Sumaiyah's+Weekly+Lecture+Summary

__**@Sumaiyah's Weekly Lecture Summary**__

**Week 1 to Week 6**

==**R H E O L O G Y **==

**~** Rheology  means something that 'flow'. Rheology is closely related to the properties of materials that control the deformation and flow behavior of a food product especially when they are subjected to external forces. Solids will deform while liquids will flow when an external force is acting on it, such as pouring, spreading and scooping.

**~** It is a characterize flow of materials that exhibits a combination of elastic, viscous and plastic behavior by properly combining elasticity and fluid mechanics.



Pouring chocolate sauce on the fresh fruits salad



Scooping ice cream



Spreading jam and peanut butter on bread

==** S T R E **** S ** <span style="color: #7000ff; font-family: 'Comic Sans MS',cursive;">**S** <span style="color: #55ff00; font-family: 'Comic Sans MS',cursive;"> **A N D S T R A I N ** == <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">~ In food, stress and strain impacts the food's appearance, processing and the most importantly, the texture. <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">**~** Rheology is mainly concerned with relationship between stress, strain and time. <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">~ Stress is simply defined as force per unit area while strain is a quantitative measure of the extent to which an element of material has been deformed. <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">The deformation implies the change of shape (dimensional change). <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">~ Thus, strain and stress are related to deformation and force, respectively.

==<span style="color: #ff0075; font-family: 'Comic Sans MS',cursive;">V <span style="color: #55ff00; font-family: 'Comic Sans MS',cursive;">I <span style="color: #ffa900; font-family: 'Comic Sans MS',cursive;">S <span style="color: #00ffff; font-family: 'Comic Sans MS',cursive;">C <span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">O <span style="color: #ffff00; font-family: 'Comic Sans MS',cursive;">S <span style="color: #ff00ff; font-family: 'Comic Sans MS',cursive;">I <span style="color: #14fa7f; font-family: 'Comic Sans MS',cursive;">T <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">Y == <span style="color: #1a8000; font-family: 'Comic Sans MS',cursive;">~ Viscosity means a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. <span style="color: #1a8000; font-family: 'Comic Sans MS',cursive;">~ It describes a fluid's internal resistance to flow and may be thought of as a measure of fluid <span style="background-color: initial; color: #0645ad; font-family: 'Comic Sans MS',cursive; text-decoration: none;">[|f] <span style="color: #1a8000; font-family: 'Comic Sans MS',cursive;">riction. As an example, we can compare the viscosity of water and honey. <span style="color: #1a8000; font-family: 'Comic Sans MS',cursive;">Honey is more viscous than water as it contain high concentration of sugar. Thus, the rate of flow of water is higher than honey as increase in concentration will increase the <span style="color: #1a8000; font-family: 'Comic Sans MS',cursive;">viscosity. <span style="color: #1a8000; font-family: 'Comic Sans MS',cursive;">~ There are various factor that affect the viscosity : <span style="color: #ff0600; font-family: 'Comic Sans MS',cursive;">> Shear rate <span style="color: #ff0600; font-family: 'Comic Sans MS',cursive;">> Time of shearing <span style="color: #ff0600; font-family: 'Comic Sans MS',cursive;">> Temperature <span style="color: #ff0600; font-family: 'Comic Sans MS',cursive;">> Pressure

**<span style="color: #ff00ff; font-family: 'Comic Sans MS',cursive;">NEWTONIAN FLUIDS **
<span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">~ Shear viscosity does not vary with shear rate. <span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">~ Viscosity is constant with time of shearing. <span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">~ Shear rate in fluids falls immediately to zero when shearing is stopped. <span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">~ Examples : water, milk and honey.

