Computational fluid dynamics (CFD) is the science of predicting fluid flow, heat transfer, chemical reactions, and related phenomena by solving mathematical equations, which govern these processes using a numerical process. CFD is sometimes referred to as flow simulation, and is a computer simulation technique that permits the fluid flowing around, or through any product, reactions, processes to be analysed in great detail.

CFD technique can be applied across the sectors for performance optimisation in different kinds of equipment; general applications are found in the following industries: aerospace, power, cement, oil and gas, automotive, paper and pulp, steel, etc. Using this technique, designers can verify that their products will conform to a client’s needs early in the design cycle, accelerating the product development process. CFD can be used to calculate design mass flow rates, pressure drops, heat transfer rates, erosion rate, chemical reaction and fluid dynamic forces such as lift, drag and pitching moments. It creates virtual prototyping which is faster, and cost-effective.

Key features:
Good, detailed insight into systems for which prototype development or experimentation is difficult. The level of detail is practically unlimited
Ability to foresee design changes and optimise accordingly, reducing time and cost involved in evolving new designs
Ability to predict mass flow rates, pressure drops, mixing rates, heat transfer rates and fluid dynamic forces accurately. CFD techniques offer the capacity of studying system under conditions over its limits
Can be used for brown field and greenfield applications

Methodology:
Modeling: Based on drawings and data provided a 3D model is developed on computers.
Pre-processing: A model is discretised into small elements known as mesh and boundary conditions (real time operating/design data) are applied to the model.
Simulation: Simulations are started and the equations are solved iteratively as steady-state or transient. Finally, post processors are used for analysis and visualisation.
Once problems are identified the model is modified and simulations help solve the problem.

Applications:
Aerodynamics
Industrial fluid dynamics
Fluid structure interaction
Heat transfer
Hydrodynamics
Multi-phase flows

Benefits of CFD:
Low cost: Generating essential engineering data via physical experiments could be expensive.
CFD simulations are relatively cheap, and costs are likely to go down as computers become more powerful
Completely offline application

Speed:
CFD simulations are quick which could be executed in a short period of time
Quick turnaround means engineering data could be introduced early in the design process

Able to simulate real conditions:
This provides the ability to theoretically simulate most physical conditions (except hypersonic flows, for example)

Able to simulate ideal conditions:
CFD permits great control over the physical processes, and offers the ability to isolate specific phenomena for study e.g. heat transfer processes can be idealised with adiabatic, constant heat flux, or constant temperature boundaries
Experiments permit data to be extracted at a limited number of locations in the system
CFD permits the analyst to examine a large number of locations in the area of interest, and yields a comprehensive set of flow parameters for examination

Case studies in different industries Power plants
Boiler: A problem with frequent boiler leaks was causing unplanned shutdowns, generation losses and necessitating replacement of boiler tubes. A physical identification of such failures would not have been possible, but CFD analysis showed how erosion would occur over time. Boiler tube failures were reduced to 1 per year from 5 to 7 per year. The total cost for CFD and modifications was Rs 1 crore and benefits were no generation loss, very less consumption of LDO as shutdowns are reduced.

Flue gas ducting: Areas often neglected by power plant manufacturers is flue gas ducting leading to generic problems such as high pressure drops, erosion of flue gas ducts, non-uniform flow in branching ducts, unequal mass flow distribution, turbulent flow, no/low ID fan margins. CFD applications in this area have proven very successful in several power plants. Simple modifications requiring short shutdown periods led to large benefits, especially reduction in specific power consumption under the PAT scheme, improving the power plant’s performance.

In power plants, CFD is used in the following areas: coal mill, boiler first pass, alternate fuel, air ducting, electrostatic precipitators (ESPs), feed water pumps, condensing water pumps, etc.

Cement plants
Pre heater system: CFD has been used in the cement industry to address problems in the pre-heater systems such as: high exit temperatures, high pressure drops, improper material distribution, material accumulation, low cyclone efficiency, high PH fan power consumption. With MWI’s expertise using CFD, cost-effective solutions were provided to cement plants with benefits in line with CFD results.

Raw mill system: Another major CFD application area in the cement industry is in the raw mill system. Major problems with material accumulation were solved at various plants.

Other areas where CFD can be used in cement plants are: cement mill, gas cooling tower, cyclones for improving collection efficiency, ESP flow as per ICAC norms, improving fan performance, improving blade profile of fans, improving combustion inside calciner, reducing castables erosion in kiln, prediction of flame propagation length in kiln, improving combustion. The CFD tool has been used in various industries with our expertise to solve problems.

A few other industrial applications of CFD-based technology are:

Oil and gas
CFD-based applications have been beneficial in design validation of burners, avoiding starvation of burners, uniform flow distribution throughout the combustion air ducts.

HVAC
To analyse flows through industrial sheds, to make work environment comfortable.
To maintain temperatures in operation theaters, to analyse smoke extraction through basement parking, etc.

Steel sector
In the cast house, stack house analysis, fume treatment plants. They use CFD analysis to carry out studies pertaining to:
Single phase flow/multiphase flow
Combustion
Heat transfer
FSI analysis

As part of the company’s FEA service, they carry out studies pertaining to:

Thermal studies
Vibration analysis
Stress analysis (static, dynamic, non-linear, impact)
Fatigue analysis

ABOUT THE AUTHORS:
Mehul Shah, General Manager – Marketing, and Akshay Shah, Sr Engineer- Marketing, Mechwell Industries. Mechwell is capable of providing CFD and FEA (finite element analysis) based analysis and solutions to optimise and enhance the design and manufacturing of existing or newly developed products and a leading supplier of flue gas desulphurisation dampers.