study on the ECRIT running in nitrogen-oxygen mixed gas. When the ECR neutralizer of typical 10-cm ECRIT running in xenon gas runs in nitrogen gas, the extracted electron current is reduced, because ions tend to drift out of the neutralizer, due to the lower molecular weight of nitrogen. The typical neutralizer is no longer suitable for running in nitrogen gas. In this work, based on the 10-cm typical ECR neutralizer, in order to inhibit ions drifting out of the neutralizer and improve the performance of electron extraction, a bipolar ECR neutralizer suitable for running in nitrogen gas is experimentally studied. The results show that under the conditions of gas mass flow rate of 0.04 mg/s and input power of 10 W, the anode voltage required by the typical ECR neutralizer running in nitrogen gas is 150 V when the extracted electron current is 134 mA. However, the bipolar ECR neutralizer requires only 50-V anode voltage, which decreases by about 67%. When the anode voltage is 40V, the power loss of the typical ECR neutralizer is 1204.82 W/A, while the power loss of the bipolar ECR neutralizer is 95.23 W/A, which is about 8.3% of the former. The ion shielding effect of the bipolar ECR neutralizer running on nitrogen gas is remarkable and the electron extraction performance is improved.

An experimental study of in-situ remediation of NAPL-polluted soils by ozonation

The effectiveness of ozonation as a method for the in situ remediation of non-aqueous phase liquid (NAPL)-polluted soils is examined. Soils were polluted artificially with a model NAPL consisting of equal mass fractions of n-decane, n-dodecane and n-hexadecane at two concentrations 1g/kg-soil, and 10g/kg-soil. The polluted soils were placed inside a stainless steel column and treated with the injection of ozone-rich gas, produced from oxygen by a corona discharge ozone generator, controlled by a gas mass flow controller, and monitored by an ozone analyzer. Soil samples collected from the soil column were used after pre-treatment to measure the concentrations of the total organic carbon (TOC), and total petroleum hydrocarbons (TPH) as function of time. The concentrations of carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOCs) were detected on-line by a multi-sensor and portable gas analyzer. .

Design and simulation of a combined flue gas and steam bagasse dryer to increase boiler efficiency of a sugar factory

Bagasse is a sugar industry residue used to generate high-pressure steam that can be utilized to generate electricity. The moisture content of bagasse is a serious issue that lowers boiler efficiency. The study conducted in Arjo Diddesa sugar factory, its moisture level of the bagasse is above 52%, which impacts boiler efficiency. In this plant uses traditional SHRD technique, this uses waste flue gas to decrease moisture content. To reduce heat losses, steam is directed through the inner tube, while bagasse and flue gas are directed through the outer rotating cylinder, leading in interaction between indirect steam and direct flue gas-bagasse. ANSYS software is used for the development of drier and optimization by considering the input parameters for the SHRD are: flue gas mass flow rate, bagasse temperature, flow Pressure of flue gas. The SHRD system is tilted to the horizontal at an angle of 4° and rotates at a speed of 4.6 rpm to aid in transporting wet bagasse. The moisture in the bagasse is dropped from 52 percent to 45 percent, and increase in efficiency of a boiler from 71.5 percent to 74.5 percent theoretically. The initial GCV and NCV with 52% moisture content are 9137.6 kJ/kg and 7129.4 kJ/kg. After drying, the45% ofmoisture content, the GCV and NCV of bagasse are 10484.8 kJ/kg and 8549.8 kJ/kg, respectively. The findings of the comparison show that the CV was raised by 1500 kJ/kg.

EFFECT OF NON-AXISYMMETRIC INLET PORTS AND OPERATING CONDITIONS ON DROP DYNAMICS OF AN INTERNAL MIXING ATOMIZER

The effect of a non-axisymmetric inlet ports configuration of an internal-mixing twin-fluid atomizer on the spray characteristics is experimentally investigated. Inside the atomizer, two water jets are impinged on each other and are further disrupted by a central gas stream coming from the top. The operating conditions consider the variation of the gas mass flow rate at Reynolds and Weber numbers in the order of 10<sup>4</sup>-10<sup>5</sup>. Phase Doppler anemometry (PDA) measurements at four radial, four axial, and two perpendicular azimuthal positions are combined with a patternator device to obtain droplet size, axial velocity, and mass flux distributions. An approach for evaluating the overall spray asymmetry based on the mass flux distributions is proposed, which enabled the detection of slight asymmetries throughout the azimuthal direction, where especially differences in droplet sizes and velocities measured between the two azimuthal positions are observed. Higher Sauter mean diameters (SMDs) and lower velocities in regions of the spray with higher liquid mass flux are observed when compared to the azimuthal position perpendicular to it. In general, the liquid is considerably faster in the spray center than at the boundaries, where the fluctuating component of the velocity is higher due to the interaction of small droplets with the surrounding air. Overall, an increase in the gas flow rate reduces the droplet sizes and increases the velocity across the spray.

