Food Processing Unit Operations Objective Questions & Answers 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
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: d
Clarification: 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
Answer: c
Clarification: 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