Hybrid semi analytical method for geothermal U shaped heat exchanger

In this paper, convective-conductive heat transfer processes between the all components of geothermal borehole heat exchanger (BHE) such as pipe-in, pipe-out and grout have been studied. A set of coupled partial differential equations subjected to general initial and boundary conditions are governed to this problem. Modified Homotopy perturbation method (MHPM) is a hybrid of discrete Fourier Transform, spectral analysis and Homotopy Perturbation Method that is developed in order to solve the partial differential equations of geothermal borehole systems. The results of MHPM are compared with the numerical solution for validation and, furthermore, the effectiveness and accuracy of the applied method have been shown. Keywords: Borehole heat exchanger, Heat conduction-convection, Discrete Fourier transformation, Homotopy perturbation metho

Investigation of convective-conductive heat transfer in geothermal system

Geothermal energy is one of the well-known types of renewable energies that can be considered as a promising alternative to fossil fuels in order to mitigate the CO2 emission in atmosphere. Geothermal energy has recently been used for heating and cooling systems in many countries of the world. Therefore, studying such kind of energy seems important and necessary. This paper studies the heat transfer processes in a borehole heat exchanger (BHE). The flow of fluid in a BHE has been considered with different geometries and heat transfer processes are modeled numerically and in a finite volume method through convection and conductivity. First, a single U-shaped BHE was modeled and its thermal properties were investigated and then other geometries were studied to obtain the best geometry and heat transfer efficiency. In order to increase the heat transfer in the inner part of the pipes, the fin with the given specifications was used and the modeling was carried out and the thermal parameters were compared for three BHE’s with different geometries. In the final part, optimization results are presented, and the interaction of parameters on the Nusselt number and friction coefficient have been investigated. Also, the desirability of optimization and reliability is given to the results presented in percentage terms. Comparing the results of this article with the results of previous research shows a very good agreement and therefore the applied method is reliable and accurate. Keywords: Borehole heat exchangers, Numerical method, Heat transfer processes, Geothermal energy, Finite volume analysi

Effects of Cu and Ag nano-particles on flow and heat transfer from permeable surfaces

Consideration is given to flow and heat transfer of nano-fluids over a permeable flat plate with convective boundary condition. The governing partial differential equations are transformed into ordinary differen- tial equations using similarity solutions, before being solved numerically. Two types of nano-fluids, Cu– water and Ag–water are considered. The effects of nano-particles volume fraction, the type of nano-par- ticles and permeability parameter on skin friction and convection heat transfer coefficient are studied and discussed. It is shown that the increment in skin friction is a considerable drawback imposed by Cu–water and Ag–water nano-fluids, especially in case of injection. In the cases of injection and imper- meable surface, increasing the nano-particles volume fraction results in augmentation of convection heat transfer rate. However, in the case of suction, adding Cu and Ag particles reduces the convection heat transfer coefficient at the surface in spite of thermal conductivity enhancement imposed by the nano- particles