La sécurité incendie dans les bâtiments à structure métallique

When a fire occurs, the collapse of a steel framed building can be a greater hazard than the conflagration itself: eg a steel beam or girder which can support 24 kg per mm² of section at 20°C will only support half this weight if it is subjected to a temperature of 540°C. In this context, the author lays particular emphasis on the use of self-supporting structures and thermal barriers to prevent the steel framework reaching temperatures which will create distortion. An unprotected steel structure will attain a temperature of 936°C after an hour in a heavy fire. Various materials can be employed to reduce the temperature of the steel and from a listing given in the report, boxing the framework in plaster facings 15 mm thick will limit the temperature of the steel to 80°C in the presence of a heavy fire, it being assumed that the insulation is of non-inflammable material.Another important recommendation is that in the laying out of large volume cold rooms, it is absolutely necessary that the structures are independent of each other by using fire-break walls, such that a structural collapse in one room can be contained.Some interesting graphs have been prepared by the author, but in two of them (Fig. 1, the influence of the quantity of combustible material on the development of a fire and Fig. 2, the influence of the influence of the ventilation area on the development of a fire) the curve established by ISO conflicts totally with those produced by the author as regards progression.

Résumé

Les structures métalliques non protégées se comportent mal au feu: elles s'échauffent vite et se déforment, quelquefois de façon considérable.Bien que des techniques aient été mises au point pour pallier ces inconvénients (en particulier augmentation de la durée pendant laquelle la structure résiste au feu), il faut néanmoins déterminer si ces améliorations permettent de garantir la sécurité des personnes et des biens. En ce qui concerne les bâtiments industriels de stockage, il est évident que les dommages subis par les structures ne sont pas la cause des risques en cours d'incendie; en conséquence la sécurité donnée par ce type de structure peut être considéree comme satisfaisante.     

Sur la dispersion de l''anisotropie et de la stabilité dans le temps des couches électrolytiques de Ni-Fe-Mo avec anisotropie biaxiale

The angular and amplitude dispersions of the anisotropy in Ni-Fe-Mo films with biaxial anisotropy have been studied. The permalloy films had a thickness of 5000 Å and those of permalloy with 5% Mo a thickness of 5400 å. The films were deposited onto plane copper substrates. The angular and amplitude dispersions, measured by the resonance absorption method, decrease with an increase in the angle between the anisotropy axes, having values of 4° and 2.8 Oe, respectively, for the permalloy films with an angle of 5° between the axes, and 2° 30′ and 2 Oe for films with an angle of 22° between the axes. For the permalloy films with Mo the dispersions decrease from 7° 30′ and 3.2 Oe to 6° 30′ and 2.9 Oe for an increase of the angle between the anisotropy axes from 10° to 20°.

The time variation (over 1000 h) of the angle between the anisotropy axes is given. Decreases from 22° to 17° and from 10° to 7° respectively for permalloy and permalloy with 5% Mo are obtained.     

Energetic efficiency of cogeneration systems for combined heat, cold and power productionEfficacité énergétique des systèmes de cogénération utilisés pour produire simultanément de la chaleur, du froid et de la puissance électrique

This paper deals with the problem of energetic efficiency evaluation of cogeneration systems for combined heat, cold and power production. Cogeneration systems have a large potential for energy saving, especially when they simultaneously produce heat, cold and power as useful energy flows. Various cogeneration systems for combined heat, cold and power production are designed by means of computer simulation to minimize consumption of the primary energy. Equations of energetic efficiency of this combined cogeneration systems are presented, that relate the primary energy rate (PER) and comparative primary energy saving (Δq_p) to energy parameters of designed systems. Comparison of energetic efficiency of combined cogeneration systems with contemporary conventional separate production of heat, cold and power shows a large potential for energy saving by designed combined cogeneration systems.     