Optimal tuning of model predictive controllers for organic Rankine cycle systems recovering waste heat from heavy-duty vehicles

The organic Rankine cycle power system is an emerging technology, which is able to recover the waste heat from the diesel engine of heavy-duty trucks and thus increase the overall engine efficiency. One of the major technical challenges for the integration of the organic Rankine cycle unit on-board trucks are the broad and rapid fluctuations of the available waste heat, caused by the unsteady driving conditions of the truck. Model predictive control has shown to be a powerful tool to ensure safe operation and optimal performance of the organic Rankine cycle unit on-board trucks. This paper presents a novel systematic method for the tuning of model predictive controllers based on a multi-objective optimization routine using a fourth-order reduced linear model. The objectives of the optimization are the settling time due to a step change of the exhaust gas mass flow rate and the cumulative controller effort due to measurement noise. The results suggest that a trade-off exists between the two objectives. Among the controller design parameters, the input rate weight has the largest influence on the controller performance. Interestingly, the simplified optimization procedure based on the reduced-order linear model of the organic Rankine cycle unit can provide key information about the controller performance based on a more complex nonlinear model of the organic Rankine cycle unit when subjected to a realistic waste heat profile. The results indicate that the settling time due to a step change of the exhaust gas mass flow rate is a good indicator of the absolute mean square tracking error over the profile, and it should not exceed 15 s for an absolute mean square tracking error below 2 K. On the other hand, the cumulative controller effort due to measurement noise is strongly correlated to the cumulative controller effort over the profile, and it should stay below 0.5 %/s for a cumulative controller effort over the whole profile below 2 %/s. The presented method is a powerful tool to help the control designer to find the optimal design parameters of model predictive controllers in a systematic way, in contrast to the time-consuming, experience-based trial and error methods.

Characteristic analysis of natural circulation residual heat removal in small reactor

In order to study the characteristics of small helium-xenon cooled nuclear reactor that only relies on natural circulation to remove residual heat after shutdown, this paper carries out geometric and physical modeling of helium-xenon cooled nuclear reactor, and uses CFD to simulate the process of natural circulation residual heat removal. Variation laws of the hot spot temperature on the surface of fuel cladding and the mass flow of helium-xenon mixed gas under different working conditions are calculated, and the transient characteristics of temperature, flow and other related parameters in the system loop are analyzed. The calculation results show that during the natural circulation residual heat removal process, the overall change trend of the hot spot temperature on the surface of the fuel cladding, the average temperature of the primary coolant and reactor outlet temperature first rises to the highest value and then decreases, and the mass flow of helium-xenon mixed gas shows an exponential decay trend; Increasing the initial mass flow of helium-xenon mixed gas and reducing the residual heat of the reactor core can reduce the maximum hot spot temperature on the surface of the fuel cladding. The relevant research results provide a useful reference for the optimal design of natural circulation residual heat removal of helium-xenon cooled nuclear reactor.

Power-heat conversion coordinated control of combined-cycle gas turbine with thermal energy storage in district heating network

Thermal energy storage, with its low energy storage cost and wide distribution in industrial processes, is an effective way to improve the operational flexibility of power plants. Due to colossal energy storage capacity and small deployment costs, this article proposes connecting district heating networks to combined cycle gas turbine (CCGT) plants as a thermal energy storage capacity, improving the flexibility of CCGTs. The main focus here is on developing an appropriate control strategy to effectively control the power-heat conversion, meet the heat and power demands of the connected network, and the operational flexibility of the plant. The major problem is that the intrinsic static and dynamic conversion relationship of power and heat in the CCGT and district heating network and the buildings are multi-factor interactive and unknown. Therefore, the CCGT bottom cycle and district heating network, and building models were built to obtain the power-heat conversion parameters and the dynamic model for control design. Then, the energy storage coefficient of 0.105 MW/kg/s is obtained through the model simulation instead of a complex thermodynamic calculation, corresponding to the 113.22 GJ energy storage capacity of the district heating network. Based on the obtained conversion rules, a new control strategy called ‘conversion coordinated control’ is designed and applied, using load signal decomposition and synergistic load response of flue gas mass flow rate and steam extraction valve. The simulation results show that the proposed method can promote a ramping load rate of 8.6 MW/min in the first 30 s with only 0.3 °C building temperature variation. The control strategy can effectively reduce the gap between the grid demand and CCGT power and ensure grid stability without compromising thermal users’ comfort.

