Heat transfer - Food Engineering - Engineering Sciences Previous Year Questions

1

2008 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2008

Match the items in Group I with the most appropriate items in Group II

A

Group I: (P) Freezing, (Q) Fat globules movement in milk, (R) Flow through packed bed, (S) Boiling temperature; Group II: (1) Stoke's law, (2) Plank's equation, (3) Ergun's equation, (4) Hagen Poiseuille's equation, (5) Raoult's law; (A) P-4, Q-1, R-3, S-5; (B) P-2, Q-1, R-3, S-4; (C) P-2, Q-1, R-4, S-5; (D) P-2, Q-1, R-3, S-5

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2

2008 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2008

Saturated steam at temperature \(T_s\) (°C) flows through a pipe and atmospheric air flows over the outer surface of the pipe. If the temperature of the air has increased from \(T_1\) to \(T_m\) the effectiveness of the heat exchange can be expressed as

A

\(\frac{T_1 - T_o}{T_s - T_1}\)

B

\(\frac{T_s - T_1}{T_s - T_o}\)

C

\(\frac{T_o - T_1}{T_s - T_1}\)

D

\(\frac{T_o - T_1}{T_s - T_o}\)

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3

2009 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2009

In a double pipe heat exchanger the outer diameter of the inner pipe is d₁ and the inner diameter of the outer pipe is d₂. The equivalent diameter of the annulus for heat transfer is

A

(d₁ + d₂)/2

B

(d₂² - d₁²)/d₁

C

(d₂ - d₁)

D

(d₂² - d₁²)/d₁d₂

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4

2010 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2010

Two faces of a metal plate having thermal conductivity 17 W m⁻¹ K⁻¹ and thickness 10 mm are maintained at 80°C and 100°C. If the thickness of the plate is increased by 20% and the temperature of the hotter face is increased to 120°C, then the percent increase in heat flux under steady state heat transfer is

A

20.67

B

40.00

C

59.99

D

66.67

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5

2014 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2014

Fish fillet having 84% moisture (wet basis) is frozen from top using an air blast freezer maintained at –32°C. The initial temperature of the fillet (density 1050 kg m⁻³) is –2°C (freezing point). Convective heat transfer coefficient of air is 25 Wm⁻² K⁻¹, thermal conductivity of frozen fish is 1.0 Wm⁻¹ K⁻¹ and latent heat of crystallization is 340 kJ kg⁻¹. The freezing time, in min, for a 20 mm thick block of fish fillet weighing 1 kg is ________

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6

2014 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2014

A 50 mm thick pack of farm fresh berries is cooled at one side from 24°C to 7°C. The relevant properties of berries are: density 1025 kg m⁻³, specific heat 3.78 kJ kg⁻¹ K⁻¹, convective heat transfer coefficient 30 Wm⁻²K⁻¹, and thermal conductivity 0.3 Wm⁻¹K⁻¹. The Fourier number for a cooling span of 30 min is ____________

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7

2015 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2015

A dilute pineapple juice is heated in a double pipe heat exchanger from 28 °C to 75 °C by heat exchanging with hot water flowing in shell in counter current direction. Hot water is entering the shell at 95 °C and leaving at 85 °C. The log mean temperature difference (°C) is __________

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8

2016 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2016

Condensing steam is used to heat vegetable oil in a double pipe co-current heat exchanger. If the inlet and outlet temperature of steam are T_hi and T_ho, and for vegetable oil T_ci and T_co respectively, the log mean temperature difference (ΔT_lm) will be _____.

A

\(\frac{T_{hi} - T_{co} - (T_{ho} - T_{ci})}{\ln \frac{T_{hi} - T_{co}}{T_{ho} - T_{ci}}}\)

B

\(\frac{(T_{hi} - T_{co}) - (T_{ho} - T_{ci})}{\ln \frac{T_{hi} - T_{co}}{T_{ho} - T_{ci}}}\)

C

\(\frac{(T_{hi} - T_{co}) - (T_{ho} - T_{ci})}{\ln \frac{T_{hi} - T_{ci}}{T_{ho} - T_{co}}}\)

D

\(\frac{T_{hi} - T_{co} - (T_{ho} - T_{ci})}{\ln \frac{T_{hi} - T_{ci}}{T_{ho} - T_{co}}}\)

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9

2017 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2017

Water flowing at a rate of 1 kg/min is heated from 12 to 80 °C with flue gas supplied at a rate of 3 kg/min. The temperature and specific heat of the flue gas are 180 °C and 1.05 kJ/kg.K, respectively. If specific heat of water is 4.2 kJ/kg.K and the flow is parallel, then the logarithmic mean temperature difference will be _____ °C.

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10

2017 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2017

A 12 mm thick fish fillet having 80% moisture content (wet basis) is to be frozen using a plate freezer. The plates are maintained at -35 °C. Assume the heat transfer coefficient, initial freezing temperature and latent heat of fusion are 2.0 W/m²·K, -2 °C and 330 kJ/kg, respectively. If the density and thermal conductivity of frozen fish fillet are 1050 kg/m³ and 1.48 W/m·K, respectively, the time required to freeze the fillet from the initial freezing temperature is ____ h.

