Inlet Air Flow Rate Research Articles

Investigating Solid and Liquid Desiccant Dehumidification Options for Room Air-Conditioning and Drying Applications

This study reports on the investigation of the performance of single and two-stage liquid and solid desiccant dehumidification systems and two-stage combined liquid and solid desiccant dehumidification systems with reference to humid climates. The research focus is on a dehumidification system capacity of 25 kW designed for room air conditioning application using the thermal models reported in the literature. RD-type silica gel and LiCl are used as solid and liquid desiccant materials, respectively. In this study, the application of proposed system for deep drying application is also explored. Condensation rate and moisture removal efficiency are chosen as performance parameters for room air conditioning application, whereas air outlet temperature is chosen as performance parameter for deep drying application. Further, for a given range of operating parameters, influences of air inlet humidity ratio, flow rate, and inlet temperature on performance parameters of the systems are investigated. In humid climatic conditions, it has been observed that a two-stage liquid desiccant dehumidification system is more effective for room air conditioning application, and two-stage solid desiccant dehumidification system is more suitable for deep drying application in the temperature range of 50 to 70 °C, while single-stage solid desiccant and two-stage combined liquid and solid desiccant dehumidification systems are more effective for low temperature, i.e., 30 to 50 °C deep drying application.

The Influence of the Shape of Granite on the Heat Storage Process in a Rock Bed

Granite is one of those materials that due to its thermal parameters is used as a filling for storage beds, including high-temperature ones. The article analyzes local material that was extracted in Strzegom, Poland. The purpose of the paper is the assessment of storage material with regard to its cooperation with a heat source that is available for a short time, e.g., a solar installation. Three different shapes of granite material were tested: rock, cube and sphere. Each shape has its advantages and disadvantages, which are associated with economic and strength aspects. The article presents experimental tests of the material, which were conducted in order to determine the efficiency of the charging process. The results show that rock-shaped granite filling elements are characterized with the best parameters during the charging process, and that they obtained the highest first- and second-law efficiency in the entire tested range of inlet air temperature and flow rate. The efficiency of the cube-shaped granite was lower than the sphere-shaped granite. This means that the efficiency does not directly depend on the coefficient of sphericity of the elements that fill the storage bed. The determination of the second law efficiency showed that the highest use of energy supplied with hot air occurs after 1 h of charging the accumulator in the case of all the analyzed geometries. At the end of the paper, the influence of the obtained results on the process of modelling the charging of a storage bed filled with elements of non-spherical geometry is also discussed.

Effects of liquid viscosity on bubble formation characteristics in a typical membrane bioreactor

The generation and formation characteristics of air bubbles have significant impact on the performance of the membrane bioreactor system. Experiments were conducted in a tank filled with Glycerine-Water solutions so as to investigate the impacts of liquid viscosity on the bubble formation characteristics. Nozzle size ranging from 2 to 10 mm, air inlet flow rate ranging from 300 to 1500 cc/min and liquid viscosity ranging from 6 to 850 cP have been investigated. Methods to compute the non-linear characteristics such as bubble diameter and bubble rising velocity have been identified. The nonlinear behaviour of the air bubbles were further correlated to the dimensionless numbers such as Reynolds number, Eötvös number and Galilei number. A bubble shape regime was constructed so as to classify the distinct regions of the air bubbles generated from different viscous solutions. Coalescence of bubbles were studied extensively and the impact of liquid viscosity on the bubble flow regimes were presented.

Numerical and experimental investigation on the performance of a ventilated chamber for low-cost PM sensor calibration

Particulate matter (PM) sensors are popular for distributed monitoring due to their portability, low-cost and networking capabilities. To provide reliable data, these sensors have to be calibrated periodically in the laboratory. This is often done in chambers with several of them co-located, alongside several research grade instruments. It is important to confirm that the aerosol is well distributed to ensure reliability and accuracy of the calibration tests. This paper describes a modeling and experimental study of these chambers used for calibration of PM sensors. The experimental setup is described and calibration results for the low-cost PM sensors (MAXIMA sensor, Applied Particle Technology, Inc.) using research-grade instruments (GRIMM 11-C, GRIMM Technologies, Inc.) are presented. A computational fluid dynamics (CFD) model including effects of turbulence and Brownian motion is used to predict particle trajectories and distribution in the chamber. The simulated particle number concentration agrees well with the measured values in the chamber. Having the CFD model, the suitability of three proposed chamber designs (fan off; fan on-parallel; fan on-diagonal) are explored for a variety of conditions. Operating conditions that result in uniform concentrations are established using the model. The recommended design for the PM sensor calibration in a rectangular ventilated chamber is: parallel fan layout, fan pressure of 12 Pa, and inlet air flow rate between 10 and 15 L/min. This study shows that the numerical modeling is available to understand the performance of a calibration chamber as well as optimizing the chamber design. A broader perspective is that the results validate the use of low-cost PM sensors for checking the distribution of aerosols in chambers.

