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SHELL AND TUBE HEAT EXCHANGER
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 1 What are the heat transfer mechanisms involved during heat transfer from the hot fluid to the cold fluid?

  1. Conduction 
  2. Convection 
  3. Radiation 
  4. All of the above 

2 In a shell and tube heat exchanger which of the following statements is true

  1. Heat transferred to the cold fluid is more than the heat transferred from the hot fluid. 
  2. Heat transferred to the cold fluid is less than the heat transferred from the hot fluid. 
  3. Heat transferred to the cold fluid is equal to the heat transferred from the hot fluid. 
  4. None of above  

3 Which of the following is the correct expression of heat absorbed by the cold fluid?

  1. Q={m.Cp.(Tf-Ti)}2 
  2. Q=m.Cp.(Tf-Ti) 
  3. Q=m.Cp.(Tf-Ti)2 
  4. None of the above 

4 Which of the following is the correct expression of heat transfer from hot fluid to the cold fluid?

  1. Q=U.A.LMTD 
  2. Q=LMTD/UA 
  3. Q=U.A2.LMTD 
  4. None of these 

5 The dimension of heat transfer co-efficient is:-

  1. Watt / Meter2/ Kelvin  
  2. Watt /meter/Kelvin 
  3. Kelvin/meter/Watt 
  4. None of these 

6 The dimension of LMTD is same as that of:

  1. Temperature/Temperature 
  2. Temperature 
  3. Temperature2 
  4. dimensionless 

7 In a shell and tube heat exchanger the flow rate of shell side liquid inlet at steady state is?

  1. more than the shell side liquid outlet 
  2. less than the shell side liquid outlet 
  3. equal to the shell side liquid outlet. 
  4. It can be any of these 

8 In the above question the correct reason for the right answer is?

  1. Law of conservation of Energy 
  2. Law of conservation of Mass 
  3. Newton’s 1st law of motion 
  4. A known phenomenon 

9 In a shell and tube heat exchanger the diameter of shell is?

  1. larger than tube 
  2. smaller than tube 
  3. equal to tube 
  4. It may be any of these 

10 What do you mean by steady state in this experiment?

  1. The Temperature of both shell and tube are not varying along the length 
  2. The Temperature of both shell and tube are not varying with time. 
  3. Both 
  4. None of the above options 

11 The hot fluid must be necessarily passed through?

  1. the shell 
  2. the tube 
  3. Any of these 
  4. None of the above options is correct 

12 The baffles are used on which side of the heat exchanger?

  1. Shell Side 
  2. Tube Side 
  3. Both 
  4. It can be any one shell side or tube side 

13 The main purpose of using baffles in heat exchanger is?

  1. To decrease the flow rate in shell 
  2. To increase the heat transfer coefficient (U) 
  3. To increase the LMTD value 
  4. To decrease the LMTD value. 

14 Which of the following represents the correct expression for calculating LMTD?

  1. LMTD= (ΔT2- ΔT1)/log(ΔT2/ ΔT1) 
  2. LMTD= log(ΔT2/ ΔT1)/ (ΔT2- ΔT1) 
  3. LMTD=log((ΔT2- ΔT1)/ (ΔT2/ vT1)) 
  4. LMTD=log((ΔT2- ΔT1)/ (ΔT2/ ΔT1))-1 

15 On one side of a heat exchanger, air enters at 72.82ºC and leaves at 90ºC. On the other side of the heat exchanger is condensing steam at one atmosphere.The value for LMTD is

  1. 10 K  
  2. 17.18 K  
  3. 27ºC 
  4. 100ºC 

16 Shell and Tube heat exchanger is which type of heat exchanger?

  1. Direct Contact 
  2. Indirect Contact 
  3. Both 
  4. None 

17 Which of the following does not belong to the category of heat exchanger?

  1. Automobile radiators 
  2. Refrigerators 
  3. Stove’s used in households 
  4. None of the above 

18 Which of the following does not belong to the category of flows in a heat exchanger?

  1. Cross Flow 
  2. Co Current 
  3. Counter Current 
  4. Over Flow 

19 The following are the types of indirect contact heat exchangers?

  1. Regenerators 
  2. Recuperators 
  3. Both 
  4. None 

20 In which of the following types of heat exchangers the hot and cold fluids pass alternately through a space containing solid particles providing a source and a sink for heat exchange?

