CFD Validation of Carbon monoxide diffusion within a ship vehicle garage

Transcription

1 CFD Validation of Carbon monoxide diffusion within a ship vehicle garage Presented by: Dr. Nasr Abdelrahman Nasr MAY 2013

2 Presentation Layout: Introduction. Field measurement and analysis. Mathematical formulation and application of the model. Results and discussion. Conclusions

3 Introduction

4 Through the years, man has built increasingly elaborate boxes to protect himself from rain and snow, warm him in the winter and cool him in the summer Most people are aware that outdoor air pollution can damage their health, but many do not know that indoor air pollution can also cause harm By shielding ourselves from the outside environment, we created an environment with a whole new set of problems.

5 Indoor Environmental Quality (IEQ) The quality of indoor Environment is achieved through procedures taken to maintain some factors within the comfort values. Factors that Affect indoor comfort: Temperature Humidity Air motion Radiant sources Odour Dust Noise Vibrations

6 What is Indoor Air Quality (IAQ) The condition of air inside closed spaces is a combination of the chemical, biological, and particulate matter in the air and air temperature and humidity.

7 Acceptable IAQ According to the ASHRAE Standard an acceptable IAQ can be defined as : 1. Air in which there are no known contaminants at harmful concentrations. 2. Air which 80% or more of the people exposed do not express dissatisfaction.

8 Some indoor air quality statistics World Health Organization (WHO) The characteristics of indoor environments significantly influence the occurrence of respiratory disease, allergy and asthma symptoms, and worker performance The Environmental Protection Agency (EPA) Air pollutants are 25 to 100 times higher indoors than outdoors.

9 The U.S. Department of Energy (DOE) The improvements in indoor environments cause Decrease of 10 to 30 % for infectious respiratory disease, and allergy and asthma symptoms

10 Different Pollutants have Different Effects Carbon Monoxide - circulatory system, heart Ozone - respiratory system, lung Lead - nervous system, brain PM - lung, potential effects on heart Diesel, Air Toxics - cancer, respiratory effects

11 Occupational Safety and Health Administration (OSHA) Facts and Figures about co One of the most dangerous industrial hazards One of the most widespread Some 2,000 persons a year are killed out right by CO gas exposure. At least 10,000 more workers suffer from exposure to debilitating levels of CO.

12 Carbon Monoxide It is a product of motor vehicle exhaust fumes, which contributes almost 100% of all CO emissions in urban areas.

13 CO is diffused perfectly into air because its density is smaller than air (1.225 kg/m 3 for air and kg/m 3 for CO).

14 Carbon monoxide health effect It is colorless, odorless, and at much higher levels, a poisonous gas is formed when carbon in fuels is not burned completely. CO is diffused perfectly into air because its density is smaller than air (1.225 kg/m 3 for air and kg/m 3 for CO).

15 Carbon monoxide health effect Several epidemiological studies in parking areas show evidence of a positive relationship between CO in the air atmosphere and hospital admissions

16 Carbon Monoxide Toxicity Levels 12,800 ppm Death within 1 to 3 minutes 6,400 ppm Headache, dizziness in 1-2 minutes. Death in minutes 3,200 ppm 1,600 ppm 800 ppm Headache, dizziness, nausea within 10 minutes. Death within 30 min. Headache, dizziness, nausea within 20 minutes. Death within 2 hours Headache, dizziness, nausea within 45 minutes, convulsions. Coma within 2 hours 400 ppm Frontal headache 1-2 hours, widespread 2 ½ to 3 ½ hours 200 ppm Slight headache, tiredness, dizziness, nausea after 2-3 hours 35 ppm 9 ppm The maximum exposure allowed by OSHA in the workplace over an eight hour period. ASHRAE recommended maximum allowable concentration in living areas.

17 Carbon monoxide health effect The following figure represents the acceptable and dangerous limits for CO concentrations inside enclosed facilities Deadly

18 Major Vehicle / Fuel Emissions Carbon Monoxide Diesel Exhaust Particulate Matter (PM) Lead Nitrogen Oxides (NOx) and Hydrocarbons (HC) Nitrogen Dioxide

19 There has been a growing public concern over indoor air quality (IAQ) in transportation Many studies have already shown that people can be exposed to much higher pollutant concentrations in automobiles,,buses, subways, and aircrafts compared to ambient atmosphere Also, wide ranges of researches have been conducted to improve the indoor air quality on these transportation On the other hand, ships have received less attention and little work has investigated the level of indoor air pollution onboard, because ships are not as popular as other transportation modes

20 Indoor Air Quality (IAQ) on Board Ships

21 Why IAQ on board ships

22 Indoor air quality (IAQ) on ships is important for the passengers comfort and the crew s work efficiency The builders and operators need to be aware of the importance and present status of IAQ. A number of problems have been identified which warrant attention in order to safeguard passenger comfort and health: Allergenic reaction Discomfort and nuisance may result from poor air quality and badly maintained ventilation systems. Poor indoor air quality may also affect the revenue potential of a passenger ship.

