EXPERIMENTAL STUDY OF THE INFLUENCE OF TEMPERATURE ON PASTEURIZATION OF PÊRA RIO IN NATURA ORANGE JUICE

Heat treatment is one of the most used methods to preserve food, such as orange juices, which are an excellent source of ascorbic acid. To avoid vitamin C degradation and reduce loss, fast heating is recommended. This work aimed to determine the vitamin C content using the iodometric method and the convective heat transfer coefficient using the method of dimensionless numbers and the experimental method. Time and temperature were controlled throughout the experiment. In pasteurization, the solution was heated to 80 °C, heating lasted 50 minutes and cooling for 42 minutes. The convective heat transfer coefficient was evaluated in two regions of the cylindrical container: near the wall and in the central region. The graphic profile of the curve follows the same trend of the literature. The convective heat transfer coefficient is higher in the region near the wall. As time passes and temperature decreases, the central region tends to equilibrium, and the coefficient becomes more constant. The vitamin C content remained constant before and after pasteurization, so it was observed that the pasteurization did not cause ascorbic acid degradation since the heating step was fast in the heat treatment. As a result of the study, it was noted that studying the thermal behavior in the cooling of orange juice is extremely important to ensure its quality. It is pertinent to mention that in order to avoid this degradation and reduce its loss, it is necessary that in thermal treatments, fast heating is carried out and that the juice has low exposure to air and heat at the time of its preparation.

Heat Transfer Modelling and Simulation of a 120 mm Smoothbore Gun Barrel During Interior Ballistics

Understanding the heat transfer phenomenon during interior ballistics and consequently presenting a realistic model is very important to predict the temperature distribution inside the cannon barrel, which influences the gun wear and the cook-off. The objective of this work is to present a new detailed numerical model for the prediction of thermal behaviour of a cannon barrel by combining PRODAS interior ballistics simulation with COMSOL simulation. In this study, a numerical model has been proposed for the heating behaviour of a 120 mm smoothbore cannon barrel, taking into account the combustion equation of the JA-2 propellant. Temperature dependent thermophysical properties of product gases were used for the calculation of the convective heat transfer coefficient inside the barrel. Projectile position, velocity of the projectile, gas temperature inside the barrel, volume behind the projectile and mass fraction during interior ballistics have been obtained by PRODAS software and used in the numerical model performed by COMSOL multiphysics finite element modelling and simulation software. Temperature simulations show that maximum wall temperature inside the cannon barrel is observed after 3 ms from fire, when maximum value of the convective heat transfer coefficient inside the barrel is observed. The results reveal that the convective heat transfer coefficient of burned gases inside the gun has major effect than the burned gas temperature on the heat transfer phenomenon.

EXPERIMENTAL STUDY OF THE INFLUENCE OF TEMPERATURE ON PASTEURIZATION OF PÊRA RIO IN NATURA ORANGE JUICE

Background: Heat treatment is one of the most used methods to preserve food, such as orange juices, which are an excellent source of ascorbic acid. To avoid vitamin C degradation and reduce loss, fast heating is recommended. However, little is known about heat transfer during juice pasteurization. Aim: Therefore, this work aimed to determine the vitamin C content and the convective heat transfer coefficient in the pasteurization of orange juice. Methods: To perform the experiment, in the juice container, two regions were analyzed: the central region and near the wall. For the time-temperature control, thermometers were installed in the two regions mentioned. Every 120 seconds, the temperature was measured. The vitamin C content in the juice was evaluated before and after pasteurization using the iodometric method. The convective coefficient was evaluated using the method of dimensionless numbers and the experimental method. Results and Discussion: In pasteurization, the solution was heated to 80 °C, where heating lasted 3000 seconds and cooling for 2520 seconds. The graph showing the relationship of the convective heat transfer coefficient and temperature follows the same trend of the literature. The convective coefficient is higher in the region near the wall. As time passes and temperature decreases, the central region tends to equilibrium, and the coefficient becomes more constant. The vitamin C content remained constant before and after pasteurization. The values of the dimensionless numbers used in the calculations are in the same order of magnitude as the literature. Conclusions: The pasteurization did not cause ascorbic acid degradation since the heating step was fast in the heat treatment. The graphic showed that there is a dependence of the dimensionless of temperature with the dimensionless Biot and Fourier. It was noted that studying the thermal behavior in the cooling of orange juice is extremely important to ensure its quality.

Procedure for calculation of the admissible continuous power transmission currents of overhead wires and contact lines

The proposed methodology summarizes published and original domestic and foreign theoretical and experimental materials on heating and cooling of spiral and shaped wires of overhead power transmission lines and electric power systems and uses those of them that best meet the fundamental laws of heat transfer. Formulas for calculating the surface area for spiral and shaped wires are given. A generalized formula for the convective heat transfer coefficient taking into account the direction and speed of the wind, including for the anti-ice regime, is given. The parameters of this formula do not coincide with the existing ones, since they are based on the experimental data for spiral and shaped wires, and not for round pipes. The formula for calculating the power of heat transfer under solar radiation is given. A generalized formula is given for calculating the continuous allowable current, all components of which are described in detail in the article.

