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An experimental study of the conjugate heat and mass transfer during the vacuum contact drying of softwood is described.The experimental results show that the drying rate is increased by means of a convective movement induced by a total pressure gradient in the gaseous phase at high free moisture content.An analysis of temperature and moisture distributions distinguishes three stages during drying (excluding the thermal transient regime): 1st stage: the wood temperature does not change in time but the drying rate decreases continuously. 2nd stage: the wood temperature increases quickly. 3rd stage: the moisture equilibrium is reached asymptotically.The previous results suggest a moisture migration mechanism for softwood drying.  相似文献   

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We develop a method for the solution of the heat equation in slowly variable situations. The validity of the solution depends on the convergence condition of an infinite series. The harmonic response of a wall has been chosen to illustrate the method for which two interpretations are proposed.  相似文献   

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The most commonly used measuring method for thermal effusivity or thermal inertia—is the Touchau method. A generalization of the theory on which this method is based is proposed which takes into account the heat losses between the sensor and the ambient medium. The modified Touchau method described in a previous paper and using local coincidence, may be applied with greater accuracy. The use of rugged miniaturized probes is made possible by the new method.In the biomedical field, this novel method shows that the measurement of live skin effusivity can be performed without disturbing the local subcutaneous blood circulation.  相似文献   

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We present here some elements in order to improve the non-destructive procedures for the measurement of the local heat transfer coefficient between a plate uniformly heated and an air-flow. We use the pulsed photothermal method which consists of analysing the transient temperature on the front face of a wall, initially subjected to a convective flow, after a sudden deposit of luminous energy. For the examination of the experimental thermograms, two models are used: in the first one the heat coefficient is assumed to remain constant during the pulsed experiment, and we take into account its variation in time in the second one. The temporal variation law of the heat transfer coefficient used in the second model is obtained by extension of the differential method to the unsteady laminar boundary-layer due to a finite duration excitation. We compare the results of the two models in transient state with those given in steady state by multi-layered heat flux sensor.  相似文献   

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It is possible to obtain, in the form of electric power, the energy of mixing of two solutions of different salinity by reverse electrodialysis.The laboratory electrodialyzer used was fitted in turn with two different pairs of permselective membranes, AMV-CMV and ARP-CRP. Solutions of ZnSO4 (216/18.8, 201/34.6, 110/40.2 and 127/14.2 g/l) and of NACl (245/13 and 250/1 g/l) were used in batch recirculation. Only NACl solutions (294/1, 295/1 and 150/1 g/l) were used in continuous flow operation. Results show the influence of type of membrane, composition and concentration of solutions and type of electrode. The maximum power obtained is 400 mW/m2.  相似文献   

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