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Active VS Passive Thermal Management

Active VS Passive Thermal Management Backgrounder

Active VS Passive Thermal Management -With the rapid development of high frequency and high speed electronic devices and integrated circuit technology, the total power density of electronic components has increased significantly while the physical size has become smaller and smaller, and the heat flow density has also increased, so the high temperature environment will inevitably affect the performance of electronic components, which requires more efficient thermal control of them.

How to solve the thermal problems of electronic components is the focus at this stage. Thermal management system solutions are gradually becoming more efficient, more refined and more integrated. The main heat dissipation methods at this stage are natural, forced, liquid, cooling, evacuation and heat pipe.

According to whether the heat dissipation method requires external energy, the chip heat dissipation method is divided into active and passive, active heat dissipation mainly includes forced convection heat dissipation, vapour compression cooling and thermoelectric cooling, etc. Passive heat dissipation mainly includes natural convection heat dissipation, heat pipe cooling and phase change heat storage heat dissipation.

Active vs Passive Thermal Management-Thermal Management

What is the difference between passive and active heat dissipation?

“Heat dissipation” refers to the process of transferring heat from the surface of an object to the environment when the temperature of the object is higher than the ambient temperature. Active cooling includes air cooling (fans), liquid cooling, heat pipe cooling, etc. Passive cooling includes heat sinks, thermal grease, thermal adhesive, thermal paste, graphite, etc.

When the laptop is powered on, hundreds of millions of transistors in the CPU and GPU heat up, making the temperature of the laptop higher than room temperature. If nothing is done at this point and the ICs are exposed to air, some of the heat will automatically be transferred to the air until the circuit temperature is the same as the room temperature and thermal equilibrium is reached, and this process is passive cooling.

Passive cooling is the use of air and heat sink temperature difference through the natural flow of air to take away the heat on the heat sink, cooling efficiency is low, but the fan does not turn more power saving, the ambient temperature is high then the host internal temperature is too high will have a negative impact on the life of the computer. Active cooling is the use of fans to draw air to take away the heat from the heatsink, which is more efficient but also more power efficient and has a negative impact on the life of the cooling fan.

Active cooling method

Active cooling is divided into air-cooled cooling, water-cooled cooling, liquid-cooled cooling and heat pipe cooling, depending on the cooling method used.

1. Air-cooled cooling

Air-cooled cooling is now the most common and highest use of a cooling method, belonging to the active cooling, this cooling method can solve our usual cooling needs, mature technology and moderate price, and therefore is commonly used in the market. Air-cooled heat sinks are simple, inexpensive, safe and reliable. However, it has some drawbacks, it does not reduce the temperature below room temperature, it is noisy due to the rotation of the fan and it can cause fan vibration if not installed properly.

The heat source transfers the heat by thermal conduction to the heat conducting medium, which in turn transfers the heat to the base of the heat sink, which transfers the heat to the ribs of the heat sink and through the fan to the air molecules by forced convection, which distributes the heat into the air. The fan continuously blows cold air into the heat sink and hot air out, completing the thermal dissipation process.

2 . Water cooling

Water-cooled cooling is the use of water instead of air, through the movement of water between the heat sinks through thermal convection to take away excess heat. The working principle of the water cooling system is very simple, it is to use the water pump to pump the water out of the water reservoir, through the water pipe into the heat exchanger that covers the top, then the water comes out of the other mouth of the heat exchanger, through the water pipe back to the water reservoir, and so on in a continuous cycle, taking the heat away from the surface. The whole water cooling system includes the heat exchanger, the circulation system, the water tank, the pump and the water. The cooling capacity of the water cooling system is very strong.

3 . Liquid cooling

The principle of liquid cooling is the same as that of water cooling, and they use the same cooling method to dissipate heat. The difference is that the flow in the circulation system is heat-conducting silicone oil instead of water, which has the obvious advantage of not causing damage to the hardware due to damage to the circulation system.

4. Heat pipe

Heat pipe belongs to a heat transfer element, which makes full use of the principle of heat conduction and the rapid heat transfer nature of the cooling medium, through the evaporation and condensation of the liquid in the fully enclosed vacuum tube to transfer heat, has a very high thermal conductivity, good isothermal, hot and cold sides of the heat transfer area can be arbitrarily changed, can be a long distance heat transfer, can control the temperature and a series of advantages, and the heat exchanger composed of heat pipe has high heat transfer efficiency, compact structure, small fluid resistance loss, etc., and heat pipe. Compact structure, small fluid resistance loss and other advantages. Its thermal conductivity has far exceeded the thermal conductivity of any known metal.

Passive cooling method

Passive heat dissipation means that the heat generated by a heat sink, such as a CPU, is dissipated naturally into the air. The effect of heat dissipation is proportional to the size of the heat sink, but because heat is dissipated naturally, the effect is of course greatly reduced, and is often used in equipment that does not require space, or to dissipate heat from components that do not generate much heat.
The liquid cooling system uses the large heat transfer coefficient of the liquid flow to transfer the high heat, which is eventually carried away by the coolant passing through the internal flow channels of the device.

Trumonytechs' system simulation engineering

Trumonytechs thermal management of battery packs is divided into component level thermal management within the pack and system and thermal management containing both inside and outside the pack. Generally, for the simulation of the thermal management performance within the battery pack, a 3D CFD simulation is carried out using STAR CCM+, while for the whole battery pack thermal management system, a 1D system simulation is carried out using Amesim. In the simulation process, we analyse the following data: pressure drop, temperature difference between the inlet and outlet of the cold plate, temperature difference between the surface of the cold plate and the maximum and minimum temperature of the cell. We use the simulation to predict the temperature distribution of the battery pack, the flow distribution and pressure distribution of the cooling system, and thus the performance of the thermal management system.

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