Jinxiang Wu

The horizontally oriented jet flame induced by rectangular source impinging upon opposite wall is actually common in chemical industry, but the related studies are limited. In this paper, the computational fluid dynamics codes are carried out to investigate the temperature profile in thermal impinging flow of horizontally oriented methane jet flame with rectangular source, which the rectangular orifice is 400mm² with three different aspect ratios (L/W=1, 2, 4), besides, the jet velocities vary from 27.5m/s to 125m/s. As the horizontally oriented methane jet flame impinges on the vertical plate in front of the fuel orifice directly, the vertical temperature along opposite plate is focused on. Results show that the temperature near the impingement point is same for different jet velocities, but the temperature along vertical direction is larger with fuel jet velocity increasing. Moreover, the orifice aspect ratio has a significant effect on temperature, which the temperature increases with aspect ratio at a given position for momentum-controlled flame. The effective heat release rate on the basis of unburned fuel and ellipse flame shape hypothesis is put forward to correlate the temperature profile. Finally, a new correlation to illustrate the vertical temperature rising along opposite plate is proposed in light of orifice aspect ratio and fuel jet velocity, and the predictions obtained by proposed model agree well with numerical results, which is applicable for horizontally oriented flame with rectangular source impinging upon the opposite wall.

Bioenergy integrated CO₂ capture is considered to be one of the viable options to reduce the carbon footprint in the atmosphere, as well as to lower dependability on the usage of fossil fuels. The present simulation-based study comprises the oxy bio-CCS technique with the objective of bringing about cleaner thermal energy production with nearly zero emissions, CO₂ capture and purification, and with the ability to remove NO_x and SO₂ from the flue gas and to generate valuable byproducts, i.e., HNO₃ and H₂SO₄. In the present work, a simulation on utilization of biomass resources by applying the oxy combustion technique was carried out, and CO₂ sequestration through pressurized reactive distillation column (PRDC) was integrated into the boiler. Based on our proposed laboratory scale bio-CCS plant with oxy combustion technique, the designed thermal load was kept at 20 kW_th using maize stalk as primary fuel. With the objective of achieving cleaner production with near zero emissions, CO₂ rich flue gas and moisture generated during oxy combustion were hauled in PRDC for NO_x and SO₂ absorption and CO₂ purification. The oxy combustion technique is unique due to its characteristic low output of NO sourced by fuel inherent nitrogen. The respective mechanisms of fuel inherent nitrogen conversion to NO_x, and later, the conversion of NO_x and SO₂ to HNO₃ and H₂SO₄ respectively, involve complex chemistry with the involvement of N–S intermediate species. Based on the flue gas composition generated by oxy biomass combustion, the focus was given to the fuel NO_x, whereby different rates of NO formation from fuel inherent nitrogen were studied to investigate the optimum rates of conversion of NO_x during conversion reactions. The rate of conversion of NO_x and SO₂ were studied under fixed temperature and pressure. The factors affecting the rate of conversion were optimized through sensitivity analysiês to get the best possible operational parameters. These variable factors include ratios of liquid to gas feed flow, vapor-liquid holdups and bottom recycling. The results obtained through optimizing the various factors of the proposed system have shown great potential in terms of maximizing productivity. Around 88.91% of the 20 kW_th boiler’s efficiency was obtained. The rate of conversion of NO_x and SO₂ were recorded at 98.05% and 87.42% respectively under parameters of 30 °C temperature, 3 MPa pressure, 10% feed stream holdup, liquid/gaseous feed stream ratio of 0.04 and a recycling rate of the bottom product of 20%. During the simulation process, production of around four kilograms per hour of CO₂ with 94.13% purity was achieved.

An experimental study on a plate gravity heat pipe (PGHP) with inner cavity size of length 100 mm (X), width 2.5 mm (Y), and height 210 mm (Z) with acetone as the working fluid was carried out. The effects of heating power inputs (80–180 W) and fluid filling ratios (25%, 48%, and 55%) on the start-up temperature, start-up time, temperature difference, and relative thermal resistance on the Z-axis of the PGHP in a vacuum of 1 × 10⁻³ Pa were studied at unsteady state. Furthermore, the gas-liquid two-phase behavior of the interior working fluid of PGHP, and the coupling heat transfer behavior of the boiling liquid and the condensate were observed through a visualizable window under different experimental conditions. The results show that, with the increase of heating power input, the start-up temperature of the PGHP increases and the start-up time is shortened. The start-up temperature of the PGHP was around 33 °C and the start-up time was about 320 s at the heating power input of 120 W and working fluid filling ratio of 55%. The relative thermal resistance and the temperature difference on the Z-axis of the PGHP increase firstly and then decrease with the increase of heating power input at unsteady state. The complex gas-liquid two-phase behavior of the PGHP mainly includes: the formation and growth of bubbles, the merging and break up of bubbles, and the coupling heat transfer between boiling liquid and condensate, which demonstrate that the novel SVPGHP can be used to effectively study the heat transfer process of PGHP.

