Available online at www.sciencedirect.com Available online at www.sciencedirect.com Available online at www.sciencedirect.com
ScienceDirect ScienceDirect ScienceDirect
Available online at www.sciencedirect.com Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000 Procedia Engineering 00 (2017) 000–000
ScienceDirect
Procedia Engineering 205 (2017) 3112–3116
www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia
10th International Symposium on Heating, Ventilation and Air Conditioning, ISHVAC2017, 19-22 October 10th Air 2017, Jinan,and China 10th International International Symposium Symposium on on Heating, Heating, Ventilation Ventilation and Air Conditioning, Conditioning, ISHVAC2017, ISHVAC2017, 19-22 19-22 October October 2017, Jinan, China 2017, Jinan, China
Simulation of Airflow Characteristics induced by Fabric Air Dispersion Simulation of Airflow Characteristics induced by Fabric Air Dispersion Simulation of Airflow Characteristics induced by Fabric Air Dispersion System with Orifices Using Direct Description Method System with Orifices Using Direct Description Method System with Orifices Using Direct Description Method ∗ Fujiang Chen ∗, Wang Lu, Qinyu Wu, Haifei Chen, Jianfang Chen, Nianyong Zhou Fujiang Chen ∗, Wang Lu, Qinyu Wu, Haifei Chen, Jianfang Chen, Nianyong Zhou Fujiang Chen , Wang Lu, Qinyu Wu, Haifei Chen, Jianfang Chen, Nianyong Zhou Department of Building Environment and Energy Engineering, Changzhou University, Changzhou 213164, China Department of Building Environment and Energy Engineering, Changzhou University, Changzhou 213164, China Department of Building Environment and Energy Engineering, Changzhou University, Changzhou 213164, China
Abstract Abstract Abstract In present work, the FADS is described using the porous media model, which is called the direct description (DD) method. The simulation is In present work, the commercial FADS is described using the with porous media model, called the direct The simulation is k - ε which model.is resultsdescription show that, (DD) when method. air is generated by FADS conducted using the software Fluent modified In present work, FADS is described using the porous media model, which isSimulation called the direct description (DD) method. The simulation is conducted using the commercial software Fluent with modified k - ε model. Simulation results show that, when air is generated by FADS with orifices, the the partcommercial of supply airflow is penetrated from the porous at a lower speed, and the left is that, jettedwhen out through orifices atbya higher k - fibre ε model. Simulation results show air is generated FADS conducted using software Fluent with modified with orifices, the part of supply airflow is penetrated from the porous fibre at a lower speed, and the left is jetted out through orifices at a higher speed, and then, airflow together at a certain distance. air velocity is lower and air temperature the upper is with orifices, the both part of supplymerge airflow is penetrated from the porousThe fibreindoor at a lower speed, and the left is jetted out throughinorifices at azone higher speed, and then, both airflow merge together at a certain distance. The indoor air velocity is lower and air temperature in the upper zone is lower the lower yettogether the vertical difference is less air thanvelocity 3 K. Furthermore, lengthinhasthegreat impact speed, than and that then,inboth airflowzone, merge at a temperature certain distance. The indoor is lower andthe airFADS’ temperature upper zone on is lower than that in the lower zone, yet the vertical temperature difference is less than 3 K. Furthermore, the FADS’ length has great impact on the distribution air zone, velocity The proper distanceisshould be determined in orderthe to obtain uniformly lower than that of in indoor the lower yetand thetemperature. vertical temperature difference less than 3 K. Furthermore, FADS’more length has greatdistribution impact on the distribution of indoor velocity and temperature. The proper distance should be determined in order to obtain more uniformly distribution of indoor air velocity and air temperature. the distribution of indoor air velocity and temperature. The proper distance should be determined in order to obtain more uniformly distribution of indoorThe airAuthors. velocity and temperature. © 2017 Published by Elsevier Ltd. of indoor air velocity and temperature. Authors. Publishedby by Elsevier Ltd. committee of the 10th International Symposium on Heating, Ventilation and Air © 2017 The Authors. Published Ltd. Peer-review under responsibility ofElsevier the scientific © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility responsibilityof ofthe thescientific scientificcommittee committeeofofthe the10th 10thInternational InternationalSymposium SymposiumononHeating, Heating,Ventilation Ventilation and Air Peer-review under and Conditioning. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. Air Conditioning. Conditioning. Keywords: Fabric air dispersion system (FADS); Orifice; Direct description (DD) method; Length; Velocity distribution; Temperature distribution Keywords: Fabric air dispersion system (FADS); Orifice; Direct description (DD) method; Length; Velocity distribution; Temperature distribution Keywords: Fabric air dispersion system (FADS); Orifice; Direct description (DD) method; Length; Velocity distribution; Temperature distribution
