Inlet Air Humidity Research Articles

Efficiency of cooled extended surfaces: Efficacité des surfaces augmentées refroidies

A three-dimensional analysis of the combined heat and mass transfer between a moist air turbulent flow and a cooled solid surface was carried out. A turbulent boundary layer was modelled using the Wilcox k–ω turbulence model. Numerical results for the extended surface efficiency under various psychrometric conditions were obtained by solving simultaneously coupled equations of the fluid and the solid. The results show that variations in moist air parameters have a significant effect on the extended surface efficiency. It is shown that an increase in the inlet air humidity decreases the surface efficiency.

Experimental studies and numerical simulation of evaporative cooling of air with a water spray—I. Horizontal parallel flow

Hollow cone water sprays are used in many humidifying, cooling and scrubbing applications. For predicting the heat and mass transfer in these spray-air flow systems a two-dimensional numerical model simulating the conservation of mass, momentum and energy of air, and water, were developed. Model inputs include drop size distribution and velocities at nozzle spray angle, inlet air DBT and humidity ratio. The set of conservation equations are time marched numerically and conditions at various downstream locations are computed. Experimental data were obtained on a horizontal once through wind tunnel at three air velocities with each nozzle at three pressures in parallel flow configuration. Nozzles of 3.2 and 4.8 mm outlet diameter were used. Drop diameter at break-up was measured from still photographs of the spray and these data were used in the model. Predictions of air condition at wind tunnel outlet for given input conditions agree well with experimental data.

Experimental Investigations on the Performance of a Packed Bed Dehumidifier for Various Climatic Conditions

ABSTRACT To simulate space cooling or drying systems for various geographical regions (low, moderate, and high humidity regions) a liquid desiccant system consisting of a humidifier and dehumidifier has been designed and constructed. This system consists of two coupled humidifying and dehumidifying packed columns filled with plastic Intalox Snowflake packing material. Experimental measurements of the dehumidifier performance utilizing a new effective liquid desiccant mixture (CELD) total desiccant salt content 40%wt.to 45%wt (salt comprised of equal portions by weight of lithium chloride and calcium chloride ), have. been carried out, The effect of different independent variables such as packing height, air inlet temperature and humidity ratio, and liquid desiccant inlet temperature, flow rate and concentration on the performance of the dehumidifier has been investigated. Experimental results demonstrate that the CELD is a promising desiccant for cooling and drying operations.

Influences of fuel sulfur content on diesel engine emission characteristics under varying temperature and humidity of inlet air

Abstract The influences of the sulfur content of diesel oils on the emission characteristics of a diesel engine were systematically investigated in this study. The temperature and humidity of the inlet air, engine output torque, speed were also varied accordingly. The sulfur content was ranged from 0.3 to 0.85 wt% while engine output torque from 0 to 10 kg‐m, and speed from 1000 to 2000 rpm. The intake air temperature and relative humidity were set at 20 °C & 40 °C and 50%RH & 90%RH, respectively. A four‐cylinder diesel engine with a displacement volume of 3856 cc associated with a computerized engine data acquisition system was employed to observe and measure the engine performance under varying operating conditions. The temperature and humidity of intake air were adjusted by an inlet‐air temperature / humidity conditioning system. A mechanically stirring machine was used to mix the diesel fuel oil and sulfur compound homogeneously. This study shows that the increase of the sulfur content would enhance the formation of SO2 and CO. In addition, higher temperature and humidity of the inlet air would result in considerable reduction of the NOx concentration while promotion of the CO formation.

Effects of Operational Variables on the Properties of Granules Prepared by Moisture Control Method in Tumbling Fluidized Bed Granulation.

Effects of operational variables such as liquid flow rate, inlet air temperature and inlet air humidity on the properties of granules, prepared by a tumbling fluidized bed granulation while controlling the moisture content with an IR moisture sensor, were investigated experimentally. An increase in the liquid flow rate, i.e. the increase of the droplet size resulted in a slight increase of granule size and size distribution, while little influence was found of the inlet air temperature and humidity on granule size, size distribution or the apparent density. Remarkably good reproducibility was obtained in the granules prepared by the moisture control method. It was therefore concluded that by applying this method to the wet granulation by a type of fluidized bed, the effects of external circumstances could be fully eliminated and good reproducibility maintained.

DRYING OF TOBACCO PARTICLES IN A MOBILISED BED

ABSTRACT The drying performance of a novel device capable of mobilising a bed of fibrous materials is evaluated. The drying kinetic of the vegetable product used for this work, cut lamina tobacco particles, was determined from fixed bed experiments. A falling-rate period was observed for the entire drying curve. The results showed that the drying rate is controlled by internal mass transfer mechanism for gas superficial velocities above 0.8 m/ s. The proposed model is based on an effective liquid diffusion coefficient that varies with solids temperature according to an Arrhenius-type relationship. Batch drying experiments were carried out in the mobilised bed apparatus under various conditions of inlet air temperature, humidity and flowrate. Assuming perfect mixing and no internal resistance to heat transfer for the solids, the performance of the mobile bed can be predicted using the proposed internal liquid diffusion model

