# Food Processing Unit Operations Questions and Answers – Heat Transfer Applications – Thermal Properties of Food

This set of Food Processing Unit Operations Objective Questions & Answers focuses on “Heat Transfer Applications – Thermal Properties of Food”.

1. Specific Heat (kJ/kg K) of apple is ________
a) 1.88
b) 1.67
c) 1.76
d) 1.42

Explanation: Specific Heat (kJ/kg K) of apple is 1.88. Specific Heat (kJ/kg K) of beef is 1.67, Specific Heat (kJ/kg K) of banana is 1.76 and Specific Heat (kJ/kg K) of bread is 1.42.

2. The specific heat of a material can be determined by ______________
a) calorimetry
b) manometers
c) barometers
d) anemometer

Explanation: The specific heat of a material can be determined by calorimetry. Manometer, barometers are used in measuring the pressure of the fluid. Anemometer is used in measuring the wind speed and also the direction of the wind.

3. Thermal energy is transported through the molecules due to _______and _______
a) lattice waves, free electrons
b) lattice waves, free protons
c) free protons, free electrons
d) lattice waves, longitudinal waves

Explanation: Thermal energy is transported through the molecules due to lattice waves and free electrons. In pure metals, the conduction of heat is based on the flow of free electrons and the effect of lattice waves is considered as negligible. In alloys and nonmetallic solids, since they are only few free electrons, conduction of heat is due to lattice vibrations in between the molecules.

4.________ is the heat content in a system per unit mass.
a) Specific heat
b) Enthalpy
c) Entropy
d) Latent heat

Explanation: Enthalpy is the heat content in a system per unit mass. Its unit is J/kg in the SI system. It is a thermodynamic property that is governed by the state of the system and it is expressed as H=U+PV, where H is the enthalpy, U is internal energy, and P is pressure and V is volume.

5. The effect of ______on the system is seen only as a phase change like the melting of ice.
a) Specific heat
b) Enthalpy
c) Entropy
d) Latent heat

Explanation: Latent heat is the also known as hidden energy. It can be defined as the heat that is released or absorbed by a system during constant temperature process is called latent heat. The effect is seen only as a phase change like boiling of water or the melting of ice.

6. Are these statements about the specific heat true?
Statement 1: Specific heat of ice is double the specific heat of water.
Statement 2: Specific heat of foods decreases during freezing.
a) True, False
b) True, True
c) False, True
d) False, False

Explanation: Specific heat of ice is 2.1 kJ/kg K and specific heat of water. 4.218 kJ/kg K. Therefore the specific heat of ice is half of the specific heat of water. Specific heat of foods decreases during freezing as there is a continuous phase change from water to ice.

7. Which of the following is not a thermal property in foods?
a) Surface heat transfer coefficient
b) Thermal diffusivity
c) Specific volume
d) Entropy

Explanation: The surface heat transfer coefficient is not a thermal property. It is required to design heat transfer equipment for processing foods where convection is involved. It depends on the fluid velocity, product size and shape, surface roughness, arrangement and packaging.

8.______ is the ability of a material to transmit a thermal disturbance.
a) Specific heat
b) Thermal diffusivity
c) Entropy
d) Latent heat

Explanation: Thermal diffusivity is the ability of a material to transmit a thermal disturbance. It determines heat propagation and diffusion through a material. It helps in estimating the process time of canning, cooking and cooling. Water content, composition, temperature and porosity affect thermal diffusivity.

9. Who discovered latent heat?
a) Joseph Black
b) Josiah Willard Gibbs
c) Henri Becquerel
d) Stephen Gray

Explanation: Joseph Black discovered latent heat. Josiah Willard Gibbs discovered enthalpy. Henri Becquerel discovered radiation. Stephen Gray discovered electrical conduction.

10. Which liquid has highest latent heat of vaporization?
a) Water
b) Alcohol
c) Oil
d) Mecury

Explanation: Water has highest latent heat of vaporization. It is determined bythe extent of the latent heat on the molecules and molecular bonding in liquid and solid states.

Sanfoundry Global Education & Learning Series – Food Processing Unit Operations.

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