VENTILATION SYSTEM FOR WELDING WORKSHOP

INTRODUCTION Exposure to welding fumes and other toxic gases is a

considerable problem in industrial environment (Kwag 1997, Byeon 1995).

Fumes generated in welding are composed of heavy metals and various materials, which have a bad effect on human health.

Welding fumes are very small particles that are formed when the vaporized metal rapidly condenses in air and are typically too small to be seen by the naked eye, but collectively, form a visible plume.

The health effects associated with metal fumes depend on the specific metals present in the fumes but may range from short term illnesses, such as metal fume fever (i.e., flu- like symptoms), to long-term lung damage and/or neurological disorders, such as lung cancer and/or Parkinson’s disease.

INTRODUCTION Gases are also generated from welding, which may include carbon

monoxide, ozone, and nitrogen oxides.

Carbon monoxide (CO) is an odorless, colorless gas that may be formed by the incomplete combustion of the electrode covering or flux and by the use of carbon dioxide (CO2) as a shielding gas. Overexposure to CO inhibits the body’s red blood cells to sufficiently carry oxygen to other tissues within the body, which subsequently results in asphyxiation.

Welding does not normally generate CO at high enough levels to be a concern; however, high levels of carbon monoxide may potentially accumulate when welding or air arc gouging in confined spaces.

There is also a potential of an oxygen deficient atmosphere if welding inside of a confined or enclosed space if an inert gas (such as argon) is used as the shielding gas.

INTRODUCTION However, there is an increasing demand for indoor

concentration measurements, especially indoor workplaces with high-expected CO2/CO concentrations (K. Papakonstantinou et al., 2003). The indoor workplaces have been reported as an important determinant of exposure to CO/CO2. Insufficient or malfunctioning ventilation inside, allows contaminated air to accumulate, and pollutant concentrations to increase.

In this study we concentrated on welding workshop which is used for lecturers at Ungku Omar Polytechnic as a facilities to teach the subject of Mechanical workshop practice.

This workshop operates for five days a week with the capacity of students and staff around 40-50 per course starting from 8.00a.m until 6.30p.m.

INTRODUCTION

During the welding activities, fumes generated in welding are composed of heavy metals and various materials will result in out hot smoke contain harmful gases (carbon monoxide and carbon dioxide).

In this case we need a good ventilation system provided to evacuate the room of hot air and welding gases and allow cool air to enter the workshop.

In this research, the studies are base on the relationship of thermal comfort with airflow pattern inside welding workshop by using CFD. The measurement will focus on three importance parameters; air temperature, air velocity and relative humidity.

PROBLEM STATEMENT Welding workshop is used for lecturers at Ungku Omar

Polytechnic as a facilities to teach the subject of Mechanical workshop practice.

The workshop is already equipped by a ventilation system, but unfortunately this existing system is not sufficient to support activities conducted in the room, as high temperature and accumulated smoke in the room are obviously observed.

Hence, the staffs and students need the aid of natural ventilation which is windows and door opening. However, the problem is still occurring. Therefore, health and comfort issues are crucial.

In the present of thermal comfort study in the welding workshop is has been proved to be poor, leading to hazardous and uncomfortable working environment.

Thus, the development of an improved ventilation system is essential. In this study will focus on finding alternative solutions and the development of the ventilation system in the room by using CFD software.

OBJECTIVES OF THE STUDY

This research in concentrating an indoor airflow pattern by comparing between CFD simulation and Standard or previous measurement to the thermal comfort range. The main objectives are as following;

I. To study the relationship of thermal comfort with air flow inside welding workshop.

II. To evaluate and propose the minimum requirement of ventilation system for a welding workshop.

SCOPES OF THE STUDYThe scope of this study will focus on

the thermal comfort and indoor airflow in welding workshop. The scopes of this research are as below;

I. To develop air flow simulation inside welding workshop by using CFD software.

II. To develop cost effectiveness method to solve the ventilation problem.

LITERATURE REVIEW- THERMAL COMFORT

(Parsons, 2000).Thermal comfort has a great influence on the productivity and satisfaction of indoor building occupants (HSE, 1999). Thermal comfort is very difficult to define. This is because we need to take into account a range of environmental and personal factors when deciding on the temperatures and ventilation that will make feel comfortable. The best that we can realistically hope to achieve is a thermal environment which satisfies the majority of people in the workplace, or put more simply, ‘reasonable comfort’

LITERATURE REVIEW- THERMAL COMFORT

(Ibrahim bin Hussein et al.,2001).present the results of a study carried out to estimate thermal comfort zone for classrooms in Universiti Tenaga Nasional (UNITEN) campus building. The comfort zone stipulated by American Society of Heating, Refrigerating and Air-conditioning Engineers, ASHRAE (ASHRAE, 1993), for summer season is in the following range:

