A Review on Applications of Computational Fluid Dynamics (CFD) in

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A Review on Applications of Computational Fluid Dynamics (CFD) in the Food

Industry

Manas Ranjan Padhi

Department of Mechanical Engineering Centurion University of Technology and

Management Odisha, India

Email: [email protected]

Manas Ranjan Padhi: A Review on Applications of Computational Fluid Dynamics

(CFD) in the Food Industry -- Palarch’s Journal Of Archaeology Of Egypt/Egyptology

17(7). ISSN 1567-214x

Keywords: cfd; food processing; fluid flow; design;simulation.

ABSTRACT

Computational Fluid Dynamics (CFD) is a powerful simulation tool to obtain fluid

flow and heat transfer simulation with the use of computers along with applied mathematics.

It is cost effective method to solve real-life problems in fluid dynamics. Mathematical models

in terms of conservation laws represent the flow physics in terms of strongly coupled non-

liner partial differential equations. CFD finds wide applications in automobiles, aerospace,

manufacturing, process industries, power plant equipment and electronic components as a

design and simulation tool. Since most of the processes in food industry involves the

application of fluid flow as well as heat and mass transfer, CFD provides a good early-stage

simulation for predicting the performance of these processes. It also allows the test engineers

to validate the test results obtained from simulation of the food processing equipment with

experimental study, thereby help them to improve the design and performance of equipment.

1. Introduction

For several years, CFD has been used extensively in many process

industries. However it has recently been used in the food processing

industry. Clean room construction, mixing of two fluids, refrigerated

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transport, static mixers and pipe flow are some of CFD's major applications.

An additional benefit in recent years has been the use of CFD to design food

processing equipment. Basically, the food processing machines such as

dryers, pasteurizers, sterilizers, freezers, mixers and baking ovens are used

to design them. The advancement of CFD by means of simulation is very

helpful in predicting the air flow movement over the food products within

the food processing equipment.

The performance of the baking oven is numerically simulated by predicting

the air flow inside it. CFD simulation also calculates the heat and mass

transfer and therefore helps to maintain the desired temperature and

moisture inside the oven. Therefore, it is apparent that CFD is a decent

technique in optimizing the performance of the food processing equipment.

The inclusion of mass transfer in CFD model is quite fruitful in controlling

the moisture content in bread to improve its quality. CFD has been used by

many researchers for numerically predicting the air flow and temperature

pattern inside the chillers and freezers. One practical example is air flow

distribution prediction in meat chillers, which is supplemented with a two-

dimensional CFD model in the design. It is obvious that current CFD

technique is useful in determining heat transfer between products and air

which takes into account the radiation effect. This will help in proper

designing the chiller wall with heat insulating material that will prevent the

heat loss and to give exact rate of cooling effect. Since, freezing process

involves phase change; it can also be modeled by using CFD particularly

the freezers which stores the frozen food for long period of time without

deterioration.

CFD has a vital role in impinging food processing equipment like spray

freezing and spray freeze drying by determining particle velocity,

temperature as well controlling the air velocity. Similarly it can be used for

the design and development of impingement jet oven. CFD has been proven

to be a good simulation tool to tackle with the problems faced in large scale

grain processing industries. One such example is to handle and control the

operating conditions of flour mill. Some food items require phase change

during their processing. The common example is processing of powdered

coffee which requires significant drying. In order to model that drier, the

turbulent flow of air inside the drier need to be considered along with heat

and mass transfer between air and coffee. The processing of some liquid

food products requires the application of pumping and mixing. Since the

modeling and analysis of these equipment can be taken proper care of with a

simulation tool like CFD. The common purpose of CFD as a numerical

simulating tool is to correctly predict the flow pattern and temperature

distribution inside the thermal processing of food. Examples of such

applications include numerical simulation of velocity and temperature

profiles for foods packed in can that are sterilized in a batch retort and

during the pasteurization of bottled wine. With the help of such CFD

simulations, the temperature distribution pattern inside the containers can be

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obtained and thereby lowest heating point can be identified. Due to the fast

development in the research of fluid dynamics in the last few years, CFD as

a tool of numerical analysis can be beneficial to several food processing

industries like drying, baking, spraying, sterilizing, mixing and

refrigeration.

