experimental study of flow system and its simulation … · prof. m j zinzuvadia, prof. s. a. shah,...
TRANSCRIPT
EXPERIMENTAL STUDY OF FLOW SYSTEM AND ITS SIMULATION
Prof. M J Zinzuvadia, Prof. S. A. Shah, Prof. S. P. JoshiAsso. Professor
Mechanical Engineering DepartmentB V M Engineering College, V V Nagar ( Gujarat )
ABSTRACTMany engineering applications demand
characteristic curve of flow system for selection of appropriate fluid machine and pumping power estimation. When flow system has valve as one of the components, different openings of the valve give different characteristic curves. These characteristic curves can be obtained either by experimental testing of the flow systems or by prediction techniques of different types. The work presented here, shows effect of loss due to frictional head and static head on flow system curves. Here different methods predicting flow system characteristic are mentioned in an introductory way and prediction by using polynomial fitting is discussed with details.
In the experimental testing, the flow system, having valve as one of the components, was used and three different flow systems were obtained by three different valve openings. These flow systems were tested experimentally to get flow system characteristic curve and the prediction was also carried out by using model, which is based on method of polynomial fitting. In this work, then comparison of predicted results with actual results is carried out and usefulness of this method of simulation is discussed.
Nomenclature:Δh = head loss, metre of air column,k = constant,Q = flow rate in m3/sechS = static lift, m,n = constant representing valve opening
INTRODUCTION Power consuming fluid machines like
pump, blower and fan are required to maintain fluid flow through a network of pipes or channels or devices, generally known as ‘Flow system’. The flow through the flow system gives head loss, which is dependent on flow rate. The
curve showing relationship between head loss or resistance of the flow system and flow rate is known as flow system characteristic and it is useful for selecting fluid machine with constraints of energy efficiency and capital economy.
REVIEW OF LITERATUREFor any flow system, head requirement
at given flow rate is composed of static lift and frictional head loss due to components of the flow system [1]. The curve of flow system having static lift only is horizontal straight line and the characteristic curve of flow system having frictional head loss only and no static lift, starts at zero flow and head as shown in Fig. 1.
Frictional head loss in turbulent flow, appearing in majority of engineering applications, varies as the flow rate raised to a power between 1.75 and 2, so this curve is nearly parabolic. It can be represented as,
Δh = k Q2 ------------------(i)
All actual flow systems have some frictional head loss and some elevation change. So head for complete flow system at any flow rate is sum of the frictional head and static lift as shown in Fig. 2. Mathematically the curve can be represented as:
Δh = hs + kQ2 -----------------(ii)
The shape of flow system curve depends on the relative importance of friction and gravity. In air handling system, static lift will be negligible, hence its flow system characteristics is described by equation (i). When air handling system has valve as one of the components, different openings of the valve give different flow systems [2]. Similar situation is also observed when air handling system has filter as one of the components and the flow system is degraded due to dust accumulation in the filter.
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Flow systems mentioned above, demands for simulation of flow system by different methods, for problem solving. Leenanunath T. and Sirivongpaisal N [3] have described degradation of air handling unit of a commercial building with the help of flow system simulation. They have prepared maintenance schedule for air handling unit with objective of minimum total cost. B V N Rama Kumar and Dr. B V S S S Prasad [4] have used a combined CFD and Network approach for simulation of flow system. Network approach of flow system analysis considers different components of flow system as resistance elements and K factor of all the components is found out experimentally. These experimental values can give characteristics of flow system. CFD analysis also used for simulation of flow system and it is observed that flow system analysis carried out by CFD is time consuming but combination of CFD and Network approach gives better simulation of the flow system.
The characteristic curves of above stated flow systems are described by equation (i) with different values of k. The value of k depends upon valve opening (denoted by ‘n’), hence it can be represented as polynomial of ‘n’ [5]. Thus for simulating given flow system, experimental testing of flow system is carried out with different valve openings and corresponding values of k are calculated. These values are used for obtaining coefficients of polynomial. The polynomial of ‘n’ gives value of k for different flow systems and their characteristic curves can be obtained by using equation (i).