1. Introduction 1. Introduction 1. Introduction The indoor environment quality not only largely influences people’s health, but also affects occupants’ work efficiency and The indoor environment quality not only largely influences people’s health, but also affects occupants’ work efficiency and production process [1], and quality it is greatly affected byinfluences the performance ventilation system, especially the work ventilation terminal The indoor environment not only largely people’sofhealth, but also affects occupants’ efficiency and production process [1], and it is greatly affected by the performance of ventilation system, especially the ventilation terminal diffusers [2-4]. As a[1], special of polymer, the fabric air dispersion system (FADS), transports and production process and ventilation it is greatlyterminal affectedmade by the performance of ventilation system, especially thewhich ventilation terminal diffusers [2-4]. As a special ventilation terminal made of polymer, the fabric air dispersion system (FADS), which transports and distributes[2-4]. the airflow into the designedterminal indoor space, many advantages over the system conventional ventilation system, such diffusers As a special ventilation made possesses of polymer, the fabric air dispersion (FADS), which transports and distributes the airflow into the designed indoor space, possesses many advantages over the conventional ventilation system, such as low air velocity, light weight, convenient installation etc. [5]. many advantages over the conventional ventilation system, such distributes the airflow into the designed indoor space, possesses as low air velocity, light weight, convenient installation etc. [5]. Recently, researches theconvenient indoor airinstallation environment by FADS have been carried out. Nielsen et al. [6] used the as low air velocity, light about weight, etc.generated [5]. Recently, researches about the indoor air environment generated by FADS have been carried out. Nielsen et al. [6] used the fullRecently, field measurement to indoor study the characteristics test room, textile et terminal researches method about the air airflow environment generatedinbya FADS haverespectively been carriedwith out. aNielsen al. [6] (FADS), used the full field measurement method to study the airflow characteristics in a test room, respectively with a textile terminal (FADS), ceiling-mounted and wall -mounted air diffusers. They concluded that system on textilewith terminals wasterminal able to (FADS), generate full field measurement method to study the airflow characteristics in the a test room,based respectively a textile ceiling-mounted and wall -mounted air diffusers. They concluded that the system based on textile terminals was able to generate the comfortable velocity temperature distribution under other conditions. Qian et al. [4] recommended the ceiling-mounted and walland -mounted air diffusers. Theyindoors concluded thatthethesame system based on textile terminals was able to generate the comfortable velocity and temperature distribution indoors under the same other conditions. Qian et al. [4] recommended the use comfortable of downwardvelocity ventilation baseddistribution on FADS with openings in isolation rooms to reduceQian the risk cross-infection the and systems temperature indoors under the same other conditions. et al.of[4] recommendedfrom the use of downward ventilation systems based on FADS with openings in isolation rooms to reduce the risk of cross-infection from airborne transmissible diseases. Chenbased et al. on [7] FADS numerically studied the effects ofrooms four layouts of the FADS mode on use of downward ventilation systems with openings in isolation to reduce risk in of penetration cross-infection from airborne transmissible diseases. Chen et al. [7] numerically studied the effects of four layouts of FADS in penetration mode on indoor airflow pattern, diseases. and found thatetthe mounted on the ceiling with of exhaust openingofon upperinsidewalls generated airborne transmissible Chen al.FADS [7] numerically studied the effects four layouts FADS penetration mode ona indoor airflow pattern, and found that the FADS mounted on the ceiling with exhaust opening on upper sidewalls generated a better indoor environment, which characteristics of more uniform temperature distribution and lower air velocity thana indoor airflowairpattern, and found thathad thethe FADS mounted on the ceiling with