ياريت الموضوع ده بسرعه بعد اذنكم
مش المفروض تعرض اكتر عن الموضوع علشان نقدر نرد عليك طيب انا اعرف هو ايه حتي مش فاهم منك حاجه كل الي قولته (ياريت الموضوع ده بسرعه بعد اذنكم) بصراحه مجهود عظيم وشرح وافي واستفسار مقنع جزاك الله خير
لا لا انا مش معاك هو صحيح معندوش زوق بس متحرجوش كده في
انت مين ياعم الامور ياللى عملى فيها احمد زويل وانت شكلك مبتفهمشى اى حاجه
وانت يا بتاع الذوق انت ايه فهمك انت فى الحاجات دى انت اخرك كلبتين ترعاهم
انت لو كنت بتفهم اساسا كنت هتلاقى اسم الموضوع موجودdesigning of heat sinksانت اللى دخلك هندسه ظلمك انت والواد التانى بتاع الذوق اللى مبيفهمشى اساسا
يا سيدى متزعلش قوى كده
أنا كنت فاكرك واحد تانى
و حبيت أعمل فيه مقلب
و على العموم أنا أسف
و يا ريت تتقبل إعتذارى
وانا قبلت اعتذارك
What characteristics make a heatsink a good one? There's a number of factors to consider:
High heatsink surface. It's at the surface of the heatsink where the thermal transfer takes place. Therefore, heatsinks should be designed to have a large surface; this goal can be reached by using a large amount of fine fins, or by increasing the size of the heatsink itself.
Good aerodynamics. Heatsinks must be designed in a way that air can easily and quickly float through the cooler, and reach all cooling fins. Especially heatsinks having a very large amount of fine fins, with small distances between the fins may not allow good air flow. A compromise between high surface (many fins with small gaps between them) and good aerodynamics must be found. This also depends on the fan the heatsink is used with: A powerful fan can force air even through a heatsink with lots of fine fins with only small gaps for air flow - whereas on a passive heatsink, there should be fewer cooling fins with more space between them. Therefore, simply adding a fan to a large heatsink designed for fanless usage doesn't necessarily result in a good cooler.
Good thermal transfer within the heatsink. Large cooling fins are pointless if the heat can't reach them, so the heatsink must be designed to allow good thermal transfer from the heat source to the fins. Thicker fins have better thermal conductivity; so again, a compromise between high surface (many thin fins) and good thermal transfer (thicker fins) must be found. Of course, the material used has a major influence on thermal transfer within the heatsink. Sometimes, heat pipes are used to lead the heat from the heat source to the parts of the fins that are further away from the heat source.
Perfect flatness of the contact area. The part of the heatsink that is in contact with the heat source must be perfectly flat. A flat contact area allows you to use a thinner layer of thermal compound, which will reduce the thermal resistance between heatsink and heat source.
Good mounting method. For good thermal transfer, the pressure between heatsink and heat source must be high. Heatsink clips must be designed to provide a strong pressure, while still being reasonably easy to install. Heatsink mountings with screws/springs are often better than regular clips. Thermoconductive glue or sticky tape should only be used in situations where mounting with clips or screws isn't possible.
Measuring heatsink performance; thermal resistance θ
Heatsink performance is measured in °C/W (or K/W - since we're dealing with temperature differences, there is no difference between Celsius and Kelvin scale here). We refer to this as thermal resistance (θ).
An example for what these values mean: if a thermal load of 20W is applied to a heatsink, and this causes the temperature of the heat source to raise by 10°C, the heatsink has a rating of of 10°C/20W = 0.5°C/W.
A θ value is valid only for a certain power load and a certain temperature range.
The thermal resistance of standard coolers for PC CPUs is usually not specified by the heatsink manufacturers, and if it is, it's often inaccurate or intentionally skewed for marketing purposes. You cannot judge heatsink performance by comparing θ specifications from different manufacturers.
The θ values specified by manufacturers specialized in heatsinks for industrial applications (especially large passive heatsinks) are usually more accurate, though.
Heatsink testing is not an easy task; many of the heatsink reviews found on the countless cooling-related sites on the net are not done properly.
The thermal conductivity of the heatsink's material has a major impact on cooling performance. Thermal conductivity is measured in W/mK; higher values mean better conductivity.
As a rule of thumb, materials with a high electrical conductivity also have a high thermal conductivity.
Alloys have lower thermal conductivity than pure metals, but may have better mechanical or chemical (corrosion) properties.
