Why Computational Fluid Dynamics is an innovative tool for industries?

Having worked in applied fluid dynamics for over five years, initially in the commercial sector on industrial flows, and now within academia, I thought it would be a good time to reflect and share my experience on what could be achieved by applying Computational Fluid Dynamics (CFD).

Before diving straight into the physics around fluids and examples of CFD, let us first take a moment to appreciate fluids and its flow in and around us. We have fluids all around us – for example, I hear external flows whilst typing this article – wind blowing over my house, snow falling on the ground and seagulls flying in the sky.

And at the same time, I imagine the internal flows, like blood flow in our arteries or the hot water flowing through the coiled radiator. There are various forms and types of fluid flows that shape our world. They exist in macroscale to invisible nanoscales, governed by the fundamental laws of nature.

A recent example I found interesting is the ‘Fluid dynamics behind why food sticks to our pans?‘ in a paper published last week. It appears that we now have some clear understanding that when a pan is heated, a process known as thermocapillary convection is caused which draws the oil to the pan's edges due to uneven heating.

This results in less oil content in the middle of the pan and the most certain area where our food sticks. Well, fluid dynamics has helped us find answers to fluid-related observations in nature and our everyday lives.

Study of fluids has intrigued and sparked the curiosity of many researchers since the days of ancient Greece. With Archimedes of Syracuse formulating and publishing the famous Archimedes principle, which is considered the first major work in fluid mechanics. This was followed by scientists such as Leonardo da Vinci, Sir Isaac Newton, and Daniel Bernoulli, who helped advance this field even further.

My personal favourite has always been Osborne Reynolds whose published ideas on fluid dynamics formed a strong application, and connection to industrial flows that have most definitely transformed the industries. His key study was the transition of fluid from a laminar state to the turbulent state. His test rig, which is now one of the world's famous experimental apparatus is an exhibit in one of the engineering buildings at The University of Manchester.

He introduced the Reynolds number that allowed for scale-up, such as fluid physics acting on a scall scale ship model to a full-size ship, strengthening the application. These equations were later applied to hydrodynamic lubrication of bearings and ship propellers. This principle was further utilised to understand the heat transfer between fluids and solids, which formed the boiler and condenser design basis as we know today.

This application of fluid flow principles to improve an engineering process or equipment is of interest to me, which is made better with the advent of computing power – in other words, CFD. Over the years, researchers and engineers worldwide have improved CFD techniques and made it available in the form of tool.

The CFD tool can simulate the fluids in a system and has been used by many industries to analyse, optimise and verify the designs related to performance before expensive prototypes, and physical testing’s are carried out. CFD is hugely beneficial when the overall system or the equipment has complex geometry or features, and using conventional calculations are not sufficient.

There are two examples I am going to write about from my own experience of working within the filtration and compressor industries:

The first is improving the design of coalescing filters used for trapping oil aerosols in an oil-injected vacuum pump. These filters are essential for reducing exhaust emissions, which, when suspended, can cause great harm to the environment, climate, life of the equipment itself and ultimately public health. More details of this work can be found in this published article.

The pressure drop through the complex fibrous filters and the aerosol loading pattern was predicted using CFD. Based on this, design optimisations can be conducted to alter the aerosol loading patterns to achieve uniform loading of oil aerosol on the filter media for improved filtration efficiency. By using CFD, the need for product development cost was reduced due to a smaller number of experiments whilst improving the vacuum pump's consumption power.

CFD application for a coalescing filter in an oil-injected vacuum pump [1]

Another example is oil-injected twin screw compressors that are largely used in industrial, oil & gas, manufacturing, and refrigeration sectors where high-pressure gases are needed. Oil injection in these high-pressure compressors serves an important purpose of cooling, sealing, and lubricating these machines. However, an excess amount of oil can lead to power losses.

Therefore, there is a need to optimise the amount of oil, but it is impossible to visualise the distribution of oil in the compression chamber. Using a CFD tool, the oil distribution is visualised and based on this; the oil-injection techniques can be optimised.

Optimisation led to a reduction in compression chamber temperature as the chamber is better cooled due to improved oil distribution, and as a result, the compressor consumes less power. Overall, this means that with better injection, the compressor will have reduced energy costs and better environmental friendliness.

CFD application for an oil-injected twin-screw compressor [2]

Other examples published in the Process Industry Informer magazine are the application of CFD tool to improve performance of a pump that is used to process food to a highest hygiene standard, original design improvements to the pump impeller, and for better mixing in tank jet mixers used for in-tank mixing in oil & gas, pharmaceutical, chemical, food and wastewater industries.

Hence, it is expected that more industries from SMEs to large organisations will and should fully exploit the power of CFD for their systems, processes and equipment. Application of CFD tool will help improve the component's efficiency, environmental friendliness,  sustainability, and reduce wastage and costs.

References