Evaluation of fire smoke and heat exhaust performance of shafts by natural venting in tunnels

Theoretical analysis and numerical simulations are performed to study the smoke and heat exhaust performance of natural venting system with different shaft forms. Based on the mass conservation for the gas flow in the shaft, equations for estimating the total gas mass flow rate are derived. The methods for determining the smoke and heat exhaust efficiencies are also proposed. A numerical model is built for series of CFD simulations considering different shaft forms (length–width ratio of shaft vent and shape). The results clearly present the details of the natural venting process by displaying the temperature and velocity fields. The boundary layer separation and plug-holing phenomena are also observed. The effects of the shaft shapes on the smoke and heat exhaust efficiencies have been discussed quantitatively. It is highlighted that when the cross-sectional area of shaft is constant, a smaller length–width ratio of the shaft vent leads to higher smoke and heat exhaust efficiencies. Moreover, the smoke and heat exhaust efficiencies of cylindrical shafts are higher than those of cubic ones. The findings of this paper could provide some principles for the design of natural ventilation shaft in urban tunnels. For example, the length–width ratio of shaft vent less than 1:3 is recommended for the design of natural venting system in tunnels.

Flow measurement based on the combination of swirler and differential pressure under slug flow

The alternating appearance of elongated bubbles and liquid slugs of slug flow in the pipe causes severe pressure fluctuation. As a result, measuring the flow rate of the slug flow with the throttling unit based differential pressure method is difficult. This paper investigates a new swirler-based flow measurement method in slug flow. The swirler converts the slug flow into a swirling annular flow, and the differential pressure method is used to measure the flow rate. The influences of gas and liquid flow rates on the differential pressure ΔPX across the swirler as well as its downstream axial differential pressure ΔPZ are investigated. ΔPX0.5 increases linearly as the liquid mass flow rate increases, and the slope of the curve increases as the gas mass flow rate increases. The influence of gas mass flow rate on ΔPX0.5 is comparable to that of liquid mass flow rate on ΔPX0.5. ΔPZ0.5 increases linearly with increasing gas/liquid mass flow rate, and the slope of the curve of ΔPZ0.5 with ml differs slightly from the slope of the curve in single-phase water conditions. Based on the research presented above, new empirical correlations of mass flow rate based on ΔPX and ΔPZ are established respectively. The superficial liquid velocity ranges from 0.6 to 2 m per second, while the superficial gas velocity ranges from 2 to 6 m per second. If the gas mass flow rate and ΔPX are known, the relative error of liquid mass flow is less than 3%. The relative error of the gas mass flow rate is less than 10% if the liquid mass flow rate and ΔPX are given. The calculation accuracy of the flow measurement model using ΔPX is better than the calculation accuracy of the flow measurement model using ΔPZ.

A new correlation to determine the Lockhart-Martinelli parameter from vertical differential pressure for horizontal venturi tube over-reading correction

Venturi tubes are widely used to measure the gas flow rate in a wet-gas stream. To calculate the gas flow rate, wet-gas Venturi tubes require the liquid loading (i.e. Lockhart-Martinelli parameter) to be known as an input to a so-called over-reading correction correlation. It is challenging to derive the Lockhart-Martinelli parameter without installing additional devices in series to the Venturi tube thus adding significant cost and complexity. A relatively low cost and easy to implement method is to derive the Lockhart-Martinelli parameter by measuring the pressure drop across the Venturi tube or along a pipe section. A correlation that predicts the Lockhart-Martinelli parameter by measuring the pressure drop along a vertical pipe section downstream of the Venturi tube is presented. The correlation was obtained by fitting experimental results from TUV-SUD National Engineering Laboratory's wet-gas test facility with nitrogen-water in a 4″ vertical pipe, Lockhart-Martinelli from 0.04 to 0.29, and gas Froude number from 1 to 2.7. Further experiments were conducted at Spirax Sarco Engineering plc to evaluate the performance of the proposed correlation under steam-water conditions. Tests were conducted with steam-water in a vertical 2″ pipe, Lockhart-Martinelli from 0.005 to 0.064, and gas Froude number from 0.55 to 1.35. The Lockhart-Martinelli parameter is predicted within ±0.035 absolute value with the proposed new correlation for both the National Engineering Laboratory and Spirax Sarco datasets. Gas flow rate values within approximately ±5% error are obtained with the proposed correlation together with ISO/TR 11583 over-reading correlation for the NEL dataset. Although further improvements to the proposed method are required, this work demonstrates the efficacy of an agile, simple, and low-cost differential pressure method to aid the Venturi meter to determine the gas mass flow rate in wet-gas flow.

