Parasitic heating

Tunneling electric current through the normal metal insulator superconductor junction is accompanied with heat flow out of normal metal when property voltage is biased. The phenomenon enables cooling of electrons and phonons (under special conditions) in the region below 1K. At lower bath temperatures, two parasitic heat sources decrease refrigerator performance ... 

Second, the efficiency of conventional reformer decreases at small scales due to heat transfer limitations and parasitic heat losses. The transfer of heat from the combustion products to the reactants is an inherently inefficient process, and in any practical system, especially for smaller scales, it is not possible to transfer all of the energy released by combustion into the process being heated. In UMR the heat transfer is more efficient as the packed bed is internally heated. The improvements in heat transfer to the packed bed are expected to result in a higher process efficiency. 

Convective cooling of an electrical heater and measuring its temperature according to method B avoids some sources of error, like measuring the heated fluid temperature or the unknown amount of heat dissipated into the substrate. For this reason, many sensors are located on a thin membrane or are fabricated on polymers or on other thermal insulations. This minimizes the parasitic heat loss and increases the sensor s... 

Samples for measurement were parallelepipeds (5 x 5 x 30 mm). Results are listed in Table IV and shown in Fig. 1. They were obtained with the double flux method, which permits the elimination of first order systematic errors owing to the parasitic heat leak. Measurements below 7 K were taken with superconducting heating leads to reduce the heat leak. The temperature difference was measured with a gold/iron - Chromel thermocouple, xsrhich constitutes a thermal shunt. This must be taken into account to calculate the sample thermal conductivity. At values near 10 W/cm K at 2 K, for instance, the calculated correction amounts to nearly 30%. 

In a real experiment, the measured heat flux g xp and temperature difference ATexp, differ fi om the aforementioned Q and AT (= T1-T2), due to parasitic heat losses, Q, heat losses due to radiation, Q and convective heat losses, Qc- Thus... 

The parasitic heat losses, 2p can be calculated (Moster et al, 1989) from... 

When measuring the thermal conductivity with this technique, some corrections should be made for (1) radiation-induced heat transfer (radiative correction) (2) parasitic heat transfer from the inner to the outer cylinder through a central solid pintle, electric wires, and thermocouples (3) convective heat transfer and (4) effects of possible temperature jumps at the interface between the liquid layer and the cylinder surface. 

The schematic of flap actuator is shown in Fig. 6. The actuator surface is supported at one end as cantilever support and the actuation takes place due to the external applied force at the other end. The disadvantage of micro coil, piezoelectric and electrostatic actuation is the large voltage requirement. Thus, the devices heat up leading to increase in temperature of the substrate with parasitic heat loss to the fluid. Magnetic... 

Fig. 6.4. Rotational population as ion thermometer. The photofragmentation spectrum of N2O+ (lowest plot) has been measured in a recently completed machine which has been developed in Basel for ion spectroscopy The ions have been cooled in collisions with 10 K He buffer gas. Comparison of the rotationally resolved intensities with the three simulated spectra (15, 25, and 35 K) indicates that the rotational temperature is about 25 K. As discussed in the text this indicates that there must be some parasitic heating.

Screen channel LADS have flight heritage with storable propellants where heat transfer effects are not as severe as they are for cryogenic propellants. Before these IADs can be routinely used in cryogenic propulsion systems, the effects of undesirable heat on the LAD must be fully quantified. This environmental parasitic heat leak into the tank or heat input from warm pressurant gas may adversely affect LAD performance by vaporizing the liquid and drying out of the LAD screen. 

When designing a PMD for a new system, galleries should only be chosen as the primary PMD when it has been analytically determined that vanes and sponges will not meet mission requirements. For vanes and sponges, additional safety factor should be included to account for degradation of performance due to parasitic heat leak into the tank. The primary mission requirements that must be identified are listed as follows ... 

In a fuel cell, the difference in reactant gas compositions at the two electrodes leads to the formation of a difference in Galvani potential between anode and cathode, as discussed in the section Electromotive Force. Thereby, the Gibbs energy AG of the net fuel cell reaction is transformed directly into electrical work. Under ideal operation, with no parasitic heat loss of kinetic and transport processes involved, the reaction Gibbs energy can be converted completely into electrical energy, leading to the theoretical thermodynamic efficiency of the cell. 

Discussion—It is approximately equal to the takeoff rate differing only by the parasitic heat losses. It is expressed in millilitres per hour for a head of any given internal diameter or millilitres per hour per square centimetre of cross-sectional area of the throat for comparative purposes. 

Discussion—It is approximately equal to the boil-up rate differing only by parasitic heat losses. 

As well as the above current production reaction a parasitic heat producing reaction occurs with the formation of hydrogen ... 

Note that a three-leg thyristor produces 50 percent more parasitic heat than a two-leg therefore, 50 percent more panel cooling capability must be provided. 

---