Maximum Permissible Temperature Research Articles

SIMULATED THERMAL PERFORMANCE OF A SOLAR-HEATED FLOOR

A low cost, simple solar heating system consisting of an active collector with an In-Floor Heat Distribution and Storage (IFHDS) system was developed in response to the energy crisis of the 1970s. A two-dimensional finite difference model was developed and used to simulate the performance of IFHDS system cross-sections. Simulation runs were conducted with a steady-periodic model for the temperature of the solar-heated air in the IFHDS system cross-section. The steady periodic simulation results indicated IFHDS system energy efficiency increases with decreasing air temperature in the room above the IFHDS system, peak temperature of the solar-heated air in the IFHDS system cross-section, and required temperature of the IFHDS system floor surface. The results also indicated that energy efficiency increases as thermal storage mass thickness decreases. The thermal storage mass thickness should be the minimum necessary to meet the requirements for maximum permissible daily floor surface temperature fluctuation, or time lag between time of peak, solar-heated air temperature in the IFHDS system cross-section and time of peak floor surface temperature.

Effects of Pd and Mg nitrate on the atomization of Ge in graphite furnace atomic absorption spectrometry

The influence of Pd and Mg nitrate, as matrix modifiers, on the atomization of Ge in the graphite furnace has been studied. These matrix modifiers can raise the maximum permissible pre-treatment temperature, reduce the premature loss of GeO and increase the sensitivity of the Ge determination. According to the results of XPS analysis, Ge-Pd and Ge-Mg bonds may be formed. Intermetallic compounds and germanates were detected by XRD. It is believed, that in the presence of Pd and Mg, the mechanisms of Ge atomization are such that intermetallic compounds Ge 9Pd 23, GePd 2, etc., directly dissociate to Ge atoms, while gennanates, MgGeO 3, etc., decompose into GeO 2 and GeO, which are further reduced to Ge atoms.

Optimization of a tubular nylon 6 reactor with radial gradients

AbstractOptimal jacket‐fluid temperature profiles for tubular Nylon 6 reactors (in the presence of radial gradients of temperature and concentration) have been obtained using an algorithm based on the continuous minimum principle developed for a distributed parameter system. A gradient search technique has been devised and implemented for obtaining these optimal profiles. The optimal temperature profiles are found to be at the maximum permissible temperature, Tmax, at the beginning of the reactor and then slowly decrease to the minimum permissible temperature, Tmin, near the end of the reactor. The effect of varying several parameters is also studied. The desired value of the chain length and the reaction time are found to be the parameters which effect the optimal profiles most significantly.

THE DESIGN AND OPTIMIZATION OF AN INDUSTRIAL DRYER FOR SULTANA RAISINS

ABSTRACT A mathematical model of a tunnel dryer for sultana grapes is presented and applied for the determination of size and optimal operating conditions of the dryer. The optimum condition is given by the minimization of heat consumption, expressed as the ratio of thermal load to production, with some constraints regarding the production rate of the dryer and the maximum permissible air temperature. The optimization variables are temperature and humidity of the drying air, and product loading thickness on the trays. The optimum condition requires the operation of the dryer on the maximum permissible air humidity, which corresponds to a high degree of recirculation of exhaust air. This can be accomplished using automatic control of fresh air and humid air inlet and exhaust dampers along the length of the dryer, during the entire drying cycle.

Determination of thallium by furnace atomic absorption spectrometry

The analytical conditions for the determination of thallium by graphite furnace atomic absorption spectrometry were studied and optimized using the peak-height mode. The charring-atomization curves for thallium from different atomization surfaces were constructed and the optimum charring and atomization conditions were established. These atomization surfaces included pyrolytic graphite-, tantalum-, zirconium- and tungsten-coated graphite tubes. The effects of different inorganic acids on the absorbance of thallium from different surfaces were studied. Using tungsten carbide-coated tubes, the interference effects due to hydrochloric and perchloric acids were eliminated. The matrix modification technique was also investigated for increasing the maximum permissible charring temperature for thallium. The matrix modifiers used included tungsten, zirconium, nickel and tantalum. The effect of adding these modifiers were studied in the presence of different acids. Tungsten increased the maximum permissible charring temperature from 400 to 1000 °C.

