GATE-CH-1988-4-b-ht-2mark

Match the following:

• A. Multiple effect evaporator

Answer 1IV. Heating of gasesI. Chilling of milkII. Steam economyIII. Condensation at reduced pressure

• B. Barometric leg

Answer 2IV. Heating of gasesI. Chilling of milkII. Steam economyIII. Condensation at reduced pressure

• C. Extended surfaces

Answer 3IV. Heating of gasesI. Chilling of milkII. Steam economyIII. Condensation at reduced pressure

• D. Plate heat exchangers

Answer 4IV. Heating of gasesI. Chilling of milkII. Steam economyIII. Condensation at reduced pressure

GATE-CH-1991-5-iii-ht-2mark

Match the following, processes with their correspoding heat transfer coefficients (W/m\(^2\).\(^\circ \)C)

• I. Dropwise condensation of steam

Answer 1D. 30,000 - 100,000B. 50 - 1500C. 1 - 5A. 1700 - 50,000

• II. Boiling water

Answer 2D. 30,000 - 100,000B. 50 - 1500C. 1 - 5A. 1700 - 50,000

• III. Heating oils

Answer 3D. 30,000 - 100,000B. 50 - 1500C. 1 - 5A. 1700 - 50,000

• IV. Heating with air

Answer 4D. 30,000 - 100,000B. 50 - 1500C. 1 - 5A. 1700 - 50,000

GATE-CH-1996-3-2-ht-2mark

Match the following:
Fluids in jacket side / vessel side, and the corresponding overall heat transfer coefficient (W/m\(^2\).\(^\circ \)C)

• I. Steam / Water

Answer 1D. 850 - 1700C. 285 - 800A. 30 - 75B. 5000 - 6000

• II. Water / Polymer-monomer mixture

Answer 2D. 850 - 1700C. 285 - 800A. 30 - 75B. 5000 - 6000

GATE-CH-1992-5-b-ht-2mark-MANY

Indirect contact heat exchangers are preferred over direct heat exchangers because

• heat transfer coefficients are high

• there is no risk of contamination

• there is no mist formation

• cost of equipment is lower

GATE-CH-1999-2-9-ht-2mark

For a counter-current heat exchanger with \(T^i_h\) = 80\(^\circ \)C, \(T^o_c\) = 60\(^\circ \)C, \(T^o_h\) = 50\(^\circ \)C, and \(T^i_c\) = 30\(^\circ \)C, and the temperature difference between the two streams being the same everywhere along \(z\), the direction of flow of the hot fluid, the temperature profile should satisfy

• \(d^2T/dz^2 > 0\)

• \(d^2T/dz^2 = 0\)

• \(d^2T/dz^2 < 0\)

• \(dT/dz = 0\)

GATE-CH-2001-2-10-ht-2mark

The overall heat transfer coefficient for a shell and tube heat exchanger for clean surface is \(U_o\) = 400 W/m\(^2\).K. The fouling factor after one year of operation is found to be \(h_{do}\) = 2000 W/m\(^2\).K. The overall heat transfer coefficient at this time is

• 1200 W/m\(^2\).K

• 894 W/m\(^2\).K

• 333 W/m\(^2\).K

• 287 W/m\(^2\).K

GATE-CH-2003-56-ht-2mark

A process stream of dilute aqueous solution flowing at the rate of 10 kg/s is to be heated. Steam condensate at 95^oC is available for heating purpose, also at a rate of 10 kg/s. A 1-1 shell and tube heat exchanger is available. The best arrangement is

• counterflow with process stream on shell side

• counterflow with process stream on tube side

• parallel flow with process stream on shell side

• parallel flow with process stream on tube side

GATE-CH-2003-58-ht-2mark

Steam is to be condensed in a shell and tube heat exchanger, 5 m long with a shell diameter of 1 m. Cooling water is to be used for removing the heat. Heat transfer coefficient for the cooling water, whether on shell side or tube side, is same. The best arrangement is

• vertical heat exchanger with steam on tube side

• vertical heat exchanger with steam on shell side

• horizontal heat exchanger with steam on tube side

• horizontal heat exchanger with steam on shell side

GATE-CH-2003-60-ht-2mark

Air is to be heated by condensing steam. Two heat exchangers are available; (i) a shell and tube heat exchanger, and (ii) a finned tube heat exchanger. Tube side heat transfer area is equal in both cases. The recommended arrangement is

