Some Effects on the Temperature of the Mine Air at the Heading Face

Currently, with the increase in mining output leading to deeper mining levels, the volume ofheading face serving production has also increased. The thermal environment tends to worsen whendigging deep due to the geothermal's effect, which increases the air temperature at the heading face.According to QCVN01/2011-BCT, the temperature at the heading face is not allowed to exceed 300C. Toensure this, in Vietnam today, mainly forced ventilation method uses local fans to provide a clean amountof air to ensure a favorable environment for workers. With the forced ventilation method, the duct positionis usually arranged on the side, and the distance from the duct mouth to the heading face is determined toensure that l < 6√s. In this study, a numerical simulation method by Ansys CFX software is applied tostudy the influence of several factors such as duct position, air temperature of duct, and roughnesscharacteristics of roadway on the temperature of the mine air at the heading face. The models are set upwith six duct positions and four air temperature of duct parameters. Model 1 (y =1.1 m) is better thanmodels 2 to 6 in terms of temperature distribution and the lowest temperature values. Four models havedifferent wind temperatures, and we can see the significant influence of the inlet air temperature of theduct on the thermal environment of the heading face. The results show that with the model T = 297.15K,the temperature value on the roadway length is guaranteed as specified < 303K. The result is a referencefor determining the duct position and cool for the high-temperature heading face.

The Efficiency of Obtaining Electricity and Heat from the Photovoltaic Module under Different Irradiance Conditions

This paper proposes a modification to the design of a standard PV module by enclosing the skeleton space and using forced ventilation. The purpose of this research was to develop a method for calculating the amount of heat gained during PV module cooling. A simplifying assumption was to omit the electrical energy consumed by the fans forcing the airflow. For testing at low irradiance, a prototype halogen radiation simulator of our own design was used, which is not a standardized radiation source used for testing PV modules. Two measurements were also made under natural, stable solar radiation. The modified PV module was tested for three ventilation rates and compared with the results obtained for the standard PV module. In all tested cases, an increase in electrical efficiency of about 2% was observed with increasing radiation intensity. The thermal efficiency decreased by about 5% in the analyzed cases and the highest value of 10.47% was obtained for the highest value of cooling airflow rate. In conclusion, the study results represent a certain compromise: an increase in electrical efficiency with a simultaneous decrease in thermal efficiency.

Ensuring Safe Working Conditions during the Operation of the Closed Coal Storages

It is noted that the relevance of the presented studies is related to the need in reducing the aerotechnogenic load on the environment, which, when the coal is stored in the open storage, is practically uncontrollable that leads to the dust pollution of the significant territories. It is shown that ensuring safe operation of the closed coal storages, which are an alternative to the open coal storage, is possible if two conditions are met: the concentration of methane released from the coal stack in the air space of the storage does not exceed the permissible values; reduction to the required level of emissions of coal dust generated during loading and unloading technological operations. The reasons for possible release of methane from the stored coal associated with its residual methane content, the value of which is determined both by the initial value, as well as its decrease during the transportation of coal from the place of its production to the closed storage were identified. It is shown that in order to prevent exceeding the permissible value of methane concentration in the closed storage, it is required to use forced ventilation with an air exchange rate of at least two. It is mentioned that the forced ventilation in combination with the significant volumes of coal dust generated during technological operations can result in an increase in its concentration to the values hazardous for the human health. The analysis of methods for normalizing the dust environment during the operation of closed coal storages is given. The scientific novelty of research is associated with a comprehensive study of the regularities of aero-, gas- and dust-dynamic processes that determine safety of operation of the closed coal storages.

A Comparative Study for Forced Ventilation Systems in Industrial Buildings to Improve the Workers’ Thermal Comfort

The appropriate ventilation for factory spaces with regard to volume flow rate and air velocity inside the factory is one of the most important factors in the improvement of the thermal comfort of workers and in the reduction of the percentage of pollution they are exposed to, which in turn helps to improve the work environment and increase productivity. It also could improve the performance of machines. Hence, overheating can cause various problems and malfunctions. In this study, three types of mechanical ventilation systems are compared: the wall fan extract ventilation system, the roof fan extract ventilation system, and the spot cooling system. The Ansys software has been used to conduct the computational fluid dynamics (CFD) simulations for the different cases and the ventilation effectiveness factor (VEF) has been used to compare the performances of the three systems. The ventilation factor notably relies on the temperature distribution produced through the modeling and the results show that the most optimal system that can be used for similar factory spaces is the forced ventilation system. Finally, it is also the best in terms of energy consumption, despite the increase in the initial cost of its installation.

