UPSC Indian Forest Service (IFoS) Main Previous Year Question Paper 2024 Chemical Engineering-1,

UPSC Indian Forest Service (IFoS) Main Previous Year Question Paper 2024 Chemical Engineering-1

1. (a) Briefly describe the working principle of a steam jet ejector, along with its performance. 8
(b) Discuss the dependency of temperature on the viscosities of gases and liquids. 8
(c) Describe various types of dryers with sketches and applications. 8
(d) In liquid-liquid extraction, describe the selection criteria of good solvents. 8
(e) A grey body of 20 m² area, radiates 10⁶ W at 1227°C. Calculate the emissivity of grey body. If the temperature is increased to 1327°C, what would be the percentage change in emissive power? 8

UPSC Indian Forest Service (IFoS) MAIN Previous Year Question Paper 2024 – CHEMICAL Engineering-I

Q2. (a) Countercurrent stripping of ammonia from a dilute solution by air is carried out in a sieve tray column having 6 trays. The equilibrium relationship is given by y_e = 0.85 x_e.

90 percent of ammonia is removed when the molar flow of air is 1.5 times that of the solution. 15

(i) Calculate the ideal stages of the column and stage efficiency.
(ii) Find the percentage removal, if the air rate of flow is increased to 2 times the solution rate.

(b) Rivers are the source of water supply for factories. Water at the rate of 2 × 10⁵ kg/hr has to be pumped from a river to a factory overhead tank, placed at a height of 25 metres from the river bed, the total length of pipeline being 1500 metres. The iron pipe having an inside diameter of 30 cm has been used for this pumping. The viscosity of river water is 0.764 cP and friction factor is given by f = 0.0014 + 0.125/Re^0.32. Calculate:

(i) The Reynolds number (Re), if ρ = 1 gm/cc
(ii) The head loss due to friction.

(c) The wall of a furnace is constructed from an inner layer of 0.6 cm thick steel (k = 40 W/mK) and an outer layer of 10 cm brick (k = 2.5 W/mK). The inner surface temperature is 900 K and the outside surface temperature is 480 K. Calculate the heat loss from the furnace per unit area and also the temperature at the interface. Assume steady state exists and effects at the corners and edges of the wall are negligible. The temperatures at the surface are uniform. 10

3. (a) A hot moving body is 0.62 m long, 0.2 m wide and 0.1 m deep. The surface temperature of the hot body is 350 K. Find the rate of heat flow (heat loss) from the hot body to the atmosphere at 276 K at a speed of 29 m/s. The conditions are such that boundary layer may be assumed turbulent over the entire surface. The radiation from the hot body may be neglected. The same average convection heat transfer coefficient, as for the bottom and sides, may be used for the front and rear surfaces. The properties of air at the average temperature are given as:

Density = 1.092 kg/m³ ; Viscosity = 19.123 × 10⁻⁶ N·s/m².
Thermal conductivity = 0.0265 W/m·K.
Specific heat = 1014 J/kg·K, Prandtl Number = 0.71.

[IMAGE: Diagram of a hot moving body with air flowing at 29 m/s, length 0.62 m, width 0.2 m, bottom of the moving body at 350 K]

(b) Crushing is an important method for size reduction of solid particles. Estimate the energy required to crush 1 × 10⁵ kg/hr of sodium silicate, if 80% of the feed passes through a screen 3.75 cm aperture and 80% of the product passes through a screen with 0.03 cm aperture. The work index (W_i) for sodium silicate is 13.1.

(c) A spherical naphthalene ball of 10 gm is kept suspended in a large volume of air at 45°C and one atm pressure. Diffusivity of naphthalene in air D_AB = 6.92 × 10⁻⁶ m²/s, and density ρ = 1.14 gm/cc. The sublimation pressure at 45°C is 0.8654 mm Hg. Calculate the time required for sublimation of 7 gm of naphthalene. Molecular weight of naphthalene is 128.

4. (a) A 20% NaOH solution is concentrated in an evaporator. 4500 kg/h of this solution enters the evaporator at 333 K and the product contains 50% solids. The pressure of saturated steam used is 172.4 kPa and the pressure in the vapour space of evaporator is 11.7 kPa. The overall heat transfer coefficient is 1565 W/m²K. Calculate the heating surface area required and the steam economy of the evaporator. The heat capacity of superheated steam may be taken as 1.884 kJ/kg.K. The required charts and steam tables are enclosed.