Characteristics of the concentration of complex odor substances according to the inlet air flow rate at the opening of malodor emission sources of public environment facilities

Characteristics of the concentration of complex odor substances according to the inlet air flow rate at the opening of malodor emission sources of public environment facilities

Evaluation of comfort levels in office space equipped with HVAC system based in personalized ventilation system using energy produced in DSF systems

In this study the numerical simulation of a Heating, Ventilating and Air Conditioning (HVAC) system, based in a personalized ventilation system, installed in an occupied office desk is made. The energy is produced in a Dual Skin Facades (DSF) system installed in the outdoor environment. The personalized ventilation system, placed above and below the writing area, installed in the desk central area. The office desk is occupied by eight virtual manikins. The numerical simulation is made in a winter typical day. This numerical study considers a coupling of a differential numerical model and an integral numerical model. The differential numerical model simulates the Computational Fluids Dynamics (CFD), evaluates the air velocity, air temperature, turbulence intensity and carbon dioxide concentration and calculates the indoor air quality. The integral numerical model simulates the Multi-Node Human Thermo-physiology Model, evaluates the tissue, blood and clothing temperatures distribution and calculates the thermal comfort level. The HVAC system, based on a DSF system, is built using three DSF unities, is equipped with internal venetian blinds. Each one, installed in a virtual chamber, is turned to south. The personalized ventilation system, made with eight upper and eight lower air terminal devices, is installed in the desk central area. On each table top two upper and two lower air terminal devices are considered in the left and right manikin area, while on each side of the table two upper and two lower air terminal devices are placed between the manikins. The office desk is occupied by eight virtual manikins, one sitting on each table top and three sitting on each side of the meeting table. In this numerical study, carried out in winter conditions, the occupants’ clothing level is 1 clo. In these situations a typical activity level of 1.2 met is considered. The evolution of indoor environmental conditions, in the DSF and in the office room, are calculated during a full winter typical day. The thermal comfort, the indoor air quality, the effectiveness for heat removal, the effectiveness for contaminant removal and the Air Distribution Index (ADI), are evaluated. In accordance with the obtained results the thermal comfort levels increase when the air renovation rate increases and the indoor air quality level increases when the air renovation rate increases. However, the ADI is quite constant when the inlet airflow rate increases, because the thermal comfort number decreases when the inlet airflow rate increases and the air quality number increases when the inlet airflow rate increases.

Use of a Vortex Whistle for Measures of Respiratory Capacity

A vortex whistle produces a tone which has a frequency proportional to the inlet air flow rate. The objectives of this study were to replicate previous studies demonstrating the use of a vortex whistle as an accurate flow meter, and to assess the degree of relationship between measures of vital capacity (VC) obtained using low-cost methods (vortex whistle and hand-held spirometry) vs. pneumotach-based spirometry. A vortex whistle was designed using 3D modeling software and manufactured using a 3D printer with non-toxic, biodegradable polylactic acid (PLA). The digitized vortex whistle tone was analyzed using custom software to produce a frequency vs. time contour. As the frequency is proportional to flow, the integral of this curve corresponds to the overall volume by a linear relationship. The accuracy of vortex whistle volume estimates were assessed using (1) controlled flow rates from a consistent volume calibration syringe, and (2) with 66 subjects between the ages of 18-30 yrs. in comparison to hand-held spirometry and two pneumotach systems. Observations from the calibration syringe experiment confirmed that the vortex whistle and software are able to effectively track the flow rate, with a correlation coefficient between the average flow and the average frequency of r2=0.9965. Results from the human VC testing showed that measures obtained using both vortex whistles and hand-held spirometry correlated very strongly (r>0.94) with computerized pneumotach systems, and the strength of correlations obtained via vortex whistles vs. hand-held spirometry were highly comparable. When coupled with the analysis software described herein, valid and reliable frequency/flow curves and volume estimates may be obtained using a vortex whistle that are highly comparable to the hand-held spirometer. The use of the vortex whistle has the potential to bring measures of basic respiratory function to clinicians and patients alike at a fraction of the cost of currently used spirometric methods.

