Gas In Tube Research Articles

Model-Based Estimation of the Flue Gas Mass Flow in Biomass Boilers

Three estimators for the estimation of the flue gas mass flow in biomass boilers are presented and compared, namely a sliding-mode observer, a Kalman filter, and a so-called steady-state estimator. The flue gas mass flow is an important process variable in biomass boilers as it contains information about the supplied mass flows of air and decomposed fuel. It is also related to the generated heat flow. Furthermore, its knowledge may be exploited in model-based control strategies which allow one to keep pollutant emissions low, on the one hand, and to achieve high efficiency, on the other hand. However, due to fouling of the equipment over time, measurements and existing estimation methods are not suitable for long-term applications. The estimators proposed in this article are based on a dynamic model for gas tube heat exchangers. They are capable of handling the fouling of the heat exchanger and, additionally, they offer the possibility of monitoring the degree of fouling. By incorporating an additional differential pressure measurement and extending the aforementioned estimators, an improvement regarding the dynamic response and the estimation accuracy is achieved. The application of the estimators to real measurement data from both, a medium-scale and a small-scale biomass boiler, demonstrates their wide applicability.

Sensitivity Analysis on Thermal Performance of Gas Heater with Finned and Finless Tubes using Characteristics-based Method

Natural gas must be preheated to prevent phase change and gas hydrate in pressure reduction stations. This paper aims to investigate the effect of the fins of gas tubes and their configuration, arrangement, and shape on the heat transfer and thermal efficiency of gas. To conduct a parametric study, two tube cases with fins and without fins, and in the finned case for the fin’s configuration, two longitudinal and circular arrangements, and the formation of the fins, two solid and interrupted forms were analyzed. Also, three types of cross-sections, including rectangular, convergent parabolic, and divergent parabolic, for the shape of the fins have been studied. For this simulation, the three-dimensional, incompressible, and steady flow was considered, and for analysis and discretization of convective heat equations, the characteristic-based method was applied. FORTRAN software was also used to implement and solve the equations. The results show that in solid and interrupted fins and increasing the number of fins in parallel, the dimensionless heat transfer coefficient increases. Also, the dimensional heat transfer coefficient decreases with increasing the ratio of fin height to the tube’s diameter. Also, the most significant heat transfer improvement was related to the divergent parabolic cross-section.

Transient forced convective heat transfer of helium gas in a narrow tube heated by exponential time-varying heat source

ABSTRACT The analysis and evaluation of transient heat transfer are essential to predict stability and safety of helium gas cooling fusion blanket due to plasma disruption. In this study, transient turbulent heat transfer characteristics of helium gas flowing in a narrow tube were experimentally investigated by using a forced convection gas loop. A narrow tube with an inner diameter of 1.8 mm was employed as test heater and heated exponentially increasing with time under various e-folding time of heat generation rate (0.04–15 s), flow velocities (101–248 m/s), inlet gas temperatures (293–313 K), and pressures (298–502 kPa). The experimental results showed that the heat transfer process can be separated into transient-state heat transfer and quasi-steady-state one at the e-folding time of near 1.5 s. The dependence of quasi-steady-state heat transfer on gas pressure and flow velocity was significant, but the transient-state one was less dependent on gas pressure and flow velocity. The influence of inlet gas temperature on the heat transfer coefficient was not obvious under both transient and quasi-steady conditions. A semi-empirical correlation of the relationship between transient-state and steady-state heat transfer was developed based on substantial experimental data by employing a nondimensional parameter of Fourier number.

Nasopharyngeal tubes in pediatric anesthesia: Is the flow-dependent pressure drop across the tube suitable for calculating oropharyngeal pressure?