• finned tube heat exchanger with air inside and steam outside

• finned tube heat exchanger with air outside and steam inside

• shell and tube heat exchanger with air inside tubes and steam shell side

• shell and tube heat exchanger with air on shell side and steam inside tubes

GATE-CH-2004-61-ht-2mark

Hot water (0.01 m³/min) enters the tube side of a cocurrent shell and tube heat exchanger at 80^oC and leaves at 50^oC. Cold oil (0.05 m³/min) of density 800 kg/m³ and specific heat of 2 kJ/(kg.K) enters at 20^oC. The log mean temperature difference in ^oC is approximately

• 32

• 37

• 45

• 50

GATE-CH-2013-16-ht-1mark

The effectiveness of a heat exchanger in the \(\varepsilon \)-NTU method is defined as

• \(\displaystyle \frac {\text {increase in temperature of the cold fluid}}{\text { decrease in temperature of the hot fluid}}\)

• \(\displaystyle \frac {\text {actual exit temperature attained by the cold fluid}}{\text { maximum exit temperature attainable by the cold fluid}}\)

• \(\displaystyle \frac {\text {actual exit temperature attained by the hot fluid}}{\text { minimum exit temperature attainable by the hot fluid}}\)

• \(\displaystyle \frac {\text {actual heat transfer rate}}{\text { maximum possible heat transfer rate from hot fluid to cold fluid}}\)

GATE-CH-2015-38-ht-2mark

In the figure below, th temperature profiles of cold and hot fluids in counter current double pipe heat exchangers (in different modes of operation) are shown on the left. For each case, match the heat exchange process for the fluid represented by the bold curve with the options given on the right.

• I-P, II-Q, III-R, IV-S

• I-P, II-Q, III-S, IV-R

• I-Q, II-P, III-S, IV-R

• I-Q, II-S, III-P, IV-R

GATE-CH-ME-2016-S3-18-ht-1mark

For a heat exchanger, \(\Delta T_{\text {max}}\) is the maximum temperature difference and \(\Delta T_{\text {min}}\) is the minimum temperature difference between the two fluids. LMTD is the log mean temperature difference. \(C_{\text {min}}\) and \(C_{\text {max}}\) are the minimum and the maximum heat capacity rates. The maximum possible heat transfer (\(Q_{\text {max}}\)) between the two fluids is

• \(C_{\text {min}}\; \text {LMTD}\)

• \(C_{\text {min}}\; \Delta T_{\text {max}}\)

• \(C_{\text {max}}\; \Delta T_{\text {max}}\)

• \(C_{\text {max}}\; \Delta T_{\text {min}}\)

GATE-CH-2017-13-ht-1mark

In a heat exchanger, the inner diameter of a tube is 25 mm and its outer diameter is 30 mm. The overall heat transfer coefficient based on the inner area is 360 W/m².^oC. Then, the overall heat transfer coefficient based on the outer area, rounded to the nearest integer, is ____________W/m².^oC.

• Answer

GATE-CH-1996-21-ht-5mark

A shell and tube steam condenser is to be constructed of 2.5 cm O.D., 2.2 cm I.D., single pass horizontal tubes with steam condensing at 54\(^\circ \)C on the outside of the tubes. The cooling water enters at 20\(^\circ \)C and leaves at 36\(^\circ \)C at a flow rate of 1 kg/sec. The heat transfer coefficient for the condensation of steam is 7900 W/(m\(^2\).\(^\circ \)C).
(i) Calculate the tube length (in m).
(ii) If the latent heat of condensation is 2454 kJ/kg, calculate the condensation rate per tube (in kg/h).

The properties of water are as follows:
Specific heat = 4180 J/(kg.\(^\circ \)C)
Viscosity = \(0.86 \times 10^{-3}\) kg/(m.s)
Thermal conductivity = 0.61 W/(m.\(^\circ \)C)

The heat transfer coefficient for turbulent flow in a pipe may be determined by \[ \text {Nu} = 0.023\; \text {Re}^{0.8} \text {Pr}^{0.4} \] 

(i) ____________
{#1}

(ii) ____________
{#2}

GATE-CH-2000-21-ht-5mark

In a 1 - 1 counter flow shell and tube heat exchanger, a process stream (\(C_P = 4.2\) kJ.kg\(^{-1}\).K\(^{-1}\)) is cooled from 450 to 350 K using water (\(C_P = 4.2\) kJ.kg\(^{-1}\).K\(^{-1}\)) at 300 K. The process stream flows on the shell-side at a rate of 1 kg/s and the water on the tube-side at a rate of 5 kg/s. If the heat transfer coefficients on the shell and tube sides are 1000 W/(m\(^2\).K) and 1500 W/(m\(^2\).K), respectively, determine

(a) the required heat transfer area (in m\(^2\)). {#1}

(b) by what percentage will the required area increase if the flow is cocurrent? {#2}

Neglect tube wall resistance and fouling resistances.

