Back to Sections

Type:ALLMCQNATMSQ

Heat and Mass Transfer(18)Preservation of Food(14)

Heat and Mass Transfer

18 Questions

GATE→2026→Dairy and Food Engineering→Heat and Mass Transfer

Q1

MCQ[1 Mark]

Dimensionless parameter among the following options is (A) heat exchanger effectiveness (B) humid heat of air-water vapour mixture (C) humid volume of air-water vapour mixture (D) overall heat transfer coefficient

(A)

heat exchanger effectiveness

(B)

humid heat of air-water vapour mixture

(C)

humid volume of air-water vapour mixture

(D)

overall heat transfer coefficient

Explanation

GATE→2026→Dairy and Food Engineering→Heat and Mass Transfer

Q2

MCQ[1 Mark]

Specific heat, coefficient of viscosity, and thermal conductivity are related in the (A) Prandtl number (B) Reynolds number (C) Froude number (D) Biot number

(A)

Prandtl number

(B)

Reynolds number

(C)

Froude number

(D)

Biot number

Explanation

GATE→2026→Dairy and Food Engineering→Heat and Mass Transfer

Q3

MCQ[2 Marks]

A refrigeration system based on reverse Carnot cycle operates between −30 °C and 20 °C. The refrigeration capacity of the system is 70 kW. Heat rejected at the condenser to atmosphere (hot reservoir), in kW, is nearest to (A) 84.40 (B) 14.41 (C) 186.67 (D) 116.67

(A)

84.40

(B)

14.41

(C)

186.67

(D)

116.67

Explanation

GATE→2026→Dairy and Food Engineering→Heat and Mass Transfer

Q4

MCQ[2 Marks]

A 2 mm diameter electric wire is insulated with 2 mm thick plastic. The plastic has a thermal conductivity of 0.5 W.m−1.K−1. The wire is exposed to air at 320 K and outside convective heat transfer coefficient is 25 W.m−2.K−1. Wire surface temperature is constant at 420 K and remains unaffected by the covering. Assuming steady state heat transfer conditions, the ratio of heat loss per metre of wire length with insulation to that without insulation is nearest to (Take π = 3.14) (A) 2.58 (B) 0.39 (C) 1.87 (D) 0.54

(A)

2.58

(B)

0.39

(C)

1.87

(D)

0.54

Explanation

GATE→2025→Dairy and Food Engineering→Heat and Mass Transfer

Q5

NAT[1 Mark]

Three straight metal wires, AC, BC and CD, having same length, diameter and thermal conductivity are connected as shown in the figure. Heat flows from points 'A' and 'B' to point 'C' and from point 'C' to 'D'. Temperatures at points A, B and D are $100^{\circ}\text{C}$, $100^{\circ}\text{C}$ and $40^{\circ}\text{C}$ respectively. Assuming steady-state condition and no heat loss from the wires, the temperature at point 'C' is ___ $^{\circ}\text{C}$. (Answer in integer)

Explanation

GATE→2025→Dairy and Food Engineering→Heat and Mass Transfer

Q6

NAT[2 Marks]

A mixture of Nitrogen ($N_{2}$) and Helium (He) gases is contained in a pipe at 1.0 atm pressure and at 298 K. At one point in the pipe, the partial pressure of $N_{2}$ is 60.80 kPa and at a point 0.22 m apart, the partial pressure of $N_{2}$ is 20.31 kPa. The diffusion coefficient of the mixture is $0.612\times10^{-4}\text{ m}^{2}\cdot\text{s}^{-1}$ Considering Universal gas constant as $8314\text{ m}^{3}\cdot\text{Pa}\cdot\text{kg}\text{mol}^{-1}\cdot\text{K}^{-1}$, the steady-state flux of $N_{2}$ is $n\times10^{-6}\text{kg}\text{mol}\cdot\text{s}^{-1}\cdot\text{m}^{-2}$ The value of $n$ is ___ (Rounded off to 2 decimal places)

Explanation

GATE→2025→Dairy and Food Engineering→Heat and Mass Transfer

Q7

NAT[2 Marks]