2. Applications of CFD in various areas of food industry

Computational Fluid Dynamics (CFD) has been used widely in the food

processing field to great advantage. Its numerous applications include

predicting the gas flow pattern and particle histories such as temperature,

velocity, residence time, and impact position during spray drying, modeling

of ovens to provide information about temperature and airflow pattern

throughout the baking chamber to enhance heat transfer and in turn final

product quality, designing of heat exchanger to carryout pasteurization,

cleaning of storage tanks, sterilization, crystallization and refrigeration. This

paper focuses on various applications and recent developments of CFD

modeling in different food processing industries.

A. Improving cleanliness of food processing tank

Food processing tanks are used to store inventories for food items. These

inventories include raw materials, finished food items and semi-finished

item needs for further processing like mixing, heating, cooling and

fermentation. It is necessary to maintain proper cleanliness of these food

processing tanks in order to avoid wastage and to improve the efficiency.

The improper cooling leads to the formation of biofilm on the equipment

surfaces that can results in the formation of corrosion and may cause health

hazards. Therefore, it is very essential to keep the tank surface clean and

adequate hygiene to be maintained. CFD as simulation tool can be used to

analyse fluid flow not only to keep the tank surface clean but also for an

improved design with respect to the cleanliness. Along with flow

simulations in tanks and pipes, CFD can also be used to deduce the shear

stress in the joints of the tank wall and determine the nature of the boundary

layer formed, whether laminar or turbulent and accordingly can suggest for

a better design. It can be used to compare the results of the preliminary

design of the storage tanks with the experimental results obtained so as to

assure the design engineers to go for an effective design without much

expense. In this way, it will be economical to use it for designing

complicated food processing tank structures consisting of many joints and

bends. Asteriadou et al. [1] used CFD for the cleaning of food processing

equipment with T-joint. They carried out the experiment to clean the salt

solution using deionized water. The comparison gave an error which is

within acceptable limit for both steady and transient condition.

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B. Drying

Drying is an important food manufacturing process. Food products like dry

fruits, chips prepared from vegetables and nuts require adequate amount of

drying during their processing. We also dry some foods to preserve it for

long time. Some organic fruits are properly dehydrated to preserve it.

Hence, drying plays a major role in food processing in recent times. Drying

not only keeps the moisture away but also inhibits the functions of bacteria

and yeast. The velocity, temperature and moisture of air are the main factors

in drying food items. Therefore, it is very important to know the velocity

and quality of air during its flow inside the drying chamber that leads to

give information about the areas of sufficient air velocities for proper

drying. The velocity and discharge of air can be measured by means of

sensors. But it is a difficult job to place sensors at so many locations and to

mount them is not cost effective. Cereals and oilseeds are dried after

harvesting to the moisture content that prevent growth of microorganisms.

Drying in vegetables not only helps in preventing the microbial growth, but

also to avoid the formation of brown colour during storage. CFD as a

powerful simulation tool can help in prediction of air flow along with

temperature pattern. Determination of pressure and velocity profiles with

the aid of CFD can estimate the drying rate and moisture content even in

complex physical model of drier. Though prediction of flow pattern and air

velocity is not a complicated job using CFD, but to go for accurate

measurement of cooling rate and energy consumption, one should go for

correct assumptions.

