Engineers designing solutions to complex thermal issues have a variety of decisions to make that affect the overall performance of the system. A common dilemma that arises is the choice of a cooling method; specifically, engineers must decide whether spot cooling or remote cooling should be utilized in their thermal management solution. This decision is critical, but it can be tricky to determine, as every project carries with it a unique set of requirements that must be evaluated. To make an informed decision, it is important to understand the difference between these two cooling methods.
Spot cooling refers to the direct cooling of a heat-generating component within proximity of the heat source, and it can provide a measure of local temperature stability. A common example is a CPU heat sink. With this method, heat spreading—often with heat pipes or vapor chambers—may be required to reduce the load on the heat sink. Spot cooling’s effectiveness is limited in situations with higher component power densities.
Remote cooling relies on an intermediate heat-transport loop to move heat from one point to another, and it is a common thermal solution for systems with tight packaging constraints. There are several types of remote cooling technologies (e.g., heat pipes, loop thermosyphons, liquid cooling, pumped two-phase), each with an appropriate range of applications for which it is well suited.
With an understanding of the differences between spot cooling and remote cooling, there still exists the question of which method should be utilized in a given system.
Key factors to consider
1. Temperature Requirements
Of course, no thermal management discussion is complete without considering the temperature requirements. After all, the primary function of a cooling system is to maintain the operating temperature of a specific component or surface within a specified range of acceptable temperatures. This is an essential requirement for almost all electronic devices, and system designers must accommodate the thermal solutions that will ensure optimal performance. The choice between spot cooling and remote cooling is often influenced by the maximum operating temperature of the hardware, and several technologies of each method may be evaluated based upon the ambient conditions and temperature requirements.
2. Duty Cycle Presence
When discussing the power dissipation of a component, engineers often talk in terms of steady-state performance. This is appropriate for most thermal management applications where operation is continuous, or when the device must operate for a significant time period. However, not all applications feature steady-state conditions; pulsed loads can result in more intricate duty cycles that must be considered when designing an efficient and effective thermal solution. Otherwise, a system may be equipped with a cooling solution that is far more powerful than truly necessary. Therefore, the choice between spot and remote cooling must also be influenced by the duty cycle presence of the system.
3. Materials Compatibility
The materials of construction are critical design elements in any engineered system, and thermal solutions are no exception. Electronic devices can be manufactured from a variety of plastics, rubbers, and metals; the challenge from a thermal management perspective is that most of these materials are either thermally insulating (e.g., plastics, rubbers) or poor thermal conductors (e.g., stainless steel, titanium). In some applications, it is possible to enhance the thermal performance by integrating a higher-performing material; for example, the thermal conductivity of a plastic or stainless-steel component can be significantly improved by fully encapsulating a heat pipe within its structure. The exterior of the device then retains its compliance with design standards, while the thermal performance of the materials can be increased up to the levels of more traditional heat transfer materials.
So, the question remains: which method should be chosen? Spot or remote cooling?
The short answer is that it depends; as disappointing as it may be, there truly is no quick and easy way to decide between the two. Each of the three factors discussed, as well as other design elements, must be carefully considered by engineers to find the perfect thermal solution for a specific application. However, there are some helpful guidelines to assist in exploring thermal technologies. The flow chart below can be used to make that determination.
These guidelines provide an excellent point of reference from which one can begin to evaluate thermal management needs. Coupled with a thorough analysis of pertinent design factors, engineers can identify potential solutions and verify those findings as they work to satisfy their requirements.