[IMAGE: Enthalpy-concentration chart for NaOH-water system]

1: Properties of saturated Steam and Water (Steam Table), SI Units

Temperature (°C) | Vapour Pressure (kPa) | Specific Volume (m³/kg) Liquid | Specific Volume (m³/kg) Sat’d Vapour | Enthalpy (kJ/kg) Liquid | Enthalpy (kJ/kg) Sat’d Vapour | Entropy (kJ/kg.K) Liquid | Entropy (kJ/kg.K) Sat’d Vapour
0.01 | 0.6113 | 0.0010002 | 206.136 | 0.00 | 2501.4 | 0.0000 | 9.1562
5 | 0.8721 | 0.0010001 | 147.12 | 20.97 | 2510.6 | 0.0761 | 9.0257
10 | 1.2276 | 0.0010003 | 106.38 | 42.01 | 2519.2 | 0.1510 | 8.9009
15 | 1.7051 | 0.0010009 | 77.93 | 62.99 | 2528.9 | 0.2245 | 8.7814
20 | 2.339 | 0.0010018 | 57.79 | 83.96 | 2538.1 | 0.2966 | 8.6672
25 | 3.169 | 0.001003 | 43.36 | 104.89 | 2547.2 | 0.3674 | 8.5580
30 | 4.246 | 0.0010043 | 32.89 | 125.79 | 2556.3 | 0.4369 | 8.4533
35 | 5.628 | 0.001006 | 25.22 | 146.68 | 2565.3 | 0.5053 | 8.3531
40 | 7.384 | 0.001008 | 19.52 | 167.57 | 2574.3 | 0.5725 | 8.2570
45 | 9.593 | 0.001010 | 15.26 | 188.45 | 2583.2 | 0.6387 | 8.1648
50 | 12.349 | 0.001012 | 12.03 | 209.33 | 2592.1 | 0.7038 | 8.0763
55 | 15.758 | 0.001015 | 9.568 | 230.23 | 2600.9 | 0.7679 | 7.9913
60 | 19.940 | 0.001017 | 7.671 | 251.13 | 2609.6 | 0.8312 | 7.9096
65 | 25.03 | 0.001020 | 6.197 | 272.06 | 2618.3 | 0.8935 | 7.8310
70 | 31.19 | 0.001023 | 5.042 | 292.98 | 2626.8 | 0.9549 | 7.7553
75 | 38.58 | 0.001026 | 4.131 | 313.93 | 2635.3 | 1.0155 | 7.6824
80 | 47.39 | 0.001029 | 3.407 | 334.91 | 2643.7 | 1.0753 | 7.6122
85 | 57.83 | 0.001033 | 2.828 | 355.90 | 2651.9 | 1.1343 | 7.5445
90 | 70.14 | 0.001036 | 2.361 | 376.92 | 2660.1 | 1.1925 | 7.4791
95 | 84.55 | 0.001040 | 1.981 | 397.96 | 2668.1 | 1.2500 | 7.4159
100 | 101.35 | 0.001043 | 1.672 | 419.04 | 2676.1 | 1.3069 | 7.3549
105 | 120.82 | 0.0010475 | 1.4194 | 440.15 | 2683.8 | 1.3630 | 7.2958
110 | 143.27 | 0.0010516 | 1.2102 | 461.30 | 2691.5 | 1.4185 | 7.2387
115 | 169.06 | 0.0010559 | 1.0366 | 482.48 | 2699.0 | 1.4734 | 7.1833
120 | 198.53 | 0.0010603 | 0.8919 | 503.71 | 2706.3 | 1.5276 | 7.1296
125 | 232.1 | 0.0010649 | 0.7706 | 524.99 | 2713.5 | 1.5813 | 7.0775
130 | 270.1 | 0.0010697 | 0.6685 | 546.31 | 2720.5 | 1.6344 | 7.0269
135 | 313.0 | 0.0010746 | 0.5822 | 567.69 | 2727.3 | 1.6870 | 6.9777
140 | 316.3 | 0.0010797 | 0.5089 | 589.13 | 2733.9 | 1.7391 | 6.9299
145 | 415.4 | 0.0010850 | 0.4463 | 610.63 | 2740.3 | 1.7907 | 6.8833
150 | 475.8 | 0.0010905 | 0.3928 | 632.20 | 2746.5 | 1.8418 | 6.8379
155 | 543.1 | 0.0010961 | 0.3468 | 653.84 | 2752.4 | 1.8925 | 6.7935
160 | 617.8 | 0.0011020 | 0.3071 | 675.55 | 2758.1 | 1.9427 | 6.7502
165 | 700.5 | 0.0011080 | 0.2727 | 697.34 | 2763.5 | 1.9925 | 6.7078
170 | 791.7 | 0.0011143 | 0.2428 | 719.21 | 2768.7 | 2.0419 | 6.6663
175 | 892.0 | 0.0011207 | 0.2168 | 741.17 | 2773.6 | 2.0909 | 6.6256
180 | 1002.1 | 0.0011274 | 0.19405 | 763.22 | 2778.2 | 2.1396 | 6.5857
190 | 1254.4 | 0.0011414 | 0.15654 | 807.62 | 2786.4 | 2.2359 | 6.5079
200 | 1553.8 | 0.0011565 | 0.12736 | 852.45 | 2793.2 | 2.3309 | 6.4323
225 | 2548 | 0.0011992 | 0.07849 | 966.78 | 2803.3 | 2.5639 | 6.2503
250 | 3973 | 0.0012512 | 0.05013 | 1085.36 | 2801.5 | 2.7927 | 6.0730
275 | 5942 | 0.0013168 | 0.03279 | 1210.07 | 2785.0 | 3.0208 | 5.8938
300 | 8581 | 0.0010436 | 0.02167 | 1344.0 | 2749.0 | 3.2534 | 5.7045

