# Heat Transfer Operations Questions and Answers – Dryers – Temperature Profile and Drying Curves

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This set of Heat Transfer Operations Multiple Choice Questions & Answers (MCQs) focuses on “Dryers – Temperature Profile and Drying Curves”.

Explanation: The correct diagram given in the answer correctly defines the heating region, the constant drying region and the falling region with most accuracy. Hence that diagram is the most correct.

2. That point when the humidity decreases linearly with the drying conditions is known as __________
a) Constant drying period
b) Falling-rate period
c) Heating region
d) Critical region

Explanation: Falling rate period is the moment from which the drying rate decreases as the moisture free for evaporation now move to the core and is unavailable for drying.

3. Name the following region of the drying curve. a) Critical drying rate region
b) Constant drying region
c) Critical temperature region
d) Critical humidity region

Explanation: The point of critical moisture content is the moment when the water stops to dry in the drying curve/ where the constant drying region ends and the drying rate becomes constant before falling.
Explanation: The correct temperature plot defines the batch drying process completely, the temperature first increases, is constant for constant drying process, increases slightly with the end of constant drying region and then sharply for falling period.
Explanation: The correct temperature plot defines the Continuous steady state drying process completely, the temperature first increases, is constant for constant drying process, increases slightly with the end of constant drying region and then sharply for falling period. The Continuous steady state drying process has longer constant drying period.

6. What do we understand by the initial heating period of the drying curve?
a) Preheating with the feed with large evaporation rate
b) Preheating the feed but evaporation is negligible
c) Temperature rises almost linearly and evaporation too increases linearly
d) Temperature falls almost linearly and evaporation too decreases linearly

Explanation: Initial heating period of the drying curve temperature rises almost linearly and evaporation too increases linearly. The Initial heating period is represented best by the diagram given – Explanation: Initial heating period is the time during which there is constantly increasing loss in moisture and the temperature rises linearly. This is the rising rate region in the curve.

8. In which one of the following regions the moisture is available as free moisture on the surface hence evaporation rates are high?
a) Constant rate period
b) Falling rate period
c) Rising rate period
d) Critical rate period

Explanation: The constant rate period is the moment of maximum drying rate as the free moisture is at the surface and no hindrance to the evaporating fluid.
Explanation: The constant rate period is the moment of maximum drying rate as the free moisture is available at the surface and there is no hindrance to the evaporating fluid, the fluid moves from core to the surface and evaporates smoothly.

10. What happens in the falling rate period?
a) The free moisture available on the surface shrinks to the core
b) The water in the substance is available as free moisture
c) The water in the substance has completely diminished
d) The water in the substance is blocked by a membrane formed

Explanation: The falling rate period- The unbound moisture has already been lost in the constant drying region and it is the bound moisture that does not escape leading this falling period.

11. The critical moisture content is the point in which the _____________
a) Constant rate period ends
b) Constant rate period starts
c) Falling rate period ends
d) Initial heating period starts

Explanation: The falling rate period is the moment of falling/decreasing drying rate as the free moisture is no longer available at the surface and there is dry region hindrance to the evaporating fluid, the fluid does not move from the core to the surface.

12. The feed temperature during the constant rate period _________ with time.
a) Increases
b) Remains same
c) Decreases
d) Oscillates

Explanation: The feed temperature during the constant rate period remains same with time. The constant rate period temperature profile is the middle flat region – Sanfoundry Global Education & Learning Series – Heat Transfer Operations. 