႔ Chapter-5 Heat Exchangers

5-1

Chapter-5 Heat Exchangers

Heat exchan work input ႔ heat transfer) device) H ႔ ႔ ႔ flui transfer)

“hot fluid” ႔ “hot medium” “cold fluid” ႔ “cold medium”

႔ ႔ (heat (transfer)

Heat exchanger transfer) transfer (phase transfer) heat exchanger Saturated s l (transfer)

ဤ h (types) selection criteria)

႔ ႔ - liquid) ႔ vapor) ႔

႔ ႔ ႔ - condens ႔ ႔ ႔ ႔

Chillers and Chilled Water Systems ႔

5-2

၅.၁ (Fundamentals) ႔

Where Rate of heat transfer Overall coefficient of heat transfer from hot fluid to cold fluid Heat transfer area of the heat exchanger associated with U Log Mean Temperature Difference (LMTD)

Overall coefficient of heat transfer fluid ႔ fluid overall coefficient of heat transfer

( ) ( )

( ) ( )

heat t overall coefficient of h Log Mean Temperature D L counter ၁

T1= Hot fluid (in) T2= Hot fluid (out) t1= Cold fluid (in) t2= Cold fluid (out)

၅-၁ Temperature distribution in conunter flow heat exchanger

၅-၁) (temperatu ႔ temperature differential) “heating fluid” H (t2) cold flu (T2) T2 < t2 100% true counter heat excha temperature cross

႔ application

lo

( )

surface area) performance)

႔ Chapter-5 Heat Exchangers

5-3

heat exch surface area) A ႔ ႔ heat transfer surface)

၅.၂ Heat Exchanger ႔

( ) Counter flow shell and tube heat exchanger ( ) Counter flow plate heat exchanger fluid

၅.၂.၁ Shell and Tube Heat Exchangers

Shell and ၭ tubular) welded) ႔ ႔ welded) U tube (both ends straight tube) tube

longitudinal center S Tube (၁) U Tube Heat Exchangers

၅-၂ U-Tube ၭ shell and tube heat exchangers

(၂ Straight Tube Exchangers

၅-၃( ) Straight Tube Exchangers ၅-၃( ) Straight Tube Exchangers

(၃ Shell and Coil Exchangers

၅-၄ Shell and coil exchangers ၅-၅ Shell and coil exchangers

Chillers and Chilled Water Systems ႔

5-4

၅-၆ Fixed tube sheet heat exchanger

၅-၇( ) U tube heat exchanger ၅-၇( ) Heat exchanger baffles

၅-၈ Flow path of gasketed plat heat exchanger ၅-၉ Flow path of welded plate heat exchanger

၅.၂.၂ Plate Heat Exchangers Plate heat exchanger

Plate plate heat exchanger Hot fluid cold fluid ႔ plate w

opening or port) ႔

“plate pack” (bar) ႔ ca ႔ pressure drop)

႔ Chapter-5 Heat Exchangers

5-5

Plate

gasket material ႔

Ga Nitrile butyl rubber ( gasket Ethylene-propylene terpolymer (EPDM) gasket Gaske ႇ counter

၅-၁၀ Flow Path of Heat Exchanger ၅-၁၁ Components of a gasketed plate heat exchanger

Plate Plate ႔ “cassette”

N - standard R

Brazing Plate b -

႔ plate) (brazing) closed ႔ (plate) ႔ Double Double shell and plate heat exchanger

Double single ႔

Chillers and Chilled Water Systems ႔

5-6

၅-၁၂ Double wall plate heat exchanger

၅-၁၂ welding p

၅.၃ Heat Exchanger (Components) HVAC ႔

ASME Boiler and Pressure Vessel Code kPa

၅-၁၃ Exploded view of straight tube heat exchanger ၅-၁၄

၅.၃.၁ Shell and Tube Components (၅-၁၄) shell and ( ) Shells (ဃ) Tube sheets ( ) Baffles tube supports tie rods spacers ( ) Heads ႔ ( ) Tubes

Shell (c (inlet nozzle) outlet nozzle) nozzle)

spacers ႔ stainless steel) V b V shell pressure drop)

Tube steel pipe) Tube diameter gauge) material exchanger (performance)

႔ Chapter-5 Heat Exchangers

5-7

Tube sheet baffle Tube sheet “pitch”

Head ႔ c ႔ ႔

၅-၁၅ Plate heat exchanger ၅-၁၆ Plate heat exchanger

(၅-၁၆) ႔

၅.၃.၂ Plate Heat Exchanger Component c Fixed Frame Plates -

cold ႔ fixed frame pla ၄ - ႔ NPT connection ႔ St

( Movable Pressure Plate movable)

