temperature in a environment, i.e. a difference of : This would be actual flow through the chassis and not the free air rating of the fan. It should also be noted that "Q", the heat transferred, is a function of the heat transfer efficiency of a CPU or GPU cooler to the airflow. Piezoelectric pump A "dual piezo cooling jet", patented by GE, uses vibrations to pump air through the device. The initial device is three millimetres thick and consists of two nickel discs that are connected on either side to a sliver of piezoelectric ceramics. An alternating current passed through the ceramic component causes it to expand and contract at up to 150 times per second so that the nickel discs act like a bellows. Contracted, the edges of the discs are pushed together and suck in hot air. Expanding brings the nickel discs together, expelling the air at high velocity. The device has no bearings and does not require a motor. It is thinner and consumes less energy than typical fans. The jet can move the same amount of air as a cooling fan twice its size while consuming half as much electricity and at lower cost. Passive cooling Passive heatsink cooling involves attaching a block of machined or extruded metal to the part that needs cooling. A thermal adhesive may be used. More commonly for a personal computer CPU, a clamp holds the heatsink directly over the chip, with a thermal grease or thermal pad spread between. This block has fins and ridges to increase its surface area. The heat conductivity of metal is much better than that of air, and it radiates heat better than the component that it is protecting (usually an integrated circuit or CPU). Fan-cooled aluminium heatsinks were originally the norm for desktop computers, but nowadays many heatsinks feature copper base-plates or are entirely made of copper. Dust buildup between the metal fins of a heatsink gradually reduces efficiency, but can be countered with a gas duster by blowing away the dust along with any other unwanted excess material. Passive heatsinks are commonly found on older CPUs, parts that do not get very hot (such as the chipset), and low-power computers. Usually a heatsink is attached to the integrated heat spreader (IHS), essentially a large, flat plate attached to the CPU, with conduction paste layered between. This dissipates or spreads the heat locally.