EXPERIMENTAL SET UP AND RESULTSThe tests were carried out on a flow
system comprising of pipeline, valve and nozzleas shown in Fig.3. The flow system was fitted with outlet of C F blower and flow rate through the system was varied by partial closing of blower inlet in steps. Total head at flow system inlet and that at flow system outlet were measured by Prandtl’s pitot tube at different flow rates. From the observations head loss (resistance) of the flow system and flow rate were calculated to obtain flow system characteristics.
Different openings of the valve give different flow system and such three flow systems were tested. For these systems k was
calculated and by polynomial representation its equation was found as below:
k =14147.768 +74.927 n +222.429 n2
This relation was then used to find k and thereby flow system characteristic curves. Fig.4 (a),(b) and (c) shows experimental and predicted flow system characteristics curves.
DISCUSSION AND CONCLUSIONMathematical model of flow system,
presented in this work describes characteristics of all flow systems obtained from different valve openings. Results presented in Fig. 3(a), (b) &(c) shows good matching between experimental curve and predicted curve. Following points can be concluded:
(1) This model predicts Characteristic curve of flow system with very good accuracy hence it can be used for all practical purposes.
(2) Accuracy of prediction can be enhanced by using more sets of experimental results for obtaining equation of k.
(3) Flow system simulation in general, and prediction method of this work in particular, can give characteristics of flow systems with minimum experimental testing. Thus problem solving becomes economical.
(4) When filter is a part of the flow system, as time passes, characteristic of flow system changes due to accumulation of dust in filter. Prediction method of this work can be used for such systems also.
REFRENCES[1] Fox Robert W., and McDonald Alen T., Introduction to Fluid Mechanics, Fifth edition, John Wiley & Sons Inc., pp 531-540. [2] Olson Reuben M., Essentials of Engineering Fluid Mechanics, Fourth edition, pp. 493-495[3] Leenanunath T., Sirivongpaisal N., “Energy Management by Simulation of Air handling Unit degradation behavior for planning maintenance schedule”, IEEE International Conference on Management of Innovation and Technology, pp. 1070-1074.[4] B V N Rama Kumar, and Dr. B V S S S Prasad, “ A combined CFD and Network approach for simulation of Flow system”, I E I, vol.86, oct.2005, pp.129-133.[5] M. W. Wambsganss, Jr., “Curve Fitting with Polynomials”, Mach. Des., vol. 35, no. 10, p. 167, April, 1963.
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Fig.1 Characteristic of Flow system with zero static lift
Fig.2 Characteristic of Flow system with static lift
0
5
10
15
20
25
30
0 1 2 3 4 5 6
FLOW RATE, Q CU. M./SEC
HE
AD
LO
SS
, M
OF
AIR
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5
FLOWRATE, CU. M./ SEC
HE
AD
LO
SS
, M O
F A
IR
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Fig. 4(a), Characteristic of Flow system, Valve full open, n = 0
0
50
100
150
200
250
300
350
400
0 0.05 0.1 0.15 0.2
FLOWRATE, CU. M./SEC
RE
SIR
TA
NC
E O
F F
FL
OW
SY
ST
EM
, M
OF
A
IR
PREDICTION
EXPERIMENTAL
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Fig. 4(b), Characteristic of Flow system, Valve 9/10 open, n=1
Fig. 3(c), Characteristic of Flow system, Valve 7/10 open, n=3
Fig. 4(c), Characteristic of Flow system, Valve 7/10 open, n=3
0
50
100
150
200
250
300
350
400
0 0.05 0.1 0.15 0.2
FLOE RATE, CU. M./ SEC
RE
SIS
TA
NC
E O
F F
LO
W S
YS
TE
M,
M O
F
AIR
PREDICTION
EXPERIMENTAL
0
50
100
150
200
250
300
350
400
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16
FLOW RATE, Q,CU.M./SEC
RE
SIS
TA
NC
E O
F F
LO
W S
YS
TE
M, M
OF
AIR
PREDICTION
EXPERIMENTAL
13-14 May 2011 B.V.M. Engineering College, V.V.Nagar,Gujarat,India
National Conference on Recent Trends in Engineering & Technology
Chart2
| 0 |
| 1 |
| 2 |
| 3 |
| 4 |
Sheet1
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 9 |
| 4 | 16 |
| 5 | 25 |
Sheet2
| 0 | 5 |
| 1 | 6 |
| 2 | 9 |
| 3 | 14 |
| 4 | 21 |
Sheet2
| 0 |
| 0 |
| 0 |
| 0 |
| 0 |