Response surface methods based in artificial intelligence for superstructure thermoeconomic optimization of waste heat recovery systems in a large internal combustion engine

In a large internal combustion diesel engine, less than half of the fuel energy is converted into useful energy, while the remaining energy is lost, mainly by the exhaust gases and cooling water. Thus, the implementation of waste heat recovery (WHR) systems has been one of the main research areas for increasing power, and reducing specific fuel consumption and pollutant emissions, which favors the improvement of these engines. Currently, there are two important challenges regarding the use of WHR systems in internal combustion diesel engines: (i) identifying the best technology, or combination of technologies, for the WHR in an internal combustion diesel engine from an economic point of view; and (ii) determining the ideal configuration and the best design parameters for the most suitable system. This paper proposes an optimization procedure for automatic selection of the most economically suitable WHR technology for a large internal combustion diesel engine, as well as the definition of its optimal configuration and ideal design parameters. For this, superstructures composed by the Organic Rankine Cycle (ORC), Kalina Cycle (KC), and Conventional Rankine Cycle (CRC) are modeled and optimized using a genetic algorithm. For the formulation of the thermoeconomic optimization problem—Mixed Integer Nonlinear Programming (MINLP)—the economic model of each component of the superstructures is evaluated and the objective function is proposed based on the specific cost. However, due to the complexity of the superstructure optimization problem, the use of the response surface method to solve this problem can become more attractive than the original modelling optimization. The superstructure optimization problem, as well as its thermodynamic modeling, economic modeling and response surfaces based on radial base function and artificial neural network, were solved using the programs Engineering Equation Solver (EES) and Octave. The results show that for a medium-sized superstructure (384 variables and 17 decision variables), despite the high computational effort, the use of the response surface method in the optimization problem proved to be more efficient than the original modelling optimization, and for a large superstructure (944 variables and 45 decision variables) it is only possible to solve the optimization problem using the response surface method. Furthermore, after the superstructure’s optimizations, the additional net power is produced by ORC through of the recovery waste heat from the exhaust gases mass flow and the cooling water mass flow provided by the diesel engine. The additional net power represents around 7% of the nominal net power.

Experimental Investigation of Gaseous Mixtures of Ethane, Methane, and Carbon Dioxide as an Alternative to Conventional Fuel in Spark Ignition Engines

Abstract This study investigates the viability and performance of certain synthetic fuels in spark ignition internal combustion engine based stationary power generation wherein the fuel comprises a mixture of methane and ethane in high dilutions of carbon dioxide (CO2). The fuel of concern is a byproduct of a novel method for producing ethylene from ethane. The byproduct gas mixture has a concentration of approximately 41% CO2, 40% ethane, and 5% methane by weight along with other minor compounds. Varying mixtures of ethane and methane combined with between 42% and 46% by weight CO2 were used to evaluate the viability and efficiency of this fuel to operate in existing internal combustion engines as a means of reducing emissions and increasing industrial process efficiency. A 13 hp gasoline generator was repurposed as a test stand by incorporating a modified fuel induction system and instrumentation for data collection. A gas metering and mixing system was installed to precisely control the mass flow of gases induced into the engine. Various instrumentations were installed to monitor in-cylinder pressure, temperature at various locations, emissions, and fuel and airflow rates. Varying fuel mixtures and loads were tested and compared to gasoline. It was found that under a high load, the mixed gas was able to generate comparable thermal efficiency and power to gasoline. But under no load or a part load condition the indicated thermal efficiency was found to be about 21% lower than that of gasoline. Further, the mixed gas also resulted in up to 50% reduction in CO and NOx emissions when compared to gasoline.

