- Level: AS and A Level
- Subject: Science
- Word count: 3609
How temperature affects the viscosity of honey
Extracts from this document...
Introduction
Abigail Durling 2068 40643
How Temperature of Honey Affects Viscosity
Introduction
Viscosity is a factor controlling resistance to flow and the speed that liquids flow is down to this. The lower the viscosity, the runnier the fluid is. Viscosity can be easily measured using the line spread test, how far and fast a fixed quantity of liquid spreads across a flat surface. Another way is by using George Gabriel Stokes’ method of a falling ball, this method includes timing a ball falling at a constant rate (its terminal velocity) through a substance, the longer it takes for the ball to fall a measured distance the more viscous the substance.
I am investigating how temperature affects the viscosity of honey, in order to do this I must use the falling ball viscometer method first conducting a preliminary experiment to find a suitable range of temperatures of honey to time a ball falling through.
Archimedes stated:
‘When a body is partially or totally immerse in a fluid, the upthrust is equal to the weight of the fluid it displaces.’
When terminal velocity has been reached by the ball bearing the forces acting upon it will be balanced and the ball bearing will fall at a constants velocity. The magnitudes of these forces are related:
Or:
This equation can be rearranged by cancelling common factors of π and r, multiplying by 3 and ten dividing by 2 to give:
η can then be made the subject:
[Salters Horners Advanced Physics Activity Sheet 5]
As you can see form the equations, the radius of the steel ball bearing is needed in order for the viscosity to be calculated, this can be done by finding the diameter of the ball bearing and then dividing it by two. I used a micrometer screw gauge to measure the diameter of the ball bearing accurately.
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Middle
25.2
24.5
25.1
25
16.1
16.7
16.5
16.4
30
12.7
11.8
11.9
12.1
35
9.0
9.3
9.8
9.4
40
4.3
5.0
5.1
4.8
Before the coefficient of friction can be calculated however, the density of both the honey and the steel ball bearing must be found, this had to be done using:
Honey
Mass of empty measuring cylinder = 113.80g
Mass or measuring cylinder containing 100cm3 of honey = 256.40g
Mass of honey = 256.40 – 113.80 = 142.6g
Steel Ball Bearing
Mass of ball bearing = 4.14g
Volume of ball bearing = = = 0.523599cm3
The co-efficient of viscosity, η, which determines the size of the viscous force can now be determined by using the equation:
where ρ is density, g is gravity and v is velocity.
Temperature (˚C) | Time taken (s) | Average Time (s) | Speed (cms-1) | Coefficient of viscosity, η, (kgcm-1s-1) | ||
10 | 104.6 | 103.9 | 104.1 | 104.2 | 0.09596929 | 0.036766293 |
15 | 41.4 | 45.4 | 43.2 | 43.3 | 0.230769231 | 0.015289885 |
20 | 25.5 | 25.2 | 24.5 | 25.1 | 0.39893617 | 0.008844610 |
25 | 16.1 | 16.7 | 16.5 | 16.4 | 0.60851927 | 0.005798395 |
30 | 12.7 | 11.8 | 11.9 | 12.1 | 0.824175824 | 0.004281168 |
35 | 9.0 | 9.3 | 9.8 | 9.4 | 1.067615658 | 0.003304967 |
40 | 4.3 | 5.0 | 5.1 | 4.8 | 2.083333333 | 0.001693649 |
Analysis
From my graph I can see that there is a strong link between the temperature and viscosity of ‘Romero’s Honey’. My graph clearly shows that the higher the temperature of the honey the lower its viscosity. This is because the heat energy that has been transferred to the honey from the water baths has been converted into kinetic energy causing the honey particles to move faster meaning the honey can flow quicker and so has a lower viscosity. The molecules of the honey are tightly bound together by intermolecular forces. As temperature increases, the kinetic energy of the honey molecules increases meaning they can more freely move lessening the intermolecular forces and hence the viscosity decreases.
I can immediately see that my graph looks very similar to the graph on the left implying that my experiment went well and accurate results were produced. My graph shows no anomalies and my line is very smooth also showing that the experiment has been carried out to a high degree of accuracy.
Errors
Conclusion
Elcometer’s Daniel Flow Gauge – Material is poured into the channel and then the devise turned vertically, the product flowing onto the graduated plate.
Brookfield DV-E Low Cost Digital Viscometer.
This viscometer provides a quick and easy determination of apparent viscosity across a broad range of viscosities by using the different sized spindles. For Quality Assurance purposes, the viscosity determination is usually made using a known spindle size at a known spindle speed at a constant temperature e.g. viscosity of sweetened skimmed condensed milk . The viscosity reading can either be cP or mPa-s. For more serious viscosity evaluations readings will be taken going up and then down the speed ranges for the relevant spindle and the results modelled and expressed manually.
For those areas where material flow parameters are critical e.g chocolate- yield and viscosity, a more comprehensive analytical tool is required. In the chocolate industry the ultimate end use/process type does require a more detailed knowledge of the products flow characteristics. Chocolate used in moulding e.g. Easter Eggs require a different set of flow characteristics to that used for enrobing e.g. Mars Bar. Whereas simple rheometers produce a quick reading of apparent viscosity, the larger research rheometers are able to split out yield and viscosity. Many of the larger chocolate processors use one the Haake Series 1 Rheometers such as the RotoVisco1 or RheoStress1.
Haake RheoStress 1 Rheometer
Rheometers such as the Haake are an invaluable tool in R & D. When developing new chocolate formulations, process optimization is vital. With chocolate being an expensive raw material, chocolate that is too ‘runny’ will result in moulded products with thin shells and high reject levels. Enrobing chocolate that is too ‘thick’ will result in too much chocolate on the bars/biscuits and therefore excessive give away. For enrobing products viscosity is vital, whilst for moulding or deposited products having a high yield point is beneficial.
This student written piece of work is one of many that can be found in our AS and A Level Modern Physics section.
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