Thermally Induced Pumping

The thermal effect is exploited to produce liquid pumping. For instance, a thermocapillary pump was constructed. The pumping method is based on surface-tension change due to local heating created by heaters fabricated on a Si-Pyrex chip. This method was used to pump reagents to perform successive PCR, gel electrophoresis, and detection [392,393], 

FIGURE 3.9 Thermopneumatic pressure generated for discrete liquid drop pumping, (a) Schematic of the discrete drop pumping device, (b)-(e) Operation of the discrete drop pump [394]. Reprinted with permission from the American Chemical Society. 

FIGURE 3.10 Principle of the thermal bubble-actuated pump. Qd flow at the diffuser Qn flow at the nozzle [395]. Reprinted with permission from the Institute of Physics Publishing. 

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Applications The common Heliflow apphcations are tank-vent condensers, sample coolers, pump-seal coolers, and steam-jet vacuum condensers. Instant water heaters, glycoLwater seivdces, and cryogenic vaporizers use the spiral tube s ability to reduce thermally induced stresses caused in these apphcations. 

Therefore the lack of an observable bleach can only be explained by the cancellation of all contributions to the pump-probe signal, which is the case for a perfect harmonic state. It can be shown that the anharmonicity of a vibrational exciton is a direct measure of its degree of delocalization [5]. Thus, we conclude that the free exciton state is almost perfectly delocalized at 90 K. As temperature increases, a bleach signal starts to be observed, pointing to a non-complete cancellation of the different contributions of the total pump-probe signal. Apparently, thermally induced disorder (Anderson localization) starts to localize the free exciton. The anharmonicity of the self-trapped state (1650 cm 1), on the other hand, originates from nonlinear interaction between the amide I mode and the phonon system of the crystal. It... 

Figure 55.13 shows another example of areal-time process control for the heat pump dryer to reduce nutrient degradation. Experiments have been carried out with hypodermic thermocouple needles to measure the transient temperature profiles of food products (Chou et al., 1997). These measured values make it possible to tune the drying air temperature to prevent the internal product tanperature from reaching a threshold value, hence reducing thermally induced nutrient degradation. 

Values of pyroelectric coefficient are calculated from equation (l),by measuring the pyroelectric current for a known controlled temperature profile. A computer-controlled system has been developed, to force the temperature of a sample under test, and log the corresponding pyroelectric current. This system is shown schematically in figure 2. Samples are mounted in an earthed vacuum chamber. Evacuation of the sample chamber removes a significant proportion of absorbed water, which is otherwise responsible for spurious, thermally induced currents. The temperature of the sample is controlled,in both heating and cooling, by a Peltier thermoelectric heat pump. 

If the pump beam was polarized in the plane, even a relatively weak pump intensity could induce a molecular reorientation in the M-z plane, in addition to the laser heating effect. The probe beam polarized perpendicular to 6. again monitored only the thermally induced refractive-index change, but when polarized parallel to H, it should feel both the thermal effect and the molecular reorientation effect. The refractive-index changes due to both effects were actually fairly small we can therefore write the laser-induced phase shift experienced by the probe beam in traversing the sample cell of thickness das... 

The accumulation of some 200,000 hr of relatively trouble-free test operation in the temperature range of 1200 to 1500°E wdth molten salts and liquid metals as the ( irculated fluids has proved the adequacy of this basic-pump design with regard to the major problem of thermally induced dis-tortion.s. Four different sizes and eight models of pumps have been used to provide flows in the range of o to loOO gpm. Several individual pumps have operated for periods of GOOO to 8000 hr, consecutively, without maintenance. 

These applications have considerably more stringent performance requirements than any other application. Circulating water pumps, boiler feed pumps, forced-draught (FD) and induced-draught (ID) fans, pulverizers (ball mills) and condensate pumps are components in a thermal power station that may require extra safety in a standard motor to make it able to fulfil these requirements and withstand abnormal service conditions and system disturbances. Abnormal operating conditions may be one or more of the following ... 

Photosynthetic reaction centers from Rhodobacter sphaeroides and bacteri-orhodopsin (BR) from purple membrane (PM) have been used for their unique optoelectronic properties and for their capability of providing light-induced proton and electron pumping. Once assembled they display extremely high thermal and temporal stability... 

If the system under consideration is chemically inert, the laser excitation only induces heat, accompanied by density and pressure waves. The excitation can be in the visible spectral region, but infrared pumping is also possible. In the latter case, the times governing the delivery of heat to the liquid are those of vibrational population relaxation. They are very short, on the order of 1 ps this sort of excitation is thus impulsive. Contrary to a first impression, the physical reality is in fact quite subtle. The acoustic horizon, described in Section VC is at the center of the discussion [18, 19]. As laser-induced perturbations cannot propagate faster than sound, thermal expansion is delayed at short times. The physicochemical consequences of this delay are still entirely unknown. The liquids submitted to investigation are water and methanol. 

During the last year we have built an FTMS instrument specifically designed for laser-induced thermal desorption from single-crystal surfaces. Figure 5 is a perspective drawing of the Instrument. The chamber is pumped by a 150 1/s ion pump and has a base pressure of 2.0 X 10- torr. Gases are Introduced through sapphire-sealed leak valves from a diffusion pumped gas manifold. 

The low-frequency shift and the broadening of the CO spectra at 0 ps suggest that the low-frequency modes of adsorbed CO, that is, stretching, frustrated rotation, and frustrated translation modes of Pt-CO, were thermally excited by pump pulses, as reported by Bonn et al. [82] Thus, it is concluded that the transient site migration of adsorbed CO on the Pt electrode surface was caused by a transient rise in the surface temperature of Pt induced by pump pulses. 

Figure 14.1 presents the main components of a typical in situ SVE system.910 Vertical extraction wells are installed inside the contaminated zone at appropriate distances from one another. The SVE wells are typically constructed of PVC pipe, with a screened interval, which is placed within the contaminated zone. The wells are connected to blowers or vacuum pumps, which induce a continuous airflow through the pores of the unsaturated zone. The soil surface is sometimes covered with an impermeable seal, made from high density polyethylene (HDPE) or bentonite clay for example, to prevent the vertical influx of air from the surface, which might cause short-circuiting problems, and promote horizontal gas flow through the contaminated area. The airstream, which contains the contaminant vapors, passes initially through an air-water separation unit to remove the entrained moisture and is then directed to the gas treatment unit, where the contaminants are thermally destroyed or removed by adsorption. 

Once closed inside its copper frame, the array was mounted and thermally connected to the mixing chamber of the Oxford DR installed in Hall A of the underground Gran Sasso National Laboratory. The tower was mechanically decoupled from the cryostat in order to avoid vibrations induced by pumps on the detectors and preamplifiers [98],... 

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