Heat Exchangers: Working Principle and Types
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🔧 Working Principle of Heat Exchangers
A heat exchanger is a device that transfers heat between two or more fluids (liquid or gas) without mixing them. The main principle behind heat exchangers is thermal conduction, where heat flows from a hot fluid to a cooler one through a solid barrier (usually metal) or directly when fluids are in contact.
🔁 Key Concepts:
No direct mixing: Fluids are usually separated by a solid wall or flow in separate channels.
Heat Transfer Direction: Heat always moves from the hotter to the colder fluid.
Types of Flow:
Parallel Flow – both fluids move in the same direction.
Counter Flow – fluids move in opposite directions (more efficient).
Cross Flow – fluids move at right angles to each other.
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🧰 Types of Heat Exchangers
1. Shell and Tube Heat Exchanger
Structure: Consists of a series of tubes inside a cylindrical shell.
Use: Common in oil refineries and power plants.
Advantage: Handles high pressure and temperature.
2. Plate Heat Exchanger
Structure: Thin corrugated plates stacked together, fluids flow between alternate plates.
Use: HVAC systems, dairy and food processing.
Advantage: High efficiency, compact design.
3. Finned Tube Heat Exchanger
Structure: Tubes with external fins to increase surface area.
Use: Air conditioning, car radiators.
Advantage: Improved heat transfer to air.
4. Double Pipe Heat Exchanger
Structure: One pipe inside another; fluids flow in inner and outer pipes.
Use: Small industries and labs.
Advantage: Simple design, low cost.
5. Air Cooled Heat Exchanger
Structure: Uses ambient air to cool process fluids.
Use: Oil refineries, chemical plants.
Advantage: No water required for cooling.
6. Regenerative Heat Exchanger
Structure: Uses a temporary heat storage medium (like a ceramic matrix) that gets alternately heated and cooled.
Use: Gas turbines, air preheaters.
Advantage: Reuses heat efficiently.
7. Condensers and Evaporators (in HVAC)
Condensers: Remove heat from refrigerant gas, turning it into liquid.
Evaporators: Absorb heat into the refrigerant, turning liquid into vapor.
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📌 Summary
Heat exchangers are critical in power generation, chemical processing, automotive, and HVAC systems. Choosing the right type depends on:
* Fluid type
* Operating pressure & temperature
* Heat transfer efficiency needed
* Space and cost constraints
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