Air Volume Flow Rate Research Articles

Low‐temperature drying characteristics of mint leaves in a continuous‐dehumidified air drying system

AbstractLow‐temperature drying seems a better alternative option for drying heat labile products, especially leafy vegetables. In this article, the thin layer drying characteristics of mint leaves are studied using a continuous‐dehumidified air produced by molecular sieve 13X based heatless pressure swing adsorption (PSA) system. The PSA system consists of an air compressor with after cooler, two adsorber towers, and drying chamber. The optimum process parameters of adsorption system are identified through Box Wilson Central Composite experimental design to produce continuous‐dehumidified air suitable for low‐temperature drying applications ranging from 35 to 37°C dry bulb temperature and 0.1% rh. The performance indices of the PSA system such as thermal effectiveness and dehumidification efficiency at optimal conditions are observed as 0.884 and 96.40%, respectively. The effect of the volume flow rate of continuous‐dehumidified air on mint leaves drying characteristics is also studied, and the initial moisture content of leaves is reduced from 83.45% (wb) to less than 10% (wb) in 6 hr at the volume flow rate of 0.160 m3/min. The effective moisture diffusivity value for varied volume flow rates of air is varying from 2.07534 × 10−11 to 3.45817 × 10−11 m2/s. The ascorbic acid retention percentage in dried mint leaves is increased with increase in volume flow rate of dehumidified air, and the maximum of 70.11% is achieved at 0.160 m3/min. Based on the regression analysis, the most suitable drying model to describe the low‐temperature drying characteristics of mint leaves is the Midilli and Kucuk model. It is noted that the low‐temperature drying is the most appropriate drying method for retaining the good amount of ascorbic acid.Practical applications Highly suitable for heat‐sensitive products' drying especially medicinal herbs, spicy (leafy) vegetables. Production of continuous‐dehumidified air (with ultra‐low dew point) for sensitive applications like pharmaceutical, lithium battery manufacturing, defense, chemicals, electronics, leather, and so forth.

Experimental Study of Continuous H2/Air Rotating Detonations

ABSTRACT An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in terms of the stability, propagation characteristics, and the number of detonation waves. Absence of a stable detonation wave at low Reynolds numbers and observation of different detonation modes with increasing Reynolds number, in different ranges of equivalence ratios, have been established in this research. This paper describes the various modes of rotating detonation wave propagation in the RDC. These modes include the single-wave detonation mode, the dual-waves unidirectional detonation mode, the dual-waves colliding detonation mode, extinguishing and re-initiating detonation mode, and the deflagration mode

Research on Heat Transfer Performance of Micro-Channel Backplane Heat Pipe Air Conditioning System in Data Center

This paper deals with the heat transfer performance of a micro-channel backplane heat pipe air conditioning system. The optimal range of the filling rate of a micro-channel backplane heat pipe air conditioning system was determined in the range of 65–75%, almost free from the interference of working conditions. Then, the influence of temperature and air volume flow rate on the heat exchange system were studied. The system maximum heat exchange is 7000–8000 W, and the temperature difference between the inlet and outlet of the evaporator and the condenser is almost 0 °C. Under the optimum refrigerant filling rate, the heat transfer of the micro-channel heat pipe backplane system is approximately linear with the temperature difference between the inlet air temperature of the evaporator and the cooling distribution unit (CDU) inlet water temperature in the range of 18–28 °C. The last part compares the heat transfer characteristics of two refrigerants at different filling rates. The heat transfer, pressure, and refrigerant temperature of R134a and R22 are the same with the change of filling rate, but the heat transfer of R134a is lower than that of R22. The results are of great significance for the operational control and practical application of a backplane heat pipe system.

Studies on pneumatic transport of ice cores in reverse circulation air drilling

Reverse circulation air drilling is considered one of the most promising technologies in ice core drilling because it can provide many benefits such as avoiding air circulation loss in snow-firn zones, promoting penetration rate, and shortening the time required for ice core recovery. The key of this technology is using a pneumatic conveying system to transport ice cores and ice chips from the bottom of the borehole to the surface. Therefore, analysis of air injection parameters is important for improved understanding of drilling ice cores with reverse circulation to enhance air drilling operations. To determine the adequate volume flow rate of the gas required to satisfy the demand for pneumatic conveying of ice cores and chips, a general theoretical model was developed in this study. A series of experiments were carried out to test the actual velocity and the pressure drop required to convey ice cores and ice chips. The experimental results exhibit reasonable agreement with the calculation data, and the maximum and the minimum errors between the calculated and experimental results are about 12.55% and 0.60%, respectively. Based on the theoretical models, the air volume flow rate profiles along the borehole depth were estimated. For a borehole depth of 500 m, to convey an ice core with diameter of 90 mm and a length of 500 mm, the minimum volume flow rate and the injection pressure of air under standard atmospheric conditions is about 5.25 m3/min and 1.06 MPa, respectively, if the clearance between the ice core and the wall of the inner drill pipes is set at 4 mm.