I. Dry Bulb Temperature is between 22C to 27C.II. Relative Humidity is between 30% to 60%.III. Air motion velocity is about 15 m/min or 0.25m/s

LITERATURE REVIEW- THERMAL COMFORT

Guidelines for Energy efficiency in buildings for Malaysia produced by the Ministry of Energy, Telecommunications and Posts, Malaysia (1989), quote the air-conditioned space requirements as follows:

I. Dry Bulb Temperature is between 22C to 26C, design temperature 24C.

II. Relative Humidity is between 55% to 65%, design relative humidity 60%.

The climate in Malaysia however, hot and humid. Data obtain by Malaysia Meteorological Service (1997), for a-ten year period records the outdoor temperatures are uniform with average temperatures between 23.7C – 31.1C throughout a day with the highest maximum recorded as 36.9C and the average relative humidity throughout a day between 67% - 95%.

LITERATURE REVIEW

- VENTILATION SYSTEM

(JH moon et al.,2005).studied the performance of the ventilation system in the large welding working place.

In Korea, the Ministry of Labor regulated the limit of fumes concentration to 5 mg/m3 in the factory (the Ministry of Labor 1997).

To protect the health of workers in welding factory, the natural or mechanical ventilation was mainly applied. The air flow rate for dilution of welding fumes is not sufficient for natural ventilation in large factory, which they should be removed by appropriate ventilation methods.

To make up for natural ventilation, it has been generally used a local ventilator or fan (Robert 1991) as a mechanical ventilation equipment.

LITERATURE REVIEW

- VENTILATION SYSTEM

In this study, the jet fans for equipments of mechanical ventilation were determined to dilute the welding fumes effectively.

The diffusion number of welding fumes to solve the concentration equation is used by Vargaftik (1996) and the source term of fumes in CO2 welding is based on Hewitt (1993). He found that the welding fumes generated 6.67 mg/s for each welding machine.

LITERATURE REVIEW

- VENTILATION SYSTEM

In this paper, the ventilation performance with jet fans in the large welding working place was investigated by using CFD and it is possible to conclude as follows.

I. When the ventilation system in the factory was not established, the natural ventilation is not efficient to dilute the fumes in occupied zone. The fumes in the factory were stagnant and their concentration exceeds the regulation limit.

II. With the ventilation system, the fumes generated in the factory were exhausted well and their concentration was maintained below the regulation limit. It is recommended that the ventilation equipments using jet fans for a large factory are useful for industrial ventilation method.

LITERATURE REVIEW

- VENTILATION SYSTEM

(Koji Sakai et al., 2007). In Japan, the following of further improvement in the amenity : washable seat, heated seat, deodorization with function stool. In this study, the examination was carried out on the usefulness of the local ventilation system using CFD analysis method on the assumption of the lavatory in office building.

In the analysis, it is examined by changing the volumetric exhaust flow rate on ceiling ventilation, local ventilation and ceiling and local ventilation combined use.

On each case, it is examined by changing air ventilation balance and outlet position.

The result showed that the local ventilation could reduce the indoor pollutant quality concentration in comparison with the ceiling ventilation at little ventilation air volume. And, it was shown that diffusion range of the pollutant to the near human head was reduced .

LITERATURE REVIEW

- VENTILATION SYSTEM

In the individual exhaust system, in which an exhaust opening was installed near a lavatory basin, results showed that concentration of indoor air contaminants could be kept low compared with others. And it was shown that the energy saving by the ventilator volume reduction could be expected by the adoption of this system.

Furthermore, when using only ceiling exhaust, it was clarified that the indoor average concentration and the concentration in a respiratory zone were high compared to other situations. Future studies of the influence of rising heat currents near a user and concentration properties with intermittent ventilation are scheduled .

LITERATURE REVIEW

- VENTILATION SYSTEM

(Liping Wang et al.,2009) .studied the coupling strategies for natural ventilation between building simulation (BS) and computational fluid dynamics (CFD) are discussed and coupling methodology for natural ventilation is highlighted.

Two single-zone cases have been used to validate coupled simulations with full CFD simulations. The main discrepancy factors have also been analyzed.

The comparison results suggest that for coupled simulations taking pressure from BS as inlet boundary conditions can provide more accurate results for indoor CFD simulation than taking velocity from BS as boundary conditions.

The validation results indicate that coupled simulations can improve indoor thermal environment prediction for natural ventilation taking wind as the major force.

LITERATURE REVIEW

- VENTILATION SYSTEM

(Du Xiaogang et al.,2008) . Studied the ventilation in guest room in hotel. To air-conditioning system with fan and fresh air, the pollutants indoor were mainly removed by fresh air.

