Maximum Product Temperature Research Articles

Experimental investigation of airflow and heat transfer by natural convection in an insulated box with a Phase Change Material using a Particle Image Velocimetry technique

Airflow and heat transfer via natural convection in an insulated box with Phase Change Material (PCM) were experimentally investigated using Particle Image Velocimetry (PIV) and temperature measurements. The effects of PCM positions (side wall and lid) on flow pattern and temperature distribution were studied under empty and loaded conditions. Two loads were considered to study the obstacle effect and the influence of heat exchange with air. When PCM was either at the side wall or at the lid of the box, laminar flow was observed and the corresponding Rayleigh number was about 10 7 . Upward flow was always observed near the side walls of the box. When PCM was on the side, downward flow occurred along the PCM; in the empty case, flow was almost 2D but became 3D when the load was added. When PCM was on the lid, the air cooled in contact with PCM, detached from it and flowed downwards. In the empty case, downward flow was unstable, and with the load, it followed preferential pathways. The type of load exerted little effect on flow patterns at thermal steady state. Thus, a simpler load (extruded polystyrene) can be used in the first approach. The maximum velocity was about 0.1 m s −1 , so free convection cannot be neglected compared with conduction. Regarding temperature performance, PCM on the side and on the lid showed no substantial difference if gaps were left between the load and the walls or PCM. • Airflow and heat transfer due to natural convection in an insulated box with PCM were studied. • Effect of PCM positions on flow and temperature fields was investigated. • The highest observed air velocities in the box were around 0.1 m s −1 . • PCM position exerted no significant effect on maximum product temperature. • Gaps should be left between the product and the box walls or PCM.

Modeling of product temperature in a supercritical fluid extrusion process through dimensional analysis

AbstractA correlation model for predicting the maximum product temperature reached during a supercritical fluid extrusion (SCFX) process was developed using the Buckingham Pi method. Two dimensionless groups, Dref (ratio of screw diameter to screw length) and Eref (ratio of energy added to energy removed), were developed to model the maximum temperature of an SCFX process using dimensional analysis. The model was validated by comparing predicted and experimental values. Experiments were conducted using two feed formulations: 1. Milk protein concentrate (MPC) with rice flour (30%), and 2. MPC with grape pomace (15%). The average percent error was 2.57% for rice flour extrudate and 1.02% for grape pomace extrudate. Based on the results, the model could be used for prediction of maximum temperature in SCFX systems.Practical ApplicationsMaintaining the extruder temperature below 100°C remains a major challenge during the supercritical fluid extrusion (SCFX) process. The model developed determines the maximum temperature of a given SCFX system based on key extrusion parameters. Hence, the developed model can be used by manufacturers for determining the optimal operating conditions while scaling up an SCFX process.

Monitoring of the freezing stage in a freeze-drying process using IR thermography

This paper presents a new Process Analytical Technology based on the use of an infrared camera and a mathematical model to estimate the ice crystal size distribution obtained at the end of the freezing stage of a vial freeze-drying process. Both empirical laws and first-principle based equations, already presented in the Literature, may be used to this purpose, if the temperature gradient in the frozen product and the freezing front rate are obtained from the analysis of the thermal images. The resistance of the dried product to vapor flux may be then calculated from the distribution of the ice crystal diameters, thus enabling the use of a one-dimensional model for process simulation and optimization. Freeze-drying of 5% and 10% w/w aqueous sucrose solutions, and of 5% w/w aqueous mannitol solutions, were considered as case study. The results were validated comparing the calculated diameters of the pores of the dried cake, corresponding to the ice crystal diameters, with the results experimentally obtained from the analysis of the SEM images, and comparing the values of drying duration and maximum product temperature calculated with the mathematical model with those measured experimentally. Results evidences the effectiveness of the proposed system for process monitoring.

Temperature-controlled microwave-vacuum drying of lactic acid bacteria: Impact of drying conditions on process and product characteristics

An efficient drying process for high-value products such as bacterial cultures is characterized by high retention of viability or activity, but low energy demand. Microwave-vacuum drying was tested in this work as a new technique for the preservation of probiotics and starter cultures, which has the potential to fulfill all of these requirements. The impact of chamber pressure (7, 15, 30 mbar), microwave power (1–5 W g−1) and maximum product temperature (30–50 °C) on drying time, drying rate, efficiency of microwave input and survival rate of the model strain Lactobacillus paracasei ssp. paracasei F19 (L. paracasei F19) was studied. Microwave drying time ranged from 50 to 240 min with microwave power as main influencing factor on drying behavior and efficiency. The maximum product temperature and vacuum pressure did not affect the drying time, absorbed energy and thus microwave efficiency significantly, but both parameters had a great impact on survival rate. The combination of 3 W g−1 microwave power input and 35 °C maximum temperature at a low chamber pressure of 7 mbar resulted in a very short drying time of 64 min, a high level of energy efficiency (27%) and also the best product quality in terms of survival rate (33%). Thus, a microwave-vacuum drying process is a potential alternative to conventional freeze or vacuum drying.

