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Papers by Alfredo Calvelo

Research paper thumbnail of Internal mass transfer coefficient within single bubbles. Theory and experiment

The Canadian Journal of Chemical Engineering, 1979

Research paper thumbnail of A simplified mathematical model for freezing time calculation in plate freezers

Research paper thumbnail of Kinetic Expressions for Reaction Rate in Noncatalytic Solid-Gas Systems

Industrial & Engineering Chemistry Fundamentals, 1970

Research paper thumbnail of Relationship between heat transfer parameters and the characteristic damage variables for the freezing of beef

Meat Science, 1980

One of the most suitable parameters for relating the freezing rate to the volume of drip produced... more One of the most suitable parameters for relating the freezing rate to the volume of drip produced during the thawing of meat is the characteristic time, defined as the time necessary to reduce the temperature of the sample from -1·1°C (initial freezing point in beef) to -7°C (80% of the water frozen). However, as the freezing of beef in factories takes place with important temperature gradients, distributions of these characteristic times must be expected along the pieces of frozen meat. In order to relate these characteristic time distributions to heat transfer parameters under industrial freezing conditions, a mathematical model which simulates the freezing of beef is developed in this paper. The model establishes the heat transfer equations with simultaneous change of phase, taking into account the dependence of the thermal properties with the ice content and considering the anisotropy of the thermal conductivity according to the direction of the fibres. Boundary conditions include the possibility of thermal resistances in the refrigerated interphase. The model developed was compared with laboratory experiments performed under factory freezing conditions and showed a satisfactory agreement between theory and experiment.

Research paper thumbnail of Rate of freezing effect on the colour of frozen beef liver

Meat Science, 1982

One problem that arises when freezing liver b~ plate freezers is the whitish colour acquired by t... more One problem that arises when freezing liver b~ plate freezers is the whitish colour acquired by the liver surface when subjected to high freezing rates.

Research paper thumbnail of Dendritic growth of ice crystals during the freezing of beef

Meat Science, 1979

The morphology adopted by ice in frozen tissues is accepted as one of the factors responsible for... more The morphology adopted by ice in frozen tissues is accepted as one of the factors responsible for freezing damage. For this reason ice nucleation and growing mechanisms have been extensively studied.

Research paper thumbnail of Freezing rate effects on the drip loss of frozen beef

Meat Science, 1980

One of the quality parameters of frozen meat is the amount of exudate which arises during thawing... more One of the quality parameters of frozen meat is the amount of exudate which arises during thawing. The amount of drip obtained by centrifugation under standard conditions, and the protein composition of the exudate, has been correlated for different thermal histories.

Research paper thumbnail of Weight loss prediction during meat chilling

Meat Science, 1980

A lumped parameter model for computing weight losses during meat chilling is proposed.

Research paper thumbnail of Heat and Mass Transfer During the Warm Water Blanching of Potatoes

Journal of Food Science, 1983

A model of heat and mass transfer with simultaneous chemical reaction is proposed for analyzing t... more A model of heat and mass transfer with simultaneous chemical reaction is proposed for analyzing the influence of operating variables on the reducing sugar content at the surface of blanched potatoes. This content is partially responsible for the color of the fished product. The involved parameters (potato thermal conductivity, heat transfer coefficient of the system and kinetic constants for overall reaction of reducing sugar generation) were evaluated in separate experiments. The apparent diffusion coefficient of reducing sugars in potatoes was the only parameter obtained from blanching experiments. Temperature and concentration profiles and effect of blanching temperature on surface reducing sugar content are analyzed using the developed model. The possible underestimation of the diffusion coefficient when simultaneous starch hydrolysis is not taken into account is also considered.

