How do phones cool down without a fan?

Phones generate heat from the battery, processor, and other components when in use. Without proper cooling, this heat can cause the phone to malfunction or overheat. So how do phones dissipate heat without needing active cooling like a fan? There are several passive cooling methods used:

Heat Pipes

Many phones contain heat pipes, which are hollow tubes filled with liquid that can quickly transfer heat. The liquid evaporates at the hot end, absorbing heat, and then condenses at the cool end, dissipating the heat. This allows heat to be rapidly transferred away from heat-producing components.

Heat Sinks

Heat sinks are materials, like graphite sheets or copper, that conduct heat well. These are placed against or near hot components like the processor to draw heat away and distribute it over a larger surface area. The heat then passively dissipates into the air.

Thermal Interface Materials

TIMs are compounds like thermal paste or thermal pads that are placed between hot components and heat sinks. By filling air pockets, TIMs facilitate better heat transfer between the surfaces so heat can be conducted away more efficiently.

Vents and Openings

Carefully placed vents, openings, and gaps in the phone casing allow hot air to escape and cooler air to enter through convection. This air circulation passively cools the hot components.

Heat Spreading

Copper heat spreaders are sometimes used to distribute heat over a larger surface area. Rather than concentrating in hot spots, this allows the heat to dissipate more evenly and passively across the phone.

Component Spacing

Proper spacing between components prevents them from heating each other up. Allowing space between heat generating components like the battery, processor, RAM etc. avoids compounding the heat in one area.

Power Management

Throttling the processor speed or limiting other power draws during intense usage prevents overheating by reducing heat generation in the first place. This power management allows passive cooling to better dissipate the heat.

Case Material

Some phones use polycarbonate or other plastics for the case rather than metals like aluminum. Plastics tend to insulate heat rather than conduct it to the outer case, keeping the interior cooler.

Heat Pipes

Heat pipes are one of the most important cooling methods used in phones. They can transfer large amounts of heat using passive liquid evaporation and condensation:

  • The heat pipe is a sealed hollow tube often made of copper or aluminum.
  • It is partially filled with a liquid such as water or alcohol.
  • One end of the tube is located near the heat source like the processor.
  • Heat from the source causes the liquid to evaporate into vapor, absorbing thermal energy.
  • The vapor travels along the tube to the cooler end where it condenses back into liquid, releasing the stored thermal energy.
  • The cycle repeats, rapidly transferring heat via the movement of the liquid/vapor.
  • Typically a porous wick along the inside of the tube returns the condensate to the hot end through capillary action.

This passive system can transfer large amounts of heat even with temperature differences as small as 5°C between the ends. Some advantages of heat pipes include:

  • Can transfer vastly more heat than solid metal rods of the same size.
  • Very low thermal resistance allowing effective heat dissipation.
  • Relatively inexpensive to manufacture.
  • Scalable – can transfer anything from a few watts to several kilowatts of thermal power.
  • Maintenance free with no moving parts.

Heat pipes are adaptable to many configurations, like multiple evaporator branches or condenser arrays, to efficiently cool all heat producing components in smartphones.

Vapor Chambers

A vapor chamber is like an extensive flattened heat pipe. It contains liquid that evaporates across a large internal surface area, transferring heat between the hot source and outer walls where heat can dissipate. This allows widespread cooling over a broad area rather than at concentrated points. Vapor chambers are often integrated with heat spreaders. Advantages include:

  • Large surface area for effective heat dissipation.
  • No mechanical/moving parts.
  • Minimal temperature gradient between heat source and casing.
  • Can be customized to required size and shape.

Vapor chambers are more expensive than heat pipes but provide very efficient cooling for hot spots like smartphone processors and batteries.

Heat Sinks

Heat sinks help transfer and dissipate heat in phones through conduction. Some ways they are used:

  • Direct contact: Heat sinks like copper or aluminum plates are placed directly against hot components. Their high thermal conductivity draws heat away into the large finned surface area where air can cool it effectively.
  • Heat spreaders: Graphite or copper sheets conduct heat away from hot spots and spread it evenly across the phone surface for better passive cooling.
  • Casing surface: Some phone materials like aluminum alloy act as large heat sink surfaces, conducting heat externally where it easily dissipates.

