Understanding the Moody Chart and R Value

• foo9008
In summary, the Moody chart is divided into four sections, with the transition zone being a function of both Reynolds No. and relative roughness. Reynolds No. is the measure of flow, and in the transition zone, there is a mix of laminar and turbulent flow characteristics. The critical zone is where the flow transitions from laminar to fully turbulent, which can occur at different Reynolds No. depending on the relative roughness of the pipe. The fully turbulent flow zone is characterized by a logarithmic scale of Reynolds No., with rougher pipes reaching fully turbulent flow at lower Reynolds No. than smoother pipes. The Moody chart can be used for various fluids, not just water, and displays the relationship between Reynolds No. and friction factor for different relative

Homework Statement

I was told that the moody chart can be divided into 4 sections , i don't really understand the 'transition part' . it is said to be a function of R and roughness . what is R ? radius of the pipe ?

The Attempt at a Solution

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foo9008 said:

Homework Statement

I was told that the moody chart can be divided into 4 sections , i don't really understand the 'transition part' . it is said to be a function of R and roughness . what is R ? radius of the pipe ?

The Attempt at a Solution

R is the Reynolds No. for the flow. Some sources use Re for this number.

In the transition zone, there is some turbulence in the flow, but complete turbulence has not yet been established. This is why the friction factor is dependent partly on the relative roughness of the pipe and partly on the Reynolds No.

What's
SteamKing said:
R is the Reynolds No. for the flow. Some sources use Re for this number.

In the transition zone, there is some turbulence in the flow, but complete turbulence has not yet been established. This is why the friction factor is dependent partly on the relative roughness of the pipe and partly on the Reynolds No.
What's the differences between critical zone and transition zone??

The critical zone is where the flow stops being wholly laminar and begins to develop turbulence. The friction factor can show large changes with a very small change in Reynolds No.

how
SteamKing said:
The critical zone is where the flow stops being wholly laminar and begins to develop turbulence. The friction factor can show large changes with a very small change in Reynolds No.

foo9008 said:
how

See Post #2, below the Moody Chart.

SteamKing said:
See Post #2, below the Moody Chart.
can you explain what is transition zone ? what's the difference between it and critical zone ?

foo9008 said:
can you explain what is transition zone ? what's the difference between it and critical zone ?
In the transition zone, enough turbulence is present in the flow so that the friction factor is only slightly dependent on Reynolds No., but is highly dependent on the relative roughness of the inside of the pipe. This is what the Moody Diagram shows, with the different friction factors for different values of relative roughness.

When the flow becomes fully turbulent, the friction factor will not depend on Reynolds No. at all.

foo9008
so , for the critical zone and transition zone shows the water begin to change from laminar to turbulent ? where the transition zone is 'closer' to turbulent than critical zone ?

SteamKing said:
In the transition zone, enough turbulence is present in the flow so that the friction factor is only slightly dependent on Reynolds No., but is highly dependent on the relative roughness of the inside of the pipe. This is what the Moody Diagram shows, with the different friction factors for different values of relative roughness.

When the flow becomes fully turbulent, the friction factor will not depend on Reynolds No. at all.
in the transition zone , there is no laminar flow at all ? or there's some laminar ?

foo9008 said:
in the transition zone , there is no laminar flow at all ? or there's some laminar ?
Laminar flow has ended when the Reynolds No. reaches about 2000-2300. After that, characteristics of turbulent flow appear rapidly with increasing Re, and by Re = 4000, the friction factor has stratified according to Relative Roughness completely.

foo9008
SteamKing said:
Laminar flow has ended when the Reynolds No. reaches about 2000-2300. After that, characteristics of turbulent flow appear rapidly with increasing Re, and by Re = 4000, the friction factor has stratified according to Relative Roughness completely.
but , as i see from the chart , when the water become complete turbulent when Re = 7000 , not 4000 , why ?

foo9008 said:
but , as i see from the chart , when the water become complete turbulent when Re = 7000 , not 4000 , why ?
Fluid flow is not like flipping a light switch on and off. There are periods when one type of flow dominates and transition periods in between where a mixture of flow characteristics is present.

It's not clear what you mean by "but , as i see from the chart , when the water become complete turbulent when Re = 7000 , not 4000 , why ?"