The effects of Ni and Fe nitrate and nitric acid on the atomization of Ge in graphite furnace atomic absorption spectrometry

The influence on the atomization of Ge in the graphite furnace has been studied in the presence of Ni and Fe as nitrates, and HNO 3. It was proved that the thermally stable intermetallic compounds and germanates were formed, respectively, when Ni(NO 3) 2 and Fe(NO 3) 3 were added. It raised the maximum permissible ashing temperature, reduced the premature loss of GeO, as a result increasing the sensitivitiy of Ge determination. We believe that the mechanisms of Ge atomization are that intermetallic compounds GeNi 2, Ge 2Ni 5, Ni 5Ge 3, etc., directly dissociate to Ge atoms, while Fe 4Ge 14O 20 and Fe 2GeO 4 decompose into GeO 2 and GeO, which are reduced to Ge atoms.

Storing strong spent ionizing-radiation sources in metal matrices

The sources are stored by discharging them from the containers into special underground stores, with a volume of 200 dm 3 at a depth of 6 m. The loading channel is a curved tube, which protects the direct radiation. A store is designed to receive 1.184 • i0 Is Bq (50 kg-eq Ra) at a maximum permissible temperature of 503 K. Such stores have been in use at the Moscow Radon Production Cooperative for over 20 years. Observations on them have shown that storing sources in these underground spaces in piles does not provide satisfactory safety [2]. Free dropping means that the sources accumulate at the bottom, with many of the radioactive carriers concentrated in a small volume, which means that the radiation and thermal loads on the materials are elevated there. For example, the radiation dose rates in the stores attain 1.419 A/kg (5.5 • 103 R/sec) [2]. Water condensing on the cold walls of the loading pipe flows into the store and increases the corrosion. Radiolysis gives rise to hydrogen concentrations representing an explosion hazard. Also, the rising hot air flows can transport hot aerosol particles into the environment, which represent a considerable radiological hazard.

Determination of lithium in serum and whole blood by graphite furnace atomic absorption spectrometry

A method has been developed for the direct determination of lithium in serum and whole blood by graphite furnace atomic absorption spectrometry using tantalum carbide coated graphite tubes in combination with ammonium nitrate matrix modification. The maximum permissible charring temperature for lithium was raised from 1050 to 1500 °C and the lifetime of the tube was also prolonged for ca. 200 more firings using the tantalum carbide coated graphite tube compared with the conventional pyrolytic graphite coated graphite tube. Matrix interferences from chlorides present in human blood samples were eliminated using the proposed method, which has been used for the determination of lithium in serum and whole blood of normal healthy individuals.

Materials issues in fluidized bed combustion

The materials issues in fluidized bed combustion systems are in many cases essentially similar to those in conventional pulverized coal systems. Those that are related to the technology itself include the erosion and corrosion of in-bed components, particularly the heat exchanger; the erosion of above-bed components; the wear (perhaps accelerated by corrosion) of the solids handling systems, particularly the ash recirculation system; and, in the case of pressurized combustors, the erosion and hot corrosion of the expander turbine. For steam-generating systems, the issue of in-bed corrosion is probably not as serious as had once appeared, provided care is taken in materials selection, in design, and in operation. In-bed erosion now appears to be the most important problem to be solved. The expander turbine problems define the degree of particulate removal from the hot gas that has to be achieved, and limit the maximum permissible bed temperature. However, both the erosion and corrosion may be easier to deal with in the low-temperature expander in the “pressurized boiler” concept.

The principle of design for double injection Ge magneto-diode

A design principle is proposed for long P+IN+ Ge magneto-diode with a high surface recombination region on one side. The optimal relation is established for design among its lengthl, depthd, widthw and resistivity ρ: (ρ/w)(l/α)8⩽10.75(ΔT)2/(I03R1h/2), where ΔT is the maximum permissible temperature rise of the chip,Rth the thermal resistance of the header,I0 the forward current of the diode.

