PROPERTIES OF BIOLOGICAL MATERIALS : Difference between an Agricultural Engineer and a Mechanical engineer in machine design.

Hi steemians, I hope you're good. I've come your way again this time, and I'll firstly like to appreciate you all for reading my posts, I'm really encouraged. However, many who have read my recent STEM posts have concluded that I'm a mechanical engineer, well, let me say clearly that I am not, at least not officially. I am instead a graduate Agricultural Engineer, specialising in Crop Processing and Post Harvest Technology. Very few things separate these fields of study, and it is one of those things I'll be explaining today.

To make you understand what I'll be discussing, let me tell you about one of my first challenges in my field of study. I noticed in my earlier days that most of the time, when I check the published works of most of the Professors in my department, I usually found more works on research of the properties of this seed or that fruit. I began wondering, why will you make an Engineer a professor just because he is studying properties of seeds, isn't he supposed to be recognised for developing machines.

Well, it didn't take me long to realise that I reached that conclusion because I knew too little at the time. In case you're wondering the same things I wondered then, well, you can be sure that the reasons are not far fetched. Let me give a real life example of something you can identify with better, in hopes that it will help you see how I was convinced.

Certainly, you've used drugs that were prescribed during a sickness, or you've been around someone who had to use such drugs. One of the first things we do is to check the side effects of the drugs and the contra-indications. We all expect the company to inform us in the effects it might have on certain individuals in certain conditions or with certain allergies. I'm sure you wouldn't want to listen to any excuses from a drug company that simply manufactured drugs without carrying out tests on side effects and contra-indications.

So, if I may ask, in this technologically advanced age :

which is more important, carrying out tests to know how substances in drugs affect disease pathogens, formulating a drug or carrying out tests on same drug to know how users will react to it?

I'm guessing your conclusion is the same as mine : all these are very important and compulsory process of drug manufacturing. At this point, I'll like to point out that as much as this doesn't bear perfect semblance to the work of Agricultural Engineers, I hope it has been able to help point out that their studies of properties of materials is a very crucial part of their job of machine design.

Just in case I need to make the point clearer, whenever you buy new clothes, you expect to find information on washing the clothing material and ironing it. You do this because you are certain it is part of the cloth manufacturing process to determine these. In the same vein Agricultural Engineers will be no different from a Mechanical Engineer if they can't develop machines that are more friendly to biological materials and more efficient.

And just then we have arrived at the subject of today's discussion : Properties of Biological Materials and and how they affect machine design and performance.

IS IT REALLY PRACTICAL?
Assuming you are wondering whether what I'm explaining is obtainable in real life or if it there is any real difference between machines designed by both sets of Engineers, let me remind you of something you most likely have seen but didn't notice. After which I'll tell you a personal experience that shows reality.

You don't need to walk far to notice the effect of machines designed with a knowledge of the properties of biological materials. For if you've once visited a poultry and seen the very simple design battery cage system used for keeping layers and how their eggs roll down to the edge of the wire mesh, or if you've seen and read 100% sortexed on the bag of rice you bought, then you've seen firsthand the benefits of those studies.

As simple as it looks, you may want to know that the angle of inclination of that wire mesh is just enough to allow the egg roll down the wire, for a lesser angel will result in the egg remaining at the spot where it was laid, leading to almost certain waste. Therefore, an engineer that designs the battery cage system without knowing this angle range will most likely be designing to fail. That is just a simple application of the frictional properties of eggs and the wire mesh. I'll be explaining this soon.

I also witnessed what happened with one of my mechanical engineering colleagues when he was designing a rice destoning machine. He appeared to have done a great job, until the time for testing came, and most f his rice grains were blown out of the machine along with the chaff. Upon seeing this, his ignorance of the Aerodynamic properties of the rice grains became very obvious to me. I assume my point is getting clearer now.

P. S : This isn't an attempt to devalue the mechanical engineering profession, it is a wonderful discipline with wonderful engineers that have produced countless brilliant machines, however, this post is aimed at showing the weapon Agricultural Engineers are equipped with that makes them better at designing machines that handle biological materials. And in case you're a mechanical engineer that is interested in designing such machines, you can take this as a crash course in the properties of biological materials.

That being said, let's get to the business of discussing these properties in their different categories and their effect on machine design.