Research paper thumbnail of Thermal Conductivity of Potato between 50 and 100°C

Journal of Food Science, 1991

Thermal conductivity (TC) of potato was calculated from heat penetration into cylindrical samples... more Thermal conductivity (TC) of potato was calculated from heat penetration into cylindrical samples between 50 and 100°C. TC ranged from 0.545 to 0.957 W/m"C for potatoes (cv Kennebec) specific gravity 1070 kg/m3 and moisture 80%. Experimental values agreed with reported values. TC, k, vari.ed with temperature in a quadratic polynomial form, and an empirical relationship was estimated. A model based on the concept of thermal resistances in parallel was compared with experimental results. These were used in a heat transfer model that simulated potato frying. Measured and simulated time-temperature curves showed good agreement.

Research paper thumbnail of Adjustment of Surface Concentration of Reducing Sugars Before Frying of Potato Strips

Journal of Food Processing and Preservation, 1988

A model of heat and mass transfer with simultaneous chemical reaction is proposed for simulating ... more A model of heat and mass transfer with simultaneous chemical reaction is proposed for simulating changes in profiles and surface concentration of reducing sugars during warm water blanching and the subsequent holding ofpotato strips in a hot-dry air stream before frying. 7his content is partially responsible for the color of the finished product. The proposed model allows the prediction of the best leaching conditions (temperature and time) in terms of the initial sugar content of the tubers, the maximum holding time before frying, and the desired maximum surface concentration of sugars.

Research paper thumbnail of Gas Particle Heat Transfer Coefficient in Fluidized Pea Beds

Journal of Food Process Engineering, 1980

Research paper thumbnail of Longitudinal dispersion coefficients for the continuous fluidization of different shaped foods

Journal of Food Engineering, 1994

Research paper thumbnail of Histological measurements of ice in frozen beef

International Journal of Food Science & Technology, 2007

A histological study of pieces of meat frozen under controlled conditions which simulate the oper... more A histological study of pieces of meat frozen under controlled conditions which simulate the operation of industrial freezers, showed differences in the ice morphology according to the registered thermal histories.

Research paper thumbnail of Internal mass transfer coefficient within single bubbles. Theory and experiment

The Canadian Journal of Chemical Engineering, 1979

Research paper thumbnail of Internal mass transfer coefficient within single bubbles. Theory and experiment

The Canadian Journal of Chemical Engineering, 1979

Research paper thumbnail of A simplified mathematical model for freezing time calculation in plate freezers

Research paper thumbnail of Kinetic Expressions for Reaction Rate in Noncatalytic Solid-Gas Systems

Industrial & Engineering Chemistry Fundamentals, 1970

Research paper thumbnail of Relationship between heat transfer parameters and the characteristic damage variables for the freezing of beef

Meat Science, 1980

One of the most suitable parameters for relating the freezing rate to the volume of drip produced... more One of the most suitable parameters for relating the freezing rate to the volume of drip produced during the thawing of meat is the characteristic time, defined as the time necessary to reduce the temperature of the sample from -1·1°C (initial freezing point in beef) to -7°C (80% of the water frozen). However, as the freezing of beef in factories takes place with important temperature gradients, distributions of these characteristic times must be expected along the pieces of frozen meat. In order to relate these characteristic time distributions to heat transfer parameters under industrial freezing conditions, a mathematical model which simulates the freezing of beef is developed in this paper. The model establishes the heat transfer equations with simultaneous change of phase, taking into account the dependence of the thermal properties with the ice content and considering the anisotropy of the thermal conductivity according to the direction of the fibres. Boundary conditions include the possibility of thermal resistances in the refrigerated interphase. The model developed was compared with laboratory experiments performed under factory freezing conditions and showed a satisfactory agreement between theory and experiment.

Research paper thumbnail of Rate of freezing effect on the colour of frozen beef liver

Meat Science, 1982

One problem that arises when freezing liver b~ plate freezers is the whitish colour acquired by t... more One problem that arises when freezing liver b~ plate freezers is the whitish colour acquired by the liver surface when subjected to high freezing rates.