This article proposes a dual heat source heat pump bathroom unit with preheater which is feasible for a single family. The system effectively integrates the air source heat pump (ASHP) and wastewater source heat pump (WSHP) technologies, and incorporates a preheater to recover shower wastewater heat and thus improve the total coefficient of performance (COP) of the system, and it has no electric auxiliary heating device, which is favorable to improve the security of the system operation. The process simulation software ASPEN PLUS, widely used in the design and optimization of thermodynamic systems, was used to simulate various cases of system use and to analyze the impact of the preheater on the system. The average COP value of a system with preheater is 6.588 and without preheater it is 4.677. Based on the optimization and analysis, under the standard conditions of air at 25 °C, relative humidity of 70%, wastewater at 35 °C, wastewater flow rate of 0.07 kg/s, tap water at 15 °C, and condenser outlet water temperature at 50 °C, the theoretical COP of the system can reach 9.784 at an evaporating temperature of 14.96 °C, condensing temperature of 48.74 °C, and preheated water temperature of 27.19 °C.

Selective catalytic reduction of NO_x with NH₃ (NH₃-SCR) has been widely investigated to reduce NO_x emissions from combustion processes, which cause environmental challenges. However, most of the current work on NO_x reduction has focused on using feed gas without CO₂ or containing small amounts of CO₂. In the future, oxy-fuel combustion will play an important role for power generation, and this process generates high concentrations of CO₂ in flue gas. Therefore, studies on the SCR process under concentrated CO₂ atmosphere conditions are important for future SCR deployment in oxy-fuel combustion processes. In this work, Mn- and Ce-based catalysts using activated carbon as support were used to investigate the effect of CO₂ on NO conversion. A N₂ atmosphere was used for comparison. Different process conditions such as temperature, SO₂ concentration, H₂O content in the feed gas and space velocity were studied. Under Mn-Ce/AC conditions, the results suggested that Mn metal could reduce the inhibition effect of CO₂ on the NO conversion, while Ce metal increased the inhibition effect of CO₂. High space velocity also resulted in a reduction of CO₂ inhibition on the NO conversion, although the overall performance of SCR was greatly reduced at high space velocity. Future investigations to design novel Mn-based catalysts are suggested to enhance the SCR performance under concentrated CO₂ atmosphere conditions.

Photo-chemical smog and acid rain formed from many pollutants including NO_x are serious problems that have attracted much attention due to their negative influences on the atmosphere, plants, animals and even building materials. Effective measures of controlling NO_x emissions are necessary. In this study, a computational fluid dynamics (CFD) software, Ansys Fluent 14.5, has been applied to research the processes of South American coal (SAm) reburning and cornstalk reburning. The influences of reburn zone excess air coefficient, reburning fuel fraction (R_ff) and the secondary air temperature on the furnace combustion and NO_x reduction have been determined. Results show that, in the simulated data range, the lower reburn zone excess air coefficient, the greater the rate of denitration for both SAm reburning and cornstalk reburning. The highest rates of denitration for SAm reburning and cornstalk reburning were 56.15% and 66.89%, respectively, in comparison to the conventional combustion. The denitration rate increases with the increase of reburning fuel fraction. However, when the reburning fuel fraction increases beyond a certain level, fuels within the furnace will undergo incomplete combustion. Under the premise of the fuel burnout, a relatively good case occurs at the reburning fuel fraction of 20% for the two kinds of reburning, and the NO_x removal rate is 60.57% for cornstalk reburning, which is 7.61% higher than that of the SAm reburning. Temperature also has certain influences on the denitration effect and it shows that, in the lower temperature range, the higher the temperature of the secondary air, the higher the denitration rate. However, as temperature reaches a certain value, the denitration effect is no longer enhanced but reduced. For the two kinds of reburning, the case with the secondary air at 500 K is a relatively good one, and the NO_x removal rate reaches 66.36% for cornstalk reburning, while it is 55% for SAm reburning. Overall, cornstalk reburning provides a higher NO_x reduction rate in comparison to SAm reburning.