14CH406. Chemical Engineering Scheme of Valuation Process Instrumentation Maximum : 60 Marks (1X12 = 12 Marks) Answer ONE question from each unit.

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1 April, 2018 Fourth Semester Time: Three Hours Answer Question No.1 compulsorily. II/IV B.Tech. (Regular/Supplementary) DEGREE EXAMINATION 14CH406 Chemical Engineering Scheme of Valuation Process Instrumentation Maximum : 60 Marks (1X12 = 12 Marks) Answer ONE question from each unit. (4X12=48 Marks) 1. Answer all questions (1X12=12 Marks) a) Types of Drift A change in an instrument's reading or set point value over extended periods due to factors such as time, line voltage, or ambient temperature effects. b) Composition of Invar Consisting of around 36% nickel and 64% iron. c) Name laws of Thermo Electricity Law of homogeneous circuits, law of intermediate metals, law of intermediate temperatures d) Dip Effect In case of a metallic bulb of mercury filled system, the metallic bulb expands before expansion ofmercury, hence volume of bulb is increased and pressure reduces e) Principle of Venturi meter The working ofventurimeter is based on the principle of Bernoulli's equation. Bernoulli's Statement: It states that in a steady, ideal flow of an incompressible fluid, the total energy at any point of the fluid is constant. f) Circular Chart Circular chart recorders archive data points on a round chart over a timed interval. Using data acquired by one or more sensors, circular chart recorders rotate uniformly while one or more pens plots the data radially in proportion to the signal received. The charts usually rotate over standard time periods (e.g. 24 hours, one week, one month, etc.) though some recorders can rotate over non-standard lengths of time. The benefits of circular chart recorders includes the ease of operation, the hardcopy it produces, and real-time output. g) Chromatography Chromatography is a physical method of separation that distributes components to separate between two phases, one stationary (stationary phase), the other (the mobile phase) moving in a definite direction. h) Pressure Indicating Elements Dial indicating pressure gauge, Bellows pressure element, Diaphragm pressure element i) Elements of Diagrammatic Control Centre layout j) Emission Spectroscopy Atomic emission spectroscopy (AES) is a method of chemical analysis that uses the intensity of lightemitted from a flame, plasma, arc, or spark at a particular wavelength to determine the quantity of an element in a sample. k) Radiation receiving elements Thermopile, Vacuum thermocouple, bolometer l) Compensation of ambient effect on expansion thermometers Compensation of ambient effect in expansion thermometer is done by Bimetalic compensator or compensating spring. UNIT I 2. a) Explain about the dynamic characteristics of an instrument The various dynamic characteristics are: i) Speed of response ii) Measuring lag iii) Fidelity iv) Dynamic error Speed of response: It is defined as the rapidity with which a measurement system responds to changes in the measured quantity. 4M

b) Time delay lag: In this case the response of the measurement system begins after a dead time after the application of the input.

2 Measuring lag: It is the retardation or delay in the response of a measurement system to changes in the measured quantity. The measuring lags are of two types: a) Retardation type: In this case the response of the measurement system begins immediately after the change in measured quantity has occurred. b) Time delay lag: In this case the response of the measurement system begins after a dead time after the application of the input. Fidelity: It is defined as the degree to which a measurement system indicates changes in the measurand quantity without dynamic error. Dynamic error: It is the difference between the true value of the quantity changing with time & the value indicated by the measurement system if no static error is assumed. It is also called measurement error. b) Derive a relation for dynamic response of first order instrument for step change The transfer function of thermometer which is a first order system is: ( ) = ( ) ( ) = The dynamic response is the behavior of the output variable (response or reading of the instrument) with time with a change given in input. The common input forcing functions are: Step change, Linear change, Sinusoidal change and Impulse change. Step function: It represents sudden change of value of the input. The step function of magnitude A is mathematically described by the equation x(t) = 0 for t < 0; = A for t > 0; The Laplace transform of the step function: L{x(t)} = L {A} =A/s. Step response: ( ) = (1 ) 8M (OR) 3. a) Discuss about Instrumentation Diagram with an example 8M

b) Describe the adequate conditions to be maintained at control center The conditions to be maintained at control center are Clean dry atmosphere Relatively constant temperature and humidity No

