Volumetric Air Flow Rate Research Articles

Performance characteristics of desiccant rotor using metal organic framework material

A desiccant rotor is often adopted for dehumidification applications, owing to the increased importance of humidity control and energy saving in air conditioning and ventilation systems for buildings. In previous studies, silica gel, zeolite, and silica composites have been widely used in the desiccant rotor. However, it is difficult to further improve the dehumidification performance of a conventional desiccant rotor, owing to the inherent limitations of the desiccant material. In this study, a desiccant rotor using a metal organic framework (MOF) material was proposed and manufactured to improve the dehumidification performance under various operating conditions. The dehumidification and regeneration performance of the MOF desiccant rotor were measured and analyzed by varying the temperature, humidity, volumetric flow rate of the process air, and temperature of the regeneration air. Furthermore, the performance of the MOF desiccant rotor was compared to that of a conventional silica composite desiccant rotor. The MOF desiccant rotor showed 53% lower sensible energy ratio and 139% higher specific moisture removal capacity than the conventional desiccant rotor. In addition, empirical correlations were developed for performance predictions for the MOF desiccant rotor.

Machine learning model for predicting blast fume dilution time in underground working areas

ABSTRACT In underground mines, accurate prediction of dilution time is crucial to protect miners from toxic fumes as well as minimize production delays and ventilation costs. Previous researchers have used empirical equations, mine ventilation software, and computational fluid dynamics to calculate dilution time. These traditional methods have high computational cost and design limitations. In this research, machine learning (ML) techniques and data analytics were used to: (i) develop a ML model to predict dilution time based on five on-site blasting and auxiliary ventilation parameters and (ii) determine the order of importance of these parameters. The advantages of using the ML model over the traditional methods are its ability to consider a large number of factors, detect complex nonlinear relationships, and predict the dilution time near-instantaneously. Results show that the normalized artificial neural network has the best prediction capability with an R 2 of 0.987. Among the blasting and ventilation parameters measured, air volumetric flow rate significantly affected the dilution time, followed by duct distance from face and the amount of explosive.

The impacts of surface roughness on Indoor aerodynamics of virus-laden particles: The case of contact, deposition, and resuspension

The increasing prevalence and high morbidity of the SARS-CoV-2 virus during the COVID-19 pandemic drew widespread global attention. Surface contact is among the most common ways for the infection to spread within people, especially in buildings and the built environment. The roughness characteristics of finishing materials used in buildings vary, affecting the surface's ability to deposit and resuspend any particles that come into contact with these interfaces. Resuspension of particles indoors may increase the risk of consequent exposure through inhalation. However, little is known about surface roughness characteristics' role in airborne transmission of virus-laden particles in building indoor environments. The study examines the impact of surface roughness characteristics on the airborne transmission of the SARS-CoV-2 virus, considering indoor aerodynamic forces and their influence on particle contact with surfaces, deposition, and resuspension. The study applies Ansys Fluent CFD simulation tools to investigate the effect of volumetric flow rates and air velocity on concentration, deposition, and resuspension. The study also employs an empirical model to estimate surface roughness characteristics' impacts on particle resuspension rate. The results indicate that particle concentration and deposition rates indoors increase with increasing volumetric airflow rates. The particle resuspension rates also decreased with the increasing surface roughness of indoor surface materials. The highest resuspension rate recorded was 3.3 x 10-6, and the lowest was 1.6 x 10-6 s-1. Therefore, the outcome provides information on the implications of surface material selection and its effects on indoor air quality, health, and virus transmission. The study will offer valuable information for building engineering and design professionals in combating airborne disease transmission due to indoor surface characteristics.

Design of aeration systems in light weight barns

The article considers design options for light-aeration lamps used in “cold” barns. Calculations were made of volumetric airflow rates through an open-type light-aeration ridge at different heights of inlet openings, the results of which are presented in the article.
 Keywords: aeration; barn; natural ventilation; microclimate; air exchange.

