• Energy Research

Abstract The phase change material (PCM) considered is a commercial paraffin wax. The main enclosure that contains the wax has a rectangular geometry and is placed in a vertical position. One of the walls is heated at constant rate during the charge process and the other wall is cooled by an airflow stream during the discharge. To describe the performance of the store a one–dimensional model based on the enthalpy method is developed. An apparent specific heat of the PCM is determined using a differential scanning calorimeter (DSC). This parameter permits the enthalpy of the PCM to be determined, and linearized for the numerical model. The results show that the simplified numerical model can be used to predict, with reasonable accuracy the dynamic performance of this kind of heat exchange unit.

Abstract The phase change material (PCM) considered is a commercial paraffin wax. The main enclosure that contains the wax has a rectangular geometry and is placed in a vertical position. One of the walls is heated at constant rate during the charge process and the other wall is cooled by an airflow stream during the discharge. To describe the performance of the store a one–dimensional model based on the enthalpy method is developed. An apparent specific heat of the PCM is determined using a differential scanning calorimeter (DSC). This parameter permits the enthalpy of the PCM to be determined, and linearized for the numerical model. The results show that the simplified numerical model can be used to predict, with reasonable accuracy the dynamic performance of this kind of heat exchange unit.

Packaging was recently identified as an essential element in addressing the key challenge of sustainable food supply and is gaining interest among researchers. It is a central element in food quality preservation due to its role in heat and mass exchange with the external atmosphere, contributing to the preservation of food quality during storage and extending food shelf life. This work proposes three new packaging configurations with the same size but different geometry and ventilation hole sizes and geometry, that change the conditions in which the heat and mass exchange occurs, during either the cooling period of fruits, inside the cooling chamber, or during the period when the packaging is exposed to ambient conditions, outside the cooling chamber. For this purpose, packages with fruit models that replicate the properties of real fruit were subjected to a cooling process inside a cooling chamber for 8 h. Subsequently, during the heating phase, the packages were exposed to ambient conditions for 10 h. Thermal conditions were also monitored, both inside and outside the chamber. Additionally, for comparative purposes, the thermal behavior of commercial packaging was also evaluated for the same operating conditions in the cooling and heating phases. The results show that the new packages do not substantially promote the preservation of fruits in the cooling phase, but in the heating phase, they ensure an extension of the period with proper thermal conditions of up to 50% in relation to the conventional packaging. This result is particularly important since the heating phase, in which fruits are outside the storage chamber, is the period with the greatest impact on the fruits’ useful life.

Packaging was recently identified as an essential element in addressing the key challenge of sustainable food supply and is gaining interest among researchers. It is a central element in food quality preservation due to its role in heat and mass exchange with the external atmosphere, contributing to the preservation of food quality during storage and extending food shelf life. This work proposes three new packaging configurations with the same size but different geometry and ventilation hole sizes and geometry, that change the conditions in which the heat and mass exchange occurs, during either the cooling period of fruits, inside the cooling chamber, or during the period when the packaging is exposed to ambient conditions, outside the cooling chamber. For this purpose, packages with fruit models that replicate the properties of real fruit were subjected to a cooling process inside a cooling chamber for 8 h. Subsequently, during the heating phase, the packages were exposed to ambient conditions for 10 h. Thermal conditions were also monitored, both inside and outside the chamber. Additionally, for comparative purposes, the thermal behavior of commercial packaging was also evaluated for the same operating conditions in the cooling and heating phases. The results show that the new packages do not substantially promote the preservation of fruits in the cooling phase, but in the heating phase, they ensure an extension of the period with proper thermal conditions of up to 50% in relation to the conventional packaging. This result is particularly important since the heating phase, in which fruits are outside the storage chamber, is the period with the greatest impact on the fruits’ useful life.

soil in shallow depths could be used as heat sink / heat source for cooling / heating devices. To predict its thermal behaviour during year, some authors use data from soil temperature records some else use data from average yearly air temperature measurements of meteorologic stations to avoid measure soil temperature in shallow depths for long time. In this research paper, we present a comparison study about the use of soil data and the use of air data for soil temperature prediction, where transient heat conduction in semi-infinite solids is utilised in the study. We measured the soil temperature of three sites for three years in Covilha -Portugal to support the current study. Later, we create reference years of soil temperature in the three sites.

soil in shallow depths could be used as heat sink / heat source for cooling / heating devices. To predict its thermal behaviour during year, some authors use data from soil temperature records some else use data from average yearly air temperature measurements of meteorologic stations to avoid measure soil temperature in shallow depths for long time. In this research paper, we present a comparison study about the use of soil data and the use of air data for soil temperature prediction, where transient heat conduction in semi-infinite solids is utilised in the study. We measured the soil temperature of three sites for three years in Covilha -Portugal to support the current study. Later, we create reference years of soil temperature in the three sites.

In the present work studies of experimental nature were made to evaluate the importance of the wall surface configuration related to its overall thermal resistance. A parameter with major importance in the value of such resistance is the convection heat transfer coefficient. In this way, several different surfaces were built and the correspondent convection coefficient was determined for natural convection conditions. As a reference for the comparative study a smooth surface has also been constructed. The value of the convection coefficient for each surface was obtained with the help of an infrared thermography system. The obtained results show a reasonable reduction in the smooth surface convection coefficient, which leads to an increase in overall thermal resistance. Therefore, if the objective is to increase the heat transfer rate between a surface and its neighbours there should be used roughness surfaces.

In the present work studies of experimental nature were made to evaluate the importance of the wall surface configuration related to its overall thermal resistance. A parameter with major importance in the value of such resistance is the convection heat transfer coefficient. In this way, several different surfaces were built and the correspondent convection coefficient was determined for natural convection conditions. As a reference for the comparative study a smooth surface has also been constructed. The value of the convection coefficient for each surface was obtained with the help of an infrared thermography system. The obtained results show a reasonable reduction in the smooth surface convection coefficient, which leads to an increase in overall thermal resistance. Therefore, if the objective is to increase the heat transfer rate between a surface and its neighbours there should be used roughness surfaces.