Numerical investigation of airflow and heat transfer characteristics and optimal design of the American ginseng drying room

The airflow and heat transfer characteristics in drying rooms have significant effects on drying behavior and product quality. Therefore, inhomogeneity has been a research hot spot in the drying industry. However, the key factors influencing the inhomogeneities of both velocity and temperature distributions are still not fully revealed. The proposed relevant optimizations are based only on the temperature distribution inhomogeneity, without considering the velocity distribution. Moreover, literature focusing on American ginseng drying is rare. In this study, we performed a numerical simulation and proposed an optimal design for an American ginseng drying room. For this purpose, a mathematical model for the airflow and heat transfer in a ginseng drying room is proposed and validated using experimental data. The inhomogeneity characteristics of the airflow and temperature distributions are investigated, and the optimal parameters for a ginseng drying room are determined based on the inhomogeneity coefficients. The results show that the inhomogeneous distributions of the airflow and temperature in the drying room are mainly influenced by the inlet airflow rate, inlet diameter, and number of partition boards with stacked ginseng. By optimizing the above three parameters, the inhomogeneity coefficients of the airflow and temperature distributions in the American ginseng drying room used in this study can be reduced by 13.67% and 11.76%, respectively. This research not only helps to deepen the understanding of the airflow and heat transfer characteristics and optimize the American ginseng drying room, but also provides useful insights for the investigation and optimization of the conditions in the other drying industries.

Exergy and economic analyses of nanoparticle-enriched phase change material in an air heat exchanger for cooling of residential buildings

This paper studies the energy, exergy, and economic analyses of phase change material (PCM)-air heat exchangers filled with SiO2 based Nano-PCM of RT25 on enabling storage of night-time free-cooling from outdoor air or indoor air during off-peak hours, numerically. The stored cooling is subsequently utilized during a day-time or peak hours as auxiliary cooling, resulting in a reduction of the day-time refrigeration requirements. A computer model for seven days from June 22 to June 28 has been created using ANSYS FLUENT 18.2, to simulate the operation of PCM-air heat exchanger for domestic application. The setpoint temperature is considered at 23–25 °C, 23–26 °C, 24–25 °C, and 25–25 °C. The inlet airflow rate is varied between 2.5 m/s and 7.5 m/s. The PCM-air heat exchanger system is studied by varying the PCM thickness (10, 20, and 30 mm) and slab length (250, 500, and 750 mm). The nanoparticles volume fraction is from 0 to 5%. The maximum cooling power, exergy efficiency, and exergy destruction increase for the nanoparticles volume fraction of 5% is 9.4%, 4.1%, and 6.3%, respectively. To obtain the best balance between the exergy destruction cost rate and the capital cost rate, the exergoeconomic factor is defined for different cases.

Synergy analysis on the heat dissipation performance of a battery pack under air cooling

Li-ion batteries are widely used for battery electric vehicles (BEV) and hybrid electric vehicles (HEV) due to their high energy and power density. A battery thermal management system is crucial to improve the performance, lifetime, and safety of Li-ion batteries. The research on the heat dissipation performance of the battery pack is the current research hotspot in the electric vehicle industry. In this paper, battery modules and battery pack are simplified to heat source and semi-closed chamber, respectively. The field synergy principle and CFD technology were used to make a synergy analysis on its heat dissipation performance. Thermal flow fields of different air outlet modes were considered in this paper, and the results show that the heat dissipation performance of air-cooled battery pack increases with the improvement of the synergy degree between velocity field and temperature gradient field. Compared with other air outlet modes, the upper air outlet mode has the best cooling effect, when the inlet air flow rate is 0.444 m/s, the maximum temperature rise and the maximum temperature difference of heat source can be controlled at 7.01 °C and 3.08 °C.