Enlarging the fresh air volume could develop the indoor air quality, but goes against to the energy saving. This paper simulated the CO2 concentration indoor under different fresh air volume when the bathroom door opens and closed.

The result indicates that only enlarging the fresh air volume affects the IAQ slightly, and exhaust fan can satisfy the ventilation indoor whether the bedroom door opens or closed.

When the IAQ satisfies the standard, enlarging the fresh air effects on the oxygen indoor slightly, but can enlarge the energy consume and exhaust fan in bathroom can satisfy the air flow in bedroom in spite of the door is open or closed.

LITERATURE REVIEW

- VENTILATION SYSTEM

(Gang Wang et al., 2009) .investigated the effect of three different fresh air modes on the indoor pollutant dispersion is analyzed by the method of CFD (Computational Fluid Dynamics) simulation and experiment.

The fresh air modes include natural ventilation, hybrid ventilation and mechanical ventilation with total heat exchanger. Performance of the fresh air modes is compared considering the factors like fresh air volume, heat/cold load and outdoor air parameters etc.

In addition, the ventilation performance under different fresh air volume and control modes is contrastively studied under running condition.

The result shows that, fresh air volume is the key factor in diluting the pollutant and heat recovery is vital for energy efficiency.

LITERATURE REVIEW

- VENTILATION SYSTEM

(Lau, J. and Chen, Q.,2007) .reported the investigation of the performance of floor-supply displacement ventilation with swirl diffusers or perforated panels under a high cooling load.

The experiment was carried out in a full-scale environmental chamber to obtain reliable data on the floor-supply displacement ventilation for the validation of a computational-fluid-dynamics (CFD) program.

Numerical simulations using CFD program were to evaluate the performance of the system for a large workshop. The impacts of several parameters, such as the air change rate, number of diffusers, diffuser location, occupant location, furniture arrangement, partition location, and arrangement of exhausts, on the indoor environment were investigated based on the thermal comfort level and indoor air quality

LITERATURE REVIEW

- VENTILATION SYSTEM

The results from this study show that a workshop with floor-supply displacement ventilation can improve indoor air quality because the contaminant concentration in the breathing zone is lower than that of mixing system.

The ventilation effectiveness is always greater than 1 for all the cases studied. However, the indoor spaces with floor-supply displacement ventilation could have a higher risk of discomfort, because of high temperature stratification between the ankle and head levels when compared to traditional mixing ventilation.

The system with the swirl diffusers can provide a better comfort level than that with the perforated panels due to the mixing by the diffusers. The draft risk can be high in an area within 0.5 m around the swirl diffuser.

METHODOLOGY CFD was used in this study to investigate

thermal comfort and indoor air quality to propose the ventilation system in the welding workshop. Since the CFD used approximations, it was necessary to validate the CFD program before it was used as a tool of study. The validation can be done by comparing the CFD results with the ASHRAE standard for ventilation of the workshop. With the CFD and experimental results, it is possible to evaluate thermal comfort and indoor air quality through appropriate indices for a room with the ventilation system.

METHODOLOGYANALYSIS FLOW CHART

METHODOLOGYRESEARCH MODEL The analysis was conducted in welding

workshop which is located in Ungku Omar Polytechnic. The general layout of the welding workshop is shown in figure 3.1. The total room area is 334.89 square m (18.3m x 18.3m) and 6.1 m high, the room has two entrances; the main entrance, E1(2.45 m x 1.95 m) and the other one is E2(2.1m x 1.05). In addition, there are three windows,W1,W2 and W3 (3m x 4.6m). The total two welding areas (5.5m x 6.5m) exist in the welding workshop.

METHODOLOGYRESEARCH MODEL

METHODOLOGY

The exhaust fans for fumes removal and ventilation, 4 total, are installed on the above walls, F1, F2, F3 and F4 (1 meter from the roof) in the welding workshop. The installment positions of exhaust fans are shown in Figure 3.2 .

METHODOLOGYRESEARCH MODEL

METHODOLOGY

The assumptions to model the welding fumes are as follows.

I. The property of welding fumes is constant.II. The flow behavior of welding fumes is similar to that of the

air.

The total amount of welding fumes generated in welding machines is small, whereas that of the air in the workshop considered as the total volume is very large. Also, the numerous particles in micro scale float together the air. We have assumed that the flow behavior of welding fumes is the same as that of the air approximately. The diffusion number of welding fumes to solve the concentration equation is used by Vargaftik (1996) and the source term of fumes in CO2 welding is based on Hewitt (1993). He found that the welding fumes generated 6.67 mg/s for each welding machine.