Shell and Tube Heat Exchanger

Table of Contents

1. Introduction to Shell and Tube Heat Exchangers
   • Overview and Industry Applications
   • Historical Development
   • Market Position
2. Design Fundamentals
   • Basic Components
   • Configuration Types
   • Flow Arrangements
3. Construction and Materials
   • Shell Design
   • Tube Configuration
   • Baffle Systems
4. Thermal Design Methodology
   • Heat Transfer Analysis
   • LMTD and NTU Methods
   • Performance Calculations
5. Hydraulic Design Considerations
   • Pressure Drop Analysis
   • Flow Distribution
   • Velocity Optimization
6. Types and Classifications
7. Performance Optimization
8. Maintenance and Troubleshooting
9. Standards and Codes
10. Case Studies
11. References and Nomenclature

1. Introduction to Shell and Tube Heat Exchangers

1.1 Overview

Shell and tube heat exchangers represent the most widely adopted heat transfer technology in industrial applications worldwide, accounting for approximately 65% of the global heat exchanger market. These robust devices facilitate thermal energy exchange between two fluid streams flowing through separate paths—one through a bundle of tubes and the other around the tubes within an enclosing shell.

Shell and Tube Heat Exchanger - Complete Assembly SHELL IN SHELL OUT TUBE IN TUBE OUT Shell Side Tube Bundle Front Header Baffle Rear Header → Tube Flow → ↓ Shell Flow ↓

Figure 1: Schematic representation of a shell and tube heat exchanger showing major components

1.2 Industry Applications

United Heat Exchangers has successfully deployed shell and tube heat exchangers across diverse industrial sectors:

1.3 Advantages and Limitations

2. Design Fundamentals

2.1 Basic Components

A shell and tube heat exchanger consists of several critical components, each serving specific thermal and structural functions:

Major Components - Exploded View SHELL Outer cylindrical vessel TUBE BUNDLE Heat transfer tubes arranged in pattern TUBE SHEETS Support and seal tubes Separate shell/tube fluids BAFFLES Direct shell-side flow Support tubes NOZZLES Inlet/outlet connections for both fluids CHANNEL/HEADER Distribute tube-side fluid Enable flow reversal Assembled Configuration

Figure 2: Detailed component breakdown of shell and tube heat exchanger

2.2 Component Specifications

Component	Function	Typical Materials	Design Considerations
Shell	Contains tube bundle and shell-side fluid	Carbon steel, stainless steel, titanium	Pressure rating, corrosion resistance, thermal expansion
Tubes	Provide heat transfer surface	Copper, brass, stainless steel, titanium, nickel alloys	Diameter, thickness, length, fouling resistance
Tube Sheets	Support tubes, separate fluids	Same as shell, often cladded	Thickness for pressure, hole drilling pattern
Baffles	Direct flow, support tubes, enhance mixing	Carbon steel, stainless steel	Spacing, cut percentage, type (segmental, disc-donut)
Channel/Header	Distribute tube-side fluid	Carbon steel, cast iron, stainless steel	Flow distribution, accessibility for maintenance
Nozzles	Fluid entry/exit points	Forged steel, stainless steel	Size for velocity limits, orientation, reinforcement

2.3 Flow Arrangements

The relative flow direction of shell and tube-side fluids significantly impacts thermal performance:

Common Flow Arrangements Parallel Flow (Co-current) HOT COLD Both fluids flow in same direction Lower thermal effectiveness Counter Flow HOT COLD Fluids flow in opposite directions Highest thermal effectiveness ✓ Cross Flow (1-shell, 2-tube pass) SHELL TUBE Perpendicular flow directions Multi-pass (1-shell, 4-tube pass) TUBE IN OUT SHELL Enhanced heat transfer, compact design Thermal Effectiveness Comparison: Counter-flow (90-95%) > Cross-flow (70-80%) > Parallel-flow (50-60%)

Figure 3: Comparison of major flow arrangements and their thermal characteristics

3. Types and Classifications (TEMA Standards)

The Tubular Exchanger Manufacturers Association (TEMA) provides a standardized classification system based on the configuration of the front end, shell, and rear end components. This three-letter designation enables precise specification of heat exchanger types.

