Test: Boiling, Condensation & Heat Exchangers - 2 - Mechanical Engineering MCQ

Assertion (A): Drop-wise condensation is associated with higher heat transfer rate as compared to the heat transfer rate in film condensation.  
Reason (R): In drop condensation there is free surface through which direct heat transfer takes place.

Consider the following statements: 
The effect of fouling in a water-cooled steam condenser is that it
1. Reduces the heat transfer coefficient of water.
2. Reduces the overall heat transfer coefficient.
3. Reduces the area available for heat transfer.
4. Increases the pressure drop of waterOf these statements:

Air can be best heated by steam in a heat exchanger of  

For a balanced counter-flow heat exchanger, the temperature profiles of the two fluids are: 

The temperature distribution curve for a heat exchanger asshown in the figure above(with usual notations) refersto which one of the following? 

Assertion (A): Thermal conductance of heat pipe is several hundred times that of the best available metal conductor under identical conditions.  
Reason (R): The value of latent heat is far greater than that of specificheat.

ε -NTU method is particularly useful in thermal design of heat exchangers when 

In a counter flow heat exchanger, the product of specific heat and mass flow rate is same for the hot and cold fluids. If NTU is equal to 0.5, thenthe effectiveness of the heat exchanger is: 

Heat pipe is widely used now-a-days because 

A counter flow shell - and - tube exchanger is used to heat water with hot exhaust gases. The water (Cp = 4180 J/kg°C) flows at a rate of 2 kg/swhile the exhaust gas (1030 J/kg°C) flows at the rate of 5.25 kg/s. If the heat transfer surface area is 32.5 m² and the overall heat transfer coefficient is 200 W/m²°C, what is the NTU for the heat exchanger? 

A heat exchanger with heat transfer surface area A and overall heat transfer co-efficient U handles two fluids of heat capacities Cmax and Cmin. The parameter NTU (number of transfer units) used in the analysis of heat exchanger is specified as

A cross-flow type air-heater has an area of 50 m². The overall heattransfer coefficient is 100 W/m²K and heat capacity of both hot and coldstream is 1000 W/K. The value of NTU is: 

The equation of effectiveness ε = 1 − e^−NTU of a heat exchanger is valid(NTU is number or transfer units) in the case of: 

In a balanced counter flow heat exchanger with ,  M_h C_h = M_cC_c, the NTUis equal to 1.0. What is the effectiveness of the heat exchanger?

A heat exchanger with heat transfer surface area A and overall heattransfer coefficient U handles two fluids of heat capacities C₁, and C₂,such that C₁ > C₂. The NTU of the heat exchanger is given by:  

After expansion from a gas turbine, the hot exhaust gases are used toheat the compressed air from a compressor with the help of a crossflow compact heat exchanger of 0.8 effectiveness. What is the numberof transfer units of the heat exchanger?  

When tc₁ and tc₂ are the temperatures of cold fluid at entry and exit respectively and th₁ and th₂ are the temperatures of hot fluid at entry and exit point, and cold fluid has lower heat capacity rate as compared
to hot fluid, then effectiveness of the heat exchanger is given by:

A designer chooses the values of fluid flow ranges and specific heats insuch a manner that the heat capacities of the two fluids are equal. Ahot fluid enters the counter flow heat exchanger at 100°C and leaves at60°C. The cold fluid enters the heat exchanger at 40°C. The mean temperature difference between the two fluids is: 

For evaporators and condensers, for the given conditions, the logarithmic mean temperature difference (LMTD) for parallel flow is:               

Assertion (A): The LMTD for counter flow is larger than that of parallelflow for a given temperature of inlet and outlet.  
Reason (R): The definition of LMTD is the same for both counter flowand parallel flow.

Assertion (A): It is not possible to determine LMTD in a counter flow heat exchanger with equal heat capacity rates of hot and cold fluids.

Reason (R): Because the temperature difference is invariant along the length of the heat exchanger.  

Match List-I with List-II and select the correct answer 
 

In a heat exchanger, the hot liquid enters with a temperature of 180ºCand leaves at 160ºC. The cooling fluid enters at 30ºC and leaves at110ºC. The capacity ratio of the heat exchanger is: [IES-2010]

Assertion (A): A counter flow heat exchanger is thermodynamically more efficient than the parallel flow type.  
Reason (R): A counter flow heat exchanger has a lower LMTD for the same temperature conditions.

Which one of the following diagrams correctly shows the temperature distribution for a gas-to-gas counterflow heat exchanger?

Consider the following statements: 
In a shell and tube heat exchanger, baffles are provided on the shellside to:
1. Prevent the stagnation of shell side fluid
2. Improve heat transfer
3. Provide support for tubes
Select the correct answer using the codes given below:

Match List-I (Application) with List-II (Type of heat exchanger) and select the correct answer using the code given below the lists: 
List-I                                                                            List-II
A. Gas to liquid                                                         1. Compact
B. Space vehicle                                                       2. Shell and Tube
C. Condenser                                                            3. Finned tube
D. Air pre-heater                                                       4. Regenerative
Codes: A B C D                                    A B C D
       (a) 2 4 3 1                                 (b) 3 1 2 4
       (c) 2 1 3 4                                 (d) 3 4 2 1