Thermal effect

The effects of increased temperature (thermolysis) of starch by conventional heating have been reviewed.2 In the present article, the effects of freezing, as well as heating by infrared and microwave radiations, are described. 

Gelatinization Temperatures of Potato Starch Dried by Various Methods275 

Gels of low concentration (0.1 -1.0%) give separated droplets and myelin. At concentrations above 4.5% the gels turn into a sponge-like continuous network of sheets and stands with small amounts of droplets and myelin. Amylose and amylo-pectin also undergo coacervation.277 

The results of freeze-drying, expressed in terms of the temperature of the loss of structure (Tc), depend on the rate of drying, according to 

Gelatinization Enthalpy of Native and Freeze-Dried Potato Starch and Effect of Water Content on It175 

Non-isothermal 1-D models for adiabatic PBMR and FBMR reactors utilizing Pd tubular membranes have been developed by Elnashaie et al [5.35], and applied to the catalytic ethylbenzene dehydrogenation reaction. In contrast to many other modelling studies their model takes into account intraparticle diffusional limitations. The catalyst particles 

The consideration of thermal effects and non-isothermal conditions is particularly important for reactions for which mass transport through the membrane is activated and, therefore, depends strongly on temperature. This is, typically, the case for dense membranes like, for example, solid oxide membranes, where the molecular transport is due to ionic diffusion. A theoretical study of the partial oxidation of CH4 to synthesis gas in a membrane reactor utilizing a dense solid oxide membrane has been reported by Tsai et al. [5.22, 5.36]. These authors considered the catalytic membrane to consist of three layers a macroporous support layer and a dense perovskite film (Lai.xSrxCoi.yFeyOs.s) permeable only to oxygen on the top of which a porous catalytic layer is placed. To model such a reactor Tsai et al. [5.22, 5.36] developed a two-dimensional model considering the appropriate mass balance equations for the three membrane layers and the two reactor compartments. For the tubeside and shellside the equations were similar to equations (5.1) and 

1 but with catalyst placed only in the shellside. The hydrocarbon (B) was fed in the shellside while the oxygen (A) was fed in the tubeside and permeated (in the case of the MR) through the membrane, which is assumed to only permeate A. For the FBR both re- 

When materials with different coefficients of thermal expansion (CTE) are joined, shear stresses result when the assembly is heated or cooled. Many engineering plastics have a CTE value in the range 80-100 x 10 mm/mm/°C but sometimes differences can occur. Eor example, liquid crystal polymer has a CTE of 10 x 10 mm/mm/°C, whereas acrylic has a CTE of 80 x 10 mm/mm/°C, and if these two substrates were to be bonded with a cyanoacrylate (CTE = 80 x 10 mm/mm/°C [5]) then the adhesive could be subjected to some quite severe stresses at the extreme operating temperature range. In this case a thicker bond line and more compliant or flexible adhesive (e.g., a flexible UV acrylic) may reduce problems. 

To estimate the likely injury or damage to people and objects from thermal radiation from incident outcomes. 

Thermal effect modeling is more straightforward than toxic effect modeling. A substantial body of experimental data exists and forms the basis for effect estimation. Two approaches are used  

Continuous bare skin exposure is generally assumed for simplification. Shelter can be considered if relevant (Chapter 5). 

Thermal effect modeling is widely used in chemical plant design and CPQRA. Examples include the Canvey Study (Health Safety Executive, 1978,1981), Rijnmond Public Authority (1982) risk assessments, and LNG Federal Safety Standards (Department ofTransportation, 1980). The API 521 (1996a) method for flare safety otdusion 2ones is widely used in the layout of process plants. 

API (1996a) RP 521 provides a short review of the effects of thermal radiation on people. This is based on the experiments of Buetmer (1957) and Stoll and Green (1958). The data on time for pain threshold is summarized in Table 4.6 (API, 1996a). It is stated that burns follow the pain threshold fairly quickly. The values in Table 4.6 may be compared to solar radiation intensity on a clear, hot summer day of about 320 Btu/hr ft (1 kW/m ). 

