Downloaded from https://www.everyspec.com MIL-STD-81OD. ; 19 July 1983 For the purposes of thi.etest, the following type of.thermodynamic.analysis ia adequate. A more detailed analysis can be utilized, if desired. The.’mission..profile time history of altitude and Mach number from paragraph I-3.2.2.3 iq,,analyzed to identify each break point at which the aloPe of either ; the altitude..or,,Machnumber;plots change. A thermodynamic analySiS is done at each break’point using eteady-state thermodynamic relationships. Between each break point, linear interpolation is done.on each Stress .toconstruct a continuous profile for each environmental stress.
At each such break point, the thermal str’essconditions for “ateat shall be determined in accordance with paragraphs 1-3.2.2.6.1 and I-3.2.2:6.2. :, 1-3,.2.2.6.1 ~. This section is to be used to determine the bay temperature for:an avionics system in a compartment that ia ram-cooled. The thermal stress in a ram-air-cooled compartment can be determined from the followipg relati,onahip. . ,, T’=.T [1 +0.18 F?] from table 520.0-111 M = Mach number being,, flown ,, 1-3.2.2.6’.2 This section is to determine the bay temperature for an avionica,system located in a bay that receives ita cooling from the.aircraft’s ECS.
The masa flow rate and temperature level of supple- mental air needs .tobe determined at each.break point in the mission profile. where T . ambient air temperature at altitude being flown in degreea Kelvin The onboard ECS is modeled in terme of its,pri~ry componepta such as Pr?ssure regulator, heat exchangers,.turbomachinery, water separator, etc. Alao, calculate the masa flow rate being injected into the bay and the location.of other aysteme in order.to determine if the heat load f,romthese aystema should be considered (refs. c end d). The calculation of the bay temperature stress can be done using the following simplified thermodynamic analyais. a.
Aasu~e that steady-state thermodynamic relationship are valid. b. Assume constant but nominal or typical efficiency constants that can be achieved from good design practices for turbomachinery and heat exchangers. c. Neglect secondary effects in components of ECS (i.e., pressure losses in heat exchanger, temperature losees in ducts). I-3.2.2.6.3 This section is used to ,,., determine the thermal and mass flow for an avionics system that requires forced or supplemental cooling from the aircraft. Paragraph I-3.2.2.6.2 recommends an aPProach to determine the bay thermal streaa for “anavionica ayatem located in a supplementally cooled compartment.
This same approach is recommended here with one addition: continue the thermodynamic analysis to determine the & temperature and mass flow being injected directly into the avionics system. The same sources used to obtain the information for paragraph I-3.2.2.6.2 are also applicable here. 1-3.2.2.7 ~. The humidity stress that an internally carried avionics system experiences is dependent upon the ambient humidity conditions and the performance of the water separator of the environmental control. (Some 520.0-13 METHOD 520.0 19 July 19.83