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The authors previously proposed and experimentally investigated a new standalone desalination system that is composed of a parabolic trough collector put under conventional solar still. In this study, an unsteady theoretical model is developed using the energy balance equations for the main components of the system to investigate the effect of different parameters on the performance of the new solar still. The model is used for calculation of productivity, and the absorber, saline water, and the glass cover temperatures. Results obtained using the present model are compared with the experimental results and a good agreement is observed between them. Moreover, as the experimental study was limited to the winter period, to thoroughly understand the new system performance at different climates conditions, its performance in four seasons is considered. Results show that in Kerman weather conditions, on average the present solar still system produces 0.961 L of freshwater per day in summer which is 55% more than the yield in winter for the Fixed parabolic trough collector. For the parabolic trough collector with tracking systems, the system would produce 1.266 L per day in summer.

In this study, the forced convective in a tube filled with porous media is investigated analytically based on the perturbation methods. Thermal conductivity of the medium is assumed to be a linear function of radius. The Brinkman–Forchheimer-extended Darcy and local thermal equilibrium models are applied for momentum and energy equations. Analytical expressions for the temperature profile and Nusselt number as functions of porous medium shape parameter and thermal conductivity variation parameter are introduced. An analytical expression of the Nusselt number based on a variable conductivity with radius for the extended model of Darcy–Brinkman–Forchheimer has not been previously proposed, and the present study aims at filling this gap. The effects of porous media shape parameter (s), Forchheimer number (F) and linear parameter of conductivity (ɛ) on the Nusselt number and temperature profile are discussed. Results show that the Nusselt number increases with a linear increase in the thermal conductivity of the medium. Keywords: Porous media, Variable conductivity, Brinkman–Forchheimer–Darcy model, Perturbation analysis

The study aimed at revealing the techno-economic analyses of the temperature management of photovoltaic (PV) modules. For this aim, an existing PV power plant (PP) located in Zanjan, north-west of Iran was analyzed experimentally. Two different cooling scenarios (cases A and B with 3 and 6 low-energy fans per module) were considered. The net energy balance showed that more net electrical energy is produced in case A. The net specific energy (kWh per kWp) could be increased up to 4.4% and 4.1% in July, respectively for cases A and B. The selected cooling system (i.e. case A) was analyzed economically according to three different possible scenarios: considering different feed-in tariff (FiT) rates, change in PV module degradation rates, and increasing the size of a PV PP vs applying the thermal management system. Results revealed that a thermal management system would be economically justifiable only at high FiT rates. Finally, considering the reduction in the degradation rate of PV modules is necessary for economic analyses due to the possible lowering in the pay-back period as up to three years seen in the present study.

In the present work the efficiency of a solar parabolic trough has been investigated experimentally. An absorber filled with metal foam is used in order to improve the heat transfer and increase the efficiency of PTC (parabolic trough collector). The porosity of copper foam is 0.9 and the pore density is 30 PPI (pores per inch). The experiments were performed in different volume flow rates from 0.5 to 1.5 Lit/min and the standard of ASHRAE 93 was used to test the solar collector’s performance. Friction factor and Nu number have been investigated for both cases. It was found that by increasing the mass flow rate, the efficiency of the collector was enhanced and the same pattern can be seen when absorber filled with copper foam. When absorber filled with metal foam the overall loss coefficient UL decreases by 45% and it causes to increase efficiency because less energy is lost.

In this study, fuel utilization (U F ) of a PEMFC have been investigated within transfer phenomenon approach. Description of the U F and fuel consumption measurement is the main factor to obtain the U F . The differences between the experimental study and theoretical calculations results in the previous research articles reveal the available theoretical equations should be studied more based on the fundamental affairs of the U F . Hence, there is a substantial issue that the U F description satisfies the principles, and then it can be validated by the experimental results. The results of this study indicate that the U F and power grew by 1.1% and 1%, respectively, based on one degree increased temperature. In addition, for every 1 kPa pressure increment, U F improved considerably by 0.25% and 0.173% in the 40 °C and 80 °C, respectively. Furthermore, in the constant temperature, the power improved by 22% based on one atmospheric growth of the pressure. Results of this research show that the U F has a differential nature, therefore differential equations will be employed to do an accurate theoretical calculation. Accordingly, it seems that the main defect of the theoretical calculation depends on Nernst equation that can be modified by a differential nature coefficient.