4 b) Describe the adequate conditions to be maintained at control center The conditions to be maintained at control center are Clean dry atmosphere Relatively constant temperature and humidity No vibration Adequate light Unfailing source of electric power and clean dry air 4M UNIT II 4. a) Explain the Principle and working of Pressure Spring Thermometer The Pressure spring thermometers are classified into three categories according to the filled material: Liquid filled thermometer. These thermometers utilize volumetric expansion of liquid with rise in temperature for indicating temperature of liquid. Gas filled thermometers: Pressure of certain fixed volume of gas varies with temperature of the gas. Thus any change in temperature of gas can be measured in terms of change in its pressure. 6M

Vapor actuated thermometers: Vapor pressure of volatile liquid varies with the temperature existing at the free surface of liquid.

Construction: The thermal system for all pressure spring thermometers consists of: Bulb, Capillary, Thermal well, Extension neck and receiving element (pressure

Working: When the bulb is sufficiently inserted in the bath whose temperature is to be measured, the bulb s liquid receives heat from the bath and its temperature

5 Vapor actuated thermometers: Vapor pressure of volatile liquid varies with the temperature existing at the free surface of liquid. Hence any change in temperature of a volatile liquid can be measured in terms of change in its vapor pressure. Construction: The thermal system for all pressure spring thermometers consists of: Bulb, Capillary, Thermal well, Extension neck and receiving element (pressure spring), Pen arm or a pointer. Working: When the bulb is sufficiently inserted in the bath whose temperature is to be measured, the bulb s liquid receives heat from the bath and its temperature rises until it equals the bath temperature, thus developing a pressure or displacement of the liquid. The capillary transmits the pressure to the receiving element that causes winding or unwinding of bourdon tube. The free end deflection of the bourdon is coupled with the pointer that moves on a calibrated scale. b) Describe the principle of millivolt meter with a neat sketch 6M (OR)

5. a) Explain the principle and working of radiation pyrometers According to Stefan- Boltzmann s law the intensity of radiant energy emitted by hot target varies as the fourth power of its absolute

It consists of a diaphragm, radiation receiving element, sighting hole and indicator or recorder.

In lens type radiation receiver, a lens is used to concentrate the radiant energy from the source on the diaphragm to the thermopile (or vacuum thermocouple.

This unit has an advantage of not having lens, since lens absorption and reflection are avoided.

6 5. a) Explain the principle and working of radiation pyrometers According to Stefan- Boltzmann s law the intensity of radiant energy emitted by hot target varies as the fourth power of its absolute temperature. In radiation pyrometer, the visible and IR energy is focused on radiation detector which converts it into proportional electrical signal that indicates the target temperature. It consists of a diaphragm, radiation receiving element, sighting hole and indicator or recorder. Radiations at all possible wavelengths from a hot body are focused by lens or mirror on the radiation receiving element. In lens type radiation receiver, a lens is used to concentrate the radiant energy from the source on the diaphragm to the thermopile (or vacuum thermocouple. In mirror type radiation receiver, a diaphragm system together with a mirror is used to focus the radiation on a thermopile. The mirror to thermopile distance is adjustable for proper focus. This unit has an advantage of not having lens, since lens absorption and reflection are avoided. When thermopile or vacuum thermocouple is used as radiation receiving elements, then radiant energy is focused on blackened measuring junction. Due to absorption of radiant energy the measuring junction temperature rises According to Seebeck effect emf develops between measuring junction and reference junction. When this element is connected with mill voltmeter type instrument, the emf developed can be calibrated in terms of the target temperature. If bolometer is used as a receiving element, then resistance of the foil changes with temperature. Hence bolometer can be calibrated in terms of target temperature with wheat stone bridge circuit. 8M Lens - type radiation pyrometers Mirror-type radiation pyrometers b) Write a short note on resistance thermometer bulbs 4M

Gauge The design of a McLeod gauge is somewhat similar to a that of a mercury-column manometer.