GATE-CH-2010-48-49-ht-4mark

Hot oil at 150^oC is used to preheat a cold fluid at 30^oC in a 1:1 shell and tube heat exchanger. The exit temperature of the hot oil is 110^oC. Heat capacities (product of mass flow rate and specific heat capacity) of both the streams are equal. The heat duty is 2 kW.

(i) Under co-current flow conditions, the overall heat transfer resistance \((1/UA)\) is

{#1}

(ii) Under counter-current flow conditions, the overall heat transfer resistance \((1/UA)\) is

{#2}

GATE-CH-2002-2-10-ht-2mark

1000 kg of liquid at 30^oC in a well-stirred vessel has to be heated to 120^oC, using immersed coils carrying condensing steam at 150^oC. The area of the steam coils is 1.2 m² and over all heat transfer coefficient to the liquid is 1500 W/m².^oC. Assuming negligible heat loss to surroundings and specific heat capacity of the liquid to be 4 kJ/kg.^oC, the time taken for the liquid to reach desired temperature will be

• 15 min

• 22 min

• 44 min

• 51 min

GATE-CH-2005-61-ht-2mark

A countercurrent flow double pipe heat exchanger is used to heat water flowing at 1 kg/s from 40^oC to 80^oC. Oil is used for heating and its temperature changes from 100^oC to 70^oC. The overall heat transfer coefficient is 300 W/(m².^oC).
If it is replaced by a 1-2 shell and tube heat exchanger with countercurrent flow configuration with water flowing in shell and oil flowing in the tube, what is the excess area required with respect to the double pipe heat exchanger?
The correction factor, \(F_t\) for LMTD (log mean temperature difference) based on the above double pipe heat exchanger is 0.5. The heat transfer coefficient remains unchanged, and the same inlet and outlet conditions are maintained.
\(C_{P,\text {water}} = 4180\) J/(kg.^oC), \(C_{P,\text {oil}} = 2000\) J/(kg.^oC)

• 0 m²

• -20.15 m²

• 22.6 m²

• 9.69 m²

GATE-CH-2006-47-ht-2mark

A process fluid has to be cooled from 22^oC to 2^oC using brine in a 2-4 shell and tube heat exchanger shown below. The brine enters at \(-3\)^oC and leaves at 7^oC. The overall heat transfer coefficient is 500 W/(m ².K). The design heat load is 30 kW. The brine flows on the tube side and the process fluid on the shell side. The heat transfer area in m² is

• 1.1

• 5.77

• 6.59

• 7.53

GATE-CH-2007-44-ht-2mark

A hot fluid entering a well-stirred vessel is cooled by feeding cold water through a jacket around the vessel. Assume the jacket is well-mixed. For the following data,

mass flowrates of the hot fluid = 0.25 kg/s
mass flow rate of cold water = 0.4 kg/s
specific heats of oil = 6000 J/(kg.K)
specific heat of cold water = 4184 J/(kg.K)
the inlet and exit temperature of the hot fluid is 150^oC and 100^oC respectively.
inlet temperature of cold water = 20^oC
the overall hat transfer coefficient is 500 W/(m².K).

the heat transfer area in m², is

• 1.82

• 2.1

• 3

• 4.26

GATE-CH-2012-35-ht-2mark

In a counter-flow double pipe heat exchanger, oil (\(\dot {m}=2\) kg/s, \(C_P=2.1\) kJ/kg.^oC) is cooled from 90^oC to 40^oC by water (\(\dot {m}=1\) kg/s, \(C_P=4.2\) kJ/kg.^oC) which enters the inner tube at 10^oC. The radius of the inner tube is 3 cm and its length is 5 m. Neglecting the wall resistance, the overall heat transfer coefficient based on the inner radius, in kW/m².K, is

• 0.743

• 7.43

• 74.3

• 2475

GATE-CH-2013-36-ht-2mark

In a double pipe counter-current heat exchanger, the temperature profiles shown in the figure were observed. During operation, due to fouling inside the pipe, the heat transfer rate reduces to half of the original value. Assuming that the flow rates and the physical properties of the fluids do not change, the LMTD (in ^oC) in the new situation is

