The gap between production and consumption of energy is growing and non-renewable fossil fuels are discharging and its pollution is growing rapidly. Therefore natural resources are researched. Efficient utilization of these resources can only be done through thermal energy storage system. The most economic system of UTES is storage in aquifers. In this system two wells are drilled in to permeable under ground water and injection and withdrawal of cold and hot water is performed through these wells. The system which is studied here is composed of a single well of radius R. Water is injected in to the aquifer at a constant rate Q at temperature that is warmer than the natural temperature of the aquifer, . The continuity and heat transfer equations are developed in cylindrical coordinate using symmetric formulation. The porous medium is assumed to be homogeneous. The longitudinal and transversal thermal dispersion influence on the effective thermal conductivity. Free convection phenomenon is disregarded and none of the physical properties are dependent on temperature. The target is to achieve the temperature distribution. The ratio of the extracted enthalpy to the stored enthalpy is defined as the system thermal efficiency. It is observed that temperature of injection of water does not influence the thermal efficiency but increasing the flow rate and porosity factor and decreasing the thermal dispersion, increase the thermal efficiency. In periodic injection thermal efficiency is higher than continuous injection and then storage in aquifer.
