Heat Joule effect

AC Calorimetry periodic heating (Joule effect, light) on one side of the sample, measurement of the amplitude of the temperature response on the other side (which is related to a heat sink through a thermal resistance). Provides values of the heat capacity. 

Compensation by electric cooling (Peltier effect) or heating (Joule effect) and measurement of the respective electric energy. 

Corresponding to the charge in the potential of single electrodes which is related to their different overpotentials, a shift in the overall cell voltage is observed. Moreover, an increasing cell temperature can be noticed. Besides Joule-effect heat losses Wj, caused by voltage drops due to the internal resistance Rt (electrolyte, contact to the electrodes, etc.) of the cell, thermal losses WK (related to overpotentials) are the reason for this phenomenon. 

Jahn-Teller distortions 309 ff Japanese separators 264, 267 Joule effect, heat losses 13 jump frequency, solid electrolytes 532 Jungner nickel cadmium batteries 22... 

Gough-Joule effect When an elastomer/ rubber is stretched adiabatically (without heat entering or leaving the system), heat is evolved, This effect was first reported discovered by Gough in 1805 and rediscovered by Joule in 1859. 

The most widely deposition technique is the ion assisted deposition (lAD). A material in a melting-pot is vaporized by heating either with an electron beam, or by Joule effect, or with a laser beam, or with microwaves, or whatever else. The vapor flow condensates on the substrate. In the same time, an ion... 

An apparatus which demonstrates the Gough-Joule effect. It comprises a pendulum adjusted so that a rubber sample is under stretch. Heat from a lamp causes the rubber to contract and swing the pendulum. This pulls the rubber into a shaded section where it extends and moves the pendulum back to the original position, whereupon the cycle is repeated. 

The first heat flow calorimeter based on Seebeck, Peltier, and Joule effects was built by Tian at Marseille, France, and reported in 1923 [156-158]. The set-up included two thermopiles, one to detect the temperature difference 7) — 7) and the other to compensate for that difference by using Peltier or Joule effects in the case of exothermic or endothermic phenomena, respectively. This compensation (aiming to keep 7) = T2 during an experiment) was required because, as the thermopiles had a low heat conductivity, a significant fraction of the heat transfer would otherwise not be made through the thermopile wires and hence would not be detected. 

Another problem related to the validity of equation 9.9 is that equation 9.6 applies only to heat conduction. If T — 12 is large, some significant fraction of heat will be transferred by convection and radiation and thus will not be monitored by the thermopile. Consequently, the use of partial compensating Peltier or Joule effects was essential in the experiments involving Calvet s calorimeter, whose thermopiles had a fairly low thermal conductivity. 

Building a heat flow microcalorimeter is not trivial. Fortunately, a variety of modern commercial instruments are available. Some of these differ significantly from those just described, but the basic principles prevail. The main difference concerns the thermopiles, which are now semiconducting thermocouple plates instead of a series of wire thermocouples. This important modification was introduced by Wadso in 1968 [161], The thermocouple plates have a high thermal conductivity and a low electrical resistance and are sensitive to temperature differences of about 10-6 K. Their high thermal conductivity ensures that the heat transfer occurs fast enough to avoid the need for the Peltier or Joule effects. 

The procedure may start with the reference experiment, which, in the case under analysis, involved a solution of ferrocene in cyclohexane (ferrocene is a nonphotoreactive substance that converts all the absorbed 366 nm radiation into heat). With the shutter closed, the calorimeter was calibrated using the Joule effect, as described in chapter 8, yielding the calibration constant s. The same solution was then irradiated for a given period of time t (typically, 2-3 min), by opening the shutter. The heat released during this period (g0, determined from the temperature against time plot and from the calibration constant (see chapter 8), leads to the radiant power (radiant energy per second) absorbed by the solution, P = /t. ... 

An electric current heats an electrical resistor sunk in a sleeve of thermoplastic and causes its melting by the Joule effect. 

Careful heat-flow calibrations have to be performed. Chemical calibrations present many disadvantages they rely on prior results, with no general agreement and no control of rate, and are generally available only at a single temperature. On the contrary, electrical calibrations (Joule effect) provide many advantages and they are easy to perform at any temperature [103],... 

The thermal device used to elevate the temperature consists of a burner fed with a gaseous combustible mixture or, alternatively, in atomic absorption, by a small electric oven that contains a graphite rod resistor heated by the Joule effect. In the former, an aqueous solution of the sample is nebulised into the flame where atomisation takes place. In the latter, the sample is deposited on the graphite rod. In both methods, the atomic gas generated is located in the optical path of the instrument. 

Figure 14.9—Thermoelectric atomisation device, a) Graphite furnace heated by the Joule effect b) example of a graphite rod c) temperature program as a function of time showing the absorption signal. The first two steps of this temperature program are conducted under an inert atmosphere (argon scan).

