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Tutorial 9 Cengel

This document contains 6 problems related to heat and mass transfer during condensation and boiling processes. Problem 1 asks about determining the power dissipation of a heated metal rod submerged in water. Problem 2 asks about determining the maximum steam production rate from a heated brass element in a boiler. Problem 3 asks about determining the maximum heat flux and surface temperature during nucleate boiling of water on a heated steel surface.

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sakinah azizan
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642 views1 page

Tutorial 9 Cengel

This document contains 6 problems related to heat and mass transfer during condensation and boiling processes. Problem 1 asks about determining the power dissipation of a heated metal rod submerged in water. Problem 2 asks about determining the maximum steam production rate from a heated brass element in a boiler. Problem 3 asks about determining the maximum heat flux and surface temperature during nucleate boiling of water on a heated steel surface.

Uploaded by

sakinah azizan
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as DOC, PDF, TXT or read online on Scribd
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HEAT AND MASS TRANSFER BMCT 3143 TUTORIAL 09

APRIL2014

HEAT AND MASS TRANSFER BMCT 3143


TUTORIAL 09 - Condensation and Boiling

1. A 2 mm diameter cylindrical metal rod with emissivity of 0.5 is submerged horizontally in


water under atmospheric pressure. When electric current is passed through the metal rod, the
surface temperature reaches 500 C. Determine the power dissipation per unit length of the
metal rod.

2.
A 65 cm
long, 2 cm
diameter
brass
heating
element is
to be used
to boil water
at 120 C. If
the surface temperature of the heating element is not to exceed 125 C, determine the highest
rate of steam production in the boiler, in kg/h.

3. Water is to be boiled at atmospheric pressure on a 2 cm diameter mechanically polished


steel heater. Determine the maximum heat flux that can be attained in the nucleate boiling
regime and the surface temperature of the heater surface in that case.

4. To understand the burnout phenomenon, boiling experiments are conducted in water at


atmospheric pressure using an electrically heated 30 cm long, 4 mm diameter nickel-plated
horizontal wire. Determine (a) the critical heat flux and (b) the increase in the temperature of
the wire as the operating point jumps from the nucleate boiling to the film boiling regime at the
critical heat flux. Take the emissivity of the wire to be 0.3.

5. Saturated steam at 1 atm condenses on a 2-m high and 10-m wide vertical plate that is
maintained at 90 C by circulating cooling water through the other side. Determine (a) the rate
of heat transfer by condensation to the plate, and (b) the rate at which the condensate drips off
the plate at the bottom.

6. Saturated ammonia vapor


at 10 C condenses on
the outside of a 4 cm
outer diameter, 15 m
long horizontal tube
whose outer surface is
maintained at -10 C.
Determine (a) the rate of
heat transfer from the
ammonia and (b) the rate
of condensation of ammonia.

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