1、VARIABLE CONDUCTANCE HEAT PIPE TECHNOLOGY Final Research Report MARCH 1974 Prepared by W. T. ANDERSON 0. K. EDWARDS J. E. ENINGER B. D. MARCUS Contract No. NAS 2-5503 Prepared for AMES RESEARCH CENTER NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Moffett Fteld, Col forna 93405 i:, i tc, where B2 is
2、a constant characteristic of the catalytic B F reaction. Here Q2 represents the potenti a1 barrier between reacti ng mol ecul es : i 1 on the catalytic surface. This temperature dependence is characteristic of many physical and chemical reactions 2-151. The area A may actually be 1 somewhat larqer t
3、han geometrical internal area depending on the surface i roughness of the stainless steel or corrosion product surfaces. i f With dry corrosion the activatton energies are generally larger than with wet corrosion, as is apparent from the activation mergies shown in lable 2-1. An explanation for this
4、 may be that the effective potential barrier is lowered by the electric field across the film created by the local corrosion cell . The use of this gas generation model in accelerated life testing is that the parameters B and Q ccn he determined experimentally from data taken under accelerated condi
5、tions by plotting log an vs. 1/T. Having determined these parameters by measuring the gasat evolution at accelerated condiionc the gas evolution at any time can be calculated from (2-6) and (2-7) ror heat pipes operated under normal conditions.The quantities tc and n,/A can be calculated from (2-8)
6、and (2-g) , as discussed below. f Least squares fits to the parabolic data are plotted n vs t1I2 1 in Figures 2-5 through 2-7. Plotting log an vs /T results in the zl / 2 Ob - curve shown in Figure 2-8, indicating gas generation in the passivating region s described by (2-6) . within the accuracy of
7、 the data. Calculating ts the parameters Q, and B1 fm the slope and intercept, respectively, i results in I 1 Q1 = 6.03 x joul er , Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Table 2-1. Activation energies for corrosion in gaseous and 1 iquid en
8、vironments. Materi a1 Mild steel Stainless steel Iron A1 mi nun Urani un Nickel Wi ckel Nickel J Y Mild steel Mild steel 18/9 Stainless steel 304 Stainless steel Iron Lead A1 mi nun Urani un Ni c kel Temperature Activ ion Envi ronment Ranqe (OC) Energy (1 0-36 joules) air oxygen oxygen oxygen ai r o
9、xygen oxygep oxygen 5-203 NaOH 10% HC1 1N H2S04 distf 1 led water 10% HC1 10% HCl ?OX HN03 water distilled water *Calculated from data contai ned i n referenced papers. References Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-FIGURE 2-5. Gas genera
10、ti on in metfranoljstai nless-steel heat pipes showing temperature dependence i n parabol i c reg1 on. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-O#6, 179.2OC, I!.$ WATTS Q 17, 179,3OC, 12.4 WATTS 0#8, 179.2“C, 16.4 WATTS ,- :., - -. range 160-1
11、7gC agrees reeiznably wl1 with Eq. (2-9). At 170C, Eq. (2-9) ,. 2 :, yields n,/A = 4.3 x 1b-riole/in . I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2.3 Concl us ions and Recnendati ons : The behavior of the gas evolution in methanol/stainless-st
12、eel heat pipes was found to depend on the amount of gas per unit area generated during accelerated testing. Below a critical value nc/A given by Eq. (2-9), or critical time tc given by Eq. (2-8), the ttne dependence is explained best by a parabolic function, indicative of the growth of a passivating
13、 film of corrosion products. The data in this region can be correlated with a model of film growth resulting in Eq. (2-6), which contains parameters to be determined by experiment. Above the critical point given by Eqs. (2-8) and (2-9), a linear time dependence was observed. In this region the data
14、can be correlated with a model of catalytic decomposition of methanol to formaldehyde and hydrogen on the surface of the corrosion products, resulting in Eq. (2-7). No flow rate dependence was found within the accuracy of the data. In application to other types of methanol/stainless- steel heat pipe
15、s, the gas generation may vary depending on the type of stainless steel, the purity of the methanol, and other factors; but it is expected that the behavior could be explained by the same form of the Eqs. (2-6) and (2-7), v!i th associated critical values (2-8) and (2-9), only the value of the param
16、eters may change. Based on the results of this and the previous study 2-l it appears that this method of accelerated life testi ngs has a broad applicabtlity to heat pipe systems, even when not a great deal is known concerning the actual gas evolution mechanisms. This method of accelerated 1 ife testing can now be appl led to other important types of heat pipes with good probability of success. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
