HEAT EXCHANGERS

INTRODUCTION


  • The devices that are used to facilitate heat transfer between two or more fluids at different temperatures are known as heat exchangers.
  • Different types and sizes of heat exchangers are used in steam power plants, chemical processing units, building heating and air conditioning, house hold refrigerators, car radiators, radiators for space vehicles etc.
  • This chapter deals with classification of heat exchangers, the overall heat transfer coefficient, LMTD, NTU method and Effectiveness of heat exchangers.

CLASSIFICATION OF HEAT EXCHANGERS

Heat exchangers are broadly classified based on the following considerations.

1. Classification based on Transfer Process

Based on heat transfer process heat exchangers are classified as direct contact and indirect contact


a) Direct contact

In direct contact heat exchangers, heat transfer takes place between two immiscible fluids like a gas and a liquid coming into direct contact.

e.g.: Cooling towers, jet condensers for water vapour, and other vapors utilizing water spray.

b) Indirect contact

In indirect - contact type of heat exchangers the hot and cold fluids are separated by an impervious surface. There is no mixing of the two fluids and these heat exchangers are also known as surface heat exchangers.

e.g: Automobile radiators.

2. Classification based on Compactness

The ratio of the heat transfer surface area on one side of the heat exchanger to the volume is used as a measure of compactness. The heat exchanger having a surface area density on anyone side greater than about 700 m2/m3 is known as a compact heat exchanger.

e.g.: Automobile radiators (1100 m2/m3),Gas turbine engines (6600 m2/m3),
Human lungs (20,000 m2/m3)

3. Classification based on type of construction

Based on the type of construction heat exchangers are classified as follows.

a) Tubular heat exchangers

  • Tubular heat exchangers are available in many sizes, flow arrangements and types. They can withstand a wide range of operating pressures and temperatures.

  • A commonly used design is shell-and-tube heat exchanger which consists of round tubes mounted on cylindrical shells with their axes parallel to that of the shell.

  • The combination of fluids may be liquid-to-liquid, liquid-to -gas or gas-to-gas.

b) Plate heat exchangers

  • In these types thin plates are used to affect heat transfer. The plates may be either smooth or corrugated.
  • These heat exchangers are suitable only for moderate temperature or pressure as the plate geometry restricts the use of high pressure and temperature differentials.
  • The compactness factor for plate exchangers ranges from 120 to 230 m2/m3.



c) Plate fin heat exchangers

  • These heat exchangers use louvered or corrugated fins separated by flat plates. Fins can be arranged on each side of the plate to get cross-flow, counter-flow or parallel-flow arrangements.
  • These heat exchangers are used for gas-to-gas applications at low pressures (10 atm.) and temperatures not exceeding 800°C.
  • They also find use in cryogenic applications. The compactness factor for these heat exchangers is upto 6000 m2/m3.

d) Tube-fin heat exchangers

  • Such heat exchanges are used when a high operating pressure or an extended surface is needed on one side. The tubes may be either round or flat.
  • Tube-fin heat exchangers are used in gas- 252 Heat and Mass Transfer turbine, nuclear, fuel cell, automobile, airplane, heat pump, refrigeration, Cryogenics etc.
  • The operating pressure is about 30 atm. and the operating temperature ranges from low cryogenic temperatures to about 870 Dc.
  • The maximum compactness ratio is about 330 m2/m3

e) Regenerative heat exchangers

  • Regenerative heat exchangers may be either static type or dynamic type.

  • The static type has no moving parts and consists of a porous mass like balls, pebbles, powders etc. through which hot and cold fluids pass alternatively.

e.g.: air preheaters used in coke manufacturing and glass melting plants.


  • In dynamic type regenerators, the matrix is arranged in the form of a drum which rotates about an axis in such a manner that a given portion of the matrix passes periodically through the hot stream and then through the cold stream.
  • The heat absorbed by the matrix from the hot stream is transferred to the cold stream during its run.

4. Classification based on flow Arrangement

Based on flow arrangement heat exchangers are classified into the following principal types.

a) Parallel-flow

In this heat exchanger, the hot and the cold fluids enter at the same end of the heat exchanger and flow through in the same direction and leave together at the other end as shown in Fig 5(a).

b) Counter flow
In this heat exchanger hot and cold fluids enter in the opposite ends of the heat exchanger and flow in opposite directions as shown in Fig 5(b).

c) Cross flow

In this heat exchanger, the two fluids flow at right angles to each other as shown in Fig 5 (c).
In this arrangement the flow may be mixed or unmixed.