Ammonia recovery from food waste digestate using solar heat-assisted stripping-absorption

The highest costs of stripping-absorption processes for ammonia recovery are related to energy (for heating and air supply) and chemical addition (for pH adjustment). In this paper, a simplified system that used no chemicals, and a renewable source of energy for heating, was tested to recover nitrogen as ammonium sulfate from food waste digestate. pH adjustment was achieved by CO2 stripping, and vacuum tube solar collectors were used to provide heating. The effect of different temperatures (25 °C and 45 °C) and gas to liquid ratios (1700 and 2600) on ammonia removal and recovery were assessed. Ammonia removal efficiencies higher than 91% were achieved for all evaluated experimental conditions. The solar heater showed adequate capacity to increase the temperature of the liquid digestate by 21 °C and maintain the temperature at 45 °C throughout the experiment. Tests carried out at 45 °C achieved the highest ammonia removal efficiency (98%) at the lowest evaluated G/L ratio (1700). Better absorption efficiencies could potentially have been achieved if lower inlet airflow rates and packing material had been used in the absorption column.

Response of lean premixed swirl tubular flame to acoustic perturbations

This study experimentally examined the response of a lean premixed methane/air swirl tubular flame to the longitudinal acoustic perturbations. Experiments were conducted by varying the acoustic frequency (f0), acoustic power (P0) and inlet air flow rate (QA) to systematically study the acoustic-excited flame dynamics, including the flame stability, flame structure, heat release rate and acoustic pressure fluctuations. The results demonstrated that the lean tubular flame was much sensitive to longitudinal perturbations below 210 Hz. Even at low power of P0, the flame was forced to oscillate intensively when the perturbation was operated in two discontinuous frequency ranges of f0 = 150–200 and f0 = 50–100 Hz, while a weakened oscillation regime was observed in the middle range of f0 = 100–150 Hz; a lower frequency (less than 50 Hz) would extinguish the flame. An increase in P0 intensified the flame oscillation under the perturbations of 50–100 Hz, and even resulted in flame lift-off and blow off with f0 between 150 and 200 Hz. In comparison to f0 and P0, the effects of air flow rate (QA) seemed to be weaker. The proper orthogonal decomposition (POD) analysis was performed to interpret the contributions from the mean mode and fluctuating axial and circumferential modes that led to combustion instability. It was found that as the energy fraction of the axial mode exceeded 5.0%, the flame lift-off appeared in the lean swirl tubular configuration.

Simulation of the Drying Process of Polysaccharide Extract Solution in a Spray Dryer

The drying process of droplets into particles on a spray dryer is influenced by several factors, including the temperature and the flow rate of inlet air as a carrier gas and a drying media. The effects of temperature of the inlet air in the spray dryer system was elucidated in this study. A solution containing 35 w% polysaccharide extract and water as the solvent was injected into a spray dryer. The inlet air temperatures were varied at 135, 170, and 200 °C with 3 L/min. The geometry of spray dryer consisted of the tubular-conical with a length of 48.8 cm and 15.2 cm diameter cylinder. The spray dryer unit was simulated using CFD code, Fluent Ansys R15.0 with the second phase of droplets/particles was modelled by the Lagrangian discrete phase model (DPM). The inlet air temperature also affected the size of the particles. The increase of the air temperature led to the increase of the average particle diameter leaving the chamber with the smaller standard deviation. The air flow rate affected the particle size. The higher the air flow rate, the smaller the size of the average diameter of the particles and smaller standard deviation would be. The evaporation rate increased with the increase of the flow rate and inlet air temperature. The resulting particles had an average size of 1.28∼1.9 μm diameter to drying with hot air that flowed continuously. The simulation result was validated by the experimental work with discrepancy less than 20%.

Simulation, equipment performance evaluation and sensitivity analysis as a comprehensive parametric study of sulfur recovery unit

AbstractThe sulfur recovery unit based on modified Claus process with split flow was simulated, so that the validation results showed satisfactory agreement with the refinery data. In this study, comprehensive investigation was carried out on various parameters of the unit. Concentration changes of compounds were investigated as the process stream passes along various equipment. Composite curves were generated, and the minimum approach temperature was calculated as one of the operational parameters of heat exchangers. Fluid condensation probability was investigated in catalytic reactors. The recovery of sulfur and the amount of sulfur production were calculated by process streams passing along catalytic reactors and condensers respectively. The most influential performance parameters including the fuel flow rate, combustion air flow rate, and bypasses fraction were considered as sensitivity analysis parameters, and their variation influences were investigated on the recovery of sulfur, the ratio of hydrogen sulfide to sulfur dioxide, the amount of produced steam, and the furnace outlet stream temperature. The optimal amounts for fuel flow rate and inlet air flow rate were calculated with the values of 0 and 202 mol/s, respectively, and according to the results, 15% of the mainstream flow rate gives the optimum amount of bypass fraction.

