Prelab

1. Read the lab procedure carefully.

2. Print this data page and bring it to the lab.

Purpose

To measure basic properties, such as the density, specific volume, specific gravity, and specific weight of a fluid. In addition, the viscosity of the sample fluid will be measured using a capillary tube and rotating viscometers.

Theory

The density of a liquid is given by ρ (rho) and is equal to mass/volume.

The specific volume υ (upsilon) is equal to  1/ρ.

The specific gravity sg is equal to ρ/ρw where ρw is the density of water.

The specific weight γ is equal to ρ.g .

The capillary tube viscometer operates on the principle that viscosity is a controlling factor in fluid flow rate. More viscous fluids experience a greater resistance to flow and will travel more slowly than a fluid of lower viscosity. Capillary tube manometers have a precisely measured capillary diameter, and the application of Newton's law of viscosity to the steady-state flow of a fluid in a circular tube due to gravity alone results in the following equation: 

v = πgΔhR4 / 8QL = Ct

where:

ν is the kinematic viscosity, equal to μ/ρ (m2/s)

μ is the dynamic viscosity (Pa⸱s or kg/(m⸱s))

ρ is the density (kg/m3)

Δh is the hydrostatic head (vertical distance between both ends of the capillary tube) (m)

g is the acceleration of gravity (m/s2)

R is the radius of capillary tube (m)

L is the length of capillary tube (m)

Q is the volumetric flow rate, V/t (m3/s)

V is the volume between etched marks (m3)

C is the viscometer constant (m2/s2)

t is the efflux time: the time required for the volume V of liquid between the two etched marks to flow through the capillary tube (s)

You will be using the Constant for your viscometer "C" and the time for efflux "t" to calculate viscosity. The equation presented is only shown for derivation purposes. Since many of the above values are constant for the same tube, it is convenient and simple to reduce them to a single variable "C" that uniquely describes that viscometer. Laboratory calibration measurements made by the manufacturer confirm or improve these assumptions to provide you with a very accurate value to use in viscosity determination measurements.

It is also possible to use a rotating viscometer that measures the resistance to circular motion in the form of a torque that is exerted on a submerged surface. A finely calibrated motor rotates a liked arm with a known force and speed and displays a value representing the resistance to motors rotation. The resistance to rotation can be measured and varies depending on the nature and viscosity of the fluid in which the rotating surface is submerged. Different shapes, materials, geometries, and sizes of rotating surface are available for different use cases. Manufacturers will provide use cases and recommendation for appropriate setups for a variety of circumstances. The typical manual for a kit of spindles will include a lookup table and equations for interpreting the results. The specific spindle chosen, and the speed of the test are the significant factors for deriving the viscosity from the test result. One such test will be completed in the lab, with the corresponding data and equation presented in the results section for your convenience. 

Problem

A.P. Analytica, a local metrology company has recently been awarded a contract to characterize several fluids. The collected data will be used in the MSDS for these products and therefore accurate, repeatable, and well evidenced data is required. You have been tasked with using several pieces of equipment specially designed to give precise results. These tools are exactly the same as those you will encounter in even large chemical industries. 

Use the results from your study to determine all of the relevant fluid properties and compare them to a reputable online or published source for that fluid or a similar one as confirmation of your determinations.

Procedure

Part 1: Basic Properties

1. Weigh your empty graduated cylinder and record the mass.

2. Fill your 1000 mL graduated cylinder about halfway with your sample.

3. Record the actual volume volume poured.

4. Measure the specific gravity of your fluid with the hydrometer.

   • Gently lower the hydrometer into the sample until it floats. If it sinks and rests on the bottom, you can add more fluid at this point.

   • Tap your hydrometer away from the edges of the cylinder if it sticks to the surface.

   • Read the value where the fluid meniscus crosses the hydrometer scale.

   • Remove your hydrometer and have a group member rinse it carefully.

   • Transfer 50 mL of your sample to the small beaker.

   • Return the remainder of your sample to the container.

5. Use the above data to calculate: 

• 1. Density

  2. Specific Volume

  3. Specific Gravity

  4. Specific Weight

6. Thoroughly clean, with soap and water, your cylinder and dry it well at your station.

Part 2: Capillary Viscometer

1. Read this section before beginning as several time dependent actions must be taken. Be sure that you understand the procedure.

2. Read the viscometer calibration sheets, and record the viscometer constants at the given temperatures.

3. Fill the  first viscometer through tube A (the wider open tube) with the appropriate liquid using your small beaker until the large bulb is half full.

4. Place a suction bulb over the end of tube B and carefully suction the liquid up past the first etched mark. 

   • While squeezing label 'A' squeeze the bulb and then release 'A'. The bulb should remain compressed.

   • To generate suction squeeze label 'S' until liquid is well above both markings.

5. Check to make sure no bubbles exist in the system.

6. Remove the suction bulb and allow free flow of the liquid by gravity.  

7. Use a timer to determine the time it takes the liquid surface to go from the first to the second etched mark.

   •  This is the efflux time 't'.

8. Make sure that you have noted the size, constant, and the serial number of the viscometer used.

9. You do not have to empty or rinse the viscometers.

10. Clean any spills from your station.

Part 3: Rotational Viscometer

1. Record the sample type and reported viscosity of the lab demonstration for a rotational viscometer.

   • Note that this value is not the viscosity, but is used in the calculation according to the spindle specific guidelines.

2. Also record the spindle type provided, and spindle speed from the knob on the left hand side of the unit closest to the silver indicator.

Results

1. From the masses and volumes recorded, determine the density of each fluid.

   • Compare to the result from the hydrometer.

2. Using the data from the capillary tube viscometer: Calculate and record the kinematic viscosity of the fluid. 

3. From the chart below, and the recorded properties for the rotating viscometer find the scale factor:

   • Find the spindle number in chart header ( 1 - 7 ) used in the test.

   • Below that find the row with the given speed value (0.5 - 100) for the RPM set on the left hand dial.

   • Read the factor next to that speed and make a note of it.

4. Calculate the Dynamic and Kinematic viscosity of the given sample.

   • Dynamic Viscosity in cP (N s/m2) = Digital Reading • Factor.

   • Kinematic Viscosity in cSt (mm2/s)  = Dynamic Viscosity / Density.

5. Find a scientific source for expected properties for your samples and compare your measurements (density & viscosity).

   • Be sure that the viscosities are reported at a similar temperature! Oil viscosities vary significantly with temperature.

   • Include a direct link or book and page number for your source value.

6. Present lab data and those calculated in a single chart with parameter, value, and units for each result.

Questions

1.  We conduct the test at room temperature. How might we incorporate some scientific control for the test temperature

   • Why is careful temperature control important in viscometry?

2. List two pros and cons for using the rotating viscometer over the capillary tube style.