The effect of air velocity on the performance of the direct evaporative cooling system

This experimental study aimed to determine the effect of airflow velocity on the performance of a direct evaporative cooling system. Rectangular-shaped honeycomb cooling pads with a length of 34 cm, a width of 25 cm, and a thickness of 3.5 cm are used as cooling media. The main parameters of the study are low air velocity (2.3 ms−1), medium (3.2 ms−1), and high velocity (3.7 ms−1). The data collected include dry bulb temperature, wet bulb temperature, output air temperature, input and output air velocity, input and output humidity, and solar radiation. These data are used to determine saturation efficiency, cooling capacity, temperature decreases, and feasibility index. The experimental results are presented in the form of tables and graphs and analysed based on existing theories. The results showed that the evaporative cooling system could produce output temperatures up to 27.5°C with input 31.4°C at low airspeed, 27.97°C with input 31.47oC at medium speed, and 27.7°C with input 31.30°C at high air speed. It was concluded that a low airflow rate would add to the cooling efficiency, and the higher the airflow rate, the lower the cooling efficiency. The results showed that evaporative cooling is achievable with a feasibility index of 19.89 ≤ F*≤ 20.67. The results also affirmed that cooling capability is higher where the feasibility indexes are comparatively low.

Mathematical modeling and thermodynamic properties in the drying of citron watermelon seeds

ABSTRACT Citron watermelon is an agricultural product of excellent economic potential. Its seeds are widely used for oil extraction, serving as an energy source, showing nutritional characteristics that make them a suitable product to be studied. Thus, the objective was to characterize citron watermelon seeds regarding their physicochemical composition, in addition to determining drying kinetics, fitting mathematical models to the data, and determining the effective diffusivity coefficients and thermodynamic properties. The seeds were dried in a convective dryer, varying the drying temperature, with air velocity of 1.0 m s-1. With the increase in drying temperature, there were reductions in moisture content, water activity (aw), ash concentration, total titratable acidity, lipids and reducing sugar. Citron watermelon seeds are rich in lipids and ash, have low sugar concentration and low acidity; their drying kinetics was very well described by the Two Terms and Approximation of Diffusion models, followed by the models of Midilli and Page, which resulted in acceptable fits. Effective diffusivity accompanied the increase in drying temperature, and this behavior was well fitted by an Arrhenius-type equation. Enthalpy and entropy variations were reduced with drying temperature, with increments in Gibbs free energy.

DESIGN, CONSTRUCTION AND TESTING OF A COLD STORE WITH WATER-COOLED CHILLER

Objective of this research was to design, construction and test of a cold store with chiller unit. Dimensions of the cold store were 5x4x3m. Heat load was calculated and capacity of cooling system was determined. Ambient temperature was set 2oC and relative humidity 90% for cold store testing. Ambient temperature, relative humidity and air velocity were measured for 3 different levels and 12 points for each level in the cold store. Total heat load and capacity of cooling system were calculated 5222 kcal/h. and 6.07 kW respectively. The descriptive statistics were calculated for the ambient temperature; mean, 2.82oC, standard deviation 0.02oC and CV(%) 0.56, and for the relative humidity; mean 88.01%, standard deviation 0.61 (%) and CV(%) 0.70 and for the air velocity mean 0.37m/s, standard deviation 0.22 m/s, CV 33.45 %. Even the air velocity CV was high, the ambient temperature and relative humidity variations were evaluated very good.

A Case Study of Post Occupancy Evaluation of an Educational Building with LEED Platinum Rating

The Building environment and the performance of its systems directly impact the experience and comfort of a building occupant. This POE study examines the relationship between building and human performance. LEED-rated building was selected as a case study to analyze its performance after being in operation. The occupants’ satisfaction was evaluated in terms of the thermal comfort and human use with the application of online questionnaire. The environmental impact was determined through various measurements including room temperature, relative humidity, air velocity, lighting levels and carbon emission. The outcomes of this study identify the building systems efficiencies as well as the systems in need of retrofit. The POE results can help building designers address user needs more effectively and fine-tune the systems to improve sustainability.

THE EFFECT OF BEND ANGLE ON THE EVAPORATIVE COOLING OF AIR FLOW THROUGH BENT DUCT

One remediation to output power drop of a gas turbine generating units during hot climates is reducing compressor inlet air temperature using fogging technique incorporating water injection into the airstream. The inlet air ductworks often include a bend or curved duct before the compressor comprising the secondary flow utilized to enhance the mixing between air and water droplets. This study investigates the effect of changing the bend angle on the resultant evaporative cooling of steadily flowing airstream. The experiments were conducted with an average air velocity range from (2.5 to 5 m/s) through (50) cm square duct. The study considered three bend angles of (45°, 90° and 135°) along with three sets of nozzle tilt angles of (- 45o, 0° and 45° ) to the axial flow direction. The results reveal that best evaporative cooling was achieved at a bend angle of (135°) when the water is axially injected, i.e., at (0o) to flow direction. These conditions were obtained at the velocity of (2.5 m/s), giving enough residence time for the injected droplets to evaporate and cool the airstream.