Influence of Local Gas Sources with Variable Density and Momentum on the Flow of the Medium in the Conduit

In this article, the analysis of mechanical energy changes in a gas medium flow with stable and variable density was presented. To determine the energy losses, the various sources of momentum and mass were used, which had an influence on air flow through the conduit in the system without heat exchange with the environment. The occurrence of varying density gas flow in the conduit (caused by local inflow of mass and momentum) in inclined pipes generates a natural depression–internal mechanical energy. The local momentum sources can facilitate or hinder the gas flow through the conduit. This phenomenon often appears in the network of underground mine workings and in ventilation and air conditioning installations. The characteristic for gas flow through a pipe or mining excavation is the equivalent aerodynamic resistance, the value of which is influenced by the mass and momentum of local sources. This value determines the facilitation or difficulty in gas transport through a section of conduit in relation to the mass stream of the medium. In this article, the dependency of mass flow and gas momentum with different densities on the value of the gas medium flow resistance in the conduit was analyzed. On the basis of the obtained results, the loss of mechanical energy and energy efficiency of flows were determined. In this work, two cases of fan work in suction and blowing modes were analyzed. For these examples, a gas inflow with three different mass streams, a density higher than the main stream density, and with a zero momentum value for this stream was modeled. Ten cases of mass inflow sources were considered. The results of the gas mass flow calculation through the fan m˙w and gas m˙0 and the coefficient of transport efficiency are graphically presented in the paper.

Gas absorption in a hydraulic air compressor. Part II: Experimental verification

Experimental verification of a one-dimensional steady-state bubbly flow model is presented. For initialisation of the liquid-phase concentrations of gas species, a formulation for modelling the time-evolution of the concentration of dissolved gas species in the circulating liquid of a hydraulic air compressor (HAC) was developed and integrated with the steady-state bubbly flow model. Observations from experiments conducted on a pilot scale HAC are presented employing CO2 as a tracer gas. The composition of the input gas inducted by the pilot HAC was deliberately varied by mixing different controlled amounts of CO2 gas while continuously monitoring the gas and liquid phase concentrations of CO2 at key points in the HAC process. Predictions of the concentration of CO2 in the compressed gas produced by the pilot HAC and the circulating liquid at system equilibrium were in good agreement with measured values. Concentrations of CO2 measured in the gas above the tailrace water level were elevated above background levels and responded in accordance with the input CO2 gas mass flow and liquid CO2 concentrations indicating exsolution of gas from the liquid as predicted. Observations of the pH of the circulating liquid identified the bicarbonate equilibrium as the likely mechanism for CO2(aq) production not captured by the model which caused the model to under predict CO2(aq) concentrations for experiment set points with CO2(aq) concentrations above 140 ppm.

Simulation and validation of the gas flow in close-coupled gas atomisation process: Influence of the inlet gas pressure and the throat width of the supersonic gas nozzle

The effectiveness of a close-coupled gas atomisation process largely depends on the operational and the geometric variables. In this study, Computational Fluid Dynamics (CFD) techniques are used to model and simulate the gas flow in the melt nozzle area for a convergent-divergent, close-coupled gas atomiser in the absence of the melt stream. Firstly, a reference case, in which the atomisation gas is nitrogen at 50 bar and a supersonic gas nozzle with a throat width of L0 has been modelled, is presented. Then, the influence of both the inlet gas pressure and this design parameter are investigated, comparing the numerical results provided by simulations varying the inlet pressure from 5 to 80 bar and modelling different convergent-divergent gas nozzles with throat widths of 0.29∙Lo, 0.5∙Lo, 0.77∙Lo and 2∙Lo respectively. The simulation results show how similarly these two parameters modify gas mass flow rates, gas velocity fields, aspiration pressures in the melt delivery tube or the size of the recirculation zones below the melt nozzle. Therefore, it can be stated that this geometric variable of the gas nozzle may be as relevant as the inlet pressure in the atomisation process. The most important novelty of this study is related to experimental validation of the numerical results using the Particle Image Velocimetry (PIV) technique and through direct measurements of gas mass flow rates, with a clear correlation between simulated and measured data. Moreover, some results obtained with experimental atomisations using copper and nitrogen are also presented. The experimental results show that finer powders are produced by increasing the atomising pressure or the throat width of the supersonic gas nozzle, which can be directly related to the gas flow dynamics calculated numerically.