System parameters in a high moisture extrusion process for microparticulation of whey proteins

Whey proteins can be texturized by thermo-mechanical treatment during high moisture extrusion. Thereby, protein aggregates with specific functional properties can be obtained. In this study, a heated co-rotating twin screw extruder was used to particulate whey protein concentrate. For data evaluation, process, product and system parameters affecting the extrusion process were distinguished. To characterize the process by system parameters is an important step towards an improved process understanding. The maximum product temperature (TP,max) correlated linearly with the extruder barrel temperature and the mass flow. The specific mechanical energy input (SME) was found to be mainly affected by screw speed and mass flow. Independent of the respective adjusted process parameters, aggregate size was only affected by the resulting SME value. Equally, the degree of denaturation was only affected by the TP,max. Thus, manipulation of system parameters (SME and TP,max) can be applied for an indirect control of micro-particle properties.

Microwave-Vacuum Drying of Lactic Acid Bacteria: Influence of Process Parameters on Survival and Acidification Activity

Freeze drying is one important step in downstream processing of probiotics and starter cultures production and requires a long duration of the drying step, which, therefore, often is the overall production bottleneck. Microwave accelerated vacuum drying already showed promising results in terms of product quality for various food products. However, poor information on drying microorganisms by microwaves is available. The aim of this work was to set up a suitable microwave-vacuum drying process for the conservation of lactic acid bacteria and to investigate the optimum process parameters to achieve dried cultures with high survival and activity. The probiotic Lactobacillus paracasei ssp. paracasei F19 was used as model strain. The influence of the process parameters chamber pressure (7–30 mbar), specific microwave power input (1–5 W/g), and maximum product temperature (30–45 °C) on the main quality parameters survival rate, metabolic activity, and water activity of the dried samples were analyzed. Continuous energy input was shown to act detrimentally to the cells due to extreme temperature rise in the second drying stage. Proper temperature regulation could be obtained by pulsed microwave input according to a maximum set temperature. Intermediate microwave power between 3 and 4 W/g, the lowest tested pressure level of 7 mbar and low product temperatures of 30–35 °C, resulted in the highest survival and activity of the bacterial cells. With these results, it could be shown that microwave-vacuum drying appears as a promising alternative drying technique for the preservation of starter and probiotic cultures.

High moisture extrusion for microparticulation of whey proteins –Influence of process parameters

Defined functional properties of whey proteins can be achieved by controlling thermal unfolding and subsequent aggregation. To achieve a controlled formation of micro-particles, thermo-mechanical treatment by high moisture twin screw extrusion was used. The aim was to control the degree of denaturation as well as the particle size by variation of the process parameters. The temperature of the extruder has a strong impact on the maximum product temperature and increasing the extruder temperature increases the degree of denaturation. An increasing mass flow in contrast decreases the specific heat transfer to the product and leads to a decrease in denaturation. Increasing the screw speed has almost no effect on the degree of denaturation, but results in an exponential decrease in particle size due to increasing mechanical shear stress. Thus, the degree of irreversible protein denaturation as well as the particle size distribution can be controlled by these process parameters and aggregates with specific properties can be produced.

Optimization of Primary Drying Condition for Pharmaceutical Lyophilization Using a Novel Simulation Program with a Predictive Model for Dry Layer Resistance

The purpose of this study was to develop a novel simulation program to accurately predict the maximum product temperature and the primary drying time in lyophilization using the predictive model for dry layer resistance, which is the resistance of dried cake against water vapor flow. Ten percent sucrose aqueous solution was selected as a model formulation. It was demonstrated that the deviations between the predicted and measured maximum product temperature were attributed to the error of dry layer resistance at a given drying condition, which was different from the measured dry layer resistance in a preliminary lyophilization run for the simulation program. However, when the predictive model of dry layer resistance was used for the simulation program, the model remarkably enhanced the accuracy of the simulation program to predict the maximum product temperature and primary drying time under various operating conditions. Furthermore, the primary drying condition required for minimized drying at a close collapse temperature was successfully discovered through one preliminary run. Therefore, it is expected that the developed simulation program is useful for designing the lyophilization cycle without a trial and error approach.