  1. Regenerators 
  2. Recuperators 
  3. Both 
  4. None 

21 Automobile Radiators belong to which of the following category?

  1. Direct Contact Heat exchanger 
  2. Regenerator 
  3. Recuperator 
  4. All of above 

22 What will happen if the flow rate of shell side liquid is made very high?

  1. more heat transfer will take place 
  2. less heat transfer will take place 
  3. heat transfer will not depend on the flow rate 
  4. none of the above 

23 Which of the following expressions represents the Heat energy balance which is used to derive the variation of temperature of both tube and shell with time and distance along the heat exchanger?

  1. Inlet = outlet + Accumulation 
  2. Outlet = Inlet +Accumulation 
  3. Inlet + outlet + Accumulation =0 
  4. None of these 

24 The differential equation governing the temperature of shell and tube is of order m in time(t) and of order n with respect to length along the heat exchanger(x), where –

  1. m=1, n=2 
  2. m=2, n=1 
  3. m=1, n=1 
  4. m=2, n=2 

25 Which of the following parameters has no effect on the temperature profiles of shell and tube liquid?

  1. The diameter of the tube 
  2. The diameter of the shell 
  3. The density of the shell fluid 
  4. The density of the tube fluid 

26  In figure-1, the variation of temperature of both hot and cold fluids along the length of the heat exchanger is given. The graph represents -

  1. Co-Current flow 
  2. Counter Current flow 
  3. Cross Current Flow 
  4. None of these 

27 In figure-2, the variation of temperature of both hot and cold fluids along the length of the heat exchanger is given. The graph represents –

  1. Co-Current flow 
  2. Counter Current flow 
  3. Cross Current Flow 
  4. None of these 

28 In figure -1 and figure-2, assuming that the temperature of shell and tube side liquids at both the ends of a heat exchanger is same, then which of the options is correct?

  1. LMTD in case of figure -1 is higher than in figure-2 
  2. LMTD in case of figure -2 is higher than in figure-1 
  3. LMTD in case of figure -1 is equal to that in figure-2  
  4. Cannot Say 

29 The correct variation of Area(A) required for heat transfer versus the LMTD value is?

  1. Aα LMTD 
  2. A α LMTD2 
  3. A α 1/ LMTD 
  4. A is independent of LMTD 

30 In figure -1 and figure-2, assuming that the temperature of shell and tube side liquids at both the ends of a heat exchanger is same, then which of the options is correct?

  1. Area required in case of figure -1 is higher than in figure-2 
  2. Area required in case of figure -2 is higher than in figure-1. 
  3. Area required in case of figure -1 is equal to that in figure-2.  
  4. Cannot Say 

31 If the length of the heat exchanger is infinitely large then which of the following options is most appropriate?

  1. The temperature of cold fluid will exceed the temperature of hot fluid. 
  2. The hot and cold lines in the above graphs will cross each other at least once. 
  3. The temperature of the hot and cold fluids will become constant after a certain distance along the length of the heat exchanger. 
  4. None of above options. 

32 For the heat exchange between hot and cold fluid, which of the following options is correct?

  1. The flow rate of tube side should be higher than shell side 
  2. The flow rate of tube side should be lesser than shell side 
  3. The flow rate of tube side should be equal to that of the shell side 
  4. It doesn’t matter which flow rate is higher. 

33 Time Constant is the time when a% of the final value is achieved, where a is?

  1. 33.3% 
  2. 63.2% 
  3. 99% 
  4. 100% 

34 As soon as the user makes a perturbation in the tube side inlet temperature-

  1. The tube side outlet will immediately change from it’s steady state value 
  2. It will take some time to change from it’s previous value 
  3. It will not change at all 
  4. None of these 

35 The main reason for the above question’s answer is:

  1. The thermometer will take some time to respond to the perturbation. 
  2. the tube inlet fluid will take some time to reach the other end. 
  3. both of the above 
  4. None of the above options 

36 Baffle spacing

  1. Should be less than one fifth diameter of shell. 
  2. Should be less than inside diameter of shell 
  3. Should be less than one fifth diameter of tube 
  4. None of these 

37 Correction is applied to LMTD for …………… flow

  1. Parallel 
  2. Cross 
  3. Counter 
  4. None of these 

38 A 2-4 heat exchanger involves

  1. Only counter flow of fluids 
  2. Only parallel flow of fluids 
  3. Both counter and parallel flow of fluids. 
  4. None of these. 

39 Double pipe heat exchanger are preferably useful, when

  1. A non corrosive liquid is to be heated 
  2. A high viscous liquid is to be heated 
  3. Requirement of heat transfer area is low 
  4. Overall heat transfer is low 

40 Fouling factor

  1. Is a dimensionless quantity. 
  2. Accounts for additional resistance to heat flow 
  3. Does not provide a safety factor for design 
  4. None of these. 

