Investigating the Properties of Oils - Coursework Example

?Investigating the Properties of Oils Introduction: Viscosity is an inherent physical property of a fluid which confers resistance to flow (Viswanath). The viscosity of a fluid depends on several factors, including and not limited to, temperature and pressure. There are several methods to determine the viscosity of a substance, the most common one being using a viscometer (Viswanath). A viscometer is a device which is used to estimate the viscosity and other flow properties of a fluid. A range of different types of viscometers are available which differ from each other based on their measurement principle and a commonly used type is a cup viscometer, which estimates the viscosity making use of the efflux time of a given substance through the cup orifice (A&D Weighing). The cup viscometer measures the kinematic velocity of a fluid and the unit of viscosity measured by such a viscometer is centistokes (Viswanath). Purpose: To determine the viscosity of a given sample of lubricating oil of unknown viscosity, with the help of a Cup Viscometer and different commercially available oils of known viscosity. It can be hypothesized that as the viscosity increases, the flow decreases and thus the efflux time increases, i.e. substances with a higher viscosity would take more time to efflux from the cup viscometer to the beaker. Methodology: In this experiment a cup viscometer will be used to determine the viscosity of a sample of lubricating oil of unknown viscosity. The cup viscometer will first be constructed by using disposable Styrofoam cups and subsequently be used to measure the viscosity. The following equipment will be required to conduct the experiment: Three different types of commonly available oils with known viscosities, viz. Olive Oil Soyabean Oil Kerosene Oil A sample of the oil whose viscosity is to be determined, viz. lubricating oil Four disposable Styrofoam cups Burette Clamp or stand Four 100 ml graduated Cylinders Four beakers A skewer of uniform diameter to punch holes Scotch Tape An accurate Stopwatch The first part of the experiment is to construct a cup viscometer using disposable Styrofoam cups and calibrating it using oils of known viscosities. Four disposable Styrofoam cups are taken and holes are punched in their bottoms using a skewer of uniform diameter. One should be extremely careful while punching holes in order to ensure that all four holes are of the same diameter. Once the holes have been punched, scotch tape has to be applied at the bottom of all the cups in order to prevent the oil from leaking once it has been poured in to the cups. The cups are then marked as A, B or C, one for each different oil of known viscosity. The next step is the calibration of the cup viscometers prepared. This is achieved via pouring measured quantities (i.e. 60 ml) of the three different oils of known viscosities in to three different cup viscometers. Olive Oil is placed in Cup A, Soyabean Oil in Cup B and Kerosene Oil in Cup C. This can be achieved by using a graduated measuring cylinder to measure out 60 ml of each oil into the respective cups. While filling the graduated cylinders, it should be ensured that the cylinder is placed in a flat horizontal surface, in order to avoid any errors in measurements. Moreover, it is important to remember that most solutions would form a concave meniscus. Thus, while reading a meniscus, the bottom of the meniscus should be read and the meniscus should be kept at eye level in order to avoid parallax errors. Moreover, the meniscus should be read against a uniform background, which can be achieved by placing a white sheet of paper behind the level of the liquid. Once all the cups have been filled, one of the cups (i.e. Cup A) is suspended in a burette clamp and a beaker is placed underneath. The scotch tape is then carefully removed and the stopwatch started in order to time the experiment. The time required for 60 ml of Olive Oil to flow from the cup in to the beaker is recorded. The timing should start immediately after the removal of the scotch tape and should end after all of the oil has flowed from the cup into the beaker. The same exercise is repeated thrice and an average is obtained in order to ensure the reliability of the results. The same procedure is then repeated for Cups B and C and the findings documented in a tabular form. The data is then plotted in the form of a graph. It is known that as the viscosity increases, the efflux time of the fluid through the cup viscometer increases, i.e. the two variables are directly proportional to each other, and thus we expect a linear relationship between the two, i.e. the graph obtained would be in the form of a straight line. The final step in this experiment is to document the time taken for 60 ml of the oil of unknown viscosity, i.e. lubricating oil to efflux from the cup viscometer to the beaker. This is done by preparing a cup viscometer for this oil sample according to the method described above and using the aforementioned procedure to document efflux time. The efflux time is then plotted on the graph and the reading for viscosity is obtained by extrapolation, i.e. plotting the efflux time on the y-axis and obtaining the reading for viscosity from the x-axis. Precautions: In order to ensure the safety of the experimenters and the reliability of the results, the following precautions should be undertaken: Each type of oil should be poured into its respective cup viscometer, measuring cylinder and beaker and using the viscometers interchangeably for different oils should be avoided since mixing of any two types of oil would affect the viscosity and lead to erroneous results. Since oil is an inflammable substance, care should be taken to keep all oil containers away from any source of flames. Timing should start as soon as the tape is removed and ended when the last drop of oil from the cup has efflux in to the beaker. Moreover, while performing the experiment, care should be taken not to spill any oil, in order to avoid any errors in volume measurements. Since temperature is an important variable which influences the viscosity, measures should be taken that all the oil samples used are at room temperature before using them in the experiment. Moreover, measures should also be undertaken to minimize any variations in environmental temperature. Results and Analysis: The results obtained from performing the above mentioned experiment are depicted in the table below. It is important to remember that in this experiment, the independent variable is the Viscosity (centistokes) and the dependant variable is the efflux time (seconds). Type of Oil Viscosity (centistokes) Efflux Time 1 (seconds) Efflux Time 2(seconds) Efflux Time 3(seconds) Average Efflux Time (seconds) Olive Oil 43.2 205 207 204 205.3 Soyabean Oil 35.4 165 167 164 165.3 Kerosene Oil 2.71 33 34 36 34.33 Lubricating Oil ? 100 107 104 103.7 A graph of viscosity against time is then plotted using the above readings as depicted below. Figure 1: Relationship between viscosity (centistokes) and efflux time (seconds) As predicted, a linear relationship between the two variables in consideration was obtained, i.e. as the viscosity increases, the average efflux time increases. Using the above depicted graph, the viscosity of Lubricating oil was found to be approximately 20 centistokes. Conclusion: The use of a cup viscometer is an effective technique to measure the kinematic viscosity of a fluid. The efflux time of a fluid through a cup viscometer is directly proportional to its viscosity and using this relationship, the viscosity. lubricating oil was found to be 20 centistokes. Evaluation: This experiment revealed that the use of a cup viscometer is an effective technique to determine the viscosity of a fluid. Simple cup viscometers can be created within the lab using the technique described above. However, this technique has certain limitations. Firstly, a very important confounding factor that needs to be controlled further in this experiment is temperature. Although all necessary steps were undertaken to ensure that there was minimal variation in the environmental temperature and the temperature of the oils, this process needs to be further streamlined using either a hot bath or any other similar technique, to immerse the cups inorder to ensure that the temperature of all oils was constant. Secondly, another variable that could confound the results is human reaction time. This can be overcome by using two independent observers to record time using stopwatches and taking an average of the times obtained. The reliability of the results in this experiment was ensured by repeating the experimental procedure thrice for each oil and taking an average value for the efflux time. Some problems which were encountered during the experiment included confusion regarding when to end the timing using the stopwatch and whether to wait for the last few drops of oil to drain from the cup to the beaker or not. References A&D Weighing. Measuring Viscosity. 2010. 26 March 2011 . Viswanath, Dabir S. Viscosity of liquids: theory, estimation, experiment, and data By Dabir S. Viswanath. Netherlands: Springer, 2007. Read More