The honey will be kept out of the sun whilst the experiment is being carried to keep it from warming up affecting the speed at which the ball bearing will travel through the honey.
Range
From looking at my preliminary results I can see that the range has reached its limits when the honey is 11˚C and 40˚C as after these temperatures it will be very difficult to take accurate readings. I have therefore decided to use temperatures of 10˚C to 40˚C going up in 5˚C intervals.
Engineering in Design
During the preliminary experiment it was found that we had problems in measuring the distance that the ball bearing had fallen and also struggled retrieving the ball bearing from the honey. In order to solve this problem I decided to attach a drinking straw to the ball bearing. This was done using araldite, a strong quick drying water resistant adhesive. This meant that the ball bearing could be retrieved easily from the honey after each reading was taken. I marked the straw twice, one marking 5cm from the ball bearing and the other 15cm from the ball bearing, I would start timing the ball bearing after the 1st line is submerged in the honey, leaving 5cm for the ball bearing to reach terminal velocity, the stopwatch would be stopped when the 2nd line gets submerged. This method ensures that for each reading the ball bearing has the same distance to reach terminal velocity and is being timed over the same distance consistently.
5cm 10cm
Attaching a straw to the ball bearing created a new problem; it was found that the straw would lean against the edge of the measuring cylinder in which the honey is. The edge of the measuring cylinder tended to be very sticky due to having small amounts of honey around it, this caused extra drag slowing the ball bearing down and giving inaccurate readings. This problem could be easily solved however using a small piece of card just big enough to cover and rest on the top of the measuring cylinder. This piece of card would have a small hole in the centre, achieved using a hole punch, that would hold the straw upright so that accurate readings can be taken.
Apparatus
- ‘Romero’s Honey’ - 10˚C to 40˚C
- 100cm³ measuring cylinder
- 10mm diameter ball bearing with attached straw
- stopwatch
- Water bath and fridge to obtain different temperature honey
- Cardboard with hole in
- Permanent marker
- Thermometer
Method
- Using a permanent marker mark both 5cm and 15cm away from the top of the ball bearing onto the straw. (I am making the assumption the 5cm will give enough time for the ball to get up to terminal velocity)
- Fill the measuring cylinder with 10˚C ‘Romero’s Honey’ (from the fridge) testing the temperature with a thermometer about 20cm high.
- Put the end of the straw through the hole in the card and hold above ‘Romero’s Honey’ in the measuring cylinder.
- Let go of the straw and ball bearing taking care to drop the ball bearing down the middle of the cylinder, start the stopwatch as soon as the first marked line becomes submerged.
- Stop the stopwatch as soon as the second line is submerged in the ‘Romero’s Honey’.
- Record these results in a table
- Repeat his two more times cleaning the ball bearing and straw with hot and room temperature water and drying it in between each drop, record these results in the table.
- Repeat the above steps with 15, 20, 25, 30, 35 and 40˚C ‘Romero’s Honey’ using the water baths and fridge to get the honey to the desired temperature.
Safety
Be sure to be very careful when dealing with hot water either when heating the honey or when cleaning apparatus. Make sure you don’t get the hot water or honey on your skin in case it burns you. If any spillages occur clear them up straight away so no one slips and injures themselves.
Results
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.
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
Due to human reaction times there will be errors and uncertainties in my results. I have therefore decided to put tolerances of ±0.5 seconds, this time period should account for my errors when timing the ball bearing falling through the honey. On the graph I have marked error bars to show the effect this human error would have on the overall viscosity.
Evaluation
There are a number of things that were wrong with my experiment even though I achieved a good set of results. Firstly it was very difficult to take accurate readings with the equipment provided. In an ideal world I would have used light gates to acquire a more accurate reading of the time taken for that ball bearing to travel the 10cm as there will have been a degree of error in my readings due to reaction time between the line on the straw being submerged and my stopping of the stopwatch. Light gates work using a laser, one side of the light gate transmits the laser and the other side is a receiver. This could be easily incorporated into my experiment, two light gates would be set up connected to a computer, one 5cm from the surface of the honey and the other 15cm from the surface of the honey. The transmitters would be on one side of the measuring cylinder and the receivers on the other, the honey is translucent and so the laser would pass through and could still be detected by the receiver. When the Ball bearing is released it still has the 5cm time in which to reach terminal velocity, when it reaches the first light gate it will break the laser beam, the receiver ill no longer detect anything and send a message to the computer to start timing. When the ball bearing reaches the 2nd light gate 10cm later it will again break the beam, the receiver will not detect anything and will send a message to the computer so the timer will stop. All this would be far more accurate as the thinking time for a computer is far less than that of a human. It would also mean that the exact moment that the ball bearing crossed the lasers would be recorded not 1 or 2 millimetres earlier or later like my results will have been.