Factors that improve heat sinks performance:

  • High thermal conductivity – copper or aluminum are often used.
  • Large surface area – finned or large flat plates improve dissipation.
  • Good contact – thermal interface material removes air gaps between hot components and heat sink.

Heat sinks provide passive cooling through conduction and are simple and inexpensive to implement in smartphones.

Thermal Interface Materials (TIMs)

TIMs are a key part of effective passive cooling in phones. They improve transfer of heat between hot components and heat sinks/spreaders, allowing efficient conduction. Some types include:

  • Thermal paste – a thick conductive compound applied between surfaces. Fills microscopic valleys and improves heat transfer.
  • Thermal pads – softer pad-like material that conforms between uneven surfaces.
  • Phase change materials – waxy substances that melt at certain temperatures to fill gaps and voids.

Benefits of using TIMs:

  • Fill tiny air pockets between hot components and cooling elements.
  • Better surface contact improves heat transfer through conduction.
  • Allow heat sinks and heat spreaders to work more efficiently.
  • Cheap and easy to apply – small amount can make big difference.

High-quality TIMs enhance passive cooling while adding minimal cost to phone manufacturing.

Convection through Vents

Creating intentional air flow paths allows convection to passively cool phones:

  • Perforations or vents in the phone case allow hot interior air to escape and cooler external air to enter.
  • No fans required – passive airflow depends on natural convection currents.
  • Strategic vent placement targets hot component locations.
  • Effective passive cooling with minimal moving parts or power draw.

Convection can also be used internally. Channels between components let hot air rise and exit while allowing cool air to flow in and circulate.

While less effective than other methods alone, convection airflow complements the phone’s overall passive cooling strategy.

Component Spacing

How phone components are positioned also affects passive cooling:

  • Adequate spacing prevents components generating significant heat from being located too close together.
  • Allows heat to dissipate over a larger area instead of compounding.
  • Spaces between hot components act as thermal insulators.
  • Allows airflow to cool surrounding board and parts.

Manufacturers use good layout practices and keep clearance between high-heat components. Cramming parts together creates hotspots that impede passive cooling. Careful spacing improves temperature management.

Power Management

Power management is an important complementary method along with physical cooling techniques:

  • Reduce power to hot components like CPU during intense usage to temporarily limit heat generation.
  • Strategically throttle CPU speed to find balance between performance and heat.
  • Switch off unnecessary components when heating up.
  • Optimize software and apps for efficiency – slower processing means less power usage and heat.

Power management gives other passive cooling methods thermal headroom needed to dissipate heat effectively. This avoids overheating without always needing to run fans.

Case Materials

The phone casing also impacts heat dissipation:

  • Plastic polymers like polycarbonate insulate heat from transferring out of the phone.
  • Metals like aluminum readily conduct heat externally where it can dissipate.
  • Glass cases trap heat inside while blocking airflow.
  • Material choice balances durability, cost, and thermal characteristics.

Lightweight plastics are an inexpensive way to passively slow heat conduction. But metal or composite materials often make better thermal paths to keep the phone internals cooler.

Other Methods

Some other passive cooling methods used in smartphones include:

  • Heat absorbing gels and foams – Applied between components to capture heat.
  • Liquid cooling – Direct contact with circulating coolant fluid for very high heat loads.
  • Thermoelectric cooling – Use power input instead of phase change to remove heat.
  • Evaporative cooling – Absorb heat using liquid that can evaporate to gasoline gas.

These can provide supplemental cooling but are less common due to higher cost and complexity compared to mainstream passive methods.


In summary, modern smartphones leverage various passive cooling techniques to dissipate heat without fans:

  • Heat pipes and vapor chambers transport heat using liquid-vapor phase change.
  • Heat sinks and heat spreaders conduct heat to external surfaces.
  • TIMs facilitate heat transfer from sources to sinks.
  • Convection moves hot air out through vents.
  • Component spacing, positioning, and power management prevent heat concentration.
  • Casing material choices affect heat flow.

Through thoughtful engineering and physics-based design, smartphones can run smoothly without overheating even under heavy loads. Multiple integrated passive methods allow modern phone processors to provide substantial performance in compact form factors without active cooling components.