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INTRODUCTION OF HEAT EXCHANGERHeat exchanger: Devices that facilitate the exchange of heat between two fluids that are at different temperatures while keeping them from mixing with each other.

Configuration of heat exchanger:1)Parallel flow

2)Counter flow

3)Cross flow

ANALYSIS OF HEAT EXCHANGERS Engineer often finds himself or herself in aposition:1)To select a heat exchanger that will achieve a specified temperature change in a fluid stream of known mass flow rate-LMTD method 2)To predict the outlet temperatures of the hot and cold fluid streams in a specified heat exchanger-NTU method .In this video we only considered on LMTD method !!!! LOG MEAN TEMPERATURE DIFFERENCE METHOD Two important formula:

Importance parameter:Q=The rate of heat loss

As=Surface area of tube

Tim=Log mean temperature difference QUESTIONSQ1 In a manufacturing plant, a stream of hydrocarbon (Cp=2200J/g.c) is to be cooled by water in a double pipe counter flow heat exchanger. The hydrocarbon enters the heat exchanger at 150 c and leaves at 40 c. For water (Cp=4180J/g.c), it enters the heat exchanger at 10 c. Determine the temperature of the water when it leaves the heat exchanger and the overall heat coefficient.

Q2 Steam in the condenser of a steam power plant is to be condensed at a temperature of 50c (hfg=2383kJ/kg) with cooling water (Cp=4180J/kg.c) from a nearby lake, which enters the tubes of the condenser at 18 c and leaves at 27 c. The surface area of the tubes is 42m^2,and the overall heat transfer coefficient is 2400W/m^2c. Determine the mass flow rate of the cooling water needed and the rate of condensation of the cooling water needed and the rate of condensation of the steam in the condenser.