Effects of various operating conditions on the performance of a CO2 air conditioning system for trains

This paper aims to investigate the effects of different operating parameters on the performance of a transcritical CO2 air conditioning system for trains. Similar designs of automotive CO2 air conditioning system are used in the train system such as internal heat exchanger (IHX) to improve the system efficiency. Experimental results are presented for the performance characteristics of the CO2 train air conditioning system with two independent circuits under different test conditions such as different refrigerant charge amount, compressor working frequency, indoor air volume flow rate and outdoor chamber temperature. Two different operating modes of the two circuits are also included in this research. For mode I while only one circuit is working, the test results show that the maximum cooling capacity and coefficient of performance (COP) is 24.3 kW and 2.7, during 55 Hz and 40 Hz compressor working frequency conditions respectively. Also, the cooling capacity and COP reach the minimum, 16.2 kW and 1.5, when the outdoor chamber temperature is 45 °C. For mode II while both two circuits are working, the results show that the cooling capacity and COP are 42.0 kW and 2.4, respectively. The system performance error between the test and numerical modeling which directs the design of the system is within ±5%. Furthermore, an optimum high pressure control algorithm for the transcritical CO2 cycle of the train AC system is also presented.

Influences of initial and transient combustor wall-temperature on thermoacoustic oscillations of a small-scale power generator

Thermoacoustic oscillations are usually investigated for events during which the combustor wall-temperature is constant. Here, we experimentally demonstrate the influence of the transient combustor wall-temperature on the thermoacoustic oscillations of a power generation system for both cold- and warm-start conditions. The experiments are performed for fixed fuel-air equivalence ratios and both fixed and varying volumetric air flowrates. The former is varied between 0.7 and 1.4, and the latter changes between 50 and 130 standard liters per minute. A data acquisition system was used to simultaneously acquire the mixture pressure along with the mixture, the combustor wall-, and the exhaust temperature using a differential pressure transducer and three thermocouples, respectively. Long time-period analysis of the pressure signal suggests the pressure oscillations feature three modes. The dominant frequencies of these modes increase with increasing the fuel-air equivalence ratio; however, they are nearly insensitive to the air volume flowrate. Probability density function, power spectrum density, phase-space trajectory, and the Poincaré map of the pressure oscillations were obtained for a sliding window and for both cold- and warm-start conditions. The results suggest that, for the cold-start condition, the pressure signal transitions from chaotic to limit cycle, chaotic, bursting, and then limit cycle oscillations. For warm-start conditions, however, the pressure signal features a combination of both large- and small-amplitude limit cycle oscillations. For these conditions, as the combustor wall-temperature increases, the possibility of the large-amplitude oscillations occurrence decreases, and that for the small-amplitude oscillations increases. For all tested conditions, the estimated Helmholtz and Strouhal numbers decrease with increasing the Reynolds number, suggesting that the system dynamics is dominated by neither the acoustics nor the vortex-shedding.

Fluid flow modulation in a domestic refrigerative dehumidifier with air-side gearing

Small refrigerative dehumidifiers have shown energy efficiency improvements when operating with air-side gearing. However, the geared domestic dehumidifier has not previously been investigated experimentally for a wide range of airflow settings typical of domestic dehumidifier operation, or with different throttling schemes, and the efficiency of these systems is not well understood under household conditions.In this work, we measure the performance of a commercial domestic dehumidifier, adapted for laboratory testing, in ungeared and geared modes at a wide range of airflows and with both capillary and thermostatic expansion valve throttling to understand how the system performance is effected, for air volume flow rates of 29 L/s - 48 L/s. The measurements show that both capillary and thermostatic expansion valve equipped domestic dehumidifiers can improve energy efficiency in the geared operation mode, but the capillary equipped system is more prone to frosting and wet compression, degrading performance.

