Heat exchangers

1. Heat exchangers

2. 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)

3. Hot In Hot Out Cold Out Cold In HEAT EXCHANGERS

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

6. Cross Flow Heat Exchanger

13. HEAT EXCHANGERS, Shell and Tube

14. HEAT EXCHANGERS, U-Tube

15. HEAT EXCHANGERS, Plate Design

16. 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.

17. HEAT EXCHANGERS 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. Heat exchanger stainless steel, serial no. 3410, 170 tubes 1 inch diameter x10 foot long, overall length of 124 inches.

18. Temperature profile in double-pipe heat exchanger

19. Heat Exchanger Analysis

20. Heat Exchanger Analysis Counterflow Parallel

21. Counterflow Heat Exchangers

22. Counterflow Heat Exchanger • What about crossflow heat exchangers? • Δtm= F Δtm,cf

28. Overall heat transfer coefficient in heat exchanger

35. 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.

36. Estimation of h • For turbulent flow Nu = 0.023Re0.8Pr0.4 • For laminar flow

37. 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

38. = Log mean temperature difference • c =cold fluid, h = hot fluid

39. =

41. 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 m2 and the overall heat transfer coefficient is 2100 W/m2.C. Determine mass flow rate of cooling water needed and the rate of the steam in condenser.

43. 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/m2.C, determine the length of the heat exchanger required to achieve the desired heating.

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

50. 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/m2.C, determine the length of the heat exchanger required to achieve the desired heating.