FINAL INDEPENDENT PROJECT
DIFFERENT PARAMETERS THAT AFFECT THE PERFORMANCE OF FLOW-THROUGH PIPES
AIM:
To simulate the pipe flow in different conditions during a pipe flow and study how they affect the mass flow rate, life span, and overall performance of the pipe system. And then, list out the important factors for creating an ideal pipe flow system.
INTRODUCTION:
In this study, we run simulations on the different configurations of a pipe joint/element and then analyze the results and study how they affect the overall flow performance of the pipe flow. After running the simulation for all the concerned configurations, we summarize our study by categorizing our configurations by the ones that have a positive impact on the pipe flow and the ones that have a negative impact on the pipe flow. This way, it becomes easier to design a pipe flow system according to our needs, with maximum efficiency and lifespan possible.
THEORY:
The purpose of pipe flow is to transport the required fluid from one point to another, which makes it a crucial necessity in a lot of industries. This makes the designing of the pipe flow even more of a critical task. This pipe flow is designed to undergo flow transport according to the needs of the industry in the most efficient way possible along with considering the lifespan of the pipe system, as setting up the pipe system is a very expensive process and it's repairing/replacement would result in spending a lot of money. Not to mention the halt in the work product of the industry caused due to the pipe system failure, which would further cost a lot of money and resources. So, it's very important to build a pipe system that not only does it's job efficiently, but also has a lifespan that the industry can count on.
While designing a pipe flow system, we should account for all the factors that affect the fluid flow. In most of the cases, the goal is to maximize the mass flow rate at the outlet with maximum efficiency. But, this is not always a very simple task. The fluid flow occurs due to the pressure difference between the inlet and the outlet. Hence, while designing a pipe flow system, we should always aim to build it with maximum efficiency or, minimum pressure head loss.
Effect of the flow velocity on the pipe system:
high velocity:
Since having a higher mass flow rate at the outlet is generally a good this, the first thing that must come to our minds to transport the fluid would be to increase the average velocity of fluid inside the pipe and eventually increase the mass flow rate at the outlet. This seems like a really simple solution, but in reality, increasing the velocity does more harm for the pipe system than good. Having a high flow velocity comes with a lot of problems such as,
- Cavitation
Having a pipe flow with high velocity would result in a sudden change in pressure at regions with a sudden turn/change in direction. This creates a comparatively lower pressure region in the normal region(high velocity) of the fluid flow. And because of this, the water starts to boil around that region, even at a lower temperature because of the reduced pressure and as a result, air bubbles are formed which eventually travel along the pipe and explode at the sudden curve region where the velocity is low and the pressure is high. This repeated explosion can cause permanent damage to the pipe in that region and would need replacement of the pipe from time to time.
- Abrasion
Higher velocity would result in the abrasion of the walls of the pipe. This will eventually increase the surface roughness of the pipe and would hinder the pipe flow which would result in a decrease in the efficiency of the pipe flow. Prolonged abrasion can even damage the pipe to a certain extent that it becomes a safety hazard for the pipe system.
- friction loss
With an increase in the velocity of the flow, we further increase the energy loss due to friction. This can be justified from the Hagen–Poiseuille equation.
Here, the friction head loss is directly proportional to the average velocity of the flow. Hence, a higher average velocity would also increase friction head loss, which would further decrease the efficiency of fluid transport.
It also includes other problems such as vibration, corrosion, and noise but we get the idea that a high velocity has a lot of problems.
low velocity:
It should be noted that the flow velocity should not be too low either as low velocity has its own problems too. These include:
- low mass flow at the outlet
While designing a pipe system, our objective is to maximize the mass flow rate at the outlet. For a pipe of a given diameter, we can have a certain velocity without triggering any of the harmful effects of too high velocity. But, the fluid running at too low velocity would mean that we are not utilizing the maximum potential of the given pipe. We are wasting the potential of obtaining a higher mass flow rate at the outlet.
- deposition of slur
When fluid velocity is very low, solid particles separate out from the fluid. Solid particles with the heavier density tend to settle down at the bottom of the pipe in a horizontal pipe run. This settling will be even more at elbows. This issue results in a reduced mass flow rate and reduced efficiency. This becomes a huge problem for the flow transport and even removing the slur from time to time would not be a permanent solution and require the maintenance from time to time while creating hindrance in the production.
