Heat dissipation rate

One remark can be made refering to the significance of the specific heat dissipation rate (dQ/dt per cell). The nutrient enrichment induced the appearence of an energetically expensive metabolic phase followed by a secondary decrease which indicated a metabolic recovery. This phenomenon was independent of oxygen availability, i.e. in "summer" microcosms where the oxygen tension was severely limited (after enrichment), a similar energetic recovery was observed as in "winter" microcosms (figure 5). 

During the increase of the heat production rate, the succession of populations was very rapid, the strains isolated at different incubation times never clustered at a similarly high level. The values of index of utilization of small molecules (amino acids, carbohydrates, alcohols) showed a net tendency to decrease and reach a minimum indicating physiological specialization, paralleled by the maximum value of the specific heat dissipation rate q. ... 

In order to measure the velocity of a stream of air, a flat plate of length 2 cm in the flow direction is placed in the flow. This plate is electrically heated, the heat dissipation rate being uniform over the plate surface. The plate is wide so a two-dimensional laminar boundary layer flow can be assumed to exist The velocity is to be deduced by measuring the temperature of the plate at its trailing edge. If this temperature is to be at least 40°C when the air temperature is 20 C and the air velocity is 3 m/s, find the required rate of teat dissipation in the plate per unit surface area. 

Multiple layers of low conductivity phenolic foam insulation and small temperature differences between the primary coolant and the ambient minimized the heat loss from the primary loop to the ambient. Also, the heat addition to this loop was minimized by using a recirculation pump with an extremely low heat dissipation rate, which was calculated from the pump curves supplied by the manufacturer. With the pump heat dissipation and the ambient heat loss being small fractions of the secondary loop duty, the test section heat load was relatively insensitive to these losses and gains. Local heat transfer coefficients were therefore measured accurately in small increments for the entire saturated vapor-liquid region. Additional details of this thermal amplification technique are provided in the paper by Garimella and Bandhauer [32]. 

The source term. S, in eqn (4) is zero in the overall domain but in the H2 release zone. The source term SQi in eqn (6) stands for the heat dissipation rate inherent... 

We conclude that the piezometric technique is capable of yielding reliable diffusivity data provided that the pressures are monitored in the uptake cell and the limitations imposed by the time constant of the valve and finite heat dissipation rates are respected. For strongly adsorbed species theses restrictions limit the applicability to relatively slow processes (half times of at least several seconds). For weakly adsorbed species somewhat faster diffusion processes can be measured. A detailed assessment of the range of validity of this method, as a function of the system variables, has been presented by Schumacher and Karge [19]. In reviewing earlier reported piezometric diffusivity data, the values derived from measuring only the pressure in the dosing cell should not be accepted without further detailed analysis. 

To ensure high quality of casting at a high production rate, the surface of the mould must be covered with a heat-insulating coat. The function of this coat is to reduce the heat dissipation rate to a low level and reduce the friction during the movement of the melt in the casting mould. The coat has a porous structure to facilitate the separation of the casting from the mould. 

The continuous generation of heat by microbial cultures can also be used as a basis for an on-line monitoring of the microbial activity and metaboUsm. If the temperature increase in the cooling water, its flow rate, and the other relevant energy exchange terms such as agitation and evaporation rates are measured systematically, the heat dissipation rate of the cellular culture can quantitatively be monitored on-line in industrial fermenters. The information contained in this signal can be used to optimize the bioprocess and for on-line process control. 

The worst case is that within a stack some cells are flooded, some cells are drying up, and the other cells have the right amount of water. This could be due to a poor stack design leading to uneven reactant or coolant distribution among cells, higher heat dissipation rates by the end cells, and nonuniform properties of the GDMs, the CLs, and the flow-field plates. It is very difficult to operate such a stack, and its life is very likely to be short. 

This equation shows that in isothennal biochemical reaction cycles, the entropy of the system changes because of the heat dissipation rate <(dis exchanged with the surrounding and the rate of free energy dissipation P due to entropy production. This equation also indicates the dissipative character of biochemical cycles. Dynamic equations similar to Eq. (11.5) can also be written for enthalpy and Gibbs ftee energy changes... 

We see from Eq. (5.25) that we could either increase the amount of enzymes of augment the number of substrate molecules (nx) to accelerate the enzymatic reaction. However, this also increases the heat dissipation rate (5.25). As a matter of fact, the only way to stop heat dissipation (and so making the enzymatic reaction thermodynamically reversible) is to make the reaction velocity equal to zero. 

The synthesis and degradation of RNA molecules is a process which, even in the stationary state, is out of equilibrium. The reason is the unbalance of chemical potentials between the substrates out of which RNA is synthesized and the pool of RNA molecules, and between the RNA pool and the products of RNA degradation. These unbalances further implies the existence of a heat dissipation rate given by... 

Although we did not smdy the dynamics of gene regulation when the promoter is regulated, we do can compute the heat dissipation rate. The reason is that, as we have seen, promoter regulation is a process that complies with chemical equilibrium, and so does not contribute to the heat dissipation rate. Therefore, we only need to take into account the effect of repressors on transcription to obtain ... 

This energy reduction is ultimately dissipated as heat. If we consider the molecule current from to / by Eq. (9.21), we can deduce the following expression for the heat dissipation rate ... 

The first law of thermodynamics implies that this energy decrease is dissipated as heat into the environment. Finally, given that the current Jei measures the net number of molecules shifting from E to I per unit time, the heat dissipation rate associated with this phenomenon is... 

In particular, the stationary heat dissipation rate is given by... 

If the voltage is the fuel cell voltage, the output is the electrical power from the fuel cell. If instead the voltage in Eq. (2.23) is the voltage potential lost due to resistance, the power generated is thermal dissipation. The delineation between electrical power and heat dissipation rate will become clear in fnture chapters if it is not now. Thus, electrical power has units of watts (J/s), as expected. Ohm s law can also be substituted into Eq. (2.17) to obtain alternate expressions for electrical power ... 

Figure 33 Heat dissipation rate

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