臺灣博碩士論文加值系統

在進行食物烹煮時，特別是在油炸過程中，通常伴隨高溫的環境以及大量的油煙。故本研究採用數值方法，發展側向吹吸式氣罩應用於油炸機之通風系統，針對大面積熱源情況並釋放硫化氫氣體，去探討傳統式氣罩與側向吹吸式氣罩之汙染物捕集性能表現，進而驗證此設計之效能。此外，更進一步考慮當人員站立在氣罩前方時，對於內部流場以及硫化氫分佈的影響。本研究以有限體積法配合k –ε紊流模型來模擬流場、溫度場及硫化氫擴散現象，並根據勞工安全衛生法所規定，勞工作業環境空氣中硫化氫的濃度不得超過10 p.p.m. 之標準，去量測開口處12點位置的濃度值以判斷硫化氫是否產生洩漏。
根據結果顯示，拉門全開的傳統式氣罩在操作時，氣罩內部後方區域會存在一大渦漩，因此，在此區域內會造成熱的堆積，相對於其他區域，此區域的溫度高出許多。藉由觀察汙染物的分佈可得知，氣罩的內部空間充滿著硫化氫，而且硫化氫會從氣罩的兩側邊壁洩漏至氣罩外。對於拉門全開的側向吹吸式氣罩而言，在不同的吸吹氣速度下，根據流場情況可歸內出三種模態，分別是擴散模態、過渡模態與包覆模態。在包覆模態下，可確保硫化氫完全被吸氣口排出，且在拉門處的12點濃度值遠低於10 p.p.m. 標準。
當有人員站立在油炸機前方時，對於傳統式氣罩而言，因尾流區的渦漩會將硫化氫捲入，並沿著氣罩與人員之間的上升氣流往人員的呼吸處移動，因此，將會導致操作人員吸入有毒之汙染物或氣體。相對於此，使用側向吹吸式氣罩時，其人員站立不但沒有造成負面影響，反而會提升氣罩的性能表現，跟沒有人員站立時相比，模態圖中的包覆模態操作範圍將會增加。整體而言，側向吹吸式氣罩比傳統式氣罩具有較佳的汙染物捕集性能以確保操作人員的安全。

Hot vapors such as oil fumes are often found in a food factory. For example, deep frying which is a common way to cook food generates tremendous oil fumes in a very hot and wide surface oil tank. In order to capture those hot oil fumes, a novel ventilation system which is called the lateral push-pull ventilation hood for hot toxic vapors from a wide area is proposed in this study. The comparison between the conventional hood and the lateral push-pull ventilation hood on capture performance is undertaken using the finite volume method. The hydrogen sulfide (H2S) which is one of toxic substances in oil fumes is chosen as a pollutant in this study. Moreover, the influence of a manikin standing in front of hood on the capture performance of those two hoods is also explored.
According to the numerical results without a manikin presence, a primary vortex occurs in the fully open conventional hood and the entire space inside the hood is filled with H2S. Meanwhile, leakage of H2S to the indoor environment is found in the edge between the side walls and the environment. For the fully open lateral push-pull ventilation hood, three dominant flow modes which are called dispersion, transition, and encapsulation are determined by the variation of speed ratio of the pull flow to the push flow. In the encapsulation mode, H2S is captured completely by the push-pull capture flow and the concentration values at selected twelve points are far below the criterion of 10 p.p.m..
When a manikin stands in front of the conventional hood, the lifting airflow comes from the gap between the hood and the manikin carries H2S to the breathing zone of the manikin. In contrast, the capture performance of the lateral push-pull hood is not reduced due to a manikin presence but enhanced in the encapsulation mode. H2S also can be expelled and the concentration values at twelve selected points on the sash opening are close to null. In conclusion, the lateral push-pull ventilation hood can effectively prevent the leakage of H2S and protect an operator from those pollutants.