A foam column system harvesting freshwater algae for biodiesel production: An experiment and process model evaluations

The purpose of this study was to examine the application of the mathematical model of drift flux to the experimental results of the effect of cationic trimethyl-ammonium bromide (CTAB)-aided continuous foam flotation harvesting on the lipid content in Chlorella vulgaris microalgae. An experiment was conducted to determine the effect of the operating conditions on the enrichment factor (EF) and percentage recovery efficiency (%RE), where the flow rates at the inlet and bottom outlet remained constant. Data for the binary system (without algae) and ternary system (with algae) in an equal-area foam column show that the EF decreases linearly with increasing initial CTAB concentrations ranging from 30 to 75 mg/L for three levels of the studied air volumetric flow rate range (1–3) L/min. The percentage harvesting efficiency increased with increasing initial CTAB concentration and air volumetric flow rate to 96 % in the binary systems and 94 % in the ternary systems. However, in the foam column with the riser used in the three systems, a lower volume of liquid foam in the upward outlet stream resulted in a lower RE% than that of the column without the riser. The objective function of EF for the system with algae increased when the initial CTAB concentration was increased from 30 to 45 mg/L in the foam column with a riser for all air flow rates, and after 45 mg/L, a sudden drop in the microalgae EF was observed. In the comparison between the foam column with and without the riser for the system with algae, the optimum EF was 145 for the design of the column with the riser and 139 for the column without the riser.

Pressure Drop in Horizontal Two-Phase Flow

In an artificial environment, the most important key in the process equipment design is determining gas-liquid two-phase flow frictional pressure drop of pipes. To achieve this, an experimental investigation was carried out in this study to analyze the pressure drops of air-water two-phase flow in a 30mm internal diameter horizontal pipe with a length of 6m at different flow conditions. The study was carried out at 20Co using tap water and air. To cover the slug flow pattern, the volumetric flow rate of water varied from 30 to 80 LPM, and the volumetric flow rate of air from 40 to 200 LPM. Pressure transmitters were used to measure pressure at four different points along the test section, each 2m apart. The results of the experiments were compared to 8 models using 3 distinct methods: Mean Absolute Percentage Error (MAPE), Relative Performance Factor (RPF), and the percentage of data included in the range of the 30% error band. All methods produced similar results, with the Sun-Mishima model being the most accurate.

Experimental and numerical study of dew-point indirect evaporative coolers to optimize performance and design

Dew-point indirect evaporative coolers (DIEC) allow to significantly reduce air temperature from supply air flow and require a low energy consumption, so they could be an interesting alternative to conventional air-cooling system. In the present work, the optimal geometric design and the optimal operational parameters of DIEC systems to achieve cooling conditions and comply with the European ventilation regulations were determined. Hence, the experimental energy performance of a DIEC under different inlet air conditions was studied, and a detailed DIEC model based on the ε-NTU method was developed and validated. The experimental results showed very high DIEC dew-point effectiveness values, up to 0.87. Additionally, the numerical results obtained with the detailed DIEC model were in very good agreement with the experimental results, so this model can be adequately used to analyse and optimise DIEC systems. The optimal geometric designs and operational parameters of the DIEC systems depended on the type of space to be conditioned and the ventilation category. The maximum COP values were always obtained for low values of volumetric air flow rate, 50.26 for an office application, 44.19 for the restaurant application and 37.14 for the auditorium application. However, the highest compactness of the DIEC designs were achieved for medium and high values of volumetric air flow rate ratio, between 0.45 and 0.8. The results obtained could significantly help to achieve the objectives of sustainable cooling and ventilation of spaces in the frame of Nearly Zero Energy Buildings.