exhaust opening on upper sidewalls generated better indoor air environment, which had the characteristics of more uniform temperature distribution and lower air velocity than the other layouts. Turbulence which intensity rate distributions indoors are important indexes and to evaluate indoorthan air better indoor air environment, hadand the draught characteristics of more uniform temperature distribution lower airthe velocity the other layouts. Turbulence intensity and draught rate distributions indoors are important indexes to evaluate the indoor air thermal et al. [8]intensity studied the of the indoorindoors air temperature and velocity in different the othercomfort. layouts.Shen Turbulence andcharacteristics draught rate distributions are important indexesfield to evaluate theconditions. indoor air thermal comfort. Shen et al. [8] studied the characteristics of the indoor air temperature and velocity field in different conditions. Chen et comfort. al. [7,9] numerically studied thethe heat capacity of the FADS in pure-penetration mode and the effect of its layout on the thermal Shen et al. [8] studied characteristics of the indoor air temperature and velocity field in different conditions. Chen et al. [7,9] numerically studied the heat capacity of the FADS in pure-penetration mode and the effect of its layout on the indooretairflow and developed studied a new description methodoftothe model FADS in simulation using porous media which Chen al. [7,9] numerically the heat capacity FADS in pure-penetration modethe and the effect ofmodel its layout on has the indoor airflow and developed a new description method to model FADS in simulation using the porous media model which has indoor airflow and developed a new description method to model FADS in simulation using the porous media model which has * Corresponding author. Tel.:+86-1396-1459-209 * Corresponding author. Tel.:+86-1396-1459-209 E-mail address:author.
[email protected] * Corresponding Tel.:+86-1396-1459-209 E-mail address:
[email protected] E-mail address:
[email protected] 1877-7058 2017 Authors. Published by Ltd. Elsevier Ltd. 1877-7058 ©©2017 TheThe Authors. Published by Elsevier 1877-7058 2017 Theresponsibility Authors. of Published by Elsevier Ltd.committee Peer-review under of the scientific of the 10thSymposium International Symposium onand Heating, Ventilation and Peer-review© under responsibility the scientific committee of the 10th International on Heating, Ventilation Air Conditioning. 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning. Air Conditioning. Peer-review under responsibility of the scientific committee of the 10th International Symposium on Heating, Ventilation and Air Conditioning.
10.1016/j.proeng.2017.10.322
Fujiang Chen et al. / Procedia Engineering 205 (2017) 3112–3116
Fujiang Chen, et al. / Procedia Engineering 00 (2017) 000–000
3113
been validated. Fontanini et al. [10] used fully three dimensional computational (CFD) simulations to quantificationally discuss airflow pattern and thermal evaluation within a room ventilated by FADS and ceiling diffuser systems under the steady and transient state, respectively. Results showed that FADS heated the room faster, more uniformly than the conventional system (ceiling diffuser systems) did. Also, Chen et al. [11] analyzed the effect of several parameters, including fibre porosity, equivalent diameter, on characteristics of airflow generated by fabric air dispersion system in penetration mode. The mentioned researches mainly discussed the case relative to FADS in penetration mode. As a matter of fact, airflow can discharge out through FADS by means of penetrating and jetting according to the case whether there is opening across FADS or not. And few studies about the characteristics of airflow generated by FADS with orifices have been conducted. This paper is aim to numerically investigate the characteristics of indoor airflow induced by FADS with orifices using the direct description method, meanwhile, the effect of FADS’ length on air velocity and temperature is also discussed. 2. Methods 2.1 Physical model A room with the dimensions of 4.2 m × 3.6 m × 2.5 m (length × width × height) is established. A half cylindrical FADS with orifices is mounted symmetrically below ceiling in the X direction. The upper and front facet of FADS is not penetrable. Air inlet of room is the inlet of FADS. Air outlet is located on the left and right walls at the floor level. There are two computers, two occupants and two tables. The heat loads from computers and occupants are 146 and 334 W, respectively. Three rows of orifices are designed across the fibre volume of FADS in the direction of 3 o’clock, 6 o’clock and 9 o’clock respectively. The FADS’ diameter is 305 mm and the thickness is 0.47 mm. The fibre porosity is 0.64. All room walls are insulated. Figure 1 shows the geometry of a simulation room with a half-cylindrical FADS with orifices.
