1

GATE ME 1999

Subjective

+5

-0

Two fluids, $$A$$ and $$B$$ exchange heat in a counter-current heat exchanger. Fluid $$A$$ enters at $${420^ \circ }C$$ and has a mass flow rate of $$1$$ $$kg/s.$$ Fluid $$B$$ enters at $${20^ \circ }C$$ and also has a mass flow rate of $$1$$ $$kg/s,$$ Effectiveness of heat exchanger is $$75\% $$. Determine the heat transfer rate and exit temperature of fluid $$B.$$ (Specific heat of fluid $$A$$ is $$1$$ $$kJ/kg$$ $$K$$ and that of fluid $$B$$ is $$4$$ $$kJ/kgK$$).

2

GATE ME 1998

Subjective

+5

-0

A hot fluid at $${200^ \circ }C$$ enters a heat exchanger at a mass flow rate of $${10^4}\,\,kg/hr.$$ Its specific heat is $$2000$$ $$J/kg$$-$$K.$$ It is to be cooled by another fluid entering at $${25^ \circ }C$$ with a mass flow rate $$2500$$ $$kg/hr$$ and specific heat $$400$$ $$J/kg$$-$$K$$. The overall heat transfer coefficient based on outside area of $$20\,\,{m^2}$$ is $$250\,\,\,W/{m^2}K.$$ Find the exit temperature of the hot fluid when the fluids are in parallel flow.

3

GATE ME 1998

Subjective

+5

-0

Hot water flows with a velocity of $$0.1$$ $$m/s$$ in a $$100mm$$ long, $$0.1m$$ diameter pipe. Heat lost from the pipe outer wall is uniform and equal to $$420$$ $$W/{m^2}$$. If the inlet water temperature is $${80^ \circ }C,$$ calculate the water temp at the exit. Neglect effect of pipe wall thickness. $${C_p}$$ (water) $$=4.2$$ $$kJ/kg$$-$$K$$ and density of water $$=1000$$ $$kg/\,{m^3}.$$

4

GATE ME 1997

Subjective

+5

-0

In a certain double pipe heat exchanger hot water flows at a rate of $$50,000$$ $$kg/h$$ and gets cooled from $${95^ \circ }C$$ to $${65^ \circ }C$$. At the same time $$50,000$$ $$kg/h$$ of cooling water at $${30^ \circ }C$$ enters the heat exchanger. The flow conditions are such that the overall heat transfer coefficient remains constant at $$2270$$ $$W/{m^2}K$$. Calculate the heat transfer area required, assuming the two streams are in parallel flow, and for both the streams $${C_p} = 4.2\,\,kJ/kg\,\,K$$

Questions Asked from Heat Exchangers (Marks 5)

Number in Brackets after Paper Indicates No. of Questions

GATE ME Subjects

Engineering Mechanics

Machine Design

Strength of Materials

Heat Transfer

Production Engineering

Industrial Engineering

Turbo Machinery

Theory of Machines

Engineering Mathematics

Fluid Mechanics

Thermodynamics

General Aptitude