• Energy Research

Extensive cost in the building industry comes from cooling and heating to create thermal comfort. Hence, it is necessary to utilize passive solutions, in addition to suitable design, in order to reduce energy consumption. This research attempts to investigate the impact of archetype patterns in office buildings on annual energy consumption for cooling, heating and daylight loads. For this purpose, the DesignBuilder software was used to compare the forms. In this study, four conventional construction forms were considered, including the single and dense form, central courtyard buildings, U form and linear form, and each was considered with two, four and six-stories. Forms were simulated in the three cities of Bushehr, Shiraz and Tabriz, with hot-humid, hot-dry and cold climates, respectively. The results revealed that the office building with a linear form in Bushehr had the lowest energy consumption in the two and four-story forms, and also in the six-story form, the central courtyard form had the lowest energy consumption. Additionally, the central courtyard forms in Tabriz and Shiraz had the lowest energy consumption in all cases. Finally, the linear form possessed the most natural daylight through all of the studied cases for the three cities in terms of natural light gain.

Abstract Shiraz solar thermal power plant is designed for 250 kW power supply during available sun radiation. It is decided to promote the field of collectors by installing a large parabolic collector and combining the system with a 500 kW hybrid boiler. For the new integrated configuration, thermodynamic analysis is required for engineering design and evaluating thermal performance. For the new system, transient simulation is performed under different working conditions. In the plant, each component is simulated transiently, by considering initial condition and capacity rate of the component as well as all the connecting pipes and instruments. Results of the simulation for thermal performance are compared with field experimental measurements for several periods. Taking into account the thermodynamic concepts and the results of numerical and experimental analysis, the best operation strategies are selected for optimum performance and control philosophy based on the new integrated collector.

Abstract An empirical method for calculation of the hourly output of a basin-type solar still over a 24-hour cycle for nine city locations in Iran has been studied. The hourly performance of the solar still is computed for each month of the year given the values of insolation for the location considered, the local ambient temperature, wind heat transfer coefficient, base and side heat transfer coefficient, water depth and a new variable called the service time. Based on the daily output, the suitability of the basin-type solar still design for providing drinking water in a number of communities in various locations in Iran is demonstrated.

AbstractThe design of parabolic trough collectors is based on the concentration of solar heat flux on its absorber tube. This may be subjected to high thermal stresses which could cause deflection of the absorber tube and failure of its cover glass tube. Investigation of earlier studies on thermal gradient and thermal stresses demonstrates that so far, the issue is considered for steady state condition based on the assumption of constant solar heat flux distribution during the day hours. However, in practice, solar heat flux distribution on the receiver tube has continues changes with respect to time and deformation is basically transient. Due the low speed of sun during a day and for specific time intervals, the average solar radiation could be considered constant for thermal stress and deflection analysis. Hence, in this study, thermal gradients as well as thermal stresses in the absorber tube are numerically investigated in quasi steady condition. Due to the wide changes of solar radiation during a year, computations are performed for four specific days of Spring Equinox, Summer Solstice, Autumnal Equinox and Winter Solstice. To compute solar heat flux distribution, SolTrace software is used and three dimensional heat flux distribution is applied as an external boundary condition to calculate temperature distribution in the absorber tube. By using Von-Misses theory, maximum equivalent of total stress is computed. Maximum deflection is evaluated for various different inlet temperatures and hot oil mass flow rates in the common range of solar thermal power plants for atypical parabolic trough collector which is under construction in Shiraz, Iran.

Abstract Nanofluids as volumetric absorbent in solar energy conversion devices or as working fluid in different heat exchangers have been proposed by various researchers. However, dispersion stability of nanofluids is an important issue that must be well addressed before any industrial applications. Conditions such as severe temperature gradient, high temperature of heat transfer fluid, nanoparticle mean diameters and types of nanoparticles and base fluid are among the most effective parameters on the stability of nanofluid. A molecular dynamic approach, considering kinetic energy of nanoparticles and DLVO potential energy between nanoparticles, is adopted to study the nanofluid stability for different nanofluids at different working conditions. Different forces such as Brownian, thermophoresis, drag and DLVO are considered to introduce the stability diagrams. The latter presents the conditions for which a nanofluid can be stable. In addition an experimental investigation is carried out to find a stable nanofluid and to show the validity of the theoretical approach. There is a good agreement between the experimental and theoretical results that confirms the validity of our theoretical approach.