BackgroundNasopharyngeal tubes are useful in pediatric anesthesia for insufflating oxygen and anesthetics. During nasopharyngeal tube‐anesthesia, gas insufflation provides some positive oropharyngeal pressure that differs from the proximal airway pressure owing to the flow‐dependent pressure drop across the nasopharyngeal tube (ΔPNPT).AimsThis study aimed to investigate whether ΔPNPT could be used for calculating oropharyngeal pressure during nasopharyngeal tube‐assisted anesthesia.MethodsIn a physical model of nasopharyngeal tube‐anesthesia, using Rohrer's equation, we calculated ΔPNPT for three nasopharyngeal tubes (3.5, 4.0, and 5.0 mm inner diameter) under oxygen and several sevoflurane in oxygen combinations in two ventilatory scenarios (continuous positive airway pressure and intermittent positive pressure ventilation). We then calculated oropharyngeal pressure as proximal airway pressure minus ΔPNPT. Calculated and measured oropharyngeal pressure couples of values were compared with the root mean square deviation to assess accuracy. We also investigated whether oropharyngeal pressure accuracy depends on the nasopharyngeal tube diameter, flow rate, gas composition, and leak size. Using ΔPNPT charts, we tested whether ΔPNPT calculation was feasible in clinical practice.ResultsWhen we tested small‐diameter nasopharyngeal tubes at high‐flow or high‐peak inspiratory pressure, proximal airway pressure measurements markedly overestimated oropharyngeal pressure. Comparing measured and calculated maximum and minimum oropharyngeal pressure couples yielded root mean square deviations less than 0.5 cmH2O regardless of ventilatory modality, nasopharyngeal tube diameter, flow rate, gas composition, and leak size.ConclusionDuring nasopharyngeal tube‐assisted anesthesia, proximal airway pressure readings on the anesthetic monitoring machine overestimate oropharyngeal pressure especially for smaller‐diameter nasopharyngeal tubes and higher flow, and to a lesser extent for large leaks. Given the importance of calculating oropharyngeal pressure in guiding nasopharyngeal tube ventilation in clinical practice, we propose an accurate calculation using Rohrer's equation method, or approximating oropharyngeal pressure from flow and pressure readings on the anesthetic machine using the ΔPNPT charts.

Modeling and analysis of heat transfer in submerged combustion vaporizer under supercritical pressure

Submerged combustion vaporizer (SCV) is widely used as a device to vaporize liquefied natural gas (LNG) stored in cryogenic state, which is effective in peak shaving and emergency response in LNG vaporization stations and receiving terminals. In this paper, a heat transfer calculation model of SCV based on numerical calculation is established and its accuracy is verified by a practical case. Based on this model, the applicability of different heat transfer models inside tube to SCV heat transfer is studied, among which the deviation of Petukhov model is the smallest, which is 0.38%. The increase of gas holdup and fouling thermal resistance inhibits the heat transfer to some extent, so it is necessary to increase the water bath temperature to make up for the lack of heat transfer coefficient under high relative load. In terms of agitating the water bath more fully and reducing the gas holdup inside overflow weir, the effect of 0.090 flue gas tube opening ratio is better than 0.022. The application of this calculation model can provide theoretical reference for heat transfer analysis and optimal design of SCV.

Investigation of the heat transfer coefficient during the condensation of small quantities of water vapour from a mixture with a high proportion of non-condensable gas in a horizontal smooth tube

During heat recovery of exhaust gas energy in a shell and tube heat exchanger, the exhaust gas is cooled down and the water vapour content may condense when the corresponding temperature is reached. In this case, a condensation heat exchanger allows recovering the latent heat in addition to the sensible heat and is therefore beneficial for a preferably high heat recovery. The database and algorithms for the design of this kind of apparatus are still nowadays quite week because only little experimental work is realized with condensation of water vapour from a mixture with a very high proportion of non-condensable gas in horizontal tubes. The actual research work improves this database with a considerable amount of experimental data and proposes a correlation for the prediction of the heat transfer coefficient in an exhaust gas heat exchanger in which parts of the gas humidity condense. All experiments were carried out under conditions, which are typical for this kind of heat exchangers, hence the presented results can be used for the design of condensation heat exchangers in industrial heat transfer systems. A gas inlet temperature of 120 °C, a range of the air-steam mixture Reynolds number 11,000 ≦ Re ≦ 31,000, three tube lengths between 1.87 m and 3.04 m, water vapour volume fractions of 7 % to 14.5 % as well as tube diameters of 22 mm and 28 mm were selected to derive the correlation. Furthermore, additional tube lengths (0.574 m, 0.973 m, 1.373 m) were investigated to determine the parameters influencing the condensation rate and comprehensive location profiles over the tube length. A correlation for a correction factor fC is derived, which enables to calculate the increase of the heat transfer coefficient due to condensation from the dry heat transfer coefficient without condensation. This dry heat transfer coefficient is calculated by the measured values in the inlet and outlet for a purely dry air-steam mixture cooling without condensation. The correction factor fC depend on the water vapour volume fraction, the Reynolds number and the geometry ratio between the inner diameter and the tube length.

