EXPERIMENTAL AND NUMERICAL STUDY OF THE EFFECT OF HEATED OBSTRUCTION WITHIN A SPACE (WELDING WORKSHOP) ON THREE DIMENSIONAL AIR FLOW CHARACTERISTIC

This study investigates experimentally and numerically the environmental conditions prevailing in a large mechanically ventilated welding workshop which lies in the Basra Oil Training Institute in Iraq. The numerical part was accomplished with the aid of the computational fluid dynamics by ANSYS 15 program. This software program was compared against the results of a resemblance research work ]1[, which shows a good agreement. Numerical results are compared with experimental data collected during different ventilation and occupational conditions of empty and full workshop daily work, and there is a good agreement between experimental data and numerical results. The experimental part was done by using suitable calibrated devices to measure the air velocity, temperature, relative humidity and concentration of CO, CO2 gases in the different locations of the indoor environment of welding workshop. The results of this study demonstrate that the occupants of the existed welding workshop suffer from healthy problems because of the harmful gases, and the inefficient ventilation system used. AL-QADISIYAH JOURNAL FOR ENGINEERING SCIENCES Vol. 11, No. 1 ISSN: 1998-4456 Page 93 Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.


EXPERIMENTAL PART
The welding workshop under study is in close vicinity of heavy-traffic roads. The area of the indoor space is 204 m 2 , while its height is 9 m. The capacity of the welding work shop is (25-35) students and the number of the welding machines is (15). There are three windows at the north wall which normally closed and no heating-ventilating-air conditioning (HVAC) system is exits, except a forced ventilation system consisting of 10 exhaust fans with of capacity (41.6) m 3   Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.

Theoretical Model
The ANSYS 15 (CFD) code [8] solves the time-averaged conservation equations of mass, momentum, and chemical species in three-dimensional flows: Equation (1) where  : Molecular stress tensor SM :Source Term P: pressure The turbulence kinetic energy, k , and its rate of dissipation,  , are obtained from the following transport equations: is the generation of turbulence kinetic energy due to buoyancy, calculated as described in where Pr t is the turbulent Prandtl number for energy and i g is the component of the gravitational vector in the ith direction. For the standard and realizable k- models, the default value of Pr t is 0.85. The coefficient of thermal expansion,  , is defined as represents the contribution of the fluctuating dilatation in compressible turbulence to the overall dissipation rate which is normally neglected in the modeling of incompressible flows and it can neglected in this study. Ji r : The diffusion flux of species i which arises due to gradients of concentration and temperature. ,.
h is the total enthalpy, related to the static enthalpy h(T,P) by:   convergence criterion was set such that the respective sum of the absolute residuals must be less than 10 -4 .

VALIDATION OF PRESENT CFD PROGRAM
In the present study, ANSYS 15 program is validated against a previous research done by All the results in this verification case were in good agreement with the previous once. As seen in the Table   1. and Figure (5), it has been taken the air temperature for twenty points in the domain of room and compered between these results and the previous results.

VERIFICATION CASE
This case corresponds to the validation process, indicated to latterly, where the program used in this Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.
there is a good matching between two results when compared between these results, as shown in the Figure   (1). This lends legitimacy to this program which used in the current study.  Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.   (8) and (9). It should be noted that the model configurations were set so that the best balance is achieved among convergence, grid independency, and runtime saving, due to the high complexity of the domain geometry as can be shown in Figure ( numerical results, as given by the Figures. (11 and 12).
The temperature distribution contours are represented graphically as shown by Figure (       Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.

Welding Workshop (Full-space case)
This is the main case-study in this research work, where the welding workshop is full of 35 students and 3 trainers, as detailed previously, all 15 welding machines are operated by 15 students, the 10 exhaust fans were operated also and the fresh air entered to the workshop from the inlet door at velocity 0.
8675 m/s, as shown in the Figures (20 and 21). The boundary conditions of this case are given in the Figure   (22 Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved. temperature, and relative humidity, also supported with some experimental measurements, as given in the table (4). After the experimental measurements and the numerical values are accomplished it is shown that a good agreement when comparison between experimental data and numerical result, as given by the Figures   (23 and 24).
The temperature of the inflow air in the workshop is 308.97K and that of the region near the exhaust fan is 317K, while reach to a value of 325K at the ceiling of the workshop and minimum value 306K at the floor. It was observed that the temperature differences are between (7-16K) in large welding workshop as shown in Figure ( CRE can be calculated from equation ( 11 ). Also some results are given in the figures 30,31 and 32.    Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.  Copyright  2018 Al-Qadisiyah Journal For Engineering Sciences. All rights reserved.

CONCLUSIONS AND RECOMMENDATIONS
From the results obtained in this study, the following conclusions can be made: 1-The results of this research work show that the indoor environment of the welding workshop is highly polluted with CO2 and CO gases. These gases need to be treated, so that a healthy atmosphere is acquired.

2-
The average air velocities provided by the existed ventilation system of the welding workshop is low, and this value is not enough to pull out the necessary percentage of harmful pollutants.
3-It can be observed from the temperature distribution in the welding workshop that, the higher temperatures are existed near the training students and in the region adjacent to the ceiling because of the heat released from the welding machines and the ceiling lights respectively. 4-The air change per hour (ACH) has an important effect on the concentration of CO, CO2 gases, and this factor will be studied in the compliment of this research work. A correct selected value of ACH will enhance the contaminate removal effectiveness (CRE). 5-It is recommended for the Basra Oil Training Institute, that the air change per hour of the welding workshop must be increased according to an engineering manner by adding some extra exhaust fans to the workshop, in order that the contaminate removal effectiveness will be enhanced more.