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What Is Heat Dissipation?
Nov 21, 2018


What is heat dissipation?


What does heat dissipation mean?



Heat dissipation is a type of heat transfer. Heat dissipation occurs when an object that is hotter than other objects is placed in an environment where the heat of the hotter object is transferred to the colder objects and the surrounding environment. 


Heat dissipation can occur through a variety of means.The way of heat dissipation is radiation heat dissipation, conduction heat dissipation, convection heat dissipation, and evaporation heat dissipation.

heat dissipation of led light

Corrosionpedia explains Heat Dissipation


Heat dissipation is closely related to energy dissipation. Energy dissipation is a measure of energy lost due to other forces. This can occur in many forms, such as kinetic energy loss caused by the forces of friction. Heat dissipation is simply a subtype of energy dissipation.


Heat can be dissipated through many different methods. One method that dissipates heat is convection, which is a transfer of heat through moving fluids. An example of this could be a convection oven that uses air (the fluid) to transfer heat. Another method is conduction, which allows heat to dissipate throughout a material and possibly into a different material that is in contact with the hot material. An example is an electric stovetop that is heated through electrical resistance. Finally, another type of heat dissipation occurs via radiation; this type of heat dissipation is illustrated by a microwave oven.



heat dissipation of led lights


Factors affecting the magnitude of the heat dissipation


1.Temperature difference between the medium to be measured and the ambient temperature of the thermometer

2.Heat capacity of the thermometer (and its components)

3.Heat penetration coefficient of the material of the thermometer

4.Thermal conductivity of the thermometer (and its components)

5.Mass ratios (thermowell, neck tube, medium to be measured)

The physical design of the thermometer is, in the final analysis, the consideration of the sum of all the mentioned influencing factors.


How to calculate heat dissipation in watts?

input power temperature

Selection Procedure:

Determine input power in watts per square feet by dividing the heat dissipated in the enclosure (in watts) by the enclosure surface area (in square feet).

Locate on the graph the appropriate input power on the horizontal axis and draw a line vertically until it intersects the temperature rise curve.

Read horizontally to determine the enclosure temperature rise.

Example:

What is the temperature rise that can be expected from a 48″ x 36″ x 16″ enclosure with 300 watts of heat dissipated within it?


Solution:

Surface Area = 2[(48×36) + (48×16) + (36×16)] divided by 144 =

42 square feet


Input Power = 300/42 = 7.1 Watts/SqFt.


From Curve: Temp. Rise = 30°F (16.7°C)


How to calculate heat dissipation from power consumption?


Heat Dissipation in LED flood lights

Heat has a certain thermal resistance during the transfer process. The thermal resistance from the device die to the bottom of the device is Rjc, the thermal resistance between the bottom of the device and the heat sink is Rcs, the heat dissipation of the heat sink to the surrounding space is Rsa, and the total thermal resistance Rja=Rjc+Rcs +Rsa. 


If the maximum power loss of the device is Pd, and the device allows a junction temperature of Tj and an ambient temperature of Ta, the allowable total thermal resistance Rja can be found by the following equation.


Rja ≤(Tj-Ta)/Pd


Then calculate the maximum allowable heat sink to ambient temperature thermal resistance Rsa is:


Rsa ≤ (Tj-Ta) / Pd- (Rjc + Rcs)


For design considerations, generally Tj is 125 °C. In the case of a bad ambient temperature, Ta = 40 ° C ~ 60 ° C is generally set. The size of the Rjc is related to the die size and package structure and can generally be found in the device data sheet. 


The size of the Rcs is related to the mounting technology and the package of the device. If the device is made of thermal grease or thermal pad, and then mounted with the heat sink, its Rcs is typically 0.1 °C / W ~ 0.2 ° C / W; if the bottom of the device is not insulated, additional mica insulation is required, then the Rcs can reach 1 °C/W. 


Pd is the actual maximum power loss, which can be calculated according to the operating conditions of different devices. In this way, Rsa can be calculated and the appropriate heat sink can be selected according to the calculated Rsa value.


heat flow

How to calculate heat dissipation of an equipment?


The heat dissipation is not the total input power of the equipment. For a motor, you have to use the motor efficiency, the use factor, the motor load ans the power rating.


If you don't have these data, I suggest you to add a frequency and efficiency factor. For example : 


Biomotor tool (200V @ 30A) = 6000W

- Factor use : 0.2, equivalent of 12min of usage in 1 hour (0.2*60min)

- Efficiency : 0.2, so 20% of the total input power is dissipated in heat

- Total heat : 6000W*0.2*0.2 = 240W, 240W*3.412 = 819 BTU/H


Unless the LED light is a electric coil, remember that not all the input power is dissipated in heat. Without these factor, your cooling load will be over estimated. Here is a rule of thumb to estimate the total cooling load.

 For more details, please contact us at email: info@razorlux.com