Because heating and cooling of a macroscopic sample is a relatively slow process, thermal detectors as a class are slower in their rate of response than photon ones, although some thermal detectors are faster than selected photon ones. It is convenient to think of thermal detectors as having millisecond response times and photon ones as having microsecond ones, but this is clearly only a rough rule to which there are many exceptions. 

In the discussions which follow, attention will be directed toward two approaches which have found the greatest utility in infrared systems, namely, bolometers and the pyroelectric effect. Others will be discussed briefly. A list of thermal effects is included in Table 2.4. 

A bolometer is the thermal analogue of a photoconductor. The effect is that of change in resistivity of a material in response to the heating effect of incident radiation. In contrast to photoconductors, bolometers can be made of any material which exhibits a temperature dependent change of resistance. The temperature dependence is specified in terms of the temperature coefficient of resistance a defined as 

Thermistor Bolometer. Thermistor (thermally sensitive resistor) material is an oxide of manganese, cobalt, or nickel which exhibits a negative temperature coefficient of resistance the resistance decreases as the temperature increases. Because it is employed under electrical bias, the self-heating effects due to 

Metal Bolometer. In contrast to thermistor materials, metals have a positive temperature coefficient of resistance, i.e., the resistance increases as the temperature increases. Usually the absolute value of the temperature coefficient 

The factors that affect an absorption column or a stripping column performance include the feed compositions and thermal conditions, the ratio of liquid to vapor feed flow rates, the column temperature and pressure, and the number of stages. 

In absorption, the transfer of molecules from the vapor to the liquid is a condensation process that is accompanied by the release of an amount of heat equivalent to the latent heat of condensation of the components being absorbed. If the process is adiabatic, where no heat crosses the system boundaries, the heat released by absorption is converted to sensible heat, resulting in a temperature rise. This thermal effect is reversed in stripping since the stripped components are transferred from the liquid state to the vapor state. The latent heat of vaporization is responsible for a temperature drop in adiabatic stripping processes. 

The temperature variation in an absorption or stripping column is a side effect and is not a required contributor to separation, as in distillation. In fact, in situations where the temperature variation is excessive, the column may have to be cooled or heated in order to counter the absorption/stripping thermal effects. The column may be operated isothermally, with all stages maintained at the same temperature, by applying the right amounts of heater/cooler duties. 

The thermal effects of absorption and stripping are demonstrated in the following example using a single equilibrium stage, that is, a flash operation with two feeds. 

EXAMPLE 8.1 SINGLE-STAGE ABSORPTION AND STRIPPING OF PROPANE 

A material burning in an enclosure will depart from its burning rate in normal air due to thermal effects of the enclosure and the oxygen concentration that controls flame heating. Chapter 9 illustrated these effects in which Equation (9.73) describes steady burning in the form  

If the fuel responds fast to the compartment changes, such a quasi-steady burning rate model will suffice to explain the expenditure of fuel mass in the compartment. The fuel heat flux is composed of flame and external (compartment) heating. The flame temperature depends on the oxygen mass fraction ( Yq2 ), and external radiant heating depends on compartment temperatures. 

The compartment net heat flux received by the fuel within the hot upper layer for the blackbody wall and fuel surfaces can be expressed from Equation (11.13) as 

The AW velocity in piezoelectric media is sensitive to changes in temperature. For most practical sensors, this fact necessitates some means of temperature control and/or compensation, as discussed in detail in Chapter 6. For most chemical sensing applications, substrates such as ST-quartz for SAW sensors and AT-quartz for TSM sensors, which have small temperature coefficients, are selected. 

Celata et al. (2005) evaluated the effect of viscous heating on friction factor for flow of an incompressible fluid in a micro-channel. By integrating the energy equation over the micro-channel length, a criterion that determines conditions when viscous dissipation effect is signiflcant was obtained  

The simplest evaluation value of the complex (Ec/Re) (AReZ) shows that it is essentially smaller than unity for the realistic conditions typical for water flow in micro-channels Re 10, 100 pm, L 500. 

The behavior of liquid flow in micro-tubes and channels depends not only on the absolute value of the viscosity but also on its dependence on temperature. The nonlinear character of this dependence is a source of an important phenomenon - hydrodynamic thermal explosion, which is a sharp change of flow parameters at small temperature disturbances due to viscous dissipation. This is accompanied by radical changes of flow characteristics. Bastanjian et al. (1965) showed that under certain conditions the steady-state flow cannot exist, and an oscillatory regime begins. 

We can estimate the effect of energy dissipation on liquid heating and values of flow parameters corresponding to arising oscillations in the flow. We assume that the density of the fluid and its thermal conductivity are constant. Then, the energy equation attains the form 

Estimation of adiabatic increase in the liquid temperature in circular micro-tubes with diameter ranging from 15 to 150 pm, under the experimental conditions reported by Judy et al. (2002), are presented in Table 3.7. The calculations were carried out for water, isopropanol and methanol flows, respectively, at initial temperature Tin = 298 K and v = 8.7 x 10 m /s, 2.5 x 10 m /s, 1.63 x 10 m /s, and Cp = 4,178 J/kgK, 2,606J/kgK, 2,531 J/kgK, respectively. The lower and higher values of AT/Tm correspond to limiting values of micro-channel length and Reynolds numbers. Table 3.7 shows adiabatic heating of liquid in micro-tubes can reach ten degrees the increase in mean fluid temperature (Tin -F Tout)/2 is about 9 °C, 121 °C, 38 °C for the water d = 20 pm), isopropanol d = 20 pm) and methanol d = 30 pm) flows, respectively. 

FIGURE 2.7 ICIOOO pad surface temperature profiles during the polishing of 200-mm and 300-mm blanket oxide wafers using silica-based slurry under 6 psi downforce and 200 ml/min slurry flow rate and with two different table/carrier speeds (Strasbaugh n-Hance Polisher). 

FIGURE 2.9 TMA scan for the pad conditioned at RT and tested using a penetration microprobe. Temperature dependence of CTE shows three different ranges  

With the assumption of a Gaussian temperature distribution (TEMoo-mode) on the laser affected zone, the temperature increase AT can be estimated by the following equation [63]  

For times t S tt PX/[8k (t 10-2 s)] the temperature becomes time independent, a continuous wave (cw) condition. The local temperature is then given by  

The temperature effect often disturbs precise measurements if isothermal conditions cannot be maintained and if it leads to damage of the sample. Equation 1.12 shows that at constant power density the temperature effect decreases with decreasing pulse times. Therefore, the application of short pulses may be of advantage to avoid damages. If, however, the modification of the surface requires a large amount of total energy, it should be delivered with low power density. On the other hand, there are numerous applications of the thermal heating. It can be used to evaporate or to dissociate the substrate (LAMMA) [64], to enhance reaction rates at the surface or the convection of the electrolyte [65-67]. Finally, it can be employed to study electrode reaction rate constants and the dynamics of the double layer [68]. 

Electrochemical Photocurrent Measurements (Optical/Electrical Method Class), Introduction of a New Model 

1 Photocurrent Model for Ultra-thin, Amorphous Films With Ti02 as an Example 

In view of the different polymerization processes occurring simultaneously, it is generally not possible to link a temperature coefficient to a specific reaction. 

Coudurier, Badru, and Dbnnet (36) obtained separate values for the energies of activation of the condensation process (disappearance of monomer), 14.6 kcal mole , and of the aggregation process, 15.1 kcal mole , at pH 4. 

Bishop and Bear (141) followed the polymerization of monomeric silica at pH 8.5 at 25r45 C by measuring the decline in unreacted monomer using the molybdate method. The initial rate constant, assuming a second-order reaction, showed a peculiar variation with temperature . . . 

The drop in activation cnergy in the 25-35 C region implied that, there was a preequilibrium step in the polymerization. It is likely this involved the same type of induction period observed by other workers under similar conditions at 25 C and the first step is the formation of some small polyiheric species with which the monomerthen reacts preferentially. 

Since solutions of silicic acid gel suddenly under certain circumstances, it might be expected that a considerable heat of reaction might be involved. This is not the case. Tourky (142) found that when silicic acid was made from sodium silicate and acid and polymerized in neutral solution, the heat of reaction, excluding the heat of neutralization of the acid by the base, was about 148 cal g of SiO corresponding to 8000 cal mole In this case, the starting material was sodium metasilicate hence this probably represents the overall heat evolved in the transformation from mono-silicic add. to high molecular weight polymer. 

An important advantage of the micro-level approach is that it enables one to analyze mechanisms that cannot be isolated experimentally. As an example. Fig. 7.66 shows 

When the drying mechanism is not included (denoted by ND on the plot) and the liquid viscosity is low x, = 0.02), the model predicts a total absence of agglomeration (the particle diameter remains constant at its initial value). This is because the liquid deposited on the particles is not able to absorb the kinetic energy of collisions. 

In reality, granulation by layering would take place under such conditions - with a growth rate which would be much smaller than in the case of agglomeration. 

H o we ver, when the droplets are allowed to dry, the agglomeration process is switched on, under otherwise exactly the same conditions. This is because the viscosity of the liquid is increased by drying to an extent that is sufficient for dissipation of the collision energy and, thus, for coalescence. 

In total, the application of the MC model enabled one to explain and quantitatively describe the influence of thermal effects on wet agglomeration (Terrazas-Velarde et al., 2011) in a never before achieved way, which is not possible by application of conventional PBE approaches. Drying is the key to this explanation - in combination with the access to micro-scale physical interactions that the model provides. 

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The Ft correction factor is usually correlated in terms of two dimensionless ratios, the ratio of the two heat capacity flow rates R and the thermal effectiveness P of the exchanger ... 

Maximum Thermal Effectiveness for 1-2 Shell-and-Tube Heat Exchangers... 

Measuring the gross heating value (mass) is done in the laboratory using the ASTM D 240 procedure by combustion of the fuel sample under an oxygen atmosphere, in a bomb calorimeter surrounded by water. The thermal effects are calculated from the rise in temperature of the surrounding medium and the thermal characteristics of the apparatus. 

In the expression for heating value, it is useful to define the physical state of the motor fuel for conventional motor fuels such as gasoline, diesei fuel, and jet fuels, the liquid state is chosen most often as the reference. Nevertheless, if the material is already in its vapor state before entering the combustion system because of mechanical action like atomization or thermal effects such as preheating by exhaust gases, an increase of usefui energy resufts that is not previously taken into consideration. 

In this paper, the performanees of laser-ultrasound are estimated in order to identify lacks of weld penetration. The laser-ultrasonic technique is applied to cylindrical metallic strucmres (few mm thick) in a single-sided control. The results obtained for different materials (gold-nickel alloy and tantalum) are presented by B-sean views for which the control configuration is discussed with regard to the thermal effects at the laser impact. This testing is performed for different lacks of weld penetration (up to 0.5 mm for a thickness of 2 mm) even in the presence of the weld bead, which corresponds to an actual industrial problem. 

Shreve A P and Mathies R A 1995 Thermal effects in resonance Raman-scattering—analysis of the Raman intensities of rhodopsin and of the time-resolved Raman-scattering of bacteriorhodopsin J. Phys. Chem. 99 7285-99... 

Reactions in porous catalyst pellets are Invariably accompanied by thermal effects associated with the heat of reaction. Particularly In the case of exothermic reactions these may have a marked influence on the solutions, and hence on the effectiveness factor, leading to effectiveness factors greater than unity and, In certain circumstances, multiple steady state solutions with given boundary conditions [78]. These phenomena have attracted a great deal of interest and attention in recent years, and an excellent account of our present state of knowledge has been given by Arls [45]. 

In order to Introduce thermal effects into the theory, the material balance equations developed in this chapter must be supplemented by a further equation representing the condition of enthalpy balance. This matches the extra dependent variable, namely temperature. Care must also be taken to account properly for the temperature dependence of certain parameters In... 

The time constant R /D, and hence the diffusivity, may thus be found dkecdy from the uptake curve. However, it is important to confirm by experiment that the basic assumptions of the model are fulfilled, since intmsions of thermal effects or extraparticle resistance to mass transfer may easily occur, leading to erroneously low apparent diffusivity values. 

There are do2ens of flow meters available for the measurement of fluid flow (30). The primary measurements used to determine flow include differential pressure, variable area, Hquid level, electromagnetic effects, thermal effects, and light scattering. Most of the devices discussed herein are those used commonly in the process industries a few for the measurement of turbulence are also described. 

Measurement by Thermal Effects. When a fine wire heated electrically is exposed to a flowing gas, it is cooled and its resistance is changed. The hot-wire anemometer makes use of this principle to measure both the average velocity and the turbulent fluctuations in the flowing stream. The fluid velocity, L, is related to the current, /, and the resistances, R, of the wire at wire, and gas, g, temperatures via... 

Heat/Solvent Recovery. The primary appHcation of heat pipes in the chemical industry is for combustion air preheat on various types of process furnaces which simultaneously increases furnace efficiency and throughput and conserves fuel. Advantages include modular design, isothermal tube temperature eliminating cold corner corrosion, high thermal effectiveness, high reHabiHty and options for removable tubes, alternative materials and arrangements, and replacement or add-on sections for increased performance (see Furnaces, fuel-FIREd). 

Most, if not all, microwave biological effects and potential medical appHcations are beheved to be the result of heating, ie, thermal effects. The phenomenon of microwave hearing, ie, the hearing of clicking sounds when exposed to an intense radar-like pulse, is generally beheved to be a thermoelastic effect (161). Excellent reviews of the field of microwave bioeffects are available (162,163). 

In contrast to the flexibiUty method, the stiffness method considers the displacements as unknown quantities in constmcting the overall stiffness matrix (K). The force vector T is first calculated for each load case, then equation 20 is solved for the displacement D. Thermal effects, deadweight, and support displacement loads are converted to an equivalent force vector in T. Internal pipe forces and stresses are then calculated by applying the displacement vector [D] to the individual element stiffness matrices. 

The simplest method of reduciag stresses and reactions is to provide additional pipe ia the system ia the form of loops or offset-bonds. When physical limitations restrict the use of additional bends, a multiple arrangement of several small-size pipe mns may sometimes be used. Owiag to stress intensification, the maximum stress generally occurs at elbows, bends, and Ts. Thus, heavier-walled fittings may reduce the stress without significantly impairing flexibiUty. FiaaHy, effectively located restraints can reduce thermal effects on the equipment. 

Due to thermal effects such devices must operate at temperatures well below the electron charging energy of 2C. With state-of-the-art fabrication technology, the capacitance is typically of the order 10 F, which requires temperatures below 1 K. Even with further miniaturisation, it is unlikely that these devices will be feasible at room temperature. Even so, there has been work in modeling this type of device for use in digital circuits (73). 

Table 3. Ferroalloy Density and Thermal Effects on Steel Baths...

Thermal effects on aquatic organisms have been given critical scientific review. Annual reviews of the thermal effects Hterature have been pubUshed beginning in 1968 (12). Water temperature criteria for protection of aquatic life were prepared by the NAS in 1972, and these criteria have formed the basis of the EPA recommendations for estabUshing water temperature standards for specific water bodies (13,14). 

If this concentration is larger than the oxygen vacancies created by thermal effects, then the conductivity from the motion of the doubly charged ions is directly proportional to the concentration of CaO (eq. 15). 

Externally impo.seddisplacements. Externally caused movement of restraints wiU impose displacements on the piping in addition to those related to thermal effects. Such movements may result from causes such as wind sway or temperature changes in connected equipment. 

A solid longitudinal baffle is provided to form a two-pass shell (Fig. 11-35F). It may be insulated to improve thermal efficiency. (See further discussion on baffles). A two-pass shell can improve thermal effectiveness at a cost lower than for two shells in series. 

Powder Insulation A method of reahzing some of the benefits of multiple floating shields without incurring the difficulties of awkward structural complexities is to use evacuated powder insulation. The penalty incurred in the use of this type of insulation, however, is a tenfold reduction in the overall thermal effectiveness of the insulation system over that obtained for multilayer insulation. In applications where this is not a serious factor, such as LNG storage facihties, and investment cost is of major concern, even unevacuated powder-insulation systems have found useful apphcations. The variation in apparent mean thermal conductivity of several powders as a function of interstitial gas pressure is shown in the familiar S-shaped curves of Fig. 11-121. ... 

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