Water

Milk

Honey

~ Any liquid that show deviation from Newtonian behavior. ~ Non-Newtonian materials can be either time independent or time dependent. > Time-independent liquids = Viscosity of fluids depend on shear rate but independent of time of sharing ( pseudoplastic, dilatant, Bingham and Casson plastic ). > Time-dependent liquids = Viscosity of fluid is dependent on shear rate and the time during which shear rate is applied ( thixotropic and rheopectic ). <span style="color: #ff5400; font-family: 'Comic Sans MS',cursive;">~ Examples : cornstarch
 * <span style="color: #ff0075; font-family: 'Comic Sans MS',cursive;">NON-NEWTONIAN FLUIDS **

<span style="color: #0000ff; font-family: 'Comic Sans MS',cursive;">Cornstarch

<span style="color: #7000ff; font-family: 'Comic Sans MS',cursive;">Newtonian and Non-newtonian curve

<span style="color: #ff00ff; font-family: 'Comic Sans MS',cursive;">**Y I E L D S T R E S S**
<span style="color: #ff005d; font-family: 'Comic Sans MS',cursive;">~ Yield stress is the minimum shear stress that need to be applied to initiate a sample to flow. <span style="color: #ff005d; font-family: 'Comic Sans MS',cursive;">~ Minimum shear stress is required to overcome the cohesive force that holds the structure of the material.

<span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">Squeezing cream in decorating the cakes

<span style="color: #ff005d; font-family: 'Comic Sans MS',cursive;">~ The yield stress is the applied stress we must exceed in order to make a structured fluid flow. <span style="color: #ff005d; font-family: 'Comic Sans MS',cursive;">~ <span style="color: #ff0075; font-family: 'Comic Sans MS',cursive;">Yield stress can be further classified into Static and Dynamic Yield Stress.



==<span style="color: #808000; font-family: 'Comic Sans MS',cursive;">M <span style="color: #ffbf00; font-family: 'Comic Sans MS',cursive;">E <span style="color: #00ffff; font-family: 'Comic Sans MS',cursive;">A <span style="color: #ff0000; font-family: 'Comic Sans MS',cursive;">S <span style="color: #e76e71; font-family: 'Comic Sans MS',cursive;">U <span style="color: #ff00ff; font-family: 'Comic Sans MS',cursive;">R <span style="color: #00ff00; font-family: 'Comic Sans MS',cursive;">I <span style="color: #ff0075; font-family: 'Comic Sans MS',cursive;">N <span style="color: #e8f410; font-family: 'Comic Sans MS',cursive;">G <span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">V <span style="color: #ff5400; font-family: 'Comic Sans MS',cursive;">I <span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">S <span style="color: #55ff00; font-family: 'Comic Sans MS',cursive;">C <span style="color: #800053; font-family: 'Comic Sans MS',cursive;">O <span style="color: #ffff00; font-family: 'Comic Sans MS',cursive;">S <span style="color: #da5d8b; font-family: 'Comic Sans MS',cursive;">I <span style="color: #4185e6; font-family: 'Comic Sans MS',cursive;">T <span style="color: #ff0075; font-family: 'Comic Sans MS',cursive;">Y ==


 * <span style="color: #ff0075; font-family: 'Comic Sans MS',cursive;">RHEOLOGY TESTINGS **

<span style="color: #15ff00; font-family: 'Comic Sans MS',cursive;">> Measurement made without changes in product shape, or control of deforming forces.

 * <span style="color: #00ff00; font-family: 'Comic Sans MS',cursive;">> Immitative of some aspect of mastication or processing. **

<span style="color: #00ff00; font-family: 'Comic Sans MS',cursive;">> Examples : Bostwick Consistometer, Falling Ball Viscometer and Glass Capillary Viscometer.
<span style="color: #ff005d; font-family: 'Comic Sans MS',cursive;">Bostwick Consistometer

<span style="color: #d75685; font-family: 'Comic Sans MS',cursive;">Falling Ball Viscometer

<span style="color: #ff0030; font-family: 'Comic Sans MS',cursive;">Glass Capillary Viscometer

<span style="color: #d75685; font-family: 'Comic Sans MS',cursive;">> Examples : Rotational viscometer.
<span style="color: #bb20bb; font-family: 'Comic Sans MS',cursive;">Rotational Viscometer