Radiator Classification
It is a device designed to dissipate the heat which the coolant has absorbed from the engine.
Two basic types of radiators relative to coolant entrance, downflow and crossflow.
The downflow permits the use of a baffled top tank that can uniformly distribute the coolant over the radiator header. It has the disadvantage of requiring a higher hood line.
The crossflow radiator, which allows a low hoodline, is popular in present passenger car design.
The radiator frontal area should be as square as possible the air distribution through the core more uniform.
The entrance of the coolant into a rectangular shaped radiator should always be through the shortest side. The coolant tube velocity will be higher which results in a greater heat rejection rate especially at low coolant flows.
Too low a coolant velocity also will accelerate scale formation which will cause gradual radiator performance degradation and eventual plugging.
The tube side velocity should generally not be less than about 2-3 ft/sec.
In order to ensure good radiator performance, the exit approach temperature between the air and coolant should be no less than 15 to 20 F. If it is much less than this, it indicates that the radiator is “oversized” for the stated condition or the flow path is too long.
Excessive flow rates can lead to erosion damage of the radiator tubes.
The tube side velocity should generally not be more than about 10 ft/sec.
The radiator is an extended surface heat exchanger where the tubes are the primary surface and the fins are the secondary surface.
Since the hi on the tube side is substantially greater than the air side coefficient, ho, it is necessary to provide a large heat transfer surface on the air side.
two most common types of extended surfaces are the tube and plate fin, and tube and spacer
The tube and spacer surface is used in passenger cars and trucks because of its cost and weight advantage.
Heavy truck and off road radiators are usually of the plate fin type because of their much greater structural strength.
Agricultural radiators have a low fin count (as low as 4 FPI) and have bumps in place of louvers.
The tube side coefficient can be increased for those radiators applications where the coolant flow is in the laminar region by using a multipass arrangement
Usually a two pass radiator should increase the tube flow velocity sufficiently to bring it into the turbulent region.
More than two passes are generally not recommended because of excessive tube side pressure drop,
In those cases of very high heat rejection and limited frontal area, it may become necessary to increase the core depth and number of tube rows.
Each additional row, however, contributes less to the radiators duty because the temperature differential between the air and coolant decreases and results in a subsequent decrease in heat transfer per row, increased weight and fan horsepower.
Increasing the outside surface area by increasing the number of fins per inch is an effective method of improving the radiator duty.
There are three degrees of freedom in selecting the radiator:
I) Radiator type
II) Radiator Depth
III) Number of fins
increasing the fin count also decreases the fin efficiency, increases air side pressure drop and increases vulnerability to air side clogging.
passenger car and light truck, a fin spacing of about 21 FPI is maximum.
Heavy truck, agricultural, off highway and military vehicles should have fin counts in the area of 14 FPI and less.
Two basic types of radiators relative to coolant entrance, downflow and crossflow.
The downflow permits the use of a baffled top tank that can uniformly distribute the coolant over the radiator header. It has the disadvantage of requiring a higher hood line.
The crossflow radiator, which allows a low hoodline, is popular in present passenger car design.
The radiator frontal area should be as square as possible the air distribution through the core more uniform.
The entrance of the coolant into a rectangular shaped radiator should always be through the shortest side. The coolant tube velocity will be higher which results in a greater heat rejection rate especially at low coolant flows.
Too low a coolant velocity also will accelerate scale formation which will cause gradual radiator performance degradation and eventual plugging.
The tube side velocity should generally not be less than about 2-3 ft/sec.
In order to ensure good radiator performance, the exit approach temperature between the air and coolant should be no less than 15 to 20 F. If it is much less than this, it indicates that the radiator is “oversized” for the stated condition or the flow path is too long.
Excessive flow rates can lead to erosion damage of the radiator tubes.
The tube side velocity should generally not be more than about 10 ft/sec.
The radiator is an extended surface heat exchanger where the tubes are the primary surface and the fins are the secondary surface.
Since the hi on the tube side is substantially greater than the air side coefficient, ho, it is necessary to provide a large heat transfer surface on the air side.
two most common types of extended surfaces are the tube and plate fin, and tube and spacer
The tube and spacer surface is used in passenger cars and trucks because of its cost and weight advantage.
Heavy truck and off road radiators are usually of the plate fin type because of their much greater structural strength.
Agricultural radiators have a low fin count (as low as 4 FPI) and have bumps in place of louvers.
The tube side coefficient can be increased for those radiators applications where the coolant flow is in the laminar region by using a multipass arrangement
Usually a two pass radiator should increase the tube flow velocity sufficiently to bring it into the turbulent region.
More than two passes are generally not recommended because of excessive tube side pressure drop,
In those cases of very high heat rejection and limited frontal area, it may become necessary to increase the core depth and number of tube rows.
Each additional row, however, contributes less to the radiators duty because the temperature differential between the air and coolant decreases and results in a subsequent decrease in heat transfer per row, increased weight and fan horsepower.
Increasing the outside surface area by increasing the number of fins per inch is an effective method of improving the radiator duty.
There are three degrees of freedom in selecting the radiator:
I) Radiator type
II) Radiator Depth
III) Number of fins
increasing the fin count also decreases the fin efficiency, increases air side pressure drop and increases vulnerability to air side clogging.
passenger car and light truck, a fin spacing of about 21 FPI is maximum.
Heavy truck, agricultural, off highway and military vehicles should have fin counts in the area of 14 FPI and less.
Radiator Materials
Brass has a low melting point and a good heat conductivity and has properties that make it easy to shape and solder.Copper is a reddish metal that has a high heat conductivity.Lead is used to bond the copper and brass joints.How come the radiators are not made of either brass or copper? Because Brass is a metal that is easy to form and solder or braze (it accepts vibration well, for example). On the other hand, copper transfers heat well, but it is a brittle material and can easily be damaged by vibration.Aluminum core radiators, while not as efficient as copper core (based on same size and construction), are much cheaper to build.Aluminum radiators are not quite strong as brass/copper radiators,The causes of this non-uniformity/maldistribution includeHeat load and flow resistance from air-conditioning and auxiliary heat exchangers placed in front of the "radiator".Non-uniform inlet conditions caused by the radiator grill.
Inherent mismatch between the annular flow of the fan and the rectangular heat exchanger (The fan shroud will never be deep enough to allow full transition)
Inherent mismatch between the annular flow of the fan and the rectangular heat exchanger (The fan shroud will never be deep enough to allow full transition)
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