Effect of Jet Disturbance on Convective Flow from a Heat Source

Transcription

1 Effect of Jet Disturbance on Convective Flow from a Heat Source Esa Sandberg Principal Lecturer Satakunta Polytechnic, Finland (since Satakunta University of Applied Sciences) Tel esa.sandberg@samk.fi Hannu Koskela and Pekka Saarinen Finnish Institute of Occupational Health, Finland

2 Effect of Jet Disturbance on Convective Flow from a Heat Source Aim of the study Modelling of the effects of jet disturbance on convective flow (=plume) characteristics Hypothesis The air flow rate of the plume will be increased by disturbances

3 A part of a project Convective Flows from Heat Sources 1. Effects of disturbances on a plume Jet Floor current Moving plate (simulating a person) 2. Effect of heat location on plumes (INRS, FIOH) 3. Real plumes Kitchen cookers Data and overhead projector

4 The content of the paper and presentation Effect of Jet Disturbance on Convective Flow from a Heat Source 1. Convective flows in room air conditioning design 2. Engineer modelling of plumes 3. Measurement methods 4. Measurement results and modelling - undisturbed cases - disturbed cases 5. Conclusions

5 Convective flows and room air conditioning design DGB Industrial ventilation 2001 ROOM AIR CONDITIONING STRATEGY The idea and the target of stratification in a space PISTON STRATIFICATION ZONING MIXING Room dimension EX EX EX EX SU SU = SUPPLY EX = EXHAUST T, C, x SU SU T, C, x T, C, x SU T, C, x T = TEMPERATURE C = CONCENTRATION x = ABS. HUMIDITY

6 Convective flows and room air conditioning design Stratification Kerrostuma Zoning Vyöhyke When the stratification and zoning strategies are applied the plumes are the key flow elements for - dimensioning the supply air flow rate - designing the air distribution method in order to achieve a high heat and contaminant removal efficiency

7 Convective flows and room air conditioning design Stratification Kerrostuma Zoning Vyöhyke Also when a local exhaust method is applied the plumes are the key flow elements for - dimensioning the air flow rate - designing and dimensioning the hood

8 Convective flows from heat sources The air flow rate and the shape of the convective flow are dependant especially on the - dimensions - shape - convective heat power of the heat source, but also on the - disturbances around the plume?

9 Engineer modelling Plume equations (r) v z r z Air flow rate (not for linear source) q = A q P 1/3 c ( z zvirt ) 5/3 In modelling can be varied the dimension Zvirt (free convection, different shapes of the heat source) or the factor Aq (partly forced convection, disturbances). z virt Momentum flow rate M = A M P 2/3 c ( z zvirt ) 4/3

10 Visualisointi videokuvauksella ja savua käyttäen Heat source Measurement cases Convection W Radiation W Total W

11 Disturbed plumes Measurements at FIOH Turku - thermal insulated test room 10m x 4m x 6m - undisturbed conditions require very even supply air distribution - nozzle ducts were used - Kaijo ultrasonic probes

12 Visualization of plumes Photo and video documentation Fast temperature measurements with Dantecin omnidirectional probes -> excel animation Smoke Helium filled soap bubbles

13 Undisturbed plume 4,0 m 12 measurement cases 1,25 m 3,0 m 2,0 m - 4 different electric power (heat power) - 3 height levels of measurement plane - area 2,1 m x 1,7 m - 1 vertical measurement plane - grid 100 mm x 100 mm - velocity, temperature, 1 min average - measurement time with 2 probes was h / case

14 Undisturbed plume vz [m/s] 0,425-0,475 S17 S15 S13 S11 0,375-0,425 0,325-0,375 0,275-0,325 0,225-0,275 Measurement and analysis S9 0,175-0, S7 S5 S3 21S1 0,125-0,175 0,075-0,125 0,025-0,075-0,025-0,025 - background velocity with Gaussian fit - air flow rate q = Σ ( A v i i ) 0,5 0,4 0,3 0,2 Vz Gauss-käyrä - momentum flow rate M = Σ( ρ A v i i 2 i - average radius / diameter -> virtual origin - coefficients of the plume equations ) r = q ρ /( πm ) 0,1 q = A q P 1/3 c ( z zvirt ) 5/ ,5 1 1,5 2 M = A M P 2/3 c ( z zvirt ) 4/3-0,1