Movable pressure plate

Plate Pack channel p

႔ titanium ႔ ႔ thermal performance (pressure drop) ႔

Chillers and Chilled Water Systems ႔

5-8

(ဃ olt Compression bolt mov f

႔

Carrying and Guide Bar Carrying and guide bar

“carrying bar” “guide bar” stainless steel) aluminum) ႔ carbon steel) zinc chromate ၅-၁၁ “ ” “ ”

Support Column Support column

Splash guard Splash guard aluminum)

Drip pan Drip pan stainless steel) shut down)

႔ ႔

၅.၄ Application) primary energy source)

heat

ASHRAE handbook heat exchanger ( ) (boiler) (steam) central water system

hot water condense

( ) hot water system

( ) (special temperature requirement) hot fluid cold fluid ႔ ႔ isolation

(ဃ) (energy saving application)

( ) Refrigeration application (evaporators condensers liquid coolers)

၅.၅ (Selection Criteria) Heat exchanger

႔ Chapter-5 Heat Exchangers

5-9

၅.၅.၁ Thermal/Mechanical Design Shell and tube heat exchanger

Plate heat exchanger

၅.၅.၂ Thermal Performance H

(heat transfer surface area) heat transfer surface) material) stainless steel) (flow rate velo (v ႔

၅.၅.၃

Fixed tube sheet heat exchan (temperature differences) ႔ gasketed plate unit

၅.၅.၄ (Pressure Drop) Shell and f

ႏိုင္ pressure drop) ႔ p ႔ pressure drop) p surface area) thermal performance ႔ pressure dr

၅.၅.၅ Heat transfer ႇ

(performance) ႔ heat transfer (surface) Fouling factor

Fouling allowance shell and tube exchanger (suspended solid) plate unit Plate unit (flow channel) Plate exchanger fluid velocity Shell and tube exchanger tube (surface area) fluid velocity ႔ thermal performance

Shell and shell

Chillers and Chilled Water Systems ႔

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Plate unit velocity (flow channel) (heat transfer surface area) channel V performance ႔

၅.၅.၆ (Cost) Approach temperature plate heat exchanger

(initial cost) Approach temperature shell and tube unit Stainless steel plate unit

၅.၅.၇ Serviceability Shell-and-tube heat exchanger service Tube

configuration ႔ Plate heat exchanger plate ႔ Gasket plate Capacity plate

၅.၅.၈ (Space Requirements) (small-diameter) tube shell and tube heat

exchanger (cost effective) ႔ ႔ ႔ (large diameters) heat exchanger Plate heat exchanger

၅.၅.၉ Steam HVAC application (steam) shell and tube unit

(industrial) (food process) ႔ (steam) plate heat exchanger

၅.၆ (Installation)

၅.၆.၁ Control Temperature sensor h Temperature sensor ႔ secondary flow Valve secondary flow ႔ regulate

၅.၆.၂ Piping Heat exchanger

(air vent)

၅.၆.၃ Pressure Relief

႔ Chapter-5 Heat Exchangers

5-11

heat exchanger safety pressure relief valve shutoff valve

၅.၆.၄ Flow Path Hot fluid cooled fluid

heat exchanger (performance)

၅.၆.၅ Condensate Removal ႔ (steam) heat exchanger

႔ (steam) ႔ condensate ႔ Condensate (drain) (capacity) ႔ ႔ modulating steam control valve system vacuum breaker (draining) steam trap Steam trap condensate removal ASHRAE chapter 10

၅.၆.၆ Insulation fluid ႔ heat exchanger insulate

2005 ASHRAE handbook Fundamentals chapter 23 insulation

၅.၇ (၇) Shell and tube heat exchanger (၇)

၅.၇.၁ Heat Exchanger Tube Diameter Heat exchanger tube diameter

velocity ႔ (pressure drop) T

၅.၇.၂ Thickness of the Tube Heat corrosion) flow resistance)

axial force) pressure

၅.၇.၃ Heat Exchanger Shell Diameter and Tube Length Shell (diameter) tube ႔ heat exchanger

Tube ႔

၅.၇.၄ Tube Corrugation Tube corrugation shell and tube heat exchanger performance

Corrugated cardboard tube fluid turbulence

Chillers and Chilled Water Systems ႔

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၅.၇.၅ Tube Layout Tube layout heat exchanger tube ႔

layout ႔ Triangular twisted triangular square rotated square ႔ Triangular tube (heat transfer) Square tubing ႔

၅.၇.၆ Tube Pitch “ ” (interconnected tube) (center

pitch (outside diameter) (၁.၂၅)

၅.၇.၇ Heat Exchanger Baffles “ ” shell and tube heat exchanger Baffle tube

႔ (sagging) (vibrating) ႔ (pressure drop) (heat transfer) ႔ baffle (spacing)

၅-၁၇ Heat exchanger baffles

၅-၁၈ Heat exchanger baffles

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