7 UNIT III 6. a) Discuss about the measurement of level in pressure vessels 6M b) Explain the principle and working of McLeod Gauge The design of a McLeod gauge is somewhat similar to a that of a mercury-column manometer. Typically it is filled with mercury. If used incorrectly, this mercury can escape and contaminate the vacuum system attached to the gauge. McLeod gauges operate by taking in a sample volume of gas from a vacuum chamber, then 6M

determined by applying Boyle's law. This method is fairly accurate for non-condensible gases, such as oxygen and nitrogen.

8 compressing it by tilting and infilling with mercury. The pressure in this smaller volume is then measured by a mercury manometer, and knowing the compression ratio (the ratio of the initial and final volumes), the pressure of the original vacuum can be determined by applying Boyle's law. This method is fairly accurate for non-condensible gases, such as oxygen and nitrogen. However, condensible gases, such as water vapour, ammonia, carbon dioxide, and pump-oil vapors may be in gaseous form in the low pressure of the vacuum chamber, but will condense when compressed by the McLeod gauge. The result is an erroneous reading, showing a pressure much lower than actually present. A cold trap may be used in conjunction with a McLeod gauge to condense these vapors before they enter the gauge. The McLeod gauge has the advantage that it is simple to use and that its calibration is nearly the same for all non-condensable gases. The device can be manually operated and the scale read visually, or the process can be automated in various ways. For example, a small electric motor can periodically rotate the assembly to collect a gas sample. If a fine platinum wire is in the capillary tube, its resistance indicates the height of the mercury column around it. Modern electronic vacuum gauges are simpler to use, less fragile, and do not present a mercury hazard, but their reading is highly dependent on the chemical nature of the gas being measured, and their calibration is unstable. For this reason, McLeod gauges continue to be used as a calibration standard for electronic gauges. (OR) 7. a) Write a detailed note on Liquid Column Manometers with neat diagrams 8M

b) Explain any one method of direct measurement of liquid level Direct measurement of Liquid Level (i)float-and-tape Liquid-Level Gage This method is employed in open vessels only.

9 b) Explain any one method of direct measurement of liquid level Direct measurement of Liquid Level (i)float-and-tape Liquid-Level Gage This method is employed in open vessels only. The float, usually of nickel-plated copper, rests on the surface of the liquid, supported by buoyant force. The float is made with a sloping top in order to avoid building up of solid material on top of the float, thereby changing its weight. The float is connected to the drum by a thin light weight, flexible tape or cable. Slipping of the tape on the drum is prevented by a direct connection of the tape to the drum. By a suitable reduction in motion the pointer indicates on a scale calibrated in feet or other units. Float-and-Shaft Liquid-Level Gage The float rests on the surface of the liquid and the motion of the float is taken through the shifting box by the shaft. The counterweight is adjustable, so that the float can be made to ride half-submerged. This is important since floats are usually spherical, and this is the point 4M

10 of maximum area. The float cage may be obtained in steel or cast iron, and the float in copper, stainless steel, nickel or aluminum. The rotation of the shaft may be converted into a change of pneumatic pressure by the use of a pneumatic transmissionn system. The movement of the float causes a displacement of a metallic bellows which is filled with oil. UNIT IV 8. a) Discuss the principle of mass spectroscopy with neat sketch MASS SPECTROMETER The mass spectroscopy is most useful in analyzing aliphatic and cyclicc hydrocarbon compounds and isotopes. The sample in a gas or vapor state at about 40 microns Hg absolute pressure is introduced to the ionization chamber. The pressure in the ionization chamber and tube assembly is maintained even lower by a vacuum pump. The gas is bombarded by an electron beam from the filament in the chamber. The gas (or vapor) is transformed into ions, neutral fragments and electrons. The electrons are collected at the plate in the ionization chamber. The neutral fragments are pumped out of the system. The ions being positively charged are attracted toward the two slits by the field caused by the electric potential of the slit pieces. The ions are accelerated through both slits and are formed into a parallel beam. Since the circular tube lies in a magnetic field of fixed direction, the ion beam is made to deflect in a circular path, the radius of which depends on the mass and the velocity of the ion. Thus several beams are formed, each consisting of ions of a specific mass. The beam to strike the collector can be selected by varying the accelerating voltage at the two slits. The charges given to the collector plate by ions are amplified and recorded by a d-c potential instrument. By automatically varying the accelerating voltage a spectrum of ion beam intensity versus ion mass is recorded. The analysis of the spectrum results in the determination of the composition of the gas or vapor. The spectrum is compared to the spectrum of a pure substance and mole fractions of the components are obtained by direct proportion. The mass spectrometer can separate masses differing by one part in 300 and in some cases, those differing by one part in M b) Describe the process of gas analysis by the principle of thermal conductivity Thermal conductivity measurement is a very simple means of analyzing certain gas mixtures. Thermal conductivity of the mixture of two gases can be related to the concentration of each component. A thermal conductivity cell is constructed of glass. The right hand tube contains a platinum filament held under constant tension by a spring. The 6M