Prévention des incendies et sécurité dans les entrepôts frigorifiques

Between 1966 and 1977 there were fifty reported store fires in the Federal Republic of Germany and excluding two cases of arson, the main causes were due to faulty electrical equipment, the use of inflammable constructional material and inadequate caution during repair and maintenance work, viz. welding operations. In one reported case a fire was started by a store worker who was attempting to defrost the evaporator with a welding torch.Effective fire prevention therefore involves careful design in the construction of the store, the use of fireproof materials, failure-proof electrical gear, efficient and adequate fire-warning and fire-fighting equipment and the proper training of personnel in matters of fire prevention and dealing with an outbreak of fire.The paper deals successively with the choice of building materials and insulation, the size of cold rooms and their layout (fire-breaks have proved to be very efficient in limiting the propagation of a fire), the main causes of fires, fire protection during the construction period and while the store is in operation, fire-fighting equipment (this is a particularly important factor because alarm systems and fire extinguishing apparatus must be able to effectively function in the low temperature environment of a cold room which can be at -30°C) and, finally, fire escapes, safety exit passages and suitably located fire-points.     

Etude des facteurs d'intensification de l'échange de chaleur dans le refroidissement des fruits et légumes

Increasing the rate of fruit and vegetable cooling is of economic significance for the following reasons: biochemical and microbiological processes are quickly suppressed; surface mass-exchange with ambient air is slowed down; power consumption is reduced, and the freezing output of cooling equipment and installations is increased.It was assumed that the fruits and vegetables in crates were arranged regularly and covered with thin paper of a negligible small thermal resistance in order to eliminate the infiltration of cold air within the layers. Crates were arranged on a pallet so that they touched horizontally. Thus, the packages form plates above and below the cooling air flow. Heat-exchange with a one-dimensional temperature field is established.It was found that intensification of cooling can be achieved by increasing the speed of cooling air as well as by stopping the process at a higher final temperature. Increasing the speed up to 5 m s⁻¹ shortens the time of the process by a factor of two compared with the low speeds (0.3–0.5 m s⁻¹) which are normally used. The product can be cooled until the temperature in the layer centre reaches 5°C, and the surface temperature about 2°C, which is low enough. Afterwards the cooled product is transferred to a freezing chamber or to a van-freezer. This factor results in a further halving of the cooling time. The combined effect of the two factors shortens the duration of the process by about 75% and increases the output of the cooling equipment from 3.5 to 4 times.     

Equivalent Carnot cycles for sorption refrigeration: Cycles de Carnot équivalents pour la production de froid par sorption

Temperature–entropy diagrams are usually used to describe heat-driven engines as well as vapour compressor refrigerators, but they have not yet been used for sorption refrigeration. Such Carnot cycles are introduced here to describe three sorption refrigeration technologies (liquid absorption, solid adsorption, chemical reaction). This is performed for basic cycles (without heat recovery) and for simple advanced cycles. Equivalent four-temperature Carnot cycles are obtained for basic cycles, whereas equivalent six-temperature Carnot cycles are obtained for advanced cycles. This approach shows that the quantity ΔH-TΔS (where ΔH and ΔS are the enthalpy and entropy variations associated with mass transfer during a cycle in/out of the sorbers) plays the same role as the mechanical energy in vapour compression cycles.     

Le froid et la sénescence des organes végétaux après récolte: quelques aspects théoriques et pratiques

Harvested plant products, flowers and fruits particularly, are mostly senescent in nature. To obtain and maintain good quality and to reduce losses as much as possible, one must possess a clear knowledge of the fundamental mechanisms which govern plant senescence. Following this, more practical work has to be done to find the most suitable storage conditions. Low temperature remains the essential factor.     

Transport de fruits et légumes frais à température dirigée

Controlled temperature transport is necessary to preserve the qualities of fresh fruit and vegetables. Refrigeration should be applied as soon as possible after harvest and possibly, under certain conditions, in the vehicle during transport. This paper describes different types of vehicles and devices for producing refrigeration during transport. The particular case of ready to use vegetables (minimal processing) is discussed.     

Simulation des performances d'un réfrigérateur solaire à adsorption: 2. Fonctionnement avec stockage de froid dans deux climats différents

The models described in this article simulate the solid-adsorption cycles of a solar refrigerator. They are used for calculating the performances of the refrigerator as a function of the climatic conditions, and thus optimizing its operation and sizing. The results show that for the same season the performances of the refrigerator are different for the climates of Rabat and Marrakesh. The study of the cold storage shows that, although the annual mean cold production is similar for both sites, the distribution of cooling-shortage days is totally different. In contrast with Rabat, where the problem of cold storage is due to sequences of successive days with low incident solar energy, the problem in Marrakesh is due to high values of ambient temperature during quite a long period of the year, which reduce significantly the refrigerator performances.     