CFD is a powerful tool to aid the prediction of drying process. Mathioulakis

et al. [2] applied CFD for the prediction of air flow in an industrial batch

type tray drier. They used different fruits for their drying test and concluded

from simulation results that the position of fruits inside the drier had

considerable impact on extent of dryness. Spray driers are often used in

food industry for effective and uniform drying. CFD can be used for

evaluating the efficiency and analysing the design and operating conditions

of spray driers in food processing industries. Zbicinski [3] carried out the

research by developing a numerical model of mass, momentum and energy

transfer during spray drying process. He used CFX, a tool of computational

fluid dynamics to determine heat and mass transfer of air inside the dryer

and to calculate particle trajectories for different phases. The experimental

results were validated with numerical results and found to be within

acceptable limit. Huang et al. [4] used FLUENT, a commercial software in

CFD to analyse the profiles of different parameters such as temperature,

velocity and humidity of air at different stages inside a spray dryer. CFD

can be a quite convenient tool for forecasting the profiles of gas flow and

estimating crucial parameters such as temperature, velocity, and residence

time and impact position of gas particles in spray drying. It can also be used

as a design tool for chamber designing of spray dryer according to the

behaviour of food item along with substantial information on air particle

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interaction. Many notable researchers like Zbicinski, Zietara, Simon Lo and

Huang have used CFD for their analysis in spray dryer. Lo [5] used Euler-

Lagrange model in CFD to calculate the motions of the spray droplets and

the heat and mass transfers between the droplets and the air stream. Many

valuable results were presented in the form of percentage of particle leaving

are exit, the operating conditions of the particle like size, temperature and

moisture content. Based on the results, the optimum operating conditions

can be selected to achieve the desired product quality at minimum cost.

During spray drying the adherence of particle to the wall of spray dryer may

occur which may affect the product quality. This practical problem can be

eliminated by the use of CFD analysis.

C. Pasteurization

Pasteurization is a heating process to keep the food product free from

pathogenic bacteria. This process is named after Louis Pasteur. It is

generally adopted in the case of liquid food products such as milk, fruit

juice and beer. The process involves heating the food products at specific

temperature, especially at low temperature for a specific period of time to

kill the harmful bacterial that could cause deterioration, disease and

undesired fermentation. Both packaged and unpackaged food can be

pasteurized. Since it a mild heat treatment process, therefore the control of

temperature and duration of heating are very crucial. In less acidic food

such as milk and liquid egg, this heat treatment in pasteurization may not be

sufficient to remove harmful bacteria. Subsequent refrigeration is also

necessary to kill harmful microorganisms. Hence it will be a wise decision

to go for simulation software like CFD that can generate temperature file for

the effective control of both heating temperature and time. Most liquid

foods are subjected to pasteurization in bulk quantities in continuous system

consisting of heating zone, holding tube and cooling zone. Therefore, proper

designing of this whole system is necessary considering the velocity and

temperature of liquid food products. CFD has bigger role to play in this

continuous pasteurization system for controlling fluid speed, quantity and

temperature. Different types of heat exchangers are used in pasteurization

process. Low viscosity food products like different animal milks, nut milks

and juices are generally pasteurized by using plate heat exchanger. A plate

heat exchanger is a compact heat exchanger which consists of many thin

stainless steel plates that separates the liquid from heating or cooling

medium. Similarly, scraped surface heat exchanger contains an inner

rotating shaft in the tube which can scrap highly viscous material from the

tube wall. Common heat exchangers used in pasteurizing plant are shell or

tube heat exchanger which are designed for the pasteurization of the Non-

Newtonian foods such as dairy products, baby food and tomato sauce. In a

concentric tube heat exchanger, food passes through the inner tube and

cooling or heating medium is circulated through the outer tube. After the

heat exchangers, the products are allowed to flow through a hold tube for a

definite period of time to achieve the required treatment. The benefits of

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heat exchangers are that they provide uniform heating or cooling and simple

to analyse because of their construction. Since basic design of all types of

heat exchangers are based on the calculation of heat flux, therefore, it is

essential to use CFD as a fluid simulation tool to calculate the heat transfer

and performance of these heat exchangers. The performance of heat

exchanger is expressed in terms effectiveness which is the ratio between

actual heat transfer and maximum heat that can be transferred. The

effectiveness can be calculated from the temperature results obtained from

heat transfer analysis using CFD.