11 and consequent temperature rise of the filament depend on the rate at which heat is conducted away from the filament. This depends mainly on the thermal conductivity of the gas. It is important that both cells be subjected to the same ambient-temperature conditions so that the only difference measured in the bridge is that due to the differing thermal conductivity of the reference gas and the measured gas. (OR) 9. a) Explain the Principle of UV-absorption spectrophotometer Absorption Spectroscopy: Absorption spectroscopy is a technique used to find out what makes up a sample of a substance, i.e, chemical analysis. When infrared, ultraviolet or x-ray radiation is passed through the sample of unknown material certain frequencies of the radiation are absorbed. This is determined by separating the radiation into a spectrum and measuring the intensity of radiation at each frequency. Absorption lines are dark lines on a light background on a photographic negative. These dark lines are called absorption lines, and every element has its characteristic pattern of absorption lines. On an atomic scale, this happens because of the electrons in the atoms of the sample - an electron can absorb light to gain energy. Electrons only ever absorb certain amounts of energy, suggesting an electron's energy must fit onto set, quantized, discrete energy levels. The process of an electron going to a higher energy level is called excitation. For any atom of a particular element, the energy needed to excite an electron from one specific energy level to another will be the same. The missing colors give us information about the energy of the photons that cause excitation. Since a color can be described as a specific frequency of light, this is why the black breaks can be used to identify element(s) which the light is passing through. 8M b) Write a note on Colour measurement Color measurement by spectrometer. Spectrometers employed in the visible band are mainly useful for color control of plastics, paints dyes, ceramics and so on. For translucent materials such as colored liquids and glasses, the usual ultra-violet absorption spectrometer can be arranged to measure the intensity of light absorbed or transmitted at various wavelengths in the visible region from 0.4 micron (violet) to 0.7 micron (red). The spectrogram would therefore indicate the transmittance in percent at each wavelength when the substance in question is irradiated by white light. For opaque materials such as plastics, powdered pigments, and paper, it is 4M necessary to measure the reflectance of the surface. The general electric company spectrometer is specifically adapted to measure the color of reflected light, but it can also be used for measuring transmitted light. A diffuse reflectance attachment is available for use with the National Technical Laboratories (Beckman) ultraviolet-absorption spectrometer, which is operated in the visible band. The diffuse reflectance is arranged to direct the monochromatic beam of light from the exit slit down on the sample which replaces the sample cell. With such instruments the color of reflecting surfaces and transmitting materials can be explicitly specified by measuring the intensity at each wavelength. For

12 critical color specification as in paints and dyes, the human eye is not reliable. For example the graph shows the spectral distribution of a color that would probably be identified by the eye as apple green.

Earlier Lecture. In the earlier lecture, we have seen non metallic sensors like Silicon diode, Cernox and Ruthenium Oxide.

Earlier Lecture. In the earlier lecture, we have seen non metallic sensors like Silicon diode, Cernox and Ruthenium Oxide. 41 1 Earlier Lecture In the earlier lecture, we have seen non metallic sensors like Silicon diode, Cernox and Ruthenium Oxide. Silicon diodes have negligible i 2 R losses. Cernox RTDs offer high response