The following materials are commonly used for heatsinks:
Aluminum. It has a thermal conductivity of 205W/mK, which is good (as a comparison: steel has about 50W/mK). The production of aluminum heatsinks is inexpensive; they can be made using extrusion Due to its softness, aluminum can also be milled quickly; die-casting and even cold forging are also possible (see part 2 of this guide for more information about production methods). Aluminum is also very light (thus, an aluminum heatsink will put less stress on its mounting when the unit is moved around).
Copper's thermal conductivity is about twice as high as aluminum - almost 400W/mK. This makes it an excellent material for heatsinks; but its disadvantages include high weight, high price, and less choice as far as production methods are concerned. Copper heatsinks can be milled, die-cast, or made of copper plates bonded together; extrusion is not possible.
To combine the advantages of aluminum and copper, heatsinks can be made of aluminum and copper bonded together. Here, the area in contact with the heat source is made of copper, which helps lead the heat away to the outer parts of the heatsink. The first heatsink for PC CPUs with an embedded copper piece was the Alpha P7125 (for first-generation Slot A Athlon CPUs). Keep in mind that a copper embedding is only useful if it is tightly bonded to the aluminum part for good thermal transfer. This is not always the case, especially not with inexpensive coolers. If the thermal transfer between the copper and the aluminum is poor, the copper embedding may do more harm than good.
Silver has an even higher thermal conductivity than copper, but only by about 10%. This does not justify the much higher price for heatsink production - however, pulverized silver is a common ingredient in high-end .
The most popular production method for heatsinks is extrusion. With the aid of high pressure and temperature, a flow of aluminum is forced through a shaped opening. This results in a long stick having the same form as the opening. Later, the aluminum is stretched, which straightens it and improves its mechanical properties (better strength through re-alignment on a molecular level). Finally, the long aluminum sticks are cut into heatsink-sized pieces, and possibly milled to improve flatness of the contact area. Even though the concept is simple, the machines involved are huge. If you are interested in how exactly extrusion works,
The classic extruded heatsink has a base plate with fins on one side. If a fan is used, the direction of the air flow is orthogonal to the direction of the extrusion.
With this classic extruded heatsink design, the air from the fan will at some point "hit" the base plate; it can escape only at two sides. A high pressure may occur within the heatsink, which is bad for air flow.
Modern CPUs have only a small contact area between die and heatsink. Therefore, it is possible to design extruded heatsinks where the direction of the air flow is identical to the direction of extrusion; they feature a thick core which leads the heat upwards. Air can more easily flow through the heatsink, and escape at all sides. The core is located below the fan motor, where little air flow occurs anyways.
Another heatsink production method is die-casting. Unlike extrusion, it also suitable for producing copper heatsinks. It gives designers a lot of freedom as far as the form of the heatsink is concerned; however, height of the fins is limited, and fins cannot be made very thin.
Heatsinks with very fine and also high fins can be produced by cold forging. Cold forging uses impression dies as well, but the material is forced into the die (roughly) at room temperature. Obviously, very high pressure is required. Alpha was the cold-forged heatsink pioneer; by now, other companies, for example Taisol, also produce such heatsinks
Heatsinks can also be milled or cut from a solid block of metal. This leaves a lot of freedom to the heatsink designer; however, such heatsinks are rather expensive to produce.
Originally developed for HP PA-RISC CPUs, these heatsinks were, at the time, years ahead of the competition. Agilent later entered the market of PC CPU coolers, but they were never available in high volume, most likely due to high production costs. For a short time, surplus PolarLogic heatsinks were available on the market, and some retailers modified them to fit Socket 370 and Slot A CPUs.
Bonded fin / folded fin
Instead of extruding, forging, or milling fins, it is also possible to simply use copper (or aluminum) plates as fins, and bond them on a base plate. If each fin is made of a separate plate, we refer to such heatsinks as bonded fin heatsinks. If all fins are made of one large plate that is folded to form the fins, we have a folded fin heatsink. Advantages of such heatsink designs include high surface, and low weight. However, the performance is only good if the bonding is done properly.
Heatsink surface treatment
Aluminum heatsinks are usually anodized; a choice of many colors is available. One might think that black is good, because it is best for heat emission by radiation. This is wrong. Heatsinks get rid of heat by convection (that is, heat is transferred to the air molecules travelling along the heatsink surface - if a fan is involved, we call it "forced convection"). For convection, the color does not matter at all.
Copper heatsinks are sometimes plated with silver or even gold (seriously - Zalman produced such a heatsink, model CNPS3000GOLD). This is supposed to prevent corrosion and improve thermal characteristics. But actually, the plating is too thin to have any effect on thermal conductivity. It is true that the surface of a copper heatsink may slightly corrode; but since they are operating in a dry environment, and do not have to withstand extreme temperatures, corrosion is not really a problem. During the lifetime of a PC heatsink, the corrosion layer will not get thick enough to have any negative effect on cooling.