The Moody diagram can be used for other fluids besides water. That's why it's developed using Reynolds No. as the independent parameter describing the fluid flow.
If you look at the long, sweeping dashed line which separates the transition zone from the fully turbulent flow zone, you will see that fully turbulent flow does not develop all of a sudden at Re = 7000, but is dependent on the relative roughness of the pipe to determine the Re at which turbulent flow does develop. The scale of Re at the bottom of the diagram is logarithmic. For a rough pipe, fully turbulent flow can develop at Re = 20,000; for a really smooth pipe, fully turbulent flow may not occur until Re = 10,000,000 or higher. That's a difference in Re of three orders of magnitude.

SteamKing said:
Fluid flow is not like flipping a light switch on and off. There are periods when one type of flow dominates and transition periods in between where a mixture of flow characteristics is present.

It's not clear what you mean by "but , as i see from the chart , when the water become complete turbulent when Re = 7000 , not 4000 , why ?"

The Moody diagram can be used for other fluids besides water. That's why it's developed using Reynolds No. as the independent parameter describing the fluid flow.
If you look at the long, sweeping dashed line which separates the transition zone from the fully turbulent flow zone, you will see that fully turbulent flow does not develop all of a sudden at Re = 7000, but is dependent on the relative roughness of the pipe to determine the Re at which turbulent flow does develop. The scale of Re at the bottom of the diagram is logarithmic. For a rough pipe, fully turbulent flow can develop at Re = 20,000; for a really smooth pipe, fully turbulent flow may not occur until Re = 10,000,000 or higher. That's a difference in Re of three orders of magnitude.
what do you mean is when the Re is larger than 4000 , the fluid flow is not necessarily complete turbulent because it's also depend on the relative roughness?

foo9008 said:
what do you mean is when the Re is larger than 4000 , the fluid flow is not necessarily complete turbulent because it's also depend on the relative roughness?
Yes, partly. When the flow is fully turbulent, the friction factor will depend entirely on the relative roughness and not on the Reynolds No.

That's why the Moody diagram is so marked with the long curved dashed line which separates the zone of complete turbulence from the transition zone.

foo9008
SteamKing said:
Yes, partly. When the flow is fully turbulent, the friction factor will depend entirely on the relative roughness and not on the Reynolds No.

That's why the Moody diagram is so marked with the long curved dashed line which separates the zone of complete turbulence from the transition zone.
I was told that when Re > 4000 , it's said to be turbulent flow , so the more accurate is the flow start to become turbulent , and not laminar at all ? am i right ?

foo9008 said:
I was told that when Re > 4000 , it's said to be turbulent flow , so the more accurate is the flow start to become turbulent , and not laminar at all ? am i right ?
The flow starts to take on the characteristics of turbulent flow for Re > 4000. Laminar flow has ceased by the time Re ≈ 2300.

foo9008
SteamKing said:
The flow starts to take on the characteristics of turbulent flow for Re > 4000. Laminar flow has ceased by the time Re ≈ 2300.
how about at the region between 2300 and 4000 ?

foo9008 said:
how about at the region between 2300 and 4000 ?
Essentially the critical zone. The characteristics of the flow are rapidly changing in this region. It's hard to describe what is going on, which is why the Moody diagram is mostly blank in this region.

foo9008
SteamKing said:
Essentially the critical zone. The characteristics of the flow are rapidly changing in this region. It's hard to describe what is going on, which is why the Moody diagram is mostly blank in this region.
transition zone is for Re >4000 ?

SteamKing said:
Essentially the critical zone. The characteristics of the flow are rapidly changing in this region. It's hard to describe what is going on, which is why the Moody diagram is mostly blank in this region.
do you mean there are times that the flow is laminar and also there are time that the flow is turbulent ?

foo9008 said:
do you mean there are times that the flow is laminar and also there are time that the flow is turbulent ?
No, I mean that the flow is somewhere in between laminar and turbulent, being neither one or the other, and it is difficult to describe physically and mathematically.

SteamKing said:
No, I mean that the flow is somewhere in between laminar and turbulent, being neither one or the other, and it is difficult to describe physically and mathematically.
transition zone occur when Re > 4000 ??

foo9008 said:
transition zone occur when Re > 4000 ??
Yes. We seem to be going round and round with this discussion.

Study the Moody diagram carefully. You can Google other source material on the internet besides the slide show you have been provided.

foo9008
SteamKing said:
Yes. We seem to be going round and round with this discussion.

Study the Moody diagram carefully. You can Google other source material on the internet besides the slide show you have been provided.