Assessment of an Exhaust Thermoelectric Generator Incorporating Thermal Control Applied to a Heavy Duty Vehicle

The road transport industry faces the need to develop its fleet for lower energy consumption, pollutants and CO2 emissions. Waste heat recovery systems with Thermoelectric Generators (TEGs) can directly convert the exhaust heat into electric energy, aiding the electrical needs of the vehicle, thus reducing its dependency on fuel energy. The present work assesses the optimisation and evaluation of a temperature-controlled thermoelectric generator (TCTG) concept to be used in a commercial heavy-duty vehicle (HDV). The system consists of a heat exchanger with wavy fins (WFs) embedded in an aluminium matrix along with vapour chambers (VCs), machined directly into the matrix, that grant the thermal control based on the spreading of local excess heat by phase change, as proposed by the authors in previous publications and patents. The TCTG concept behaviour was analysed under realistic driving conditions. An HDV with a 16 L Diesel engine was simulated in AVL Cruise to obtain the exhaust gas temperature and mass flow rate for each point of two cycle runs. A model proposed in previous publications was adapted to the new fin geometry and vapour chamber configuration and used the AVL Cruise data as input. It was possible to predict the thermal and thermoelectric performance of the TCTG along the corresponding driving cycles. The developed system proved to have a good capacity for applications with highly variable thermal loads since it was able to uncouple the maximisation of heat absorption from the regulation of the thermal level at the hot face of the TEG modules, avoiding both thermal dilution and overheating. This was achieved by the controlled phase change temperature of the heat spreader, that would ensure the spreading of the excess heat from overheated to underheated areas of the generator instead of wasting excess heat. A maximum average electrical production of 2.4 kW was predicted, which resulted in fuel savings of about 2% and CO2 emissions reduction of around 37 g/km.

A novel negative carbon-emission, cooling, and power generation system based on combined LNG regasification and waste heat recovery: Energy, exergy, economic, environmental (4E) evaluations

In this paper, a novel negative carbon-emission, cooling, and power generation (NCCP) system was proposed to improve the energy efficiency of the liquid natural gas (LNG)-powered hydrogen production plant. With LNG cold energy and waste heat recovery, the NCCP system integrated organic Rankine cycle (ORC) power generation, data center cooling, and CO2 capture. The NCCP system could operate under seven scenarios and the system performance evaluations were performed via energy, exergy, economic and environmental (4 E) analysis. It was found that the NCCP system showed the best performance when all subsystems were running simultaneously. The system could produce 31.67 MW of power, 24.92 MW of cooling capacity, and 29.97 t/h of CO2 capture. The levelized energy cost and the payback period of the NCCP system were 0.071 $/kWh and 7.9 years, respectively. LNG cold energy utilization efficiency, system energy efficiency, and exergy efficiency were 43.20%, 19.08%, and 29.28%, respectively. The environmental profits are validated with the negative carbon index of 29.47 t/h. Moreover, the effects of the LNG pressure, flue gas mass flow rate, and the temperature of the medium temperature shift gas on the NCCP system performances were investigated. The results show that the proposed system is a polygeneration system with the advantages of high efficiency, diversified energy output, fast return on investment, and CO2 capture. It is expected to be an energy conversion technology that could be used for reference in practical applications.

Investigations on Spray Characteristics and Self-Pulsation of a Gas-Centered Shear Coaxial Injector

The spray characteristics of a gas-centered shear coaxial injector under different conditions and recess ratios (RR) were studied through experiments and numerical simulations. The numerical study was carried out based on the coupled level set and volume-of-fluid (CLSVOF) method and the adaptive mesh refinement (AMR) method. The results indicated that without recess, the spray angle first stayed almost constant and then dropped linearly with an increase in the gas mass flow rate (m˙g) when holding the liquid mass flow rate (m˙l) constant. In contrast, with recess, the spray angle was found to increase with m˙g, which could be attributed to the secondary expansion of the central gas flow. Under specific conditions, self-pulsation occurred and was accompanied by a loud scream. The frequency of the self-pulsation increased with both m˙g and m˙l. Moreover, the self-pulsation frequency decreased with RR. Meanwhile, the mechanism of self-pulsation was initially explored through numerical simulation. It was concluded that self-pulsation was caused by the surface tension and the pressure difference between the inside and outside of the liquid sheet, together with the central airflow impact extrusion.