• 0

• 20

• 40

• indeterminate

GATE-CH-2016-40-ht-2mark

In a 1-1 pass shell and tube exchanger, steam is condensing in the shell side at a temperature (\(T_s\)) of 135^oC and the cold fluid is heated from a temperature (\(T_1\)) of 20^oC to a temperature (\(T_2\)) of 90^oC. The energy balance equation for this heat exchanger is \[ \ln \frac {T_s-T_1}{T_s-T_2} = \frac {UA}{\dot {m}C_P} \] where \(U\) is the overall heat transfer coefficient, \(A\) is the heat transfer area, \(\dot {m}\) is the mass flow rate of the cold fluid and \(C_P\) is its specific heat. Tube side fluid is in a turbulent flow and the heat transfer coefficient can be estimated from the following equation: \[ \text {Nu} = 0.023 (\text {Re})^{0.8} (\text {Pr})^{1/3} \] where \(\text {Nu}\) is the Nusselt number, \(\text {Re}\) is the Reynolds number and \(\text {Pr}\) is the Prandtl number. The condensing heat transfer coefficient in the shell side is significantly higher than the tube side heat transfer coefficient. The resistance of the wall to heat transfer is negligible. If only the mass flow rate of the cold fluid is doubled, what is the outlet temperature (in ^oC) of the cold fluid at steady state?

• 80.2

• 84.2

• 87.4

• 88.6

GATE-CH-2019-16-ht-2mark

Consider the two countercurrent heat exchanger designs for heating a cold stream from \(t_{\text {in}}\) to \(t_{\text {out}}\), as shown in figure. The hot process stream is available at \(T_{\text {in}}\). The inlet stream conditions and overall heat transfer coefficients are identical in both the designs. The heat transfer area in Design I and Design II are respectively \(A^{\text I}\) and \(A^{\text {II}}\).

If heat losses are neglected, and if both the designs are feasible, which of the following statement holds true:

• \(A^{\text I}>A^{\text {II}}\)      \(T^{\text I}_{\text {out}}<T^{\text {II}}_{\text {out}}\)

• \(A^{\text I}=A^{\text {II}}\)      \(T^{\text I}_{\text {out}}=T^{\text {II}}_{\text {out}}\)

• \(A^{\text I}<A^{II}\)      \(T^{\text I}_{\text {out}}>T^{\text {II}}_{\text {out}}\)

• \(A^{\text I}<A^{\text {II}}\)      \(T^{\text I}_{\text {out}}=T^{\text {II}}_{\text {out}}\)

GATE-CH-ME-2008-45-ht-2mark

The logarithmic mean temperature difference (LMTD) of a counterflow heat exchanger is 20^oC. The cold fluid enters at 20^oC and the hot fluid enters at 100^oC. Mass flow rate of the cold fluid is twice that of the hot fluid. Specific heat at constant pressure of the hot fluid is twice that of the cold fluid. The exit temperature of the cold fluid

• is 40^oC

• is 60^oC

• is 80^oC

• cannot be determined

GATE-CH-ME-2012-41-ht-2mark

Water (\(C_P = 4.18\) kJ/kg.K) at 80^oC enters a counterflow heat exchanger with a mass flow rate of 0.5 kg/s. Air (\(C_P = 1\) kJ/kg.K) enters at 30^oC with a mass flow rate of 2.09 kg/s. If the effectiveness of the heat exchanger is 0.8, the LMTD (in ^oC) is

• 40

• 20

• 10

• 5

GATE-CH-1988-4-c-ht-2mark

An organic liquid is cooled continuously in a stirred tank by water flowing through a cooling coil. The organic liquid may be considered to be perfectly mixed. Inlet and outlet temperatures of the organic liquid are 50\(^\circ \)C and 30\(^\circ \)C respectively and those of the cooling water are 20\(^\circ \)C and 25\(^\circ \)C. Calculate the log mean temperature difference (in \(^\circ \)C) for heat transfer through the coil.

• Answer

GATE-CH-1990-14-i-ht-6mark

In a 1-1 shell and tube heat exchanger, steam is condensing on the shell side at \(T_s\)\(^\circ \)C, and the cold fluid is being heated on the tube side from \(t_1\)\(^\circ \)C to \(t_2\)\(^\circ \)C. The following equation relates \(t_2\) to the other variables: \[ \ln \frac {T_s - t_1}{T_s - t_2} = \frac {UA}{WC_P} \] where \(U\) is the overall heat transfer coefficient, \(A\) is the heat transfer area, \(W\) is the mass flow rate and \(C_P\) is the heat capacity. The tube side coefficient is controlling and the tube side is in turbulent flow, \(T_s\) = 130\(^\circ \)C, \(t_1\) = 30\(^\circ \)C and \(t_2\) = 80\(^\circ \)C. If the mass flow rate of the cold fluid is doubled while keeping all the other conditions same, find the new value of \(t_2\) (in \(^\circ \)C) at steady state.

