Evaporation and Drying - Agricultural Process Engineering - Agricultural Engineering Previous Year Questions

1

2007 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2007

Peas of 1.1 cm diameter are dried by air at 65.8 °C in a packed bed drier. The void fraction of the bed is 0.35 and the bed has a diameter of 0.5 m and a height of 0.8 m. The flow rate and the viscosity of air are 0.12 kg s⁻¹ and 2.03 × 10⁻⁵ Pa s respectively. Reynolds number for the packed bed is

A

13

B

340

C

908

D

1359

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2

2008 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2008

Heated air at 50 °C and 10% relative humidity is used to dry rice in a bin dryer. The air leaves the bin under saturated condition. The corresponding data for humidity ratio as read from the psychrometric chart are 0.0078 and 0.019 kg water per kg dry air. The amount of water removed per kg of dry air will be

A

0.0112 kg

B

0.021 kg

C

0.112 kg

D

0.121 kg

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3

2008 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2008

The drying time will be

A

1.7 h

B

2.3 h

C

3.2 h

D

7.1 h

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4

2010 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2010

Carrot slices of 2 mm thickness are freeze dried (from initial free moisture content of 80% (wet basis) to a final free moisture content of 2% (wet basis). Mass density of fresh carrot is 1100 kg m^-3. Thermal conductivity of dried layer is 0.005 W m^-1 K^-1. Latent heat of sublimation at –35°C is 2840 kJ kg^-1 and product surface temperature is –5°C. The total drying time in hour is

A

1.2

B

2.3

C

3.2

D

5.4

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5

2010 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2010

Mass diffusivity of water vapour in m² s^-1 during the falling rate phase of drying is

A

7.01 × 10^-4

B

5.07 × 10^-4

C

3.71 × 10^-5

D

1.07 × 10^-5

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6

2011 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2011

300 kg of parboiled and wet paddy having an initial moisture content of 28% (dry basis) was dried in a batch type dryer. During drying operation, grain sample was drawn at regular time intervals to measure its moisture content (dry basis). It was found that the moisture content of the grain borne a linear relationship with drying time till 30 minutes of drying operation at which moisture content was measured to be 20%. The drying rate (kg h^-1) during this interval was

A

22.3

B

37.5

C

41.7

D

48.1

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7

2011 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2011

The humidity (kg of water vapour / kg of dry air) of the outlet air is

A

0.0027

B

0.0172

C

0.0335

D

0.0483

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8

2013 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2013

A rotary dryer is used to dry \(1200 \text{ kg h}^{-1}\) of paddy containing 30% moisture (wet basis) to give a product containing 15% moisture (wet basis). Alternately, a portion of the dry product may be recycled and mixed with the fresh feed such that the mixed feed enters the dryer with moisture content of 20% (wet basis). The moisture evaporation rate without recycle and the paddy recycle rate in \(\text{kg h}^{-1}\) respectively in the dryer are

A

211.76 and 2400

B

211.76 and 600

C

256.5 and 2400

D

256.5 and 600

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9

2013 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2013

Select the pair that best expresses a relationship similar to that expressed in the pair:
water: pipe:

A

cart: road

B

electricity: wire

C

sea: beach

D

music: instrument

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10

2018 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2018

Mass flow rate of outside air through a duct is 735 kg h⁻¹. Absolute humidity of air is 0.025 kg water vapour per kg dry air at 40°C. This air is mixed with equal quantity of moist exhaust air coming out of a counter current dryer at 55°C. The mixed air is heated up to 75°C to dry barley, fed at 174 kg h⁻¹ at an initial moisture content of 31% (wet basis) to a final value of 7% (dry basis). The absolute humidity of the exhaust air from the dryer in ‘kg water vapour per kg dry air’ will be ______.

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11

2019 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2019

A batch of 100 kg grain at 32% moisture content (wet basis) is being dried using hot air at 70 °C and 30% RH. The values of Henderson's equation's constants c and n for the grain are 8.5×10^-6 and 2.07, respectively. Considering the maximum possible drying of the batch, the quantity of moisture removed in kg is

A

10.20

B

17.05

C

21.98

D

25.07

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12

2019 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2019

In an air blast freezing operation, a flat tray of 1.0 m × 1.0 m × 0.02 m dimensions is used to freeze filled depodded peas. Bulk density and moisture content of peas are 550 kg m^-3 and 85% (w.b.), respectively. Latent heat of freezing from water to ice at -1 °C is 335 kJ kg^-1 and heat transfer occurs identically from the top and the bottom surfaces of the tray. Convective film heat transfer coefficient on the heat transfer surfaces of the tray is 30 W m^-2 K^-1 and the thermal conductivity of frozen peas is 0.54 W m^-1 K^-1. Assuming the tray to be a semi-infinite slab, the freezing time (in minutes) to completely freeze the product (rounded off to one decimal place) is ____________.