Influence of Measurement Methodologies for the Volumetric Air Flow Rate of Mobile Positive Pressure Fans on Drive Unit Performance

Since there are no legally defined testing requirements for mobile positive pressure fans, they may be tested based on methods that do not correspond to their actual operating conditions. Adequate assessment of the technical and operating conditions for this type of equipment is particularly important for equipment used in rescue operations. Such units should be characterized by efficient and reliable operation. This article investigates the influence of measurement methods of the volumetric airflow rate on the performance of a power unit. The article shows that the applied measurement method, whether it is PN-EN ISO 5801 (test conditions in a pipe duct—Method A) or other methods, i.e., ANSI/AMCA 240-15 and testing of the characteristics of the velocity profile (tests in open flow—Method B), can cause differences in the power demand of fans of from 3.2% to 4.5%. The differences in the requirements of propulsion power translate into fuel consumption and emissions of harmful exhaust gases generated by the combustion drive units (4 kW). It was also observed that fans with conventional impellers (W1) show a lower power demand when applying Method B (open flow) tests, while fans with turbo impellers (W2) show a lower power demand when Method A (duct) tests are applied. Comparative analysis of the parameters of the drive unit in the test group of fans without taking into account the measurement method can cause errors of up to about 7.7%, 6.4%, and 2.4% for the power, torque, and speed, respectively.

Evaluation of Clinical and Instrumental Results of Lung Examination in Patients with Diabetes Mellitus, Coronary Artery Disease, and Obesity

BACKGROUND: There are a large number of works devoted to the study of the state of the bronchopulmonary system in diabetes mellitus in the literature in the last 20 years. However, these studies are often conflicting. Some researchers identify a deterioration in the function of external respiration and a connection with metabolic changes and complications of the disease, others associate it with vascular pathology. There are a number of reports of increased pulmonary ventilation in diabetes.
 AIM: To assess the structural and functional state of the lungs in patients with diabetes mellitus and in combination with coronary heart disease and obesity.
 METHODS: 395 patients with type 1 and type 2 diabetes mellitus were under observation. The diagnosis of diabetes mellitus was verified in accordance with International Programs and was based on WHO criteria. The glycemic level of patients was determined using a One Touch® basic glucometer (Johnson&Johnson, USA). The degree of carbohydrate metabolism compensation was assessed by the level of glycated hemoglobin (HbA1c), determined using a laboratory analyzer DCA-2000 MT (BAYER, Germany). The concentration of C-peptide in the blood serum was determined by the method of immunoluminometric analysis "Immunotech" (Czech Republic). Caro and HOMA-IR indices were calculated to identify and assess the insulin resistance (IR). The indices of hormone metabolism were determined by ELISA using DSL kits (USA) with subsequent measurement of optical density on a Spectra Classic reader from Tecan (Austria): corticotropic hormone (CTG), adrenaline, noradrenaline, cortisol, free hydrocortisone; 17-ketosteroids, 17-oxycorticosteroids, glucogone, insulin, somatotropic hormone (STH); thyroid stimulating hormone (TSH); thyroxine (T4); thyroxine (T3).
 Instrumental-functional and radiation research methods:
 X-ray methods for lungs examining, computer spirography, fibrobronchoscopy of the bronchi was performed in all patients. Morphological changes were assessed using histological and morphometric methods.
 
 RESULTS: Pathogenetic mechanisms of the bronchopulmonary system disorders in patients with type 1 diabetes mellitus are associated with a decrease in the function of external respiration due to the volumetric air flow rates of the predominantly central airways and an increase in bronchial resistance. Alveolar hypoventilation of a restrictive type with impaired diffusion of gases through the alveolar-capillary membrane was detected in patients with type 2 diabetes mellitus. Restrictive and obstructive type disorders with impaired ventilation-perfusion ratios and pulmonary blood flow are formed in patients with type 2 diabetes mellitus combined with coronary artery disease and obesity.
 
 CONCLUSION:
 
 A decrease in the function of external respiration due to the central respiratory tract and an increase in bronchial resistance were noted in 38.4% of patients with type 1 diabetes mellitus. Restrictive alveolar hypoventilation was registered in 23.3% of patients with type 2 diabetes mellitus, catarrhal endobronchitis – in 21.31% of patients with type 2 diabetes mellitus.
 Damage and fibrosis of the alveolar tissue, damage to the endothelium and disorganization of the connective tissue of the lungs were characteristic of microscopic examination of the ultrastructure of the lungs in patients with diabetes mellitus.

