3. Tom Tat Tieng Anh.pdf

THE UNIVERSITY OF DANANG UNIVERSITY OF SCIENCE AND TECHNOLOGY NGUYEN THI TAM THANH RESEARCH ON THE APPLICATION OF MAGNETIC FIELDS TO IMPROVE THE FREEZING EFFICIENCY OF VIETNAMESE PANGASIUS HYPOPHTHALM[.]

THE UNIVERSITY OF DANANG

UNIVERSITY OF SCIENCE AND TECHNOLOGY

NGUYEN THI TAM THANH

RESEARCH ON THE APPLICATION OF MAGNETIC FIELDS TO IMPROVE THE FREEZING EFFICIENCY OF VIETNAMESE PANGASIUS HYPOPHTHALMUS FILLETS

Major: Thermal Engineering Code: 9520115

SUMMARY OF DOCTORAL THESIS IN ENGINEERING

DA NANG - 2023

The work was completed at the University of Science and Technology, University of Da Nang

Supervisor:

1 Assoc Prof Dr Vo Chi Chinh

2 Dr Nguyen Thanh Van

INTRODUCTION

1 The necesssity of the research

With the objectives of developing the fisheries sector to 2030 into an important economic sector of the country, producing large goods associated with sustainable development, the promotion of research into technologies related to farming, Processing and preserving seafood is urgent today

Pangasius is the most farmed and exported freshwater fish compared to other freshwater aquatic products and is considered a billion-dollar export industry of Vietnam Pangasius fillet is a semi-finished product that has passed the processing stages such as organ, bone and skin separation, It can be used for a variety of processing purposes However, they are easy spoiled if not properly preserved, usually these products are preserved in the form of freezing, the temperature at the center of the pangasius fillet is not greater than -18°C (TCVN 8338:2010)

The process of freezing food is affected by their main component is water The final quality of the frozen product depends on the process of converting the phase from water to ice The size of the ice crystals is important for the final quality of frozen food as it can have an irreversible effect on the cellular structure thereby degrading the structure and color of the product For this reason, many novel freezing technologies have been developed to control the crystallization process and improve the rate of formation and development of ice crystals Electrical and magnetic interactions are factors that can rearrange hydrogen-bonding networks that exist in water

With the above analysis, the study of magnetic assisted freezing process for

Pangasius Hypophthalmus fillet in Vietnam is necessary to improve the quality

of products after freezing while reducing energy costs during freezing, thereby improving the competitive advantage in the export market for pangasius products

− The effect of the magnetic field on the quality of pangasius fillet products after freezing based on criteria such as color, hardness, stringiness, gumminess, chewiness and the rate of mass loss after defrosting has been analyzed At the same time, analysis and comparison with commercial frozen pangasius fillet products in the export market

3 Research subjects and scope

(iv) Calculate and compare heat transfer coefficients when freezing with and without magnetic field assisted based on the semi-experimental method (v) Develop and conduct single-factor, multi-factor experimental research to determine technological parameters suitable for the process of freezing pangasius fillet with magnetic field assisted, based on reducing energy costs while improving product quality

(vi) Analysis of the basic quality indicators of the product after freezing including color, hardness, elasticity, stringiness, gumminess and the rate

of mass loss after defrosting From there, it is possible to analyze and compare with commercial frozen pangasius fillet products in the export market

5 Structure of the thesis

− Chapter 1: Overview

− Chapter 2: The theoretical study of magnetic filed assisted freezing

− Chapter 3: Theoretical results and experimental study on influence of magnetic fields on air blast freezing process

− Chapter 4: Optimize the operating parameters of the air blast freezing process with assisted static magnetic field

− Chapter 5: Quality assessment of frozen products applied magnetic field

CHAPTER 1 OVERVIEW

Seafood quality and the effects of freezing

During food freezing occurs the phenomenon of water displacement due to the difference in the internal and the surface temperature of the product, the water moves outwards in large quantities, so it forms large ice crystals that puncture the cell membrane When defrosted, water flows out of food carrying large amounts of nutrients For rapid freezing processes, a short freezing time will help reduce the size of ice crystals and increase the quality of food after defrosting Therefore, freezing time is the most important factor, determining the quality of food in general as well as the quality of seafood in particular

