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?
(c) It is proposed to use a katharometer to measure the amount (about 5%) of oxygen in nitrogen, in the presence of a small amount (0.5%) hydrogen. How constant would the proportion of hydrogen have to be in order to limit errors in measurement of % oxygen to ± 0.1%?
The thermal conductivities are:
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nitrogen
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0.993
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oxygen
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1.052
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hydrogen
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6.993
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(d) FIGURE 1 shows a lcatharometer which allows the use of a reference gas.
How could this be used to measure the effectiveness of a chemical process designed to remove one of the components from a gas mixture?
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.
(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°?
(c) It is sometimes necessary to measure the refractive index of a fluid which does not transmit light well, or has gas or solids entrained. Describe a method which can be used.
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?
(b) It is intended to automate the operation of an Ostwald capillary viscometer as shown below (FIGURE 5).
It must be automatically fed with a sample, and then the sample viscosity measured at three different shear rates. What additional equipment would be required? Sketch a typical installation and set out the operational steps.