Particle size and distribution of oil mist from cooking equipments in electrical commercial kitchens

Transcription

1 Indoor Air 8, 7- August 8, Copenhagen, Denmark - Paper ID: 4 Particle size and distribution of oil mist from cooking equipments in electrical commercial kitchens Ryohei oshida, asushi Kondo, Hajime oshino,, Shunsuke Ogita and Miwako Fujita 3 Musashi Institute of Technology TONETS Corporation 3 CHUBU Electric Power * Corresponding g78534@sc.musashi-tech.ac.jp SUMMAR The required ventilation rate in electrical commercial kitchens can be designed to be less than that in gas kitchens because electrical cooking equipment does not produce combustion gas. Therefore, the energy for HVAC (Heating, Ventilation, and Air Conditioning) can be saved in electrical commercial kitchens. However, since electrical cooking equipment generates less heat than gas equipment does, the velocity of the thermal plumes above electrical cooking equipment is relatively lower and they can be disturbed easily by ambient flow, such as air jets from the air-conditioning system and air movement caused by cooking operations. Consequently, the exhaust hood cannot capture a part of the oil mist due to these air disturbances. The behavior of the oil mist from cooking equipment such as fryers should be investigated to design HVAC systems appropriately. In this paper, the particle size of oil mist was measured with a wide-range particle counter (WPC), distribution of oil mist was examined with full-scale experiments and computational fluid dynamics (CFD) simulations. KEWORDS Commercial kitchen, Oil mist, CFD INTRODUCTION In recent years, countries have established their own reduction targets of greenhouse gas emission in the Kyoto protocol as a global warming preventative measure. In Japan, various actions have been conducted to achieve -6% reduction of CO. Because HVAC facilities consume about 6% of the energy of Japan, HVAC in commercial kitchens especially requires a huge amount of energy. The energy savings in commercial kitchens is a very important consideration in the reduction of greenhouse gas emissions. Compared with gas cooking equipment, electrical cooking equipment is useful for reducing ventilation rates and saving energy for HVAC because electrical cooking equipment needs a smaller ventilation rate due to no combustion gas and the heat efficiency is high. However, there is no standard for the ventilation rate in electrical commercial kitchens in Japan. Even though electrical cooking equipment does not exhaust combustion gas, there is a problem with the diffusion and absorption of oil mist in electrical as well as gas kitchens. These behaviors of oil mist should be considered in the design of electrical commercial kitchens. When oil mist can be captured effectively by an exhaust hood, the problems due to oil mist are resolved and the required ventilation rate in electrical commercial kitchens can be reduced. Several research studies aimed at electrical commercial kitchens have been performed in recent years in Japan, but most of these studies investigated indoor thermal conditions and did not consider oil mist distribution. For example, not even the particle size of oil mist emitted from cooking equipment has been studied.

2 In this paper, the measurement results of the particle size of oil mist are discussed. Furthermore, the distribution of oil mist emitted from a fryer was investigated experimentally and computational fluid dynamics (CFD) simulations were conducted. PARTICLE SIE OF OIL MIST Outline of measurements Figure shows the experimental room (4, mm 4, mm,5 mm). Experimental conditions are shown in Table. The particle size of oil mist was measured with a WPC. A fryer was installed at the center of the room and an exhaust hood covered the fryer. Measurement cases Table shows the frozen foodstuffs and measurement cases. In case, the oil temperature was maintained at 8 C without any food in the fryer. In case, french fries were cooked in oil at 8 C. Croquettes and fried chicken were cooked in cases 3 and 4, respectively. In cases, 3 and 4, 3 g of the foodstuffs were fried for 5 minutes and this operation was repeated three times; therefore, one measurement took about 7 minutes. Supply Opening WPC Oil WPC 3,,, 4, 3,, 3 4,, 3 WPC Supply Opening EA EA WPC 3,,, 4, Figure. Experimental room. a) Plan and b) Section. [mm] 3 3,,5 Table. Experimental conditions. Floor, Wall and Ceiling Non-burnable insulation panel 4[mm] thick. Overall heat transfer coefficient =.49[W/m K] Opening Supply opening Area=,5[mm] [mm]. Number = 8. Supply velocity=.[m/s]. Temperature =.[ C]. Exhaust opening Area=,[mm],[mm]. Flow rate=,8[m 3 /h]. face velocity=.3[m/s]. Internal heat generation Dimension= 35[mm] 6[mm] 65[mm]. Maximum heat generation = 4.[kW] Induction heating + Booster heating Lighting 4 [W] 8 Table. Measurement cases. Case Foodstuff Fried volume Case None --- Case French fries 3g 3 times Case 3 Croquettes 3g 3 times Case 4 Fried chicken 3g 3 times