• Answer

GATE-CH-1990-14-ii-ht-6mark

A hot fluid flows through a well mixed stirred tank which is provided with a cooling jacket. The fluid in the cooling jacket can also be assumed to be well mixed. Calculate the heat transfer area (in m\(^2\)) of the jacket required given the following data:
Hot fluid:
Flow rate, \(W_h\) = 50 kg/sec; \(T_{hi}\) = 205\(^\circ \)C; \(C_{Ph}\) = 2 kJ/kg.\(^\circ \)C.
Cold fluid:
Flow rate, \(W_c\) = 100 kg/sec; \(T_{ci}\) = 25\(^\circ \)C; \(T_{co}\) = 45\(^\circ \)C; \(C_{Pc}\) = 4 kJ/kg.\(^\circ \)C.
\(U\) = 2.5 kW/m\(^2\).\(^\circ \)C

• Answer

GATE-CH-1993-21-a-ii-ht-2mark

In a counter-current heat exchanger which has been in service for some time, due to formation of scale, the heat transfer rate is reduced to 85% of its original value based on clean surface. Assuming that the terminal temperatures of fluids are same in both cases, and the effective heat transfer area does not change appreciably due to scale formation, determine the overall fouling factor (in m\(^2\).K/W) if clean overall heat transfer coefficient is 500 W/m\(^2\).K
____________\(\times 10^{-4}\) m\(^2\).K/W

• Answer

GATE-CH-1995-8-ht-5mark

Estimate the heat transfer area (in m\(^2\)) for an exchanger to cool an organic liquid from 105\(^\circ \)C to 50\(^\circ \)C. The hot liquid will flow at a rate of 10,000 kg/h and will be cooled by circulating foul water containing some salt. The cooling water will leave at 40\(^\circ \)C. It is proposed to use one shell pass and two tube pass exchanger for the above duty.
Cooling water inlet temperature = 25\(^\circ \)C
Heat capacity for water = 4.2 kJ/kg.\(^\circ \)C
Heat capacity for hot liquid = 2.84 kJ/kg.\(^\circ \)C
\(F_t\), the correction factor for the design will be 0.85
The recommended overall heat transfer coefficient \(U\) will be 600 W/m\(^2\).\(^\circ \)C.

• Answer

GATE-CH-1999-13-ht-5mark

150 kg of water is to be heated in a steam-jacketed vessel from 25\(^\circ \)C to 80\(^\circ \)C. Steam is condensing at 120\(^\circ \)C, and the heat transfer area is 0.25 m\(^2\). The heat transfer coefficients for condensation of steam and heating of water by convection are 1000 W/m\(^2\).\(^\circ \)C and 500 W/m\(^2\).\(^\circ \)C respectively. Write appropriate unsteady state balance equations and find the time required (in hour) for heating the water. Assume that the specific heat of water in the temperature range of interest is \(4.18 \times 10^3\) J/kg.\(^\circ \)C.

• Answer

GATE-CH-1989-4-iii-ht-2mark

List the following in the increasing order of heat transfer coefficients:

1. Forced convection for air flow at 35 m/s over 0.75 m square plate
2. Boiling water in container
3. Condensation of water vapor at 1 atm outside horizontal tubes
4. Condensation of water vapor at 1 atm for vertical surfaces

• Answer

GATE-CH-1998-17-ht-5mark

A fluid is heated from a temperature \(T_i\) to \(T_o\) in a double pipe heat exchanger with steam condensing in the outer pipe at a temperature \(T_s\). The flow rate of fluid in the inner pipe (inside diameter \(D\)) is \(Q\), and the heat transfer coefficient is \(h_i\). The film heat transfer coefficient for the condensing steam is \(h_o\), and the wall resistance and fouling are negligible.

1. Obtain an expression for the length of the heat exchanger required to carry out the heating operation. Assume that the outer diameter of the inner pipe is nearly equal to its inside diameter. The specific heat capacity of the fluid is \(C_P\) and its density is \(\rho\).

2. Obtain an expression for the optimum diameter at which the heat exchanger length is minimum assuming \(h_i = C D^{-1.8}\) where \(C\) is a constant.

• Answer