^{A Universal Testing Machine from Wikimedia under CCO license}

PROPERTIES OF BIOLOGICAL MATERIALS

Firstly, it should be known that biological materials have general properties like being heterogeneous, bio-degradable, hygroscopic among others, however, the properties we will be focusing on are those that personally describe each material's behaviour distinguishing it from another much like you could say humans have general characteristics but then you could choose to describe someone in terms of his emotional, physical and financial characteristics.

Therefore, without further ado, biological materials are also described based on the following qualities :

• Physical properties

• Mechanical properties

• Aerodynamic and Hydrodynamic properties

• Frictional properties

• Di-electric properties

• Electrical properties

• Optical properties

• PHYSICAL PROPERTIES : These are the properties that determine the visible nature of materials an they include the shape, size, volume, surface area, thousand grain-weight, porosity, bulk density, true density among others. Putting this into perspective, there is an obvious reason why fashion designers request that you show up for measurements before proceeding to make a dress for you. In the same vein, I wouldn't have to explain the folly of an engineer that designs a machine without knowing the dimensions of the fruits or seeds that the machine will handle.

Also, size of seeds must be determined to design a machine which separates them from impurities, the screens of a rice destoner take very good advantage of this. However, when you are designing to separate those seeds using floatation principle, the densities of the materials come into play. The bulk and true densities of materials also give information on how fruits or tubers affect the walls of the machine, silo or storage bin, and how many the machine can hold at once while maintaning optimum operation.

• MECHANICAL PROPERTIES : These are properties that describe the behaviour of biological materials under load (either tensile or compressive), or upon impact ion a surface. This is where you have properties like compressive strength and tensile strength and coefficient of restitution. My colleagues once laughed at the fact that I was conducting studies on the copressive strength of pepper (I was even nicknamed Pepe Terra), of course what they didn't understand at the time was that it was a preliminary study for the design of pepper processing machines.

This is needed to avoid the undesirable effect of having a machine that crushes too many peeper fruits just because the designer didn't determine the load tolerance of those fruits before designing. The Universal Testing Machine is usually employed to determine these two properties.

As for the coefficient of restitution which describes how a material responds when it drops on a surface from varying heights, it is needed in the design of the hoppers of machines as this is where the materials first land upon reaching the machine. Inadequate information on this property may lead to the design of a hopper that isn't high enough to contain bouncing seeds or the hopper being too far away from the source to the extent that impact will affect the quality of the materials.

• FRICTIONAL PROPERTIES : I have decided to separate these from other mechanical properties as I felt their importance would have been buried inwgat wow have turned out to be bulky explanation of the all the mechanical properties. These properties include coefficient of friction (both static and dynamic) and angle of repose and describe how friction affects the movement of biological materials on different surfaces.

To put this in context, after determining the coefficient of friction of maize seed on galvanized steel you will arrive at an angle below which the maize seeds can't slide. So let's say I refuse to study this property of maize and go ahead to design a maize planter with a galvanized steel hopper inclined at an angle lower than the coefficient of friction between maize and galvanized steel, do you think the seeds will move from the hopper into the seed metering unit? Certainly not, it's just simple physics.

Along with the coefficient of friction, information on angle of repose is also needed in designing screw conveyors, to design flat storage facilities so that one can know how the materials will pile inside it. Also when designing material handling equipment like the belt and screw conveyors which are employed in the loading, unloading and movement of materials within a production factory or storage site, these properties are of utmost importance as the materials ability to slide on the surface is mainly the point of focus.

The three categories of properties described above are sometimes collectively referred to as engineering properties of biological materials.

Apparatus for determining Coefficient of Friction. Picture taken by me @sogless

• AERODYNAMIC and HYDRODYNAMIC PROPERTIES : these are those properties that describe the movement of biological materials in fluid, be it air or water. They mainly include terminal velocity and drag coefficient. These properties are related to each other and you can check here to know more.

Let's revisit that my colleague that had the problem of both his rice grains and chaff being blown out together by the fan. As earlier said, terminal velocity describes how the materials will move in air, therefore a study of this property of rice would have provided him with enough information on the terminal velocity of rice, and this in conjunction with the information on the terminal velocity of the chaff will enable him to design the blower speed such that it will blow out the chaff but wouldn't blow at enough speed to eliminate the rice, at least that is how the professionals do it.

Furthermore, knowledge of these properties come in handy when designing machines for the pneumatic conveyance and separation of materials.

