Determination of the heat transfer coefficient between bulk medium and packed containers in a batch retort

The external heat transfer coefficient in steam retort processing was determined experimentally in a pilot scale retort. The heat transfer equations were solved applying finite elements and using the actual retort temperature profile as boundary condition. The instantaneous values of the heat transfer coe cient were determined, to analyse its time-variability along a retort cycle. It was found that reliable results for the external heat transfer coefficient at time t could be obtained from the derivatives of the average heat transfer coefficient calculated between time zero and time t. The results showed a sharp increase of the heat transfer coe cient in the earlier times of heating (up to 4±5 min of processing), followed by a slightly increasing pattern during the remaining heating period. Using average heat transfer coe cients for the heating phase (and for the cooling phase) also resulted in quite accurate estimates of the temperature at the geometric centre of a can. The influence of the two average heat transfer coe cients, heating and cooling, on the lethality was studied by building a response surface. It was concluded that the variability of the coe cient during heating has a greater impact, especially in the range 150±260 W/m2 K

HMM modeling of additive noise in the western languages context

This paper is concerned to the noisy speech HMM modelling when the noise is additive, speech independent and the spectral analysis is based on sub-bands. The internal distributions of the noisy speech HMM’s were derived when Gaussian mixture density distributions for clean speech HMM modelling are used, and the noise is normally distributed and additive in the time domain. In these circumstances it is showed that the HMM noisy speech distributions are not Gaussians, however, fitting these distributions as a Gaussian mixture, only a little bit of loss in performance was obtained at very low signal to noise ratios, when compared with the case where the real distributions were computed using Monte Carlo methods

Spectral bi-normalisation for speech recognition in additive noise

The changing on peaks structure of the speech spectrum is perhaps the most important cause of degradation of speech recognition systems under adverse conditions. Another drawback concerned to the additive noise effect occurs on the flat spectral zones which are usually raised proportionally to the noise level. These combined effects on both the peaked and the flat spectral zones can be alleviated by trying to restore its original structure, which assumes noise knowledge. However, the random nature and the variability of the noise, the difficulty in discriminating speech pauses, among others, discourage the use of noise estimates as the basis of robust speech recognition algorithms. Alternative approaches based on normalisation procedures become very promising since the noise effect can be alleviated without any knowledge regarding to its existence. This paper suggests a spectral normalisation that though being different can be viewed as a noise estimation procedure in a frame by frame basis, so assuming the clean database as lightly corrupted. This speech normalisation is used to restore the normalised speech spectrum. This normalised spectrum is then re-normalised by a baseline spectrum normalisation method, which concentrates essentially in the speech regions of small energy, since in these regions the noise is more dominant, so they require a better degree of robustness

Measurement of glass transition in native wheat flour by dynamic mechanical thermal analysis (DMTA)

This work describes a method to study glass transition on native starch powders, based on dynamical mechanical thermal analysis using compression tests, and was applied to wheat flour (13.5% water content). This method will allow the determination of Tg in native (unprocessed) starchy materials, with minimal disturbance of the natural structures. The influence of the test conditions (heating rate, frequency and strain) on the glass transition measurements was determined using factorial designs. The values of Tg determined as the maxima of the energy dissipation (peaks in E ) of native flour and of freezedried pre-gelatinized flour were not statistically different (around 64 C). The heating rate did not affect the measurements in the range tested (0.25 to 1 C min 1). An interactive effect of the strain amplitude and the frequency was detected. The significance of this interaction can be caused by differences in mechanical energy dissipation, which would indicate that not only temperature but also the total energy input may affect this transition. Slight effects of phase separation between gluten and starch were found on native flour

Optimal experimental design for estimating the kinetic parameters of processes described by the Weibull probability distribution function