In general, in a cross flow exchanger, three idealized flow arrangements are possible

1.    The fluids are unmixed
2.    One fluid is mixed, and the other is unmixed
3.    Both fluids are mixed.

d) Multipass flow

Since multi passing increases the overall effectiveness over individual effectiveness they are frequently used in heat exchanger design.

Different multipass flow arrangements are "One shell pass, two tube pass" known as "one - two" heat exchanger, "two shell pass, two  tube pass", etc. as shown in Fig 6.



5. Classification based on heat transfer mechanism

Heat exchangers are classified based on the following modes of heat transfer.

1.    Single phase forced or free convection.

2.    Phase change due to boiling and condensation.

3.    Radiation or combined convection and radiation.

3 comments:

  1. I really enjoyed this post. You describe this topic very well. I really enjoy reading your blog and I will definitely bookmark it! Keep up the interesting posts! Thanks for sharing informative blog. Visit here: “ Heat Exchanger Manufacturers

    ReplyDelete
  2. It was very useful information thanks for share it and you explained it well.
    heat exchanger manufacturers

    ReplyDelete
  3. A Plate Type Heat Exchanger plates are simple to maintain because they can be taken out and cleaned separately. But, since they may gather debris or smell, you should avoid them.

    ReplyDelete

Labels

PROJECTS 8086 PIN CONFIGURATION 80X86 PROCESSORS TRANSDUCERS 8086 – ARCHITECTURE Hall-Effect Transducers INTEL 8085 OPTICAL MATERIALS BIPOLAR TRANSISTORS INTEL 8255 Optoelectronic Devices Thermistors thevenin's theorem MAXIMUM MODE CONFIGURATION OF 8086 SYSTEM ASSEMBLY LANGUAGE PROGRAMME OF 80X86 PROCESSORS POWER PLANT ENGINEERING PRIME MOVERS 8279 with 8085 MINIMUM MODE CONFIGURATION OF 8086 SYSTEM MISCELLANEOUS DEVICES MODERN ENGINEERING MATERIALS 8085 Processor- Q and A-1 BASIC CONCEPTS OF FLUID MECHANICS OSCILLATORS 8085 Processor- Q and A-2 Features of 8086 PUMPS AND TURBINES 8031/8051 MICROCONTROLLER Chemfet Transducers DIODES FIRST LAW OF THERMODYNAMICS METHOD OF STATEMENTS 8279 with 8086 HIGH VOLTAGE ENGINEERING OVERVOLATGES AND INSULATION COORDINATION Thermocouples 8251A to 8086 ARCHITECTURE OF 8031/8051 Angle-Beam Transducers DATA TRANSFER INSTRUCTIONS IN 8051/8031 INSTRUCTION SET FOR 8051/8031 INTEL 8279 KEYBOARD AND DISPLAY INTERFACES USING 8279 LOGICAL INSTRUCTIONS FOR 8051/8031 Photonic Transducers TECHNOLOGICAL TIPS THREE POINT STARTER 8257 with 8085 ARITHMETIC INSTRUCTIONS IN 8051/8031 LIGHTNING PHENOMENA Photoelectric Detectors Physical Strain Gage Transducers 8259 PROCESSOR APPLICATIONS OF HALL EFFECT BRANCHING INSTRUCTIONS FOR 8051/8031 CPU OF 8031/8051 Capacitive Transducers DECODER Electromagnetic Transducer Hall voltage INTEL 8051 MICROCONTROLLER INTEL 8251A Insulation Resistance Test PINS AND SIGNALS OF 8031/8051 Physical Transducers Resistive Transducer STARTERS Thermocouple Vacuum Gages USART-INTEL 8251A APPLICATIONs OF 8085 MICROPROCESSOR CAPACITANCE Data Transfer Instructions In 8086 Processors EARTH FAULT RELAY ELECTRIC MOTORS ELECTRICAL AND ELECTRONIC INSTRUMENTS ELECTRICAL BREAKDOWN IN GASES FIELD EFFECT TRANSISTOR (FET) INTEL 8257 IONIZATION AND DECAY PROCESSES Inductive Transducers Microprocessor and Microcontroller OVER CURRENT RELAY OVER CURRENT RELAY TESTING METHODS PhotoConductive