MIL-DTL-917F(SH)
3.15 Thermal design.
3.15.1 Selection of the cooling system. The removal of heat to maintain proper operating temperatures shall be
accomplished by one of the following, listed in order of preference:
a.
Natural convection, conduction, and radiation.
b.
Forced air (self-contained).
c.
Forced air (not self-contained).
d.
Fresh water air cooler.
e.
Salt water air cooler.
f. Other methods such as cooling oil or water in proximity or indirect contact with active electrical
components.
The individual equipment specification shall indicate the type of cooling to be used. The method selected shall
apply the design principles using the guidance provided in MIL-HDBK-251.
3.15.1.1 Air coolers.
3.15.1.1.1 General design requirements. For forced air plenum designed systems for cooling electronic
components, a redundant design system shall be used requiring full performance if any one of the redundant forcing
elements is non-operational. An alarm system shall be incorporated to indicate loss of forced air or status of
redundant element.
3.15.1.1.2 Specific cooling systems.
3.15.1.1.2.1 Air coolers for motors and generators. Air coolers for motors and generators shall be in
accordance with MIL-C-19836 and the applicable air cooler part of MIL-DTL-2036.
3.15.1.1.2.2 Air coolers for assembled hardware. Guidance for air coolers for assembled hardware consisting
of transformers, semiconductor devices, resistors, capacitors, and so forth, can be found in MIL-HDBK-454.
In addition, heat dissipaters for semiconductor devices shall be constructed of metallic material (see 3.3.2)
which is corrosion-resistant, or which is treated or coated (see 3.14.1) to resist corrosion. Heat conduction surface
contacts and electrical surface contacts shall not be painted or anodized, but shall be plated, or otherwise coated, to
form surfaces to which the connections or junctions are made. These surface windows shall retain mechanical,
thermal, and electrical effectiveness for the life of the equipment.
3.15.1.2 Liquid coolers. Liquid coolers for electronic equipment shall be in accordance with
DOD-STD-1399-532. Visual indication for liquid coolant level shall be provided.
3.15.1.2.1 General design requirements. The design of electrical equipment using liquid cooling shall include
the following:
a. Provisions for thermal shutdown following alarm with continual operation of cooling devices to avoid
continued increase in temperature.
b. The degree of operability as well as the time period of operability for 100 percent loss of cooling fluid
clearly marked on the cooler.
c.
Provisions for cooling during maintenance.
3.15.1.2.2 Design and placement of parts. The design and placement of all parts of the water cooling circuit
shall include the following:
a.
Vents and drains, as necessary, to allow complete filling, draining, and venting of the cooling system.
b.
Minimum possibility of water striking electronic parts or electrical circuitry should a leak occur.
c.
Means to prevent liquid level build up in the event of a leak.
d.
Electrical components removable and replaceable without disrupting the cooling circuit, if possible.
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