Hence, it's very important to determine the correct velocity for the pipe flow such that we can obtain the maximum velocity possible with the given pipe and without triggering any hindrances of too high or too low velocity. We can choose the appropriate velocity from the table below-
courtesy: https://www.engineeringtoolbox.com/steel-pipes-flow-capacities-d_640.html
If we desire to get a higher mass flow rate, we should try to increase the diameter of the pipe first as it would be a better and efficient choice than simply increasing the diameter.
PLOTS:
To run the simulation, we chose a pipe section of the internal diameter 50 mm. For the first case, we apply an initial velocity 4.3m/s, which is the suggested velocity for the given diameter according to the chart and for the second case, we apply an initial velocity of 12m/s, which is a high velocity for the given pipe diameter.
mesh:
case-1:
velocity contour
pressure contour
case-2:
velocity contour
pressure contour
From the above plots, we can observe that the range of the maximum and minimum pressure in the first case is from 97060.78 pa to 105856.37 pa and 86916.22 pa to 135442.59 pa with case-2. We can also notice that this drastic variation occurs only at the diversion junction. This means that a high-pressure difference is generated along a very short region. And this sharp pressure drop is prone to cause all of those high-velocity problems that we had discussed.
All those problems wouldn't occur in case-1 because the pressure drop generated is not that high in that case. Hence, it is a better choice to go with the suggested velocity for a pipe rather than blindly increasing the velocity to obtain a higher mass flow rate.
Effect of adding elbows on the pipe system:
The addition of elbows is needed when we need to change the direction of the fluid transport system. But, the addition of the elbows can result in a pressure drop from the flow system. This is because some pressure head is utilized while going through the sudden change in the flow direction and this results in the wastage of the pressure head energy.
Pressure drop in pipes is always a phenomenon we need to avoid because it is a loss of energy, which can not be recovered and is even wasted on an unnecessary thing such as the flow path of the pipe itself. Due to the energy lost, more energy will be required to move the fluid across the pipeline or less fluid can be moved with the same amount of energy used to run a pump. This means that the overall efficiency of the pipe flow system is reduced, which is not a good thing from the economic perspective.
We run a pipe flow simulation with a straight pipe, pipe with short bend radius, and elbow with a long radius. And then, compare the results. All the simulations were carried with the same pipe diameter and the same boundary conditions.
case-1:
mesh
velocity contour
pressure contour
pressure drop:
case-2(short radius):
mesh
velocity contour
pressure contour
pressure drop
case-3(large diameter):
mesh
velocity contour
pressure contour
pressure drop
From the above simulation, we get to know that the pressure drops in the case of straight pipe, short bend, and long elbow is, 10476.47 pa, 15753.50 pa, and 12850.13 pa respectively. Hence, we can conclude that the addition of elbows results in a pressure drop. And the shorter the bend radius, the greater is the pressure drop.
We can use a tilted pipe to make the connection for the source and sink instead and avoid any losses due to the bend. but, it should be taken care that the inlet velocity for the tilted pipe is set at an angle, normal to the direction of the path of the pipe or, the tilted pipe will produce even more pressure drop than using a bend.
The following simulation was solved to connect two points, 1698.52 mm apart, vertically and 525 mm apart, horizontally. First, it was done by simply using elbows with the pipe path. Then, a tilted pipe was used with inlet velocity normal to inlet cross-section and then velocity profile, along the direction of the pipe path.
case-1:
mesh
pressure contour
pressure drop
case-2(velocity normal to inlet cross-section):
mesh
pressure contour
pressure drop
case-3(velocity along the direction of the pipe flow):
pressure contour
pressure drop
From the above study, we observe that the pressure head loss in case of a bend, a tilted plane with velocity along the pipe, and tilted pipe with normal inlet velocity is, 31703.24 pa, 27489.11 pa, and 34491.03 pa respectively. We notice that we get a reduced pressure head loss with the use of a tilted pipe. But, this happens only when the inlet velocity is fed at a certain angle or, along the path of the pipe. If the inlet velocity is just normal to the inlet cross-section, we end up having an even higher pressure drop than with the use of the bend. This happens so because, when the flow is normal to the inlet cross-section, it somewhat crashes onto the tilted side of the pipe. This creates distortion and a lot of pressure head is wasted just to maintain the flow. Hence, the use of a tilted pipe will only work when the inlet velocity is along the direction of the flow.
