Welcome to the course in Heat Transfer (MMV031) – L1Martin Andersson & Zan Wu

Agenda

• Organisation

• Introduction to Heat Transfer

• Heat Exchangers (Ex 108)

Course improvement compared to last years

• 2016: The lectures and tutorial sessions are integrated, mainly because it is hard for most students to focus on theory (lectures) for 90 minutes.

• 2015: Exercises where students are expected to solve problems themselves or in small groups are added. Instead the amount of tutorial sessions (where the teacher solved problems) are decreased.

• 2014: 3 DLs for home assignments was implemented (instead of 1)

Contents of the course

• Heat Conduction• Convection• Thermal Radiation• Condensation• Evaporation, Boiling• Heat Exchangers

Organisation

• Lectures with tutorials• Guest lectures• Exercises

• Mandatory home assignments

• Exam (mandatory)

Organisation

• Examiner: Associate Professor Martin Andersson

• Teachers: Martin Andersson and Zan Wu (offices at 5th

floor M-building)

• Course administrator: Elna Andersson (office at 5th floor M-building)

Organisation

• Course literature: Introduction to Heat Transfer, SundénB., WIT Press

• Examination: Tuesday 22nd March, 14-19 (Vic 1C-D) – Exam is 50 p + 5 p if all home assignments are delivered in

time

– 40 % theoretical part + 60 % problem solving part

– Grade 3 requires 22 p (min 5p on theoretical part)

– Grade 4 requires 33 p (min 5p on theoretical part)

– Grade 5 requires 44 p (min 5p on theoretical part)

Guest lectures and Study Visit

• Alfa Laval (study visit)– World leading company in plate heat exchangers

• Guest lecture(s):– John Weisend, ESS

– Fredrik Nilsson, Heatex– Magnus Genrup, LTH (guru in turbines)

– Mats Annerfeldt, Siemens (date not confirmed)

Introduction

• Heat is energy passing a system boundary due to a temperature difference

• Heat is a form of energy in transition.

• Heat conduction• Heat convection (natural (no pump, fan etc) or forced)• Thermal radiation

Introduction

Introduction

Heat conduction

T1T2

T1 > T2

qThickness b

λ

q = λ(T1-T2)/b

Heat conduction

Solids Carbon Steel λ = 15- 50 W/mK

Polymers, λ = 0.1-0.5 W/mK

Liquids

Water λ = 0.6 W/mK

Oil λ = 0.15 W/mK

Gases

Air λ = 0.025 W/mK

H2 (hydrogen) λ = 0.2 W/mK

Thermal conductivity (examples)

Convection

q = α(TS-T∞) = h(TS-T∞)

Tsq

U∞ T∞ Ts > T∞

How to determine α or h

• Depends on: – Flow velociy– Fluid (gas or liquid)– Geometry – sometimes on temperature– Forced convection, Natural convection, Mixed convection

• Nu = αL/λf = function (Re=UL/ν, Pr=µcp/λf , geometry) or• Nu = αL/λf = function (Gr=gβΔΤL3/ν2, Pr=µcp/λf , geometry) or• Nu = αL/λf = function (Re, Gr, Pr, geometry)

Thermal Radiation

Qnet = A1F12εeff (T14-T2

4)

q1

q2 T2

T1

Introduction to heat exchangers (ch 15)

What is a Heat Exchanger?

A heat exchanger is a device that is used to transfer thermal energy (enthalpy) between two or more fluids, between a solid surface and a fluid,

or between solid particulates and a fluid,at different temperaturesand in thermal contact.

Classification of heat exchangers

• Transfer process• Number of fluids• Degree of surface contact• Design features• Flow arrangements • Heat transfer mechanisms

Classification of heat exchangers

Fig. 1 Heat transfer surface area density spectrum ofexchanger surfaces ( Shah, 1981).

Fig. 2 Fluidized-bed heat exchanger.

Fig. 3 (a) Shell-and- tube exchanger with one shell passand one tube pass;

(b) shell-and- tube exchanger with one shell pass and two tube passes.

Fig. 4 Standard shell types and front- andrear-end head types (From TEMA, 1999).

Fig. 5 Gasketed plate-and-frame heat exchanger.

Fig. 6 Plates showing gaskets around the ports (Shah and Focke, 1988).

Fig. 7 Section of a welded plate heat exchanger.

Fig. 9 Spiral plate heat exchanger with both fluids in spiral counter flow.

Fig. 10 (a) Lamella heat exchanger;(b) cross section of a lamella heat exchanger,(c) lamellas

Fig. 11 Printed-circuit cross flow exchanger

Fig. 12 Corrugated fin geometries for plate-fin heat exchangers:(a) plain triangular fin; (b) plain rectangular fin; (c) wavy fin; (d) offset strip fin; (e) multilouver fin; (f) perforated fin.

Fig. 13 (a) Individually finned tubes;(b) flat (continuous) fins on an array of tubes.

Fig. 14 Individually fin tubes.

Fig. 15 Heat wheel or a rotary regenerator madefrom a polyester film.