Determination for dry layer resistance of sucrose under various primary drying conditions using a novel simulation program for designing pharmaceutical lyophilization cycle

Dry layer resistance, which is the resistance of dried cake against water vapor flow generated from sublimation, is one of the important parameters to predict maximum product temperature and drying time during primary drying in lyophilization. The purpose of this study was to develop the predictive model of dry layer resistance under various primary drying conditions using the dry layer resistance obtained from a preliminary lyophilization run. When the maximum dry layer resistance was modified under the assumption that the chamber pressure is zero, the modified dry layer resistance, which is defined as specific dry layer resistance, correlated well with the sublimation rate. From this correlation, the novel predictive model including the empirical formula of sublimation rate and specific dry layer resistance is proposed. In this model, the dry layer resistance under various conditions of shelf temperature and chamber pressure was successfully predicted based on the relationship of the sublimation rate and specific dry layer resistance of the edge and center vials obtained from the product temperature in one preliminary cycle run. It is expected that this predictive model could be a practical and useful tool to predict product temperature during primary drying.

On the Use of Artificial Neural Networks to Monitor a Pharmaceutical Freeze-Drying Process

This paper is focused on the use of artificial neural networks to monitor a pharmaceutical freeze-drying process. A detailed phenomenological model of the process is used to provide the dataset for the learning phase of the neural network development. Then, a methodology based on a self-adaptive differential evolution scheme is combined with a back-propagation algorithm, as local search method, for the simultaneous structural and parametric optimization of the neural network which models the freeze-drying process. Using some experimentally available measurements at a generic time t, the neural network is able to estimate the temperature of the product and the thickness of the dried cake (the amount of residual ice, as well as the sublimation flux, can be easily calculated from the cake thickness) at a future time t + Δt, for the given operating conditions (the temperature of the heating shelf and the pressure in the drying chamber). Also, the duration of the primary drying phase and the maximum product temperature in the future are predicted, in case the operating conditions are not modified. In this way it is possible to understand if it is necessary to modify the operating conditions, in case the product temperature should trespass the limit value before the ending point of the primary drying. Despite the fact that the artificial neural network is obtained using a learning set determined for specific values of heat transfer coefficient (between the heating shelf and the product at the bottom of the container) and of mass transfer resistance (of the dried cake to vapor flow), reliable and accurate estimations are also obtained in case the sensor is used to monitor a process characterized by different values of heat and mass transfer coefficients.

Numerical modelling of temperature fluctuations in superchilled fish loins packaged in expanded polystyrene and stored at dynamic temperature conditions

An appropriate thermal insulation of fresh fish packaging can substantially reduce negative effects of poor temperature management in chill chains. The aim of the current study is to experimentally and numerically investigate the performance of two types of EPS (expanded polystyrene) boxes in protecting superchilled fresh fish products subjected to temperature fluctuations, simulating conditions during transport. One EPS box type is a new improved version designed by utilising numerical heat transfer modelling for minimising the maximum product temperature during thermal load. This box weighed 11% less than the older box type. The performance of the boxes was evaluated by means of temperature monitoring and sensory evaluation. The thermal insulation of the new boxes was significantly better compared to the old boxes. According to sensory evaluation, storage in the new boxes resulted in approximately 2 days longer storage life. A satisfactory agreement between numerical results and experimental results was obtained.

Experimental investigation on a vertical display cabinet with central air supply

The frosting and defrosting of air cooler in a display cabinet usually lead to a large temperature fluctuation, thus increase the energy consumption of the display cabinet. In this paper, a vertical display cabinet with central air supply (VDCCAS) is established, experimented and compared with a conventional vertical display cabinet (CVDC). The refrigeration system of the VDCCAS consisting of a compressor, a condenser, a thermostatic expansion valve (TEV) and an evaporator is independent of the cabinet in a VDCCAS, and the cold air cooled by the evaporator is supplied through the air duct to the cabinet to realize refrigeration. Comparing to the CVDC, the VDCCAS can easily control the air curtain velocity, decrease the frost magnitude, increase the defrost cycle from 6 h to 9 h, and reduce the maximum product temperature rise in the defrost cycle from 3.0 °C to 2.0 °C. To reach the lowest temperature distribution in the cabinet, the optimum velocity of the air curtain is 0.7–0.8 m/s and the optimum Reynolds number is 4350–5000. When two cabinets work together, the airflow ratio of the two cabinets should be 1.1–1.2 in order to keep the temperature balance between the two cabinets.