Low-Temperature Rupture Behavior of Zircaloy-Clad Pressurized Water Reactor Spent Fuel Rods Under Dry Storage Conditions

Creep rupture studies on five well-characterized Zircaloy-clad pressurized water reactor spent fuel rods, which were pressurized to a hoop stress of about145 MPa, were conducted for up to 2101 h at 323/sup 0/C. The conditions were chosen for limited annealing of in-reactor irradiation hardening. No cladding breaches occurred, although significant hydride agglomeration and reorientation took place in rods that cooled under stress. Observations are interpreted in terms of a conservatively modified Larson-Miller curve to provide a lower bound on permissible maximum dry-storage temperatures, assuming creep rupture as the life-limiting mechanism. If hydride reorientation can be ruled out during dry storage, 305/sup 0/C is a conservative lower bound, based on the creep-rupture mechanism, for the maximum storage temperature of rods with irradiation-hardened cladding to ensure a 100-yr cladding lifetime in an inert atmosphere. An oxidizing atmosphere reduced the lower bound on the maximum permissible storage temperature by about5/sup 0/C. While this lower bound is based on whole-rod data, other types of data on spent fuel behavior in dry storage might support a higher limit. This isothermal temperature limit does not take credit for the decreasing rod temperature during dry storage. High-temperature tests based on creep rupture as the limiting mechanism indicatemore » that storage at temperatures between 400 and 440/sup 0/C may be feasible for rods that are annealed.« less

The thermal rating of overhead-line conductors part II. A sensitivity analysis of the parameters in the steady-state thermal model

The thermal rating of an overhead-line conductor is the current required to produce a certain maximum permissible temperature under specified atmospheric and other conditions. The thermal rating is found by solving the heat equation, which contains a large number of parameters. The sensitivity of the thermal rating to a variation of each parameter over a practical range is examined, and the relative importance of each parameter is given.

Thermal processes in tokamaks of the next generation and future reactors

In future tokamaks heating power will increase considerably compared with present-day machines. This leads to increased heat loads to surfaces exposed to the plasma. In this paper the models used to calculate the limits for thermal flux imposed by maximum permissible surface temperature and maximum permissible stress are reviewed. Additional constraints for the design resulting from damage caused by disruptions and from erosion by the plasma are mentioned. Different methods of laboratory testing of small samples are surveyed. The designs of the limiters of the next generation of tokamaks are compared.

Determining the maximum permissible operating temperatures for ceramics in aggressive media

The permissible temperatures for such materials have been indicated in some references. For instance, in the case of porcelain and dunitic ceramics, from which chemical-plant equipment is made at present, the maximum permissible operating temperature in acidic media is indicated as 120~ [1]. However, no recommendations regarding the methods of its determination are found in the existing literature.

The thermal rating of overhead-line conductors Part I. The steady-state thermal model

The stead-state current rating of short transmission and distribution lines is often determined by the maximum permissible temperature of the conductors to avoid excessive sag or long-term annealing of the conductors. A thermal model to calculate the relationship between the current and the conductor temperature is proposed, and the parameters in the model are examined in detail.

Computations of Temperature Profiles in the Medium/Low-level Waste Cement and in the Rock Salt Surrounding the Disposal Cavern

Prior to disposal of cemented medium level waste and low level waste in large caverns 1000 m below ground it is important to know what temperatures will be caused by heat generation in the waste product. During the disposal period the heat produced by hydration of the cement used as the binder as well as by decaying radionuclides in the waste may give rise to inadmissibly high temperatures in the waste product resulting in a deterioration of the produc:t qualities. To avoid such undesirable processes, a maximum permissible product temperature of 90°C was specified for the investigations, i.e. a temperature that is significantly below the boiling point of the water contained in the cemented product.

Skin damage due to heat transfer by conduction

AbstractThis study provides basic data with respect to pain and burns produced on short‐term contact of bare skin with heated substances. The data may also be used to determine the thermal properties and thicknesses of fabrics or coatings required to prevent injury in such contacts. The maximum temperature any material might attain without causing injury on contact with bare skin was determined from measurements of pain threshold during contact with heated materials representing a wide spectrum of thermal properties form good conductors to good insulators. Pain threshold times were converted to blister times and the latter extrapolated to predict those temperatures at which blistering would result form ‘instantaneous’ (0.3 s) contact. The predicted temperatures were verified experimentally in contacts with four different materials. From these data, charts and equations were derived by which the maximum permissible temperature for safe contact could be determined for any material solely form a knowledge of its thermal conductivity, density and specific heat. Additionally, equations for transient heat flow in two‐layer systems yield the thickness of coatings, fabrics or other thermal barriers of known properties which would be required to protect the skin form pain or burn on contact with materials at excessive temperatures.

The Application of Automatic Control for Energy Saving in Heating Furnaces

The fuel consumption in heating furnaces can be reduced, in some cases substantially, by the optimization of process control. A system for the control of energy utilization must become the part of a conventional furnace equipment. Reasonable physical assumptions about the process of heating enables us to construct simple control algorithms. These algorithms make it practical the extensive use ot microprocessors tor optimal control of energy utilization in furnaces. The development of such algorithms is studied in this paper.The optimization of heating of a lumped batch is discussed. The technological requirements and maximum permissible temperature of the refractory lining furnish the process constraints. The problem is solved by the use of maximum principle. The optimal firing rate and variation of the furnace temperature are determined by the problem solution. The optimal control algorithms for the batch furnace are given. The thermodynamic minimum of the energy consumption for given conditions is obtained and employed as the criterion for the estimation of efficiency of a control system. Simplified algorithms are constructed for the control of furnaces when heat losses are comparatively high and comparatively small. The optimal control of heating of massive bodies is discussed.The conditions of the process linearization are considered. The minimization of fuel consumption is posed as the problem of linear programming. Dynamic programming provides the most general technique for the optimization of the heating process. The paper depicts the procedure of the use of dynamic programing for the minimization of fuel consumption in furnaces. The application of linear and dynamic programming for optimal control of continuous furnaces is discussed. The information necessary for the optimal control of fuel utilization is determined.

Ge/GaAs heterojunction IMPATT's

The fabrication and first successful operation of Ge/GaAs heterojunction IMPATT's are described. Theoretical analyses were employed to establish the optimum materials specifications for maximum microwave performance. The analyses revealed that the heterojunction IMPATT's should be inherently more producible than the conventional Read-type GaAs structures because their efficiencies should be less dependent on critical control of the avalanche region width. On the other hand, the maximum conversion efficiencies of both structures should be similar. Since the potential for detrimental effects due to solid-state diffusion of species across the Ge/GaAs interface increases strongly with temperature, development of special low-temperature fabrication processes was required for the heterojunction devices. The Ge epitaxial avalanche layers were deposited on the GaAs portions of the structures by vapor phase epitaxy at 325°C using an open-tube iodide-transport process. Ion implantation and partial low-temperature annealing at 275°C were employed to produce p-n junctions in the Ge layers. Heterojunction IMPATT's were produced that yielded powers of 410 mW at 6.3-percent efficiency and 320 mW at 4.4-percent efficiency at 10.7 and 15.2 GHz, respectively. The conversion efficiencies are limited, in part, by residual implantation damage that could not be removed at the maximum permissible annealing temperatures.

Mathematical Modelling -- A Basis for Bushing Loading Guides

A simple mathematical thermal model is proposed as a basis for a bushing loading guide. It is demonstrated to have adequate accuracy for both steady-state and transient bushing hot-spot temperature calculations. Model constants can be derived from a set of Overload Qualification tests and recommendations are made for the parameters of significance to these tests. Three possible thermal failure modes are examined to establish a basis for setting a maximum permissible hot-spot temperature during overloads. Limitations on environmental factors which influence the bushing hot-spot temperature are also discussed.