Classification according to transfer process

Indirect contact type Direct contact type

Direct transfer Storage Fluidized bed Immiscible fluids

Gas-liquid Liquid-vapour

Single-phase Multiphase

Classification according to number of fluids

Two-fluid Three-fluid N-fluid (N > 3)

Classification according to surface compactness

Gas-to-liquid Liquid-to-liquid and phase-change

Compactβ≥ 700 m2/m3

Non-compactβ < 700 m2/m3

Compactβ ≥ 400 m2/m3

Non-compactβ < 400 m2/m3

Classification according to design or type

Tubular Plate-type Extended surface Regenerative

PHE Spiral Plate coil Printed circuit

Gasketed Welded Brazed

Double-pipe Shell-and-tube Spiral tube Pipe coils

Cross-flow to tubes

Parallel flowto tubes

Plate-fin Tube-fin

Ordinary Separatingwall

Heat-pipewall

Rotary Fixed-matrix Rotatinghoods

Classification according to flow arrangements

Single-pass Multipass

Counter flow Parallel flow Cross flow Split flow Divided flow

Extended surface

Cross-Counter flow

Cross-parallel flow

Compound flow

Shell-and-tube Plate

Parallel counter flowm-shell passesn-tube passes

split-flow Divided-flow

Fluid 1 m passesFluid 2 n passes

Classification according to heat transfer mechanisms

Single-phase convection on both sides

Single-phase convection on one side, Two-phase convection on other side

Two-phase convection on both sides

Combined convection and radiative heat transfer

Classification according to process function

Condensers Liquid-to-vaporphase-changeexchangers

Heaters Coolers Chillers

Convective heat transfer

vägg

Fluid1

Fluid2

Overall heat transfer coefficient

mm1 tTR

tUAQ Δ⋅=Δ⋅=!

Expression for overall thermal resistance

oóoFvlw

w

iiFii

1111

oAAA

bAA

TRα

+α

+λ

+α

+α

=

Values of the heat transfer coefficient W/m2K

• Air atmospheric pressure 5-75• Air pressurized 100 - 400• Water, liquid 500-20 000• Organic liquids 50 000• Boiling 2 500 -100 000• Condensation 3 000-100 000

Correlations for the heat transfer coefficient

• Nu = hL/k = function (flow velocity, physical properties, geometry) = function (Re, Pr, geometry)

General research needs

• How to achieve more compact heat exchangers• High thermal efficiency

• Balance between enhanced heat transfer and accompanied pressure drop

• Material issues especially for high temperature applications• Manufacturing methodology

• Fouling

• Non-steady operation

Fouling factors - Försmutsningsfaktorer

Tabell 15-I. FörsmutsningsfaktorerStrömmande medium F/1 α [m2K/W]

Destillerat vatten4101 −×

Sjövatten ( K 325<T ) 4101 −×

Sjövatten ( K 325>T ) 4102 −×

Matarvatten till ångpannor 4102 −×

Bränsleolja 4109 −×

Industriluft 4105.3 −×

Counter current heat exchanger

t

A

dth

dtcdA

Δt

th,in

tc,ut

th,ut

tc,in

Δtb

Δta

)(utin hhh ttCQ −=! )(

inut ccc ttCQ −=!

ch ttt −=Δ ch)( dtdttd −=Δ

hph )( cmC != , cpc )( cmC !=

Counter current Hex

⎟⎟⎠

⎞⎜⎜⎝

⎛−⋅=Δ

hc

11)(CC

Qdtd !

⎟⎟⎠

⎞⎜⎜⎝

⎛−Δ=Δ

hc

11)(CC

tdAUtd

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

Δ

Δ

hc

11)(CC

dAUttd

ccphhp )()( dtcmdtcmtdAUQd !!! −=−=Δ⋅=

Counter current Hex

∫∫ ⎟⎟⎠

⎞⎜⎜⎝

⎛−=

ΔΔ

Δ

Δ

A

CCdAU

ttd

0 hc

t

t

11)(b

a

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

ΔΔ

hca

b 11lnCC

UAtt

⎟⎟⎠

⎞⎜⎜⎝

⎛ −−

−

Δ=

Δ

Δ

Q

tt

Q

tt

tQ

tt

!!! )()(

ln utininut hhcc

ma

b

a

b

abm

lntttt

LMTDt

Δ

ΔΔ−Δ

==Δ

)(

)(ln

)()(

utin

inut

utininut

ch

ch

chchm

tt

tttttt

LMTDt

−

−

−−−==Δ

Expression for overall thermal resistance

Parallel flow Hex,Co-Current Hex

)(

)(ln

)()(

utut

inin

ututinin

ch

ch

chchm

tt

tttttt

t

−

−

−−−=Δ

a

b

abm

lntttt

t

Δ

ΔΔ−Δ

=Δ

t

A

dth

dtcdA

Δt

th,in

tc,in

th,ut

tc,ut

ΔtbΔta

Arbitrary Hex

LMTDFUAQ ⋅⋅=!

F korrektionsfaktor som beror av två parametrar P och R;

F correction factor depending on two parameters P and R

inin

inut

ch

cc

tt

ttP

−

−=

hp

cp

)(

)(

cm

cmR

!

!=

R kan också skrivas; R can also be written

inut

utin

cc

hh

tt

ttR

−

−=

F vs P och/and R; Shell-and-tube heat exchanger; one shell pass, two tube passes

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10.5

0.6

0.7

0.8

0.9

1.0

P

Korre

ktio

nsfa

ktor

, F

R =

6.0

4.0

3.0

2.0 1.5

1.0

0.8

0.6

0.4

0.2

0.1

tc,in

tc,ut

th,ut

th,in

inin

inut

ch

cc

tt

ttP

−

−=

inut

utin

cc

hh

tt

ttR

−

−=