^{Graph showing terminal or settling velocity of sand grain in water from Wikimedia under CCO license}

• DI-ELECTRIC PROPERTIES : These properties describe the relationship that exist between biological materials and electromagnetic energy. If you've used microwave to heat food, you've enjoyed a machine designed based on the study of these properties. The properties in this category include Di-electric constant which describes the material's ability to store electromagnetic energy, Di-electric loss factor which also describes how well the material can convert electromagnetic energy into heat and loss tangent which is a ratio of the two previous properties tells us how good a material is at absorbing microwave energy.

In case you think I'm going all too scientific on you. Let's try this real life scenario, if you put food substance A in your microwave and it heats up under 1 minute, but food substance B takes 2 minutes to heat up under the same conditions, then you have successfully shown yourself that good substance A has a higher loss tangent than food substance B.

A procedure similar to this albeit in a more controlled and sophisticated environment and under expert supervision is what Agricultural engineers use to study these properties and apply the information gathered in the designing of effective sterilization, drying and thermal processing machines and systems.

• ELECTRICAL PROPERTIES : As suggested, these properties describe how biological materials respond to the flow of current through them. Properties under this category include Electrical resistance, conductivity and impedance. Well, if you're doubting whether biological materials possess these properties, you may want to check here to see that even your body does.

A very good application of these properties is in ohmic heating, where food materials are being heated by passing electric current through them, it depends greatly on the material's conductivity. The knowledge of the electrical conductivity and resistivity is therefore necessary to design an efficient ohmic heating system.

• OPTICAL PROPERTIES : Properties here describe how biological materials reflect and transmit light. Colour is a very good example of these. If you remember my mention of sortexed rice earlier. Sortex machines make use of the colour of rice seeds to separate them, they make use of high speed cameras to detect difference in colour and trigger a process that results in the ejection of materials having unacceptable colours.

They find application beyond the rice industry, as I've once witnessed how they are used to clean sesame seeds. Also, these characteristics are employed in determining moisture content of biological materials.

^{A Color sorting Machine from Wikimedia under CCO license}

EFFECT OF MOISTURE CONTENT and MATHEMATICAL MODELLING
As mentioned earlier, biological materials are hygroscopic, that is they adjust their moisture content based on the relative humidity and temperature of their environment. Therefore, the properties described above are usually studied at varying levels of moisture contained in the materials. Critical moisture contents are selected based on literature.

Also, if there is need to raise a particular biological material above it's natural moisture content, certain seed conditioning techniques are employed to achieve this.

However, to make the whole process more interesting, after conducting these studies, which sometimes include the relationship between these properties and other conditions like varying moisture content or surface change.

Mathematical equations are generated to describe the relationship between these parameters. These equations can either be linear, exponential, polynomial or logarithmic, depending on which best describes the parameters, often indicated by the highest regression coefficient. These equations are sometimes referred to as characteristic equations.

CONCLUSION
As much as Agricultural engineers are those trained to carry out these studies are mostly those carrying them out, it doesn't mean that the information they gather will be restricted to that field, thus,any engineer in any field who desires to design an effective system for handling biological materials is expected to avail himself of these information, this is of course the beauty of the whole educational process.

I have tried to limit the amount of information provided in this post so as to ensure that the main purpose of this post is not lost on the readers in the face of too much details.

However, I understand that some may be interested in knowing more about the exact procedures of determining these properties, and for that reason I have gathered some recently published works that can help in this regard that you can find under references. I hope you find them useful.

REFERENCES
Aydin C. and Ozcan M., 2002. Some physico-mechanic properties of terebinth (Pistacia terebinthus L.) fruits. J. Food Eng., 53, 97-101.

Bamgboye, A. I., and Adebayo, S.E., (2012). Seed moisture dependent on physical and mechanical properties of Jatropha curcas. Journal of Agricultural Technology, 8(1) 13-26. Biographical Notes.

Davies R. M., (2009). Engineering properties of three varieties of Melon seeds as a potential for development of Melon processing machines. Advance Journal of Food Science and Technology 2(1): 63-66.

Galedar, M. N., Jafari A., Tabatabeefa A. (2008). Some physical properties of wild pistachio nut and kernel as a function of moisture content. J. Phy. Environ. Agr. Sci. 2008. 22: 117-124.

Ilori, T.A., Akinyele, O.A. and Aremu, D.O. (2016). Effect of Moisture Content on Some Engineering Properties of Celosia Argentea Seed. Journal of Environmental Science, Toxicology and Food Technology, 10(9), 157-160.

APPLICATION OF ENGINEERING PROPERTIES OF BIOLOGICAL MATERIALS | TERMINAL VELOCITY | OHMIC HEATING IN THE FOOD INDUSTRY