Increasing Air Flow Rate Research Articles

Combustion and mass loss behavior and characteristics of a single biomass pellet positioning at different orientations in a fixed bed reactor

This study aims to investigate the combustion characteristics and mass loss behaviors of rice straw and wheat straw biomass pellets experimentally in a laboratory fixed bed combustor under various operating conditions. High-speed photography was used to record images of the combustion process, and a sensitive balance was utilized for recording the particle mass history during the combustion process in addition to K-type thermocouples for temperature measurements. For both materials, the single pellet was exposed to various air temperatures and different flow rates of air. The orientation of the biomass pellet was positioned at various angles from 0 (horizontal), 30°, 45°, 60° (inclined), and 90° (parallel) to the hot air stream at different flow rates. Both glowing reactions and flameless ignition have been noticed in all experiments at all pellet orientations. All pellets experienced low and high luminosity volatiles without flames, followed by a bright radish color and short-lived combustion of the chars. Although the volatile contents of the two materials are identical, the volatile combustion duration of wheat straw (17–258 s) is less than that of rice straw (20–300 s), which could be due to differences in particle sizes, shapes, and structural compositions. The results also show that increased air temperatures lessen the time it takes for volatile and char to ignite and burn off. It also raises the temperature of surface ignition. Starting from the horizontal position and increasing the orientation angle of the pellet, the volatile and char ignition times increase up to 30° and then drop up to 90°, with angle 45° giving the lowest value. The same pattern was also noticed for volatile and char burnout times. The pellet horizontal position (0°) exhibits reduced combustion and mass loss (%) time intervals. The order of increasing the maximum temperature at the pellet surface was 30° > 60° > 90° angles. Increasing the air temperature reduces the times of char combustion, devolatilization, volatile burnout, and char burnout. As the air flow rate increases, the effect on the combustion parameters alternates between increasing and decreasing values.

Numerical and experimental study of aerosol dispersion in the Do728 aircraft cabin

The dispersion of aerosols originating from one source, the ‘index’ passenger, within the cabin of the aircraft Do728 is studied experimentally using an aerosol-exhaling thermal manikin and in Reynolds-averaged Navier–Stokes simulations (RANS). The overall aim of the present study is the experimental determination of the aerosol spreading for the state-of-the-art mixing ventilation (MV) and to evaluate the potential of alternative ventilation concepts for controlling the aerosol spreading in RANS. For MV, the experiments showed that the ratio of inhaled to exhaled aerosol particles drops below 0.06% (volume ratio) for distances larger than two seat rows from the source. However, within a single row, the observed ratio is higher. Further, the dispersion is much weaker for a standing than for a seated index passenger. High air exchange rates and a well-guided flow prevent a dispersion of the aerosols in high concentrations over larger distances. Additionally, the positive effect of a mask and an increased air flow rate, and especially their combination are shown. In the complementary conducted RANS, the advantages of floor-based cabin displacement ventilation (CDV) which is alternative ventilation concept to MV, regarding spreading lengths and the dwell time of the aerosols in the cabin were determined. The obtained results also underline the importance of the flow field for the aerosol dispersion. Further, additional unsteady RANS (URANS) simulations of the short-term process of the initial aerosol cloud formation highlighted that the momentum decay of the breathing and the evaporation processes take place within a few seconds only.

Properties of turbulent non-premixed methane/air flames in a miniature-scale swirl burner under different coaxial airflow swirl numbers