Investigation on Heat Transfer and Pressure Drop Performance Utilizing GNP-based Colloidal Suspension Flow in Finned Conduit

Heat exchangers have been widely used in various engineering applications. It is important to develop a highly efficient heat transfer equipment to reduce carbon footprint. In the current research, the effect of 0.025wt% CGNP/water nanofluid on convective heat transfer and pressure drop performance is investigated numerically in finned conduits with circular and square geometry. ANSYS FLUENT is used to analyze the turbulent flow inside the conduits with Reynolds number ranging from 7360 to 28011 and constant heat flux 12254.90W/m2 and 9615.38W/m2 in circular and square geometry, respectively. Only 1/8 of the pipe was constructed in the simulation as the geometry is symmetrical. The numbers of mesh elements are 465488 and 469144 for circular and square conduits. SST k-omega viscous model, SIMPLEC scheme and second-order upwind solvers are used in this model, where SST k-omega viscous model is good at solving turbulence parameters in the near wall boundary regions. It is found that the use of CGNP/water nanofluid can increase convective heat transfer coefficient without increasing pressure drop compared with water. Besides, the circular pipe shows higher heat transfer enhancement compared with square pipe. Furthermore, the increase in Reynolds number enhances the Nusselt number and heat transfer coefficient in both circular and square geometries. It is recommended that circular finned pipe and CGNP/water colloidal suspension could be applied in low turbulence flow setting heat exchanger.

Some aspects of plate number estimation of plate heat exchangers (PHEs). A case study

For the proper estimation of the plate number (N) of a plate heat exchanger (PHE) – in addition to the flow rates and thermophysical properties of fluids –, an appropriate correlation is needed for convective heat transfer coefficient (α) calculation. When one does not have a criterial equation for the corresponding plate shape, we propose a selecting method for α. With the suggested relationships from literature, we calculate the plate number of a geometrically known, similar heat duty PHE and choose those relationships that give the same plate number with the known heat exchanger. In our case study, the plate number determined by any of the screened equations for whole milk preheating has almost the same value (n = 10 ± 1) regardless of the method used to solve the PHE model (plate efficiency and Nconverg or Kconverg convergence methods). For liquids’ thermophysical property estimation, we recommend averaging the values given by equations from literature, followed by equation fitting.

Enhancement of PV Panel Power Production by Passive Cooling Using Heat Sinks with Perforated Fins

This paper presents a numerical model regarding the passive cooling of PV panels through perforated and non-perforated heat sinks. A typical PV panel was studied in a fixed position, tilted at 45 degrees from the horizontal with the wind direction towards its backside. A challenging approach was used in order to calibrate the base case of the numerical model according to the NOCT conditions. Further validation of the accuracy of the numerical simulation consisted of a comparison between the results obtained for the base case, or heat sink, with horizontal non-perforated fins and the experiments presented in the literature. Six types of heat sink attached to the backside of the PV panel were numerically studied. The analyzed configurations focused on heat sinks with both perforated and non-perforated fins that were distributed horizontally and vertically. The CFD simulation was also conducted by modeling the air volume around the PV panel in real wind conditions. The main output parameters were the average temperature and the convective heat transfer coefficient on the front and back of the PV panel. The most important effect of cooling was achieved in low wind conditions and high levels of solar radiation. For vair = 1 m/s, G = 1000 W/m2 and ambient temperature tair = 35 °C, the percentage of maximum power production achieved 83.33% for the base case, while in the best cooling scenario it reached 88.74%, assuring a rise in the power production of 6.49%.

Magneto-thermal coupling simulation and experimental verification for a three-winding high-frequency transformer

As a core component of the power electronic transformer (PET) in DC network, the multi-level high-frequency power transformer has received great attention due to the insulation material fatigue problems resulting from the hot-spot temperature rises. To solve this problem, a three-winding high-frequency transformer for 10 kVA PET application is designed and made in the laboratory, and the loss and temperature rise distribution is calculated by means of the finite element (FE) electromagnetic-thermal coupling simulation. The influence of temperature on the hysteresis and loss properties of core material has been carefully considered and measured. The influence of skin effect and end effect on the winding loss is taken into account through the establishing three-dimensional FE model. Besides, the convective heat transfer coefficient is solved based on the principle of heat transfer instead of the empirical coefficient method. By compared with the experimental results, the calculated results are validated to be effective in predicting the loss and hot-spot temperature rises of the transformer.