Milk enters at $25^{\circ}\text{C}$ through inner pipe of a concentric double pipe heat exchanger. Hot water enters at $82.5^{\circ}\text{C}$ and flows countercurrently (flow rate $=1.2\text{ kg}\cdot\text{s}^{-1}$) through the annular region. The diameter of inner pipe, length of the pipe and average overall heat transfer coefficient are 60 mm, 6 m, and $2100\text{ W}\cdot\text{m}^{-2}\cdot\text{K}^{-1}$, respectively. The average values of specific heat capacity of water and milk are $4.18\text{ kJ}\cdot\text{kg}^{-1}\cdot\text{K}^{-1}$ and $3.95\text{ kJ}\cdot\text{kg}^{-1}\cdot\text{K}^{-1}$, respectively. The effectiveness of the heat exchanger is 0.572 and the NTU is 1.01. Assuming the steady-state condition and considering $\pi$ as 3.14, the temperature of hot water at exit of the pipe is ___ $^{\circ}\text{C}$. (Rounded off to 1 decimal place)

Explanation

GATE→2024→Dairy and Food Engineering→Heat and Mass Transfer

Q8

MCQ[1 Mark]

Critical thickness of insulation ($r_{cr}$) for a pipe having thermal conductivity ($k$) and outer convective heat transfer coefficient ($h_{o}$) is

(A)

2k/h_0

(B)

k/h_o

(C)

h_o/k

(D)

2h_o/k

Explanation

GATE→2024→Dairy and Food Engineering→Heat and Mass Transfer

Q9

MCQ[2 Marks]

Match the following in material types (Column I) with their rheological properties (Column II). Column I: P. Bingham plastic, Q. Dilatant, R. Pseudoplastic, S. Newtonian Column II: 1. Viscosity increases with increase in shear rate 2. Finite yield stress 3. Shear rate proportional to shear stress 4. Viscosity decreases with increase in shear rate

(A)

P-1, Q-2, R-4, S-3

(B)

P-2, Q-1, R-4, S-3

(C)

P-2, Q-4, R-1, S-3

(D)

P-4, Q-3, R-2, S-1

Explanation

GATE→2024→Dairy and Food Engineering→Heat and Mass Transfer

Q10

NAT[2 Marks]

A steam jacketed kettle is filled with a 250 kg liquid food with a specific heat of $3.1\text{ kJ}\cdot\text{kg}^{-1}\cdot\text{K}^{-1}$. Steam used at $121^{\circ}\text{C}$ has a heat transfer coefficient of $2\text{ W}\cdot\text{m}^{-2}\cdot\text{K}^{-1}$. The area of heat transfer is $0.15\text{ m}^{2}$. Using lumped capacity method, the time required to heat the product from $30^{\circ}\text{C}$ to $95^{\circ}\text{C}$, in minutes, is ___ (Rounded off to 2 decimal places)

Explanation

GATE→2024→Dairy and Food Engineering→Heat and Mass Transfer

Q11

NAT[2 Marks]

Fruit juice entering at $30^{\circ}\text{C}$ is being pasteurized in a double pipe counter flow heat exchanger using hot water entering at $97^{\circ}\text{C}$ and leaving at $65^{\circ}\text{C}$. Specific heat of juice and water are $3.8\text{ kJ}\cdot\text{kg}^{-1}\cdot\text{K}^{-1}$ and $4.2\text{ kJ}\cdot\text{kg}^{-1}\cdot\text{K}^{-1}$, respectively. Flow rate of juice is $0.3\text{ kg}\cdot\text{s}^{-1}$ and that of water is $0.4\text{ kg}\cdot\text{s}^{-1}$. Considering an overall heat transfer coefficient of $1\text{ kW}\cdot\text{m}^{-2}\cdot\text{K}^{-1}$ the area of heat exchanger required, in $\text{m}^{2}$, is ___ (Rounded off to 3 decimal places)

Explanation

GATE→2023→Dairy and Food Engineering→Heat and Mass Transfer

Q12

MCQ[1 Mark]

The log mean temperature difference (LMTD) correction factor is not required during heat transfer rate calculation in

(A)

plate heat exchanger

(B)

1 shell pass and 1 tube pass heat exchanger

(C)