Decision making viva genetic algorithm for the utilization of leftovers

Pipes have been using for different construction purposes, such as tube wells, oil wells, gas wells, and other sanitary purposes. These pipes have different sizes that can be used according to the need. In a particular construction, most of them can be used but some of them are left unused, which are known as leftovers. There are some usable leftovers (standards), whereas others are nonusable (nonstandards) leftovers. These leftovers could be difficult to manage to know which of them could be reused. The reuse of such leftovers become difficult for the construction companies to use them properly. On the other hand, these leftovers would be useful for other construction purposes rather than throw them into the bin. In this paper, we have presented a model and used a heuristic approach to make sure that the leftovers after different constructions could be reused according to the given demand. For this purpose, a genetic-based decision support system is applied to validate the solution feasibility of the problem. Experimental results validate the effectiveness of this novel proposed model by numerical experiments, and the leftovers are minimized up to a high extent.

Ефективність газопідігрівачів різного типу для антикорозійного захисту димових труб котельних установок

The of researches results of exergy efficiency and optimization of parameters of different types gas heaters by used for anticorrosion protection of gas exhaust ducts of heating boiler plants equipped with exhaust gas heat recovery systems are presented. The choice of a complex technique for analyzing the efficiency of gas heaters, which makes it possible to obtain functional dependences of the selected efficiency criteria on the geometric parameters of the heat exchange surface of gas heaters for solving optimization problems is substantiated. Such a technique can be a technique based on exergy methods and statistical methods of experiment planning theory. This technique by an insignificant number of initial parameters required for calculation, and by the simplicity of calculation and analytical methods for obtaining exergy characteristics is characterized. The work considered three types of gas heaters: water-heating (water-gas) and two gas-heating (gas-gas) pipe and plate type. The heat exchange surface of the water-heating gas heater is assembled from transverse-finned bimetallic (steel base and aluminum fins) pipes, gas-heating pipe-type - from steel pipes with circular turbulators flow, and gas-heating plate-type - from smooth steel plates. The general system of balance equations used in this complex technique, and also its the basic stages, are presented. It is noted that the choice of complex criteria for assessing the efficiency of gas heaters is carried out according to the degree of sensitivity of the criteria to changes in the operating and geometric parameters of gas heaters. Using the proposed sensitivity coefficient, the degree of sensitivity of different efficiency criteria has been analyzed and it has been established that one of the most sensitive to changes in the geometric parameters of the heat exchange surface of gas heaters is the heat-exergy criterion. The results of the corresponding calculations for each of the three gas heaters are presented. It has been established the most exergetically effective is a water-heating gas heater, followed by gas-heating gas heaters, of plate and tube types respectively.

Simulation and performance evaluation of trans-critical CO2 refrigeration system with modified evaporative cooled finned tube gas cooler in Indian context

The gas cooler is the most sensitive component which affects the performance of the CO2 system in the trans-critical cycle, and its performance highly depends on the climatic conditions. The CO2 system operating in high ambient conditions has lower performance; therefore, it is necessary to improve the system. The present work investigates the performance of trans-critical CO2 refrigeration system with proposed modified evaporative cooled finned tube gas cooler and with finned tube gas cooler for typical Indian climatic conditions. A mathematical model of CO2 refrigeration system finned tube gas cooler has been developed and validated with experimental data (literature), for different operating conditions. Further, it is integrated with a separate subroutine developed for the modified evaporative cooler (experimentally validated). The simulation has been performed in MATLAB to evaluate and compare the annual performance of systems for five selected cities in India of different climatic conditions, with different operating conditions. The result shows a maximum increase in seasonal energy efficiency ratio is 28% at 8 MPa for Ahmedabad city using the system with modified evaporative cooled finned tube gas cooler compared to a system with finned tube gas cooler. The overall improvements in SEER for all the selected cities are in the range of 10–28%.

Improvement of a Nusselt-Based Simulation Model for Heat Transfer in Rotary Heat Exchangers

In the last 50 years, the technology of rotary heat exchangers has not changed considerably. A reliable simulation can help improve the design of this technology. In this work, a simulation for rotary heat exchangers was developed and validated with multiple experimental data. This simulation takes an innovative approach based on locally calculated heat transfer coefficients and considers the entry region effect. This approach proved to be accurate since the average difference between the experimental results and the proposed model with a constant heat boundary condition is 0.1% and the maximum absolute deviation 1%. Experimental, as well as simulation results, indicate that lower empty tube gas velocity (1 m/s) and higher rotational speed (12 rpm) improve thermal efficiency compared to commonly used operating conditions. Additionally, a new model for predicting the local internal Nusselt number for sine ducts in the rotor channels is proposed, which considers the entry region effect.

Impact of heat pipes on the thermodynamics properties of natural gas in heat exchangers

Due to the high rate of heat transfer, especially heat transfer coefficient, which is produced by welding and condensing processes, heat pipes are considered as one of the most efficient and effective heat transfer equipment. In this paper, we aimed to provide a parametric study on the thermodynamics impact of natural gas in heat pipes and regular tubes in heat transfer processes. R410A and R 2 are used as working fluid through the heating processes, and their considerable influence on the thermodynamic properties was investigated in both outlet and inlet. According to the results of this study, heat pipes can provide fewer energy performances in the thermal, electrical and total section which indicated that heat pipes would be a good substitution for regular tubes in heat exchangers. As pressure drop decreases by the gas flow rate decrease, it has provided better efficiency in both regular tubes and heat pipes. Furthermore, R 410A has better performance rather than R 2 in both heat pipes and regular tubes in inlets and outlets.

Pressure drop and heat transfer of ZoneFlowTM structured catalytic reactors and reference pellets for Steam Methane Reforming

Structured catalytic reactors have the potential to combine reduced pressure drop and improved heat transfer compared to conventional pellets. In the present study, the pressure drop and heat transfer coefficient between the tube wall and the process gas were measured experimentally for annular structured ZoneFlowTM reactors of different design and for two commercial reference pellets. The ZoneFlowTM reactors differ by the design of the central rod that supports the near-wall annular casing. The experiments were carried out in a 1 m long reactor, at atmospheric pressure and with air flow rates from 70 to 330 Nm3/h. To measure the heat transfer coefficient, the furnace was set at a constant temperature that was varied in the range 100–500 °C and the axial profiles of the tube wall and gas temperatures were measured. Using the experimental data, correlations for the friction factor and the Nusselt number were derived and the introduced parameters estimated using non-linear regression. A correlation for the static contribution to heat transfer for the structured reactors was derived from 3D numerical simulations. The correlations were then used to evaluate the pressure drop–heat transfer advantage of the structured reactors compared to the reference pellets at typical industrial steam methane reforming conditions. The data show that ZoneFlowTM reactors can provide a roughly doubled heat transfer coefficient at comparable pressure drop than the tested reference pellets. Furthermore, modification of the central rod support structure was found an efficient way to balance the pressure drop–heat transfer advantage of ZoneFlowTM reactors using an identical design casing.

The effect of natural rubber on physical and mechanical properties of rubber seal for LPG tube valve

The price of natural rubber (NR) continues to decline. In early January 2020 the price of Standard Indonesian Rubber (SIR) 20 was around 1.83 US$/kg and in May 2020 dropped to 1.09 US$/kg. Under this condition, NR downstream program becomes a necessity to increase domestic consumption of NR so that the sustainable rubber industry can be achieved. One prospective product and can be substituted using NR is the rubber seal for Liquified Petroleum Gas (LPG) tube valve. Based on the rubber seal quality requirements in Standar Nasional Indonesia (SNI) 7655: 2010, the rubber raw material should use rubber which is resistant to n-pentane. Nitrile Butadiene Rubber (NBR) synthetic rubber is suitable, meanwhile NR is not resistant to n-pentane so it is not suitable to produce rubber seal for LPG tube valve. Hence, this research studied the effect of NR on physical and mechanical properties of rubber seal compared to NBR compound. The results showed that NR improved elastic properties such as tensile strength, elongation at break and compression set, but decreased the resistance to n-pentane. Mixing NBR and NR with appropriate compositions can produce a better rubber seal for LPG tube valve.