Fig.1. Geometry of a simulation room with half-cylindrical FADS with orifices
2.2 Governing equations In the simulation, we assume that the air is incompressible and all room walls are adiabatic. In addition, the fibre material is assumed to be rigid, isotropic and saturated. And the fibre volume of FADS is described as a porous media with a certain depth. Based on the above assumptions, the conservation of mass, momentum, energy equations [2,12,13] can be written as:
∂ ( ρφ ) + div ( ρU φ ) = div ( Γφ gradφ ) + Sφ + Si ∂t
(1)
Where ρ is air density, kg/m3, U is air velocity vector, m/s, φ is general variable, Γφ is the generalized diffusion coefficient and Sφ is the generalized source. When φ = 1,U ( u, v, w ) , T , k , ε , the Eq. (1) represents continuity equation, momentum equation, energy equation, k equation and ε equation, respectively. Si represents the total resistance when airflow flows through the porous fibre structure (Neale 1974), and it can be expressed by the Forchheimer equation: μU ρ C f U U Si = − + α α
Here α represents the permeability of porous fibre and expressed as the following equation [14]:
(2)
Cf
is a dimensionless constant of porous fibre. They can be
Fujiang Chen et al. / Procedia Engineering 205 (2017) 3112–3116
3114
α=
Fujiang Chen, et al. / Procedia Engineering 00 (2017) 000–000 DP2η 2
(3)
100 (1 − η )
Cf =
2
1.2 100η
3
2
(4)
2.3 Boundary conditions and solution Inlet air is defined as a uniform velocity, and outlet air is set to be outflow condition. The no-slip condition is applied to all solid surfaces. The heat load produced by the occupants, computers are uniform distributed on their surface with the heat flux of 28.18 and 312.5 W ⋅ m-2 , respectively. The standard wall functions for the k − ε turbulence model are adopted to link the solution variables at the near-wall cells and the corresponding quantities near the wall. The SIMPLEC algorithm is used to solve the control equations. The convergence criteria of velocity, turbulent kinetic energy and its dissipation rate is 10-3. Similarly, the convergence criteria of temperature is 10-6. The computational domain is divided into two parts. One includes the cavity and fibre structure layer of FADS, which is discretized using the structured grids, and the left part is discretized using the unstructured grids. The total number of grid is 17,479,958, among them, the number of grid from the cavity and fibre structure layer of FADS is 7,832,976. 3. Results and discussion In order to remove the excessive heat load produced from the internal thermal resources, the conditioned air with flow rate of 0.079 m3 ⋅ s-1 and air temperature of 292.9 K is supplied. Two typical sections are chose to analyze the air flow characteristics. Cross section A splits the left person, computer, and desk at x = 1.05 m, and Cross section C crosses through the central FADS in the vertical direction at z = -1.8 m. 3.1. Air velocity and temperature distribution
a)
b)
Fig.2. Air velocity distribution (m/s) on: a) cross section A and b) cross section C with FADS’ length of 2.5 m and orifices’ distance of 50 mm.
Figure 2 shows the air velocity distribution on cross sections A and C with FADS’ length of 2.5 m and orifices’ distance of 50 mm. After air is supplied into the cavity of FADS with orifices, part of supply air is discharged from the porous fibre at a lower velocity, and the left is jetted through orifices at a higher velocity. The air velocity below the ceiling reduces gradually due to the viscosity of the ceiling (seen in Figure 2a). The jet air induces the penetrated air and merges together at a distance (seen in Figure 2b). As a result, the mixed air flows to the work area at a certain speed, and changes its flow direction when meeting with objects. Therefore, the air quality in the region of human breathing zone is higher. Yet, the facial and neck part of the peoples’ body is the most sensitive to cold wind, therefore, the air velocity at the part of facial and neck can be one of the most essential factors for designing the air-conditioning based on the FADS with orifices.
Fujiang et al. / Procedia00Engineering 205 (2017) 3112–3116 Fujiang Chen, et al. Chen / Procedia Engineering (2017) 000–000
a)
3115
b)
Fig.3. Air temperature distribution (K) on a) cross section A and b) cross section C with FADS’ length of 2.5 m and orifices’ distance of 50 mm.