3.1 TEMA Type Designations

TEMA Heat Exchanger Classifications FRONT END SHELL TYPE REAR END Type A Channel & Removable Cover Easy tube access Type E One-pass Shell Most common Type L Fixed Tubesheet Like front end Type B Bonnet (Integral Cover) High pressure Type F Two-pass Shell Longitudinal baffle Type M Fixed Tubesheet Like type L Type C Channel Integral with Tubesheet Type G Split Flow Center inlet/outlets Type N Fixed Tubesheet Like channel Type P Divided Flow Double split flow Type S Floating Head with Backing Device Type X Cross Flow Pure crossflow Type T Pull-through Floating Head Type U U-Tube Bundle Thermal expansion free Example: AES Designation A (Channel & Cover) + E (One-pass Shell) + S (Floating Head) = Most Versatile

Figure 4: TEMA standard classifications for shell and tube heat exchangers

3.2 Selection Criteria by Type

TEMA Type	Best Applications	Advantages	Limitations
AEL/BEL (Fixed Tubesheet)	Clean services, low thermal expansion, cooling water	Lowest cost, compact, easy to seal	No shell-side cleaning, thermal stress issues
AES/BES (Floating Head)	Fouling services, large temperature difference	Bundle removable, no thermal stress, shell-side cleanable	Higher cost, more complex sealing
AEU/BEU (U-Tube)	High temperature difference, clean tube-side	Low cost, thermal expansion free, bundle removable	Tube-side difficult to clean, no individual tube replacement
AET/BET (Pull-through)	Severe fouling, frequent cleaning required	Easy bundle removal, full shell-side access	Highest cost, large shell diameter required

4. Thermal Design Methodology

4.1 Heat Transfer Analysis

The fundamental heat transfer equation for shell and tube heat exchangers is:

Where:

• Q = Heat transfer rate (W or Btu/hr)
• U = Overall heat transfer coefficient (W/m²·K or Btu/hr·ft²·°F)
• A = Heat transfer area (m² or ft²)
• ΔTLMTD = Log-mean temperature difference (K or °F)
• FT = Temperature correction factor for flow arrangement

4.2 Overall Heat Transfer Coefficient

The overall heat transfer coefficient accounts for all thermal resistances in series:

Where:

• ho = Shell-side heat transfer coefficient
• hi = Tube-side heat transfer coefficient
• Rfo = Shell-side fouling resistance
• Rfi = Tube-side fouling resistance
• kw = Tube wall thermal conductivity
• do, di = Tube outer and inner diameters

Thermal Resistance Network Ts (Shell Bulk) Tt (Tube Bulk) Shell-Side Convection 1/ho Fouling (Shell) Rfo Wall Conduction Rwall Fouling (Tube) Rfi Tube-Side Convection 1/hi Total Resistance: Rtotal = Σ(All Resistances) Heat Transfer Rate: Q = ΔT/Rtotal = U × A × ΔT Note: Fouling resistances typically dominate in long-term operation

Figure 5: Thermal resistance network showing all heat transfer barriers

4.3 Log-Mean Temperature Difference (LMTD)

For counter-current flow (most efficient):

For other flow arrangements, apply correction factor FT:

4.4 Typical Heat Transfer Coefficients

Service	Shell Side (W/m²·K)	Tube Side (W/m²·K)	Overall U (W/m²·K)
Water to water	3,000 - 8,500	3,500 - 11,000	850 - 1,700
Water to oil (light)	900 - 1,900	400 - 1,150	110 - 350
Water to oil (heavy)	450 - 900	55 - 170	50 - 200
Steam to water	5,700 - 17,000	3,500 - 11,000	1,500 - 4,000
Gas to gas	30 - 300	30 - 300	10 - 50
Condensing organic vapor to water	700 - 1,150	3,500 - 11,000	230 - 850

5. Hydraulic Design Considerations

5.1 Pressure Drop Analysis

Pressure drop must be evaluated for both shell and tube sides to ensure pumping power requirements are acceptable:

Tube-Side Pressure Drop

Where:

• f = Friction factor (Moody diagram or Darcy-Weisbach)
• L = Tube length
• Np = Number of tube passes
• Ï� = Fluid density
• v = Tube-side velocity
• di = Tube inner diameter

Shell-Side Pressure Drop

Shell-side pressure drop is more complex due to flow pattern variations. The Kern method or Bell-Delaware method provides detailed calculations.

5.2 Velocity Guidelines

Fluid Type	Tube Side (m/s)	Shell Side (m/s)	Considerations
Water	1.0 - 2.5	0.3 - 1.0	Higher velocities reduce fouling, increase erosion
Light oils	0.5 - 1.5	0.2 - 0.6	Lower viscosity allows moderate velocities
Heavy oils	0.3 - 1.0	0.1 - 0.4	High viscosity limits velocity, increases ΔP
Steam/vapor	15 - 50	10 - 30	Low density allows high velocities
Gases	10 - 30	5 - 15	Keep below Mach 0.3 to avoid noise

5.3 Baffle Design

Baffles serve multiple functions: directing shell-side flow, supporting tubes, and enhancing heat transfer.

