Humidity-temperature cycling

Table 7.13 80% relative humidity temperature cycled between 25 and 65°C steel and stainless steel examined after 2 yrs... 

It is difficult to compare the results obtained on the basis of different norms, because unfortunately, the test conditions (in terms of humidity, temperature cycle, etc.) vary from one norm to another. 

Five variables are critical to the EtO process. They are EtO concentration, relative humidity, temperature, time, and pressure/vacuum. Temperature is the easiest variable to measure and monitor, therefore temperature is used as the indicator of the worst-case location within the loaded EtO sterilizer. Once the worst-case location is identified the validation studies are conducted with the goal of inactivating a known concentration of indicator micro-organisms in the worst-case location using a specific loading pattern with a specific EtO cycle with all variables defined and controlled. 

Representative test pieces may be subjected to a series of cycles of exposure to differing conditions of temperature and humidity—the cycles and conditions being decided by the circumstances likely to be encountered in practice in the transport and use of the articles concerned. Meanwhile, an appropriate number of control specimens taken from the same production batches are kept under ambient or standard atmospheric conditions. 

Environmental and accelerated ageing tests were performed on the indoor dye modules described in Sect. 7.6 in order to detect failure mechanisms. Contrary to expectations, many modules survived humidity/freeze cycling tests (10 cycles, 85%, 20 h at 55°C per cycle) without major degradation, demonstrating the capability of the sealing concept (see Fig. 7.8). This was also true for temperature cycling (between —5 and 55°C). However, it has... 

The adhesion of PI to Cr as measured by peel strength is excellent and does not degrade with temperature cycling, thermal shock, or high humidity adhesion to TiW and Mo is about 1/3 to 1/2 that of Cr and an amino-silane adhesion promoter is required to obtain acceptable adhesion of PI to AI2O0 and to prevent degradation of adhesion after temperature shock and humidity ... 

The electrolyte membrane presents critical materials issues such as high protonic conductivity over a wide relative humidity (RH) range, low electrical conductivity, low gas permeability, particularly for H2 and O2, and good mechanical properties under wet-dry and temperature cycles has stable chemical properties under fuel cell oxidation conditions and quick start-up capability even at subfreezing temperatures and is low cost. Polyperfluorosulfonic acid (PFSA) and derivatives are the current first-choice materials. A key challenge is to produce this material in very thin form to reduce ohmic losses and material cost. PFSA ionomer has low dimensional stability and swells in the presence of water. These properties lead to poor mechanical properties and crack growth. 

Enviromnental conditions, such as humidity, temperature, and availability of food, can alter the rate of growth of insects and thus affect the length of the life cycle. Optimum environments (usually warm and humid) can decrease the time of development from egg to adult. 

It is clear that the chemical properties of sodium nitrate, coupled with the unique environmental conditions found in the Atacama, may contribute to the effectiveness of breakdown processes in such an extreme terrestrial environment. This is supported by experimental work in the laboratory, which has shown that if the right temperature and humidity cycles are used (Goudie, 1993), sodium nitrate can be at least as effective as some other common salts at causing rock breakdown and decay of concrete (Malone et al., 1997). Indeed, Goudie et al. (2002) used a temperature cycle derived from rock surface field monitoring in the Atacama, together with simulated fog application, which showed conclusively that under simulated Atacama conditions, rapid weathering can occur. 

Operating temperature range Storage temperature range Thermal shock/temperature cycling Humidity exposure... 

Stabilisation by climate control. The most desirable method to prevent damage induced by the repeated cycles of crystallisation and hydration would probably be environmental control. However, neither the selection nor the maintenance of such an ideal environment is possible if looked at realistically. Predictions of salt crystallisation and hydration from mixed salt solutions are more or less impossible, taking into account all the different parameters that influence the process. Sawdy provides a brilliant overview of the subject and considers relative humidity, temperature, air movement, type and structure of the porous support, salt mixture composition and salt concentration. It is necessary to consider not only consolidation treatments of the plaster or the paint layer, which as such may influence the transition behaviour of the salts, but also the influence of microbial extracellular slimes on the porosity of the system. 

Stresses are herein defined as conditions that will degrade system performance. For solar systems these stresses can include temperature, humidity, UV radiation, and temperature cycling. Once stresses are identified, then tests are designed to subject the system to each particular stress Independently... 

The simple predictive method assumes the solution of equations for sorbed concentration as a function of thickness and time, c(x,t), as given in standard monographs on diffusion (14). For a model prediction it is necessary to choose a representative set of temperature and humidity cycles. The choice made for present purposes is a uniform sinusoidal temperature cycle and the condition of constant water content. This leads to a temperature-related variation in relative humidity in which the relative humidity increases with decreasing temperature and vice versa. 

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