# Calculate Pressure Drop through Expansion/Reduction for Gas

• engjare
In summary, a common issue in sizing flow projects for piping systems is the calculation of pressure drop across a fixed diameter for compressible gases. However, the pressure changes through an expansion or contraction with gas are not typically taken into account. This type of problem could be addressed using CFD, but it may not be easily incorporated into Excel. From a theoretical standpoint, there will be a decrease in flow velocity and an increase in static pressure when the pipe size is enlarged, resulting in a reduction in flow friction loss. While there is a formula for estimating pressure loss in sudden expansions, it is considered negligible for well-formed pipe expansion fittings.
engjare
Something that routinely comes up as a problem at work is when we size flow projects for piping systems. We calculate pressure drop across a length of fixed diameter for compressible gasses, but we do not calculate pressure changes through an expansion or contraction with gas (for example, pressure drop of air flowing at 3,500 scfm through 2" SCH 40 piping, expands to 4" SCH 40 piping). I can recall from my time in school that we would have used CFD to assist with a problem like this.

Am I overlooking a way to be calculating this? I had envisioned something that could be incorporated into Excel, but it may be more difficult than that for compressible flow.

From a theoretical standpoint for there will be a reduction in velocity in the enlarged section and therefore an increase in the static pressure component and a resulting reduction in flow friction loss due to the lower flow velocity in the larger pipe..
For sudden expansion, there is a formula for estimating the pressure loss based upon the ratio of the small to large diameters but for a well formed pipe expansion fitting the pressure loss is considered to be negligible.

## 1. What is pressure drop through expansion/reduction for gas?

Pressure drop through expansion/reduction for gas is the decrease in pressure that occurs when a fluid (in this case, gas) flows through a constricted area, such as a nozzle or valve.

## 2. How is pressure drop through expansion/reduction calculated?

Pressure drop through expansion/reduction can be calculated using the Bernoulli's equation, which relates the pressure, velocity, and elevation of a fluid at different points along a streamline. The equation takes into account the fluid's density, velocity, and the area of the constriction to determine the pressure drop.

## 3. What factors affect pressure drop through expansion/reduction?

The factors that affect pressure drop through expansion/reduction include the fluid's density, velocity, and viscosity, as well as the size and shape of the constriction. The type of fluid and the temperature can also have an impact on the pressure drop.

## 4. Why is it important to calculate pressure drop through expansion/reduction?

Calculating pressure drop through expansion/reduction is important because it can help determine the flow rate and efficiency of a system. It is also crucial for selecting the appropriate equipment and designing pipelines in order to prevent damage or inefficiency.

## 5. Can pressure drop through expansion/reduction be reduced?

Yes, pressure drop through expansion/reduction can be reduced by using a larger constriction area, reducing the fluid's velocity, or using a different type of fluid with a lower viscosity. Properly designed and maintained pipelines can also help reduce pressure drop through expansion/reduction.

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