91Ó°ÊÓ

The level of toluene (a flammable hydrocarbon) in a storage tank may fluctuate between 10 and \(400 \mathrm{cm}\) from the top of the tank. Since it is impossible to see inside the tank, an open-end manometer with water or mercury as the manometer fluid is to be used to determine the toluene level. One leg of the manometer is attached to the tank \(500 \mathrm{cm}\) from the top. A nitrogen blanket at atmospheric pressure is maintained over the tank contents. (a) When the toluene level in the tank is 150 cm below the top \((h=150 \mathrm{cm})\), the manometer fluid level in the open arm is at the height of the point where the manometer connects to the tank. What manometer reading, \(R\) (cm), would be observed if the manometer fluid is (i) mercury, (ii) water? Which manometer fluid would you use, and why? (b) Briefly describe how the system would work if the manometer were simply filled with toluene. Give several advantages of using the fluid you chose in Part (a) over using toluene. (c) What is the purpose of the nitrogen blanket?

Step by step solution

01

Establish the Relationship between pressure and height

The pressure at a point in a fluid column is given by the formula \( P = \rho gh \). Here, \( P \) is pressure, \( \rho \) is the fluid density, \( g \) is the acceleration due to gravity, and \( h \) is the height.

02

Determine Manometer Reading when Fluid is Mercury

Mercury is denser than toluene. Therefore, when the toluene level in the tank is 150 cm below the top, the mercury level in the open arm will be at the same height as the point of attachment. Hence, manometer reading, \( R = 0 \) cm.

03

Determine Manometer Reading when Fluid is Water

Water is less dense than toluene. Therefore, when the toluene level in the tank is 150 cm below the top, the water level in the open arm will be lower than the point of attachment. Hence, the manometer reading, \( R \) will be negative.

04

Explain the Choice of Manometer Fluid

Mercury would be a better choice of manometer fluid because its higher density allows for easy interpretation of the manometer reading. In contrast, water would produce more complicated readings due to its lower density.

05

Explain the Effect of Using Toluene in the Manometer

If toluene were used in the manometer, there would be no differential pressure to create a differential height and, consequently, no manometer reading. Using mercury or water as the manometer fluid creates a pressure difference across the toluene-manometer fluid interface, which in turn, produces a height difference that can be easily read off the scale on the manometer.

06

Describe the Purpose of Nitrogen Blanket

The purpose of the nitrogen blanket is to prevent the toluene from coming into contact with atmospheric oxygen. This reduces the risk of fire or explosion, and slows down the evaporation of toluene, thereby minimizing loss.

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Chemical Engineering Principles

Chemical engineering integrates principles from chemistry, physics, and mathematics to process materials into useful forms. In relation to our exercise,
which involves monitoring toluene level in a storage tank using a manometer, several chemical engineering principles come into play.

Application of Fluid Statics

The principle of fluid statics is directly applied in manometer reading to determine the tank level. By understanding the different densities of the fluids - toluene, mercury, and water - engineers can deduce the toluene level using pressure differences.

Choice of Materials

Chemical compatibility and safety considerations drive the choice of manometer fluid. Mercury's high density compared to water greatly simplifies the reading process, a critical factor in chemical engineering where accuracy is paramount. This principle is reflected in Step 4 of the solution.

Fluid Mechanics

Fluid mechanics, a subset of physics, involves the study of fluids (liquids, gases, and plasmas) and the forces on them.

Pressure Measurement

For pressure measurement using manometers in our example, fluid mechanics principles are crucial. The static liquid in the manometer balances the pressure of the toluene in the tank. The relationship between pressure and liquid height is captured by the formula \( P = \rho gh \) from Step 1 of the solution, where \( P \) is pressure, \( \rho \) is the density of the fluid, \( g \) is acceleration due to gravity, and \( h \) is the height of the fluid column.

Pressure Measurement

Pressure measurement in chemical engineering is crucial for process control, safety, and efficiency.

Interpreting Manometer Readings

The exercise involves using a manometer for indirect measurement of the toluene level, a practice reliant on accurate pressure readings. A manometer translates the pressure difference into a measurable height difference. As outlined in Steps 2 and 3, the choice between mercury (higher density) and water (lower density) affects the ease of reading the pressure, with mercury being preferred for its simplicity.

Safety in Chemical Processes

Maintaining safety in chemical processes is an overarching concern in chemical engineering. The use of a manometer and a nitrogen blanket in monitoring toluene levels addresses this concern.

Fire and Explosion Prevention

As detailed in Step 6, the nitrogen blanket serves as an inert barrier, suppressing the risk of fires or explosions by preventing the toluene from interacting with atmospheric oxygen. Similarly, the selection of manometer fluid also factors in safety, as mercury reduces risks associated with misreading the tank levels, which is crucial in maintaining safe operations within the chemical process environment.