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13

2019 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2019

In an air blast freezing operation, a flat tray of 1.0 m×1.0 m×0.02 m dimensions is used to freeze filled depodded peas. Bulk density and moisture content of peas are 550 kg m−3 and 85% (w.b.), respectively. Latent heat of freezing from water to ice at -1 °C is 335 kJ kg−1 and heat transfer occurs identically from the top and the bottom surfaces of the tray. Convective film heat transfer coefficient on the heat transfer surfaces of the tray is 30 W m−2 K−1 and the thermal conductivity of frozen peas is 0.54 W m−1 K−1. Assuming the tray to be a semi-infinite slab, the freezing time (in minutes) to completely freeze the product (rounded off to one decimal place) is ________.

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14

2020 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2020

Fresh tomato juice containing 6% (w/w) total solids enters in a single effect evaporator at a feed rate of 500 kg h⁻¹ to concentrate up to 36% (w/w) solids. In this process, the rate of water removal in kg h⁻¹ (round off to 1 decimal place) is ______________.

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15

2022 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2022

Parboiled paddy is to be dried in a tray dryer under steady state conditions from an initial free moisture content of 0.40 kg H₂O (kg dry solid)⁻¹ to final free moisture content of 0.02 kg H₂O (kg dry solid)⁻¹. The dry solid mass is 99.8 kg and the top surface area for drying is 4.654 m². The drying is occurring in both constant and falling rate periods. If constant drying rate of 1.51 kg H₂O m⁻² h⁻¹ is followed up to a critical moisture content of 0.195 kg H₂O (kg dry solid)⁻¹, then the total drying time in hour will be _______. [round off to two decimal places]

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16

2022 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2022

In an effort to conserve energy, a grain dryer is being modified to reuse a part (10 m³ s⁻¹) of the exhaust airflow at 70 °C and 30% relative humidity. This part of exhaust is mixed with 20 m³ s⁻¹ of ambient air at 30 °C and 60 % relative humidity. The details of the two air-stream conditions are given below.

Temperature (°C)	Relative humidity (%)	Absolute humidity (kg H₂O (kg dry air)⁻¹)
70	30	63.35 × 10⁻³
30	60	16 × 10⁻³

The absolute humidity of the mixed air will be _______. [round off to three decimal places]

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17

2024 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2024

Falling rate period of drying can be explained by one/more of the following:

A

Capillary rise of water

B

Molecular diffusion of water

C

Surface cooling

D

Surface evaporation

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18

2024 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2024

A single effect evaporator concentrates 9090 kg.h^-1 herbal extract of 12 % solids entering at 300 K to a final solid concentration of 20 %. Assuming negligible product loss through vapor, the amount of concentrated product, in kg, is __________. (Answer in integer)

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19

2024 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2024

Mango pulp at an initial temperature of 25 °C and a moisture content of 70 % (wb) is to be dried into leather to a final moisture content of 10 % (wb) using hot air at 95 °C. The latent heat of vaporization of water at 95 °C and at standard atmospheric pressure is 2250 kJ.kg⁻¹. Considering the specific heat of mango pulp as 3.8 kJ.kg⁻¹.°C⁻¹, the energy required for drying per kg of mango pulp, in kJ, is __________. (Rounded off to 1 decimal place)

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20

2025 · Agricultural Engineering · Agricultural Process Engineering · Evaporation and Drying

Agricultural Engineering (AG) 2025

Apple slices are dried from a moisture content of 65% (dry basis) to 10% (dry basis) in a hybrid solar dryer under falling rate period. The apple slices have a drying rate constant of \(\frac{1}{104}\) minute⁻¹. Considering an equilibrium moisture content of 2% (dry basis), the time required for drying is ______ minutes. (Rounded off to 2 decimal places)

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