Download GTU (Gujarat Technological University) BE/BTech (Bachelor of Engineering / Bachelor of Technology) 2018 Winter 4th Sem New 2141407 Food Drying And Dehydration Previous Question Paper
1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?IV (NEW) EXAMINATION ? WINTER 2018
Subject Code:2141407 Date:12/12/2018
Subject Name:Food Drying & Dehydration
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) What is equilibrium moisture content? Write its significance also. 03
(b) Differentiate between direct and indirect dryer. List out the characteristics
and properties of various types of dry powders and particulate.
04
(c) Describe the drying rates periods for agricultural products. Derive
equation for constant rate drying.
07
Q.2 (a) List out all the unique features of drying. 03
(b) Discuss Parallel, Series and Krisher models to predict thermal
conductivity.
04
(c) The initial moisture content of a food product is 70% (wet basis), and the
critical moisture content is 25% (wet basis). If the constant drying rate is
0.1 kg H2O/(m
2
s), compute the time required for the product to begin the
falling rate drying period. The product has a cube shape with 5-cm sides,
and the initial product density is 900 kg/m
3
.
07
OR
(c) Draw the following generalised curve for the agricultural materials:
(i) Drying curve
(ii) Drying rate curve
(iii) Water activity stability diagram
(iv) Moisture content and bed depth for different inlet temperature
07
Q.3 (a) Compute the equilibrium moisture content for popcorn at 20?C and 50%
relative humidity. Given that constant c = 6.5 x 10
-4
and n=1.8
03
(b) What is moisture sorption curve? Describe the phenomena of hysteresis. 04
(c) (i) Define wet and dry basis moisture content and write the expression to
convert wet basis to dry basis moisture content.
(ii) 500 kg of paddy at 22 % moisture content (wb) is dried to14 %
moisture content (wb) for milling. Calculate the amount of moisture
removed in drying
07
OR
Q.3 (a) Discuss in brief the features of solar drying. 03
(b) Give a detail classification of dryers used in food industry. 04
(c) A food containing 80% water is to be dried at 100?C down to moisture
content of 10%. If the initial temperature of the food is 21?C, calculate the
quantity of heat energy required per unit weight of the original material,
for drying under atmospheric pressure. The latent heat of vaporization of
water at 100?C and at standard atmospheric pressure is 2257 kJ kg
-1
. The
specific heat capacity of the food is 3.8 kJ kg
-1
?C
-1
and of water is 4.186
kJ kg
-1
?C
-1
. Find also the energy requirement/kg water removed.
07
Q.4 (a) Discuss the advantage of osmotic dehydration. 03
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1
Seat No.: ________ Enrolment No.___________
GUJARAT TECHNOLOGICAL UNIVERSITY
BE - SEMESTER ?IV (NEW) EXAMINATION ? WINTER 2018
Subject Code:2141407 Date:12/12/2018
Subject Name:Food Drying & Dehydration
Time: 02:30 PM TO 05:00 PM Total Marks: 70
Instructions:
1. Attempt all questions.
2. Make suitable assumptions wherever necessary.
3. Figures to the right indicate full marks.
Q.1 (a) What is equilibrium moisture content? Write its significance also. 03
(b) Differentiate between direct and indirect dryer. List out the characteristics
and properties of various types of dry powders and particulate.
04
(c) Describe the drying rates periods for agricultural products. Derive
equation for constant rate drying.
07
Q.2 (a) List out all the unique features of drying. 03
(b) Discuss Parallel, Series and Krisher models to predict thermal
conductivity.
04
(c) The initial moisture content of a food product is 70% (wet basis), and the
critical moisture content is 25% (wet basis). If the constant drying rate is
0.1 kg H2O/(m
2
s), compute the time required for the product to begin the
falling rate drying period. The product has a cube shape with 5-cm sides,
and the initial product density is 900 kg/m
3
.
07
OR
(c) Draw the following generalised curve for the agricultural materials:
(i) Drying curve
(ii) Drying rate curve
(iii) Water activity stability diagram
(iv) Moisture content and bed depth for different inlet temperature
07
Q.3 (a) Compute the equilibrium moisture content for popcorn at 20?C and 50%
relative humidity. Given that constant c = 6.5 x 10
-4
and n=1.8
03
(b) What is moisture sorption curve? Describe the phenomena of hysteresis. 04
(c) (i) Define wet and dry basis moisture content and write the expression to
convert wet basis to dry basis moisture content.
(ii) 500 kg of paddy at 22 % moisture content (wb) is dried to14 %
moisture content (wb) for milling. Calculate the amount of moisture
removed in drying
07
OR
Q.3 (a) Discuss in brief the features of solar drying. 03
(b) Give a detail classification of dryers used in food industry. 04
(c) A food containing 80% water is to be dried at 100?C down to moisture
content of 10%. If the initial temperature of the food is 21?C, calculate the
quantity of heat energy required per unit weight of the original material,
for drying under atmospheric pressure. The latent heat of vaporization of
water at 100?C and at standard atmospheric pressure is 2257 kJ kg
-1
. The
specific heat capacity of the food is 3.8 kJ kg
-1
?C
-1
and of water is 4.186
kJ kg
-1
?C
-1
. Find also the energy requirement/kg water removed.
07
Q.4 (a) Discuss the advantage of osmotic dehydration. 03
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2
(b) What are the major chemical changes that take place during drying of food
materials?
04
(c) A cabinet dryer is being used to dry a food product from 70 % moisture
content (w.b.) to 6% moisture content (w.b.). The drying air enters the
system at 54
0
C and 10% RH and leaves at 30
0
C and 70% RH. The product
temperature is 25
0
C throughout. Calculate the quantity of air required for
drying on the basis of 1 kg of product solid. Given absolute humidity of
air at
30
0
C & 70% RH=0.0186 kg H2O/kg dry air
54
0
C & 10% RH=0.0094 kg H2O/kg dry air
07
OR
Q.4 (a) Define thin layer and deep bed drying. 03
(b) Describe the physical properties of dried foods. 04
(c) Write short notes on:
(i) Water activity
(ii) Rehydration ratio
(iii) Shrinkage during drying
(iv) Heat utilization factor
07
Q.5 (a) What are features of fluidized bed dryer? 03
(b) Describe the principle for selection of dryer in food industry. 04
(c) Explain the construction, working and application of following:
(i) Freeze Dryer
(ii) Spray Dryer
07
OR
Q.5 (a) Explain the concept of hybrid drying. 03
(b) What is heat pump dryer? Explain its working. 04
(c) Describe the construction and features of super heated steam drying? 07
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This post was last modified on 20 February 2020