 

Numerical Problems

1.Find the Overall heat transfer coefficient for a shell and tube counter flow heat exchanger where the heat exchanged is 11.27 GJ/hour with the heat transfer area of 96 m2. Assume the LMTD as 76 oC.

2.. In a double pipe heat exchanger hot fluid is entering at 220°C and leaving at 115°C. Cold fluid enters at 10°C and leaves at 75°C. Mass flow rate of hot fluid 100 kg/hr, Cp of hot fluid 1.1 kcal/kg°C. Cp of cold fluid 0.95 kcal/kg°C. Calculate LMTD?

  1. If the flow is parallel
  2. If the flow is counter current
  3. Find the mass flow rate of cold fluid if the heat loss during the exchange is 5%.

 

3. When a heat exchanger was designed its overall heat transfer co-efficient was 600 kcal/hr mt²°C. The heat transfer area provided = 10mt². Over a period of time, its overall heat transfer co-efficient has fallen to 450 kcal/hr mt²°C due to fouling. Assume Counter flow.Data:

  • Specific heat of hot fluid = 1 kcal/kg °C
  • Hot fluid entering temperature = 80°C
  • Hot fluid leaving temperature = 60°C
  • Cold fluid entering temperature = 25 °C
  • Cold fluid leaving temperature = 40°C

 

Calculate: How much additional area is to be added to maintain the same rate of heat transfer?

4. In a parallel flow double-pipe heat exchanger water flows through the inner pipe and is heated from 20°C to 70°C. Oil flowing through the annulus is cooled from 200°C to 100°C. It is desired to cool the oil to a lower exit temperature by increasing the length of the heat exchanger. Determine the minimum temperature to which the oil may be cooled?

5. The flow rates of hot and cold water streams running through a parallel flow heat exchanger are 0.2 kg/. and 0.5 kg/s respectively. The inlet temperatures on the hot and cold sides are 75°C and 20°C respectively. The exit temperature of hot water is 45°C. If the individual heat transfer coefficients on both sides are 650 w/m2°C, calculate the area of the heat exchanger.

6. In a counter flow double pipe heat exchanger, water is heated from 25°C to 65°C by an oil with a specific heat of 1.45 kJ/kg K and mass flow rate of 0.9 kg/s. The oil is cooled from 230°C to 160°C. If the overall heat transfer coefficient is 420 W/m2°C, calculate the following:

  1. The rate of heat transfer
  2. The mass flow rate of water, and
  3. The surface area of the heat exchanger

 

7. An oil cooler for a lubrication system has to cool 1000 kg/h of oil (cp = 2.09kJ/kg°C) from 8°C to 4O°C by using a cooling water flow of 1000 kg/h at 30°C. Give your choice for a parallel flow or counter-flow heat exchanger, with reasons. Calculate the surface area of the heat exchanger, if the overall heat transfer coefficient is 24 W/m2°C. Take Cp of water = 4.18 kJ/kg°C.

8. A counter-flow double pipe heat exchanger using superheated steam is used to heat water at the rate of 10500 kg/h. The steam enters the heat exchanger at 180°C and leaves at 13O°C. The inlet and exit temperatures of water are 30°C and 80°C respectively. I f overall heat transfer coefficient from steam to water is 814 W/m2°C, calculate the heat transfer area. What would be the increase in area if the fluid flows were parallel?

9. The amount of F¬12 used in compression refrigeration system is 4 tonnes/hour. The brine flowing at 850 kg/min, with inlet temperature of 12°C is cooled in the evaporator. Assuming F¬12entering and leaving the evaporator as saturated liquid and saturated vapour respectively, determine the area of evaporator required. Take the following properties: For F¬12 : Saturation temperature : - 23°C; cp = 1.1 7 kJ/kg°C; hfg = 167.4 kJ/kg Cp(brine) = 6.3 kJ/kg°C; U = 8368 kJ/m2h°C.

10. An after cooler of shell and tube type with single pass is used for cooling compressed air from 85 oC to 35 oC. The compressed air generated is 1350 m3/h at mean air temperature. Calculate:

  1. The amount of cooling water to be circulated at a temperature of 30 oC. Assume the cooling water outlet temperature as 35 oC.
  2. The LMTD and no of tubes if the dia of the tube is 25.4 mm and 2500 mm length. Assume overall heat transfer coefficient for air to water is 150 W/m2.K.
  3. The hp of the pump required if the pressure required is 3.5 kg/cm2.g.

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