Segmental Baffle Configuration Baffle Cut Cross-flow Window flow Design Parameters Baffle Cut: 15-45% • 25% typical • Larger cut = lower ΔP Baffle Spacing: • Minimum: 0.2 × Ds • Maximum: Ds • Typical: 0.3-0.5 × Ds Number of Baffles: Nb = (L/B) - 1 L = tube length, B = spacing

Figure 6: Segmental baffle design showing flow patterns and key parameters

Baffle Type	Characteristics	Applications
Segmental (Single)	Most common, 15-45% cut, alternating orientation	General purpose, balanced performance
Double Segmental	Two segments per baffle, lower pressure drop	Low ΔP applications, clean fluids
Disc and Donut	Alternating disc and ring baffles	Longitudinal flow, low ΔP
Rod Baffles	Rods instead of plates, minimal flow restriction	Very low ΔP, vibration-sensitive
No-tubes-in-window	Tubes only in crossflow zone	High performance, complex fabrication

6. Performance Optimization

6.1 Tube Layout Patterns

Tube Layout Patterns Square (90°) Pattern ✓ Easy to clean mechanically ✓ Straight cleaning lanes ✗ Lower tube density Pitch: Typically 1.25 × do Best for: Fouling services Triangular (30°) Pattern ✓ Highest tube density ✓ Compact design ✗ Difficult to clean Pitch: Typically 1.25 × do Best for: Clean services Rotated Square (45°) ✓ Good compromise ✓ Moderate tube density ✓ Better cleaning than 30° Pitch: Typically 1.25 × do Best for: General purpose

Figure 7: Tube layout patterns and their respective advantages

6.2 Performance Enhancement Techniques

6.3 Fouling Mitigation Strategies

Fouling Type	Causes	Mitigation Strategies	Typical Rf (m²·K/W)
Particulate	Suspended solids, rust, scale	Filtration, high velocity (>1 m/s), larger tube diameter	0.0002 - 0.001
Crystallization	Salt precipitation, hardness	Water treatment, temperature control, acid cleaning	0.0002 - 0.0005
Biological	Algae, bacteria, biofilm	Chlorination, UV treatment, biocides, higher temperature	0.0001 - 0.0004
Chemical Reaction	Polymerization, coking	Temperature limits, inhibitors, inert atmosphere	0.0005 - 0.002
Corrosion	Oxidation, galvanic action	Material selection, coatings, cathodic protection	0.0002 - 0.0005

7. Maintenance and Troubleshooting

7.1 Preventive Maintenance Schedule

Frequency	Activity	Purpose
Daily	Monitor temperatures, pressures, flow rates	Detect performance degradation early
Weekly	Check for leaks, unusual vibration, noise	Identify mechanical problems
Monthly	Verify gasket condition, tighten bolts if needed	Prevent leaks and maintain seal integrity
Quarterly	Inspect for corrosion, erosion at nozzles	Assess material degradation
Semi-Annual	Clean tube bundle (chemical or mechanical)	Restore heat transfer performance
Annual	Hydrostatic test, NDT inspection, tube integrity check	Ensure safety and structural integrity
3-5 Years	Replace gaskets, inspect for tube plugging needs	Major overhaul and component replacement

7.2 Cleaning Methods

7.3 Common Problems and Solutions

Problem	Symptoms	Possible Causes	Solutions
Reduced Heat Transfer	Higher outlet temp, lower duty	Fouling, scaling, air in system	Clean exchanger, vent air, check fluid properties
High Pressure Drop	Increased ΔP readings	Fouling, partial plugging, high velocity	Clean tubes, check flow rate, inspect for blockages
Tube Leakage	Cross-contamination, pressure loss	Corrosion, erosion, vibration fatigue	Plug leaking tubes, replace tube bundle if severe
Shell Leakage	External fluid leaks	Gasket failure, flange corrosion	Replace gaskets, retorque bolts, inspect flanges
Vibration/Noise	Rattling, humming sounds	Flow-induced vibration, loose baffles	Check velocities, add tube supports, reduce flow
Uneven Temperature Distribution	Hot/cold spots	Flow maldistribution, plugged tubes	Check tube passes, clear blockages, verify flow rates

