Process Heat GroupMajor Challenges

Lecture 222.033/22.33 Nuclear Engineering Design Project

September 14, 2011

MIT Dept. of Nuclear Science and Engineering Dr. Michael P. Short, 2011 22.033/22.33 Nuclear Design Course Page 1

The Three Challenge Problems

Heat exchanger (Hx) design Heat transport Heat storage (if necessary)

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First, Some Nomenclature

Sensible heating temperature change .

Q = m c p T Latent heating phase change

. Q = m h fg

Bond energy storage enthalpy of chemical reactions

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Where Do We Find Them?

Courtesy of the Generation IV International Forum. Used with permission.

Source: http://www.gen-4.org/Technology/systems/gfr.htm

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Heat Exchangers Fundamental Parameters

Hx effectiveness () Measures how

much heat is transferred compared to how much is possible

=1 is ideal, but American Institute of Physics. All rights reserved. This content is excluded from ourCreative Commons license. For more information, see http://ocw.mit.edu/fairuse. practically

Source: Dean Bartlett. The Fundamentals of Heat Exchangers The Industrial Physicist, AIP, p. 20 (1996) impossible (big Hx)

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Heat Exchangers Fundamental Parameters

Diagram of heat exchanger removed due to copyright restrictions. See lecture video for details.

***Source: Ramesh K. Shah, Dusan P. Sekulic. Fundamentals of Heat Exchanger Design. John Wiley & Sons, Inc. p. 102 (2003).

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Heat Exchangers Fundamental Parameters

Q = UAFTlm Q = Heat transfer rate (W)U = Thermal conductance (W/m2K)A = Heat transfer area (m2)Tlm = Log mean temperature difference (K)

F = Factor (for flow configuration)

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Heat Exchangers Log Mean Temperature Difference (LMTD)

( TH TC ) T = lm ln

TH TC

LMTD is a good measure of the effectiveness of simlar heatexchangers of different designs

Often, LMTD (counter flow) > LMTD (parallel flow)

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Heat Exchangers Finding Key Parameters

Figure 1 A big, complicated heatexchanger chart

Source: Wolverine Tube Heat Transfer Data Book, p. 93 (2001), accessed at

http://www.wlv.com/products/databook /ch2_5.pdf

Courtesy of Wolverine Tube, Inc. Used with permission.

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Heat Exchangers Fundamental Parameters

For all flow configurations

Hx is balanced when C* = 1

NTU = Number of Transfer Units John Wiley & Sons, Inc. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/fairuse.

***Source: Ramesh K. Shah, Dusan P. Sekulic. Fundamentals of Heat Exchanger Design. John Wiley & Sons, Inc. p. 116, 118-119 (2003).

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Hx Flow Types

***After Ramesh K. Shah & Dusan P. Sekulic. Fundamentals of Heat Exchanger Design. John Wiley & Sons, Inc. (2003).

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Heat Exchanger Classification by Flow Arrangement

Parallel counter-flow

m-shell passesn-tube passes

Fluid 1 m passesFluid 2 n passesSplit-flow Divided-flowCross-

counter-flowCross-

parallel-flowCompound

flow

Extended surface Shell-and-tube Plate

Counter-flow Parallel-flow Cross-flow Split-flow Divided-flow

Single-pass Multi-pass

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Parallel Flow vs. Counterflow

See http://www.engineeringtoolbox.com/arithmetic-logarithmic-mean-temperature-d_436.html

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tpi

tsi

tpo

tso

Parallel-flow

tpi

tsi

tpotso

Counter-flow

tito

ti

to

Tem

per

ature

Tem

per

ature

Image by MIT OpenCourseWare.

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Hx Flow Configurations

After Ramesh K. Shah, Dusan P. Sekulic. Fundamentals of Heat Exchanger Design. John Wiley & Sons, Inc. (2003).

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Tubular Extended surface Regenerative

Heat Exchanger Classification by Construction

Double-pipe Pipe coilsShell-and-tube Spiral tube

Plate-type

PHE Plate coilSpiral Printed circuit

Gasketed Welded Brazed

Plate-fin Tube-fin

Cross flow to tubes

Parallel flow to tubes

Ordinaryseparating

wall

Heat-pipewall

Rotary

Fixed-matrix

Rotating hoods

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Hx Flow Configurations - Tubular

Source: Wikimedia Commons

Courtesy of Wikipedia User:H Padleckas. Used with permission. Courtesy of Harlan Bengtson. Used with permission.

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Hx Flow Configurations Plate Plate (brazed) type Spiral type

Alfa Biz Limited. All rights reserved. This content is excluded from our CreativeCommons license. For more information, see http://ocw.mit.edu/fairuse.

Source: http://www.alfa-biz.com/Gasketed-Plate-Heat-Exchanger.asp Source: http://www.hiwtc.com/photo/products/16/02/14/21470.jpg

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Jooshgostar Equipments Manufacturing Company (JEMCO). All rightsreserved. This content is excluded from our Creative Commons license.For more information, see http://ocw.mit.edu/fairuse.

http://www.alfa-biz.com/Gasketed-Plate-Heat-Exchanger.asphttp://www.hiwtc.com/photo/products/16/02/14/21470.jpghttp://ocw.mit.edu/fairusehttp://ocw.mit.edu/fairuse

Hx Heat Transfer Mechanisms

Other design parameters should largely determine this choice

After Ramesh K. Shah, Dusan P. Sekulic. Fundamentals of Heat Exchanger Design. John Wiley & Sons, Inc. (2003).

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Heat Exchanger Classification by Heat Transfer Mechanism

Single-phase convectionon both sides

Single-phase convectionon one side, two-phaseconvection on other side

Combined convection andradiative heat transfer

Two-phase convection on both sides

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Heat Exchangers - Questions

What type to use?What working fluids?What geometry? Flow considerations? Laminar or

turbulent? Where is the tradeoff between cost & performance? Materials concerns? See also: T. Kuppan. Heat exchanger design handbook.

and Som, Introduction To Heat Transfer.

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Heat Transport

Main problem: Get process heat from the reactor to the hydrogen & biofuels plants

How? Must consider: Temperatures Losses Flow rates Flow transients

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Heat Transport Long Distance

How to model it? Thermal resistances FEM Loop analysis

How to pump it? Forced? Gravity? Distance from Rx to H2, biofuel plant is one

of the most important parameters

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Heat Transport - Questions

What are the constraints? (TH-Rx ) , TC-H2, TC-bioHow far does the heat have to go? Where to take the heat from? How to transport it? How to model it? What/where are losses? Should some of it be stored...

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