Table 2 : Properties of Superheated Steam (Steam Table), SI Units (v, specific volume, m³/kg; H, enthalpy, kJ/kg; s, entropy, kJ/kg.K)

Absolute Pressure kPa (Sat. Temp., °C) | Temperature (°C)
100 | 150 | 200 | 250 | 300 | 360 | 420 | 500
v 17.196 | 19.512 | 21.825 | 24.136 | 26.445 | 29.216 | 31.986 | 35.679
10 H 2687.5 | 2783.0 | 2879.5 | 2977.3 | 3076.5 | 3197.6 | 3320.9 | 3489.1
(45.81) s 8.4479 | 8.6882 | 8.9038 | 9.1002 | 9.2813 | 9.4821 | 9.6682 | 9.8978
v 3.418 | 3.889 | 4.356 | 4.820 | 5.284 | 5.839 | 6.394 | 7.134
50 H 2682.5 | 2780.1 | 2877.7 | 2976.0 | 3075.5 | 3196.8 | 3320.4 | 3488.7
(81.33) s 7.6947 | 7.9401 | 8.1580 | 8.3556 | 8.5373 | 8.7385 | 8.9249 | 9.1546
v 2.270 | 2.587 | 2.900 | 3.211 | 3.520 | 3.891 | 4.262 | 4.755
75 H 2679.4 | 2778.2 | 2876.5 | 2975.2 | 3074.9 | 3196.4 | 3320.0 | 3488.4
(91.78) s 7.5009 | 7.7496 | 7.9690 | 8.1673 | 8.3493 | 8.5508 | 8.7374 | 8.9672
v 1.6958 | 1.9364 | 2.172 | 2.406 | 2.639 | 2.917 | 3.195 | 3.565
100 H 2672.2 | 2776.4 | 2875.3 | 2974.3 | 3074.3 | 3195.9 | 3319.6 | 3488.1
(99.63) s 7.3614 | 7.6134 | 7.8343 | 8.0333 | 8.2158 | 8.4175 | 8.6042 | 8.8342
v 1.2853 | 1.4443 | 1.6012 | 1.7570 | 1.9432 | 2.129 | 2.376
150 H 2772.6 | 2872.9 | 2972.7 | 3073.1 | 3195.0 | 3318.9 | 3487.6
(111.37) s 7.4193 | 7.6433 | 7.8438 | 8.0720 | 8.2293 | 8.4163 | 8.6466
v 0.4708 | 0.5342 | 0.5951 | 0.6548 | 0.7257 | 0.7960 | 0.8893
400 H 2752.8 | 2860.5 | 2964.2 | 3066.8 | 3190.3 | 3315.3 | 3484.9
(143.63) s 6.9299 | 7.1706 | 7.3789 | 7.5662 | 7.7712 | 7.9598 | 8.1913
v 0.2999 | 0.3863 | 0.3714 | 0.4126 | 0.4533 | 0.5070
700 H 2844.8 | 2953.6 | 3059.1 | 3184.7 | 3310.9 | 3481.7
(164.97) s 6.8865 | 7.1053 | 7.2979 | 7.5063 | 7.6968 | 7.9299
v 0.2060 | 0.2327 | 0.2579 | 0.2873 | 0.3162 | 0.3541
1000 H 2827.9 | 2942.6 | 3051.2 | 3178.9 | 3306.5 | 3478.5
(179.91) s 6.6940 | 6.9247 | 7.1229 | 7.3349 | 7.5275 | 7.7622
v 0.13248 | 0.15195 | 0.16966 | 0.18988 | 0.2095 | 0.2352
1500 H 2796.8 | 2923.3 | 3037.6 | 3169.2 | 3299.1 | 3473.1
(198.32) s 6.4546 | 6.7090 | 6.9179 | 7.1363 | 7.3323 | 7.5698
v 0.11144 | 0.12547 | 0.14113 | 0.15616 | 0.17568
2000 H 2902.5 | 3023.5 | 3159.3 | 3291.6 | 3467.6
(212.42) s 6.5453 | 6.7664 | 6.9917 | 7.1915 | 7.4317
v 0.08700 | 0.09890 | 0.11186 | 0.12414 | 0.13998
2500 H 2880.1 | 3008.8 | 3149.1 | 3284.0 | 3462.1
(223.99) s 6.4085 | 6.6438 | 6.8767 | 7.0803 | 7.3234
v 0.07058 | 0.08114 | 0.09233 | 0.10279 | 0.11619
3000 H 2855.8 | 2993.5 | 3138.7 | 3276.3 | 3456.5
(233.90) s 6.2872 | 6.5390 | 6.7801 | 6.9878 | 7.2338