3 7.5E+4 7.5E+4 5.E+4 5.E+4.5E+4.5E+4 E+ 7.5E+4.E-.7E-.6E- 4.E- 6.3E-.E-.7E- 3.E- 5.E- 7.5E-.3E+.3E+ 3.7E+ 6.5E+ 9.5E+ E+ 6.E+6 5.E+6.E-.7E-.6E- 4.E- 6.3E-.E-.7E- 3.E- 5.E- 7.5E-.3E+.3E+ 3.7E+ 6.5E+ 9.5E+ 5.E+4 4.E+6 3.E+6.5E+4.E+6 E+.E-.7E-.6E- 4.E- 6.3E-.E-.7E- 3.E- 5.E- 7.5E-.3E+.3E+ 3.7E+ 6.5E+ 9.5E+.E+6 E+.E-.7E-.6E- 4.E- 6.3E-.E-.7E- 3.E- 5.E- 7.5E-.3E+.3E+ 3.7E+ 6.5E+ 9.5E+ c) d) Figure. Particle size of oil mist. a) Case (No foodstuff), b) Case (French fries), c) Case 3 (Croquettes) and d) Case 4 (Fried chicken). * Vertical scale: number of oil mist particles [unit/cc] and Horizontal scale: particle size [μm] Results and discussions Figure shows the results of the measurement of the particle sizes of oil mist. Suspended particles and water vapor were generated due to the cooking operation in the experimental room, and the measured data contained these particles. The preliminary experimental results confirmed that they did not have a large effect on the measured data. The horizontal scale of Figure shows the particle size from μm to μm. The vertical scale shows the number of mist particles per cc. The measurements were carried out ten times in each case and the measured data were averaged. In case (Figure a)), the number of particles was slightly larger than the background value of the room, which is not shown in Figure. The peak particle number was.e+4 unit/cc when the particle size was 5 μm. In case (Figure b)), the particle size does not exceed 8 μm. The peak particle number was.7e+4 [unit/cc] at μm. More smaller particles were generated than in case. In case 3 (Figure c)), the particle size does not exceed 8 μm, as in case. The peak particle number was 5.6E+4 unit/cc at 3 μm. Twice as many particles of oil mist were generated than in case. Also, as in case, smaller particles were generated. In case 4 (Figure d)), the maximum particle size was 65 μm and the peak particle number was much larger than in the other cases. The peak number was 4.E+6 unit/cc when the particle size was 5 μm. The particle number of oil mist emitted in case 4, in which fried chicken was cooked, was 5 times as many as that in case, in which french fries were cooked, and 7 times as many as that in case 3, in which croquettes were cooked. In summary, the particle sizes of the three foodstuffs ranged from μm to 8 μm.

