Gas-liquid Heat Research Articles

Research on mercury re-release model in wet flue gas desulfurization (WFGD) in coal-fired power plants

Mercury (Hg), a toxic heavy metal, has triggered regulations for emission control from coal-fired power plants. It has been found that mercury re-release occurs in WFGD slurry, which is affected by WFGD process parameters. The coal co-combustion with bromide technology proves to be an efficient approach for enhancing mercury removal ratio but the accumulation of introduced bromine in WFGD slurry would impact the re-emission behavior of mercury significantly. Model study is efficient method to reveal the physicochemical processes in WFGD systems. However, previous model studies were carried out under Hg2+ contained simulated slurry systems without consideration of Hg2+ transformation process from gas to liquid phase, and co-combustion with bromide technology was not considered. Here, a model which encompasses droplets motion sub-model, gas–liquid heat transfer sub-model, gas–liquid mass transfer sub-model and the mercury re-release kinetic sub-model is developed and validated against experimental data. The effects of bromine concentration, slurry temperature, pH value and S(IV) concentration were investigated. It was found that introduced bromine has significant inhibitory effects on the re-release of mercury. When the slurry temperature is higher, the absorption rate of Hg2+ is lower and more Hg0 is released. Moreover, the increase in the slurry pH value and S(IV) concentration has certain inhibitory effects on the re-release of Hg0 in WFGD. Above all, the developed model has high prediction accuracy for the absorption of Hg2+ and the re-release of Hg0 in WFGD which is expected to be beneficial for guiding the operation of WFGD systems.

Numerical study on the interface characteristics of gas–liquid falling film flow considering the interface forces

As an energy quality improvement device, an air source heat pump plays an important role in clean heating applications. When operating in a cold and wet environment in winter, the outdoor evaporator will have the problem of frost, which affects the operation efficiency. To solve the frosting problem, the development of frost-free evaporators has attracted more and more attention. The fluctuation characteristics of the gas–liquid interface are the key factors affecting the intensity of gas–liquid heat transfer on the air side of this kind of heat exchanger. Therefore, a mathematical model is established to describe the falling film flow on the surface of the flat finned tube heat exchanger in a closed-type heat source tower. The model takes into account the interfacial tension and interphase friction force between the air flow and the liquid film. On this basis, the fluctuation intensity of the central channel interface during falling film flow with different inlet parameters is studied. It is found that there is a critical value of 1.5 m/s (i.e., Reg = 1643.0) in the air flow rate under the study conditions. When the air flow rate is higher than this velocity, the interface near the gas–liquid outlet fluctuates more frequently and the stability is poor. The distributions of interfacial velocity and pressure are also studied, and the relationship between them and interface fluctuation is analyzed. This paper aims to provide theoretical support for enhanced heat and mass transfer on the air side of finned tube heat exchangers in the closed-type heat source tower.

Pore-scale Simulation of Two-phase Flow in Foamed Porous Materials

This paper establishes a pore cell model of foamed silicon carbide material based on a tetradecahedron structure, and uses FLUENT software to numerically study the flow rate and pressure drop changes in the porous structure at different flow rates and the gas-liquid two-phase flow state of the channel. The research results show that the porous skeleton structure has a great influence on the velocity and pressure distribution in the calculation domain; the inlet flow velocity has a certain impact on the gas-liquid mixing zone and gas-liquid interface area in two-phase flow. The application of tetradecahedral porous media increases the thickness of the gas-liquid mixing zone and the phase interface area are increased, with a maximum increase of 11.5%, thus promoting gas-liquid heat and mass transfer.

CFD analysis and conjugate heat transfer modeling of ionic compressors

Ionic compressors are promising applied in hydrogen refueling stations. Ionic liquid covers a solid piston for sealing and cooling. It is necessary to investigate flow and heat transfer processes inside the cylinder. This study performs a two-phase CFD simulation incorporating valve motion by dynamic mesh method. Results show that the flow through the valves enhances heat transfer over the liquid surface. It is hard to transform the compression stage into an isothermal process, which is attributed to the low velocity of hydrogen flow. The liquid surface produces relatively severe deformation when the piston moves downward, since the flow through the suction valve impinges on the liquid surface. Furthermore, a novel conjugate heat transfer (CHT) model is proposed for calculating heat transfer between hydrogen and ionic liquid, which has a good agreement with the CFD results. Ionic liquid can decrease the hydrogen temperature at the initial stage of a multi-cycle process. The cooling effect of the ionic liquid abates as its temperature increases. This study can provide a technical reference for fast calculation of gas-liquid heat transfer of ionic compressors.