This study investigates the dynamics and properties of non-premixed methane/air flames under three swirl numbers by segmenting flame images using the Otsu thresholding technique. Under three operating conditions, the lean blow out (LBO) and flame length, lift-off height, maximum width, flame angle, and flame pulsing displacements in terms of flame center of gravity, length, and width are measured and compared. A high-speed camera is used to record video of flames, and the image processing of frames collected from a high-speed video was accomplished by using the intermittency distribution method to quantitatively compare flame attributes. The findings show that increasing the swirl number from 0.5 to 0.7 generally has an unfavorable effect on the LBO at given fuel flow rates, and the LBO of flames under 35° (0.6 swirl number) and 40° (0.7 swirl number) swirlers has decreased up to about 15% and 40%, respectively when compared with a 30° swirler (0.5 swirl number). Additionally, observations indicate that the flame length (𝐿) and lift-off height (𝐿𝑂) drop as the swirl number rises, although the flame width (𝑊) and angle (𝛼) show an ascending tendency. Besides, flame lift-off reveals an increasing-decreasing trend with an increment in the airflow, and flame length decreases as the airflow rate increases. It was also observed that flame pulsating displacements in terms of center of gravity (𝛿𝐶𝐺), length (𝛿𝐿), and width (𝛿𝑊) increases with an increase in the fuel flow rate, and as the swirl number is increased, 𝛿𝐶𝐺 and 𝛿𝐿 lessens, while 𝛿𝑊 increases.

Kinetics of uncatalyzed oxidation of ammonium sulfite from wet ammonia desulfurization

AbstractThe kinetics of oxidation of ammonium sulfite from flue gas desulfurization by ammonia process was studied by changing initial ammonium sulfite concentration, pH, air flow rate, temperature, and concentration of ammonium sulfate in a bubble reactor. The experimental results show that the oxidation rate of ammonium sulfite decreased with the increase of pH but increased with the increase of temperature and airflow rate when the concentration of ammonium sulfate is 0.15 mol/L, temperature of 25–60°C, and an airflow rate of 150–400 L/h. When the concentration of ammonium sulfate increases from 0.2 to 1.0 mol/L, the oxidation rate of ammonium sulfite decreases. At pH 5.0, the activation energy of the apparent oxidation is 26.40 kJ/mol. A kinetics model containing SO32−, SO4, and O2 is used to simulate the oxidation of ammonium sulfate. The results can provide a theoretical basis for the uncatalyzed oxidation of ammonium sulfite in the process of wet ammonia desulfurization process.

Ozone Concentration Measurement of an Atmospheric Pressure Air Plasma Jet by Ultraviolet Absorption Spectroscopy

Atmospheric pressure plasma jets have great potentials for various biomedical applications due to abundance with active oxygen species. In this article, an air plasma jet with a geometry of microhollow cathode discharge has been developed, which operates in a pulsed mode or a continuous mode depending on the dissipated power of the plasma jet. There are some continuous spectra emitted from the plasma jet, whose integrated intensity indicates that electron density increases with the increase of dissipated power, while decreases with increasing air flow rate for both of the two modes. Moreover, the electron density in the continuous mode is higher than that in the pulsed mode. Gas temperature of the plasma jet is obtained by the best fitting of the simulated and the experimental optical emission spectrum of OH (A-X), and ozone concentration produced by the plasma jet is measured by means of ultraviolet absorption spectroscopy. Results indicate that both ozone concentration and gas temperature decrease with increasing distance from the jet nozzle. At the jet nozzle, both of them increase with increasing dissipated power. However, ozone concentration decreases, while gas temperature increases with increasing air flow rate. The results are very important for the biomedical application of plasma jet.

Experimental Study on a Generic Side-View Mirror with Slotted Cylindrical Foot

A simple model consisting of a mirror-housing and its cylindrical foot is applied to represent the automobile side-view mirror that causes unwanted aerodynamic noise and wind drag during high-speed driving. An additional slot is made on the solid foot to modify the flow around the mirror and thus reduce the side wall pressure fluctuation and aerodynamic drag. Flow fields and wall pressure fluctuations of these side-view mirror models have been investigated experimentally in a wind tunnel. The airflow rate through the slot varies with the changing of the slot area. Wall surface pressure sensors, particle image velocimetry (PIV), and six-component balance were applied to measure the acoustic and flow characteristics. The results demonstrated that, with the increase of slot airflow rate to 30%, the side wall pressure fluctuations were reduced by 5.1 dB and the drag coefficient decreased by 10.2%. The PIV measurements showed that the vortex cluster center behind the mirror was moved upward from the wall surface due to the slot airflow injection into the wake. The turbulent kinetic energy in the side-view mirror wake near the wall decreased with the increment of the airflow rate, reducing the side wall pressure fluctuations and thereby suppressing the noise generation.

