This work presents an application of lattice Boltzmann method (LBM) for solidification of phase change material (PCM) within a rectangular finned container. To do this, an implicit lattice Boltzmann ...method is applied into two rectangular containers. At first the problem of PCM solidification within a rectangular fined container with constant wall temperatures is solved and compared with available approximate analytical results. The LBM results are compared with results of finite volume method (FVM), and then it was used to analyze accuracy condition for presenting the analytical solutions. Second, the LBM is used to obtain the temperature distribution through the composite plane wall containing rectangular PCM container with convective boundary conditions. The effect of PCM within the composite plane wall is studied as a heat source during freezing. It is shown that locating the PCM container inside the wall could efficiently prevent the heat losses, when it is exposed to the cold air flow, and the rate of solidification is extremely controlled by containers material. Also, it is confirmed that the current LBM effectively saves the running time several times compared to finite volume method.
•LBM is used to simulate the PCM solidification inside the rectangular container.•The maximum required time for freezing the PCM occurs at the aspect ratio of 0.5.•Analytical solution overestimates the required time for PCM solidification.•Maximum analytical overestimation occurs at aspect ratio of 0.5.•Heat loss decreases by locating the PCM inside the composite plane wall.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The main aim of this work is devoted to present a numerical analysis for studying effect of splitter on the hydro-thermal behavior of a pin fin heat sink. The concept of application of pins in the ...heat sinks arises from increasing the heat transfer area to reach maximum rate of heat losses in a limited space. On the other hand, flow separation behind the pin will enhance the pressure drop. To avoid or weaken the flow separation and reduce the pressure drop through the heat sink, a thin plate is located on the back of the pin. Two common pin fin heat sinks with circular and square pin shapes are compared together with and without splitters. Results showed that the use of splitter improves the hydro-thermal performance of both circular and square pins, so that the maximum improvement will be occurred for the case of Q=10W and V=4.5m/s. Results indicates that for circular pin fin heat sink with splitter pressure drop reduces by 13.4%, thermal resistance decreases by 36.8% and profit factor grows by 20%. Also for square pins the same results of 8.5% reduction for pressure drop, 23.8% reduction for thermal resistance and 14% increase in profit factor are observed. Also reliability analysis showed that for low-frequency and bipolar power transistor, the number of failure is reduced for circular and square splitter pin fin heat sinks.
•This paper presents a new kind of heat sink using splitter behind pin fins.•Splitter locating behind the pin-fin reduces thermal resistance and pressure drop.•Splitters streamline the flow around the pins, so decrease driven power, the operation costs and energy consumption
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
► Numerical analysis on the performance of a thermal storages as free cooling system. ► Employing multiple PCMs to enhance heat transfer rate in thermal storages. ► Using an effective heat capacity ...method, the phase change parameters are determined. ► The effect of the slabs size and air channel thickness on COP is investigated.
As demand for refrigeration and air conditioning increased during the last decade, the opportunities have expanded for using thermal energy storage (TES) systems in an economically advantageous manner in place of conventional cooling plants. Many cool storage systems use phase change materials (PCMs) and achieve peak load shifting in buildings. This work presents numerical investigations of the performance enhancement of a free cooling system using a TES unit employing multiple PCMs. The TES unit is composed of a number of rectangular channels for the flowing heat transfer fluid, separated by PCM slabs. Using the effective heat capacity method, the melting and solidification of the PCM is solved. The forced convective heat transfer inside the channels is analyzed by solving the energy equation, which is coupled with the heat conduction equation in the container wall. The effect of design parameters such as PCM slab length, thickness and fluid passage gap on the storage performance is also investigated using an energy based optimization. The results show that a system which can guarantee comfort conditions for the climate of Tabriz, Iran has an optimum COP of 7.0. This could be achieved by a combination of CaCl2·6H2O with RT25 with the optimum air channel thickness of 3.2mm, length of 1.3m and PCM slab thickness of 10mm.
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GEOZS, IJS, IMTLJ, KISLJ, NUK, OILJ, SAZU, SBCE, UL, UM, UPCLJ, UPUK
► Simplified analytical model for solidification of PCM in shell and tube finned storage. ► We formulate energy equation in the presence of a heat thermal fluid on the walls. ► We compare ...solidification time for PCM in cylindrical shell and rectangular storages. ► We investigate the effects of inlet air temperature on thermal storage performance. ► We investigate the effects of air flow rate on thermal storage performance.
Due to the advantages offered by latent heat thermal storages, phase change materials (PCM) are used in numerous applications including building air conditioning systems. In this study, the development is reported of an approximate analytical model for the solidification process in a shell and tube finned thermal storage. A comparative study is presented for solidification of the PCM in cylindrical shell and rectangular storages having the same volume and heat transfer surface area. The PCM solidification rate in the cylindrical shell storage is found to exceed that for the rectangular storage. The effects are investigated of heat thermal fluid (HTF) inlet temperature and flow rate on thermal storage performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•An air-conditioning system integrated with a LTES is analyzed thermoeconomically.•A novel semi-analytical solution method for phase-change process is proposed.•The proposed and numerical results are ...compared with one another.•The results obtained from proposed and numerical methods are in good agreement.•The performances of the overall system are compared for three types of PCMs.
