فهرست مطالب javad abolfazli esfahani

Phase change materials (PCMs) can be used in solar water heaters to store excess heat energy available during sunny hours. The purpose of this study is to investigate the performance of the solar water heater system with heat pipe, along with the energy storage system containing phase change materials (PCMs). In this study, a cylindrical galvanized tank with double spiral coil and containing PCM acts as a thermal energy storage unit. Paraffin is used as PCM and water is used as a heat transfer fluid (HTF) to transfer heat from the water heater tank to the spiral tubes and from there to the energy storage tank. The charging and discharging process tests are carried out on sunny days and in real operating conditions. The importance of temperature changes of HTF heat transfer fluid and PCM phase change material as well as the range of changes have been discussed. Functional variables of charge and discharge energy and thermal energy efficiency have been studied. The calculated charging efficiency, 75.7 %and the efficiency of the energy storage unit for the discharge process was 61.1 %. PCM saved 2700 kJ of heat in 70 minutes for 80 ° C during charging and 1650 kJ of heat in 50 minutes at 25 ° C and 42 liters per minute in storage, discharge. He made energy. From the tests, it was found that PCM improves the performance of the system by increasing the charging energy efficiency and the thermal efficiency of the hot water storage tank.

In this paper, an electrokinetic micromixing system with conductive mixing-enclosure is proposed. The simulated micromixer can be fabricated easily and accordingly, it can be used in the microfluidic systems effectively. The mixing process is intensified by controlling the geometry of the mixing-enclosure and electric field strength. The effects of different parameters including existence of mixing-enclosure, horizontal and vertical sizes of mixing-enclosure, orientation angle of mixing-enclosure, and electric field strength on the mixing index are studied. The mixing efficiencies and mixing lengths of current electrokinetic micromixer and those previously proposed by other researchers are compared. The results showed that the mixing efficiency can be enhanced significantly as a micromixer with conductive mixing-enclosure is employed. As an advantage of the proposed micromixer, the maximum mixing efficiency does not change by boosting the electric field strength in the range of 100 V.cm-1 to 200 V.cm-1, while the mixing time diminishes as the electric field strength increases in this range. For the conductive mixing-enclosure with the orientation angle of 45°, maximum mixing efficiency of 96.6% is achieved by exerting electric field with strength of 75 V.cm-1. The current electrokinetic micromixer has superior mixing efficiency and mixing length as compared with other electrokinetic micromixers.

Vacuum frying is a new technology that can be used to improve the quality attributes of fried food because of the low temperatures employed and minimal exposure to oxygen. In this paper، the atmospheric and vacuum frying of Reshte-Khoshkar (a traditional Gilan-Iran sweet cookie) were compared. Four pressure levels (47. 4، 57. 83، 70. 1 and 101. 325 kPa)، with three frying times (130، 160 and 190 s) and three thermal driving forces (ΔT=40، 60، and 80°C، constant difference between the oil temperature and the boiling point of water at the applied pressure) were used for frying. The effects of frying time، vacuum level and frying temperature on physical properties، such as moisture loss، oil absorption، and shrinkage were investigated. Moisture loss and oil absorption of fried Reshte-Khoshkar were significantly affected by frying pressure، frying time and frying temperature. The results showed that the moisture content decreased with increasing the frying pressure، frying time and frying temperature and fat content increased. Interestingly، a strong relationship between water loss and oil content was observed in both techniques. Vacuum frying was shown to be a promising technique that could be used to reduce oil content in the fried Reshte-Khoshkar. Shrinkage was not directly related to the frying condition of Reshte-Khoshkar.

In the present work we simulate rarefied gas flow between two moving parallel plates maintained at the same uniform temperature using direct simulation Monte Carlo (DSMC) method.We perform simulations for monatomic argon and diatomic nitrogen gas and compare mon/diatomic gas behaviors. For both gases, we study heat transfer and shear stress and investigate the effects of compressibility and rarefaction in the entire Knudsen regime and for a wide range of wall Mach number.Slip velocity, temperature jump, wall heat flux and wall shear stress are directly sampled from the particles striking the surfaces and reported for monatomic and diatomic cases for different rarefaction regimes. We also study deviation from theequilibrium using the probability density function for argon and nitrogen gas molecules.