Analysis of a Wind-Driven Air Compression System Utilising Underwater Compressed Air Energy Storage

The increasing push for renewable penetration into electricity grids will inevitably lead to an increased requirement for grid-scale energy storage at multiple time scales. It will, necessarily, lead to a higher proportion of the total energy consumed having been passed through storage. Offshore wind is a key technology for renewable penetration, and the co-location of energy storage with this wind power provides significant benefits. A novel generation-integrated energy storage system is described here in the form of a wind-driven air compressor feeding underwater compressed air energy storage. A direct drive compressor would require very high intake swept volumes. To overcome this difficulty, some prior compression is introduced. This paper discusses the constituent technologies for this concept, as well as the various configurations that it might take and the logic behind operating it. Special consideration has been given to the differences resulting from utilising a near-isothermal wind-driven compressor versus a near-adiabatic one. Multiple iterations of the system have been simulated. This has been done using a price-matching algorithm to optimise the system operation and using volumetric air flow rates to calculate exergy flow. Simulated operation has been performed for a year of real wind and electricity price data. This work has been performed in order to clarify the relationships between several key parameters in the system, including pressure and work ratios, volumetric flowrates, storage costs and profit rates. An additional objective of this paper was to determine whether the system has the potential for economic viability in some future energy grid, especially when compared with alternative wind and energy storage solutions. The results of the simulation indicated that, with proper sizing, the system might perform competitively with these alternatives. Maximum one-year return on investment values of 9.8% for the isothermal case and 13% for the adiabatic case were found. These maxima were reached with ~15–20 h of output storage. In all cases, it was found that maximising the power of the wind-driven compressor compared with the initial compressor was favourable.

Visualization of the evolution of bubbles in the spray sheet discharged from the air-induction nozzle.

The air-induction nozzle greatly reduces drift potential by increasing spray droplet size compared with a standard flat-fan nozzle. The current study aims to reveal the mechanism behind the formation of large droplets through the air-induction nozzle from the aspect of bubble evolution in the spray sheet. Bubble break-up leads directly to the formation of perforations because large bubbles reach both sides of the spray sheet. The surface disturbance induced by bubble break-up modulates spray sheet thickness, which indirectly leads to the generation of perforations. Compared with the spray pressure, nozzle configuration has a more significant effect on both the volumetric flow rate of intake air and the thickness of the spray sheet. As the nozzle is changed from ID-120-01 to ID-120-05, the volumetric flow rate of intake air increases by 801.30% at a spray pressure of 0.3MPa, whereas spray sheet thickness increases by 412.50% at a radial distance of 10 mm. Bubble break-up is the main reason for the generation of perforations within an air-induction nozzle, leading to early break-up of the spray sheet and the production of large spray droplets. Bubble break-up can be effectively controlled by modifying the nozzle configuration.

Experimental evaluation and prediction model development on the heat and mass transfer characteristics of tumble drum in clothes dryers

• Heat and mass transfers of water in clothes are measured for a tumble dryer. • Heat loss in a tumble drum during drying process is investigated. • Temperature has a higher effect on heat and mass transfer than airflow rate. • Prediction models of heat, mass transfer, and heat loss are developed using ANN. An accurate heat and mass transfer model of a tumble drum has not been developed yet owing to complicated random motions of clothes in the tumble drum. In this study, heat and mass transfers of water from clothes to air, including the heat loss in the tumble drum of a clothes dryer, are measured with the temperature, humidity, airflow rate, and water content of clothes. The mass transfer rate increases as the air temperature, airflow rate, and water content of clothes increase; however, it decreases with an increase in the relative air humidity. The mass transfer rate enhancement is dominated by the increase in the temperature over the airflow rate; the increased temperature from 40 ℃ to 80 ℃ results in an increase in the mass transfer rate of 196%–238%, and the increased volumetric airflow rate from 2.5 CMM to 3.1 CMM leads to an increase in the mass transfer rate of 21%–23%. The heat loss in a tumble drum increases as the air temperature increases and continues to increase as the relative air humidity and water content of clothes decrease. Furthermore, although the heat loss is linearly proportional to the difference between the temperatures of ambient air and clothes, it has an insignificant relationship with the airflow rate. In addition, the prediction models of heat and mass transfers of water and heat loss in the tumble drum are developed using artificial neural network, exhibiting optimal agreements with the measured data. The developed prediction models can be used to optimize the tumble drum dryer, considering energy efficiency and short drying time.