Numerical analysis of the heat transfer of radiant tubes and the slab heating characteristics in an industrial heat treatment furnace with pulse combustion

For a heat treatment furnace, the precise study of the flow characteristics, combustion and heat transfer in the furnace is essential to know the temperature distribution in a slab during the heating process. In this context several different three-dimensional CFD (Computational Fluid Dynamics) models have been developed to simulate the combustion and heat transfer process in the furnace. These models were developed based on direct fired reheating furnaces with continuous fuel input. In this paper, a novel three-dimensional transient CFD model used to investigate the slab heating characteristics in the heat treatment furnace with pulse combustion was developed. The transient calculation in the furnace was performed based on the steady-state simulation of the furnace temperature, and the movement of slabs on the rollers in the furnace was simulated using dynamic mesh. By comparison, the results from the EDC with two different reaction mechanisms showed good consistency. However, the EDC with the two-step reaction mechanism required one fifth the calculation time of the EDC with the GRI-Mech3.0, and was thus the preferred model. In contrast to direct fired reheating furnaces, the outer radiant tube walls were treated as the coupled boundary conditions in the model to realize indirect heat transfer between the process gas in the furnace and the combustion gas in the radiant tubes. Furthermore, a pulse combustion method was proposed to control the working states of the burners based on UDF (User-Defined Function), in order to realize the pulse combustion process in the heat treatment furnace. By the validation of “Black Box”, the temperature variation of the slab and the gas temperature in the furnace predicted by the model agreed well with the experimental results. The simulation revealed that the temperature distribution of the radiant tubes and furnace gas was uniform and the maximum temperature difference on the outer radiant tube walls was less than 84 K. During the slab transient heating process, the slab temperature distribution became more uniform in the soaking zone and the maximum temperature difference along the thickness of the slab was below 13 K at discharge.

The effect of water cooling conditions on the mechanisms of porous ice formation

Experimental data on the freezing rate and formation of cylindrical and spherical gas inclusions occurring in ice during the cooling of distilled water being in equilibrium with air at different initial temperatures of water and air and during the nonuniform cooling of a vessel with water have been obtained. The shape, size, and location of emerging gas formations are explained in a qualitative manner. It is shown that, with sufficiently slow freezing of water, conditions are created for the formation of thin (0.05 to 0.4 mm) and long (5 to 40 mm) fairly uniform gas tubes. With the acceleration of water freezing, the length of the gas tubes decreases significantly, whereas spherical gas inclusions are formed. The main processes occurring in water are mathematically analyzed. The specified processes include the temperature reduction, variation of the water aggregate state, gas concentration, and creation of conditions for the formation of gas cavities. The quantitative estimates of typical sizes of the forming tubular pores and the distances between them are obtained.

CFD Modeling of CO2 Absorption in Membrane Contactors Using Aqueous Solutions of Monoethanolamine–Ionic Liquids

The effects of addition of an ionic liquid to pure water as a physical absorbent and monoethanolamine (MEA) solutions as a chemical absorbent on carbon dioxide (CO2) absorption through hollow fiber membrane contactors were investigated using a 2D axisymmetric model. A numerical simulation was developed based on finite element method using computational fluid dynamics techniques. Liquid phase flowed in the tube side and gas mixture containing CO2 passed in the shell side of the membrane contactor in co-current and countercurrent modes. The simulation results are consistent with experimental data, and the root-mean-square error was calculated as 9 and 13% for pure water and 25 wt % for ionic liquid solution. The results showed that addition of 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]) to the base fluids increases CO2 absorption in both physical and chemical absorbents. However, the effects of an ionic liquid in physical absorption is higher than that in chemical absorption. Addition of 10 wt % [Bmim][BF4] to 3.5 wt % MEA solution could increase the absorption rate by 12% in countercurrent flow compared to a 6 wt % MEA solution without [Bmim][BF4] despite lower MEA concentration. Also, the results indicate that reaction term in a chemical absorbent is more important in low liquid flow rates. It can also be found that addition of 25 and 50 wt % of [Bmim][BF4] to pure water can enhance absorption performance up to 30 and 75%.