An air-conditioning system equipped with a latent thermal energy storage is analyzed thermodynamically and economically. A new solution method is introduced and used to solve the phase change problem. In addition, based on the 2-D modified enthalpy method, a numerical solution is carried out. The numerical results are validated using the existing experimental ones. The results obtained from the proposed method are compared with those of the numerical ones for some effective parameters. A maximum difference of 2.7% is obtained between them. By applying the proposed method, the effects of parameters such as the inlet and outlet air temperatures on the operating parameters including the coefficient of performance, exergy efficiency, total product unit cost, total investment cost, phase change material (PCM) slabs’ thickness, and length are investigated. The thermodynamic and economic performances of the overall system are compared for three types of PCMs with identical melting point temperatures, namely; RT27, S27 and PureTemp27. It is shown that the total product unit cost decreases as the air temperature difference in passing through the air-conditioning system increases. This occurs in spite of the increment of investment cost because of the thermal efficiency enhancement. In the proposed method, the desired output can be obtained at any time and location with no need to previous time steps and other discretized points. This improves the optimization process for the system. The results show that, compared to the other PCM types, the PureTemp27 brings about better thermodynamic and thermoeconomic performances for the system.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A novel combined cooling/power cogeneration system, including a modified Kalina cycle and an absorption refrigeration cycle is proposed. The cycle uses ammonia-water as working fluid and is driven by ...geothermal energy. The cycle is flexible for producing different ratios of power to cooling capacities. It is observed that the ambient temperature and the split mass flow ratio at the condenser exit play major roles on the system performance. The results show that in summer time a better economic performance and also a higher cooling to power ratio is achieved. It is also seen that the overall system exergy efficiency is maximized at a specific value of the split mass flow ratio and that the total product unit cost is minimized at some specific values of the generator temperature and split mass flow ratio. The system performance is optimized considering the exergy efficiency and total product unit cost as criteria. The optimization results show that when the criterion is selected as exergy efficiency, a better economic performance is also achieved for the system. It is found that the highest exergy efficiency of the system is achieved as 33.61% and the lowest total product unit cost is obtained as $ 39.93/GJ.
•A novel combined cooling and power cogeneration system is proposed.•Exergeoconomic analyses are performed in different seasons.•Exergy efficiency is maximized and unit cost is minimized at different seasons.•Effects on system performance is investigated of key parameters in proposed cycle.•Higher condenser temperature is in favor of cooling and against power outputs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, a matrix based method is considered for solving a class of 2DNVFIEs (Two Dimensional Nonlinear Volterra-Fredholm Integral Equations) of the second kind based on the operational Tau ...method. We developed this method with arbitrary polynomial bases (Standard, Legendre or Chebyshev polynomials) to obtain numerical solution of these equations. Some theoretical results are given to simplify and reduce the computation costs. In addition,
L
2
-convergence of the proposed method is proved when the given data are sufficiently smooth. Finally, some numerical examples are given to illustrate efficiency and accuracy of the proposed method.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this paper, we will give some results for developing the two-dimensional differential transform (TDDT) for double integrals. Then the TDDT method will be developed for solving a class of ...two-dimensional linear and nonlinear Volterra integral equations. We also give some examples to demonstrate the accuracy of the method.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
It has been widely known that for complicated beam-like structures with various types of attachments and/or discontinuities analytical techniques are not always applicable. In this paper, a very ...efficient numerical method based on the Tau method is proposed to tackle the mentioned problem. A general form of the linear vibrational eigen-equation, based on the Euler–Bernoulli bending theory, together with its boundary conditions and continuity equations is considered. The problem is then formulated using a segmented form of the operational Tau method which is called the segmented operational Tau method. To investigate the reliability and accuracy of the proposed method some vibrational problems are solved and compared with the analytical solutions providing the exact frequencies and mode shapes. For a complicated case of a non-uniform beam with various types of attachments, since there was no analytical solution, results are validated with the finite element method. This paper has provided a platform for solving free vibrational problems of many complicated constrained systems through a very simple, highly accurate technique.
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NUK, OILJ, SAZU, UKNU, UL, UM, UPUK
Thermal energy storage units that utilize phase change materials have been widely employed to balance temporary temperature alternations and store energy in many engineering systems. In the present ...paper, an operational approach is proposed to the Tau method with standard polynomial bases to simulate the phase change problems in latent heat thermal storage systems, that is, the two-dimensional solidification process in rectangular finned storage with a constant end-wall temperature. In order to illustrate the efficiency and accuracy of the present method, the solid-liquid interface location and the temperature distribution of the fin for three test cases with different geometries are obtained and compared to simplified analytical results in the published literature. The results indicate that using a two-dimensional numerical approach can predict the solid-liquid interface location more accurately than the simplified analytical model in all cases, especially at the corners.
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FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UL, UM, UPUK
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