The optimum experimental design for determining the kinetic parameters of the model resulting from the Weibull probability density junction was studied, by defining the sampling conditions that lead to a minimum confidence region of the estimates, for a number of observations equal to the number of parameters. It was found that for one single isothermal experiment the optimum sampling times corresponded always to fractional concentrations that are irrational numbers (approximately 0.70 and 0.19) whose product is exactly l/e’. The experimental determination of the equilibtium conversion (for growth kinetics) is vety important, but in some situations this is not possible, e.g. due to product degradation over the length of time required. Sampling times leading to a maximum precision were determined as a function of the maximum conversion (or yield) attainable. For studies of kinetic parameters over a range of temperatures, performed with a minimum of three isothermal experiments, it was proved that the optimum design consists of two experiments at one limit temperature with two sampling times (those corresponding to fractional concentrations of approximate[v 0.70 and 0.19) and another at the other limit temperature for a sampling time such that the fractional concentration is lie. Case studies are included for clarijication of the concepts and procedures

The technology, chemistry, and microbiology of Serra Cheese: a review

This paper comprehensively reviews fundamental and applied aspects of the manufacture of Serra cheese, its composition, the biochemical reactions that take place during coagulation and ripening, and the microbial ecology. Serra cheese is the most traditional cheese manufactured in Portugal. Aspects that make it unique are 1) its manufacture by the coagulation of raw ewe milk using a vegetable rennet (cardoon flower) and 2) its final buttery texture and flavor. The wide variation of the final quality of this “Appelation d’Origine Controllée” cheese has been explained by the intrinsic variabilities of raw materials, cheese-making practices, and maturation. The available studies pertaining to Serra cheese have indicated that 1) the coagulant activity of cardoon flower extract on ewe milk is higher and is more affected by pH and salt concentration than that of animal rennet, 2) the best coagulation temperature is 27 to 29°C, 3) the best ripening conditions are 8°C and 90% relative humidity, 4) the lactic acid fermentation results mainly from the action of lactic acid-type Streptococcus, Leuconostoc, and Lactobacillus species, 5) a yellow to reddish surface viscous material (mainly composed of yeasts) is important in the ripening process, 6) maturation is essentially surface-driven, and 7) the low temperatures prevailing during winter help to control the extensive microbial contamination that occurs from the poor sanitary conditions during cheese manufacture. These points are described and critically discussed in light of the principles of dairy science

Computational model to predict the temperature distribution produced by bone cement

Bone is the third frequent location for haematogenous dissemination of malignant tumors. Patients with multiple bone metastases are exponentially growing. Bone metastases, which are frequently diagnosed late, are associated to imminent and pathological bone fractures. Metastatic disease translates an advanced tumor stage and it has a high impact in patients’ quality of life and survival. The main objective is to study the thermal effect induced by the bone cement polymerization, in the bone metastatic tumor reduction and to understand the role of such procedure and its biomechanical stabilization. To assess the clinical effect, it is important to test this methodology before its application and obtain sustained results. In this work, a computational model was developed to predict the temperature distribution produced by cement polymerization, and verify the reduction of the metastatic tumor area due the thermal effect. Different simulations produced to evaluate the necrosis effect for two cement amount sizes introduced in a cortical and spongy bone tumor. The same computational models were reproduced introducing an endomedular nail in titanium and a femoral stem in cobalt-chrome material in pathological bone fractures.info:eu-repo/semantics/publishedVersio

Dimensionless analysis of the flow of spherical particles in two-phase flow in straight tubes

In the aseptic processing of particulate fluid foods, the residence time distribution of particles and the fluid-to-particle heat transfer are intimately related to the linear and rotational velocities of the particles. The development of models correlating these velocities with fluid and particle characteristics and with operating conditions is therefore very useful, as it provides a fast method to estimate fluid-to-particle heat transfer coefficients without measuring the actual particle velocities. The models can further be used to estimate the average residence time of the particles. Data for modelling particle linear and rotational velocities were obtained by videotaping the flow, along the wall, of individual spherical particles in transparent 2-m long straight tubes. Linear and rotational velocities were correlated with generalized Reynolds, Archimedes and Froude numbers, to the particle-to-fluid density simplex and to the particle/tube diameter ratio. The models obtained had correlation coefficients of 0.89 and 0.86 for the particle linear and rotational velocities, respectively