In-line control of the lyophilization process. A gentle PAT approach using software sensors

A lyophilization process is usually only specified in terms of a ‘recipe’ (shelf temperature and chamber pressure vs. time); according to the recent PAT guidelines issued by FDA, there is the need to develop in-line tools to enable better monitoring and control freeze-drying. In this work an advanced Manometric Temperature Measurement approach, called DPE (Dynamic Parameters Estimation) is first presented, based on a detailed mathematical model. In alternative, the “ smart vial” concept is proposed, a Kalman filter based observer allowing an almost continuous monitoring without probes physically inserted into the product. Results obtained for pharmaceutical products in vial in a small industrial prototype equipped with the DPE-based LyoDriver control software, are presented. The software is capable to determine the optimal shelf temperature for primary drying, ensuring the fastest drying time without overcoming the maximum allowable product temperature both in scouting and production cycles. Finally, the two complementary monitoring systems, the DPE and the “ smart vial”, are combined in an even more robust hybrid control system.

Rapid determination of dry layer mass transfer resistance for various pharmaceutical formulations during primary drying using product temperature profiles

Mass transfer resistance of the dry layer during the primary drying phase of a lyophilizaton cycle is probably the most important factor affecting maximum product temperature and drying time. Product resistance parameters should be determined for each formulation because of their dependence of formulation composition and concentration. The purpose of this study was to determine the dry layer mass transfer resistance, using a simple and rapid method, for various pharmaceutical formulations during primary drying in a laboratory dryer, using monitored product temperature profiles. The mathematical tools used for the determination were a primary drying simulation program in conjunction with Powell's optimization algorithm. For each formulation studied, primary drying was performed using a shelf temperature of −15 or −20 °C and the chamber pressure controlled at 100 mTorr (0.1 Torr). The product temperature profiles ( T b) during primary drying were recorded and became the input data for the parameter estimation. The normalized product resistance, R pN, as a function of the dry layer thickness, ℓ , can be described by: R pN = R 0 + A 1 ℓ / ( 1 + A 2 ℓ ) , where the constants R 0, A 1 and A 2 are product resistance parameters of water vapor through the dry layer. Even when the parameter A 1 was negative, indicating that product temperature atypically decreased over time, the dry layer product resistance parameters of the various pharmaceutical formulations could be rapidly and successfully determined using the proposed approach. The product resistance equation obtained in this work for 5% marmitol, expressed as R pN = 0.0002025 + 20.23 ℓ , is similar to that obtained by Pikal [Pikal, M.J., 1985. Use of laboratory data in freeze drying process design: heat and product resistance parameters and the compute simulation of freeze drying. J. Parent. Sci. Technol. 39, 115–138.] using the microbalance method, expressed as R pN = 1.40 + 16.0 ℓ . The product resistance values obtained for the 3% lactose–LDH formulation are also very close to those obtained by (Milton, N., Pikal, M.J., Roy, M.L., Nail, S.L., 1997. Evaluation of manometric temperature measurement as a method of monitoring product temperature during lyophilization. PDA J. Pharm. Sci. Technol. 51, 7–16.) for 5% lactose using the MTM (manometric temperature measurement) method. With the obtained values of the parameters R 0, A 1, and A 2, simulations can be performed to determine the maximum product temperature and the drying time during primary drying. As such, optimum cycle parameters can be determined to avoid collapse of the product. The proposed approach requires only accurately measured product temperature profiles, easily obtained in a laboratory dryer.

Correlation of laboratory and production freeze drying cycles

The purpose of this study was to develop the correlation of cycle parameters between a laboratory and a production freeze-dryer. With the established correlation, key cycle parameters obtained using a laboratory dryer may be converted to those for a production dryer with minimal experimental efforts. In order to develop the correlation, it was important to consider the contributions from the following freeze-drying components: (1) the dryer, (2) the vial, and (3) the formulation. The critical parameters for the dryer are the shelf heat transfer coefficient and shelf surface radiation emissivity. The critical parameters for the vial are the vial bottom heat transfer coefficients (the contact parameter K cs and separation distance ℓ v), and vial top heat transfer coefficient. The critical parameter of the formulation is the dry layer mass transfer coefficient. The above heat and mass transfer coefficients were determined by freeze-drying experiments in conjunction with mathematical modeling. With the obtained heat and mass transfer coefficients, the maximum product temperature, T bmax, during primary drying was simulated using a primary drying subroutine as a function of the shelf temperature and chamber pressure. The required shelf temperature and chamber pressure, in order to perform a successful cycle run without product collapse, were then simulated based on the resulting values of T bmax. The established correlation approach was demonstrated by the primary drying of the model formulation 5% mannitol solution. The cycle runs were performed using a LyoStar™ dryer as the laboratory dryer and a BOC Edwards™ dryer as the production dryer. The determined normalized dried layer mass transfer resistance for 5% mannitol is expressed as R pN = 0.7313 + 17.19 ℓ, where ℓ is the receding dry layer thickness. After demonstrating the correlation approach using the model formulation 5% mannitol, a practical comparison study was performed for the actual product, the lactate dehydrogenase (LDH) formulation. The determined normalized dried layer mass transfer resistance for the LDH formulation is expressed as R pN = 4.344 + 10.85 ℓ. The operational templates T bmax and primary drying time were also generated by simulation. The cycle run for the LDH formulation using the Edwards™ production dryer verified that the cycle developed in a laboratory freeze-dryer was transferable at the production scale.