In this study, 4E analysis for feasible integrated systems for cogeneration of fresh water was investigated. Steam generation provided by a steam boiler, designed to supply the thermal heat requirements of MED-TVC and MED-TVC.FH systems. Parametric analysis is made to determine CO2 emission rate, gain output ratio, exergy destruction rate and special heat rate for each system. By using Artificial Bee Colony algorithm, systems were optimised for maximum exergy efficiency and minimum cost of the produced distilled water. The results showed that by selecting final optimum solutions, the distillated water cost reduced by 18.1% and 28.8% for MED-TVC and MED-TVC.FH systems respectively. Also exergy efficiency increased from 3.2% and 4.04% in the base case to 3.63% and 4.47% for MED-TVC and MED-TVC.FH respectively in the optimum case. The system with feed water preheater, has more exergy efficiency and less CO2 emission, also the cost of distilled water reduced by 7.86%.

Abstract The objective of the present work is to investigate theoretically the basics of natural convection heat transfer of nanofluids. On this regard thermophoresis of nanoparticles and the Dufour effect on natural convective heat transfer on nanofluids are investigated simultaneously. Positive thermophoresis implies that nanoparticles move from a hot wall to a cold wall and the Dufour effect implies that heat transfer will induce by volume fraction gradients. By using simple formulation the combined effects of Brownian motion and thermophoresis are considered to get the volume fraction distribution and its difference between hot and cold walls. Having volume fraction gradient of nanofluid, the implication of Dufour effect on the variation of heat transfer and Nusselt number of natural convection is computed. For approximate conditions closed form expression is derived to estimate Nusselt number of natural convection heat transfer for different volume fractions based on the pure water (base fluid) Nusselt number. This expression is used to predict natural convective Nusselt number for three kinds of nanofluids related to three experimental measurements of other investigators and also compared to the most recent theoretical developments. Good agreements are observed between experimental results and the present estimation due to the Dufour effect and similar trends are found by comparing with theoretical computations.

In the present article attempt is made to develop an exergoeconomic optimization model to integrate solar energy into trigeneration system producing electricity, heating and cooling according to the exergetic, economic and environmental targets. The results show that by selecting final optimum solution for the trigeneration system, the unit cost of products reduced by 11.5% and exergy efficiency increased from 44.38% in the base case to 56.07% in the optimum case. The application of optimization process shows that exergoeconomic analysis improved significantly the total performance of the trigeneration system in a way that fuel cost, exergy destruction cost and environmental impacts (CO2 emissions cost) are reduced by 24.17%, 38.87% and 24.17%. Finally, sensitivity analysis is carried out to examine the effect of changes in the trigeneration Pareto optimal solutions and the unit cost of products to the important economic parameters, such as interest rate, fuel cost, system operation period, and construction period.

Abstract Optimizing heat transfer for internal combustion engines requires application of advanced development tools. In addition to experimental method, numerical 3D-CFD calculations are needed in order to obtain an insight into the complex phenomenas in-cylinder processes. In this context, fluid flow and heat transfer inside a four-valve engine cylinder is modeled and effects of changing engine speed on dimensionless parameters, instantaneous local Nusselt number and Reynolds number near the surface of combustion chamber are studied. Based on the numerical simulation new correlations for instantaneous local heat transfer on the combustion chamber of SI engines are derived. Results for several engine speeds are compared for total heat transfer coefficient of the cylinder engine with available correlation proposed by experimental measurements and a close agreement is observed. It is found that the local value of heat transfer coefficient varies considerably in different parts of the cylinder, but it has equivalent trend with crank angle position.