1 shell pass and 2 tube pass heat exchanger

(D)

2 shell pass and 4 tube pass heat exchanger

Explanation

GATE→2023→Dairy and Food Engineering→Heat and Mass Transfer

Q13

MSQ[2 Marks]

Dimensionless numbers play an important role in correlating transfer coefficients during forced convection. In relation to the dimensionless numbers, the correct statement(s) is/are

(A)

Prandtl number in heat transfer is analogous to Schmidt number in mass transfer

(B)

Small value of Prandtl number signifies lower thermal diffusion as compared to momentum diffusion

(C)

Prandtl number is the ratio of momentum diffusivity to the thermal diffusivity of the fluid

(D)

Lewis number is the product of Schmidt number and Prandtl number

Explanation

GATE→2023→Dairy and Food Engineering→Heat and Mass Transfer

Q14

NAT[2 Marks]

The apparent wall shear stress in a 0.6 m long pipe line carrying refined oil is 12.5 Pa. If the pressure drop along the length is 300 Pa and flow rate is $0.25\text{ m}^{3}\text{s}^{-1}$, the absolute viscosity of oil in $10^{-3}$ Pas is ___ (rounded off to 3 decimal places).

Explanation

GATE→2023→Dairy and Food Engineering→Heat and Mass Transfer

Q15

NAT[2 Marks]

A copper ball and a steel ball having diameters $d_{1}$ and $d_{2}$, respectively, are initially at a uniform temperature of $200^{\circ}\text{C}$. Both the balls are exposed to the atmosphere at $30^{\circ}\text{C}$. If both the balls attain a temperature of $120^{\circ}\text{C}$ after equal exposure duration, then the ratio of $d_{1}$ to $d_{2}$ is ___ (rounded off to 3 decimal places). Assume Biot Number to be less than 0.1. The thermo-physical properties of copper and steel are given below: [Table: Copper & Steel density, specific heat, thermal conductivity]

Explanation

GATE→2022→Dairy and Food Engineering→Heat and Mass Transfer

Q16

NAT[2 Marks]

A falling ball viscometer is used to determine the dynamic viscosity of sunflower oil. The viscometer has a tube length of 10 cm with the ball diameter of 0.68 mm. The densities of oil and the ball are $921\text{ kg }\text{m}^{-3}$ and $2420\text{ kg }\text{m}^{-3}$, respectively. If the ball takes 44.5 s to fall from top of the tube, the viscosity of the oil in Pas is [round off to three decimal places]. (Take $g=9.81\text{ms}^{-2}$)

Explanation

GATE→2022→Dairy and Food Engineering→Heat and Mass Transfer

Q17

NAT[2 Marks]

A walk-in deep freezer wall is made of 120 mm thick brick layer on the outside followed by 75 mm thick concrete and 50 mm thick cork layers inside. The mean temperatures measured over inside and outside wall surfaces are $-18^{\circ}\text{C}$ and $24^{\circ}\text{C}$ respectively. The thermal conductivity of brick, concrete and cork are 0.69, 0.76 and 0.043 W $\text{m}^{-1}\text{K}^{-1}$, respectively. Considering one square meter wall surface area, the heat transfer rate in W is [round off to one decimal place]

Explanation

GATE→2022→Dairy and Food Engineering→Heat and Mass Transfer

Q18

NAT[2 Marks]

In an effort to conserve energy, a grain dryer is being modified to reuse a part $(10\text{ m}^{3}\text{s}^{-1})$ of the exhaust airflow at $70^{\circ}\text{C}$ and 30% relative humidity. This part of exhaust is mixed with 20 $\text{m}^{3}\text{s}^{-1}$ of ambient air at $30^{\circ}\text{C}$ and 60% relative humidity. The details of the two air-stream conditions are given below [Table provided]. The absolute humidity of the mixed air will be [round off to three decimal places]

Explanation

Preservation of Food

14 Questions

GATE→2026→Dairy and Food Engineering→Preservation of Food

Q19

MCQ[1 Mark]

