Heating, current techniques

Hall, D.W., Scott, K., and Jachuck, R.J.J. (2001), Determination of mass transfer coefficient of a cross-corrugated membrane reactor by the limiting-current technique, International Journal of Heat and Mass Transfer, 44(12) 2201-2207. 

Currently the most popular cooling method is the externally controlled passive cooling technique using traditional convection heat transfer and heat exchanging techniques such as fins [1], a fan [3], and compressed air for microfluidic device cooling. Integrated cooling techniques for microfluidic devices are very limited such as the Peltier thermoelectric cooler [2] and endothermic cooler [7] mentioned above. 

Thermopower measurements used the differential technique [48,49] two isolated copper blocks were alternately heated with the sample mounted between the copper blocks with pressure contacts. The heating current was accurately controlled by computer. The temperature difference between the two copper blocks was measured by a chromel-constantan thermocouple and did not exceed 0.5 K for each thermal cycle. The voltage difference across the sample was averaged for one complete cycle. Any temperature difference between sample and thermocouple was less than 10% of the temperature gradient across the sample the thermometry was carefully calibrated for the entire temperature range (5 K < T < 300 K). The absolute thermopower of the sample was obtained from the absolute scale for lead [48,49]. 

The effectiveness of the approach is demonstrated on two rqjresentative NDT techniques intapretation of data acquired with an ultrasonic rail inspection system and interpretation of eddy-current data from heat exchangers in (petro-)chemical industry. The results show that it is possible to provide a high level of automation in combination with efficient operator support for highly variable NDT measurements where up to now use of automated interpretation was only limited. 

In a similar fashion. Thermally Stimulated Current spectrometry (TSC) makes use of an appHed d-c potential that acts as the stress to orient dipoles. The temperature is then lowered to trap these dipoles, and small electrical currents are measured during heating as the dipoles relax. The resulting relaxation maps have been related to G and G" curves obtained by dynamic mechanical analysis (244—246). This technique, long carried out only in laboratory-built instmments, is available as a commercial TSC spectrometer from Thermold Partners L.P., formerly Solomat Instmments (247). 

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