5×2=10

(i) Minimum fluidization velocity
(ii) Navier-Stokes equation

(c) An oil is being cooled in a heat exchanger from 372 K to 350 K and flows inside the tube at a rate of 3600 kg/h. A flow of 1450 kg water per hour enters at 289 K for cooling and flows outside the tube. Mean heat capacity of the oil, C_pm = 2.30 kJ/kg.K and for water, C_pm = 4.187 kJ/kg.K.

(i) Calculate the outlet temperature of water and heat transfer area if the overall heat transfer coefficient U_i = 340 W/m².K and the streams are countercurrent.
(ii) Find the above two values for parallel flow streams as mentioned in part (i).

Q5. (a) Find the solution to the following Laplace equation :

F(s) = s/((s + 1)(s + 4))

(b) What do you understand by the term "steady state temperature"? Steady state temperature of a thermometer (time constant 0.2 min) is 30°C. At time t = 0, the thermometer is placed in a bath maintained at 40°C. What will be the temperature read by the thermometer after 9.0 seconds ?

(c) What are the types of heads used for vertical tall vessels? Explain each type with neat diagram.

(d) Explain the applications of supercritical fluid in separation processes.

(e) Explain mechanism of separation by dialysis with a neat concentration profile diagram.

Q6. (a) Two tanks are connected in series (non-interacting mode) as shown in the figure. The time constants are τ₂ = 1 and τ₁ = 0.5 ; R₂ = 1. Plot the response of the level in tank 2 if a unit-step change is made in the inlet flow rate to tank 1. (Graph paper is enclosed)

[IMAGE: Diagram of two tanks connected in series, with q(t), A1, h1, R1, q1, A2, h2, R2, q2]

(b) It is proposed to remove Ca²⁺ from water which contains 0.15 gm/litre by using Na-resin. The percentage removal of Ca²⁺ ions is to be 90%. The resin has ion exchange capacity of 3 eq/litre. Find out the quantity of resin needed to remove Ca²⁺ ion of 40,000 litres water. Selectivity is given as K'_Ca/K'_Na = 2.5.

(c) Explain the following with neat sketch:

(i) Ultimate stress
(ii) Proof stress
(iii) Yield stress
(iv) Resilience

15

Q7. (a) A vessel is to be designed for maximum operating pressure of 450 kN/m². The vessel has a nominal diameter of 1.4 m and tangent to tangent length 2.5 m. The maximum allowable design stress of the material is 120 MN/m² at working temperature. Corrosion allowance is 1.5 mm. The weld joint efficiency of vessel material is 0.80.

Calculate the thickness of standard plate to fabricate this vessel.

15

(b) Define the term "Final value theorem". Also find an analytical expression for n unit impulse response of a system whose transfer function is given by

Y(s)/X(s) = 23/(s² + 3s + 2)

(c) In an industrial township it is required to supply drinking water of 2×10⁷ litres/day from raw water containing 3.3% salt concentration. It is decided to use RO unit, so that it can supply drinking water with < 300 ppm of salt. Membrane used was of thickness 0.8 micrometer and having water permeability of 70 L/m².h.MPa and salt rejection 98%. The pressure applied in feed side is 75 atm and on the permeate side is 1.0 atm. Assume polarization modulus is 1.2.

Calculate area of membrane needed if only 30% of the feed water permeates through the membrane.

8. (a) Explain the general categories of chemical attacks for handling corrosive liquids in vessel. For handling and storage of 98% sulphuric acid and phosphoric acid, what materials do you recommend for storage economically? 15

(b) An organic solution in 0.05 molar NaCl needs to be separated by ultrafiltration. The filtration is gel layer controlled. The feed concentration is 0.01 gm/mL and gel concentration is 0.4 gm/mL. The charge number of organic molecule is 10 e and radius 0.005 micrometer. Calculate the permeate flux. Data : Mass transfer coefficient 5 × 10⁻⁵ m/s. 10

(c) Express the transfer function (C/R), for the following block diagram. 15

[IMAGE: Block diagram with R, G_b, G_c, G_a, and feedback loops]

Indian Forest Service (Main) Examination, 2024-CHEMICAL-ENGINEERING-I

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