Camelia Bhattacharyya, Amity University Kolkata
“A matter is something that takes up space and has volume. It can be classified into solid, liquid, and gas” – we’ve come across this sentence as early as our elementary school days. Then as we grew up, we understood the differences among these matters, the different properties and performed quite a number of calculations related to force, tension, gravity, viscosity, density, etc in our Physical Science classes. When asked to describe liquids, we’ve always described it as something having mass and volume but not a particular shape (takes up the shape of the container it’s in) and has more molecular distance than solid and less than gas. When asked a bit more, we’ve described its viscosity as well. But as we grew up, all the branches of science that were once separated, established an interlink again. This article would further describe how the physical properties of the fluid are used in biological processing with the help of external forces.
Rheology and fluid rheology:
Rheology is the study that focuses on the flow of matter like:
liquids,
gases, and
semi-solids.
When speaking of fluid rheology, we put our entire attention on only the fluids i.e., liquids. In bioprocess, this term is used mostly when taking into consideration the working of the biogas reactors. Other than this the term is also used when speaking of body fluids, liquid cosmetic products, etc.
These fluids are further classified on the basis of those following or not following Newton’s laws of viscous flow, the former being termed as Newtonian fluid while the later as non-Newtonian fluid. The equation to be followed here is, τ=Kγn where K= consistency coefficient, n=flow of behavior/power-law index, γ=shear rate (rate of velocity of the fluid in a particular area) and τ= sheer stress (viscous force/distance between two parallel areas)
Types of fluid rheology and formulas used for calculation purposes:
Bingham plastic rheology: τ = τ0 + nγ (τ0 = yield stress, n = coefficient of rigidity)
Pseudoplastic rheology: τ = K(γ)n
Dilatants rheology: τ = K(γ)n
Casson body rheology: = √0 + Kc√ (Kc = Casson viscosity)
Few uses of fluid rheology:
Used in joint pathology diagnosis by measuring the viscoelasticity of the synovial fluid in the presence of different amounts of hyaluronic acids.
The making of cosmetic products which are based on all types of emulsions. The proper function and delivery and also the sensitivity on the skin depend on the concentration and the manufacture of the product. So, to ensure proper functionality, a proper rheological study is required during the bioprocess of these products.
The study of the total solid and total volatile solids along with the pH, the hydraulic retention time, etc is required while working with stirred tank biogas reactors since a certain change in amounts or concentration can change the rheological calculations this interfering with the final product preparation. Even the pumping and mixing of substituents in fluids need to be accurate and thus fluid rheology plays a major role here.
It’s also used in the measurement of the amount of sludge in bioreactors and the proper handling and disposal of the same.
Hemolysis and erythrocyte rheology needs to be studied while handling blood samples. Body fluids are mostly too sensitive and thus when studied for a particular test, should be handled with care. The temperature can change the viscosity which might affect the fluid. Thus, fluid rheology of the blood should be well studied before handling clinical samples of the same.
It is also used to control fouling and thus save operational hazards and maintain membrane safety. Performance is highly increased when the rheology inside the bioreactor is well understood and the cleaning is done on time.
There are many other roles of fluid rheology directing our attention to a proper study of the properties of fluids for a better and cost-effective bioprocess production.
Future perspectives:
A better understanding of the rheology of fluids in all portions of the body might help in developing better processes to control health and better techniques might be present in the near future in the field of medical science. Also, a proper understanding of these processes might lead to safer manufacture of food products that might have fewer impurities and chemicals thus causing fewer threats on human health due to artificial food preservatives, colors, and ingredients. It might even help the cosmetics industry since proper cosmetics is something today’s youth pay a lot of attention to; a proper get-up goes hand-in-hand with talents and understanding of a subject in an interview and thus a proper cosmetic working on different skin types is of much need. All the industries might flourish on an entirely new level by just understanding the rheology of the fluids they are handling on a daily basis. So let’s make it known that “fluid rheology” is something of utmost importance both for a proper economy and for the wellbeing of the countrymen.
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Sources:
Fam H, Bryant JT, Kontopoulou M. Rheological properties of synovial fluids. Biorheology. 2007;44(2):59-74. PMID: 17538199.
Davies A, Amin S. Rheology of Cosmetic Products: Surfactant Mesophases, Foams and Emulsions. J Cosmet Sci. 2020 Nov-Dec;71(6):481-496. PMID: 33413789.
Björn A, Šafarič L, Karlsson A, Danielsson Å, Ejlertsson J, Svensson BH, Yekta SS. Substrate and operational conditions as regulators of fluid properties in full-scale continuous stirred-tank biogas reactors – implications for rheology-driven power requirements. Water Sci Technol. 2018 Sep;78(3-4):814-826. doi: http://10.2166/wst.2018.352. PMID: 30252659.
Martí-Calatayud MC, Schneider S, Yüce S, Wessling M. Interplay between physical cleaning, membrane pore size and fluid rheology during the evolution of fouling in membrane bioreactors. Water Res. 2018 Dec 15;147:393-402. doi: http://10.1016/j.watres.2018.10.017. Epub 2018 Oct 10. PMID: 30336342.
Kim HJ, Yoo SM, Chung JH, Kim TS, Lee SH, Son HS. Evaluation of fluid warmer safety using hemorheologic analysis with outdated human blood. Clin Hemorheol Microcirc. 2016;62(1):13-7. doi: http://10.3233/CH-151926. PMID: 25633567.
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