23 MARITIME SAFETY COMMITTEE 88th session Agenda item 23 MSC 88/23/7 10 August 2010 WORK PROGRAMME Proposal to amend SOLAS regulation II-2/20 in order to include the possibility of air quality management for ventilation in closed vehicle spaces, closed Ro-Ro spaces and special category spaces.

24 Scope of the proposal Air quality management should at least include measurements of carbon monoxide (CO). On the basis of these measurements the capacity of the ventilation can be regulated automatically, either by adjusting the number of revolutions of the fans or by switching off and, when necessary, switching on again, certain fans.

25 SOLAS regulation II-2/20 Include the possibility of air quality management for ventilation in closed vehicle spaces, closed Ro-Ro spaces and special category spaces. Regulating the airflow by air quality management instead of ventilation via a fixed number of air changes per hour saves energy, results in lower CO emissions and reduces noise levels whilst maintaining the high level of fire safety as required in SOLAS chapter II-2.

26 Field measurements and analysis

27 In this study a real vehicle garage onboard an existing fast ferry, working as a liner between Egypt and Saudi Arabia ports, is selected as a case study. Field measurements were taken to survey the CO diffusion throughout the space for the evaluation of the problem.

28 An existing ship vehicle garage was selected to investigate experimentally the CO distribution. The garage incorporates two decks, the main deck and the upper deck. The main deck dimensions are 70 m length x 23 m width x 2.8 m height. It can load up to 70 cars and 8 buses. The upper deck is U-shaped corridor with one ramp in each end. Its dimensions are 119 m length x 7 m width x 2.2 m height. It can load up to 62 cars. Both decks are in the same interior, i.e. there is no separation between them

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31 Carbon monoxide measurements, at different points inside the selected space including inlets and outlet, were taken by means of TSI IAQ-CALC model Indoor Air Quality Meter

32 Carbon Monoxide CO Sensor Type Range Resolution Accuracy Response Time Electro-chemical 0 to 500 ppm 0.1 ppm ±3.0% of reading or ±3 ppm (whichever is greater) <60 sec to 90% step change All sensors were connected to Omega RD8900 data logger which displays and saves data to a 256 MB removable flash memory. Before starting, the IAQ-CALC instrument was tested and calibrated. Then a sensitivity study was carried out to justify the number of measuring points and the number of readings for each point, based on the reading s average and root mean square value

33 Fifty measuring points were selected to cover the whole garage, they were divided into two levels (1.5 and 3.5 m above main deck). The main deck level contained a grid of thirty points and the upper U-shaped deck level contained twenty points The main deck level The upper deck level

34 The following procedures were followed to obtain the experimental data: Preparation of the recording sheet before the ship arrive Recording an average of four readings for each point. Continuous testing and recording data through the car discharge period. Repeating the test during the period of loading new cars. Repeating all the discharge/loading tests for three consecutive trips.

35 Mathematical formulation and application of the model

36 The upper deck The main deck

37 Garage Ventilation System Upper deck fans Natural ventilation The main deck fans Ramp

38 Car modeling: Assuming a car with the following specifications: 1.(1600 cc) engine size 2.The fuel consumption of this car at idling is about (0.25 kg fuel /hp.hr) 3.The combustion efficiency at idling is (60%) 4.The air to fuel ratio is (15/1) and the air density is (1.2 kg/m 3 )

39 Car modeling: Assuming a car with the following specifications: 1.(1600 cc) engine size 2.the fuel consumption of this car at idling is about (0.25 kg fuel /hp.hr) 3.the combustion efficiency at idling is (60%) 4.the air to fuel ratio is (15/1) 5.and the air density is (1.2 kg/m 3 )

40 Bus modeling : Assuming a car with the following specifications: 1.(3000 cc) engine size 2.The fuel consumption of this car at idling is about (0.40 kg fuel /hp.hr) 3.The combustion efficiency at idling is (60%) 4.The air to fuel ratio is (15/1) and the air density is (1.2 kg/m 3 )

41 The model used in solving the problem was the standard (k & ε model) with: Thermal diffusion full multi-component diffusion applied to the solution. The solver used was the 3D segregated solver. The convergence criterions for all variables were set to 10-3 except for the energy equation 10-6.