Thermodynamic properties of oil droplets in oil-injected screw compressors and their influencing factors

As a typical positive displacement compressor, screw compressors are widely used in various industrial fields with a fast-growing trend, especially with the boost of the application of oil injection technology. The oil injection process inside the screw compressor is complicated and difficult to be captured by direct observation experiment, so is the accompanying heat transfer process. On the basis of single particle dynamics, the Lagrangian method is used to establish a spatial kinematic model of oil droplets in the simplified chamber of an oil-injected screw compressor, the droplet trajectory is analyzed. The relationship between the oil droplet diameter, injection velocity and temperature and the free flight time of oil droplets in the compression chamber is obtained. In order to investigate the liquid-gas two-phase flow after oil injection, the Level Set Method is adopted to simulate the oil distribution in the compression chamber. The impacting process of oil droplet on a hot wall is simulated, the influence of oil injection parameters such as the injection speed, temperature difference, droplet diameter, and the initial velocity on the heat transfer between oil droplets and hot gas and the wall is analyzed theoretically. For the simulated cases studied, the oil droplet diameter has the greatest effect on the gas-liquid heat transfer, while the temperature difference plays a greater role in the heat transfer between the oil droplet and the hot wall than other factors. The research in this paper helps to further understand and accurately predict the heat transfer process in oil-injected screw compressors, which is important for improving the energy efficiency of screw compressor.

Liquid-gas heat transfer characteristics of near isothermal compressed air energy storage based on Spray Injection

Isothermal compressed air energy storage (I-CAES) could achieve high roundtrip efficiency (RTE) with low carbon emissions. Heat transfer enhancement is the key to achieve I-CAES, thus the liquid-gas heat transfer characteristics of near I-CAES system based on spray injection was analyzed in this paper. The liquid-gas heat transfer model and thermodynamic model were established and the effects of design variables on heat transfer rate and energy efficiency were analyzed. The results showed that spray injection can produce considerable heat transfer capacity and effectively suppress air temperature change, but spray injection at initial compression stage will not bring much heat transfer enhancement. Increasing spray flow rate shifts the dominant heat transfer contribution from water bulk to spray heat transfer and increases total heat transfer rate and RTE, however the increase effect of spray injection is more obvious in small-scale CAES. Low water flow rate and large working cylinder volume are recommended to achieve slow compression and expansion processes with enough liquid-gas heat transfer duration, realizing near I-CAES with high RTE. High air storage pressure increases heat transfer rate, but deviates CAES from isothermal system, resulting in low RTE. This research will provide scientific basis for heat transfer enhancement, system design and performance optimization of I-CAES.

Turbulent thermal-hydraulic characteristics in a spiral corrugated waste heat recovery heat exchanger with perforated multiple twisted tapes

Waste heat recovery technology can undoubtedly improve energy saving and reduce carbon emissions, as one of the key equipment, heat exchangers always determine the waste heat recovery efficiency. In this study, to improve the heat transfer potentiality of conventional plain tube heat exchangers, a synergistic thermal enhancement technology of a spiral corrugated tube (SCT) with multiple twisted tapes (TTs) was devised by taking liquid-gas heat exchanging as a typical waste heat recovery scenario. The impacts of the TTs numbers, transverse space ratios (S/D), and longitudinal perforation length ratios (L/D) on tubular turbulent heat transfer-fluid flow characteristics were numerically investigated, consisting of flow fields, temperature contours, local Nusselt number (Nu) distributions, vortex structures, and turbulent kinetic energy contours, as well as average Nu, friction factor (f), and overall thermal performance evaluation index (η). The findings proved that the fitting of multiple TTs into the SCT greatly homogenized the flow fields and temperature distributions, and increased the Nu and f, in which both of them also raised with the increase of the number of TTs. The η dropped and subsequently augmented as the quantity of TTs increased. Furthermore, perforations on the surface of the quadruple TTs could attenuate the f with a relative less reduction in the Nu, which caused higher η values than the ones without perforations. Notably, as demonstrated by the vortex structures, this could be ascribed to the fact that the perforations reduced excessive longitudinal vortex interactions in the mainstream regime without reducing the impingement to the thermal boundary layer too much. Both the Nu and f generally declined with rising S/D and L/D. Overall, by means of simple mounting perforations on the surface of the quadruple TTs, the maximum η could be further enhanced up to around 7.9% and a maximum η of 1.23 was obtained by the SCT with S/D = 0.152 and L/D = 0.348.