Experimental research on four-stage cross flow humidification dehumidification (HDH) solar desalination system with direct contact dehumidifiers

A novel Four-stage cross flow humidification and dehumidification (HDH) solar desalination system with direct contact dehumidifiers was proposed in this paper. Firstly, the composition and operation principle of the system were introduced. Then, the heat and mass exchange models of main parts in the system were established, and some indexes to evaluate system performance were given. Next, an indoor experiment was set up and tested. Based on the experimental results, this paper analyzed the effects of seawater spraying temperature, spraying quantity and the air volume flow rate on freshwater production rate and the gain output ratio (GOR). Finally, the economic analysis and freshwater yield per unit volume of this system were discussed. The results show that when Ts1 = 83 °C, ms1 = 1.1 t/h and mc1 = 0.94 t/h, the water yields of the HDH system with 560 m2 total heat transfer area are 47 kg/h and 63 kg/h respectively under V·a = 0 m3/h and V·a = 300 m3/h. Compared with conventional systems, the current system has higher water yield per unit volume (34.1 kg/(m3·h)) and lower pure water yield cost (3.86 $/ton) when the investment cost of the whole solar desalination device with 42 m2 solar collectors is about $ 6563.

Enhancing the exergetic performance of a pilot-scale convective dryer by exhaust air recirculation

In this study, an air recirculating pilot-scale convective dryer operating at various exhaust air recycle fractions was exergetically investigated in detail. Two drying air temperatures (55–70 °C), two air volume flow rates (360–450 m3/h), and six exhaust air recycle fractions (0–100%) were considered for drying of poplar wood chips. The effects of drying variables were studied on the exergetic efficiencies of drying system and drying chamber. The total exergy of air exhausting from drying chamber was also fractionated into thermophysical and wet exergies for further evaluating the effect of recycle fraction. The universal exergetic efficiency of drying chamber ranged from 41.84% to 98.07%, while the average overall functional exergetic efficiency of drying system varied from 1.32% to 4.01%. Exhaust air recirculation profoundly improved the overall functional exergetic efficiency of drying system as a decision-making parameter up to over two times. Although the recycle fraction of 100% showed the highest improvement in the overall functional exergetic efficiency of drying system, the drying time drastically increased at this condition as expected. Overall, a compromise should be made between drying time and exergetic improvement in order to select a proper recycle fraction for recovering exergy from outflow air.

Performance of a new type of solar air collector with transparent-vacuum glass tube based on micro-heat pipe arrays

In this study, a novel solar air collector with transparent-vacuum glass tube is designed and investigated through experiment and numerical simulation. The collector consists of micro-heat pipe arrays (MHPA), selective absorption film and transparent-vacuum glass tube. The absorption film is directly pasted on the MHPA by using heat-conducting glue, which is then placed into transparent-vacuum glass tube. The efficient heat conduction of MHPA and good thermal insulation of the transparent-vacuum glass tube contribute to the high efficiency and low pressure loss of the collector. The collector average efficiency can reach 82.7% and the pressure loss is less than 20 Pa. This collector form for heating spaces and drying crops is new and effective. Increasing the air volume flow rate can considerably improve the collecting efficiency. The ambient temperature in winter results in a higher efficiency than that in summer. Furthermore, a calculation numerical model, which is used to develop 20 collecting units, is established and verified for validity. This model can obtain temperature increase in each collecting unit. Considering the temperature increase in each collecting unit and the thermal efficiency, the proposed maximum collecting unit quantity is 20. Study results provide a theoretical guidance for designing MHPA solar air collector.

왕복동식 미소 유량 공기압축기의 설계 및 성능예측 이론연구

In this theoretical study, a design and performance analysis theory of a micro flowrate and high pressure air-compressor is developed. The governing equations are from the gas state equation and fluid dynamic theories because the working fluid in the air compressor is in a gas phase. A case study was conducted to design a reciprocating type of air compressor which the target performance was 0.6liter/min in the volume flowrate with 5atg in air pressure at 1,600rpm rotational speed. Geometrical size of the model air compressor designed is 10mm in stroke, 20mm in bore with 4.79 compression ratio. From the performance analysis of the model compressor, it was found that the air volume flowrate produced was 0.6liter/min with 5.81atg in pressure. The design theory of a micro-size high-pressure air compressor developed in this study is expected to be very useful design tools in NANO technology industry.