Utilization of Spiked Pepper (Piper aduncum L.) as Feedstock for Gasification

The massive spread and growth of invasive alien plant species (IAPS) such as Piper aduncum L. (PA) endanger the natural ecosystem. Utilizing their woody biomass as feedstock through gasification to produce renewable energy can reduce risk and provide better incentives to rural communities. Heating value (HV), fixed carbon (FC), volatile combustible matter (VCM), and ash content were used to compare PA with five other tree species – namely, Calliandra calothyrsus L. (CC), Gliricidium sepium L. (GS), Broussonetia papyrifera L. (BP), Eucalyptus marginata L. (EM), and Eucalyptus urophylla L. (EU) – as fuel for gasification. The effects of particle size (ps), air volumetric flow rate (υair), and carbonization and their interactions to cold gas efficiency (CGE), producer gas flow rate (υsyngas), and specific gasification rate (SGR) were also studied. The economics and environmental impact of spiked pepper as feedstock were evaluated by hypothetically putting up a 100 kWe gasification plant in the Upper Bauyan Watershed serving 138 households. With an electrical efficiency of 17.1%, the plant would need 990 tons of PA. Feedstock supply would be adequate even after 20 yr of operation since biomass growth rate would be faster than consumption rate. The computed carbon dioxide (CO2) emissions annually for harvesting was 9.72 tons (shelterwood method) – 781.11 tons for gasification and electrical production against direct combustion, which theoretically emits 1,729.73 tons annually. Financial analysis indicated a profitable investment with a positive net present value of PHP 6,240,257.08 or USD 122,358 (USD 1 = PHP 51), IRR of 12%, payback period of 6.97 yr, and levelized cost of electricity (LCOE) of PHP 8.90 (USD 0.17). Overall, the study indicates the economic feasibility and ecological soundness of utilizing PA as feedstock provided that silvicultural management is applied in replanting indigenous trees in eradicated lands. This method can also be effective in restoring the landscape of affected watersheds.

Experimental investigation of a new combined refrigeration system

In this paper, experimental study has been performed to investigate the performance of a new combined cooling system (CCS) included indirect evaporative cooler and 4-bed solar adsorption cooling system. Solar adsorption cooling system acted as pre-cooling for the CCS. in this study, two mass flow rates passing from evaporator of 0.1 and 0.15 kg s−1, and also three volumetric air flow rates passing from indirect evaporative cooler of 700, 850 and 1000 m3 h−1, were investigated. Results were shown that, the highest average efficiency was 104% and obtained for minimum of mass flow passing from solar adsorption cooling system (0.1 kg s−1) and minimum of volumetric air passing from indirect evaporative coolind system (700 m3 h−1). Also, the average efficiency of combined cooling was in the range of 84–104%.

Air-Cooled Loop Thermosyphon Cooling System for High Heat Load CPUs—Part II: Experimental Results and Validation