Use of Engineering Methods in Assessment Ventilation of Protected Fire Escape Routes

The design of protected fire escape routes is a process in which a number of technical aspects that are set by Czech technical standards must be considered. The assessment of protected fire escape route's ventilated premises is subject to strict values, which when designed, or when created additionally, often force us to resort to specific measures, like a forced ventilation, enlargement of openings, which leads to expensive construction. This paper focuses on the use of so-called engineering methods to solve this problem, specifically the computational fluid dynamics method, which finds application in the revalidation of otherwise unmet ventilation criteria.

Effect of Top Ventilation on Cooling Characteristics of Passenger Cabin

In order to solve the hot soak effect of car during summer parking, the CFD numerical method was used to simulate the cooling law of passenger cabin under different inlet area, inlet velocity and inlet angle at the top vent. From the two dimensions of cooling rate and cooling effect, the influence of top natural ventilation and top forced ventilation on the cooling characteristics of passenger cabin were studied. The results show that under the condition of top natural ventilation, the cabin can reach thermal balance at about 10 min under different vent area conditions, and the cooling rate is the largest when the vent is fully opened, and the minimum temperature can reach about 45 °C within 4 min, which is 10 °C higher than the ambient temperature. Under forced ventilation, the inlet velocity has a great influence on the cooling rate and cooling effect of cabin. When the inlet angle is 90° and the inlet velocity is 5 m / s, the cooling rate is the largest and the cooling effect is the best.

Elevator (Lift) Car Ventilation Design to Mitigate the Risk of Spread of COVID-19

Recent studies, on the airborne transmission of the SARS-CoV-2 and the new CDC guidelines confirming the aerosol transmission of the virus, make immediate attention to the airflow in elevators imperative. While several versions have been thought of for contactless rides, there is little that has been considered for lessening the anticipated viral load in the elevator car.In this paper, a two-step approach is used. The first is the risk assessment, and the second is the risk mitigation through an improved lift car ventilation design. The risk is assessed by computing the probable viral load during the journey in a lift car. It is seen that the ventilation typically provided as per the minimum permissible requirements by codes is inadequate to handle the current situation.The computations show that one-minute exposure, to a coughing high emitter in the lift car, creates a viral load to dangerous levels well above the possible acceptable level of 10,000 virus copies/m3. To come up with the risk mitigation strategies, the required ventilation in the car was computed. The main recommendation suggests the use of forced ventilation using pressure fans and 3 to 6 air changes per minute depending on the operating environment. Such a design will help us achieve our objective of bringing the density of virus copies in the lift car to an acceptable level. A properly designed ventilation system for the elevator car will benefit in both pandemic situations as well as non-pandemic situations.

Effect of Mechanical Ventilation on Accidental Hydrogen Releases—Large-Scale Experiments

This paper presents a series of experiments on the effectiveness of existing mechanical ventilation systems during accidental hydrogen releases in confined spaces, such as underground garages. The purpose was to find the mass flow rate limit, hence the TPRD diameter limit, that will not require a change in the ventilation system. The experiments were performed in a 40 ft ISO container in Norway, and hydrogen gas was used in all experiments. The forced ventilation system was installed with a standard 315 mm diameter outlet. The ventilation parameters during the investigation were British Standard with 10 ACH and British Standard with 6 ACH. The hydrogen releases were obtained through 0.5 mm and 1 mm nozzles from different hydrogen reservoir pressures. Both types of mass flow, constant and blowdown, were included in the experimental matrix. The analysis of the hydrogen concentration of the created hydrogen cloud in the container shows the influence of the forced ventilation on hydrogen releases, together with TPRD diameter and reservoir pressure. The generated experimental data will be used to validate a CFD model in the next step.

VENTILATION METHOD FOR LONG BLIND DRIFTS WITH LONGITUDINAL BAFFLES

The study focuses on aerodynamic processes in long blind drifts ventilated owing to ejection effect generated thanks to construction of longitudinal baffles. The numerical modeling of air distribution at the junction with a blind drift with a longitudinal baffle is implemented in ANSYS. The change in the local air drag in case of forward and reverse air flows is shown. The velocity variation in air flow in a long blind drift with adjustment of ventilation efficiency by alteration of the opening angle of the longitudinal baffle flap is estimated. Based on the obtained results, the author shows that construction of longitudinal baffles allows efficient ventilation in long blind drifts owing to the ejection effect, without forced ventilation arrangement.