It should be recognized that food safety goes hand in hand with food quality and is a determinant of human health Therefore, major export markets such as Europe and the US often have very strict food safety regulations For fish and fish products, due to the existence of largely free water and high nutrient content makes these products vulnerable to short-term damage when not stored at low temperatures Therefore, the process of freezing products at low temperatures helps to limit adverse biochemical reactions, ensure food quality and increase the competitiveness of products in the export market

Therefore, the study of modern freezing technologies helps reduce the time and cost of freezing, increase product quality is an inevitable trend in the seafood export industry, especially pangasius and pangasius products

Pangasius and pangasius fillet

Pangasius hypophthalmus belongs to catfish in the Pangasiidae family

distributed in the Mekong basin Pangasius is the most farmed and exported freshwater fish compared to other freshwater fisheries and is considered a billion-dollar export industry of Vietnam

Pangasius fillet is a piece of fish cut / out from the body of the fish, along the spine, this is a semi-finished product that has gone through the processing stages such as organ separation, bone and skin, It can be used for a variety of processing purposes

a solid state

Common freezing methods

a) Blast freezing

b) Contact freezing

c) Cryogenic freezing

Novel freezing technologies

− High pressure freezing

− Electric field assisted freezing

− Magnetic field assisted freezing

− Radiofrequency assisted freezing

− Microwave assisted freezing

− Ultrasound assisted freezing

Current status of application of freezing technologies with magnetic field

assisted

− Application of magnetic field assisted freezing on experimental scale

Through these studies, the effect of magnetic fields on various experimental

samples (water, solution, food) has been demonstrated However, with the

limitations in terms of the number of experiments as well as related studies to be

able to compare and contrast each other, these research results can not be applied

on an industrial scale as well as on many different food subjects

− Application of magnetic field assisted freezing on industrial scale

In recent years, many patents have been registered to try to take advantage of

the effects of the magnetic field on the characteristics of water to improve the

process of freezing food All of these patents suggest that applying magnetic

fields during freezing will help control water freezing and increase

supercoolation However, the magnetic field with a low magnetic density of

magnetic field flux when used raises doubts about the impact of the magnetic

field on water, which is a substance with low magnetic sensitivity

Shortcomings in the study of magnetic field-assisted freezing technology

Theexperimental data published in the papers has yet to clearly demonstrate

the impact of magnetic fields on the freezing process and product quality in

commercial magnetic field assisted freezers, which the companies have asserted

have a positive impact and have been patented However, it should also be noted

that, although there are some reports of the effects of magnetic fields in freezing,

most studies have not yet been conducted on the same subjects and under the

same freezing conditions so it is difficult to compare with each other Therefore,

it is essential to have a scientific study that demonstrates the influence of the

magnetic field on the freezing process and/or improving the quality of the

product or that it is just a promotional publication of the manufacturer

CHAPTER 2 THE THEORETICAL STUDY OF MAGNETIC

FIELD ASSISTED FREEZING Magnetic field and phase modification of water

The magnetic field also has the ability to affect the properties of water Water can be considered a magnetic material, which means that magnetic dipole moments develop under the influence of the external magnetic field The effect

of the magnetic field on the process of water crystallization can have positive implications for the quality of the frozen material Based on the initial results of scientists published in this field, it shows the positive properties when applying magnetic fields in food freezing

Principles of operation of magnetic field assisted freezing

Figure 2.4 Principle diagram of magnetic field assisted freezing

Magnetic field assisted freezing is not a refrigeration system but an existing method of supporting the process and method of freezing to improve product quality and freezing speed Combining traditional freezing methods with magnetic fields during freezing can be beneficial in terms of energy costs and ensuring the quality of frozen products

Factors affecting the freezing process with magnetic field assisted

a Air temperature in freezing environment

b Air velocity in freezing environment

c The size and shape of the freezing product

c Magnetic field flux density

d Other factors

Pangasius fillet freezing problem model

The study model of pangasius fillet freezing with assisted magnetic field is presented in Figure 2.5, in which the pangasius fillet pattern is placed on the support tray surface located between the receiver and magnetic field The cold air is blown by the fan from the cooler parallel through the upper and lower surfaces of the sample

