Sharif Digital Repository

Solar heat energy, one of the typical renewable energy absorbs radiation energy from the sun and converts it into heat energy. Since it is sustainable and eco-friendly, it can be a good alternative to solve the problem of the depletion of fossil fuels. But it has low density. So, solar collector is very important to use more efficiently. There are some possible approaches to scaling-up the effectiveness of a collector by re-thinking of using the collector as a heat exchanger. In the design of dual-purpose collector with rectangular fin (DPCRF), can be used for heating air and water simultaneously using incident solar radiation resulting in optimum usage of energy and space  

The effect of the corona wind on the natural convection at a rectangular channel was investigated experimentally. The results indicate that the natural convection in the absence of electric/corona wind at obtuse angles outperforms than acute angles and keeps improving by increasing the angle. However, the efficiency of the electric/corona wind at acute angles is higher than obtuse angles. Generally, in the presence of electric/corona wind, heat transfer coefficient was increased. The effect of the electric/corona wind was decreased by raising heat flux. This mainly stems from the fact that the temperature gradient raises the thermal boundary layer and reduces the secondary flow power.... 

Labyrinth side weirs provide a potentially effective way to shorten the length of a channel opening with the desired water height, but the discharge coefficient needs to be found experimentally. Experiments were carried out for triangular labyrinth side weirs with one and two cycles in order to obtain the discharge coefficient. The test variables included channel opening, head angle, number of cycles, weir height, upstream water depth and discharge in a subcritical situation. The resultsshow that the discharge coefficient ratio for a triangular labyrinth to a conventional side weir could rise to more than 2 with the same flow and geometric conditions. Relationships for the De Marchi... 

Labyrinth side weir is one type of weirs, which can be used when the length of opening is limited. One of the advantages of labyrinth side weir is to increase the effective length of weir perpendicular to the flow and, therefore, diverting more discharge with the same flow depth and weir geometry (opening and height). Discharge coefficient should be determined to investigate the weir performance and estimate the discharge passing over the weir. In this paper, hydraulic performance of labyrinth side weir with asymmetric geometry has been experimentally studied. The change to the geometry of ordinary labyrinth side weirs causes an increase in the effectiveness of the length of weir as being... 

Design and fabrication of solar collectors with high performance of energy efficiency to convert solar energy to utility energy is vitally important. This article reports the results obtained from design, construction and investigation of the performance of a Combined Multi-Purpose Vacuum Solar Collector (CMPVSC). This collector consists of three sections: the vacuum section, the liquid section and the air section. In the present collector, it is capable of transferring heat to two flows (liquid and air) simultaneously and separate with the possibility of multipurpose applications. The CMPVSC is compared with the existing individual collectors and the effects of different parameters on the... 

In the present study, methods for improving the hydraulic performance of labyrinth side weirs in a rectangular channel are reported based on model experimentation. For this purpose different arrangements and configurations of groups of guide vane plates and piles in the side weir flow field were tested. Experiments were conducted on labyrinth side weirs of different lengths and sill heights fitted in the test section of a rectangular glass-walled channel. Depths of flow were measured in both longitudinal and crosswise directions at regular intervals and their profiles were studied. It was found that the discharge coefficient of the labyrinth side weirs under these conditions gave... 

In the present article, thermal behavior and heat transfer deterioration (HTD) of transcritical methane as well as the fluid state change in regenerative cooling with straight/curved rectangular channels are studied numerically. Simulations are conducted with a finite-volume based CFD solver utilizing reliable turbulence models and thermo-fluidic relations in transcritical conditions. The experimental and numerical results of hydrogen inside a heated tube in the literature are used for validation. The effects of mass flow rate, outlet pressure, wall temperature, surface roughness, and the channel geometry on the thermal behavior of the coolant fluid are studied in detail. According to the... 

Side weirs are frequently used in many water projects. Due to their position with respect to the flow direction, side weirs are categorized as plain, oblique and labyrinth. One of the advantages of an oblique side weir is the increase in the effective length of the weir for overflowing and, therefore, diverting more discharge with the same channel opening, weir height and flow properties (i.e., upstream discharge, upstream Froude number and so on). In this paper, an experimental set-up of a new design of an oblique side weir with asymmetric geometry has been studied. The hydraulic behavior of this kind of oblique side weir, with a constant opening length, different weir heights and... 

Thermal conductivity, thermal dispersion, and structural effects in resin transfer molding (RTM) process are studied numerically. The injection part of the RTM process is modeled as a transport of resin flow through a fibrous porous medium in a long rectangular channel. The fluid flow is modeled using the Darcy-Brinkman-Forchheimer model and the heat transfer process using the energy equation based on local thermal equilibrium assumption. Both isotropic and anisotropic heat transfer in porous media are investigated. The governing equations are solved numerically for the isotropic heat transfer case and analytically for the anisotropic case. The numerical results are fitted to the available... 

Microchannels are at the forefront of today's cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections: parallel plate channel, circular duct, rectangular channel,...