CFD not only useful in designing heat exchanger but also can optimize the

important parameters like pressure, velocity and temperature. The leakage

inside the pasteurizers can be detected by the effective utilization of CFD by

the maintenance engineers. Therefore, both design and maintenance of these

foods processing equipment used in the pasteurization process can be taken

care of by CFD. There are some investigations using CFD carried out by the

researchers. Denys et al. [6] used CFD in their analysis to carry out thermal

pasteurization of eggs and validated the experimentally obtained results.

Similarly Paul et al. [7] carried out the numerical simulation to determine

the temperature distribution inside the canned milk. They took the rotation

of can into consideration during their investigation and obtained the

effective results. Augusto et al. [8] used packaged pasteurization for beer to

increase microbiological stabilization. They carried out their research by

changing the orientations of the cans in packaged pasteurization.

D. Sterilization

Sterilization is an important process in food processing industries. It

involves applying sufficient heat to a food to minimize the chances of

survival of microorganisms or enzymes that is capable of producing

enzymatic changes in the food. Sterilization is ideal for packaged foods like

sauces, vegetables pickled in oil, jams, creams, candied fruit, canned fruit,

soups and juices. The difference between pasteurization and sterilization is

that former is applicable to liquid food products while sterilization is used

for solid and liquid food products that remove all types of bacterial by

supplying sufficient heat. CFD can be used to obtain the flow pattern and

temperature distribution in sterilization process to improve the quality of

food. Thermal processing deactivates the functions of microorganism but in

some cases decreases in quality is observed particularly flavour due to

excessive heating. In that context, CFD can be useful for calculation of

exact amount of heat transfer without hampering the quality of food

products.

Optimization of thermal sterilization of food without compromising with the

food quality as well as retaining its nutritional value has been carried out by

different researchers from time to time. CFD was used for obtaining

transient temperature distribution, generating velocity profile along with the

determination of slowest heating zone for carrot soup in pouches. Most of

the sterilization of liquid foods is conducted along with packed cans. Some

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researchers worked to find out the orientation effect of metal can and its

shape and size on sterilization. Tattiyakul et al. [9] carried out the research

in canned corn by using CFD simulation considering the axial rotation of

the can. They observed that the rotation effect prevented the heat transfer in

radial direction at higher speed. Kannan and Gourisankar Sandaka [10]

carried out numerical analysis of heat transfer on canned food sterilized in a

still-retort. Varma and Kannan [11] studied the effect of sterilization by

taking different shapes can. They observed that the inclination of can wall

as well as its geometry has substantial effect on the sterilization system. The

thermal effect on nutritional value during sterilization of packed liquid food

was investigated by using CFD by several researchers. Abdul Ghani et al.

[12] prevented the destruction of Vitamin C in carrot orange soup packed in

pouches. They found that the temperature and concentration profiles of

Vitamin C were strongly affected by convection. Shahsavand and Nozari

[13] carried out their research on continuous thermal sterilization process

for both laminar and turbulent flow. They told that sterility can be enhanced

by putting a mixer at the entrance of the holding zone while maintaining

quality of food products for laminar condition. They investigated the

turbulent flow using CFD and concluded that the thermal resistance of solid

particles has considerable effect on performance of continuous thermal

sterilization process.

There are many modern techniques which being implemented in food

processing in recent time such as ultra-violet, visible and infrared light

surface sterilization, plasma sterilization, electrons and X-rays sterlization,

pressure sterlization of fresh fruit juices. CFD will be great asset for all

these modern techniques in terms of simulation and analysis.

E. Mixing

Mixing is one of the most common operations in food processing industries.

Mixing applications involve the substances of gas, liquid and solid.

Thought, it appears to be simple but modelling the mixing process and

designing the mixing chamber is difficult job without the aid of fluid flow

simulation tool. Most of the mixing cases deal with multiphase and

turbulent in nature. CFD is a versatile tool not only in modelling such

mixing processes but also to give adequate information regarding fluid flow.