In this study, convection-radiation heat transfer in solar air-heater filled with a porous medium is investigated. The effects of porous media shape parameter (s), Forchheimer number (F) and radiation parameter (ζ) on the collector efficiency are discussed. Approximate analytical solutions for the dimensionless velocity, temperature, and Nusselt number are obtained using perturbation method. The radiation heat transfer has been modeled using the Rosseland approximation method. A discussion on the accuracy and limiting cases of the solution is represented and a good agreement has been found between the analytical solutions and previous works. The results showed that by increasing the radiation parameter, the efficiency of the collector was improved. Also, the collector heat removal factor enhances when the porous media shape parameter increases.

Identification of solvents for dissolving polymer dielectrics and organic semiconductors is necessary for the fabrication of solution-processed organic field effect transistors (OFETs). In addition to solubility and printability of a solvent, orthogonality is particularly important when forming multilayer structure from solutions. Currently, the process of finding orthogonal solvents is empirical, and based on trial-and-error experimental methods. In this paper, we present a methodology for identifying orthogonal solvents for solution-processed organic devices. We study the accuracy of Hildebrand and Hansen solubility theories for building solubility boundaries for organic semiconductor (Poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT) and polymer dielectrics (Poly(methyl methacrylate) (PMMA), Polystyrene (PS)). The Hansen solubility sphere for the organic semiconductor and polymer gate dielectrics are analyzed to identify solvents that dissolve PMMA and PS, but are orthogonal to PBTTT. Top gate/bottom contact PBTTT based OFETs are fabricated with PMMA gate dielectric processed with solvents that are orthogonal and non-orthogonal to PBTTT. The non-orthogonal solvents swell the semiconductor layer and increase their surface roughness.

In this paper, thermal performance of a room heated with an attached sunspace has been experimentally investigated and has been modeled using the EnergyPlus software. A fixed porous bed was placed beneath the room's floor to store the heat. To increase the heat storing capacity, water tanks was also used. The room with attached sunspace was built and tested in Karaj (Iran). Results illustrated that applying water tanks in the sunspace had a noticeable role in heat storing capacity. For example, the porous bed together with water tanks saved at least 37% (up to 87%) of energy cost compared to 10% (up to 15%) saved energy cost without water tanks. In addition, the simulation of annual thermal performance of the room by Energy-Plus software confirmed the applicability of the used configuration of sunspace along with added water tanks and porous bed made form arranged bricks as heat storing media a step forward to a completely green room (net zero energy building). The sunspace with water tanks showed a more stable condition (lower temperature variations) which is a base of thermal comfort.

Measurement of instantaneous air flow velocity with high frequency can be carried out by using a hot wire anemometer (HWA). HWA works on the basis of heat transfer rate from hot wire to the fluid flow, therefore directional identification of the air flow using hot wire anemometer is a difficult task. By using two parallel cylindrical hot film sensors a probe was built. By considering the wake and heat effect of the upstream sensor on the downstream sensor, direction of the air flow can be identified. In this work, the wake and heat effect resulting from the upstream sensor to the velocity measurement, by the downstream sensor was studied. This measured velocity is dependent of the following factors namely; air velocity, upstream sensor overheat ratio, distance between the two sensors and turbulence intensity of the flow. As a result it was found that the manufactured probe with sensor distance of 1 mm apart is capable of measuring reverse flow measurements of up to 20 m/s for a moderate turbulent flow.