It is given that the water activity of a food is equal to the relative humidity of the atmosphere that is in equilibrium with the food. The partial pressure of water vapour of the food at a specific temperature is (A) equal to the partial pressure of water vapour in air (B) lesser than the partial pressure of water vapour in air (C) greater than the partial pressure of water vapour in air (D) not dependent on the partial pressure of water vapour in air

(A)

equal to the partial pressure of water vapour in air

(B)

lesser than the partial pressure of water vapour in air

(C)

greater than the partial pressure of water vapour in air

(D)

not dependent on the partial pressure of water vapour in air

Explanation

GATE→2026→Dairy and Food Engineering→Preservation of Food

Q20

MCQ[2 Marks]

Pasteurisation of milk can be carried out either at 91 °C for 3 s or at 73 °C for 30 s to inactivate vegetative cells of microorganism(s). The sterilisation value is 10 in both the cases. Thermal death time constant (z value) for reference temperatures of 73 °C and 91°C, in °C, is nearest to (A) 18.0 (B) 1.8 (C) 9.0 (D) 0.9

(A)

18.0

(B)

1.8

(C)

9.0

(D)

0.9

Explanation

GATE→2025→Dairy and Food Engineering→Preservation of Food

Q21

MCQ[1 Mark]

The condition of refrigerant at the exit of the compressor in a vapor compression refrigeration system is:

(A)

Saturated liquid

(B)

Wet vapor

(C)

Dry saturated vapor

(D)

Superheated vapor

Explanation

GATE→2025→Dairy and Food Engineering→Preservation of Food

Q22

MSQ[1 Mark]

In general, result(s) of blanching fresh fruits and vegetables is/are:

(A)

Complete elimination of microorganisms

(B)

Removal of entrapped air pockets between plant tissues

(C)

Leaching of nutrients

(D)

Inactivation of enzymes

Explanation

GATE→2025→Dairy and Food Engineering→Preservation of Food

Q23

MSQ[2 Marks]

The assumption(s) which is/are not correct for deriving the Plank's equation for estimation of food freezing time:

(A)

Ice front moves from the freezing medium into the food block at a uniform rate.

(B)

Physical property data of food material are accurate.

(C)

Initially the whole food material is at a distinct freezing point.

(D)

Sensible heat changes during the freezing process are sufficiently high.

Explanation

GATE→2025→Dairy and Food Engineering→Preservation of Food

Q24

NAT[2 Marks]

In an inoculated pack study, 0.5 kg peas per can are thermally processed at $121^{\circ}\text{C}$. One group of cans contain Clostridium spp. spores with initial spore level of $5\times10^{10}$ per can. Another group of cans contain Bacillus spp. spores. It is desired to have spoilage probability of 5 in 100 cans after thermal processing. The decimal reduction time of Clostridium spp. and Bacillus spp. at $121^{\circ}\text{C}$ are 2.5 minutes and 6.0 minutes, respectively. If all the cans receive same lethality, the initial number of spores of Bacillus spp. per g of peas is ___ (Answer in integer).

Explanation

GATE→2024→Dairy and Food Engineering→Preservation of Food

Q25

NAT[1 Mark]

Freshly harvested shrimps of 100 kg having initial temperature of $25^{\circ}\text{C}$ are frozen to $-18^{\circ}\text{C}$. The specific heat ($c_{p}$) of shrimp above and below freezing point ($0^{\circ}\text{C}$) are $3.64\text{ kJ}\cdot\text{kg}^{-1}\cdot^{\circ}\text{C}^{-1}$ and $2.01\text{ kJ}\cdot\text{kg}^{-1}\cdot^{\circ}\text{C}^{-1}$, respectively. Considering the latent heat of fusion as $240\text{ kJ}\cdot\text{kg}^{-1}$, the heat load removed during the process, in kJ, is ___ (Rounded off to 1 decimal place)

Explanation

GATE→2024→Dairy and Food Engineering→Preservation of Food

Q26

MCQ[2 Marks]

The decimal reduction time $D_{121}$ and the z value of thermophilic spores in milk were found to be 60 seconds and $11^{\circ}\text{C}$, respectively. Heating time required at $141^{\circ}\text{C}$ for a 10 log cycle reduction in population, in seconds, is (Rounded off to 2 decimal places)