Another problem will have been inconsistency in temperature of the honey throughout the measuring cylinder, due to the glass of the measuring cylinder and the outside temperature being cooler that the honey, the honey on the outside of the measuring cylinder will have cooled far quicker than that in the centre causing viscous drag in the honey. The speed of the honey at the wall will be zero and will be at its maximum in the centre, in the centre the honey will be much less viscose that that on the outside and so the cooler honey in the outer regions of the measuring cylinder will have less energy and not allow the ball bearing to pass through so easily slowing it down. This could be reduced significantly by keeping the measuring cylinder in a water bath of the desired temperature throughout the experiment so all the honey in the measuring cylinder is flowing at the same speed. Vortices may also form as the ball bearing moves through the honey. As the vortices flow past the ball bearing energy transfers occur and heat is transferred from the honey to the ball bearing and the honey temperature drops. This in turn will increase the viscosity slowing the ball bearing down.
In my experiment I did not take into account the effect of the bubbles in the honey if they have any effect at all. Even though in liquids, such as honey, the higher the temperature the lower the viscosity meaning the ball bearing falls faster in the warmer honey, gases are the opposite. I have found out that in gases, the higher the temperature the more viscous they are and so any object moving through them will move slower in the warmer temperatures. This should not slow the ball bearing down however as gases are far less dense that the honey no matter what temperature and so when the ball bearing passed through the bubbles it would speed up slightly. This would give me inaccurate results for the viscosity of honey as the ball bearing will not have only passed through one medium but both the honey and the bubbles of air. The amount of bubbles in the honey can be reduced but is a lengthy process. The honey must be left at least overnight to allow the bubbles to rise out. In the production of honey this process is called ‘ripening’ and works best when the honey is warm as the hotter the honey the less viscous it is and so the bubbles will be able to escape more easily and the ‘ripening’ will happen much more quickly than with cooler honey.
When the straw was attached to the ball bearing the shape of the ball bearing was altered significantly, this is both due to the araldite and the straw itself. The glue made small changes to the shape of the ball bearing meaning it was no longer spherical, this could also cause vortices (Eddys) to form lowering the temperature and slowing the ball bearing down. The straw itself will have also caused extra drag and will not have been perfectly cylindrical due to the soft flexible plastic it is made from again slowing the ball bearing down. This could be avoided by getting rid of the straw and the araldite. With the use of the light gates the straw would no longer be needed to aid the timing of the falling ball bearing. If I were to use a strong magnet I would be able to ease the magnet up the inside of the measuring cylinder in order to remove it from the honey, this would be more time consuming and fiddly however would mean I could obtain a more accurate set of results.I did not take into account the density of the straw or araldite when calculating my coefficient of viscosity and so this would again make my results more accurate if the straw and araldite were removed from the experiment.
The Use of Viscometers in the Food Industry [Chris Durling, General Manager, Research & Development, Aimia Foods]
The determination of material flow characteristics is vital in many areas of the food industry. Viscometers are common place, both in Quality Assurance/Control laboratories as well as R & D laboratories.
Viscosity of food materials is crucial both for consumer acceptance e.g Tomato Ketchup and for process efficiency/consistency. Many food laboratories make use of simple relatively low cost viscometers or flow meters to provide a quick determination of viscosity or flow. Examples of these would be Elcometer’s Daniel Flow Gauge or Brookfield’s DV-E Digital Viscometer.
For thick liquids and paste e.g tomato ketchup, honey etc; a very simple Quality Control test can be performed. A known volume of material is poured into a reservoir and then allowed to flow for a known time over a graduated plate or trough. The reading is then expressed as the distance flowed. This relates to a products viscosity.
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.