Computational studies of gas-liquid flow in a multi-branch manifold

Three-dimensional, time-dependent numerical simulations of gas-liquid flow in a multi-branch manifold (an idealised model of the header/feeder system of a CANDU nuclear reactor) were carried out using the volume of fluid approach to separate the phases and the detached eddy simulation model to simulate turbulence. Interest was focusse n the distribution of the liquid to different feeders. Numerical results for a header connected to a small number of vertical feeders were in fair agreement with in-house experimental data. The rates of change of liquid discharge following changes of inlet conditions were estimated and found to depend on feeder location. The interface between an upper region of the header that was occupied by mostly air and a lower region that was occupied by an air-water mixture was found to rise with an increase in either air or liquid inlet flow rate. Simulations were performed to quantify the effects of differences in the values of fluid properties of air-water mixtures at approximately standard atmospheric pressure and temperature from those of saturated steam-water mixtures at significantly higher pressures (up to 10 MPa) and temperatures (up to 310 °C). The liquid flow rate through a feeder that was directly below the header inlet was found to decrease markedly with increasing mixture pressure and temperature. Pilot simulations of air-water flows in a header connected to multiple feeders with inlets at different elevations and orientations revealed that, under certain conditions, some of these feeders discharged little liquid.

Study of the performance of double pass solar air heater of a new designed absorber: An experimental work

An experimental study on the performance of double pass Solar Air Heater (SAH) having a new designed absorber is performed. The new SAH absorber is constructed from conductive aluminum tubes adjacent to each other and installed in the same direction of the air flowing inside the SAH. The new SAH performance (called Tubular Solar Air Heater (TSAH)) is studied at various mass flow rates of air inside the SAH. Moreover, it is compared with the performance of Flat plate Solar Air Heater (FSAH) having the same dimensions and materials of the TSAH except the absorber design. Findings indicate that the TSAH has higher outlet air temperature, efficiency and net energy gain and lower top heat loss compared to FSAH. TSAH achieves maximum air temperature rise more than 6 °C compared to FSAH at 0.025 kg/s. TSAH efficiency is greater than FSAH efficiency by about 19.4%, 21%, and 40.3%, at inlet air flow rate of 0.075 kg/s, 0.05 kg/s and 0.025 kg/s, respectively. The outlet air temperature and top thermal energy loss of the TSAH decrease with increasing the air mass flow rate, while its efficiency, energy output, and pressure drop increase. Moreover, TSAH efficiency in case of double air pass is greater than single air pass. Despite the TSAH pressure drop is greater than FSAH pressure drop, but its value is very small to impact the TSAH net thermal energy gain. The designed TSAH performance is found greater than the performance of FSAH and previous designs of published SAHs.

Effects of spherical adsorbent fluidization and self-rotation on removal of VOCs in a cyclonic fluidized bed

A fluidized bed has the advantages of treating large flows, intensifying mass and heat transfer, and lowering costs. This study proposed a cyclonic fluidized bed packed with spherical activated carbon adsorbents for volatile organic compounds adsorption. The fluidization and self-rotation of the AC particles in a 25mm cyclonic fluidized bed were studied with high-speed camera testing technology. The effects of the particle movement on the adsorption efficiency of toluene were also tested. The results show that most of the particles at the inlet side of the cyclonic fluidized bed were moving up when the inlet airflow rate was greater than 2.0m3/h. The particles began to move in clusters when the relative packing height increased to a critical value of 0.57. Increasing the gas flow rate and the diameter and height of the core column will increase the self-rotation speed of the total particles. The maximum self-rotation speed of spherical adsorbents reached 1700rad/s at the inlet flow rate of 2.5m3/h. In the case of the same axial velocity of the gas phase in the upper space of the core column, increasing the particle self-rotation speed can slightly improve the adsorption efficiency. The maximum adsorption efficiency reached 99% when the inlet flow rate is 1.0m3/h with relative packing height 0.65.