4 3 4 Lighting Result Explaining Section 7 8 9,,,, 4, Disturbance Generator Pole,,,, 4, FL+,45 FL+,5 FL+,65 FL+,5 FL+85 FL+45 FL+5 8 Lighting Figure 3. Experimental room. a) Plan and b) Section. [mm] Pol e Disturbance Generator 5, Fr yer , EA 3,5 7,5 :air temperature :surface temperature : gas concent r at i on :radiant temperature Table 3. Experimental conditions. Mad of Non-burnable insulation panels 4[mm] thick. Floor, Wall and Ceiling Overall heat transfer coefficient =.49[W/m K] Supply opening Area=,5[mm] [mm]. Number = 8 Opening Internal heat generation Exhaust opening Area=, [mm], [mm] Dimension=35[mm] 6[mm] 65[mm] Maximum heat generation = 4.[kW] Induction heating + Booster heating Electrical Dimension=37[mm] 6[mm] 65[mm] Gas Maximum heat generation=8.4[kw] Lighting 4 [W] 8 DISTRIBUTION OF OIL MIST IN EPERIMENTAL ROOM Outline of measurements Figure 3 shows the experimental room (4, mm 4, mm,5 mm). Experimental conditions are shown in Table 3. The measurement of particle size shows that gravity sedimentation of oil mist can be neglected. Therefore, oil mist can be treated as a passive scalar such as a tracer gas (SF 6 ). In this section, the distribution of SF 6 concentration was measured in the experimental room. Several points of oil mist concentration were also measured and the relationship between SF 6 and the oil mist concentration was examined. Measurement cases Table 4 shows the measurement cases. Three parameters were examined: the type of fryer (electrical or gas), hood face velocity (.3 m/s or.5 m/s) and existence or non-existence of air disturbance. In the experiments, a fryer was installed along the wall, a hood covered the fryer, and the oil temperature was set at 8 C. SF 6 was injected at a constant flow rate of.5 [L/min] from the center top of the fryer. The air temperatures were measured with thermocouples at 78 points and the concentrations of SF 6 were measured in real time with a gas monitor. The measurement results confirmed that the indoor temperature and SF 6 concentration became steady state. Then, the data for 3 minutes was averaged and examined. A mist of canola oil was emitted by the aerosol generator with constant flow rate of.56 [mg/h] at the same point where SF 6 was injected (center top of the fryer), and the concentrations of oil mist were measured by a piezo-balance dust monitor at three points: FL + mm, FL +,5 mm and FL +,5 mm of pole No. 5, shown in Figure 3.

5 Table 4 Experimental cases. Cases Heat source Case I Electrical Case G Gas Case Id Electrical Case Gd Gas Case I-5 Electrical Case G-5 Gas Case I-5d Electrical Case G-5d Gas Flow rate ( face velocity) Supply air temperature 35[m 3 /h] (.3[m/s]) T in =[ C] 58[m 3 /h] (.5[m/s]) T in =3[ C] Disturbance Off On Off On Distance between and.[m] Oil mist y = 6 x SF 6 Figure 4. Relationship between SF 6 and oil mist concentration. *Vertical scale= mg/m 3 and horizontal scale= ppm. In order to apply a load to the fryer, a metal pipe was set in the oil tank of the fryer. In the pipe, water of constant temperature ran at a constant flow rate. In the case of the disturbed condition, a disturbance generator was used. The disturbance generator is prescribed in the test method of hood efficiency for commercial kitchens in North Europe (Nordtest method VVS88). Results and discussions The relationship between SF 6 concentration and oil mist concentration is shown in Figure 4. Figure 5 shows the indoor air temperature distribution, SF 6 concentration and oil mist concentration on the vertical section at the center of the experimental room (=. mm). The concentration of oil mist in Figure 5 was estimated from the measurement value of SF 6 based on the relationship between SF 6 concentration and oil mist concentration. () Temperature distribution The disturbance generator makes the air temperature (Figure 5 b), d), f), h)) much higher than that of the case without the disturbance (Figure 5 a), c), e), g)). The air temperature of the electrical fryer case was lower than that of the gas fryer case, because the temperature of the thermal plume above the gas fryer was high and part of the plume leaked out of the exhaust hood. () Distribution of SF 6 (oil mist) concentration Type of flyer: The concentration at the upper area of experimental room in case G was higher than that in case I (see Figure 5 a) and c)) because part of the thermal plume above the gas fryer leaked out of the hood. face velocity: In the case of the high face velocity, the concentration was smaller than that in the low face velocity. Especially in case G-5, the concentration was much smaller than in case G (see Figures 5 c) and g)).

6 c) d) [ ] 3. e) f) [ ] g) h) Figure 5. Air Distribution. a) Case I, b) Case Id, c) Case G, d) Case Gd, e) Case I-5,f) Case I- 5d, g) Case G-5, h) Case G-5d. *Contour line means temperature [ C]. Upper numbers in white squares are SF 6 concentrations [ppm] and lower numbers in red square are oil mist concentrations [mg/m 3 ]. Air disturbance: When the disturbance generator was operated, the concentration was large because the thermal plume was disturbed and high temperature and contaminant air were diffused to the occupied zone. CFD SIMULATION Outline of CFD simulation The experimental room was analyzed by CFD simulations with the same condition as the experiments (Figure 3). The two cases in Table 5 were studied with the conditions shown in Table 6.