Theoretical and experimental study of the influence of temperature, humidity and density on the processes of drying, cleaning and filtration of cotton raw materials

The article presents information about existing problems and their solutions in the process of drying cotton raw materials at cotton gin plants, patterns of changes in the humidity of cotton raw materials at different values of the warm air velocity are obtained. The influence of the density of cotton raw materials and the relative air velocity on the change in the moisture loss coefficient at different temperatures of the air flow was investigated and it was established using a laboratory device that at a density of 0.5 g/cm3, the moisture loss process in cotton raw materials.

Impact of the measurement uncertainty on the monitoring of thermal comfort through AI predictive algorithms

This paper presents an approach to assess the measurement uncertainty of human thermal comfort by using an innovative method that comprises a heterogeneous set of data, made by physiological and environmental quantities, and artificial intelligence algorithms, using Monte Carlo method (MCM). The dataset is made up of heart rate variability (HRV) features, air temperature, air velocity and relative humidity. Firstly, MCM is applied to compute the measurement uncertainty of the HRV features: results have shown that among 13 participants, there are uncertainty values in the measurement of HRV features that ranges from ±0.01% to ±0.7 %, suggesting that the uncertainty can be generalized among different subjects. Secondly, MCM is applied by perturbing the input parameters of random forest (RF) and convolutional neural network (CNN) algorithm, trained to measure human thermal comfort. Results show that environmental quantities produce different uncertainty on the thermal comfort: RF has the highest uncertainty due to the air temperature (14 %), while CNN has the highest uncertainty when relative humidity is perturbed (10.5 %). A sensitivity analysis also shows that air velocity is the parameter that causes a higher deviation of thermal comfort

Innovative Low-Cost Naturally Ventilated Maize Seed Storage System

A 22-m3 residential room was converted to a seed storage facility by retrofitting a solar collector on the roof. Three different chimney sizes of diameter and height of 200 mm x 3.6 m, 200 mm x 4.8 m, 300 mm x 3.6 m, and 300 mm x 4.8 m were investigated to determine the best size of the chimney to be used for ventilation in a storage facility. The parameters measured were the air velocity in the chimney duct, as well as the air temperature and relative humidity at the inlet, centre, and outlet of the storage facility. The diameter of the chimney had a significant effect (P<0.05) on the ventilation rate achieved in the storage facility. Significant differences were found between the different chimney diameters and heights (P≤0.05). The 300 mm diameter chimneys were able to extract hot air from the roof solar collector; however, the 200 mm diameter failed. The modified naturally-ventilated seed storage room was able to reduce the relative humidity from 69.7% to a safe relative humidity of 37.9%, while at the same time the temperature increased from 23.3℃ to 35℃ in the 300 mm x 4.8 m chimney.

Numerical Study of Large-Scale Fire in Makkah’s King Abdulaziz Road Tunnel

Tunnel fires are one of the most dangerous catastrophic events that endanger human life. They cause damage to infrastructure because of the limited space in the tunnel, lack of escape facilities, and difficulty that intervention forces have in reaching the fire position, especially in highly crowded areas, such as Makkah in the Hajj season. Unfortunately, performing experimental tests on tunnel fire safety is particularly challenging because of the prohibitive cost, limited possibilities, and losses that these tests can cause. Therefore, large-scale modeling, using fire dynamic simulation, is one of the best techniques used to limit these costs and losses. In the present work, a fire scenario in the Makkah’s King Abdulaziz Road tunnel was analyzed using the Fire Dynamics Simulator (FDS). The effects of the heat released per unit area, soot yield, and CO yield on the gas temperature, radiation, concentrations of the oxygen and combustion products CO and CO2, and air velocity were examined. The results showed that the radiation increased with the heat released per unit area and the soot yield affected all parameters, except the oxygen concentration and air velocity. The CO yield significantly affects CO concentration, and its influence on the other studied parameters is negligible. Moreover, based on the validation part, the results proved that FDS have limitations in tunnel fires, which impact the smoke layer calculation at the upstream zone of the fire. Therefore, the users or researchers should carefully be concerned about these weaknesses when using FDS to simulate tunnel fires. Further comprehensive research is crucial, as tunnel fires have severe impacts on various aspects of people’s lives.