Performance Study of Water Harvesting Unit Working Under Iraqi Conditions

The scarcity of water facing the world is one of the biggest challenges of this century. This challenge requires research plans in the field of water desalination that is not suitable for human use or the harvesting of water from the air. In this work, the performance of the water harvesting unit from the ambient air is studied. For this purpose, a vapor compression system is designed and built, a 372[Formula: see text]W reciprocating compressor is selected depending on the use of a small family consisting of four persons. The components of the vapor compression system are designed depending on the compressor power. The unit evaporator is modified to condensate the water vapor associated with the air instead of cooling the air. The effect of volume flow rate of air across the evaporator is studied. The range of air volume flow rate is from 224 to 244[Formula: see text]m3/h, as well as the operation mode of the unit which either continues to condensate or freeze the water vapor on the evaporator is also studied. The result showed that the water harvesting unit can work at a relative humidity as low as about 20%. The maximum water production for the unit is 7.9[Formula: see text]l/day with a power consumption of 1.76[Formula: see text]kW-h/l at the volume flow rate of air is 230[Formula: see text]m3/h. When an evaporative cooler is turned on in the test chamber, the amount of water production increases to about 13.11[Formula: see text]l/day with a power consumption of 1.068[Formula: see text]kW-h/l, for the same volume flow rate of air mentioned above.

Effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing

This paper studies the effect of angular misalignment on the static characteristics of rotating externally pressurized air journal bearing with four degrees of freedom (4-DOF). A clearance function is used to describe the film thickness of air journal bearings with angular misalignment along two perpendicular directions. The finite different method (FDM) and an iterative procedure are applied to solve the Reynolds equation and obtain the air film pressure distribution. Various eccentricity ratios and rotating speeds are taken into considerations for the comparisons of static performances of the air journal bearing under different tilt angles. The results show that the air film thickness, load capacity, stiffness, load moment, attitude angle and volume flow rate are affected greatly by the angular misalignment.

Generation and control of helium-filled soap bubbles for PIV

The operating regimes of an orifice-type helium-filled soap bubbles (HFSB) generator are investigated for several combinations of air, helium and soap flow rates to establish the properties of the production process and the resulting tracers. The geometrical properties of the bubbles, the production regimes and the production rates are studied with high-speed shadowgraphy. The results show that the bubble volume is directly proportional to the ratio of helium and air volume flow rates, and that the bubble production rate varies approximately linearly with the air flow rate. The bubble slip velocity is measured along the stagnation streamline ahead of a cylinder via particle image velocimetry (PIV), yielding the particle time response from which the neutral buoyancy condition for HFSB is inferred. The HFSB tracing capability approaches that of an ideal tracer (i.e., minimum slip and shortest response time) when the volume flow rate of helium is approximately one thousandfold the soap flow rate. This study provides guidelines for operating HFSB generation systems, intended for PIV experiments.Graphical abstract

Flat bed desiccant dehumidification: A predictive model for desiccant transient characterisation using a species transport model within CFD

As opposed to steady state characteristics which have been, in the past, estensively investigated, the transient dehumidification characteristics of silica gel under different flat bed configurations, has not been studied in detail with respect to varying mass and air flow rates. Such data is essential in the design of systems employing this method of dehumidification. Moreover, numerical models of the performance of flat bed desiccant configurations generally take the form of fundamental studies with explicit modelling of the desiccant particle geometries. The primary objective of this work aims is to generate dehumidification characteristics in high humidity environments. Secondly, a more simplified and practical approach is proposed here on the basis of experimental calibration. The methodology consists of two main approaches: (i) the development of a test rig for the experimental determination of the transient dehumidification characteristics and, (ii) the development of a Computational Fluid Dynamics (CFD) model using experimental data as input to provide easy extrapolation of experimental data. This paper presents detailed dehumidification results for varying air volume flow rate and desiccant mass. The numerical model, on the other hand, successfully predicts the dehumidification performance of varying silica gel masses by using only a single experimental test case. This proves the validity of using such a model to extrapolate on experimental data.

A Study on In-Cylinder Flow of Small Engine Using Steady-State Flow Benches

In-cylinder air flow structures are known to strongly impact on the performance and combustion of internal combustion engines (ICE). Therefore, the aim of this paper is to experimentally study an IC engine in-cylinder flow under steady-state conditions. Steady-state flow bench methods can be used to characterize the in-cylinder flow engine. The experiments were carried out on the small cylinder head with pressure difference across the inlet valves of 100 to 300 mmH2O. The experimental results are presented in terms of the measured air flow rate, flow coefficient and discharge coefficient. Moreover, the CFD used to illustrate the evolution of tumble motion in-cylinder engine. The results show that air volume flow rate and flow coefficient increased as the valve lift increases but the coefficient of discharge decrease if valve lift increase. The higher the pressure drop the higher the mass flow rate value. However, the higher the pressure drop the lower the value of flow coefficient and discharge coefficient.

