Dairy Engineering Questions and Answers – Heat Exchangers – 2

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This set of Dairy Engineering Questions and Answers for Freshers focuses on “Heat Exchangers – 2”.

1. Which among the following surface promote heat transfer?
a) Plain
b) Shiny
c) Corrugated
d) Wet
View Answer

Answer: c
Explanation: The partition is often corrugated to create a more turbulent flow, which results in better heat transfer. The thickness is also important. The thinner the partition, the better the heat transfers.
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2. _______ Heat exchanger is needed for cream than for milk, if capacities and temperature programs are identical.
a) Larger
b) Smaller
c) Similar
d) Stagnant
View Answer

Answer: a
Explanation: A liquid with high viscosity develops less turbulence when it flows through the heat exchanger compared to a product with lower viscosity. This means a larger heat exchanger is needed, everything else being constant.

3. Which of the following material is used for heat transfer in the dairy industry?
a) Iron
b) Platinum
c) Copper
d) Stainless steel
View Answer

Answer: d
Explanation: For food processing, the normal material is stainless steel. It has fairly good heat transfer characteristics.

4. The rate of buildup of fouling does not depend on which of the following?
a) Milk quality and Air content of the product
b) Temperature difference between product and heating medium
c) Pressure conditions in the heating section
d) Thickness of stainless steel
View Answer

Answer: d
Explanation: The rate of buildup of fouling depends on many factors such as temperature difference between product and heating medium, Milk quality, Air content of the product and Pressure conditions in the heating section.

5. What is the method of using the heat of a hot liquid, such as pasteurized milk, to preheat cold incoming milk?
a) Heating
b) Cooling
c) Regeneration
d) Standardization
View Answer

Answer: c
Explanation: Regeneration (Heating): The raw cold incoming milk is partially and indirectly heated by the hot outgoing milk (milk-to-milk regeneration). This adds to the economy.
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6. Zigzag tube in heat treatment is used for which purpose?
a) Fouling
b) Standardization
c) Holding for a long holding time
d) Discard
View Answer

Answer: c
Explanation: Correct heat treatment requires that the milk is held for a specified time at pasteurization temperature. This is done in an external holding cell. A holding cell usually consists of a pipe arranged in a spiral or zigzag pattern and often covered by a metal shroud to prevent people from being burned if they touch the holding cell.

7. Which heat exchanger used for heating and cooling viscous, sticky and lumpy products?
a) Plate heat exchanger
b) Tubular heat exchanger
c) Scraped surface heat exchanger
d) Spray dryer
View Answer

Answer: c
Explanation: The scraped-surface heat exchange is designed for heating and cooling viscous, sticky and lumpy products and for crystallization of products. The operating pressures on the product side are high, often as much as 40 bar. All products that can be pumped can therefore be treated.

8. PHE (Plate Heat Exchanger) is more efficient in terms of heat transfer than THE (Tubular Heat Exchanger).
a) True
b) False
View Answer

Answer: a
Explanation: The given statement is true. From the standpoint of heat transfer, the tubular heat exchanger is less efficient than a plate heat exchanger.

9. Which of the following is/are the category of Tubular Heat exchanger?
a) Multi/mono channel
b) Multi/mono tube
c) Cubical channel
d) Multi/mono channel and Multi/mono tube
View Answer

Answer: d
Explanation: Tubular heat exchangers (THE) are in some cases used for pasteurization/ UHT treatment of dairy products. Tubular heat exchangers are available in two fundamentally different types; multi/mono channel and multi/mono tube.
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10. Heat exchanger characterized by pack of stainless steel in a frame is ________
a) Plate heat exchanger
b) Tubular heat exchanger
c) Scraped surface heat exchanger
d) Spray dryer
View Answer

Answer: a
Explanation: Most heat treatment of dairy products is carried out in plate heat exchangers. The plate heat exchanger (often abbreviated PHE) consists of a pack of stainless steel plates clamped in a frame.

11. Scraped Heat exchanger has a ______ design.
a) Simple
b) Vertical
c) Planar
d) Horizontal
View Answer

Answer: a
Explanation: Thanks to the vertical design, the product can be displaced by water with minimum intermixing which helps assure product recovery at the end of every run. Following this, completely drainage facilitates CIP and product changeover.

12. Plate heat exchanger was patented in which year?
a) 1890
b) 1990
c) 2009
d) 1790
View Answer

Answer: a
Explanation: The plate heat exchanger was patented in 1890 by the German inventors Langen and Hundhausen.

13. “R” in the below equation refers to what?
dairy-engineering-questions-answers-freshers-q13
a) Recycle
b) Regeneration efficiency
c) Regression
d) Reuse
View Answer

Answer: b
Explanation: We can take the simplest operating profile – heat treatment of raw milk –as an example. Using this formula: where R = regenerative efficiency %, tr = milk temperature after regeneration, ti = temperature of raw incoming milk, tp = pasteurization and temperature.
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14. The unwanted buildup of material on a surface is called?
a) Secretion
b) Plating
c) Fouling
d) Layering
View Answer

Answer: c
Explanation: Fouling is the accumulation of unwanted material on solid surfaces to the detriment of function. Dairy industry also experiences fouling problems by chemical reactions.

15. Heat must be supplied to a substance in order to increase its temperature by 1°C is called?
a) Plate heat
b) Specific heat
c) Heat of chemical reaction
d) Heat of crystallization
View Answer

Answer: b
Explanation: Specific heat, cp, is also determined by the product. The specific heat is basically the amount of heat per unit mass required to raise the temperature by one degree Celsius.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn