Contact temperature

Contact temperature measurement is based on a sensor or a probe, which is in direct contact with the fluid or material. A basic factor to understand is that in using the contact measurement principle, the result of measurement is the temperature of the measurement sensor itself. In unfavorable situations, the sensor temperature is not necessarily close to the fluid or material temperature, which is the point of interest. The reason for this is that the sensor usually has a heat transfer connection with other surrounding temperatures by radiation, conduction, or convection, or a combination of these. As a consequence, heat flow to or from the sensor will influence the sensor temperature. The sensor temperature will stabilize to a level different from the measured medium temperature. The expressions radiation error and conduction error relate to the mode of heat transfer involved. Careful planning of the measurements will assist in avoiding these errors. 

With contact temperature measurement, placing the measurement probe in contact with the object of measurement (duct, surface, etc.) produces an additional route for heat conduction to or from the object. This perturbation error changes the initial temperature field in the vicinity of the contact point and creates measurement errors. 

Tetraethylene glycol—More expensive than triethylene but less losses at high gas contact temperatures. Reconcentrate at 400°F to 430°F. 

When selecting a lubricant, both the temperature at the contact area and the ambient temperature at important factors to be considered. Measuring the peak contact temperature is very difficult. The maximum rise in temperature of the oil leaving the gears and the maximum oil temperature are specified for various types of gears. For spur, bevel, helical and spiral level gears, the temperature rise should not normally exceed 30°C (86°F) with a maximum oil temperature of70°C (158°F). 

With the modern ABS braking system contact temperatures are kept low, particularly on wet surfaces so that the log a v is relatively high and the silica-filled compound is superior to the standard black-filled one. With locked wheel braking the contact temperamres are high and log a-iv values are low, and the ranking of the braking performance of these two compounds reverses. 

Activity will depend on concentration, time of contact, temperature, etc. (see Chapter 11) but these are activities expected if in-use concentrations were being employed. 

The first clinical IRET used thermopile sensors to achieve non-contact temperature measurement in the ear. In 1991 a tympanic thermometer for home use was first introduced to the consumer market (Thermoscan HM 1). It utilized a pyroelectric sensor which requires the use of a suitable mechanical shutter or chopper mechanism, since it is only sensitive to temperature changes [3]. The main advantage of the pyroelectric sensor unit was its lower cost. However, prices for thermo-... 

In Fig. 6.1, an attempt is made to show to what extent sensors have been penetrating the appliance market over the past years, a trend which is set to continue in the next decade. In the beginning, there were relatively simple sensors for temperature, pressure, flow, etc. Over the last years, non-contact measuring devices have attracted much attention, such as non-contact temperature monitoring for toasters or for hair blowers. The introduction of more complex sensor systems, such as water quality sensors or multi gas sensing artificial noses is imminent. 

Automatic baking control, e.g. by introduction of intelligent multi-gas sensors (artificial noses) in combination with non-contacting temperature distribution recognition... 

Remote non-contacting temperature, humidity and color detection for hair care equipment... 

Thermopiles have been used for non-contacting temperature measurement in hairdryers, to prevent damage to the hair and to speed up the drying process. 

In the subsurface, arsenic may readily accumulate in coal. Specifically, groundwater percolating through volcanic deposits may leach arsenic and transfer it to underlying coal beds during or after coalification. Contact metamorphism and any associated hydrothermal fluids are other processes that sometimes locally enrich arsenic in coal seams. At a site in British Columbia, a Cretaceous bituminous coal seam was contact metamorphosed by a mafic dike. The contact temperatures were about 700-900 °C, which could volatilize arsenic and/or dissolve it into associated hydrothermal fluids. The arsenic was then transported and deposited into cooler sections of the seam (Yudovich and Ketris, 2005), 163. 

This case study is interesting because it exemplifies many of the key factors that determine migration and that were described in sections 9.2 and 9.4 - the effect of food type and of contact temperature in driving migration, along with the need for concrete numerical limits based on toxicological information coupled with realistic estimates of exposure. 