Energy, exergy, exergoeconomic, economic, and environmental analyses and multiobjective optimization of a SCMR–ORC system with zeotropic mixtures

This paper proposes a SCMR–ORC system with zeotropic mixtures. Zeotropic mixtures are separated into two pure fluids in a partial condenser, the pure fluids recover condensation heat in a gas–liquid heat exchanger, and are then compressed, mixed, and recycled. Energy, exergy, exergoeconomic, economic, and environmental (5E) models based on the residual Helmholtz free energy are established to analyze the SCMR–ORC system performance, which is then compared with that of a SCR–ORC system with pure fluids. Multiobjective optimization is performed to obtain 3D Pareto frontiers, and TOPSIS is used to reveal the best performance. The results indicate that when the mass fraction of the low-boiling-point fluid (θ) is low, the SCMR–ORC system can reduce the condensation heat released and increase the condensation heat recovery, and its 5E performances are better than those of the SCR–ORC system. The exergy destruction sum of the partial condenser and gas–liquid heat exchanger can be reduced by 101.03 kW, and their capital cost rate can be saved by 34.89 $/h. The optimal bubble point evaporation temperature of three zeotropic mixtures is approximately 80 °C, their optimal outlet temperature at expander 1 is in the range of 42–45 °C, and their optimal θ is small.

Investigation of heat and mass transfer and gas–liquid thermodynamic process paths in a humidifier

A humidifier is crucial for water evaporation in a humidification–dehumidification desalination system. Its performance has a significant impact on system efficiency. However, existing models are not fully applicable to the estimation of heat and mass transfer in a humidifier. In this paper, a novel gas–liquid heat and mass transfer model for a humidifier is proposed. It can accurately predict the heat and mass transfer performance in the humidifier. It is observed that increasing liquid inlet temperature improves the humidifier performance most significantly. In the humidifier, the temperature and humidity ratio of air increase in waves along the height. The distributions of the heat and mass transfer rates are primarily dominated by the transfer driving forces. Heat and mass transfer primarily occur at the top and bottom of the humidifier because of the considerable difference in the temperature and humidity ratio at the two terminals. The air rapidly reaches supersaturation during the heated and humidified processes, whereas the supersaturation is low, with the highest being 2.1%. The thermodynamic process path of air in the supersaturation stage can be simplified as lying on the saturation curve. The resulting error is less than 4%.

Vaporization enthalpies of benzanthrone, 1-nitropyrene, and 4-methoxy-1-naphthonitrile: Prediction and experiment

Determination of the vaporization enthalpies of low-volatile organic compounds in the wide temperature range is a non-trivial experimental task. A number of predictive approaches were proposed to resolve this problem. Independent validation is necessary for the further development. In this work the saturated vapor pressures of 3 substituted polyaromatic compounds, 1-nitropyrene, benzanthrone, and 4-methoxy-1-naphthonitrile, were measured between 375 and 480 K using fast scanning calorimetry. From the measured vapor pressure – temperature dependences the vaporization enthalpies were derived. The experimental vaporization enthalpies were compared to the literature data and empirical approaches. The vaporization enthalpies of the studied compounds were calculated at 298.15 K from the molecular structure and then adjusted to the measurement temperatures, following two different schemes. The first is based on the approach employing a correlation between the difference of ideal gas phase and liquid heat capacities, on the one hand, and the vaporization enthalpy at 298.15 K, on the other hand, recently proposed by our group. The second is widely known Chickos et al. scheme. Consistence of the experimental, literature, and predicted data was critically analyzed.

