Heat exchangers

Device that facilitate the exchange of heat between fluids that are at different temperatures while keeping them from mixing with each other. Heat exchanger involves convection in each fluid and conduction through wall that separating the two fluids It is convenient to use an overall heat transfer coefficient (U)

HEAT EXCHANGERS Hot In Hot Out Cold Out Cold In

Heat Exchangers Parallel flow Counterflow Crossflow Ref: Incropera & Dewitt (2002)

Cross Flow Heat Exchanger

HEAT EXCHANGERS, Shell and Tube

HEAT EXCHANGERS, U-Tube

HEAT EXCHANGERS, Plate Design

HEAT EXCHANGERS, Condenser Watt Equipment, Inc., Equip. No. E-203-TR, 2690 Sq. Ft. Surface, 400 PSI Shell, 400 PSI Tubes, 3/4" Stainless Steel Tubes, Stainless Steel Shell.

HEAT EXCHANGERS Heat exchanger stainless steel, serial no. 3410, 170 tubes 1 inch diameter x 10 foot long, overall length of 124 inches. APV condenser/shell and tube heat exchanger. The shell side is 316L and the tube side is Titanium. It is 18 foot 10 in. and has a tube surface of 1,752 square feet. There are (2)16 in, shell side inlets. There are (558) 3/4 in. od tubes, and the shell is 31 in. inside diameter.

Temperature profile in double-pipe heat exchanger

Heat Exchanger Analysis

Counterflow Parallel

Counterflow Heat Exchangers

Counterflow Heat Exchanger What about crossflow heat exchangers? Δt m = F Δt m,cf

Overall heat transfer coefficient in heat exchanger

Example Hot oil is to be cooled in a double-tube counter- flow heat exchanger. The copper inner tubes have a diameter of 2 cm and negligible thickness. The inner diameter of the outer tube (the shell) is 3 cm. Water flows through the tube at a rate of 0.5 kg/s, and the oil through the shell at a rate of 0.8 kg/s. Taking the average temperatures of the water and the oil to be 45C and 80C, respectively, determine the overall heat transfer coefficient of this heat exchanger.

Estimation of h For turbulent flow Nu = 0.023Re 0.8 Pr 0.4 For laminar flow Di/DoNu i Nu o

Analysis of heat exchangers Select a heat exchanger when specified temperature change in a fluid stream of known mass flow rate  log mean temperature difference method (LMTD) Predict the outlet temperature of hot and cold fluid streams in a specified heat exchanger  effectiveness-NTU method

Log mean temperature difference c = cold fluid, h = hot fluid =

=

Example-the condensation of steam in a condenser Steam in condenser of a steam power plant is to be condensed at a temperature of 30  C with cooling water from a nearby lake, which enters the tube of the condenser at 14  C and leaves at 22  C. The surface area of the tubes is 45 m 2 and the overall heat transfer coefficient is 2100 W/m 2.  C. Determine mass flow rate of cooling water needed and the rate of the steam in condenser.

Example-heating water in a counter-flow heat exchanger A counter-flow double-pipe heat exchanger is to heat water from 20  C to 80  C at a rate of 1.2 kg/s. The heating is to be accomplished by geothermal available at 160  C at a mass flow rate of 2 kg/s. The inner tube is thin-walled and has a diameter of 1.5 cm. If the overall heat transfer coefficient of the heat exchanger is 640 W/m 2.  C, determine the length of the heat exchanger required to achieve the desired heating.

The effectiveness-NTU method Dimensionless parameter Actual heat transfer rate Maximum possible heat transfer rate

Example-heating water in a counter-flow heat exchanger A counter-flow double-pipe heat exchanger is to heat water from 20  C to 80  C at a rate of 1.2 kg/s. The heating is to be accomplished by geothermal available at 160  C at a mass flow rate of 2 kg/s. The inner tube is thin-walled and has a diameter of 1.5 cm. If the overall heat transfer coefficient of the heat exchanger is 640 W/m 2.  C, determine the length of the heat exchanger required to achieve the desired heating.

Example-cooling hot oil by water in a multipass heat exchanger Hot oil is to be cooled by water in a 1-shell-pass and 8- tubes passes heat exchanger. The tube are thin walled and are made of copper with an internal diameter of 1.4 cm. The length of each tube pass in the heat exchanger is 5 m, and the overall heat transfer coefficient is 310 W/m 2  C. Water flows through the tube at a rate of 0.2 kg/s, and the oil through the shell at a rate of 0.3 kg/s. The water and the oil enter at temperature of 20  C and 150  C, respectively. Determine the rate of heat transfer in the heat exchanger and the outlet temperature of the water and the oil.