Part -1:
1. The figure below shows two sample points in a process line.
(a) What is the nature of the process fluid?
(b) What are the objectives of the two sample points and in what way do the samples reaching the instruments differ?
(c) Could the effectiveness of the second sample probe be improved and if so how?
(d) What additional feature would be necessary for the second sample line and why?
e) Before deciding on a pump to supply a sample, what information must be collected and why?
(a) For what purposes is it important to obtain a rapid response to changes in process stream composition and what methods are used, when designing a sample system, to achieve this?
(b) In the same situations as in (a) above, it is also essential to provide analyser systems which do not break down and which maintain their calibration.
What steps should be taken when designing the sampling system and the installation generally in order to ensure this?
4. (a) An X-ray fluorescence analyser requires a sample consisting of a thin layer of powder on a small conveyor belt. The material to be measured consists of a very large flow of solids of widely variable size and it is not certain that large and small pieces have the same composition. The material is also often damp, but the water content is of no interest. The material is transported on a large conveyor and finally dropped into a bunker off the end of the conveyor. Changes in composition are slow, so intermittent sampling can be used.
Explain, with diagrams as necessary, how you would supply a representative sample to the instrument.
(b) In the above example, how often would the sample have to be taken?
(c) If the objective was to determine the average value of the material in the bunker, how could this be done by making one measurement?
Part -2:
1. (a) Basic physical properties (e.g. density, refractive index and thermal conductivity) can sometimes be useful for analysing the composition of a fluid. In what circumstances can this be done?
(b) What information has to be obtained in order to ensure that the method will be a satisfactory one?2. (a) A measure of refractive index can be used to determine changes in composition of a fluid. Define what is meant by refractive index, and give the relationship between the incident and refracted rays.
1.(a) A measure of refractive index can be used to determine changes in composition of a fluid. Define what is meant by refractive index, and give the relationship between the incident and refracted rays.
(b) A ray of light passes through a material of refractive index 1.5 and then meets material of refractive index 1.3. What is the angle of refraction at the interface between the two materials when the angle of incidence is:
(i) 30°
(ii) 65°?
3. (a) On an existing plant, the manager decides that he must know the density of the liquid flowing in part of it; he wishes to use the measurement as a guide to the composition of the liquid. For economic reasons, the plant cannot be shut down. What possibilities are open to him, and what measurements other than density would have to be made; why would they be required and how would the measurements be done?
A diagram of the relevant part of the plant is as shown in FIGURE 2. The density required is of the reactor products; it is not possible to get at the point where it enters the storage tank to draw off a sample.
(b) The level of the contents of a vessel are often measured by using a torque tube with the displacer in an external tube which has its top connection above the maximum level and its lower connection near the bottom. A similar instrument can be used to measure density. FIGURE 3 shows an installation for level. Why would it not be satisfactory for density measurement? If you wished to use this type of instrument how would you install it to give satisfactory measurement?
4. (a) Below is a diagram of a rotating disc viscometer (FIGURE 4). Explain its operations and limitations as to use. If, in a similar works situation, it is necessary to make measurements on a non-Newtonian liquid, what would be a better instrument to use and why?
5. (a) Power stations are often sited near the coast, which allows them to use sea water for cooling in the condensers at the outlets from their turbines. What analysis measurement would be particularly important in this situation and why? How could the measurement be made?
6. A long length of compensating cable is joined as shown in FIGURE 3. The conductors are not touching directly and the connection is made via the connectors themselves. What effect (if any) will the connection have on the accuracy of the system? Give reasons for your answer.
7. (a) With the aid of a sketch describe the construction and principle of operation of a total radiation pyrometer.
(b) Explain how the following parameters affect the total amount of radiation which is emitted from a hot object :
(i) object temperature
(ii) object surface area
(c) Explain why the emissivity of a black body is equal to I.