The collapse temperature in freeze drying: Dependence on measurement methodology and rate of water removal from the glassy phase

Accurate determination of the maximum allowable product temperature during primary drying is critical to optimization of the freeze drying process. For an amorphous solute system, this maximum temperature is normally the collapse temperature. Methodologies for determining the collapse temperature involve direct microscopic observation of collapse during freeze drying and methods which, in effect, determine the glass transition temperature of the amorphous phase. While one might be tempted to assume that the collapse temperature is a property only of the material, and independent of details of the measurement method, both theoretical concepts and limited experimental observations suggest that this assumption may not be wholly correct. The main objective of this research is to determine the magnitude of variations in measured collapse temperature caused by variations in experimental methodology. The approach taken is both experimental, using moxalactam di-sodium formulated with 12% mannitol as a model, and theoretical. The theoretical analysis is based on two fundamental concepts. Firstly, for collapse to be observed, viscous flow of the amorphous phase must occur over a finite distance during the measurement time. Secondly, during a freeze drying process, water is removed from the amorphous phase once the ice-vapor boundary recedes past the region of interest. Since water removal increases viscosity, viscous flow, and therefore, collapse is partially arrested, and the effective collapse temperature will be increased, the effect being greater the faster the sublimation rate. A quantitative model based on these concepts is developed with key parameters being evaluated by experimental studies. The observed variation in collapse temperature of moxalactam di-sodium with sublimation rate is quantitatively predicted by the theory. The theory is used to investigate differences between collapse temperatures determined by laboratory procedures and the observation of collapse in production processes. The collapse temperature will increase as the sublimation rate increases (i.e., as the solute concentration decreases), and at constant sublimation rate, the collapse temperature may increase as the surface area of the solid increases. In general, product freeze drying in a vial will collapse at a slightly higher temperature than collapse measured by the microscopic method. However, the calculated variations in collapse temperatures are modest (1–3°C). Collapse temperature and glass transition temperature, T ′ g , are not identical, the latter being slightly lower when measured at low rates of temperature increase. A secondary but important experimental result is that, contrary to some opinion in the literature, water in a glassy system has sufficient mobility to be in approximate ‘equilibrium’ with the ice phase during the relatively slow temperature changes relevant to freeze drying operations.

Comparative experiments on three-wall and one conventional road vehicle

In 1984 international research took place which compared the transport conditions of quick-frozen foods in thin-wall vehicles and conventional vehicles. This work was done at the request of the group of experts of the UNECE/TRANS/GE.11 in Geneva, Switzerland. In the Netherlands measurements have been carried out on three road vehicles — one conventional and two thin-wall vehicles — in the test station and on the road. The road transport involved taking a commercial cargo of frozen fish from Holland to Italy during the summer (July). Later on an additional test was performed in the test station with a fourth thin-wall vehicle at an ambient temperature of 30°C. The results show, that in the conventional vehicle, equipped with a bulk head and a ceiling air duct, and working on a temperature setting of −25°C, a maximum product temperature of −18°C could be maintained. The maximum temperature difference in the cargo was 6 K. Thin-wall vehicles appeared to have a temperature difference of 12 K between air inlet temperature and warmest product temperature. The maximum product temperature could be held below −12, −15 or −20°C, depending on the air distribution and, in particular, on the cooling power of the thermal appliance.

Anthocyanin colourants from elderberry (Sambucus nigra L.). 2. Process considerations for production of a freeze dried product

Summary.Freeze drying of elderberry anthocyanin extract under the proper conditions produces an intensely coloured powder with retention of both anthocyanins and physical structure. The various conditions examined included extract concentration, stabilizer concentration, pH and freeze drying conditions. It was found that minimum antho‐cyanin degradation and product structure alteration occur, when the undiluted extract is adjusted to pH = 3, has DE 20 maltodextrin structure stabilizer added to a 2.5% level and is freeze dried at a maximum platen temperature of 75â°C and maximum product temperature of 60â°C. Under these conditions, the recovery of anthocyanin is 94% and physical structure and solubility is preserved.

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.