SIMULATION of CANOLA and BARLEY DRYING IN A DEEP BED

ABSTRACTA mathematical model for a radial, continuous‐crossflow dryer was modified and used to simulate the drying process in a fixed bed dryer. the predictions of the adapted model were compared with experimental test results for canola drying at the following drying conditions: airflow rates of 0.4 and 0.6 kg/(m2s), inlet air humidity 0.098 and 0.0114 kg/kg of dry air, initial grain moisture content 0.221 and 0.251 kg/kg dry basis. In both tests the inlet drying air temperature was kept at an average of 67.5°C. At the end of canola drying, the mean drying air temperature predicted by our model was within 1°C of the measured temperature and the mean predicted moisture content was within 0.5% of the measured moisture content, dry basis. Also, our model was verified against experimental results for barley published by other authors and against predictions from a published model for barley. the predictions from our model were in good agreement with the published experimental and predicted data. Simulations results for canola and barley drying in the same thickness of a deep bed were compared. Simulations were conducted to investigate the effects of canola properties such as bulk density and dryinig conditions of air such as airflow rate and air humidity on drying in deep beds of canola.

Development of an air-conditioning system for greenhouses in hot and dry climates

Plant production in greenhouses in hot and dry climates needs sufficient cooling for optimal production. Conventional pad and fan cooling systems require desalinated water which limits their application. Furthermore, the horizontal ventilation causes undesirable temperature and humidity gradients in the cropped area. To overcome these disadvantages a new air-conditioning system was developed and tested in Greece and Kuwait. This system consists of an air washer, an air distribution unit, a movable thermal screen and an electronic controller. The air washer can be operated with low quality water. Effective cooling, cleaning of the inlet air and uniform temperature and humidity distribution are also points in its favour.

The Use of Dehumidifiers in Desiccant Cooling and Dehumidification Systems

The use of rotary dehumidifiers in gas-fired open-cycle desiccant cooling systems is investigated by analyzing the performance of the rotary heat exchanger–rotary dehumidifier subsystem. For a given cooling load, the required regeneration heat supply can be minimized by choosing appropriate values for the regeneration air mass flow rate and the wheel rotation speed. A map is presented showing optimal values for rotational speed and regeneration flow rate as functions of the regeneration air inlet temperature and the process air inlet humidity ratio. This regeneration temperature is further optimized as a function of the process humidity ratio. In the analysis, the control strategy adjusts the process air mass flow rate to provide the required cooling load. Additional control options are considered and the sensitivity of the regeneration heat required to the wheel speed, regeneration air mass flow rate, and inlet temperature is discussed. Experimental data reported in the literature are compared with the analytical results and indicate good agreement.

Heat Transfer Analysis in Environmental Control Using an Underground Air Tunnel

This paper presents heat transfer analysis of a passive summer cooling and winter preheating technique, which utilizes the underground temperature at a depth of 6 ft (1.83m) or more. In this study, a computer model solution has been developed for predicting the air temperature at any point, at any time while passing through the underground pipe. The air temperature is a function of the inlet air temperature and humidity, soil temperature, soil properties, the pipe (length, diameter, shape, and material), and the air flow velocity. Experiments were performed to measure air temperature, soil temperature, and pipe surface temperature at different lengths and different intervals of times. The results of the experiments are compared with theoretical calculations, which showed very good agreement. Thus the theoretical model may be used for predicting the performance of such systems in the future.

Simulation of near-ambient grain drying: I. Comparison of simulations with experimental results

Freshly harvested barley was dried in bins 2·2 m high by 1·37 m in diameter specially constructed for near-ambient drying experiments. Inlet air temperature and humidity, and air flow rate were controlled at nominally constant values typical of in-bin drying with near-ambient air. Initial moisture contents ranged from 0·22 to 0·395 (dry basis). Changes in physical parameters were recorded in some detail and product quality assessments were made. Simulation models in current use are described and the predicted and experimental results compared. The Ingram and Near-Equilibrium models gave good predictions of the drying parameters but the Ingram model used considerably more computing time. The logarithmic model was adequate, and the moisture deficit model only of use for rapid calculation.

Aqueous Film-Coating Vaporization Efficiency

A steady-state condition is achieved during most of an aqueous film-coating cycle, i.e., the rate of application of moisture to the tablet bed is equal to its rate of evaporation. A mathematical model was developed for the steady-state condition to describe the efficiency of evaporation of the aqueous solvent for any set of drying conditions (inlet air flow rate, temperature, and humidity) and spray rate of coating suspension. The model was tested utilizing a series of different coating conditions and coating compositions. A vaporization efficiency, Es, was defined as a means to assess a reproducible coating end point. Es values for each coating formula fell within a narrow range. The hydroxypropyl cellulose coating system had a significantly lower Es value due to the higher tackiness that occurs with this polymer during film formation.

Nitric Oxide Emissions From Stratified Charge Engines: Prediction and Control

Abstract A model is developed for calculating NO emissions for stratified charge engines in which the fuel is completely vaporized prior to combustion. The validity of the model is limited to single chamber geometry as it does not treat bulk gas motion typical of prechamber or divided chamber designs. The parameters of the model are fuel type, humidity of inlet air, overall equivalence ratio, stratification function, per cent EGR, intake manifold pressure, intake manifold temperature, compression ratio, piston connecting rod to crank radius ratio, RPM, and position and duration of combustion in the cycle. Stratification in which the first elements to burn are rich and the last elements to burn are lean is most effective relative to a uniform air-fuel mixture at overall air-fuel ratios near stoichiometric. Under these conditions almost all elements in the uniform charge are being “replaced” by elements of lesser NO-producing air-fuel ratios. On the overall rich side smaller reductions in NO level are possi...