A water block is the watercooling

Watercooling

Water cooling is a method of heat removal from components and industrial equipment. As opposed to air cooling, water is used as the heat conductor. Water cooling is commonly used for cooling automobile internal combustion engines and large industrial facilities such as steam electric power plants,...

 equivalent of a heatsink. It can be used on many different computer components including the central processing unit

Central processing unit

The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...

 (CPU), GPU

Graphics processing unit

A graphics processing unit or GPU is a specialized circuit designed to rapidly manipulate and alter memory in such a way so as to accelerate the building of images in a frame buffer intended for output to a display...

, PPU

Physics processing unit

A physics processing unit is a dedicated microprocessor designed to handle the calculations of physics, especially in the physics engine of video games. Examples of calculations involving a PPU might include rigid body dynamics, soft body dynamics, collision detection, fluid dynamics, hair and...

, and Northbridge

Northbridge (computing)

The northbridge has historically been one of the two chips in the core logic chipset on a PC motherboard, the other being the southbridge. Increasingly these functions have migrated to the CPU chip itself, beginning with memory and graphics controllers. For Intel Sandy Bridge and AMD Fusion...

 chipset on the motherboard. It consists of at least two main parts, the "base", which is the part that makes contact with the device being cooled, usually made of a high conductivity metal such as aluminum or copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 and in some cases silver

Silver

Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...

 as is found in many newer blocks. The second part, the "top" ensures the water is contained safely inside the "block" and has connections that allow hosing to connect it with the water cooling loop. The top can be made of the same metal as the base, transparent Perspex, Delrin, Nylon

Nylon

Nylon is a generic designation for a family of synthetic polymers known generically as polyamides, first produced on February 28, 1935, by Wallace Carothers at DuPont's research facility at the DuPont Experimental Station...

, or HDPE. Most newer high end water blocks also contain mid-plates which serve to add jet tubes, nozzles, and other flow altering devices.

The base, top, and mid-plate(s) are sealed together to form a "block" with some sort of path for water to flow through. The ends of the path have inlet/outlet connectors for the tubing that connects it to the rest of the watercooling system. Early designs included spiral

Spiral

In mathematics, a spiral is a curve which emanates from a central point, getting progressively farther away as it revolves around the point.-Spiral or helix:...

, zig-zag pattern or heatsink like fins to allow the largest possible surface area for heat to transfer from the device being cooled to the water. These designs generally were used because the conjecture was that maximum flow was required for high performance. Trial and error and the evolution of water block design has shown that trading flow for turbulence

Turbulence

In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...

 can often improve performance. The Storm series of water blocks is an example of this. Its jet tube mid plate and cupped base design makes it more restrictive to the flow of water than early maze designs but the increased turbulence results in a large increase in performance. Newer designs include "pin" style blocks, "jet cup" blocks, further refined maze designs, micro-fin designs, and variations on these designs. Increasingly restrictive designs have only been possible because of increases in maximum head pressure of commercially viable water pump

Pump

A pump is a device used to move fluids, such as liquids, gases or slurries.A pump displaces a volume by physical or mechanical action. Pumps fall into three major groups: direct lift, displacement, and gravity pumps...

s.

A water block is better at dissipating heat than an aircooled

Aircooling

Air cooling is a method of dissipating heat. It works by making the object to be cooled have a larger surface area or have an increased flow of air over its surface, or both. An example of the former is to add fins to the surface of the object, either by making them integral or by attaching them...

 heatsink due to water's higher specific heat capacity and thermal conductivity

Thermal conductivity

In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

. The water is usually pumped through to a radiator

Radiator

Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...

 which allows a fan pushing air through it to take the heat created from the device and expel it into the air. A radiator is more efficient than a standard CPU or GPU heatsink/air cooler at removing heat because it has a much larger surface area.

Installation of a water block is also similar to that of a heatsink, with a thermal pad

Thermal pad (computing)

In computing and electronics, thermal pads are a pre-formed square or rectangle of solid material commonly found on the underside of heatsinks to aid the conduction of heat away from the component being cooled and into the heatsink .As an alternative to thermal grease In computing and...

 or thermal grease

Thermal grease

Thermal grease is a viscous fluid substance, originally with properties akin to grease, which increases the thermal conductivity of a thermal interface by filling...

 placed between it and the device being cooled to aid in heat conduction

Heat conduction

In heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....

.