Thermal flow

Differential-Temperature Thermal Flow Meters. Meters of this type inject heat into the fluid and measure the resulting temperature rise or, alternatively, the amount of power required to maintain a constant temperature differential. The power required to raise the temperature of a flowing stream by an amount AT is given by the relation ... 

Fig. 18. (a) Differential-temperature thermal flow meter, (b) Tube length-temperature profiles for (—) 2ero flow and ( ) flow. AT is the temperature... 

If the Carnot cycle is used to calculate the work embedded in the thermal flows with the assumption that the heat-transfer coefficient, U, is constant and the process temperature is much greater than AT, a simple derivation yields the following ... 

Booths are partially enclosed workplaces with one or more open facefs) for access by workers. These openings at one or more sides of the enclosure function not only to capture air contaminants directly through their short-distance capture capability but also to cause an airflow in a certain direction (normally away from the worker/work process and into the enclosure). The capture efficiency could be increased by using an existing main flow direction (e.g., thermal flows caused by heat sources) to support the capture process. 

Boundary conditions in space and time thermal, flow (venrilation, mechanical, and natural), sources of contaminants... 

Ya.B. ZeFdovich, FizGoreniyaVzryva 7 (4), 463-76 (1971) CA 77, 64194 (1972) The influence of turbulence and nonturbulence is examined relative to a proplnt burning in a gas flow. Equations indicate exptl methods for determining the magnitudes of the thermal conductivity and viscosity under turbulent flow, and permit a study of thermal flow distribution and temps in a gas wherein an exothermic chem reaction occurs. Equations for non turbulent conditions can be used to calculate the distance from the surface of the proplnt to the zone of intense chem reaction and establish the relation of bulk burning rate to the vol reaction rate. 

Kroger, D. G. (2004) Air-cooled Heat Exchangers and Cooling Towers Thermal-flow Performance Evaluation and Design, Vol. 1 (PennWell). 

Chao, C. Y. Guo, L. J., Thermal flow technique for reducing surface roughness and controlling gap size in polymer microring resonators, Appl. Phys. Lett. 2004, 84, 2479 2481... 

To ease the dissipation of thermal flow, it is worthwhile to use dissipative additives such as ceramics, metal powders or carbon fibres that have a high thermal conductivity. 

Sensitivity performance has improved greatly in the last two decades. The benchmark noise level of 1x10 AU/cm, thought at one time to be the physical limit of UVWis detection imposed by short-term source fluctuations, thermal flow noise and electronic noise, is now surpassed by... 

Figure 3.14 shows a DSC trace obtained at the scan rate of 4°C/min from the mixtures milled for 5, 10, and 40 h. A very small thermal flow effect of either exothermic or endothermic nature is seen around 140°C at the DSC traces of mixtures milled for 5 and 10 h only. At temperatures >180°C, mixtures milled for 5 and 10 h exhibit three strong endothermic effects centered at around 271, 315 and 452°C but the one milled for 40 h shows only two endo effects at around 292 and 452°C. 

ASTM D3795, Test Methodfor Thermal Flow/ Cure Properties of Thermosetting Plastics by Torque Rheometer, Vol. 8.02, ASTM, Philadelphia, Pa., 1993. 

Fig. 4.14. Rapid thermal flow reactor as used to determine the kinetics of the fast first-order reaction between CO2 and OH ions COj + OH" = HCOj ...

Fig. 19. Resistor temperatures as function of the flow with constant power dissipation in the heater resistor. The insert shows the layout of the thermal flow sensor with three resistive elements in the center of the flow channel...

Other approaches for measuring thermal resistance or conductivity of fibers and fabrics include the use of calorimetry (28), thermal flow through a heat sink of known emissivity (2 ), immersion of fibers or fabrics in liquids of known thermal conductivity (30), and measurement of the rate of cooling of textiles or insulating materials by a Cenco-Fitch apparatus (2). 

Table II also includes an estimate of the elevated temperatures reached in the contact areas. These estimates were developed on the basis of the TGA analysis as well as the IR data and appearance of the damage. Any evidence of thermal flow, charring, or chemical change in the impacted area of the film was taken as an indication that the T min of the TGA analysis was exceeded. As shown, these estimated local temperatures are quite high, and the question immediately arises as to their sources under impact conditions. There are three possible sources for this increase in temperature (a) internal damping, (b) differential surface displacement resulting from contact, or (c) fretting motion at the interface induced by the impact.

The oligoesterified woods thus obtained are of interest in that they will be crosslinked at high temperatures and under high pressures, accompanying thermal flow of the wood components, to give plastic-like crosslinked woods. 

Morita and Sakata [20] reported that cyanoethylated wood meal showed thermal flow at around 250°C. The temperature at which the wood could flow decreased with increasing cyanoethyl content of the wood. Treatment of the wood meal before cyanoethylation with sodium periodate or sodium chlorite lowered the flow temperature. The flow temperature was also decreased by blending the cyanoethylated wood with appropriate synthetic polymers or plasticizers. Treatment of the cyanoethylated wood with chlorine solution was found to be the most effective method of lowering the flow temperature. The lowering may be interpreted in terms of the plasticizing effect of chlorination on the lignin moiety in the wood. 

Further, Yamawaki et al. [24] hot-pressed surface cyanoethylated wood fibers at 240°C to make a board by autoadhesion of the thermally melted fibers. When the cyanoethylated fibers were chlorinated, the pressing temperature was reduced to 130 C. The thermal flow temperature was decreased... 

While untreated wood meal shows a thermal softening point of 260°C, esterified wood meals prepared in the N204-DMF-pyridine solution have a softening point of around 100 C or less and a thermal flow temperature of 220-250°C [98]. The flow temperature shows a tendency to decrease with increase in the C number of acyl group. This was first found by Shiraishi et al. [98] that wood meal is converted as a whole to thermoplastic material. In this case, a very high degree of acylation is not always required to provide wood with the thermally meltable property. The products become thermoplasticized materials when almost one-third of the hydroxyl groups in wood are acylated [99]. 

Both at high temperatures (150-190°C) and under high pressure (18.0-27.0 MPa), the wood components thermally flow to give reddish, yellowish, or blackish brown, crosslinked wood boards whose surfaces are smooth, glossy, and plastic-like. In this case, it is advantageous that BADG works as a plasticizer for the wood components. 

Figure 5 shows scanning electron micrographs of hot-pressed control and esterified kenaf fiber. The control fiber (a) shows little tendency to thermally flow under the pressure of the hot press at 190 C whereas the esterified fiber... 

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