Cooling period

Cryogenics We use several types of evacuated stainless steel cryostats of about 1 htre capacity to provide the 77 K cooling with hquid nitrogen. The simplest, best valued and easiest to handle one is a ordinary thermos flask available from the supermarket (see fig.3). It is sufficient for a measurement period of more than 12 hours. A specially designed stainless steel vessel gains cooling periods of 30 hours. 

In the cooling phase (assuming t. is non-/ero), the velocities are periodically rescaled to change the system temperature from the run temperature to the final temperature Tj in increments of the temperature step AT. The cooling period for rescaling the velocities. P... is defined by ... 

As noted earlier, gamma-ray emission is measured following a cooling period in which short-lived interferents are allowed to decay away. The initial activity therefore, is determined by extrapolating a curve of activity versus time back to f = 0 (Figure 13.15). Alternatively, if the samples and standards are irradiated simultaneously, and the activities are measured at the same time, then these activities may be used in place of Aq) and (Ao)s in the preceding equations. 

The concentration of Mn in steel can be determined by a neutron activation analysis using the method of external standards. A 1.000-g sample of an unknown steel sample and a 0.950-g sample of a standard steel known to contain 0.463% w/w Mn, are irradiated with neutrons in a nuclear reactor for 10 h. After a 40-min cooling period, the activities for gamma-ray emission were found to be 2542 cpm (counts per minute) for the unknown and 1984 cpm for the standard. What is the %w/w Mn in the unknown steel sample ... 

Nomenclature (Use consistent units.) A = heat-transfer surface C, c = specific heats of hot and cold fluids respectively Lq = flow rate of liquid added to tank M = mass of fluid in tank T, t = temperature of hot and cold fluids respectively Ti, ti = temperatures at beginning of heating or cooling period or at inlet To, to = temperature at end of period or at outlet To, to of liquid added to tank ... 

Where applicable, dry steam is passed through the dehquored cake to raise the temperature of the residual moisture, reduce its viscosity, and lower its content. The final diying or cooling period which follows steam filtration uses the residual heat left in the cake to evaporate some additional moisture. 

Considering the factors shown above and the heterogeneous, transient nature of the mechanical, kinetic, and thermal components, the most favorable time for chemical reaction is during the loading pulse, not during the post-shock thermal-cooling period. 

Modern low-density insulation such as those based on ceramic fibers can be used to save energy in plant operating on a batch basis. The low thermal mass permits a rapid heating and cooling period that can save a substantial amount of energy. With continuously operating plant the advantages are not so pronounced. 

The checkers found that the maintenance of a flow of oxygen during the cooling period prevented clogging of the glass frit and a building up of pressure in the gas-inlet tube in their apparatus. 

During the cooling period, the energy balance for the jacket is dT ... 

In equation 11.77, 4 is a numerical constant depending on the geometry and decay constant of the parent radionuclide. If the half-life of the parent is long in comparison with the cooling period, A takes a value of 55, 27, or 8.7 for volume diffusion from a sphere, cylinder, or plane sheet, respectively. If decay rates are faster, A progressively diminishes (see table 1 in Dodson, 1973, for numerical values). 

Synthesis of plutonium in significant quantities requires a sufficiently long reactor fuel irradiation period. Uranium, plutonium, and the fission products obtained after neutron irradiation are removed from the reactor and stored under water for several weeks. During such cooling periods most neptunium-239 initially formed from uranium and present in the mixture transforms to plutonium-239. Also, the highly radioactive fission products, such as xenon-133 and iodine-131 continue to decay during this period. 

The mean diffusion distance over the cooling period subsequent to Tc is proportional to (fD where the integration is from the time of Tc to the time of room temperature. The concept of Tc dictates that mid-diffusion distance (fDdty subsequent to Tc is significantly smaller than the half-thickness of a thin slab (one-dimensional diffusion), or the radius of a sphere or long cylinder. Denote the half-thickness and radius as a. Therefore,... 

Because of fhe cooling period between pulses, these lamps operate at much lower temperatures and are suitable for manufacturing processes where the product does not tolerate high temperatures. 

The diene polymerizations were generally allowed to proceed for 48 hours, which ensured quantitative conversion. In the case of butadiene, the reactor was cooled periodically to draw residual butadiene monomer into the solution from the void volume of the reactor. 

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