对数平均温度差（LMTD）

Oxy-fuel cutting, or flame cutting, severs ferrous metals by a rapid, exothermic oxidation process. First, a preheating flame raises the steel's surface to its kindling temperature (approx. 870 °C or 1600 °F). A high-pressure jet of pure oxygen is then directed at the spot, initiating a chemical reaction, [latex]3Fe + 2O_2 \rightarrow Fe_3O_4[/latex], which forms molten iron oxide (slag) and releases heat.

The separation factor, α (alpha), quantifies the selectivity of an extraction system for two different solutes, A and B. It is defined as the ratio of their individual distribution ratios, [latex]\alpha_{A,B} = \frac{D_A}{D_B}[/latex]. For a separation to be effective, α must be significantly different from unity. A larger α value implies an easier and more efficient separation.

回火脆化是指某些合金钢在特定温度范围内（约 375-575 °C）保温或缓慢冷却时，其韧性会降低。这种现象是由于杂质元素（例如磷、锡、锑）偏析至晶界，削弱了晶粒间的结合力，从而导致沿晶断裂。

For materials that do not have a distinct yield point on their stress-strain curve, like aluminum or high-strength steel, 'proof stress' is the engineering equivalent. It is defined as the stress required to produce a small, specified amount of permanent (plastic) deformation, typically 0.2% of the original gauge length. This value, [latex]\sigma_{0.2}[/latex], is used in design calculations as the material's practical elastic limit.

Fouling is the accumulation of unwanted material on heat transfer surfaces, which introduces an additional thermal resistance and degrades the performance of a heat exchanger. This fouling resistance ([latex]R_f[/latex]) reduces the overall heat transfer coefficient (U). The effect is quantified in the overall heat transfer equation: [latex]\frac{1}{U} = \frac{1}{h_i} + \frac{1}{h_o} + R_f + R_w[/latex].

氧乙炔火焰的特性取决于氧气与乙炔的体积比。中性火焰（体积比 ≈ 1.1:1）是钢焊接的标准火焰。渗碳火焰或还原火焰（体积比 1.1:1）氧气过剩，温度更高，用于钎焊。

TNT 的一个关键特性是其熔点低，仅为 80.6 °C (177.1 °F)，远低于其 240 °C 的自燃温度。如此大的温差使得 TNT 能够安全地用蒸汽或热水熔化，并浇铸到弹药外壳中，这一过程称为熔铸。这使得生产致密、均匀且无裂纹的炸药成为可能。

用于氧燃料焊接的气瓶储存气体或其他工业或医用气体，压力非常高。压力调节器对于将气体减压至安全可用的工作压力至关重要。两级调节器分两步进行减压，即使气瓶压力因使用而下降，也能提供高度恒定的输送压力。这确保了稳定的流量，从而产生稳定的火焰，确保焊接质量始终如一。

Acoustic impedance ([latex]Z[/latex]) is a material's intrinsic resistance to acoustic flow, defined as its density ([latex]\rho[/latex]) multiplied by its acoustic velocity ([latex]c[/latex]), so [latex]Z = \rho c[/latex]. The percentage of ultrasonic energy reflected at the boundary between two materials is governed by the difference, or mismatch, in their respective acoustic impedances. This principle is what makes flaw detection possible.

发动机爆震，或称爆燃，是奥托循环发动机热效率的主要限制因素。虽然更高的压缩比可以提高效率，但也会导致压缩过程中空燃混合物的温度和压力升高。这可能导致混合物过早自燃，产生冲击波，发出“爆震”声，并可能损坏发动机。

The international standard for paper sizes, ISO 216 (e.g., A4, A3), is based on the square root of 2. The aspect ratio of every sheet is [latex]1:\sqrt{2}[/latex]. This unique property means that when a sheet is cut or folded in half parallel to its shorter sides, the resulting two smaller sheets have the exact same [latex]1:\sqrt{2}[/latex] aspect ratio as the original.