Enhanced ammonia removal from skim latex using air bubbles in an agitated column

AbstractThe initial aim of the paper is to improve the ammonia removal efficiency from skim latex using air stripping in an agitated column. The effects of air flow rate, bubble sizes, types of impellers, and rotational speed were investigated. The results showed that ammonia decreased with the increased air flow rate and the decreased bubble size. More ammonia could be removed by the use of impellers at a low rotational speed. The axial flow impeller showed higher ammonia removal than that gained from the radial flow impeller. It could be concluded that the stripping process in an agitated column should be operated at an air flow rate under the homogeneous regime without pH and temperature adjustment. The use of axial flow impeller at a rotational speed below the turbulent flow is recommended for more ammonia removal. In addition, smaller bubbles than the working range proposed in this research should be avoided because of foaming formation of the skim latex.

Effects of Fe(II) on As(III) oxidation in Fe(II)-As(III) co-oxidation: Limiting and driving roles

The co-oxidation of Fe(II) and As(III) occurs under aerobic conditions, and Fe(II) may largely determine the fate of As(III), but the effect of Fe(II) on the As(III) oxidation is barely explored. In this research, the limiting and driving roles of Fe(II) in As(III) oxidation were systematically studied through batch kinetic studies in combination with X-ray photoelectron spectroscopy (XPS) depth profiling, scanning electron microscopy and energy dispersive X-ray spectrometry (SEM-EDS), and quenching experiments. The results showed that As(III) oxidation efficiency increased with the increase of Fe/As molar ratio (from 63.1% to 98.3%), but decreased with the increase of pH (from 96.0% to 44.2%) and the increase of air flow rate (from 88.1% to 75.1%). The Fe(II) oxidation rate increased with the increase of pH and air flow rate. When Fe(II) was oxidized rapidly, As(III) was more likely to be immobilized in the “inner sphere” of formed Fe (hydr)oxides, limiting As(III) oxidation. On the other hand, Fe(II) was oxidized to produce Fe (hydr)oxides to adsorb or fix As(III); meanwhile, the ROS generated by Fenton-like reaction of Fe(II) promoted As(III) oxidation, especially, •O2− and H2O2 were important ROS that drove the As(III) oxidation. These findings might provide a new insight for Fe(II) and As(III) geochemistry cycling in naturally occurring environment.

Particle swarm optimization of phase change and indoor setpoint temperatures in a phase change material‐air heat exchanger for free cooling of two climate zones

AbstractThe simulation and free‐cooling economic optimization of a phase change material (PCM)‐air heat exchanger (PAHX), including containers filled with fictitious SiO2 nano‐enhanced PCM (NEPCM), are investigated. The airside, PCM side and heat balance governing equations are solved numerically by employing analytical solutions during the 3‐month summer from June 22 to September 22. Two climate zones of Tehran and Mashhad have been selected due to temperature contrast, especially at off‐peak times. Particle swarm optimization is employed to determine indoor setpoint temperatures (SPTs) and phase change temperatures (PCTs) to optimize the total cooling energy cost of a residential building. The effects of local climate, airflow rate, nanoparticle concentrations, and SPT range on optimization variables are studied. Two SPTs for day and night and two PCTs for melting and solidifying are between 22°C and 26°C. The mass percentage of nanoparticles is considered to be from 0% to 14%. Based on optimization analysis, Toff‐peak = 22°C, and Tpeak = 26°C are considered the best SPTs for both cities, for Mashhad Ts = 24.05°C, Tl = 18.97°C while for Tehran Ts = 24.83°C, Tl = 25.35°C are considered as the best PCTs. The optimum electrical cost increases significantly with increasing airflow rate and SPT range, while nanoparticle concentration has a low influence of up to about 3% for all desired days.

Performance characterization of M-cycle indirect evaporative cooler and heat recovery ventilator for commercial buildings – Experiments and model

Evaporative cooling systems in buildings can dramatically reduce greenhouse gas emissions due to their low energy consumption, lack of ecologically harmful refrigerants and their diverse applications. Indirect evaporative cooling (IEC) uses water in the secondary air stream to cool the primary air without adding humidity to the indoor environment. The Maisotsenko Cycle (M−Cycle) design of an IEC has the potential to approach dew-point on the primary air by pre-cooling the secondary air stream before extracting heat in cross-flow with the primary air. Separately, a variety of technologies exist for energy recovery in commercial buildings to pre-condition ventilation air. In this study a M−cycle heat and mass exchanger was used as a heat recovery ventilator (HRV) to recover energy from the exhaust air stream during winter and as an IEC during summer to cool the ventilation air. Experiments were performed by operating the full-size IEC/HRV system with a maximum air flow rate of 2210 m3/hr in conjunction with indoor and outdoor environmental chambers simulating respective environments. The experimental results showed HRV heating sensible effectiveness between 67 % and 63 % and IEC cooling total effectiveness between 81 % and 71 % with increasing air flow rates. A detailed numerical model was developed to predict the performance of the IEC/HRV over a large range of operating conditions. The IEC model simulates heat and mass transfer from water evaporation in the secondary air and potentially from condensation in the primary air during summer season operation. The HRV model simulates heat transfer and potentially mass transfer from secondary air condensation during winter season operation. The detailed physics-based model was compared with experimental data, and it predicted the performance with high accuracy for both summer and winter operating conditions. The average absolute errors for supply air temperature between the experimental results and model predictions were 0.2 °C in HRV winter mode and 1.0 °C in IEC summer mode. The validated IEC model was used to further explore the possibility of combined ventilation and passive space cooling without a supplemental air-conditioner. The analysis shows that utilizing IEC for summer operation offers high cooling COP and even the potential for passive space cooling, which is not possible with conventional energy recovery ventilators (ERV).

Effect of the Design Parameters of the Combustion Chamber on the Efficiency of a Thermal Oxidizer

Carbon monoxide is often produced during the incomplete combustion of volatile organic carbon compounds in industry. In the combustion chamber for oxidizing carbon monoxide emissions, a penta-coaxial port device can be used to improve the process of mixing the fuel and oxidizer. In this study, the conjugate heat transfer analysis was conducted by solving both Reynolds-averaged Navier–Stokes equations with the eddy dissipation model and solid heat conduction equation in the wall using Fluent 2019R2 to simulate the reaction flow of a volatile organic carbon compound burner and heat transfer of the stack insulation layer. The mass fractions of the O2, CO2, and CO gases; the temperature; and the velocity distribution in a combustion chamber were computed to investigate how various design parameters of the combustor, including air inlet size and stack height, and air inflow conditions affected the combustion performance. Results show that the size of the air inlet had only a minor effect on combustion efficiency and that the airstream forced by a fan significantly enhanced the combustion performance. In particular, increasing the height of the stack from 2 m to 4 m greatly increased combustion efficiency from 63% to 94%, with a 50% increase in the incoming air flow rate by natural convection, which demonstrates the importance of stack height in combustor design.

