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Hirbodi K.,Shiraz University | Yaghoubi M.,Shiraz University | Yaghoubi M.,The Academy of science of IR Iran
Heat and Mass Transfer/Waerme- und Stoffuebertragung | Year: 2015

In the present study, structure of water drops formation, growth, coalescence and departure over a horizontal finned-tube during natural dehumidification is investigated experimentally. Starting time of repelling the drops as well as heat transfer rate and the rate of dripping condensates in quasi-steady-state conditions are presented. Furthermore, cold airflow pattern around the horizontal finned-tube is visualized by using smoke generation scheme during natural dehumidification process. The finned-tube has a length of 300 mm, and inner and outer fin diameters, fin thickness and fin spacing are 25.4, 56, 0.4 and 2 mm, respectively. The tests are conducted in an insulated control room with dimensions of 5.8 m × 3 m × 4 m. Ambient air temperature, relative humidity and fin base temperature are selected from 25 to 35 °C, from 40 to 70 % and from 4 to 8 °C, respectively. Observations show that natural condensation from humid air over the test case is completely dropwise. Droplets only form on the edge of the fin and lateral fin surfaces remain almost dry. Dehumidification process over the tested finned-tube is divided into four stages; nucleation, formation, growth and departure of drops. It is also observed that the condensate inundation leaves the tube bottom in the form of droplets. Smoke visualization depicts that humid airflows downward around the cold finned-tube surface without noticeable turbulence and separation in the initial stages of dehumidification process. But the airflow has some disturbances in the intermediate stage and especially during drop departure on the edge of the fins. © 2015 Springer-Verlag Berlin Heidelberg

Mohamadi Z.M.,Islamic Azad University at Tehran | Zohoor H.,The Academy of science of IR Iran
Evolutionary Ecology | Year: 2011

Using hybrid energy storage system is a method for increasing the storage capability of solar thermal energy. If multiple energy storage devices with complementary performance characteristics are used together, the resulting system will be a 'Hybrid Energy Storage System'. In other words, a Hybrid Energy Storage System (HESS) has several media available for storage at any time. In this way, increase in storable energy is obtained without increasing collectors' area. When there are more than one storage mediums, the system should be able to choose the best medium for storing energy according to the conditions. In the previous works, an optimizer program was used to find the proper medium along time. But running a computer optimizer program is almost time consuming. So, in this work, a recognition parameter is introduced which helps to select the proper tank in different conditions. Using this dimensionless parameter, the hybrid storage system won't be always dependent to the optimizer. The results have been checked theoretically and experimentally. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.

Hirbodi K.,Shiraz University | Yaghoubi M.,Shiraz University | Yaghoubi M.,The Academy of science of IR Iran
Experimental Thermal and Fluid Science | Year: 2014

In this study, heat and mass transfer during natural condensation of humid air over a horizontal annular finned-tube is investigated experimentally. The finned-tube is made by extruded process and fins are circular with rectangular cross-section. Outer diameter of central tube, fin diameter, fin thickness and fin density are 25.4. mm, 0.4. mm, 56.0. mm and 433 FPM (fins per meter), respectively. The test case is placed in a specially constructed insulated test room to control test conditions and simulate pure natural dehumidification. Ambient air temperature and relative humidity are controlled by heating, cooling and humidifying equipment. Ethylene glycol-water solution is used as refrigerant to control and keep fin base temperature constant. Experiments are performed for ambient air temperature of 25. °C, 30. °C and 35. °C, relative humidity of 40%, 50%, 60% and 70% and fin base temperature of 4. °C, 6. °C and 8. °C. Observations indicate that the water drops form mainly on tip of the fins and for the conducted tests, no condensation is observed between the fins which is mainly due to small fin spacing (2.0. mm) and lack of convective heat and mass transfer between the fins. The test results also show that condensation and heat transfer rate depend mainly on the temperature and relative humidity of the surrounding air and fin base temperature. The increase in ambient air temperature and relative humidity and the decrease in fin base temperature lead to increase in heat and mass transfer rate. Furthermore, based on the results, new correlations are developed for heat and mass transfer during natural dehumidification over compact annular finned-tubes. © 2014 Elsevier Inc.

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