15 Undisturbed plume 25, , S18 S17 S16 S15 S14 S13 S12 S11 S10 S9 S8 S7 S6 S5 S4 S3 S2 21 S1 T T [C] Gauss-käyrä 27, ,5 26, ,5 25, ,5 24, ,5 23, ,5 22, ,5 21, ,5 20, ,5 Measurement and analysis - background temperature with Gaussian fit - low temperature differences -> inaccuracy - radiation heat flow rate was determined using 25 measured surface temperatures on the cylinder and calculated view factors to surrounding surfaces 24 - in the model P conv = P electr -P rad 23, , ,5 1 1,5 2

16 Undisturbed plume radius / diameter -> virtual origin z virt = - 0,16 m (under the floor) Radius Plume radius 0 m/s (undisturbed) 1,0 0,9 0,8 0,7 r = q ρ /( πm ) 148 W 297 W Plume radius (m) 0,6 0,5 0,4 0,3 R 2 = 0,9962 R 2 = 0,9961 R 2 = 0,9923 R 2 = 0, W 890 W Ave Lin. (148 W) Lin. (297 W) Lin. (594 W) Lin. (890 W) 0,2 y = 0,1321x + 0,0213 R 2 = 0,9998 Lin. (Ave) 0,1 0,0-1,0-0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 Floor level Virtual origin / average Measurement height level (m) Measurement height level

17 Undisturbed plume Plume air flow rate vs. convection heat, fit result -> A q = 3,38 Plume air flow rate as a function of plume convection heat flow rate, 0 m/s (undisturbed) q = A q P 1/3 c ( z zvirt ) 5/3 Plume air flow rate (l/s) m/s, 2 m 0 m/s, 3 m 0 m/s, 4 m 0 m/s, 2 m model 0 m/s, 3 m model 0 m/s, 4 m model Plume convection heat flow rate (W)

18 Undisturbed plume Measurements and modelling Air flow rate Measured and modelled plume air flow rate, undisturbed Momentum flow rate Measured and modelled plume momentum flow, jet distance 1 m, height 2 m, all cases q = A q P 1/3 c ( z zvirt ) 5/3 0,10 M = A M P 2/3 c ( z zvirt ) 4/ ,08 y = 0,9855x R 2 = 0,9896 Modelled plume air flow rate (l/s) y = 0,9988x R 2 = 0,9937 Modelled plume momentum flow (N) 0,06 0 m/s Lin. (0 m/s) 0,04 0 m/s Lin. (0 m/s) 100 0, Measured plume air flow (l/s) 0,00 0,00 0,02 0,04 0,06 0,08 0,10 Measured plume momentum flow (N)

19 Disturbed plumes / Jet 4,0 m Horizontal jet, 40 measurement cases 2,5 m 1,0 m 3,0 m - φ100 mm duct - 4 flow velocities 0,25, 0,5, 0,75, 1,0 m/s 2,0 m 2,0 m -> 0 8 l/s 1,5 m - distances 1 m (basic) ja 2 m 1,0 m - 4 jet height levels (basic 2m) 0,5 m

20 Measurement arrangement of jet disturbance

21 S 1 6 S 1 Disturbed plumes / Jet Example Air velocity distribution at a horizontal measurement plane at height 2 m with jet velocities 0 1 m/s 0 m/s 0,25 m/s 0,50 m/s 0,75m/s 1,0 m/s S16 S16 S16 S16 S16 S13 S13 S13 S13 S13 S10 S10 S10 S10 S10 S7 S7 S7 S7 S7 S4 S4 S4 S4 S S S S S S1-0,025-0,025 0,025-0,075 0,075-0,125 0,125-0,175 0,175-0,225 0,225-0,275 0,275-0,325 vz [m/s] tendence for spreading

22 Undisturbed Jet velocity 0 m/s S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 S14 S15 S16 S17 S18 S19 S20 S Jet velocity 0,75 m/s Disturbed plumes / Jet Convection 200 W Temperature Velocity

23 Disturbed plumes Radius of plume -> Virtual origin of undisturbed case Z virt =-0,16 m was used in modelling Radius Plume radius with disturbance, all plume power cases, jet distance 1 m and height 2 m 1,0 0,9 Plume radius (m) 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0 m/s 0,25 m/s 0,5 m/s 0,75 m/s 1 m/s Lin. (0 m/s) Lin. (0,25 m/s) Lin. (0,5 m/s) Lin. (0,75 m/s) Lin. (1 m/s) 0,1 0,0-1,0-0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 Measurement height level (m) Measurement height level