7 The particle size distribution experiment showed that the gravity sedimentation of oil mist was negligible and oil mist could be regarded as a passive scalar in the CFD simulations. The absorption of oil mist on solid surfaces such as walls should be considered in the CFD simulations. In this study, the solid surface concentration and the mass-transfer coefficient were assumed to be mg/kg and.3 m/h, respectively. Table 5. Simulation cases. Cases type Case I Electric Case G Gas Flow rate (Face velocity) 35 [m 3 /h] (.3 [m/s]) Air disturbance Off Distance between and. [m] Table 6. Simulation conditions. Simulated Area (,, ) Mesh division Turbulence model Electrical fryer Heat conditions Emit conditions Surface conditions Gas fryer Lighting SF 6 Oil mist Velocity Temperature Concentration (Oil mist).5[m] 4.3[m].8[m] 68() 9() 98()=599,76 Meshes Standard k-ε Model Oil : 99 [W] Oil : 5, 59[W], Front part : 5.6 [W], Side part :.5 [W], Front upper part : 6.3 [W] 8[W] =6[W] From the center top of fryer :.5[L/min] From the center top of fryer :.56[mg/h] Generalized log-law Interaction of convection and radiation is concerned Solid surface concentration = [mg/kg] Mass-transfer coefficient =.3 [m/h] フード 3 9 フライヤー 7 5 [ ] a-) - section a-) - b-) - section b-) - Figure 6. Temperature distribution. a) Case I ( type. Electrical), b) Case G ( type. Gas) [ C] [mg/m3]] ] a-) - section a-) - b-) - section b-) - Figure 7. Distribution of oil mist. a) Case I ( type. Electrical), b) Case G ( type. Gas) [mg/m 3 ]

8 RESULTS AND DISCUSSIONS () Temperature distribution (see Figure 6) Figure 6 shows the air temperature distribution. The air temperature of the upper part in case G was approximately 6 C higher than that in case I. The thermal plume leaks through the side surfaces of the hood along the wall in both cases. In case G, the thermal plume leaks from the front surface of the hood, too. A situation similar to this result was observed in the visualization experiment () Oil mist distribution (see Figure 7) Figure 7 shows the distribution of oil mist. The numbers in white squares in Figure 7 are the experimental results. The oil mist distribution was similar to the air temperature distribution and the hood in both cases and does not capture any part of the oil mist. In case I, the oil mist concentration was relatively low compared to that in case G. CONCLUSIONS The particle size distribution of oil mist was measured when three types of frozen foods were cooked. Also, the air temperature and oil mist distribution in a commercial kitchen were measured in a full-scale experimental room and then reproduced by CFD simulations. () The particle size of oil mist from the fryer was less than.5 μm. Therefore, the gravity sedimentation oil mist was negligible and oil mist could be treated as a passive scalar in CFD simulations. () The correlationship between SF 6 concentration and oil mist concentration was confirmed by the experiments. The air temperature in the case with the electrical fryer was about 6 C lower than that in the gas fryer. The oil mist concentration of the upper area of experimental room was higher than in the lower part and the concentration in the case of the electrical fryer was lower than that in the case of the gas fryer. (3) The temperature distributions given by CFD were similar to the experimental ones. The experimental results and the CFD results of the oil mist concentration corresponded well when the mass-transfer coefficient was assumed to be.3 m/h. ACKNOWLEDGEMENT The authors appreciate Syuji Sasaki and Jinya Takeuchi of TONETS Corporation. REFERENCES Shunsuke O., asushi K. et al. 6. Convection and Diffusion of Oil Mist in Electrical Commercial Kitchens Part. Experiments on Particle Size and Emission Method of Oil Mist from Cooking Equipments. Technical Papers of Annual Meeting, The Society of Heating, Air-conditioning and Sanitary Engineers of Japan. (In-Japanese) Nordtest method VVS88, BUILDING LARGE SCALE KITCHEN RANGE HOODS- HOOD EFFICIENC AND PRESSURE DROP Toshinari M., Ryuji S. et al.. The Influence that Ambient Flow Give to Capture Efficiency of in Commercial Kitchen. Journal of designing, The Architectural Institute of Japan, No. 56, pp. 5-. Qingyu., Shinsuke K. et al. 4. Test Chamber Experiment and. Journal of environmental engineering, The Architectural Institute of Japan, No. 58, pp