Figure 3 shows the air temperature distribution on cross sections A and C with FADS’ length of 2.5m and orifices’ distance of 50 mm. Indoor air temperature close to the jet throw path is relative lower than other zones. Meanwhile, the air temperature in the upper zone is lower than the lower zone, yet, the vertical air temperature difference is less than 3 K 3.2. Effect of FADS’ length on air velocity and temperature Figure 4 shows the distribution of air velocity and temperature on cross section C with FADS’ length of 3.5 m and orifices’ distance of 50 mm. Compared with Figure 4, both indoor air velocity and temperature decrease with the increase of FADS’ length from 2.5 to 3.5 m. As a result, both indoor air velocity and temperature distribution become more uniformly.
a) b) Fig.4. a) Air velocity and b) temperature distribution on cross section C with FADS’ length of 3.5 m and orifices’ distance of 50 mm.
5. Conclusions Simulation results show that, when air is generated by FADS with orifices, the part of supply airflow is penetrated from the porous fibre at a lower speed, and the left is jetted out through orifices at a higher speed, and then, both airflow merge together at a certain distance. The indoor air velocity is lower and air temperature in the upper zone is lower than that in the lower zone, yet the vertical temperature difference is less than 3 K. Furthermore, the FADS’ length has great impact on indoor air velocity and temperature. The fitting distance should be determined in order to obtain more uniformly distribution of indoor air velocity and temperature. In future, simulation results will be validated by the experiment measurements. Acknowledgment The research was partially granted by the Natural Science Foundation of China (No. 51308077), and the Natural Science Foundation of the Jiangsu Higher Education Institutions of China (No. 13KJB560001). References [1] G. Clausen. Ventilation filters and indoor air quality: a review of research from the International Centre for Indoor Environment and Energy. Indoor Air, 2004 (14) 202-207. [2] Z. Jiang, Q. Chen, A. Moser. Comparison of displacement and mixing diffusers. Indoor Air, 1992, 2 (3) 168-179.
3116
Fujiang Chen et al. / Procedia Engineering 205 (2017) 3112–3116
Fujiang Chen, et al. / Procedia Engineering 00 (2017) 000–000
[3] J. Fontaine, R. Rapp, H. Koskela, et al. Evaluation of air diffuser flow modeling methods experiments and computational fluid dynamics simulations. Building and Environment, 2005, 40 (3) 377-389. [4] H. Qian, Y. Li, P.V. Nielsen, et al. Dispersion of exhalation pollutants in a two-bed hospital ward with a downward ventilation system. Building and Environment, 2008, 43 (3) 344-354. [5] C. Pinkalla. Fabric duct air dispersion for HVAC systems. Construction Specifier, 2003, 56 (6): 57-64. [6] P.V. Nielsen, C. Topp, M. Sonnichsen, et al. Air distribution in rooms generated by a textile terminal–comparison with mixing and displacement ventilation. ASHRAE Transctions, 2005, 111： 733-739. [7] F. Chen, H.Chen, J. Xie, et al. Numerical simulation on air dispersion of the fabric air distribution system in pure-penetration mode. Proceedings of the 6th International Symposium on Heating, Ventilating and Air Conditioning, Nanjing, China, 2009. [8] G. Shen, W. Li. Fabric air distribution system and its application. Refrigeration and Air-conditioning, 2007, 7 (3) 99-104. (In Chinese) [9] F. Chen, H.Chen, J. Xie, et al. Characterizing airflow through fabric air dispersion system using a porous media model. Energy and Buildings, 2011, 43 (2-3) 665-670. [10] A. Fontanini, M.G. Olsen, B. Ganapathysubramanian. Thermal comparison between ceiling diffusers and fabric ductwork diffusers for green buildings. Energy and Buildings, 2011, 43 (11) 2973-2987. [11] F. Chen, H.Chen, H. Wang, et al. Parametrical analysis on characteristics of airflow generated by fabric air dispersion system in penetration mode. Energy and Buildings, 2013, (67) 365-373. [12] G. Neale, W. Nader. Practical significance of brinkman's extension of darcy's law: coupled parallel flows within a channel and a bounding porous medium Canadian. Canadian Journal of Chemical Engineering, 1974, 52 (4): 475-478. [13] D.A.S. Rees. The onset of Darcy-Brinkman convection in a porous layer: an asymptotic analysis. International Journal of Heat and Mass Transfer, 2002, 45 (11) 2213-2220. [14] F. Chen, H.Chen, J. Xie, et al. Air distribution in room ventilated by fabric air dispersion system. Building and Environment, 2011, 46 (11) 2121-2129.
