Heat Exchanger Level - 2 - GATE ME Transfer Free MCQ Test with solutions

Test: Heat Exchanger Level - 2 - Question 1

In a counter flow heat exchanger, the working parameters for hot fluid are as follows: heat capacity = 2 kJ/kg K, mass flow inlet temperature 150^oC , outlet temperature 100^oC. For the cold fluid, the parameters are: heat capacity = 4 kJ/kg K, - mass flow rate 10 kg/s, and inlet temperature is = 20^oC. The outlet temperature of the cold fluid in ^oC is

A. 7.5
B. 32.5
C. 45.5
D. 70.0

Detailed Solution: Question 1

From steady state flow energy equation

m_hc_ph(T_hi - T_he) = m_cc_pc(T_ce - T_ci)

∴ 5 x 2000(150 -100) = 10 x 4000(T_ce - 20)

T_ce = 32.5^oC

Test: Heat Exchanger Level - 2 - Question 2

Cold water at 10^oC enters a counter flow heat exchanger at a rate of 8 kg/s , where it is heated by a hot water that enters the heat exchanger at 70^oC and flows at a rate of 2kh/s . Assume specific heat of water to be cp = 4.18 kJ/kg^oC . Determine the maximum theoretical heat transfer rate?

A. 250 kW
B. 400 kW
C. 501.6 kW
D. 450 kW

Detailed Solution: Question 2

Given m_h = 2 kg/s

M_c = 8 kg/s

c_ph = c_pc = 4.18kj/kg^o-C

∴ m_hc_ph 2 x 4.18 = 8.36 kW/^oC

m_hc_ph 8 x 4.18 = 33.4 kW/^oC

∴ m_hc_ph <>_cc_pc

For maximum heat exchanger rate,

Q_max = (mc_p)_min(T_hi - T_ci)

⇒ Q_max = 8.36(70-10)

⇒ Q_max = 501.6 kW

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Test: Heat Exchanger Level - 2 - Question 3

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

A. 1000
B. 500
C. 5
D. 0.2

Detailed Solution: Question 3

By definition

NTU = UA/(mc_p)_min

In the given situation, both capacity rate (mc_p) of both hot and cold fluid are equal

∴ NTU = 100 x 50/1000 = 5

Test: Heat Exchanger Level - 2 - Question 4

The overall heat transfer coefficient for a shell and tube heat exchanger for clean surfaces is U_o = 400 W/m²- K. The fouling factor after one year of operation is found to be h_fo = 200 W/m² -K. The overall heat transfer coefficient at this time is

A. 1200 W/m² - K
B. 894 W/m² - K
C. 33 W/m² - K
D. 287 W/m² - K

Detailed Solution: Question 4

Given U_o = 400 W/m²- K

Fouling factor, h_FO = 200 W/m²-K

∴ New overall heat transfer coefficient can be predicted as follows

1/U = 1/U+1/h_FO

1/U = 1/400 + 1/200

U = 33.33 W/m²-K

Test: Heat Exchanger Level - 2 - Question 5

In a solar assisted air conditioning system, 1 kg/sec of ambient air is to be preheated by the same amount of air leaving the system. A counter-flow heat exchanger having an area of 60m² with overall heat transfer coefficient of 25 W/m² - K is used for this purpose. Assuming for air is 1kJ/kg K. The effectiveness of the heat exchanger is

A. 0.
B. 0.6
C. 1.6
D. 25

Detailed Solution: Question 5

This is the case of a balanced counter flow heat exchanger.

∴ ε = NTU/1+NTU

Where NTU = UA/(mc_p)_min

For balanced heat exchanger,

(mc_p)_h = (mc_p)_c

∴ NTU = 60 x 25 / 1000 = 1.5

∴ ε = 1.5/1+1.5 = 0.6

Test: Heat Exchanger Level - 2 - Question 6

In a double-pipe heat exchanger, the cold fluid is water with inlet temperature of 20^oC and mass flow rate of 20 kg/s and the hot fluid which also has water inlet temperature of 80^oC and mass flow rate of 10 kg/s. For water c_p = 4.2kj/kg ^oC.

. What is the maximum temperature to which the cold fluid can be heated in a parallel flow and in a counter flow heat exchanger?

A.
80°C in both parallel flow and counter flow
B.
40°C in parallel flow and 80°C in counter flow
C.
40°C in parallel flow and 50°C in counter flow
D.
50°C in both parallel flow and counter flow

Detailed Solution: Question 6

For parallel flow heat exchanger maximum temperature of cold fluid will be reached when both hot and cold fluid exit at the same temperature.

Thus by steady state flow energy equation

⇒ 20 x 4.2 x (T - 20) = 10 x 4.2 (80-T)

∴ T = 40^oC

For counter flow heat exchanger, maximum exit temperature of cold fluid is achieved when effectiveness of the heat exchanger is 1

i.e.

ε = 1

i.e.

