نشریه مهندسی مکانیک ایران
سال بیست و دوم شماره 4 (پیاپی 61، زمستان 1399)

In this article an adsorption refrigeration system with Activated Carbon/Methanol as adsorption working pair placed in a parabolic trough solar collector have been studied. A one dimensional numerical model based on heat and mass transfer equation and adsorption thermodynamic within the porous medium is developed. Equations has been discretized through fully implicit finite difference method in cylindrical coordinate. Discretized equations is written in FORTRAN program. The simulated code has been validated by comparison via experimental work and former numerical results. The code at each point computes bed temperature, pressure and adsorbed mass of refrigerant inside the adsorbent bed. In additional effect of some parameters such as bed diameter, solar irradiance, cooling source temperature, evaporator and condenser temperature and pressure has been investigated. Effect of these parameters on the refrigeration adsorption system has shown through variation of the solar coefficient of performance (COPS) and specific cooling power (SCP). Under the operating conditions of evaporation temperature T_ev=0 ℃, condensing temperature T_con=30 ℃ and adsorption temperature T_ads=25 ℃ according to the experimental model, COPS and SCP are found to be 0.12 and 45.6 w1kg-1 respectively.

In the present numerical study, the effect of conical obstacle on heat transfer and pressure drop in turbulent flow inside a tube is investigated. Although the effect of different stationary obstacles on heat transfer and pressure drop has been investigated so far, the use of the rotating obstacle is a new issue. Rotating obstacles create powerful rotating flow and increase flow turbulence and vortices through the effective displacement of the fluid particles affects the heat transfer rate. Therefore, the present research investigates the effect of cone obstacle rotation speeds of 25, 50, 75, 100 on the flow characteristics and thermal performance coefficients of the shell-and-tube heat exchanger in the Reynolds number range 4000 to 24000. The results show that for all Reynolds numbers in rotational speed 50 rpm, the heat transfer coefficient reaches its maximum value, and no significant change is observed, with increasing rotational speed. Heat transfer is about 2.2-2.9 times increased compared to smooth pipe and the thermal coefficient performance is in the range of 0.5-1.8. The maximum thermal performance coefficients, using rotating obstacle in comparison to the obstacle stationary one, is 120%.

In the current paper thermal buckling of cylindrical shells reinforced with GPL graphene sheets subjected to uniform temperature rise is investigated. Nanocomposite shell reinforced by graphene platelets (GPLs). It is assumed that the GPLs are randomly oriented and uniformly distributed along in each layer. Variation of volume fraction from each layer to other is based on the several functionally graded types. The effective material properties are obtained using the Halpin-Tsai rule. The equilibrium equations are obtained considering the first order shear deformation shell theory, Donnell assumption, and Von-karman type of geometrical nonlinearity. The linear obtained stability equations are discrete utilizing the generalized differential quadrature procedure along the shell domain. Then the eigenvalue problem is solved and critical buckling temperature is calculated. In the section of numerical results, after validation, the effects of geometric parameter, boundary conditions, mass fraction of GPL, and also type of functionally graded on the stability of structure are studied.

In this study the free convection heat transfer of a nanofluid, including water and nanoparticles suspended in a square cavity is simulated numerically for a laminar flow. Open source framework i.e. OpenFOAM was used to develop the equations and make changes in the desired terms such as relative velocity between the nanoparticles and the base fluid. To achieve the purpose of the research and to ensure the accuracy of the numerical algorithms used in this framework, at first the free convection inside the cavity was investigated using two-phase mixture model and the results of the present study were compared with the results presented in the literature. Then, with the help of existing mathematical equations, important parameters in simulating the forces acting on nanoparticles in the free convection inside the cavity were studied and as a result, the forces that had a significant impact were selected as the most important and corrected relative velocity was entered in the continuity, momentum, heat transfer and continuity equation of the second phase (nanoparticles) as a parameter called JP. This simulation was performed using the PIMPLE algorithm (SIMPLE + PIZO). To consider free convection, nanofluid’s density changes with Boussinesq relationship. The mixture two-phase model has used for modeling with higher speed and more accuracy and also effective thermophysical properties of nanofluid, related to JP parameter have been used in order to increase the accuracy of work. As a result, the effect of these forces on different conditions was investigated.

Rising fuel prices and limited fossil fuels have motivated scientists to find some new methods to recover the heat dissipation from the internal combustion engines exhaust gases in recent decades. Only 30 percent of the fuel energy is converted to the useful work and the rest of it is lost through the exhaust gases of the engine and the engine coolant system. In this paper this issue has been considered and hence two different configurations of organic Rankine cycle with two operating fluids R113 and R123 have been designed and energy and exergy analysis have been applied in order to recovering the heat dissipation from the six cylinder internal combustion engine exhaust gases (in full load operating mode). Next, the performance of these cycles has been optimized by sensitivity analysis to find the optimum working temperature and pressure of these two cycles. the results shows the optimum points of the system which is calculated by the mention technique.

In this paper, the effect of shape and aspect ratio of wall on natural convection heat transfer of non-Newtonian fluid with power law model within two-dimensional enclosure in the presence of a uniform magnetic field by lattice Boltzmann method (LBM) is investigated. The left wall is at a constant hot temperature, while the right wall is kept on cold constant temperature and other walls are considered adiabatic. In this simulation, the flow field and temperature are calculated by simultaneously solving the flow and temperature distribution functions. The effect of various parameters such as Hartmann number, aspect ratio, different shape of the wall and power index of non-Newtonian fluid is investigated. The results show that increasing power index, aspect ratio and Hartmann number decrease the average Nusselt number. Also, the highest amount of heat transfer is generally associated with the case of a triangular wall. In addition, increasing the power index reduces the effect of the magnetic field.

In design and analysis of total site of heat and power cogeneration, how to arrange equipment has a unique importance in production process. Due to high cost of turbines setting up and fuel demand for power plants that generates required steam for turbines, suitable design of these arrangements can save or in front of it create unjustified extra costs. In this paper, using an Iterative Bottom-to-Top Model (IBTM) which is a new modified cogeneration targeting method, cogeneration potential is estimated and fit to it, temperatures of steam levels, power generation, fuel and steam flows and the amount of boiler heat load are calculated. First steam turbines arrangement between steam levels for case study is designated and if required power is not provided in total site by steam turbines, use of gas turbine or condensing turbine to generate additional power are checked. The results of the research showed that the selected scenario of back pressure steam turbines arrangement beside gas turbine system, has maximum exergy efficiency, minimum exergy destruction and minimum total capital cost rate and exergy destruction cost rate. Finally, mixed use of back pressure steam turbines beside gas turbine system, were suggested as the best arrangement from an exergoeconomic approach.

Plate heat exchangers are one of the new ways of exchanging heat energy between two or more fluids at different temperatures.In this paper the hydraulic and thermal performance of a new design of a plate heat exchanger using simulation and laboratory methods is investigated. In the proposed plate heat exchanger design, first the special geometry including the proposed curved Chevron pattern for the heat transfer zone in the plates is introduced.The results of this proposed plate heat exchanger are evaluated by laboratory method with M6B plate heat exchanger. The simulation and laboratory results show that while maintaining the heat efficiency of the converter, the pressure drop is significantly reduced. This significant reduction in pressure drop of the proposed model leads to a reduction in the number of plates and savings in raw material consumption, reducing the capacity and energy consumed by the pump for fluid transfer, production time and installation space.