CHE433: Considering a pump that is used to pump seawater at different depths, shown here in Figure: Thermodynamics Assignment, UTM, Malaysia

Question 1.

Considering a pump that is used to pump seawater at different depths, shown here in Figure:-

• By using a suitable diagram and formula, explain the relationship between pressure and the depth of seawater.
• Determine pressure in kPa at three different points shown in Figure
• What is the pressure difference for pumping up water from point C to D?
• Supposed that the pump is used to pump up water from point C, with heat loss to the surrounding estimated is 35 kW. What is the minimum power required to pump seawater to point D
• In your opinion, is the density difference in seawater pumped at different depth affects the power required by the pump?
• Assuming there is no density variation of seawater and the point of seawater intake goes lower than point C, pressure is expected to increase. Do you think that pressure variation at different seawater depths affects the power of the pump?
• Consider a situation where a larger volume flow rate is needed at point D. What are two possible options that you could do to achieve this target?

Question 2.

Figure 1 is an example of a bicycle pump that represents the relationship of gas parameters when subjected to compression and expansion. As a person is holding the bicycle pump, with the rigorous movement of compressing and expanding, she experiences a slight warmer when the pump is compressed, but she feels slightly colder when the pump is expanded.

• By relating this with the ideal gas equation and thermodynamic example, conduct your study about it and explain this phenomenon.
• In a case where slower compression and expansion are done, do you think you can have the same condition as in rigorous movement? Explain your answer

Question 3

Considering a non-adiabatic cylinder-shaped piston that contains air in two different cases, shown in Figure 2. The first case is in slow compression mode and the second case is in fast compression mode. Both cases have identical volume changes.

• Both cases are considered to be a closed system where expected heat is lost to the surroundings as a result of compression. Explain this observation using any appropriate diagram or formula
• Upon compression, it is expected that the enthalpy change in both cases to be identical. However, the work profile in both cases may be different, despite the same volume change in both cases. Justify this statement.

Question 4

A final year research student has been tasked with conducting hydrothermal carbonization (HTC) experiments to convert palm kernel shells biomass to solid hydrochar product. The student was required to design a typical HTC experiment by considering the following aspects.

• Conduct a brief literature survey and explain using your own words what is meant by the “hydrothermal carbonization” process.
• The experiment will be conducted in a rigid stainless-steel reactor with a volume of 100 mL. The student added 0.01kg of palm kernel shells (bulk density 740kg/m3), 30mL of liquid water at room temperature, and the rest of the reactor volume is air (air density of 1.15kg/m3). Sketch a typical hydrothermal reactor vessel and calculate the average specific volume of the reaction system.
• The student decided to heat the reactor using an electric heater set at a constant temperature of 250°C. The targeted final temperature inside the reactor is 200°C. Calculate the rate of heat transferred across the 1.0 cm stainless-steel wall per unit area of the wall using Fourier’s law of heat conduction equation.
• Air in the reactor was heated from room temperature of 25°C to the targeted final temperature of 200°C. Determine the change in internal energy of air per unit mass, using (a) data from the air table, (b) the functional form of the specific heat, and (c) the average specific heat value.
• If the student decided to consider only the contribution of water in determining the pressure of the system, determine the final pressure of the water. In your opinion, will the decision taken by the student leaders to a significant error in estimating the overall pressure of the reactor?

Answer

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