24-04-2012, 12:40 PM
Heat Exchanger
Basic Concepts of Heat Exchangers.doc (Size: 120.5 KB / Downloads: 76)
A heat exchanger is a device designed for the purpose of allowing heat transfer from one medium to another at different temperatures. Most commonly, these mediums consist of two fluids that flow close to each other and are separated by a material, often metals, with good heat transfer properties. The fluids are primarily characterized by their temperatures at the entrance to the heat exchanger. The hot (warm, in figure below) fluid, the fluid with the highest temperature initially, transfers heat to the cold fluid as they both pass through the heat exchanger, thus lowering the temperature of the hot fluid and raising the temperature of the cold fluid.
Physics of basic heat exchangers
Two methods are readily used to physically and mathematically explain the purpose of heat exchangers. These two techniques are known as the Log Mean Temperature Difference (LTMD) method and the Effectiveness-NTU method. However, for these techniques to be useable, several assumptions must be made.
• Uniform flow
• Steady flow
• All of the heat transferred from the hot stream is deposited into the cold stream
• No phase change
• Constant specific heats
• Negligible kinetic and potential energy
• U (over heat transfer coefficient) is constant
Heat Exchanger Principles in Automobiles
Most automotive heat exchangers are similar to shell and tube cross flow design, with multiple tube passes. But instead of having a defined shell around the tubes, with another controlled fluid forced across the tubes by means of a pump, there is no limited control volume for the shell. The tubes are open to the air and are dependant upon outside conditions.
Types of Vehicle Heat exchangers
Some types of Automotive Heat Exchangers include but are not limited to radiators, oil coolers and intercoolers. It is possible to use heat exchangers for almost any of the fluids in a vehicle. Air conditioners and heaters are also examples, however they are not restricted to vehicles.
A radiator is a cooling device used in the engine in which hot liquid flows through exposed pipes and transfers heat to the air by fans. Fins are used to conduct the heat from the tubes and transfer it to the air. The fluid used is typically a mixture of ethylene glycol, water and a small amount of corrosion reducer.
Basic Concepts of Heat Exchangers.doc (Size: 120.5 KB / Downloads: 76)
A heat exchanger is a device designed for the purpose of allowing heat transfer from one medium to another at different temperatures. Most commonly, these mediums consist of two fluids that flow close to each other and are separated by a material, often metals, with good heat transfer properties. The fluids are primarily characterized by their temperatures at the entrance to the heat exchanger. The hot (warm, in figure below) fluid, the fluid with the highest temperature initially, transfers heat to the cold fluid as they both pass through the heat exchanger, thus lowering the temperature of the hot fluid and raising the temperature of the cold fluid.
Physics of basic heat exchangers
Two methods are readily used to physically and mathematically explain the purpose of heat exchangers. These two techniques are known as the Log Mean Temperature Difference (LTMD) method and the Effectiveness-NTU method. However, for these techniques to be useable, several assumptions must be made.
• Uniform flow
• Steady flow
• All of the heat transferred from the hot stream is deposited into the cold stream
• No phase change
• Constant specific heats
• Negligible kinetic and potential energy
• U (over heat transfer coefficient) is constant
Heat Exchanger Principles in Automobiles
Most automotive heat exchangers are similar to shell and tube cross flow design, with multiple tube passes. But instead of having a defined shell around the tubes, with another controlled fluid forced across the tubes by means of a pump, there is no limited control volume for the shell. The tubes are open to the air and are dependant upon outside conditions.
Types of Vehicle Heat exchangers
Some types of Automotive Heat Exchangers include but are not limited to radiators, oil coolers and intercoolers. It is possible to use heat exchangers for almost any of the fluids in a vehicle. Air conditioners and heaters are also examples, however they are not restricted to vehicles.
A radiator is a cooling device used in the engine in which hot liquid flows through exposed pipes and transfers heat to the air by fans. Fins are used to conduct the heat from the tubes and transfer it to the air. The fluid used is typically a mixture of ethylene glycol, water and a small amount of corrosion reducer.