Contents
Chinese abstract I
Abstract III
Acknowledgements V
Contents VII
Nomenclatures IX
List of tables XIII
List of figures XV
1 INTRODUCTION 1
1.1 Motivation 1
1.2 Literature review 3
1.3 Problem discriptions 8
2 MATHEMATICAL MODEL AND NUMERICAL ANALYSIS 9
2.1 Mathematical formulae 9
2.2 Boundary conditions 12
2.3 Discretization methods 14
2.4 Grid independence test 15
3 ANALYSIS OF DIFFERENT VENTILATION SYSTEMS FOR A DEEP FRYER 17
3.1 Analysis of conventional hood 17
3.1.1 Analysis of flow patterns 17
3.1.2 Analysis of temperature fields 18
3.1.3 Analysis of concentration distributions 19
3.2 Analysis of lateral push-pull ventilation hood 20
3.2.1 Analysis of flow patterns under three different modes 20
3.2.2 Analysis of temperature fields under three different modes 21
3.2.3 Analysis of concentration distributions under three different modes 21
4 INFLUENCE OF A MANIKIN STANDING IN FRONT OF A HOOD 25
4.1 Analysis of conventional hood with a manikin presence 25
4.1.1 Effect of manikin on flow patterns 26
4.1.2 Effect of manikin on temperature fields 26
4.1.3 Effect of manikin on concentration distributions 27
4.2 Analysis of lateral push-pull ventilation hood with a manikin presence 27
4.2.1 Effect of manikin on flow patterns 28
4.2.2 Effect of manikin on concentration distributions 28
5 CONCLUSIONS AND SUGGESTIONS 31
5.1 Conclusions 31
5.2 Suggestions 33
Bibliography 35
Curriculum vitae 61
List of tables
Table 1: The physical properties of the hydrogen sulfide39
List of figures
Figure 1: Schematic diagram and computational domain of the lateral push-pull ventilation hood for a deep fryer. (a) schematic diagram; (b) lateral view; (c) front view 40
Figure 2: Computational domain of the conventional hood for a deep fryer. (a) lateral view; (b) front view 41
Figure 3: Boundary conditions. (a) conventional hood; (b) lateral push-pull ventilation hood 42
Figure 4: The grid independence tests. (a) conventional hood; (b) lateral push-pull ventilation hood 43
Figure 5: The locations of origins and the three directions of the coordinates. (a) conventional hood (b) lateral push-pull ventilation hood 44
Figure 6: The streamtrace patterns of the conventional hood. (a) three-dimension; vertical planes at (b) z = 0cm; (c) z = 30cm; (d) z = 48cm; (e) z = -30cm; (f) z = -48cm 45
Figure 7: The temperature fields of various vertical planes of the conventional hood. (a) z = 0cm; (b) z = 30cm; (c) z = 48cm; (d) z = -30cm; (e) z = -48cm 46
Figure 8: The positions of selected twelve points of concentration sampling of the conventional hood 47
Figure 9: The concentrations of the conventional hood. (a) iso-volumes; vertical planes at (b) z = 0cm; (c) z = 48cm; horizontal planes at (d) y = 5cm; (e) y = 30cm 48
Figure 10: The streamtrace patterns in the encapsulation mode of the lateral push-pull ventilation hood. (a) three-dimension; vertical planes at (b) z = 0cm; (c) z = 30cm; (d) z = 48cm; (e) z = -30cm; (f) z = -48cm 49
Figure 11: The temperature fields at z = 0cm in different flow modes of the lateral push-pull ventilation hood. (a) dispersion mode(Vb = 1.4 ms-1, VS = 14 ms-1); (b) transition mode(Vb = 4 ms-1, VS = 14 ms-1); (c) encapsulation mode(Vb = 5.6 ms-1, VS = 14 ms-1) 50
Figure 12: The positions of selected twelve points of concentration sampling of the lateral push-pull ventilation hood 51
Figure 13: The concentrations of the iso-volumes and at z = 0cm in different flow modes of the lateral push-pull ventilation hood. (a)(d) dispersion mode(Vb = 1.4 ms-1, VS = 14 ms-1); (b)(e) transition mode(Vb = 4 ms-1, VS = 14 ms-1); (c)(f) encapsulation mode(Vb = 5.6 ms-1, VS = 14 ms-1)52
Figure 14: The flow mode diagram without a manikin presence of the lateral push-pull ventilation hood 53
Figure 15: The streamtrace patterns with a manikin presence of the conventional hood. (a) three-dimension; vertical planes at (b) z = 0cm; (c) z = 48cm; horizontal velocity vector fields at (d) y = 30cm; (e) enlarged picture of the marked area A 54
Figure 16: The temperature fields with a manikin presence of the conventional hood. (a) iso-volumes; (b) z = 0cm; (c) z = 30cm; (d) z = 48cm; (e) z = -30cm; (f) z = -48cm 55
Figure 17: The concentrations with a manikin presence of the conventional hood. (a) iso-volumes; vertical planes at (b) z = 0cm; (c) z = 48cm; horizontal planes at (d) y = 30cm; (e) y = 60cm 56
Figure 18: The local concentration values at selected twelve points with a manikin presence of the conventional hood 57
Figure 19: The streamtrace patterns with a manikin presence in the encapsulation mode of the lateral push-pull ventilation hood. (a) three-dimension; vertical planes at (b) z = 0cm; (b) z = 30cm; (d) z = 48cm; (e) z = -30cm; (f) z = -48cm 58
Figure 20: The concentrations with a manikin presence in the encapsulation mode of the lateral push-pull ventilation hood. (a) iso-volumes; vertical planes at (b) z = 0cm; (b) z = 30cm; (d) z = 48cm; (e) z = -30cm; (f) z = -48cm 59
Figure 21: The flow mode diagram with a manikin presence of the lateral push-pull ventilation hood 60

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