42 The boundary conditions used in solution were as follows: boundary conditions Suction fan pressure Inlet air conditions Inlet fresh air mass fractions Assumption (-30 pa). (300 K and bar). (0.233 O 2, N 2 and 0 CO). Car exhaust conditions (1 m/s and 340 K) The under relaxation factors For the cases with fresh air supply, the air conditions are (0.3 for pressure, 1 for density and body forces, and 0.7 for the momentum). (1.5 m/s, 300 K, O 2, N 2 and 0 CO).

43 The case study modeled and introduced to a CFD package in order to solve the partial differential equations governing CO levels and ventilation conditions in the threedimensions.

44 MESH SETUP: For all faces the mesh is triangular of size 1.0. the faces of interest such as suction ports, exhaust openings, ventilation inlets, and supply ports the mesh is triangular of size 0.5. The volume is then meshed in tetrahedral shape of size 1

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50 The model after mesh generation

51 Preprocessor

52 Solver

53 Postprocessor

54 Results and discussion

55 The ships vehicle decks CO diffusion was monitored at various parts including supply and exhaust locations. Using the solver package Fluent and introducing the boundary conditions, results were obtained in the form of CO concentration. horizontal planes were also defined to verify CO diffusion patterns. A report for the pre-defined 50 positions was created and summarized in the following Table.

56 Upper deck Main deck Coordinates (m) CO concentration (ppm) Point X Y Z EXP CFD Difference S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S S Max

57 For the purpose of quantitative validation, the root mean square error RMSE was calculated for CO concentration. The RMSE is a quadratic scoring rule which measures the average magnitude of the error. The difference between forecast and corresponding observed values are each squared and then averaged over the sample, the square root of the average is then taken. Since the errors are squared before they are averaged, the RMSE gives a relatively high weight to large errors. This means the RMSE is most useful when large errors are particularly undesirable (Kreyszig, 1979).

58 where RMSE is the root mean square error, n is the number of points, x i is the differences between experimental and CFD results, RMSE% is the root mean square error percentage, and Av ex is the average value of the experimental results. Substituting data from the previous Table in equation 1 and 2, the CO RMSE% is found to be 7.2%, which is acceptable (Senthooran et al, 2004).

59 S-1 S-3 S-5 S-7 S-9 S-11 S-13 S-15 S-17 S-19 S-21 S-23 S-25 S-27 S-29 S-31 S-33 S-35 S-37 S-39 S-41 S-43 S-45 S-47 S-49 CO concentraion (ppm) EXP CFD Measuring points CO validation curve

60 The main deck level garage is in the risky level More specifically, plane P-1 at 35 cm above the main deck (car exhaust level) shows an average of 250 ppm.

61 The main deck level garage is in the risky level, plane P-2 at 150 cm above the main deck (human breathing zone) show an average of 130 ppm.

62 The main deck level garage is in the risky level, plane P-3 at 200 cm above the main deck (human breathing zone) show an average of 110 ppm.

63 The upper deck level garage is still in risky level, plane P-4 at 315 cm above main deck (car exhaust level) shows an average of more than 50 ppm.

64 The upper deck level garage is still in risky level, plane P-5 at 430 cm above main deck(human breathing zone) shows an average of more than 50 ppm.

65 The upper deck level garage is still in risky level, plane P-6 at 480 cm above main deck(human breathing zone) shows an average of more than 50 ppm.

66 CFD SIMULATION FOR MAIN AND UPPER GARAGE

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68 Conclusions

69 Experimental measurements and CFD simulations were performed in order to characterize the carbon monoxide diffusion patterns inside a ship s vehicle garage. The CFD model was validated through quantitative and qualitative comparisons between both sets of results, which were generally acceptable; the percentage root mean square error in carbon monoxide concentration was found to be 7.2 %. The study also revealed severe CO concentration values in relation to the standard codes at most of the study points (OSHA, 2010), (WHO, 2012) and (ANSI/ASHRAE, 2004). Hence, another study is currently being carried out using the same numerical model to find out the optimum air supply and exhaust configurations, in order to reduce CO concentration values to meet standard requirements for workers throughout most of the breathing zone.

70 THANK YOU