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11

2018 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2018

Green pea (average diameter 0.8 cm) is frozen in a blast freezer operating at -40°C and with a surface heat transfer coefficient of 30 W m⁻² K⁻¹. The thermal conductivity of pea is 2.5 W m⁻¹K⁻¹, and latent heat of crystallization is 2.74 x 10⁵ kJ kg⁻¹. If the freezing point of pea is -1°C and the density is 1160 kg m⁻³, the freezing time in minutes will be ______. (up to two decimal points)

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12

2019 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2019

A mixed fruit beverage with 12 °Brix having specific heat of 4298 J kg⁻¹ K⁻¹ is being heated from 30 °C to 95 °C for pasteurization at a flow rate of 1000 L h⁻¹ in a tubular heat exchanger. Steam at 100 °C is used as heating medium which is converted into condensate at 100 °C. If the density of beverage is 1075 kg m⁻³ and the latent heat of steam at the given temperature is 2257 kJ kg⁻¹, the mass flow rate of steam (kg min⁻¹) is __________ (round off to 2 decimal places).

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13

2019 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2019

Fruit juice was cooled in a tubular heat exchanger from 50 °C to 7 °C using water at 2 °C, which gets heated to 5 °C. Assume, Pr = 0.72, Re = 20000 and thermal conductivity = 0.6 W m⁻¹ °C⁻¹ and no viscous effect. If pipe diameter was 10 cm, the convective heat transfer coefficient (W m⁻² °C⁻¹) is __________ (round off to 1 decimal place).

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14

2019 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2019

Freezing of 100 mm spherical meat ball with 60% moisture at 35 °C is being done in an air blast freezer maintained at -45 °C. Given, latent heat of fusion for water is 333.2 kJ kg⁻¹, thermal conductivity of meat is 1.5 W m⁻¹ °C⁻¹, convective heat transfer coefficient is 40 W m⁻² °C⁻¹, density of frozen meat is 980 kg m⁻³ and initial freezing temperature of meat ball is -10 °C. Using Plank’s equation, freezing time (h) is __________ (round off to 2 decimal places).

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15

2020 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2020

An orange juice flowing at 0.80 kg s⁻¹ enters a counter current double pipe heat exchanger at 20 °C and leaves at 72 °C. Inlet and outlet temperatures of the hot water used as heating medium in the exchanger are 81 °C and 74 °C, respectively. The specific heat of the orange juice is 3.74 kJ kg⁻¹ K⁻¹ and overall heat transfer coefficient is 492 W m⁻² K⁻¹. The heat transfer surface area (round off to 2 decimal places) will be ______ m².

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16

2021 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2021

An orange juice sample is concentrated from 10% to 40% (by weight) total soluble solids in a single effect evaporator with a feed rate of 3600 kg hr-1 at 25°C. The evaporator operates at sufficient vacuum to allow the product moisture to evaporate at 55°C. The specific heat of both feed and concentrated juice is 4.0 kJ kg-1 °C-1. If enthalpy of water vapour at 55°C is 2600 kJ kg-1, heat transfer rate through the heating surface area of the evaporator in kilowatt (in integer) will be________.

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17

2022 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2022

Apple juice flows through a steel pipe having thermal conductivity of 50 W m⁻¹ K⁻¹. The outer surface of pipe is exposed to ambient environment. The inside diameter and thickness of the pipe are 3 cm and 1.5 cm, respectively. The overall heat transfer coefficient based on inside area is 25 W m⁻² K⁻¹. If the internal convective heat transfer coefficient is 30 W m⁻² K⁻¹, the external convective heat transfer coefficient (in W m⁻² K⁻¹) will be ______ (round off to two decimal places).

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18

2023 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2023

Identify the correct pair(s) of governing law with respective process operation.

A

Stoke’s law - Mass transfer

B

Kirchhoff’s law - Radiation heat transfer

C

Fourier’s law –Conduction heat transfer

D

Fick’s law - Molecular diffusion

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19

2023 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2023

Cow milk is pasteurized at a flow rate of 1 kg.s^-1 in a counter-current heat exchanger using hot water as the heating medium. The milk enters the heat exchanger at 15 °C and exits at 50 °C. The specific heat of cow milk is 3.5 kJ.kg^-1.°C^-1 and remains constant at the inlet and exit of the heat exchanger. The inlet and exit temperatures of the hot water are 75 °C and 60 °C respectively. If the overall heat transfer coefficient is 1800 W.m^-2.°C^-1, the heat transfer surface area in m² is _____ (rounded off to 2 decimal places). Assume steady state conditions.

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20

2026 · Engineering Sciences · Food Engineering · Heat transfer

Engineering Sciences (XE) 2026

Hot oil is being cooled in a countercurrent, double-pipe heat exchanger from 410 K to 340 K by chilled water entering at 290 K and exiting the exchanger at 330 K. The Log Mean Temperature Difference (LMTD) for this heat transfer is ______K. (Round off to one decimal place)

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