A two-phase passive loop thermosyphon cooling system (LTS, whose design and simulation are described in a companion Part I) was prototyped and tested with R1233zd(E) and R1234ze(E) as environmentally friendly working fluids. The lightweight and compact aluminum LTS cooling system (patent Error! Reference source not found.) has a height of 66 mm and can be fit as two units side-by-side to cool two central processing units (CPUs) in 2U data center servers. The prototype operates safely for R1233zd(E) under heat loads between 100 and 700 W, air inlet temperatures from 25 °C to 30 °C, and air volumetric flow rates from 40 to 178 CFM. For this working fluid and test conditions, the junction temperature remained in the range between 35 °C and 90 °C with a minimum thermal resistance of 0.085 K/W. When operating with R1234ze(E), heat loads between 50 and 500 W, air inlet temperatures from 26 °C to 30 °C, and air volumetric flow rates from 40 to 118 CFM were tested. For this case, the junction temperature stayed between 32 °C and 92 °C with a minimum thermal resistance of 0.081 K/W. The pseudo-CPU footprint area (copper block with cartridge heaters) was 16 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , and thus, heat fluxes from 3.125 to 43.75 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Cold startup of the pseudo-CPU/LTS assembly was done and no critical instabilities were observed. Finally, a validation of JJ Cooling Innovation’s solver (considered in the companion Part 1) is presented, which showed a high accuracy to predict the performance of the LTS cooling system (mean error of 2.1 K and maximum error of 5.8 K for junction temperature).

CFD SIMULATION OF PRESSURIZATION SYSTEM IN FIRE STAIRS WTC 6 BUILDING

Pressurization system in fire stairs is required for high-rise building for safety evacuation in fire attack. This paper has highlighted on the problem of WTC 6 high-rise building with 18 floors related to safety evacuation in fire attack. In real situation, the minimum air pressure (12.5 Pa) at closed condition and minimum air velocity (1 m/s) at open door chamber in fire stairs as stated in the SNI 03-6571-2001 requirements are not fulfilled by the WTC 6 high-rise building. Therefore, a CFD (Computational Fluid Dynamics) simulation has been used to overcome the problems. The CFD results show that volumetric air flow rate of 7.24 m3/s injected to fire stairs in multiple injection system yielded pressure difference of 39.5–44.7 Pa and air velocity of 1.1–1.2 m/s. The CFD simulation implemented in real situation yields air pressure difference of 38.2 Pa in closed condition and air velocity in open door chamber of 1.16 m/s assumed to solve the problem.

Experimental and numerical evaluation of wind-driven natural ventilation of a curved roof for various wind angles

The paper experimentally and numerically investigates the capability of the semi-cylindrical curved roofs in providing natural ventilation. Extensive measurements around a 1:17 scale model of a typical room with a semi-cylindrical roof have been conducted to determine the pressure and velocity field for gaining the discharge coefficients of apertures. Besides, smoke flow visualization and three-dimensional RANS simulations have been performed to correlate the ventilation characteristics, the induced volumetric airflow rate, and the flow trajectories. The prior studies were carried out on the domed roofs, but in the present study, the focus is on the semi-cylindrical curved roofs. It is found that the natural ventilation performance of the curved roof is profoundly sensitive to the wind angle (i.e. α) so that the extreme ventilation takes place at α = 0°, while the α = 75° - 90° gives the lowest airflow rate. The dependence of the airflow rate on α is attributed to variation in the pressure difference between openings (known as the main driving force) caused by flow acceleration and flow separation. Further increase of α slightly ameliorates the airflow rate, although still not comparable with that of α = 0°. Flow visualization results reveal that the height of the curved roof is a key factor in the enhancement of recirculation flow inside the building. Finally, a comparison discloses that the semi-cylindrical curved roof is prone to enhance the natural ventilation inside buildings as much as the wind-catchers, although presumably is cheaper in terms of the structural costs.