Experimental microwave-assisted air gasification of biomass for syngas production

Syngas production from biomass is a clean way to supply energy for our economy and society. In this study, a microwave-assisted air gasification system was developed and the preliminary results of syngas yields, syngas compositions, syngas lower heating values (LHVs), carbon conversion efficiencies, and cold gas efficiencies obtained from corn stover (CS) gasified at varied air flow rates (200, 400, and 600 mL/min), gasification temperatures (500, 600, and 700 °C), and retention times (10, 20, and 30 min) were reported for the first time. The results showed that the increase in air flow rate increased the syngas yield and carbon conversion efficiency, decreased the syngas LHV whereas first increased then decreased the cold gas efficiency. Higher gasification temperature favored the syngas yield, syngas LHV, carbon conversion efficiency and cold gas efficiency. Longer retention time favored the syngas yield and carbon conversion efficiency whereas lowered the syngas LHV and cold gas efficiency. Syngas yield of 38.90–76.14 wt% and LHV of 4.95–6.34 MJ/m3 were observed for the syngas at air flow rate of 200–600 mL/min, gasification temperature of 500–700 °C and retention time of 10–30 min. The most significant contribution of this study is the high syngas yield, which is even higher than that from a microwave-assisted pyrolysis process at a high temperature of 900 °C.

Computational investigation of natural ventilation induced by solar chimneys: Significance of building space on thermofluid behavior

A solar chimney is a typical device to harness naturally available energy resources to power ventilation inside buildings. A comparative computational fluid dynamics study of the flow and thermal mechanics inside solar chimneys is performed in this study. We utilize a variational multiscale formulation to model the combined turbulent/laminar flow regimes presented in the natural ventilation problem in the sense of large eddy simulation. Nitsche type weak enforcement of Dirichlet boundary conditions is integrated into the numerical framework to address the excessive mesh resolution requirement in flow and thermal boundary layers. Numerical methodology is verified and validated against experimental data in a model room with a solar chimney, and good agreement between the present results and the reference data is obtained. Finally, the thermofluid characteristics are investigated in a building equipped with different solar chimney designs. Particular emphases are placed on the effects of attached building spaces to the flows within the chimneys. The results indicated that the complex and realistic building space in this paper reduces the turbulence entering the solar chimney inlet and, thus, increases the air flow rate by up to 48.9% compared with the frequently used standalone chimney simulation paradigm. In addition, the thermal comfort indices are presented. With increased air flow rate in the chimney, the overall thermal comfort in the building is likely to be decreased, suggesting the necessity in the future studies to consider thermal comfort as an optimization objective.

Ammonia recovery from anaerobic digestion effluent by aeration-assisted membrane contactor

The ammonia recovery from anaerobic digestion (AD) effluent offers a low cost and low carbon footprint strategy for N recovery. To enhance ammonia recovery performance, the aeration-assisted membrane contactor (MC) process was presented with aeration applied on the feed side. The ammonia recovery performance with different pH adjustment methods and operating parameters were tested. Results illustrated that a high ammonia mass transfer coefficient (Kov = 4.85 ×10−7 m/s) could be achieved in the aeration-assisted MC. With the increase in air flow rate from 0 L/min to 0.6 L/min, the Kov increased from 1.21 × 10−7 m/s to 4.85 × 10−7 m/s by about 300%, and the ammonia separation factor (St) increased from 5.75 to 8.91 by about 55%. Additionally, the Kov increased sharply with the increase in feed temperature. Notably, the ammonia removal efficiency can reach 82% after 6-h experiment, which might be due to the large contact area of membrane contactor and the high mass transfer efficiency caused by the optimal conditions. The greenhouse gas (GHG) emission evaluation showed that compared with that of Haber-Bosch process (4.2 kg-CO2 eq/kg-N), the GHG emission of aeration-assisted MC was 1.86 kg-CO2 eq/kg-N under room temperature. The aeration-assisted MC can provide a high-efficient and low GHG-emission ammonia recovery process.

In Vitro and In Silico Investigations on Drug Delivery in the Mouth-Throat Models with Handihaler®.