Study on Downhole Throttling Characteristics of High Water Content Gas

In order not to hinder gas production, we usually hope that the bottom hole effusion can be discharged to the surface with high-pressure natural gas. For the production data of high water content gas wells, the problems of insufficient water content and liquid-carrying capacity affecting gas well production should be considered. Based on the wellbore gas-liquid two-phase pipe flow theory and heat transfer theory, the temperature and pressure coupling prediction model of a high water-bearing gas well is established. Combined with the downhole throttling mechanism and gas-liquid two-phase homogeneous flow theory, the temperature and pressure field distribution model is established. The results show that compared with the Ramey model and Hassan and Kabir model, the temperature and pressure coupling prediction model of high water-bearing gas wells established in this study has the smallest coefficient of variation in the four groups of data tests. Based on this, the effects of different working conditions and choke diameter on downhole throttling characteristics of high water-bearing gas wells are analyzed. The findings of this study are helpful to better predict the wellbore temperature and pressure coupling of high water-bearing gas wells and provide more effective help for the smooth production of gas wells.

Experimental Study on Horizontal Fire Spread Characteristics of Transformer Oil

Abstract In order to study the horizontal fire spread characteristics of transformer oil, a series of experiments were carried out on the experimental platform developed, the influence of the initial temperature and the width of the oil pool on the flame propagation, including the propagation speed, flame morphology and the temperature field distribution of the gas-liquid two-phase, was analyzed to reveal the flame propagation characteristics and the oil surface temperature rise law in the process of transformer oil fire propagation, and a theoretical model of coupled liquid-phase convective heat transfer and flame radiation heat transfer was established by combining thermodynamic theory to quantitatively calculate the heat transfer process of surface flow in flame propagation process. Through the theoretical analysis and quantitative calculation of gas-liquid heat transfer, it is proved that the surface flow is mainly driven by surface tension and the flame spreads in the form of pulsation. Combined with the experimental data for verification, it is found that the proportion of liquid-phase convective heat transfer to the total heat flow is much larger than that of flame radiation to the total heat flow, which proves that liquid-phase convective heat transfer is the main mode of surface flow heat transfer.

Multi-objective optimization of an innovative power-cooling integrated system based on gas turbine cycle with compressor inlet air precooling, Kalina cycle and ejector refrigeration cycle

In this paper, an innovative power-cooling integrated system based on gas turbine, Kalina cycle system, ejector refrigeration cycle (GT-KCS-ERC) is proposed. The ERC driven by GT flue gas and KCS low concentration liquid waste heat is utilized to precool GT inlet air for producing extra power from GT and provide some cooling capacity for users, simultaneously. The comprehensive thermodynamic and thermo-economic analyses are conducted to demonstrate the feasibility of novel GT-KCS-ERC hybrid system by comparing with standalone GT-KCS system. Furthermore, the effects of seven key operation parameters on the system performances are investigated. The multi-objective optimization of GT-KCS-ERC hybrid system and standalone GT-KCS system is carried out through Non-dominated Sorting Genetic Algorithm-II, in which the objectives are maximum total energy efficiency and minimum levelized cost of energy (LCOE). The results show that the total energy efficiency of GT-KCS-ERC increases with increasing pinch point temperature difference of boiler ΔTKCS,boi and decreasing ammonia concentration of working solution in KCS, while that of standalone GT-KCS shows opposite trends. The LCOE of GT-KCS-ERC is lower than that of standalone GT-KCS as ΔTKCS,boi is larger than 21℃ or turbine inlet pressure of KCS is higher than 6.6 MPa. The optimal saturated evaporator temperature and pressure ratio of vapor generator to condenser in ERC with optimal refrigerant of R290 are 0℃ and 4, respectively. Under the optimal condition, the GT-KCS-ERC with an ERC secondary flow split ratio of 0.162 for precooling GT inlet air presents 219.4 kW more net power and 764.2 kW more cooling capacity than standalone GT-KCS system. The LCOE decreases by 0.802% and total energy efficiency increases by 5.347% in novel GT-KCS-ERC system comparing with standalone GT-KCS system.