If the thermal penetration number is known, the contact temperature Tc, which results when two bodies A and B, which are at different temperatures, touch, can easily be computed using... 

Non-contact temperature measurement inside microfluidic channels was achieved by using fluorescence quenching of a rhodamine dye. The intensity of the dye fluorescence is temperature-sensitive in a range temperature of 5-95°C [795], Another on-chip temperature measurement method was achieved by measuring... 

Slyadnev, M.N., Tanaka, Y., Tokeshi, M., Kitamori, T., Non-contact temperature measurement inside microchannel. Micro Total Analysis Systems, Proceedings 5th [lTAS Symposium, Monterey, CA, Oct. 21-25, 2001, 361-362. 

The considerable influence of the food simulant can be observed in many cases for non-polyolefins. For example, the migration of an additive with Mr = 549 from IPS into 50 % ethanol in water in Table 15-4 shows a decrease of the migration amount measured at 49 °C after an initial contact temperature of 66 °C This phenomenon cannot be explained by changes in diffusion. The decrease in migration must be a consequence of a strong increase of the partition coefficient, KPR with decreasing temperature that shifts the equilibrium concentration of the migrant to the plastic phase. 

One option from UOP for olefin reduction is the revamp of an FCC unit to RxCat technology (10). In the RxCat process, Figure 4.6, a portion of coked catalyst is recycled to mix with regenerated catalyst at the bottom of the riser reactor. This feature allows the unit to run at a higher catalyst-to-oil ratio and a lower catalyst contact temperature. Moreover, ZSM-5 additive is more effective with RxCat because coked ZSM-5 retains more activity than coked Y zeolite. 

In contrast to plastics, rubbers are rarely used in the packaging of food products. Exceptions to this rule are the use of rubber in flip top seals on beer bottles and the seal that is present in food cans. However, in the processing of food, there are a number of situations where significant contact with rubber products can occur. This is due to the fact that the unique properties of rubber lead to it being used in a wide range of products (see Table 12.1). It is also the case that the range of contact conditions encountered (i.e. food type, contact temperature, time and area) mean that a wide variety of rubber compounds are employed (see section 12.2). 

These three categories take into account the wide variety of applications for which rubber products are used and the fact that migration may vary with the application. The level of migration for rubber products may be estimated by taking into account four factors, Ri, R2, R3 and R4, referring respectively to the relative contact area, contact temperature, contact time and number of times that the article is used. Categories are based on the intended use or on the result of multiplying the four factors (Ri x R2 x R3 x R4 = R-total). The factors R, R2, R3 and R4 can be defined as follows ... 

R2 refers to the temperature during the contact period of the mbber product with the food or beverage. At a temperature lower than or equal to 130 °C, R2 has a value calculated according to the formula R2 = 0.05e° where e is the base of the natural or Napierian logarithms and T is the contact temperature, expressed in °C. For temperatures higher than 130 °C, R2 always has the value 1.00. 

Relatively high levels for the worst-case migration potential for styrene were also calculated (the SML for styrene is currently under review) and the concentration of styrene in the appropriate foodstuffs was determined. Low levels of styrene were measured but in all cases were less than 5 ppb. Thus despite the high contact temperatures between the foodstuff and the packaging, the relatively high packaging area mass of food ratio and the presence of fat on the food surface, the migration levels observed were low. 

The treated oil-bitumen is collected in the bottom of the vessel, while the vapors exit at the top. The contact temperature in the vessel is approximately 150 C (300 T), and the total area of the three trays is approximately 3.34 m (36 sq ft). The treated oil, which should contain less than 0.5% (v/v) water, is then pumped from the bottom of the evaporator, fan-cooled and sent to the treated-oil storage tank (T-2). The water-diluent vapors are also fan-cooled, sent to an accumulator, and then transferred to a gravity separator for diluent recovery. Water is sent to the produced-water tank (T-3) before being processed through the IGF unit. 

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