Figure 2.5 Arrange the product in the freezing chamber

700 700

Kh«ng khÝ l¹nh, tm, 

Kh«ng khÝ l¹nh, tm,  Qu¹t Dµn l¹nh Bé läc C¸ch nhiÖt Bé thu ph¸t tõ tr-êng

100 100

Fillet c¸ tra

t m = 30  40°C t m = 30  40°C

Thus, the problem that the thesis studied is the process of freezing pangasius fillet in the air environment of forced movement, convection from 2 sides of the sample

Methods for determining heat exchange coefficients

The heat transfer coefficient k from the freezing medium to the center of the product is determined based on the formula:

1 1

= +

(2.12)

One of the methods for determining convectiven heat transfer coefficient is

to use product temperature measurement results over time during freezing, thereby determining according to Biot number

.Z



All air blast freezing processes have a similar curve form Initially, they have

a certain lag and then the temperature at the center of the food decreases with the exponential Non-dimension temperature is determined as follows:

The 'lag' between the start of freezing and the non-dimension temperature is

measured by a factor j, as shown in Figure 2 7

Figure 2.7 Typical freezing curves by non-dimension temperature

From Figure 2 7, it can be seen that the linear part of the freezing curve can

2

a Fo Z



Mathematical model determines theoretical freezing time

Methods for determining freezing time: Plank (1941), Nagaoka (1956), Levy (1958), Cleland & Earle (1984) and Pham Q T (1986)

Simulation of pangasius fillet freezing process

The problem of simulating the freezing process of pangasius fillet is set in a 3D domain with a limited size of 210x110x15 mm For simplicity, the underside and side of the head and tail side of the piece of fish are considered flat

Set for heat transfer problem:

The assumptions of the numerical simulation problem of freezing:

- The freezing environment temperature is assumed to be constant during the freezing process under each different mode

- The air velocity through the pangasius fillet surface is assumed to be constant during freezing

- The thermal conductivity of the tray is ignored, so the boundary condition

of the simulation is a symmetry type 3 condition

- Neglecting the radiation due to the small size of the freezing chamber, the temperature difference between the environment and the pangasius fillet is low

- The freezer chamber is considered to be completely insulated, so heat loss

to the environment is ignored

- Moisture is considered to be evenly distributed inside the pangasius fillet

Simulation of magnetic field distribution in freezing equipment

In order to observe the distribution of magnetic fields in the freezing chamber when OMF and SMFs are used, and to help install temperature sensors in the right locations, the magnetic field distribution has been simulated on comsol Multiphysics v5.5 software

Conclusion of Chapter 2

The method of measuring unstable temperature combined with the relationship between homogeneous standards is determined to be suitable for calculation of heat transfer coefficient during freezing Due to the combination

of theory and experiment, this method is more reliable, suitable for complex freezing processes but also requires temperature measuring equipment during freezing to be more accurate

To calculate the theoretical freezing time to compare with simulation results and experimental results, 05 mathematical models: Plank, Nagaoka, Levy, Cleland and Earle, Pham Q T were proposed Theoretical research shows that these 05 models are suitable for calculating theoretical freezing times for products with complex shapes

CHAPTER 3 THEORETICAL RESULTS AND EXPERIMENTAL

STUDY ON INFLUENCE OF MAGNETIC FIELDS

ON AIR BLAST FREEZING PROCESS Survey of magnetic field distribution in the freezing chamber

The magnetic field is measured using the Tenmars TM-197 magnetic field meter (range 0~30000 Gauss, error 0.1G) The measuring position is the cross section between the center of the fillet, evenly 02 sets of magnetic fields above and below Each measurement is at 9 points (in figure 3.6), each data for 3 minutes (180s) and take the average result

Figure 3.6 Magnetic field measurement positions in the experiment

The results of measuring the oscillating and static magnetic field are presented on figures 3.7 and figure 3.8