All types of mixing processes adopt some methods for mixing due to which

there is a change in properties like pressure and temperature occurs. It is

obvious to control these parameters during mixing process. Since the mixer

is basically meant for mixing viscous materials, therefore the proper design

of this equipment is essential in order to increase efficiency with a reduction

in energy consumption. To make steering effective, a paddle wheel or

stirring is often used in mixing. CFD code has been used to enhance the

stirrer design with an optimum mixing time that could reduce the energy

consumption. Recently, CFD has been employed for study in the modelling

of impeller-vessel geometry, energy balance and linkage between the flow

fields. The effect of configurations of impeller on hydrodynamics and

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mixing performance in stirring was numerically optimized by the use of

CFD. Aubin and Xuereb [14] carried out their research on multiple impeller

stirring tanks by varying the distance and rotation angle between impellers

and the system was observed to give better performance when the impellers

were rotating at 45

rather than 90

F. Baking

Baking is a process of preparing food products such as bread, biscuits and

cakes that require dry heat inside an oven. During baking, heat is transferred

from the surface of the baked item to their center. The baking quality of

breads improves as heat travels through it, results a formation of firm dry

crust and a softer centre. Baking process involves the simultaneous heat and

mass transfer where heat is allowed to transfer into the food from the hot

surfaces and both air and moisture gets transferred from the food to air that

surrounds it and then removed from the oven. Therefore the role of oven is

crucial for retaining the baking quality. With the help of CFD, the

temperature and velocity profile of air moving over food inside the oven can

be generated with a substantial control of air rate. Since, removal of

moisture also determines the baked quality of food, a fluid simulation tool

like CFD can be very useful in predicting the mass transfer.

CFD can be used to numerically determine the heat transfer, temperature

and velocity profile of air inside the baking oven for laminar flow

conditions. For baking industry which employs indirect heating baking

process, the heating is carried out four different zones. The temperature

profile at each zone is important, on which the final bread quality gets

affected. Here the computation fluid dynamics can provide the transient

temperature distribution for analysis. Therdthai et al. [15] built a two

dimensional mathematical model of continuous baking process which is

often used in industry in an oven to study the air flow and temperature

distribution pattern inside the baking chamber for different operating

conditions. The CFD simulation results helped to modify configuration of

oven for better heat distribution. With the help of CFD, the position of the

heating source which affects the air circulation can also be optimized. Thus

CFD serves as a practical tool for design, optimization and validation of the

process control. It can also be used a versatile tool for design, scale up and

optimization of baking ovens.

G. Refigeration

The consumption of frozen food has increased its demand in recent years

due to good quality and safety aspect. Refrigeration can slow down bacterial

growth and preserve food. Hence researchers have used CFD for the

modeling of heat and mass transfer in foods during refrigeration (chilling

and freezing). Hu and Sun [16] investigated the heat and moisture transfer

for determining the cooling rate and weight loss of cooked ham during air

blast chilling process by using CFD simulations.

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CFD can give correct information regarding design based on temperature

modelling with minimum cost before manufacturing the actual refrigeration

system. It is very important during refrigeration design that accurate control

of temperature is maintained with less cost in short period of time. Taking

all these points into consideration, CFD can effectively be used for design

optimization of equipment used in refrigeration such as chillier and freezers.

With the help of computational fluid dynamics, the simulation of air flow

over the food products can be done inside the refrigeration. It can be used as

modelling technique for the successful prediction of airflow inside

refrigerated space including cold stores, transport equipment and retail

display cabinets. Gaspar et al. [17] carried out heat transfer and air flow

simulations in an open refrigerated display cabinet to predict air

temperature, relative humidity and air velocity.

3. Conclusion

CFD is a possible simulation method for the flow pattern modelling process.

It can be used to build performance-enhanced food processing equipment.

Storage tank washing, pasteurisation, conventional cyclones, drying,

sterilisation, crystallisation, mixing and refrigeration, fermentation, baking,

etc. are the key applications. CFD practicability depends on CFD packages,

device settings, and the basic knowledge of fluid flow analysis. By

performing experiments for validation, it is also important to validate the

simulation results since some instances of CFD are based on approximate

models with certain assumptions. The versatility and wide range of CFD

applications, however is a boon for the food processing industry.

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