Be Cool, Be Cool

A laser calculator I find online (I think some of its assumptions are simplified) says that the waste heat of a 10 MJ laser is 882.353 watts, assuming 85% efficiency (50% is considered the max for the near future—currently we top out at around 12%—but the 24th century isn't quite "near" future, and the zledo are 300 years more advanced than we are). I find an efficiency for micro-channel heat-exchangers of 1.5 kW/cm2 (presumably per second); at .882 kilowatts, that means almost exactly 1.7 shots per square centimeter.

A zled laser's power mainsprings can supply it with power for 48 shots. One face of the hexagonal prism casing on a zled laser is 4.053 centimeters wide; suppose we put a band of micro-channel heat-exchangers around the laser (toward the end), but not covering the bottom face or the bottom half of the two faces touching the bottom. If we do that, we basically have 3 whole faces and 2 half-faces to work with, giving us (3+(2×(1/2)=)4, for a total width of the heat-exchanger of (4×4.053=)16.212 centimeters. That, right out of the gate, means that merely by being one centimeter wide, we can exchange the waste-heat of (4.053×4×1.7=)27.56 shots. Make it an eighth of a bãgh—"aliens don't use nice round numbers of Earth units"—or 1.60875 centimeters, and it's got the ability to dump the heat of 44.34 shots, meaning that, if that cooling-efficiency is per-second, it can dump the heat of firing its entire charge, in one and one-elevenths seconds.

The hand laser has a waste-heat of a bit over 282 watts; assuming the same kind of heat-exchanger, that comes to 5 and 5/16ths shots per square centimeter. The faces of the hand laser's hexagonal casing are a little over half the width of those of the long laser (not exactly half because though the lens has half the diameter, its casing is the same thickness), 2.533 centimeters. The hand laser's springs power it for sixteen shots; a band a centimeter wide can dump 17.23 shots. Make it a twelfth of a bãgh, or 8.58 millimeters, and it can dump 14.78 shots' worth of heat in one second, and the whole spring in just over 1.08 seconds.

Incidentally, my old calculations for laser power-supplies forgot the fact that lasers are inefficient; I just went by the power of the beams themselves. What 85% efficient actually means is that for every twenty joules you pour into the laser, you get seventeen joules out as laser (and what our current best, 12%, means, is that for every twenty-five joules you put in, you get three joules of laser—we're not looking at laser weapons except on nuclear ships for a long, long time). So I guess that, assuming the .1 megajoule/kilogram minimum for polymer molecular springs, powering the 3.2 kilojoule hand laser for 16 shots would require a 602 gram power supply, while powering the 10 kilojoule long laser for 48 shots would take one weighing 5.6 kilos. Fortunately, polymer molecular springs have a theoretical maximum of ten megajoules (their range is apparently two orders of magnitude wide); merely going up to the "1 megajoule/kilo" kind gives us a lighter spring than the one the hand laser uses. Except it probably weighs a bit more, the extra weight being reinforcement (you really, really don't want a spring under that kind of tension breaking on you).

Note: I messed up the calculations, earlier, for the width of the hexagon. It's better now. I think I was also doing something wrong on the calculations for the hand laser's heat exchangers.

No comments: