Measurements of Enthalpy in Low-Density Arc-Heated Flows
Measurements of Enthalpy in Low-Density Arc-Heated Flows
复制标题
低密度电弧加热流中的焓测量
作者：
R. Pope
本文研究了在低于0.5大气压的压力下，预热气体膨胀的热化学状态和总蒸汽焓。发现在电弧加热器出口处流动处于平衡，并且化学成分在储液器和喷嘴中冻结。自由射流无粘核心的总焓的三个独立的方法来确定，并通过每种方法得到的值进行了比较。它表明，如果化学状态的流动是已知的，焓可以很容易地确定冻结音速流方法。用电弧加热器上的能量平衡确定冻结流的化学组成。总焓也确定与流焓分布和对流加热速率测量。当用于测量加热速率的量热计被假定为完全催化时，从这些测量和传热理论确定的焓低约40%。这种差异可以用非平衡态理论来解释。然而，由于非平衡流的加热率与焓之间的关系复杂，表面反应性的不确定性，以及涡量相互作用对传热的未知影响，加热率法不适合用于低密度流的焓计算。A =测量加热速率的测试模型表面的面积;此外，喷嘴中的横截面积，m2 A *=喷嘴喉部的横截面积，m2 C =由等式定义。(8)c =解离物质的质量分数Cp =总比热，Mjoule/kg ° K E =电压，V F（T）=由等式定义(7)H =总焓，（μ ^/2）+h，M焦耳/kg H $_=在流中心线处的总焓，M焦耳/kg #T ° =在温度T下的热含量，M焦耳/kg #Hhr =由方程定义。(2)，Mjoule/kg Hne =由方程定义(4)，Mjoule/kg Hrn =由方程定义(3)，Mjoule/kg Δ Hf，T ° =在温度T下的标准生成热，Mjoule/kg h =静态焓，Mjoule/kg h ° =复合热，Mjoule/kg I =电流，amp K =方程中的常数。(14)，kwkg/Mjoule-m3/2 atm 1/2
The thermochemical state and the total stream enthalpy of are-heated gases expanding from reservoir pressures less than 0.5 atm were investigated. The flow was found to be in equilibrium at the arc-heater exit, and the chemical composition was frozen in the reservoir and nozzle. The total enthalpy of the inviscid core of the freejet was determined by three independent methods, and the values obtained by each method are compared. It is shown that if the chemical state of the flow is known, the enthalpy can be determined quite easily by the frozen sonic flow method. The chemical composition of the frozen flow was determined with an energy balance on the arc heater. The total enthalpy was also determined with stream enthalpy profiles and convective heating-rate measurements. When the calorimeters used to measure the heating rate were assumed to be fully catalytic, the enthalpy determined from these measurements and a heat-transfer theory were low by about 40%. This difference can be accounted for with the nonequilibrium theory. However, because of the complex relationship between heating rate and enthalpy for the nonequilibrium flows, the uncertainty of the surface reactivity, and the unknown effects of vorticity interaction on heat transfer, the heating-rate method is not recommended for determining the stream enthalpy in low-density flow. A = area of test model surface on which heating rates were measured; also, cross-sectional area in nozzle, m2 A* = cross-sectional area of nozzle throat, m2 C = defined by Eq. (8) c = mass fraction of dissociated species Cp = total specific heat, Mjoule/kg °K E = voltage, V F(T) = defined by Eq. (7) H = total enthalpy, (u^/2) + h, Mjoule/kg H$_ = total enthalpy at stream centerline, Mjoule/kg #T° = heat content at temperature T, Mjoule/kg ~Hhr = defined by Eq. (2), Mjoule/kg Hne = defined by Eq. (4), Mjoule/kg Hrn = defined by Eq. (3), Mjoule/kg AHf,T° = standard heat of formation at temperature T, Mjoule/kg h = static enthalpy, Mjoule/kg h° = heat of recombination, Mjoule/kg I = current, amp K = constant in Eq. (14), kwkg/Mjoule-m3/2 atm 1/2