Practical No. 11: Determination of Effect of Temperature on Viscosity using Redwood Viscometer-I
XIII. Interpretation of Results
Viscosity of lubricating oil decreased with increasing temperature. Flow time was highest at 40°C and lowest at 80°C, confirming an inverse relationship between viscosity and temperature.
XIV. Conclusions and Recommendations
- Conclusion: Viscosity decreases with an increase in temperature, which increases the flow rate of the oil.
- Recommendation: Filter the oil thoroughly before testing, level the viscometer properly, and ensure accurate temperature control for reliable measurements.
XV. Practical Related Questions & Answers
Q1. Describe the process for cleaning of Redwood viscometer.
- Answer: Clean the viscometer by following these steps:
- (i) Removing all residual oil from the cup.
- (ii) Using a suitable solvent (like petroleum ether or benzene) to dissolve any remaining oil.
- (iii) Rinsing thoroughly with the solvent and then with distilled water.
- (iv) Passing a stream of air to remove all traces of the solvent.
- (v) Ensuring the jet is completely clean and unobstructed.
- (vi) Drying the viscometer completely before its next use.
Q2. Explain the importance of water bath in the Redwood viscometer.
- Answer: The water bath provides a constant and uniform temperature for heating the oil sample. It ensures that the oil reaches the desired temperature uniformly without any localized overheating. Maintaining a constant temperature during the experiment is essential because the viscosity of oil is highly dependent on temperature.
Q3. Write precautions to be taken while performing the practical.
- Answer: Precautions include:
- (i) Filter the oil to remove any solid particles or impurities.
- (ii) Level the viscometer perfectly using the leveling screws.
- (iii) Place the receiving flask correctly to avoid foaming.
- (iv) Maintain an accurate temperature by constant stirring of the water bath.
- (v) Start and stop the stopwatch precisely when the oil reaches the markers.
- (vi) Ensure the oil stream strikes the neck of the receiving flask.
- (vii) Completely drain the oil after each reading.
Q4. Explain proper way to place the receiving flask.
- Answer: The receiving flask should be placed immediately below and in line with the discharging jet. The oil stream from the jet should strike the neck of the receiving flask to prevent foaming. The flask must be kept steady and not moved during the experiment, and the 50 ml mark should be clearly visible at eye level for accurate timing.
Q5. Name various types of viscometer.
- Answer: Types of viscometers include:
- (i) Redwood Viscometer (No. I and No. II)
- (ii) Saybolt Viscometer
- (iii) Engler Viscometer
- (iv) Ostwald Viscometer
- (v) Brookfield Viscometer (rotational)
- (vi) Falling Ball Viscometer
- (vii) Capillary Viscometer
- (viii) Rotational Viscometers
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