So, do not worry about the surface treatment of your heatsinks, and do not spend extra for some special surface treatment (such as silver plating). Technically, there is no justification for it.
Ex for heat sink :
AMD ATHLON 1.5GHz+
INTEL PIII 1.13GHz & TUALATIN up to 2.0GHz
Fan Dimension 60x60x25 mm
Rated Voltage 12VDC
Started Voltage 7VDC
Power Input 4.44W
FAN Speed 7000±10% RPM
Max. Air Flow 38CFM
Interface Material Bergquist 225U
Dimensions 80x60x65 mm
Bearing System Ball Bearing
Life Time 50,000 hours
Connector 3 PIN
Heat sinks for transistors
Heat sinks are needed for transistors passing large currents.
Why is a heat sink needed?
Waste heat is produced in transistors due to the current flowing through them. If you find that a transistor is becoming too hot to touch it certainly needs a heat sink! The heat sink helps to dissipate (remove) the heat by transferring it to the surrounding air.
The rate of producing waste heat is called the thermal power, P. The base current IB is too small to contribute much heat, so the thermal power is determined by the collector current IC and the voltage VCE across the transistor:
P = IC × VCE (see diagram below)
The heat is not a problem if IC is small or if the transistor is used as a switch because when 'full on' VCE is almost zero. However, power transistors used in circuits such as an audio amplifier or a motor speed controller will be partly on most of the time and VCE may be about half the supply voltage. These power transistors will almost certainly need a heat sink to prevent them overheating. Power transistors usually have bolt holes for attaching heat sinks, but clip-on heat sinks are also available. Make sure you use the right type for your transistor.
Many transistors have metal cases which are connected to one of their leads so it may be necessary to insulate the heat sink from the transistor. Insulating kits are available with a mica sheet and a plastic sleeve for the bolt. Heat-conducting paste can be used to improve heat flow from the transistor to the heat sink, this is especially important if an insulation kit is used.
Heat sink ratings
Heat sinks are rated by their thermal resistance (Rth) in °C/W. For example 2°C/W means the heat sink (and therefore the component attached to it) will be 2°C hotter than the surrounding air for every 1W of heat it is dissipating. Note that a lower thermal resistance means a better heat sink.
This is how you work out the required heat sink rating:
Work out thermal power to be dissipated, P = IC × VCE
If in doubt use the largest likely value for IC and assume that VCE is half the supply voltage.
For example if a power transistor is passing 1A and connected to a 12V supply, the power P is about 1 × ½ × 12 = 6W.
Find the maximum operating temperature (Tmax) for the transistor if you can, otherwise assume Tmax = 100°C.
Estimate the maximum ambient (surrounding air) temperature (Tair). If the heat sink is going to be outside the case Tair = 25°C is reasonable, but inside it will be higher (perhaps 40°C) allowing for everything to warm up in operation.
Work out the maximum thermal resistance (Rth) for the heat sink using: Rth = (Tmax - Tair) / P
With the example values given above: Rth = (100-25)/6 = 12.5°C/W.
Choose a heat sink with a thermal resistance which is less than the value calculated above (remember lower value means better heat sinking!) for example 5°C/W would be a sensible choice to allow a safety margin. A 5°C/W heat sink dissipating 6W will have a temperature difference of 5 × 6 = 30°C so the transistor temperature will rise to 25 + 30 = 55°C (safely less than the 100°C maximum).
All the above assumes the transistor is at the same temperature as the heat sink. This is a reasonable assumption if they are firmly bolted or clipped together. However, you may have to put a mica sheet or similar between them to provide electrical insulation, then the transistor will be hotter than the heat sink and the calculation becomes more difficult. For typical mica sheets you should subtract 2°C/W from the thermal resistance (Rth) value calculated in step 4 above.
If this all seems too complex you can try attaching a moderately large heat sink and hope for the best. Cautiously monitor the transistor temperature with your finger, if it becomes painfully hot switch off immediately and use a larger heat sink!
Why thermal resistance?
The term 'thermal resistance' is used because it is analagous to electrical resistance:
The temperature difference across the heat sink (between the transistor and air) is like voltage (potential difference) across a resistor.
The thermal power (rate of heat) flowing through the heat sink from transistor to air is like current flowing through a resistor.
So R = V/I becomes Rth = (Tmax - Tair)/P
Just as you need a voltage difference to make current flow, you need a temperature difference to make heat flow.
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