(A)

A

(B)

B

(C)

C

(D)

9.12

Explanation

GATE→2024→Dairy and Food Engineering→Preservation of Food

Q27

NAT[2 Marks]

Mango pulp at an initial temperature of $25^{\circ}\text{C}$ 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 $95^{\circ}\text{C}$. The latent heat of vaporization of water at $95^{\circ}\text{C}$ and at standard atmospheric pressure is $2250\text{ kJ}\cdot\text{kg}^{-1}$. Considering the specific heat of mango pulp as $3.8\text{ kJ}\cdot\text{kg}^{-1}\cdot^{\circ}\text{C}^{-1}$, the energy required for drying per kg of mango pulp, in kJ, is ___ (Rounded off to 1 decimal place)

Explanation

GATE→2024→Dairy and Food Engineering→Preservation of Food

Q28

NAT[2 Marks]

Fish fillets at $-1^{\circ}\text{C}$ are being frozen in Individual Quick Freezing (IQF) system using air at $-40^{\circ}\text{C}$. The product has a characteristic dimension of 10 cm with a density of $1200\text{ kg}\cdot\text{m}^{-3}$. Thermal conductivity of the product is $2.5\text{ W}\cdot\text{m}^{-2}\cdot\text{K}^{-1}$ [Note: units of k], the convective heat transfer coefficient is 100 and the latent heat of fusion is $300\text{ kJ}\cdot\text{kg}^{-1}$. If the fillet is considered as an infinite plate, the freezing time, in minutes, is ___ (Rounded off to 2 decimal places)

Explanation

GATE→2023→Dairy and Food Engineering→Preservation of Food

Q29

MCQ[1 Mark]

The microbial death kinetics for a food suspension follows the equation: $\log\frac{N_{0}}{N}=1+\frac{t-t_{l}}{D}$ where $N_{0}=$ initial microbial load, $N=$ microbial load after time t, $t_{l}=$ lag time and $D=$ decimal reduction time. The correct statement for this equation is

(A)

the time required to reduce 10% of the initial population is lag time.

(B)

the time required to reduce the initial 90% of population is lag time

(C)

time required to kill the first 90% population is lower than D value at the same temperature

(D)

lag time approaches D value as $N_{0}$ becomes smaller and temperature decreases.

Explanation

GATE→2023→Dairy and Food Engineering→Preservation of Food

Q30

MCQ[2 Marks]

The rotor shaft of an ice cream freezer consists of 3 scraper blades. The temperature difference between the ice cream mix and the refrigerant during freezing of ice cream is $30^{\circ}\text{C}$ Density and latent heat of fusion of ice are $917\text{ kg }\text{m}^{-3}$ and $335\text{ kJ }\text{kg}^{-1}$, respectively. The overall heat transfer coefficient is $2000\text{ kJ }\text{m}^{-2}\text{h}^{-1~0}\text{C}^{-1}$. If the maximum thickness of ice formed before being scraped off is $10\mu\text{m}$ the minimum speed of the scraper shaft in rpm is

(A)

88

(B)

109

(C)

121

(D)

149

Explanation

GATE→2023→Dairy and Food Engineering→Preservation of Food

Q31

NAT[2 Marks]

The carrot slices (water activity $=0.89$) are to be preserved using osmo-dehydration. Addition of salt (NaCl) to 20% sucrose solution (water activity $=0.987$) reduces the water activity to 0.85. Percentage of NaCl added to the solution is ___ (rounded off to 2 decimal places). Consider molecular mass of Sucrose $=342$ and molecular mass of NaCl $=58.44$

Explanation

GATE→2022→Dairy and Food Engineering→Preservation of Food

Q32

NAT[1 Mark]

A milk sample contains $4\times10^{5}$ spores of C. botulinum (D value of 1.2 min at $121.1^{\circ}C)$ and $7\times10^{6}$ spores of L. monocytogenes (D value of 0.9 min at $121.1^{\circ}C)$ per mL. If the milk is heated at a uniform temperature of $121.1^{\circ}C$ to obtain a probability of spoilage of 1 in 1000 cans, the minimum heating duration in minutes is [round off to two decimal places]

Explanation