24 Relative plume equation coefficient A q vs. disturbance jet velocity Aq/Aq0 Relative plume coefficient A q, jet distance 1 m and 2 m, height 2 m 2,0 1,8 Relative coeeficient Aq 1,6 1,4 1,2 q = A q P 1/3 c ( z zvirt ) 5/3 Aq/Aq0 Aq/Aq0 (2m) Lin. (Aq/Aq0) Aq/Aq0 (2m) 1,0 0,8 0,00 0,25 0,50 0,75 1,00 Jet velocity (m/s)

25 Relative plume air flow rate vs. relative disturbance M jet /M 02m M 02m is the momentum flow rate at 2 m level in the undisturbed case Relative air flow rate, jet distance 1 m and height 2 m 5,5 5,0 4,5 4 m Relative air flow rate q / q02m 4,0 3,5 3,0 2,5 2,0 1,5 3 m 2 m 2 m 3 m 4 m Lin. (2 m) Lin. (3 m) Lin. (4 m) 1,0 0,5 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 Relative disturbance M jet / M 02m

26 Increase of plume air flow rate vs. relative disturbance jet distance 1 m and jet height 2 m Corrected increase of relative air flow rate, jet distance 1 m and height 2 m 100 % 80 % Increase of relative air flow rate 60 % 40 % 20 % 3m R 2 = 0,7544 y = -0,2813x 2 + 0,8746x Ave R 2 = 0, m 3 m 4 m polyn Polyn. (2 m) Polyn. (3 m) Polyn. (4 m) Polyn. (polyn) 0 % 0,0 0,2 0,4 0,6 0,8 1,0 1,2-20 % Relative disturbance M jet / M 02m

27 Plume air flow rate and radius vs. relative disturbance M jet /M 02m Air flow rate, jet distance 1 m Air flow rate, jet distance 2 m Corrected relative air flow rate, jet distance 1m and height 2 m Corrected relative air flow rate, jet distance 2m and height 2 m 5,5 5,5 5,0 5,0 Relative air flow rate (q/q02m) / (M/M02m)^0,5 4,5 4,0 3,5 3,0 2,5 2,0 1,5 1,0 R 2 = 0,864 R 2 = 0,9247 R 2 = 0, m 3 m 4 m Lin. (2 m) Lin. (3 m) Lin. (4 m) Relative air flow rate (q/q02m) / (M/M0/M02m) 4,5 4,0 3,5 3,0 2,5 2,0 1,5 1,0 R 2 = 0,9362 R 2 = 0,2133 R 2 = 0, m 3 m 4 m Lin. (2 m) Lin. (3 m) Lin. (4 m) 0,5 0,5 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 Relative disturbance Mjet / M02m 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 Relative disturbance Mjet / M02m Radius, jet distance 1 m Radius, jet distance 2 m Plume radius, jet distance 1 m and height 2 m Plume radius, jet distance 2 m and height 2 m 1,0 0,9 1,0 0,9 0,8 R 2 = 0,864 0,8 Plume radius (m) 0,7 0,6 0,5 0,4 0,3 R 2 = 0,9247 R 2 = 0, m 3 m 4 m Lin. (2 m) Lin. (3 m) Lin. (4 m) Plume radius (m) 0,7 0,6 0,5 0,4 0,3 R 2 = 0,9362 R 2 = 0, m 3 m 4 m Lin. (2 m) Lin. (3 m) Lin. (4 m) 0,2 0,2 R 2 = 0,0424 0,1 0,1 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 Relative disturbance M jet / M 02m 0,0 0,0 0,2 0,4 0,6 0,8 1,0 1,2 1,4 Relative disturbance M jet / M 02m

28 Air flow rate at 3 m vs. jet height level Plume air flow rate at height 3 m, 594 W Plume air flow rate (l/s) m/s 0,25 m/s 0,5 m/s 0,75 m/s 1 m/s 0,75 m/s (2m) ,0 0,5 1,0 1,5 2,0 2,5 3,0 Jet height (m)

29 Summary and conclusions 1. Air flow rate was increased by the jet disturbance up to 60%. 2. Correlation between the increase of air flow rate and radius is high. 3. The increase was continued when the disturbance increased until the plume skipped out from the measurement area. 4. The increase of the air flow rate must be paid attention to when the stratification and zoning room air condition strategies are applied. & Even in laboratory environment the undisturbed flow field is not easy to arrange

30 Thank You Esa Sandberg