Evaluate the operation of the model

To determine the freezing time, the product center temperature must reach no greater than -18°C, according to TCVN 8338:2010

a The freezing process without assisted magnetic field

Conduct test freezing runs for pangasius fillets at different air temperatures

(-30, -35, -40C) and measure the product center temperature as well as air temperature in the freezing chamber Freezing time at -30C, -35C, -40C is 2457s, 2381s and 2210s, respectively The air temperature drops by 5C, the freezing time decreases by about 5%

105 105

ChiÒu dµi miÕng c¸

PhÇn ®Çu PhÇn ®u«i

4 1 2

a) air temperature -30C; b) air temperature -35C; c) air temperature -40C Figure 3.12 Freezing curve on the ABF model with no magnetic field

b The process of OMF assisted freezing

a) air temperature -30C; b) air temperature -35C; c) air temperature -40C

Figure 3.13 Freezing curves of OMF assisted freezing

- OMF with an average magnetic density above 40 Gauss are having an effect on freezing time Freezing time is reduced by about 2% to 25% compared to conventional freezing

c The process of SMF assisted freezing

a) air temperature -30C; b) air temperature -35C; c) air temperature -40C

Figure 3.14 Freezing curves of SMF assisted freezing

- SMF with an average magnetic flux density above 400 Gauss are having

a major effect on freezing time Freezing time decreased by about 34%

to 56% compared to conventional freezing

d Assessing the impact of magnetic fieldson freezing processes

- OMF with an average magnetic flux density above 40 Gauss help to reduce freezing time by 2% to 25% compared to conventional freezing

- SMF reduce freezing time more than magnetic fields that range (from 34%

to 56%) but require greater magnetic density (over 400 Gauss) With SMF having a magnetic flux density lower than 80 Gauss, the experiment showed

no obvious effect on freezing time

- The OMF also has an effect on the freezing process but this is a parameter that is difficult to control the desired value so it is not possible to perform multi-factor experiments as well as optimize this parameter

Simulation results of OMF distribution in the freezing chamber

The grid type is free tetrahedral, with a total number of elements of 34728, the total number of nodes is 203850 The total number of freedoms of the problem is 284167

Figure 3.18 Magnetic field distribution oscillating at the center, t = 0.005s

Compared with experimental results on the model, at the same distance between two 80mm transceivers and transmitters, the average flux density at 9 measurement locations reached 68.2 Gauss, 7.83% lower than the value measured average value Thus, the simulation results show more clearly the magnetic field distribution over the entire cross-section of the fish

Simulation results of SMF distribution in the freezing chamber

The total number of elements of 20492, the total number of nodes is 115896 The total number of freedoms of the problem is 159225

Figure 3 23 Distribute the magnetic field at the cross section at the center of the fish piece with the

distance between 02 magnets:

a) 80mm; b) 70mm;

The area between the magnetic fish pieces differs from the fish head area at the distance between the two magnets 30mm and 40mm up to 732, 544 Gauss, 70% and 64% respectively Therefore, in experimental research, it is necessary

to avoid experiments with too low distances between two magnets

Results simulating the freezing process without magnetic fields

Figure 3.28 Freezing curve at the surface and center of pangasius fillet

a)

b ) b)

When compared to the results of calculations using calculus models , the difference between the method of calculus and simulation is very large (from 22.6% to 55%), it is recommended to use in cases of simple calculation

Figure 3.29 Temperature simulation results during freezing at 11 cross sections

Calculation of heat transfer coefficient during freezing

In fact, to evaluate the accuracy of experimental data in the method of calculating the heat transfer coefficient as described in section 2.4, the pangasius fillet temperature sensors during freezing are installed at the surface of the pangasius fillet and the product center, as shown in Figure 3.32a An 8-channel temperature data logger with type J thermocouple (VersaLog TC, Canada) with

an accuracy of 0.2% was used to determine pangasius fillet temperature during freezing

a) Temperature sensor location b) Temperature datalogger

Figure 3.32 Description of the method of measuring temperature during freezing

Table 3.15 Compare mean heat transfer coefficient

Mean heat transfer coefficient, W/(m 2 K) Freezing method Temperature sensor location

At surface At center Error (%)