МОДЕЛЮВАННЯ ТА ОПТИМІЗАЦІЯ ПРОЦЕСУ ОЧИЩЕННЯ ПОВІТРЯ ВІД ЗЕРНОВОГО ПИЛУ ЗАСОБАМИ ОБЧИСЛЮВАЛЬНОЇ ГІДРОГАЗОДИНАМІКИ

The article is dedicated to the development of generalized methods of calculation, modeling and optimization of the cyclones’ parameters that are used to clean the air from the grain dust. The basis of the developed methods is the usage of computational hydraulic gas dynamics, in particular the SOLIDWORKS software package and the integrated CFD-package SOLIDWORKS Flow Simulation, as well as the principles of theory of similarity and dimensions. The deposition efficiency coefficient was chosen as the optimization criterion that can be calculated as the ratio of the mass of deposited particles to the total mass of grain dust particles entering the working volume of the cyclone. By means of SOLIDWORKS, a parametrized solid model of cyclone with the necessary elements of adaptation for further study of gas-dynamic processes was created. The dependence of the deposition efficiency on various parameters that can be optimized, in particular, on the pressure at the inlet and outlet nozzles of the cyclone was studied; volumetric flow rate of air to be purified; design dimensions of the working chamber of the cyclone etc. The usage of the simulation methods allowed to obtain an extended database of optimization parameters and values of the objective function that correspond to them. The generalization of the obtained data set in the form of dimensionless criteria was enabled by the analysis of the dimensions of the quantities that affect the deposition efficiency. Using the basics of similarity theory, the type of functional dependence between similarity criteria was established. The constant parameters of the mentioned power function are determined using a two-dimensional approximation using a software package for mathematical calculations – Mathcad 15. The obtained mathematical model allows to select the optimal operating modes (volumetric air flow, inlet and outlet pressures of cyclone etc.) depending on the design and the size of the cyclone that allows to maximize the efficiency of grain dust deposition.

Improving the estimation of methodological errors in reproducing the volumetric air flow rate by reference critical nozzle

In the development of the previously obtained results a more accurate estimate of the methodological error in reproducing the volumetric air flow rate by reference critical nozzle is given, associated with the choice of the gas flow model and due to taking into account the initial kinetic energy of the flow at the nozzle inlet. Based on improved flow model an analytical evaluation of the methodological error in reproducing the volumetric air flow rate by reference critical nozzle, which is due to a change in the humidity of the working air, has been carried out. It is shown that the methodological error in reproducing the volumetric air flow rate by reference critical nozzle, associated with a change in the air humidity, as well as the analogies methodical error caused by the existence of the initial kinetic energy of the flow, must be taken part in accuracy characteristics at the real operating conditions of the standard volumetric air flow rate using critical nozzles.

Experimental investigation of a novel thermal storage solar air heater (TSSAH) based on flat micro-heat pipe arrays

A novel thermal storage solar air heater (TSSAH) is proposed in this study. This TSSAH is composed of a vacuum glass tube, flat micro-heat pipe arrays (FMHPA), and a thermal storage material (i.e., paraffin) with a phase change temperature of 58 °C. The FMHPA acts as the core heat transfer component. Considering the low heat conductivity coefficient of paraffin, louver fins are utilized to enhance heat transfer. Thermal performance is analyzed and discussed. During thermal collection, natural convection evidently contributes to enhancing heat transfer. Increasing solar radiation intensity can improve collection efficiency. Thermal collection efficiency increases from 70.22% to 77.28% when solar radiation is increased from 675 W/m2 to 835 W/m2 under an ambient temperature range of 20.8 °C–23.3 °C. A high ambient temperature results in high collection efficiency that can reach 80.59%. During thermal discharge, enhancing the air volumetric flow rate can evidently increase the amount of useful energy and shorten discharge time. From 80 m3/h to 170 m3/h, the amount of useful energy is increased from 335 W to 550 W, and discharge time is shortened from 309 min to 195 min under inlet temperatures ranging from 24.1 °C to 24.2 °C. A high inlet temperature generates a high outlet temperature but decreases the amount of useful energy. From 19.7 °C to 32.0 °C, outlet temperature is increased from 30.4 °C to 36.6 °C, and the amount of useful energy is reduced from 692 W to 287 W at an air volumetric flow rate of 200 m3/h. During thermal discharge, the average amount of useful energy can reach 692 W at an inlet temperature of 19.7 °C and an air volumetric flow rate of 200 m3/h, indicating that the proposed TSSAH can release heat quickly. In the experiment scale, the discharged heat is 6150–6450 kJ at a phase change material temperature scale of 85 °C–35 °C.