Effect of strip location on the air-side pressure drop and heat transfer in strip fin-and-tube heat exchangerEffet de la localisation des gaufrures d’ailettes sur la chute de pression de l''air et sur le transfert de chaleur dans un échangeur à tubes à ailettes

This work discusses about the pressure drop and heat transfer characteristics of a plain fin, a strip fin and combinations thereof in the fin-and-tube heat exchanger. Experimental apparatus and test algorithm using scale-up model fin geometry are discussed. The present work uses the electric heaters inside of the tube as the heating source to simulate the hot water loop in the wind tunnel test. The test results of the plain and strip fins are compared with the existing correlation and experimental data. It was found that a hybrid fin, plain fin at front row and strip fin at rear row, was more effective to enhance the heat transfer than that of the whole strip fin at the same fan power.

Résumé

Dans l’article, on traite des caractéristiques de la chute de pression et du transfert de chaleur d’une ailette lisse, d’une ailette gaufrée et de combinaisons de ces deux types d’ailettes dans un échangeur de chaleur à tubes ailetés. Le dispositif expérimental et l’algorithme utilisant une géométrie des ailettes échelonnées sont présentés. On utilise des équipements de chauffage électriques à l’intérieur du tube, comme source de chaleur, pour simuler la boucle d’eau chaude dans le tunnel expérimental. Les résultats expérimentaux concernant les ailettes lisses et les ailettes gaufrées sont comparés avec la corrélation existante et les données expérimentales. On a observé que des ailettes hybrides, c’est-à-dire lisses à la rangée frontale et gaufrées à la rangée arrière, étaient plus efficaces pour intensifier le transfert de chaleur que des ailettes entièrement gaufrées, à la même puissance du ventilateur.     

Influence de la réfrigération et de la congélation sur la qualité et l'aptitude à la germination des graines

The high dehydration level of seeds provides them with an exceptional survival period, nevertheless seeds are living organs which can die. Refrigeration can prevent the germination of seeds which are destined for human or animal consumption or, on the contrary, produce germination in a required time. The article first describes some of the biological particularities of seeds which can be considered as survival or reproductive organs. As a survival organ, refrigeration can be used to preserve seeds to: Prevent germination: the storage of seeds of tropical and sub-tropical origin at +5°C: the maintenance of a cold and dry atmosphere for the bulk storage of seeds in silos. Prevent parasitic attack: a low temperature and low relative humidity to protect against bacterial or fungal growth: it is more difficult to combat insect invation. Protect product viability: the drier the seed and the lower the temperature, the longer the seed life. Refrigeration can also be used to facilitate germination by eliminating dormancy. It is already well known that humid cold promotes germination by eliminating embryonic dormancy (in general, from one to a few months at a temperature of about +5°C). Furthermore, good germination of ‘hard seeds’ (with teguments impermeable to water) can be obtained by immersing them in liquid nitrogen and repeating the operation if necessary.

Résumé

Les graines sont des organes très particuliers en ce sens qu'elles prérentent le plus souvent un état de déshydration très poussé. Les problèmes de stockage qui en résultent sont de ce fait très différents de ceux que l'on recontre généralement avec les autres produits végétaux. Les basses températures empêchent leur germination pendant la conservation, limitent les altérations dues aux parasites et prolongent leur durée de vie. La réfrigération et la congélation des graines ont permis la mise au point d'applications originales. Quelques graines ne peuvent germer qu'après un séjour au froid en milieu humide. Des graines imperméables à l'eau deviennent capables de germer facilement aprés traitement à très basse température (azote liquide).     

Carbon dioxide as a working fluid in drying heat pumpsLe dioxyde de carbone comme fluide actif dans des séchoirs à pompe à chaleur

Carbon dioxide as a working fluid in refrigeration and heat pump systems is increasingly important in view of the CFC substitution problem. It is both under ecological and economical aspects an attractive alternative to the HFC working fluids at present in practical use. The thermophysical properties and characteristics of carbon dioxide are quite different from those of refrigerants used in conventional vapour compression cycles. Its application in conventional vapour compression refrigerating systems is limited by its critical parameters (t_c=31.1°C and p_c=73.8 bar). The possibility to use carbon dioxide also beyond these limits in high temperature processes, e.g. heat pumps, is given by the application of a trans-critical process. The design and construction of a commercial drying heat pump system (batch type cabinet dryer with 12 kW heating capacity and closed air circuit) using the natural working fluid carbon dioxide is shown and experimental results of investigations carried out are presented. Energy savings are given compared to manufacturer's data of energy consumption.     

