Pressure losses in hoses : how to calculate
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1. Introduction
2. What is a Hose?
3. Different Types of Hoses
1. Introduction
Understanding pressure losses in hoses is crucial for engineers in designing and optimizing fluid transport systems. This article aims to provide a comprehensive understanding of hoses, their types, and how to calculate pressure losses in them.
2. What is a Hose?
A hose is a flexible conduit designed to transport fluids from one location to another. Hoses are used in a myriad of applications, from garden watering to high-pressure industrial processes. The functionality of a hose is largely dependent on its ability to withstand the operating pressure and temperature while minimizing pressure losses.
3. Different Types of Hoses
Hoses can be categorized based on their material construction,
diameter, length, and the type of connectors used. Common materials
include rubber, PVC, stainless steel, and Teflon, each with unique
properties affecting flexibility, durability, pressure handling,
and, consequently, pressure loss.
For instance, rubber hoses are flexible and resistant to wear,
making them suitable for high-pressure applications. On the other
hand, stainless steel hoses, while less flexible, offer high
temperature and chemical resistance.
Hoses come in a wide array of types, categorized based on the materials they are constructed from and their design:
3.1 Classification Based on Material
a. Rubber Hoses: Known for their excellent flexibility, resistance
to abrasion, and compatibility with a wide range of fluids. They are
often used for applications involving water, air, and hydraulic
fluids.
b. PVC Hoses: PVC (polyvinyl chloride) hoses are lightweight and
cost-effective. They are commonly used for the transfer of
non-corrosive fluids, such as water and some chemicals.
c. Thermoplastic Hoses: These hoses are lightweight, durable, and
suitable for applications where resistance to chemical attack and
high pressure is required.
3.2 Classification Based on Construction
a. Reinforced Hoses: These hoses have an inner tube for fluid
transfer and additional layers of reinforcement, such as textile,
steel wire, or fiber, to provide strength and prevent kinking or
collapsing under pressure.
b. Non-Reinforced Hoses: Non-reinforced hoses are suitable for
low-pressure applications and may consist of a single layer of
material. They are generally used for light-duty tasks.
The choice of hose type depends on factors like the nature of the
fluid being transported, the working environment, and the required
flexibility and strength.
4. How to Calculate Pressure Loss in a Hose
Pressure loss in a hose, often referred to as head loss, is a
decrease in fluid pressure as the fluid moves through the hose. It's
primarily caused by frictional forces between the fluid and the
inner surface of the hose.
Several factors contribute to pressure loss in a hose:
- Length of the Hose : Longer hoses result in higher pressure losses due to the increased contact between the fluid and hose material.
- Diameter of the Hose : Smaller diameters lead to higher pressure losses as they create more resistance to fluid flow.
- Flow Rate : Higher flow rates increase the velocity of the fluid, leading to greater pressure losses.
- Fluid Viscosity: More viscous fluids experience higher frictional forces, resulting in increased pressure losses.
The method found in the literature to calculate the pressure loss in a hose is to calculate the equivalent length considering a steel pipe with a roughness of 0.05 mm and then apply an equivalence to the length of the hose according to the following references [1] :
| Hose | Equivalent length vs stell pipe 0.05 mm roughness |
| Rubber hose, smooth | 0.6-0.9 |
| Rubber hose, with wire reinforcement | 0.7-1.3 |
| Metal hose corrugated | 2.3-2.5 |
Step 1 : Calculate the hose length in the circuit considered
Calculate the hose length of the circuit considered.
Step 2
Convert this length to equivalent length with the hose. For example, if the hose length (without singularities) of a metal hose corrugated is 10 m, the equivalent length in carbon steel will be 10*2.5 m = 25 m.
Step 3
Add the equivalent length of singularities to the equivalent straight pipe length calculated before
Step 4
Calculate the pressure loss in the circuit thanks to the Darcy Weibach equation, considering the total equivalent length applied to a steel pipe with roughness = 0.05 mm
The formula to calculate pressure loss in a hose is given by the
Darcy-Weisbach equation:
f/2=friction factor, f is Fanning friction factor
DH=Hydraulic diameter in m
um=mean velocity in m/s
ΔPf=pressure drop due to friction in Pa
L=length of pipe in m
ρ=specific gravity in kg/m3
5. Conclusion
Accurately calculating pressure loss in hoses is vital for system efficiency and safety. Understanding the types of hoses and their impact on pressure loss allows engineers to make informed decisions when designing fluid transport systems. As engineers, we must continue to refine our calculations and understandings to optimize our designs and operations.