Research paper thumbnail of Dendritic growth of ice crystals during the freezing of beef

Meat Science, 1979

The morphology adopted by ice in frozen tissues is accepted as one of the factors responsible for... more The morphology adopted by ice in frozen tissues is accepted as one of the factors responsible for freezing damage. For this reason ice nucleation and growing mechanisms have been extensively studied.

Research paper thumbnail of Freezing rate effects on the drip loss of frozen beef

Meat Science, 1980

One of the quality parameters of frozen meat is the amount of exudate which arises during thawing... more One of the quality parameters of frozen meat is the amount of exudate which arises during thawing. The amount of drip obtained by centrifugation under standard conditions, and the protein composition of the exudate, has been correlated for different thermal histories.

Research paper thumbnail of Weight loss prediction during meat chilling

Meat Science, 1980

A lumped parameter model for computing weight losses during meat chilling is proposed.

Research paper thumbnail of Heat and Mass Transfer During the Warm Water Blanching of Potatoes

Journal of Food Science, 1983

A model of heat and mass transfer with simultaneous chemical reaction is proposed for analyzing t... more A model of heat and mass transfer with simultaneous chemical reaction is proposed for analyzing the influence of operating variables on the reducing sugar content at the surface of blanched potatoes. This content is partially responsible for the color of the fished product. The involved parameters (potato thermal conductivity, heat transfer coefficient of the system and kinetic constants for overall reaction of reducing sugar generation) were evaluated in separate experiments. The apparent diffusion coefficient of reducing sugars in potatoes was the only parameter obtained from blanching experiments. Temperature and concentration profiles and effect of blanching temperature on surface reducing sugar content are analyzed using the developed model. The possible underestimation of the diffusion coefficient when simultaneous starch hydrolysis is not taken into account is also considered.

Research paper thumbnail of Thermal Conductivity of Potato between 50 and 100°C

Journal of Food Science, 1991

Thermal conductivity (TC) of potato was calculated from heat penetration into cylindrical samples... more Thermal conductivity (TC) of potato was calculated from heat penetration into cylindrical samples between 50 and 100°C. TC ranged from 0.545 to 0.957 W/m"C for potatoes (cv Kennebec) specific gravity 1070 kg/m3 and moisture 80%. Experimental values agreed with reported values. TC, k, vari.ed with temperature in a quadratic polynomial form, and an empirical relationship was estimated. A model based on the concept of thermal resistances in parallel was compared with experimental results. These were used in a heat transfer model that simulated potato frying. Measured and simulated time-temperature curves showed good agreement.

Research paper thumbnail of Adjustment of Surface Concentration of Reducing Sugars Before Frying of Potato Strips

Journal of Food Processing and Preservation, 1988

A model of heat and mass transfer with simultaneous chemical reaction is proposed for simulating ... more A model of heat and mass transfer with simultaneous chemical reaction is proposed for simulating changes in profiles and surface concentration of reducing sugars during warm water blanching and the subsequent holding ofpotato strips in a hot-dry air stream before frying. 7his content is partially responsible for the color of the finished product. The proposed model allows the prediction of the best leaching conditions (temperature and time) in terms of the initial sugar content of the tubers, the maximum holding time before frying, and the desired maximum surface concentration of sugars.

Research paper thumbnail of Gas Particle Heat Transfer Coefficient in Fluidized Pea Beds

Journal of Food Process Engineering, 1980

Research paper thumbnail of Longitudinal dispersion coefficients for the continuous fluidization of different shaped foods

Journal of Food Engineering, 1994

Research paper thumbnail of Histological measurements of ice in frozen beef

International Journal of Food Science & Technology, 2007

A histological study of pieces of meat frozen under controlled conditions which simulate the oper... more A histological study of pieces of meat frozen under controlled conditions which simulate the operation of industrial freezers, showed differences in the ice morphology according to the registered thermal histories.

Research paper thumbnail of Internal mass transfer coefficient within single bubbles. Theory and experiment

The Canadian Journal of Chemical Engineering, 1979