Today heat pipes are widely used by the designers in industries such as air conditioning and heat transformers for optimizing energy consumption. Existence of a permeable cylinder at the beginning and ending part of the heat pipe was considered on the basis of two assumptions for surface temperature of the cylinder and the mainstream velocity at the outer edge of the boundary layer vary linearly with the axial distance x from the leading edge. In this paper solution has been presented analytically with introduction of mixed convection parameter and coefficient of porosity . Various forms of flow were examined and the optimum state for minimum entropy generation was suggested. پرونده مقاله

Springs are the mechanical parts which have many application in industries. Static and dynamic forces cause relaxation in these parts so that they lose some of their free length and reaction force. Springs constant are very important in airplane and vailway industry since constant and variable forces are applied to them in period time, therefore it is necessary to avoid decreasing in spring constant in this condition. In this research, at first manufactured springs were stress relieved under different temperatures. In the next step constant displacements were applied to stress relieved springs by means of designed fixture. Springs constant changes and rate of these changes during different stages of the test were obtained. Results shownd that the stress relieving at 300 ° C has the best effect on prevention of decreasing in springs constant and free length under static long-term load. پرونده مقاله

Applying two-phase flows improves heat transfer rate which is an important objective in most of applications. Due to environmental concerns and corresponding regulations, carbon dioxide ( ), naturally exists in the atmosphere, has been reintroduced as a possible replacement for the most of commonly used refrigerants in air conditioning applications. High pressure working conditions of carbon dioxides had been the only difficulty in applying it in industrial applications for many years. Nowadays, by progressing in manufacturing technologies, the mentioned difficulty can be simply solved and attempts are resumed for replacing HFCs by carbon dioxide. There are limited numbers of experiments applying carbon dioxide as working fluid and due to common laboratories restrictions, that decrease the possibilities of repetition of experiments, there are dominant differences in results of present experiments in the literature. Having specific thermo-physical characteristics, carbon dioxide behaves different from other refrigerants in two-phase conditions. Therefore applying models based on other refrigerants for simulating carbon dioxide behavior results in dominant deviations from reality. In the present article the most recent experiments on carbon dioxide is gathered and investigated from aspect of heat transfer and pressure drop. Most of internal two-phase flows reach the annular flow pattern which has further heat transfer rate in compare with other flow patterns. This issue leads us to select this flow pattern in this article. The most important objective of the present study, apart from having a review on the performed studies, is to compare carbon dioxide efficiency with that of other refrigerants. At last it will appear that applying carbon dioxide as working fluid results in much more heat transfer rate and much less pressure drop level in compare with similar conditions of other refrigerants. پرونده مقاله

After springs production, different residual stresses are created in the inner and outer surfaces of spring wires. Some of these stresses for example compressive residual stresses are useful and some are harmful. The effects of vareation of these stresses are caused spring relaxation and decrising in their free length when they are loaded intermittently. For review this phenomena in this research, first a test device with 0.5 Hz operational frequency was made. Then with the idea of operation mechanism of milling machines dividing attachment and cams mechanism and performance, a fixtures was designed and manufactured in order to apply displacement and preload to springs. In the next step manufactured springs were stress relieved under different temperatures and times.After that they were loaded intermittently and their free lengths after 10,000 cycles were measured. Investigation on tests results showed the effects of changes in temperature and time of stress relieving on springs free length decreasing. Two approximate equations with first and second degree were extracted from experimental data. Finally, optimal operation of stress relieving was obtained . پرونده مقاله

The subject we discussion about are Nucleation and Meta stable phenomena’s , superheat liquids , supercold liquids and meanwhile applications of this liquids. all in all Meta stable situation can occur in three condition: First while changing liquid phase to gas phase by heating , Second changing liquid phase to solid phase by cooling , Third while moving water stream in subsonic nozzles or supersonic nozzles before condensation process occur. Of curse first and second conditions more than third condition view in nature and various industrials and productions of engender in first and second conditions are more than third condition. Of curse skews and turbulences that explain about them can disassemble this conditions. Meanwhile getting relations show that superheat degree have maximum and minimum amount . پرونده مقاله

This study is considering a micropolar fluid flow over a porous stretching sheet in the presence of thermal radiation and uniform magnetic field. The effects of local variation in thermal conductivity of micropolar fluid on heat transfer rate from the sheet are investigated; besides, the impacts of radiation, magnetic field and porous sheet on variations of thermal boundary layer thickness are considered. The results show that the increase of thermal conductivity thickens thermal boundary layer, so heat transfer rate decreases. In addition, intensification of magnetic field and the presence of radiation lower the absolute values of temperature gradient on the wall, and reduce the cooling rate of the sheet. On the contrary, the increase of suction and material parameter has positive influence on cooling rate of the sheet. پرونده مقاله

In the present study, a numerical model is developed to predict time-dependent temperature variations inside a solar greenhouse by solving the continuity, Navier-Stokes, and energy Equations using ANSYS Fluent. This paper considers all heat transfer mechanisms into and out of the greenhouse, including convection, radiation, and conduction. The surface-to-surface model and SIMPLE method are employed to analyse thermal radiation between surfaces within the greenhouse and to couple pressure and velocity in solving the flow-field Equations numerically, respectively. This study specifically investigates the unsteady temperature distribution within a solar greenhouse located in Makran, Iran (latitude: 25.3054°N, longitude: 60.6411°E). The numerical method of this study is validated by comparing its results with experimental data. The high accuracy demonstrated by this approach supports the conclusion that the model can effectively study the flow field and thermal behaviour inside solar greenhouses. It is demonstrated that fluctuating boundary conditions cause the thermal conditions inside the greenhouse to vary dynamically over time. The results depict the spatial variation of temperature distribution at different levels from the soil surface at 13:00 on the first and second days of modelling in Makran. These insights are expected to play a crucial role in improving greenhouse design and management practices in agriculture. پرونده مقاله