This work aimed to evaluate the relative inhalation parameters that affect the deposition of inhaled aerosols, including mouth-throat morphology, airflow rate, and initial condition of emitted particles. In vitro experiments were conducted using the US Pharmacopeia (USP) throat and a realistic mouth-throat (RMT) with Handihaler®. Then, in silico study of the gas-solid flow was performed by computational fluid dynamics and discrete phase method. Results indicated that aerosol deposition in RMT was higher compared to that in USP throat at an airflow rate of 30 L/min, with 33.16 ± 7.84% and 21.11 ± 7.1% lung deposition in USP throat and RMT models, respectively, which showed a better correlation with in vivo data from the literature. Increasing airflow rate resulted in better drug aerosolization, while the fine particle dose trend ascended before declining, with the peak value obtained at a flow rate of 40 L/min. Overall, the effect of geometrical variation was more significant. Additionally, in silico results demonstrated clearly that the initial conditions of the emitted particles from inhalers affected the subsequent deposition. Larger momentum possessed by the central aerosol jet entering the mouth directly led to stronger impaction, which resulted in the deposition in the front region of mouth-throat models. This study is beneficial to develop an in silico method to understand the underlying mechanisms of in vivo mouth-throat deposition.

PENGARUH JARAK NOSEL UDARA DENGAN OUTLET TERHADAP DIS-TRIBUSI UKURAN BUBBLE YANG DIHASILKAN OLEH MBG TIPE SWIRL

This research uses a swirl type MBG (MBG) with the gap variation between the air nozzle and the outlet of 1, 5 and10 mm. In this experiment, we used a tangential inlet of 25 mm and an outlet of 20 mm with a water flow rate of 20 – 70 l/min and an air flow rate range of 0.1 – 0.8 l/min, to determine the characteristics of MBG which include bubble distribution, pressure drop, hydraulic power, and efficiency. The probability of the diameter of the microbubble formed was in the range of 90 – 150 µm for all variations of the air nozzle gap. The larger the incoming water flow rate, the smaller the diameter of the bubbles formed, whereas if the water flow rate decreases, the diameter of the bubbles formed will increase. In contrast to the water flow rate, if the air flow rate increases, the diameter of the bubbles formed will increase, whereas if it decreases, the diameter of the bubbles will decrease. From the signal processing data, information was obtained about the comparison of the pressure drop of the three variations of the air nozzle gap, as follows: The higher the water flow rate, the pressure drop and hydraulic values increase significantly, while for air flow rate, the higher the air flow rate, the pressure drop and hydraulic power values will increase albeit not significantly. As for MBG efficiency, it will decrease significantly with increasing water flow rate and will increase insignificantly with decreasing water flow rate.

Development of phase change material assisted evacuated tube solar dryer: Investigation of thermal profile, drying characteristics, and functional properties of pumpkin slices

The present work aimed to develop a phase change material-assisted evacuated tube solar dryer (PCM-ETSD) and experiments were performed with and without PCM for drying pumpkin slices. Thermal performance, drying characteristics, and quality attributes were analyzed with and without PCM at different airflow rates: 34.64 kg/h, 51.96 kg/h, and 69.28 kg/h. The average temperature elevation between the ambient and drying chamber was achieved at 29.62 °C to 36.33 °C and 25.64 °C to 28.93 °C without and with PCM-assisted drying respectively. PCM-ETSD extended the drying period by 2 h and maintained the temperature ranges from 50.78 °C to 61.29 °C after sunshine hours. The PCM-ETSD reduced the moisture content of pumpkin slices by 4–5% and 8% more as compared to without PCM and sun drying respectively. Drying rate and effective moisture diffusivity are enhanced with the increase of airflow rate in the drying process and higher without PCM-assisted drying followed by PCM and sun drying. The total phenolic content and total flavonoid content are higher in PCM-assisted drying and continuously decreased with the increases in airflow rate in both drying processes. Antioxidant activity and total carotenoid content are higher in PCM-assisted drying. FTIR analysis confirmed the presence of active functional groups and phenols in dried pumpkin. The inferior color changes were observed in PCM-assisted drying of pumpkin slices. The developed PCM-ETSD could be capable of drying other food commodities on a pilot scale after sunshine with retention of quality attributes.