But, the construction of a pipe system with such complex requirements requires a lot of skills and is a lot harder than simply using a bend. And if something goes wrong, we end up getting even more pressure drop than the bend. So, the use of the bend should bee prioritized as it is a lot simpler and easier for its use.
effect of the location of the bend:
We run the simulation for the position of the bend at different locations in the pipe and then compare the results. The length of the pipe is set at 1800mm, diameter at 50mm, and the position of the bend was set at 450mm, 900mm, and 1350mm from one end.
case-1(distance = 900mm):
mesh
velocity contour
pressure contour
pressure drop
case-2(d = 450mm):
mesh
velocity contour
pressure contour
pressure drop
case-3(d = 1350mm):
mesh
velocity contour
pressure contour
pressure drop
From the above study, we can observe that the pressure drop values for the bend location at 450mm, 900mm, and 1350mm are, 12225.79 pa, 12890.65 pa, and 12953.31 pa respectively. This concludes that the further the bend is from the source of the flow, the more the pressure drop it creates. This can be justified by the fact that the velocity keeps on increasing from the source of the flow. And when it hits the bend with higher velocity, it results in a greater pressure head loss than when it hits with a lower velocity.
comparison of 45 degrees bend and 90 degrees bend:
To compare the pressure drop generated with the use of a 45-degree bend joint and a 90-degree bend joint, we run a simulation with those two types of joints applied on the pipe path that connects two points, 800 mm apart, horizontally with an inlet flow velocity of 6m/s.
case-1(45-degree bend):
mesh
pressure contour
velocity contour
pressure drop
case-2(90-degree bend):
mesh
pressure contour
velocity contour
pressure drop
From the above results, we observe that the pressure head loss in the 90-degree bent is a lot higher than that of the two 45-degree bends. This can be justified by the fact that in the case of the 45-degree bend, the maxima and the minima of the pressure occupy only a tiny region of the space whereas, in the case of 90-degree bend, they occupy a lot larger region. Also, the shape of the 45-degree bend lets the fluid pass-through without consuming too much pressure head loss.
RESULTS AND DISCUSSION:
From the above simulations, we studied the effect of various parameters in a pipe flow. These results help us in optimizing a pipe system such that it transports the fluid with maximum efficiency without having any long term worries. To summarise, we should take note of the following observations while designing a pipe flow system:
- Set the flow velocity of the fluid according to the diameter of the pipe. We should not increase the flow velocity just to have a higher mass flow rate. Instead, we should consider increasing the diameter of the pipe to increase the lifespan of the pipe system as having a high velocity for a given pipe diameter can have a lot of harmful effects on the pipe system.
- The excessive use of bends should be avoided and its number should be kept as low as possible. Since the use of bends increases the pressure head loss which means that the overall efficiency of the system is compromised.
- Even if they reduce the efficiency of the system, they cant be completely avoided. They are very essential in changing the direction of the flow at certain points. In this case, we can reduce the pressure head loss at those bends by using a bend of a larger radius. This makes sure that the flow becomes as smooth as possible, without providing much resistance to the fluid flow.
- In some cases, the bends can be replaced with a tilted pipe. This results in a straight flow path for the fluid flow without and hurdles such as bends. But, a lot of attention should be given while placing the pipe to make the fluid velocity parallel with the axis of the pipe. Else, if the flow velocity is perpendicular to the inlet cross-section, then the fluid flow experiences resistance from the tilted walls, and as a result, a pressure drop of magnitude even higher than bends are formed. Hence, this replacement should only be done with professional help.
- The use of 45-degree bend should always be prioritized over the 90-degree because they provide a much smoother path for the fluid and provide much lower head loss compared to the 90-degree bend.