When ions flow from one side of the electrolyte to the other, there is ohmic loss and generated heat, due to the Joule effect. 

Heat generated inside the cell, due to Joule effect and the electrochemical reactions, is released into the inlet air and fuel. In particular, the inlet air, while flowing in the injection pipe, receives heat by the up flowing air in the annular section. Considering a single cell, the temperature profile of the gases and solid parts is presented in the next section. 

The first three terms on the left hand side are the net convective, radiative and conductive heat transfers, whose expressions are reported in Equations (7.6-7.8). The fourth term is the heat generated by the chemical/electrochemical reactions (m-T As) and by Joule effect, while the last term is the electrical power generated in the slice. 

The sample to be analyzed, say C60 fullerene, is mixed with an appropriate amount of KBr in an agate mortar and then transferred into a press and compressed at 4,000 Kg into a pellet with a diameter of 1.2 cm and a thickness of 0.2 cm. The pellet was mounted into the sample holder of the Specac variable temperature cell and inserted into the cell. The cell was then evacuated with the aid of a pump to a vacuum of 0.1 torr and then heated gradually at 120°C in order to permit the humidity absorbed on the internal surfaces of the cell and in the KBr pellet to evaporate. The sample was then cooled to the desired temperature to record the infrared spectrum. In order to go below room temperature, use was made of liquid nitrogen, added cautiously and in small amount in the cavity present inside the cell. Such cavity is connected with the sample holder and permits to cool the sample to the desired temperature. The temperature of the sample was monitored with adequate thermocouples. The lowest temperature reached with this apparatus was -180°C (93K) while the highest temperature was +250°C. Heating is provided by the Joule effect and an external thermal control unit. 

A catalytic reaction must be performed in aqueous solution at industrial scale. The reaction is initiated by addition of catalyst at 40 °C. In order to evaluate the thermal risks, the reaction was performed at laboratory scale in a Dewar flask. The charge is 150 ml solution in a Dewar of 200 ml working volume. The volume and mass of catalyst can be ignored. For calibration of the Dewar by Joule effect, a heating resistor with a power of 40 W was used in 150ml water. The resistor was switched on for 15 minutes and the temperature increase was 40 K. During the reaction, the temperature increased from 40 to 90 °C within approximately 1.5 hours. The specific heat capacity of water is 4.2 kj kg K 1. 

E. Applied Voltage The mobility of the EOF increases with increasing applied voltage. This effect is attributed primarily to an increase in temperature with increasing applied voltage as a result of Joule heating. Joule heating is discussed in detail in section 4.3.4,i,D. 

In most of the industrial applications, several DLCs are connected either in series or in series/ parallel. They are generally subjected to very high currents. Consequently, the heat produced by Joule effect must be dissipated with cooling systems like fans or air distribution channels. The choice of the cooling system depends on the level of the heat transfer coefficient and the maximum allowed operating temperature. The chosen cooling system should be sufficient to keep the DLC temperature at a tolerable temperature level which leads to a longer lifetime. 

For the evaporation experiment, an A1 wire is placed in a V shape tungsten filament heated through Joule effect. The A1 wire is first outgased for a few minutes before condensing the evaporated A1 onto the polymer film which is located about 8 cm apart from the AI source. 

As discussed above a certain buffer concentration is required to perform optimal analyses. The minimum ionic strength required determines the current and Joule heating. This effect can be measured as a deviation from Ohm s law. With organic buffers the conductivity is much smaller for a given ionic strength. Consequently organic zwitterionic buffers, or at least buffers with counterions of low mobility, should be preferred especially when long capillaries have to be used. 

Adiabatic calorimetry is particularly useful for the study of closed adsorption systems at low temperatures (where radiation losses are small) and for temperature scanning experiments. It is the preferred type of measurement for the determination of the heat capacity of adsorption systems, especially in the temperature range 4-300 K (Morrison et al., 1952 Dash, 1975). The temperature scan is obtained by means of the Joule effect applied to the sample container the sample heating coil shown in Figure 3.14 is used for this purpose. 

At the present state, only some qualitative explanations are available. When the sample is prepared, the carbon particles get compressed to come in contact with others. During the flow of the current, the particles are heated because of the Joule effect and the heat is transmitted to the surrounding epoxy matrix. As a result of the matrix dilatation, the contacts between the carbon particles disappear and the sample becomes an insulator. The process being gradual, one observes the regular increase of R with time. 

Graphite ovens heated by the Joule effect where the whole sample is introduced at once leading to a variable, peak-shaped, signal. 

Figure 20 shows the test section and its instrumentation. Both ends are equipped with 90° manifolds for the fluid distribution. The tube diameter used for these manifolds is ten times that of the minichannels in order to suppress fluid distribution problems. The test section is made of two functional parts an adiabatic section for the hydrodynamic entry length and a heating zone placed between two pairs of electrodes brazed on the tube to produce a Joule effect heating. 

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