Transfert de chaleur et de masse au cours du refroidissement des denrées périssables à bord des navires-durée minimale de refroidissement des cargaisons de fruits et légumes (dans les cales ou à l'intérieur des conteneurs)

Perishable goods (mainly fruit) are usually loaded aboard ships without precooling¹. The first phase of transport is therefore to cool the cargo down to the contractual carrying temperature as rapidly as possible. A priori, this implies that the ship's equipment can do this and in particular that the air distributing arrangement has been fitted for this purpose. The paper mainly deals with homogeneous cargoes having an even air permeability.In this Paper, the author adopts the conditions (extremely favourable) where the goods are directly exposed to the cooling fluid (with or without any protection against their drying out). These are conditions resulting in the minimum cooling time. The same calculation is applicable to any homogeneous cargo provided that the air distribution is properly balanced including that inside the packages (cases, boxes, etc). It may be locally applicable as well with the same conditions taking into account an unbalanced cooling air distribution system.The problems of cooling goods in large packages which the cooling air moves around is not dealt with: it leads moreover to prohibitive cooling durations and this case is to be avoided. This case is roughly approximated by a similar problem: the cooling of bodies with comparable sizes and shapes (plates, cylinders, spheres) with equivalent apparent conductivity which are suddenly put in a cold air flow maintained at an even and steady temperature. With such optimistic assumptions (where the heating is assumed to be negligible), the core and surface temperatures can be determined from the set of curves by Jacob⁹.The minimum cooling duration contemplated is the time needed to achieve a temperature in the whole cargo not too far from the carrying temperature. That temperature may exceed the latter by 2 or 3°C. In order to obtain it, all the basic cargo features are taken into account: breathing and, if necessary, desiccation as well as the rate of air circulation in horizontal and vertical ventilation.The functioning capabilities of the ship's equipment are also considered, on the one hand when starting and during the cooling down, if the available refrigerating capacity does not allow a step function as an initial condition, and, on the other hand, when the cooling air distributing system brings about a well known unbalance in the overall air flow distribution.     

Etude quantitative de la structure à l'état congelé de muscle et de steak haché

The structure of frozen meat is studied after freeze-drying, with the technique of image analysis. The variable parameters are the freezing rate, the type of meat and the effect of grinding and mixing or not with pork fat.After freezing, the samples were cut (10 μ thick), freeze-dried, fixed and stained with Regaud's haematoxylin.Using a Quantimet 720 we measured the total volume occupied by ice crystals, the distribution in size of ice crystals and the specific area of freeze-dried samples. These results were compared with those obtained by two physical methods, mercury intrusion porosimetry and the volumetric method of krypton adsorption.The comparison of stereological and physical methods suggests a spindle-shaped model for the ice-crystals in frozen whole meat.Concerning the technological parameters, the results show that grinding involves an increase of the size of ice crystals and that mixing pork fat with ground meat induces a decrease in the size of ice crystals in the pieces of meat.

Résumé

On étudie la structure de la viande congelée, aprés lyophilisation, par analyse des images. Les variables sont la vitesse de congélation, le type de viande et l'influence du hachage et de l'addition ou non de tissue adipeux de porc.Aprés congélation, les échantillons ont été coupés (10 μm d'épaisseur), lyophilisés, fixés, puis colorés à l'hématoxyline de Regaud.En utilisant un Quantimet 720 nous avons mesuré le volume total occupé par les cristaux de glace, la répartition de leurs dimensions et la surface spécifique des échantillons lyophilisés. On a comparé ces résultats à ceux obtenus par deux méthodes physiques, la porosimétrie au mercure et la méthode volumétrique d'adsorption de krypton.La comparaison des méthodes stéorologiques et physiques améne à penser que les cristaux de glace du muscle de viande congelé entier ont une forme en fuseau.Quant aux paramétres technologiques, les résultats montrent que le hachage implique une augmentation de la taille des cristaux de glace et que le mélange de tissu adipeux de porc avec la viande hachée provoque une diminution de la taille des cristaux de glance dans les morceaux de viande.