Experimental investigation on operation parameters of 3Å molecular sieve desiccant coated total energy recovery wheel for maximum effectiveness

The object of this research study was to investigate the maximum effectiveness values of the energy wheel by experimental tests conducted under extreme difference ambient air conditions parameters, different air volume flow rates, and energy wheel rotation speeds. Air temperature and humidity experimental tests were performed using a test facility that was developed and installed into the Indoor Air Quality and Thermal Comfort Laboratory of Budapest University of Technology and Economics. Our objective was to get the effectiveness values of sorption coated air-to-air energy recovery wheel for steady-state conditions under different ambient air (as supply air inlet) conditions. It was found that the sensible effectiveness increases by decreasing the volumetric flow rate through the wheel, and the optimum values of the effectiveness were given at the maximum wheel rotation speed based on the tests. As for the latent and total effectivenesses, their characteristics show an increasing trend by decreasing the air volume flow rate, ambient air temperature and relative humidity and increasing the wheel rotation speed.

Experimental investigation on a coconut coir packed humidifier for a solar desalination plant

Desalination by humidification dehumidification processes is a promising simple, cost effective and low maintenance concept. It works on the principle of air humidification at high temperature and dehumidification at relatively low temperatures. The present study is for evaluating the performance of the humidifier with coconut coir as packing material used for air humidification in the solar humidification dehumidification (HDH) desalination plant. Experiments were carried out on the humidifier packing for different flow rates of water and its temperature. Humidifier range, effectiveness and efficiency, evaporation rate of water, heat and mass transfer rates are studied by experimentally for different flow rates of hot water and its temperature. The hot water flow rate is varied from 125 to 225 LPH with an increment of 25 LPH and water temperature from 38 to 54°C. It is found that at water flow rate of 200 LPH and at 0.55 m3/s volume flow rate of air, effectiveness of humidifier found to be maximum of 0.74.

An Investigation of Natural Convection of Air Flow through A Vertical Duct with Rectangular Cross-Section Heated from A Singled-Side.

An experimental investigation is made to study the effect of different parameters affecting the process of natural air flowing through vertical ducts. The experimental setup has been designed and installed in the Air Conditioning Laboratory, Faculty of Engineering, Mansoura University. The test rig is consisted of mainly of rectangular cross-section duct of 25 cm width with different heights and gap thicknesses. The air gap thickness ranges from 3 to 20 cm while the height is ranged from 50 to 200 cm. All duct sides are well insulated with one side heated under heat flux density ranges from 191.04 to 440.75 ⁄ . Experimental results are plotted to indicate the relation between air volume flow rate through the vertical duct and different parameters discussed, namely, gap thickness, duct height and heat flux density. Based on measured results the air volume flow rate increases with increasing both heat flux density and duct height. It is concluded also that, the air volume flow rate increases with increasing the gap thickness until it reaches maximum values, namely at gap thickness of 10 cm and then decreases with further increase in gap thickness. The results of the present study could be useful in the design and application of buoyancy-assisted natural ventilation systems.

Effects on the Ventilation of a Two-Storey Building under Different Thermal Conditions

In this paper it is shown how the air flow rate of decentralized ventilation devices can be affected by a staircase of a two-storey building under different thermal conditions. Since these devices need local fans for supplying the requested volume flow, pressure loads have a significant impact on the delivered volume flow rates. Regarding this, the study comprises two analyses: First, a CFD-model is developed to simulate the ventilation air flow through a simplified staircase. By varying parameters for rooms’ temperature and ventilation direction, the hydrostatic pressure in the staircase is evaluated. The simulations – characterized by high Archimedes numbers – are successfully validated with findings from preliminary work. In a second part, the pressure conditions inside the staircase are referred to outside conditions. Consequently, a static pressure difference at the ventilation device on each storey can be observed.We found that the deliverable volume air flow rate can decrease up to 10 % from the nominal flow rate due to temperature differences between the storeys and outside. Therefore, heat recovery and ventilation effectiveness may also be impaired.