Types

Heat Exchanger Types

Heat exchangers are ubiquitous to energy conversion and utilization. They involve heat exchange between two fluids separated by a solid and encompass a wide range of flow configurations.

• Concentric-Tube Heat Exchangers

Parallel Flow Counterflow

Simplest configuration.

Superior performance associated with counter flow.

Types (cont.)

• Cross-flow Heat Exchangers

Finned-Both FluidsUnmixed

Unfinned-One Fluid Mixedthe Other Unmixed

For cross-flow over the tubes, fluid motion, and hence mixing, in the transverse direction (y) is prevented for the finned tubes, but occurs for the unfinned condition.

Heat exchanger performance is influenced by mixing.

Types (cont.)

• Shell-and-Tube Heat Exchangers

One Shell Pass and One Tube Pass

Baffles are used to establish a cross-flow and to induce turbulent mixing of the shell-side fluid, both of which enhance convection. The number of tube and shell passes may be varied, e.g.:

One Shell Pass,Two Tube Passes

Two Shell Passes,Four Tube Passes

Types (cont.)

• Compact Heat Exchangers Widely used to achieve large heat rates per unit volume, particularly when one or both fluids is a gas.

Characterized by large heat transfer surface areas per unit volume, small flow passages, and laminar flow.

(a) Fin-tube (flat tubes, continuous plate fins)(b) Fin-tube (circular tubes, continuous plate fins)(c) Fin-tube (circular tubes, circular fins)(d) Plate-fin (single pass)(e) Plate-fin (multipass)

Heat Exchangers

Double-pipe heat exchangerShell and tube heat exchangerPlate and frame heat exchangerSpiral heat exchangerPipe coil exchangerAir-cooled heat exchangers

Double-Pipe Heat Exchanger

A double-pipe exchanger has a pipe inside a pipeThe outside pipe provides the shell. And the inner pipe

provides the tube The warm and cool fluids can run parallel flow or

countercurrent,because it is more efficient Flow rates are very low in a double-pipe heat exchanger

Double-Pipe Heat Exchanger The chemical processing industry commonly uses hairpin

heat exchangers Hairpins are typically rated at 500psig shellside and 500

psig tubeside Fins can be added to the internal tube’s external wall to

increase heat transfer

Double-Pipe Heat Exchanger• Advantages:• Its excellent capacity for thermal expansion• It is easy to install and clean • Its modular design makes it easy to add new sections• Replacement parts are inexpensive and always in supply• Disadvantages• It is not as cost effective as most shell and tube

exchangers • it requires special gaskets

Shell and Tube Heat Exchangers

• The shell and tube heat exchanger is the most common style found in industry

• As the tubeside flow enters the exchanger, flow is directed into tubes that run parallel to each other. these tubes run through a shell that has a fluid passing through it

• Heat energy is transferred through the tube wall into the cooler fluid

• Heat transfer occurs primarily through conduction and convection

Shell and Tube Heat Exchanger---Head

The head can be classified as front-end or rear-end types, the front-end head has five primary designs, the rear-end has eight possible designs

Shell and Tube Heat Exchanger---Shell

• In most cases, the shell is designed to withstand the greatest temperature and pressure condition

• The shell is the largest single part of the heat exchanger

• The shell can be classified as single-pass, double-pass, split flow, double split flow, divided flow, cross-flow

Shell and Tube Heat Exchanger---Tube

• Tube can be plain or dinned• Plain tubes are commonly used in fabrication• Finned tube are starting to make an impact, fins can be

located externally or internally• Tube materials include brass, carbon, …

Shell and Tube Heat Exchanger---Tube Sheet

• Tube sheets are often described as fixed or floating, single or double

• Tube sheets have carefully drilled hole, the ends of the tubes in a heat exchanger are fixed by rolling, welding, or both

• Double tube sheets are used to prevent tubeside leakage of highly corrosive fluids

Shell and Tube Heat Exchanger---Tube Sheet

Engineering specifications take into account thermal tube expansion

If the tube sheet is welded or bolted to the shell, it is called fixed

If the tube sheet is independently secured to the tub head and is allowed to move freely inside the shell, it is called floating

Shell and Tube Heat Exchanger---Baffle

Baffles provide the framework to support and secure the tubes and prevent vibration

The baffle layout increases or decreases fluid and directs flow at specific points

Tubeside baffles are built into the heads to direct tubeside flow

In multipass exchangers, cost goes up with each pass, provide adequate fluid velocities to prevent fouling and to control heat transfer

Shell and Tube Heat Exchanger---Baffle

Each segmental baffle supports half of the tubes Baffles are evenly spaced Segmental baffles may be horizontal or vertical cut Systems transferring large quantities of suspended solids may

use vertical arrangement, which allows liquid and solids to flow around baffles

Horizontal baffles are used in clean service with notches at the bottom to allow liquid drainage on removal from serve

Shell and Tube Heat Exchanger---Baffle

Impingement baffles are used to protect tubing from direct fluid impact

Longitudinal baffles are used inside the shell to split or divide the flow, increase velocity, and provide superior heat transfer capabilities, longitudinal baffles do not extend the entire length of the exchanger since at some point the fluid must flow around it

Shell and Tube Heat Exchanger---Tie Rod

Tie rods and concentric tube spacers keep the baffles in place and evenly spaced

Each hole in the baffle plates is 1/64” larger than the tube’s outside diameter

Shell and Tube Heat Exchanger---Nozzles and Accessory Part

Nozzles and accessory part Inlet and outlet nozzles are sized for pressure

drop and velocity considerations Thermowells, pressure indicator connections,

safety and relief valves, product drains, vents, block valves and control valves

Shell and Tube Heat Exchanger---Fixed Head

In a fixed head, single pass shell and tube heat exchangers, the tubes are connected to two tube sheets which are firmly attached to the shell

in the multipass Shell and tube heat exchangers, the baffle added to the channel head and the lack of a tube side outlet on the discharge head

Temperature differential is less to 200 ℃

Shell and Tube Heat Exchanger---Floating Head

One side of the tube bundle is fixed to the channel head, the other side is unsecured

Floating head exchangers, with their high cross-sectional areas(fins), are designed for high temperature differentials and high flow rate, produces the highest heat transfer efficiency

Shell and Tube Heat Exchanger---U-Tube

The tube sheet connects a series of tubes bent in a U shape, the ends of the tubes are secured to the tube sheet

The total number of tubes is limits Large temperature differentials Each complete U tube has a single fundamental frequency

Plate and Frame Heat Exchanger• It consist of a series of gasketed plates, sandwiched

together by two end plates and compression bolts

Plate and Frame Heat Exchanger

• Easy to disassemble and clean and distribute heat evenly so there are no hot spots

• Plates can easily be added or removed• Low fluid resistance time, low fouling, high heat transfer

Plate and Frame Heat Exchanger• If gaskets leak, they leak to the outside, and gasket easy to

replace• Prevent cross-contamination of products• High turbulence and large pressure drop and small• This device is best suited for vicious or corrosive fluid

slurries• High-pressure and high-temperature limitations (2.5MPa

and 180℃) for protect internal gasket• Gaskets are easily damaged and may not be compatible

with process fluids

Spiral Heat Exchanger• Spiral heat

exchangers are characterized by a compact concentric design that generates high fluid turbulence

• Type 1: spiral flow on both sides

• Type 2: spiral flow-cross-flow

Pipe Coil Exchanger

• Pipe coils are submerged in water or sprayed with water to transfer heat

• This type of operation has a low heat transfer coefficient and requires a lot of space

Air-Cooled Heat Exchanger• Air-cooled heat exchangers provide plain or

dinned tubes connected to an inlet and return header

• Air is used as the outside medium to transfer heat away from the tubes

• Fans are used in a variety of arrangements to apply forced convection for heat transfer coefficients

• Provides a 40 temperature differential between ℃the ambient air and the exiting process fluid

Air-Cooled Heat Exchanger

• simple to construct and cheaper to maintain• Cannot fouling or corrosion• Low operating costs and superior high temperature

removal• Limited in use• High outlet fluid temperature and high initial cost of

equipment• In cases of loss of containment, they would be fire or

explosion

Heat Exchangers and Systems ---Parallel and Series Flow

• in series flow, the tubeside flow in a multipass heat exchanger is discharged into the tubeside flow of the second exchanger

• In parallel flow, the process flow goes through multiple exchangers at the same time

Heat Exchangers and Systems ---Cooling Towers

• The system consists of a cooling tower, heat exchanger, pump

• Cooling water is pumped into the shellside of a heat exchanger and returned (much hotter) to the top of the cooling tower

Heat Exchangers and Systems---Reboilers, Distillation Column

• Rebolier---add heat to a liquid that was once boiling until the liquid boils again

• Associated with the operation of a distillation column, which is energy of heat balance, reboilers are used to restore this balance by adding additional heat for the separation processes

Heat Exchangers and Systems--- Reboilers, Distillation Column

• Take kettle reboiler for example, reboilers take suction off of the bottom products and pump them through their system, so column temperatures are controlled at established set-points

• Other type of reboilers: vertical and horizontal thermosyphon reboilers stab-in reboilers hot oil jacket reboilers

At the End >>• We know the shell and tube heat exchanger consist of Shell side and the tubes

inside it • Two fluids of different temperatures are brought into close contact but they are

not mixing with each other , one fluid flows through the shell and the other fluid flows through the tubes

• The temperature of the two fluids will tend to equalize . The heat are simply exchanged from one fluid to the other and vice versa.

• There are three common types of the shell and tubes heat exchanger 1- U-Tube2- Straight-Tube ( 1-Pass )3 - Straight-Tube ( 2-Pass )• Shell and Tube Heat Exchanger comes with a lot of different shapes and sizes , It

could be large or small or ….

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Heat ExchangersA heat exchanger is a device for transferring heat from one fluid to another. There are three main categories: Recuperative, in which the two fluids are at all times separated by a solid wall; Regenerative, in which each fluid transfers heat to or from a matrix of material; Evaporative (direct contact), in which the enthalpy of vaporization of one of the fluids is used to provide a cooling effect.