EE- Enerji Bilim ve Teknoloji Lisansüstü Programı

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http://hdl.handle.net/11527/197

Gözat

Yazar "Akhlaghi, Yousef Golizadeh" ile EE- Enerji Bilim ve Teknoloji Lisansüstü Programı'a göz atma
  • Öge
    Modeling The Temperature Behavior Of The Ground Source Heat Exchanger Systems
    (Energy Institute, ) Akhlaghi, Yousef Golizadeh ; Türeyen, Ömer İnanç ; 444203 ; Energy Sciences and Technologies ; Enerji Bilim ve Teknoloji
    Ground Source Heat Exchanger Systems (GSHES) are becoming more popular everywhere in the world. GSHES use pipes which are buried in the garden in order to extract heat from the ground. The heat can then be used to heat radiators, underfloor, swimming pools or to warm air heating systems and water in homes for several uses. Mixture of water and antifreeze circulates within the single or series of u tubes which are buried in the ground. Heat from the ground is absorbed by the circulating fluids and then by passes through a heat exchanger into the heat pump. The temperature of the ground remains approximately constant during the year. There are several different factors influencing the performance of the GSHES such as mass flow rate of circulating water, length of the u tubes, number of u tubes, number of boreholes, surface temperature, injection temperature, presence or absence of underground water flow, thermal conductivity of the fluid and formation, radius of u tube, radius of borehole, piping type, depth of operation, ground characteristics, capacity of heat pump system, size of system, building system, etc. Mathematical models that are used for modeling the performance of the GSHES are well established and have a significant role on studying the GSHES. These models usually consider conductive heat transfer for the formation and the convective heat transfer for the fluid circulating within the u tube. Also convective heat transfer is considered for the underground water flow. Underground water flow is one of the most common factors which occurs inside the earth. It can have positive and negative effects on the performance of the GSHES. Recently researchers have focused on studying the effect of underground water flows due to their significant effects. In this study, we have developed a numerical model in order to study the effect of underground water flow. Our model is based on solving the energy balance equation. This equation is treated in fully implicit manner so that it becomes highly nonlinear. Hence, one numerical method must be used in order to overcome the nonlinearity. The Newton Raphson procedure is used in order to solve the equation. Numerical derivatives are used in order to construct the Jacobian matrix. After solving the equation, in order to have trustable results we have verified our numerical model with one analytical model. In order to apply the same inputs and have the same situation in both numerical and analytical model or mimic the analytical model, we have to apply some simplicity in our numerical model. For instance, because temperature distribution using geothermal gradient is not considered in the analytical model, it is taken to be zero. We have used several cases in order to make sure the verification is completed. We have studied above-mentioned parameters in two radial and Cartesian systems. In the radial system we have studied the behavior of the produced water. Additionally, the effect of mass flow rate of the circulating water within the u tube have been studied. As a result, we saw that by increasing the mass flow rates from 0.01 to 100 kg/s the temperature profiles decline quickly to the value which is very close to the injecting water temperature that is 5ºC in this study. Furthermore, in the radial system, different initial temperatures have used in order to simulate the presence of underground water flow in the system. Since when underground water is present, it is normally cooler than the ground temperature. Mass flow rate of underground water flow is important too, so that the effect of mass flow rate of underground water is studied too. We have chosen two different mass flow rates in this case. Based on results, we saw that the effect of different initial temperature is significant. In the Cartesian system we have studied the effect of underground water flow. In this case, forth layer is chosen to bear the underground water flow so that the temperature of this layer is assumed to be 15 ºC. In this case, several mass flow rates are chosen for the underground water flow. Based on results we have concluded in the presence of underground water flow the temperature of the formation grids decrease less. This decrease become more efficient by increasing mass flow rate of the underground water. Furthermore, the overall increase for the temperature of the grid blocks can be seen due to the conductive heat transfer among the layers. In the final step, we have studied the effect of thermal conductivity. Value of thermal conductivity is one of the crucial parameters that could have significant effects on the performance of GSHES which is very common in the actual systems. Three different thermal conductivities have been chosen for the formation. Based on results, for the lower thermal conductivities the borehole cools the most because of little amount of heat transfer among the borehole grids and formation grids.