Optimal Device for Waste Heat Recovery Process Based on Convective Drying Technology

With the development of chemical industry, medicine, food and other industrial production in China, the amount of drying to wet materials is increasing, and the energy consumption of drying is also increasing year by year. Among them, the hot and humid waste gas produced by convective drying technology contains a large amount of waste heat, and the recovery and utilization of waste heat through the two-stage combination of gas-gas heat exchange and gas-liquid heat exchange is a method to reduce energy consumption, which has good economic value and energy conservation and emission reduction value.

Using CFD to improve the performance of a heat exchanger from a gasifier

In this paper, a Computational Fluid Dynamics (CFD) analysis is performed on a gas-liquid heat exchanger fitted on a gasification equipment. The flow and temperature patterns are preliminary investigated using SolidWorks Flow Simulation software, in order to gain insight into the involved physical processes, and to find the exchanger weak points before being manufactured and tested. The analysed equipment tranfers heat from the flue gasses generated by a gasification system, towards a liquid heat transfer medium. This is subsequently sent to a second liquidliquid heat exchanger used to heat water from a boiler. As a result of the analysis, solutions aiming at performance improvement of the equipment are discussed and proposed.

Modeling of engine warm-up with the use of an exhaust gas recuperator at low ambient temperatures

The paper describes the modeling of the cooling system of an internal combustion engine with an installed exhaust gas recuperator. During operation at low temperatures, the heat of the burnt fuel is not sufficient for the simultaneous warm-up of the engine and the cab. In the course of the study, changes in the temperature of exhaust gases after engine ignition were analyzed. The paper presents the calculations of the heat capacity of exhaust gases at the warm-up stage. As we established, up to 1.5 kW of heat energy at the engine’s idle running can be derived from exhaust gases. Based on the data on engine warm-up and exhaust gas heat capacity after ignition, we developed a mathematical warm-up model. Its output parameter is the time required by the engine to reach the set temperature. With the studies applying this model, it became possible to establish the effectiveness of using a liquid-gas heat exchanger and model the operation of the entire cooling system. We obtained engine warm-up vs. time diagrams with the cab heater enabled in different modes. A controlled liquid-gas heat exchanger embedded into the ICE cooling system was used as the exhaust gas recuperator in the calculations.

Experimental study of temperature profile and gas-liquid heat transfer in flame spread over jet fuel under longitudinal air flow

The rectangular pools with the same length of 100 cm but different widths of 4 and 20 cm are used to conduct experiments of flame spread over jet fuel of RP-3. The direction of longitudinal air flow is same and opposite to direction of flame spread respectively. Six air flow velocities 0.45, 0.88, 1.3, 1.73, 2.15 and 2.57 m/s are employed. The spatial temperature distributions and convective heat dissipation at pool bottom are examined using thermocouples. The heat loss is negligible for 10 mm-thick fuel layer, but it is evident for 3 mm-thick fuel layer. The integral method is proposed to calculate the flame radiation imposed to subsurface flow region. The gas-liquid heat transfer model including liquid-phase convection, flame radiation and convective heat dissipation is established for calculating energy balance involving flame spread over RP-3. The calculated heat fluxes follow well with experimental measurements, regardless of direction and magnitude of air flow. The current findings possess potential application and practical guidelines for fire prevention of liquid fires under longitudinal air flows. In order to restrict flame spread, it is a feasible method to cut off liquid convection or shield flame radiation.

A phase change calcium looping thermochemical energy storage system based on CaCO3/CaO-CaCl2

