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Problems: Heat Exchangers | Heat Transfer - Mechanical Engineering PDF Download

Questions for Practice (Module 8)

Q.1Under what conditions it is advantageous to use U-tube heat exchanger?
Q.2What is the physical meaning of LMTD?
Q.3Why correction factor for LMTD is required?
Q.4If we have to process a corrosive liquid in a heat exchanger, where will you prefer to send it, tube-side or shell-side of the heat exchanger. Support your answer with the reasoning.
Q.5

Show the temperature profile of a heat exchanger (condenser) where saturated water vapour is condensing in the shell side and the cold liquid is flowing in the tube side. It should be noted that the condensed water is not sub-cooled and the tube-side water is not vaporized.

Q.6

What are the different types of tube arrangements in a shell-and-tube heat exchanger? Explain the advantages and drawbacks of the arrangements.

Q.7

What is the basic difference between 1-1 and 2-4 heat exchanger? What is the basis to choose a particular type (with respect to pass) of heat exchanger.

Q.8

Liquid ammonia feed is to be pre-heated from 30° C to 60° C before pumping to the reactor. The liquid ammonia is heated with the help of another stream of hot water at 90° C. The properties of the streams may be collected from the available literatures.

Q.9

Bombay high crude oil is to be heated from 15° C to 55° C at the rate of 1,50 ton/h using a stream from the plant. The crude oil is pumped in to the tube and the heating stream is pumped into the shell side of an available heat exchanger. The heating stream enters in to the tube at 150° C and leaves the tube at 110° C. The average properties of both the fluids are given below. The available heat exchanger (1-2 pass) has shell diameter of 23¼ in. The shell has 324 tubes, ¾ in. OD, BWG 14 (wall thickness), 12 feet long arranged on 1 in. Square pitch and supported by baffles with a 25% cut, spaced at 9 in interval. You need to find the suitability of this exchanger for the purpose. What will be the allowable fouling factor?

 

Heating stream

Crude oil

cp , J/g. ° C

2.2

2

µ, cP

5.2

2.9

ρ, kg/m3

866

822

k, W/m.° C

0.12

0.138

Q.10

Hot water enters a counterflow heat exchanger at 95°C. This hot water is used to heat a cool stream of water from 8 to 40° C. The flow rate of the cool water is 1.2 kg/s, and the flow rate of the hot water is 2.7 kg/s. The overall heat-transfer coefficient is 850 W/m2°C. What is the area of the heat exchanger and its effectiveness?

The document Problems: Heat Exchangers | Heat Transfer - Mechanical Engineering is a part of the Mechanical Engineering Course Heat Transfer.
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FAQs on Problems: Heat Exchangers - Heat Transfer - Mechanical Engineering

1. What is a heat exchanger and how does it work?
Ans. A heat exchanger is a device that allows for the transfer of heat between two or more fluids at different temperatures. It works by having two separate fluid streams that are in close proximity to each other, allowing heat to transfer from one fluid to the other through conduction.
2. What are the common types of heat exchangers used in chemical engineering?
Ans. The common types of heat exchangers used in chemical engineering include shell and tube heat exchangers, plate heat exchangers, and finned tube heat exchangers. Each type has its own advantages and is suitable for different applications.
3. How can fouling affect the performance of a heat exchanger?
Ans. Fouling refers to the accumulation of unwanted deposits, such as scale or corrosion products, on the heat transfer surfaces of a heat exchanger. This can reduce the heat transfer efficiency and increase pressure drop, leading to a decrease in overall performance. Regular cleaning and maintenance are necessary to prevent or minimize fouling.
4. What is the significance of the heat transfer coefficient in heat exchangers?
Ans. The heat transfer coefficient is a measure of how effectively heat is transferred between the two fluids in a heat exchanger. It represents the rate of heat transfer per unit area and per unit temperature difference between the fluids. A higher heat transfer coefficient indicates better heat transfer efficiency and faster heat exchange.
5. What are some factors that can affect the design and sizing of a heat exchanger?
Ans. Several factors can influence the design and sizing of a heat exchanger, including the desired heat transfer rate, temperature and pressure limits, flow rates of the fluids, fluid properties, and the available space for installation. Proper consideration of these factors is essential to ensure the heat exchanger meets the required performance and operational requirements.
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