Thermodynamics MTX 311
Special Exam: June 2015
Examiner
Dr AS Lexmond (University of Pretoria)
Instructions
1 Time: 90 min.
2 Full marks: 90
3 Neatness saves you points, especially when only part of the question is correct.
4 Give the equations before you start filling in numbers; for the questions marked with an
*, also give a short but clear solution strategy
5 You are allowed to take fundamentals of thermodynamics (7th or 8th edition), non-ideal
gas hand-out, one page, A4, with your own notes (both sides) and all the material from
the click-up page “lectures”
6 For all questions: use a reference temperature and pressure of T0=25°C, P0=1 bar
A group of four MOX students had to design a energy recovery system for me this year. This
question is about the design that one of them came up with, where I was quite unhappy with the
low efficiency of his system.
In the current factory, a process steam of 16kg/s of hot ore of 1000°C is mixed with a large amount
of water to cool it down; the water evaporates and gets lost and the heat is lost as well. In an
improved design, the student proposes to generate steam in a fluidized bed. Equipment design is
given in fig. 1. Air is blown through the hot ore, which make the ore pellets float. As a result, the ore
pellets mixture behaves as a fluid, resulting in very high heat transfer rates.
Fig. 1 process design of a fluidized bed heat regenerator
Special Exam: June 2015
Examiner
Dr AS Lexmond (University of Pretoria)
Instructions
1 Time: 90 min.
2 Full marks: 90
3 Neatness saves you points, especially when only part of the question is correct.
4 Give the equations before you start filling in numbers; for the questions marked with an
*, also give a short but clear solution strategy
5 You are allowed to take fundamentals of thermodynamics (7th or 8th edition), non-ideal
gas hand-out, one page, A4, with your own notes (both sides) and all the material from
the click-up page “lectures”
6 For all questions: use a reference temperature and pressure of T0=25°C, P0=1 bar
A group of four MOX students had to design a energy recovery system for me this year. This
question is about the design that one of them came up with, where I was quite unhappy with the
low efficiency of his system.
In the current factory, a process steam of 16kg/s of hot ore of 1000°C is mixed with a large amount
of water to cool it down; the water evaporates and gets lost and the heat is lost as well. In an
improved design, the student proposes to generate steam in a fluidized bed. Equipment design is
given in fig. 1. Air is blown through the hot ore, which make the ore pellets float. As a result, the ore
pellets mixture behaves as a fluid, resulting in very high heat transfer rates.
Fig. 1 process design of a fluidized bed heat regenerator