Calcium looping thermal energy storage (CaL-TES) is promising because of its high operating temperature, excellent energy storage density, and low material cost. However, a significant problem with the CaL-TES system is the rapid degradation of CaO. To overcome this degradation problem and also improve the energy storage performance, a novel phase change calcium looping thermal energy storage (PCCaL-TES) process has been developed based on the solid solution system of CaCO3/CaO-CaCl2. In the charging process of the PCCaL-TES system, surplus energy is stored via sensible heat, latent heat, and chemical energy with the calcination and melting of the solid solution CaCO3/CaO-CaCl2. In the discharging process, the carbonation and solidification of CaCO3/CaO-CaCl2 takes place and thus the stored energy is retrieved. Compared to the conventional CaL-TES system, the innovative PCCaL-TES system can help maintain a high activity of CaO over long-term operation due to the enhanced heat and mass transfer in the liquid-state carbonation. In this study, the energy storage performance of PCCaL-TES was assessed using the simulation package Aspen Plus v10. According to the modeling results, the PCCaL-TES system can achieve a round-trip efficiency of up to 49% and an energy storage density of nearly 1.5 GJ/m3, presenting improvements of about 4% and 20%, respectively, compared with the conventional CaL-TES system. Meanwhile, a parametric analysis was carried out to examine the effect of key operating parameters on the system performance of PCCaL-TES. The calculations show that the round-trip efficiency of the PCCaL-TES system can be improved by raising the mole fraction of CaCl2, increasing the carbonator temperature, or employing an optimum carbonator pressure. It was also found that a low mole fraction of CaCl2, a high activity of CaO, or a low temperature of CO2 storage was beneficial to achieving a high energy storage density. Finally, the impact of other operating factors on the round-trip efficiency of PCCaL-TES was summarized in a sensitivity analysis. It revealed the round-trip efficiency of the PCCaL-TES system was dominantly determined by the performance of the CO2 turbine (W-TURB) and compressor (W-COMP), the gas–liquid heat exchanger (HX3) and the exhaust CO2 cooler (CL3).

A novel drying tower technology for zero liquid discharge of desulfurization technology

ABSTRACT The wet limestone/gypsum flue gas desulfurization (WFGD) technology has been attracting much interest, while handling with wastewater produced in WFGD is indispensable but difficult. Zero liquid Discharge (ZLD) technology is to recycle water content and reuse salt content of wastewater, which has becoming developing trend because of the strict wastewater emission regulation in China. However, existing ZLD technology cannot realize low investment and low power consumption. Therefore, in this paper, a novel drying tower applied in ZLD system was proposed. Wurster fluidized bed was introduced into drying of desulfurization wastewater and high gas-liquid heat transfer can be achieved with inert particles as immediate heat carrier. Industrial experiment and numerical simulation were applied to verify the feasibility of this novel drying tower, research flow structure in tower and offer optimization for future operation. The results indicate that this novel drying tower applied for a 300 MW power plant performs well in ten-day pilot run. Through numerical simulation applying computational particle fluid dynamics (CPFD), gas-solid-liquid flow structure of inner circulation is detected. With the increase of particle size, the evaporation efficiency increases firstly and then decreases while power consumption increases. The working condition with particle size of 1.6 mm performs best. With more bed material in dryer, higher efficiency and pressure drop can be obtained. Overall considering working effect, bed material of 380 kg is recommended for future operation. In simulation range, high efficiency and low power consumption can be obtained with higher wind supply ratio of central part. With the work of experiment and simulation, the novel drying tower is proved to be applicable and recommended operating parameters for future operation are offered through simulation results.

Computational Study of the Effect of Homogeneous and Heterogeneous Bubbly Flows on Bulk Gas-Liquid Heat Transfer.

A numerical investigation is performed on buoyancy-driven homogeneous and heterogeneous bubbly flows to compare the bulk gas-liquid heat transfer effectiveness for Prandtl (Pr) numbers 0.2-20 and void fractions 0.3-0.5. For this purpose, transient two-fluid model simulations of bubbles rising in a stagnant pool of liquid are conducted in a rectangular box by applying periodic boundary conditions to all the sides. The temperature difference ( ) between gas and liquid phase is averaged over the rectangular box and monitored with respect to time, the heat transfer rate is studied based on the time at which the tends to zero. The results of numerical study show that at low Pr numbers, faster decay of is observed for homogeneous flow of bubbles indicating higher heat transfer rate in comparison with the heterogeneous flow of bubbles for the same void fraction. On the contrary, for high Pr numbers, higher heat transfer rate is observed in heterogeneous flow compared to the homogeneous. The comparison of heat transfer behavior between different void fractions for heterogeneous flow show that, for low Pr numbers higher heat transfer rate is achieved for void fraction 0.4 in comparison with void fraction 0.5. And for high Pr numbers, higher heat transfer is observed for void fraction 0.5 in comparison with void fraction 0.4.