Thermal Performance and Energy Saving Analysis of Indoor Air–Water Heat Exchanger Based on Micro Heat Pipe Array for Data Center

According to the temperature regulations and high energy consumption of air conditioning (AC) system in data centers (DCs), natural cold energy becomes the focus of energy saving in data center in winter and transition season. A new type of air–water heat exchanger (AWHE) for the indoor side of DCs was designed to use natural cold energy in order to reduce the power consumption of AC. The AWHE applied micro-heat pipe arrays (MHPAs) with serrated fins on its surface to enhance heat transfer. The performance of MHPA-AWHE for different inlet water temperatures, water and air flow rates was investigated, respectively. The results showed that the maximum efficiency of the heat exchanger was 81.4% by using the effectiveness number of transfer units (ε-NTU) method. When the max air flow rate was 3000 m3/h and the water inlet temperature was 5 °C, the maximum heat transfer rate was 9.29 kW. The maximum pressure drop of the air side and water side were 339.8 Pa and 8.86 kPa, respectively. The comprehensive evaluation index j/f1/2 of the MHPA-AWHE increased by 10.8% compared to the plate–fin heat exchanger with louvered fins. The energy saving characteristics of an example DCs in Beijing was analyzed, and when the air flow rate was 2500 m3/h and the number of MHPA-AWHE modules was five, the minimum payback period of the MHPA-AWHE system was 2.3 years, which was the shortest and the most economical recorded. The maximum comprehensive energy efficiency ratio (EER) of the system after the transformation was 21.8, the electric power reduced by 28.3% compared to the system before the transformation, and the control strategy was carried out. The comprehensive performance provides a reference for MHPA-AWHE application in data centers.

An integrated system for ammonia production from renewable hydrogen: A case study

This study presents an analysis and assessment study of an integrated system which consists of cryogenic air separation unit, polymer electrolyte membrane electrolyzer and reactor to produce ammonia for a selected case study application in Istanbul, Turkey. A thermodynamic analysis of the proposed system illustrates that electricity consumption of PEM electrolyzer is 3410 kW while 585.4 kW heat is released from ammonia reactor. The maximum energy and exergy efficiencies of the ammonia production system which are observed at daily average irradiance of 200 W/m2 are found as 26.08% and 30.17%, respectively. The parametric works are utilized to find out the impacts of inlet air conditions and solar radiation intensity on system performance. An increase in the solar radiation intensity results in a decrease of the efficiencies due to higher potential of solar influx. Moreover, the mass flow rate of inlet air has a substantial effect on ammonia production concerning the variation of generated nitrogen. The system has a capacity of 0.22 kg/s ammonia production which is synthesized by 0.04 kg/s H2 from PEM electrolyzer and 0.18 kg/s N2 from a cryogenic air separation unit. The highest exergy destruction rate belongs to PEM electrolyzer as 736.2 kW while the lowest destruction rate is calculated as 3.4 kW for the separation column.

Natural convection energy recovery loop analysis, part I: energy and exergy studies by varying inlet air flow rate

The natural convection energy recovery loop is analyzed experimentally in different airflow rates. The system was introduced previously as a prototype of the standalone air conditioning system and its transient and steady performance was verified. As a new generation of energy recovery tool between the building return and fresh air, the system is rated from the viewpoints of energy and exergy. Different forms of effectiveness and 2nd law efficiency are studied and their values extracted for inlet airflow rates of 2–6 m3/h. The results show that the prominent factor that controls the system behavior is the concentration ratio from which the solution free- motion originated. The maximum sensible, latent, and total effectiveness of the system are 0.23, 062, and 0.54 respectively and are for the airflow rate of 2m3/h. It is confirmed that the number of a transfer unit (NTU) and capacity ratio (Cr*) are not independent and are varied oppositely to each other. By increasing the airflow rate, the mass flow rate and heat capacity rate of desiccant solution increase more than that of air streams. For flow rates less than 3.5m3/h, external heat transfer is just enough to induce natural motion of desiccant and in this way the loop performance is similar to a forced convection energy transfer loop which exchanges heat and moisture only between the air streams.