8. Standards and Codes

8.1 Design Standards

Standard	Title	Scope	Application Region
ASME BPVC Section VIII	Pressure Vessel Code	Design, fabrication, inspection of pressure vessels	USA, widely adopted internationally
TEMA Standards	Tubular Exchanger Manufacturers Association	Mechanical standards for shell and tube exchangers	Global industry standard
PED 2014/68/EU	Pressure Equipment Directive	Safety requirements for pressure equipment	European Union
EN 13445	Unfired Pressure Vessels	European standard for pressure vessel design	European Union
API 660/661/662	API Heat Exchanger Standards	Shell-and-tube exchangers for petroleum industry	Oil & gas industry worldwide
HEI Standards	Heat Exchange Institute	Standards for power plant heat exchangers	Power generation industry

8.2 TEMA Classes

TEMA defines three service classes based on application severity:

8.3 Material Standards

Component	Common Materials	Standards
Tubes	Carbon steel, copper, brass, stainless steel, titanium, nickel alloys	ASTM A179, A213, B111, B338, B622
Shell	Carbon steel, stainless steel, clad steel	ASTM A516, A240, SA-285
Tube Sheets	Carbon steel, stainless steel, clad materials	ASTM A516, A240, A265 (clad)
Baffles	Carbon steel, stainless steel	ASTM A516, A240
Gaskets	Rubber, graphite, PTFE, spiral wound	ASME B16.20, B16.21

9. Case Studies from United Heat Exchangers

Case Study 1: Crude Oil Preheater - Refinery Application

Parameter	Shell Side (Hot)	Tube Side (Cold)
Fluid	Distillate product	Crude oil
Flow rate	85,000 kg/hr	120,000 kg/hr
Inlet temperature	290°C	95°C
Outlet temperature	180°C	220°C
Pressure	4.5 bar	22 bar
Pressure drop (max)	0.7 bar	1.2 bar

Design Solution:

• Shell: 1,200 mm ID × 12,000 mm length, carbon steel A516-70
• Tubes: 622 tubes, 25.4 mm OD × 2.11 mm wall, 6 m length, SS 316L
• Configuration: 1-shell pass, 4-tube passes (floating head design)
• Heat duty: 3.85 MW
• Baffle spacing: 450 mm, 25% cut segmental baffles

Results: Unit operating successfully for 8+ years with bi-annual cleaning. Achieved 12% energy savings compared to previous design. Fouling rate within predicted limits.

Case Study 2: Chiller Evaporator - HVAC Application

Parameter	Shell Side	Tube Side
Fluid	R-134a refrigerant (evaporating)	Chilled water
Flow rate	18,500 kg/hr	380 m³/hr
Temperature	4.5°C (saturated)	12°C in / 7°C out
Pressure	3.2 bar (evaporation)	4.5 bar

Design Solution:

• Shell: 800 mm ID × 4,500 mm, carbon steel with internal coating
• Tubes: 440 U-tubes, 19.05 mm OD, enhanced (internal grooves)
• Configuration: Flooded evaporator, 2-tube passes
• Heat duty: 7.04 MW (2,000 TR)
• Overall U: 2,850 W/m²·K (with enhancement)

Results: Exceeded rated capacity by 4%. Energy efficiency ratio improved by 8% compared to standard smooth tubes. Low maintenance—only annual inspection required.

Case Study 3: Steam Condenser - Power Plant

Parameter	Value
Steam flow rate	285 tons/hr
Condensing temperature	45°C (vacuum conditions)
Cooling water flow	48,000 m³/hr
Cooling water temp rise	28°C to 38°C
Heat duty	645 MW

Design Solution:

• Type: Two-pass surface condenser with divided waterbox
• Tubes: 42,000 tubes, titanium Grade 2 (seawater cooling)
• Tube size: 25 mm OD × 0.7 mm wall × 12 m length
• Total surface area: 39,500 m²
• Vacuum: 94% (0.1 bar absolute)

Results: Plant operating at design efficiency. Titanium tubes showing no corrosion after 5 years in seawater service. Tube cleaning performed every 6 months using ball cleaning system.

10. Nomenclature

Symbol	Description	Units (SI)
A	Heat transfer area	m²
Cp	Specific heat capacity	J/(kg·K)
di, do	Tube inner and outer diameter	m
Ds	Shell inside diameter	m
f	Friction factor	-
FT	LMTD correction factor	-
h	Heat transfer coefficient	W/(m²·K)
k	Thermal conductivity	W/(m·K)
L	Tube length	m
�	Mass flow rate	kg/s
Np	Number of tube passes	-
P	Pressure	Pa
Q	Heat transfer rate	W
Re	Reynolds number	-
Rf	Fouling resistance	m²·K/W
T	Temperature	°C or K
U	Overall heat transfer coefficient	W/(m²·K)
v	Velocity	m/s
ΔP	Pressure drop	Pa
ΔT	Temperature difference	K
μ	Dynamic viscosity	Pa·s
�	Density	kg/m³