Experimental investigation of dehumidification performance of a vapor compression refrigeration system

The dehumidification performance of a vapor compression refrigeration system (VCRS) is investigated in this work, including total refrigerating capacity (TRC), total dehumidification capacity (TDC), latent heat ratio (RLH), and power consumption per unit dehumidification capacity (PCPDC). Experiments were performed for the VCRS with the rated refrigerating capacity of 7 kW. The influence of indoor air parameters including the temperature, humidity and flowrate on the dehumidification performance were studied. TDC and RLH decreased with an increase in the air temperature at a fixed humidity ratio, and increased with an increase in the air humidity at a fixed temperature. PCPDC decreased with an increase in the air humidity. The effect of the air flowrate was more complex than that of the air temperature and humidity. There was a maximum value in TDC and a minimum value in PCPDC with an increase in air flowrate for each humidity. For example, TDCmax was 2.45 kg/h for 38% rh and 6.62 kg/h for 80% rh, accordingly, PCPDCmin was 3383.48 kJ/kg for 38% rh and 1286.5 kJ/kg for 80% rh at 26 °C. As the humidity increases, the maximum and minimum values shifted towards larger flowrates. The experimental results are useful for the operation of VCRS and the design and control of convection-radiation air conditioning (CRA/C) system for the improvement of the environmental comfort.

Impact of inlet and outlet opening height variation on the air quality and ventilation efficiency in the on-top wind catcher buildings: A CFD simulation

This paper examines the role of wind-catcher height on the quality of ventilation inside the building. The base sample in this study includes a single-zone isolated building combined into a one-sided wind catcher as an inlet. Difference between inlet and outlet opening height is considered as an independent variable and ventilation quality and efficiency are considered as dependent variables. The results showed that by increasing the height of opening as a wind-catcher in the inlet facade, the airflow rate increases, the velocity decreases and the age of air increases. By increasing the height of the outlet opening, as a window from the floor to the ceiling of the room, there is no noticeable change in mean velocity, mean age of air and airflow rate. However, by transforming the outlet opening form a window to an on-top wind-catcher, the mean velocity and airflow rate decrease and the mean age of air increase. Also, by increasing the height of the wind catcher on the outlet facade, the ventilation efficiency increases too. High-resolution 3D steady RANS CFD simulations of cross ventilation are performed for all case studies.

Simulation investigation on a novel open-loop air cycle heat pump drying system

Different from conventional drying technology, the novel technology of an air cycle heat pump drying (ACHPD) system, using air as its working medium, is proposed to solve the problems of low energy efficiency, HCFC refrigerant use, and so on. A mathematical simulation model is constructed to evaluate system performance under various working conditions, and its verification via experimental results from a constructed test bench produced errors of temperature within ±1.6%, of drying rate within ±0.01%, and of system power within ±7%. Compared with a conventional electric heater drying (EHD) system, the energy-saving rate of the ACHPD system reaches about 15–27% when the mass evaporation rate increases from 0.75 kg h−1 to 3.45 kg h−1. Under set working conditions, an increase of inlet air flow rate (150–400 kg h−1) improved the dehumidification energy efficiency ratio (MER) by about 1%. However, the increase of inlet air temperature (10–40 °C) and relative humidity (30–80%) reduced MER by about 7% and 21% respectively. The efficiency improvements of heat exchanger (0.3–0.8) can improve the energy efficiency of system by 20%; however, the efficiency improvements of expander (0.55–0.8) and compressor (0.4–0.9) can deteriorate the energy efficiency of system by 17% and 36% respectively. These results would provide new technical references for the application of heat pump technology in drying field from a different perspective.