(m_cc_pc)(T_co - T_ci)/(m_cc_pc)(T_hi - T_ci) =1

1 = 20 x 4.2 x [T - 20]/10 x 4.2 x [80 - 20]

T = 50^oC

Test: Heat Exchanger Level - 2 - Question 7

In a double-pipe counter flow heat exchanger 1000kh/h, oil having a specific heat 20 j/kg -K is cooled from 150^oC to 125^oC by 1250 kg/h of fluid having specific heat 16j/kg-K. The cold fluid leaves the heat exchanger at 75^oC . In this case, the temperature at which the cooling fluid enters the heat exchanger and LMTD are __________

A. 25^o C and 50^oC
B. 50^o C and 50^oC
C. 50^o C and 75^oC
D. 75^o C and 50^oC

Detailed Solution: Question 7

x = 0 x x = l

m_hc_ph = 1000 x 20 = 20,000j/hr-K

m_cc_ph = 1200 x 16 = 20,000j/hr-K

m_hc_ph = m_cc_ph

Hence for a balanced Counter flow heat exchangers

ΔT_m = ΔT_i =ΔT_e

∴ ΔT_m = 150 -75 - 75^oC

T_hi - T_ce = T_he - T_ci

T_ci - T_he = T_ce - T_hi

T_ci = 50^oC

*Answer can only contain numeric values

Test: Heat Exchanger Level - 2 - Question 8

A counter flow shell and tube type heat exchanger is used to heat water with hot exhaust gases. The water (c = 4180 j/kg-K ) flows at the rate of 2 kg/s and the exhaust gases (c = 1000 j/kg - K) flow at the rate of 5 kg/s. If the heat transfer surface area is 32 m² and the overall heat transfer coefficient is 200 W/m² -K , the effectiveness of the heat exchanger is __________.

Detailed Solution: Question 8

Hot fluid [Exhaust gases]

C_H = m_Hc_H

∴ C_H = 1000 x 5 = 5000 Watt/ ...①

Cold fluid [Water]

C_c = m_cc_c

∴ C_c = 4180 x = 8360 Watt/K ...②

From ① & ②

C_H < />_c

∴ C_min = C_H = 5000 Watt/K

By definition,

C = C_min/C_max,

C = C C_H/C_C

C = 5000/8360

= 0.598

& NTU = UA/_min

∴ NTU = 32 x 200/ 5000

= 1.28

For counterflow heat exchanger

∴ ε = 0.626

Test: Heat Exchanger Level - 2 - Question 9

In a counterflow heat exchanger, hot gases enter the system at 200°C and leave at 80°C. the temperature of the outside air entering the unit is 35°C. Its temperature at the exit 90°C. the heat exchanger has an effectiveness of

A.
0.35
B.
0.34
C.
0.7272
D.
0.32

Detailed Solution: Question 9

By steady state flow equation

C_h(T_hi - T_he) = C_c(T_ce - T_he)

C_h/C_c = T_ce - T_ci/T_hi - T_he

C_h/C_c = 90-35/200-80 = 55/120

C_h < />_C

∴ ε = C_h(T_hi - T_he)/C_h(T_hi - T_ci)

ε = 200-80/200-35

ε = 0.7272

Test: Heat Exchanger Level - 2 - Question 10

A counter flow shell and tube heat exchanger is used to heat water with hot exhaust gases. The water (C = 4180 J/kg K) flows at the rate of 2 kg/s and the exhaust gases (c = 1000 J/kg K) flow at the rate of 5 kg/s. If the heat transfer surface area is 32 m² and the overall heat transfer coefficient is 200 W/m²K, the NTU of the heat exchanger i

A.
4.5
B.
2.4
C.
8.6
D.
1.28

Detailed Solution: Question 10

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Heat Exchanger Level - 2 - Free MCQ Practice Test with solutions, GATE

MCQ Practice Test & Solutions: Test: Heat Exchanger Level - 2 (10 Questions)

Cold water at 10^oC enters a counter flow heat exchanger at a rate of 8 kg/s , where it is heated by a hot water that enters the heat exchanger at 70^oC and flows at a rate of 2kh/s . Assume specific heat of water to be cp = 4.18 kJ/kg^oC . Determine the maximum theoretical heat transfer rate?

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

The overall heat transfer coefficient for a shell and tube heat exchanger for clean surfaces is U_o = 400 W/m²- K. The fouling factor after one year of operation is found to be h_fo = 200 W/m² -K. The overall heat transfer coefficient at this time is

In a counterflow heat exchanger, hot gases enter the system at 200°C and leave at 80°C. the temperature of the outside air entering the unit is 35°C. Its temperature at the exit 90°C. the heat exchanger has an effectiveness of

Heat Transfer

Heat Transfer

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Heat Exchanger Level - 2 - Free MCQ Practice Test with solutions, GATE

MCQ Practice Test & Solutions: Test: Heat Exchanger Level - 2 (10 Questions)

Cold water at 10oC enters a counter flow heat exchanger at a rate of 8 kg/s , where it is heated by a hot water that enters the heat exchanger at 70oC and flows at a rate of 2kh/s . Assume specific heat of water to be cp = 4.18 kJ/kgoC . Determine the maximum theoretical heat transfer rate?

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

The overall heat transfer coefficient for a shell and tube heat exchanger for clean surfaces is Uo = 400 W/m2- K. The fouling factor after one year of operation is found to be hfo = 200 W/m2 -K. The overall heat transfer coefficient at this time is

In a counterflow heat exchanger, hot gases enter the system at 200°C and leave at 80°C. the temperature of the outside air entering the unit is 35°C. Its temperature at the exit 90°C. the heat exchanger has an effectiveness of

Heat Transfer

Heat Transfer

Top Courses for Mechanical Engineering

About this Mechanical Engineering Practice Test

Explore more Mechanical Engineering Study Resources

Cold water at 10^oC enters a counter flow heat exchanger at a rate of 8 kg/s , where it is heated by a hot water that enters the heat exchanger at 70^oC and flows at a rate of 2kh/s . Assume specific heat of water to be cp = 4.18 kJ/kg^oC . Determine the maximum theoretical heat transfer rate?

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

The overall heat transfer coefficient for a shell and tube heat exchanger for clean surfaces is U_o = 400 W/m²- K. The fouling factor after one year of operation is found to be h_fo = 200 W/m² -K. The overall heat transfer coefficient at this time is