Detectors PhotoVoltaic Detectors Registers Of 8051/8031 Microcontroller Testing Methods ADC INTERFACE AMPLIFIERS APPLICATIONS OF 8259 EARTH ELECTRODE RESISTANCE MEASUREMENT TESTING METHODS EARTH FAULT RELAY TESTING METHODS Electricity Ferrodynamic Wattmeter Fiber-Optic Transducers IC TESTER IC TESTER part-2 INTERRUPTS Intravascular imaging transducer LIGHTNING ARRESTERS MEASUREMENT SYSTEM Mechanical imaging transducers Mesh Current-2 Millman's Theorem NEGATIVE FEEDBACK Norton's Polarity Test Potentiometric transducers Ratio Test SERIAL DATA COMMUNICATION SFR OF 8051/8031 SOLIDS AND LIQUIDS Speed Control System 8085 Stepper Motor Control System Winding Resistance Test 20 MVA 6-digits 6-digits 7-segment LEDs 7-segment A-to-D A/D ADC ADVANTAGES OF CORONA ALTERNATOR BY POTIER & ASA METHOD ANALOG TO DIGITAL CONVERTER AUXILIARY TRANSFORMER AUXILIARY TRANSFORMER TESTING AUXILIARY TRANSFORMER TESTING METHODS Analog Devices A–D BERNOULLI’S PRINCIPLE BUS BAR BUS BAR TESTING Basic measuring circuits Bernoulli's Equation Bit Manipulation Instruction Buchholz relay test CORONA POWER LOSS CURRENT TRANSFORMER CURRENT TRANSFORMER TESTING Contact resistance test Current to voltage converter DAC INTERFACE DESCRIBE MULTIPLY-EXCITED Digital Storage Oscilloscope Display Driver Circuit E PROMER ELPLUS NT-111 EPROM AND STATIC RAM EXCITED MAGNETIC FIELD Electrical Machines II- Exp NO.1 Energy Meters FACTORS AFFECTING CORONA FLIP FLOPS Fluid Dynamics and Bernoulli's Equation Fluorescence Chemical Transducers Foil Strain Gages HALL EFFECT HIGH VOLTAGE ENGG HV test HYSTERESIS MOTOR Hall co-efficient Hall voltage and Hall Co-efficient High Voltage Insulator Coating Hot-wire anemometer How to Read a Capacitor? IC TESTER part-1 INSTRUMENT TRANSFORMERS Importance of Hall Effect Insulation resistance check Insulator Coating Knee point Test LEDs LEDs Display Driver LEDs Display Driver Circuit LM35 LOGIC CONTROLLER LPT LPT PORT LPT PORT EXPANDER LPT PORT LPT PORT EXTENDER Life Gone? MAGNETIC FIELD MAGNETIC FIELD SYSTEMS METHOD OF STATEMENT FOR TRANSFORMER STABILITY TEST METHODS OF REDUCING CORONA EFFECT MULTIPLY-EXCITED MULTIPLY-EXCITED MAGNETIC FIELD SYSTEMS Mesh Current Mesh Current-1 Moving Iron Instruments Multiplexing Network Theorems Node Voltage Method On-No Load And On Load Condition PLC PORT EXTENDER POTIER & ASA METHOD POWER TRANSFORMER POWER TRANSFORMER TESTING POWER TRANSFORMER TESTING METHODS PROGRAMMABLE LOGIC PROGRAMMABLE LOGIC CONTROLLER Parallel Port EXPANDER Paschen's law Piezoelectric Wave-Propagation Transducers Potential Transformer RADIO INTERFERENCE RECTIFIERS REGULATION OF ALTERNATOR REGULATION OF THREE PHASE ALTERNATOR Read a Capacitor SINGLY-EXCITED SOLIDS AND LIQUIDS Classical gas laws Secondary effects Semiconductor strain gages Speaker Driver Strain Gages Streamer theory Superposition Superposition theorem Swinburne’s Test TMOD TRANSFORMER TESTING METHODS Tape Recorder Three-Phase Wattmeter Transformer Tap Changer Transformer Testing Vector group test Virus Activity Voltage Insulator Coating Voltage To Frequency Converter Voltage to current converter What is analog-to-digital conversion Windows work for Nokia capacitor labels excitation current test magnetic balance voltage to frequency converter wiki electronic frequency converter testing voltage with a multimeter 50 hz voltages voltmeter

Search More Posts

Followers