Experimental research on the performance of a gas lift bubble pump based on a diffusion generation process

The refrigerant generating bubble pump, in which the generation of refrigerant vapor and the pumping of solution both take place, is used to transport refrigerant, absorbent and diffusion gas in a diffusion absorption heat transformer. In this paper, experiments of refrigerant generating bubble pump were performed with H2O (water) as refrigerant, HCOOK (potassium formate) as absorbent and air as diffusion gas. The influences of motive head, inner diameter of lifting tube, generating temperature and diffusion gas flow rate on the refrigerant generating and solution pumping performance were investigated. Increasing motive head or inner diameter of lifting tube led to the decrease of solution flow rate and pumping ratio. While the diffusion gas flow rate increased, the solution flow rate and pumping ratio decreased, and the refrigerant flow rate increased under most conditions. It was observed that the refrigerant flow rate was the largest when the inner diameter was 9 mm and the generating temperature was 95 °C. These results will facilitate the design and development of diffusion absorption heat transformers in the future.

Process Development for a Superplastic Hot Tube Gas Forming Process of Titanium (Ti-3Al-2.5V) Hollow Profiles

Tube forming technologies based on internal forming pressures, such as hydroforming or hot tube gas forming, are state of the art to manufacture complex closed profile geometries. However, materials with excellent specific strengths and chemical properties, such as titanium alloys, are often challenging to shape due to their limited formability. In this study, the titanium alloy Ti-3Al-2.5V was processed by superplastic hot tube gas forming to manufacture a helically shaped flex tube. The forming process was investigated in terms of process simulation, forming tool technology and process window for the manufacturing of good parts. Within a simulation study, a strain rate optimized forming pressure–time curve was defined. With the newly developed tool design, forming temperatures up to 900 °C and internal forming pressures up to 7 MPa were tested. A process window to manufacture good parts without necking or wrinkling has been successfully identified. The experiment data showed good agreement with the numerical simulations. The detailed study of the process contributes to an in-depth understanding of the superplastic forming of Ti-3Al-2.5V during hot tube gas forming. Furthermore, the study shows the high potential of superplastic hot tube gas forming of titanium alloys for the manufacturing of helical flex tubes and bellows.

Numerical investigation on thermoelectric generators in an exhaust automotive line with aluminium foam

In the present paper a two-dimensional convective heat transfer problem in a partially filled channel with metal foam is numerically solved in steady state regime. An external thermoelectric generators (TEG) component is placed on the top surface of the channel. The numerical analyses are accomplished assuming the local thermal equilibrium (LTE) model to simulate the presence of the aluminum foam. The working fluid is exhaust gas with properties equal to the air for fixed temperature of the upper surface of the thermo-electric generator (TEG). The thermophysical properties are assumed temperature independent and the TEG component is considered as a solid with an internal energy generation. The Ansys-Fluent code is applied in order to resolve the governing equations for gas, porous media and TEG. Several mass flow rates of exhaust gas on the inlet section of the channel are considered. Different thicknesses of aluminum foam are assumed into the duct. The foam is characterized by different porosity equal to 0.90, 0.95, 0.97. Moreover, the number of pores per inch also changes and assumes the following values of 5, 20, 40. Results are showed in terms of temperature distributions, pressure drop, thermoelectric efficiency for different exhaust gas flow rates and metal foam characteristics and thicknesses. The results highlight that the use of metal foams significantly increases the heat transfer between the surface of exhaust gas tube and hot gas. Consequently, the effectiveness improves, and it increases between three-ten times with respect to the one for tube without metal foams. It is shown that the pore density does not affect the effectiveness.

A numerical study of the ammonia desulfurization in the spray scattering tower

Spray scattering tower with ammonia desulfurization has been drew a widespread attention for its low energy consumption and high desulfurization efficiency. In this work, we presented the results of numerical simulations on ammonia desulfurization characteristics in the spray scattering tower. Firstly, according to the structure and the flow characteristic of spray scattering tower, the flow, heat transfer and mass transfer model was established for the spray and bubble zone, respectively. Compared with the traditional model, the model is consider the flow characterize of bubbles and liquid, including bubbles size distribution, the dynamic change of bubble size, and turbulent kinetic exchange between bubbles and liquid due to flow characterize significantly affect the SO2 absorption in bubble zone. Secondly, the operation parameters, such as liquid gas ratio, inlet SO2 concentration, immersion depth of scattering tube and amount of flue gas, were investigated to show the influence on the overall desulfurization efficiency. At last, a new spray scattering tower equipped with the double inlets was proposed to increase the desulfurization efficiency than that with the single inlet under the same condition.