Mohammed Al-Khawaja

Numerical Solutions of Two Heat Transfer Limits of MFM Square Duct Flow Using MatLab Program

The heat transfer of a magneto-fluid-dynamics (MFM) laminar flow in an electricallyinsulated square duct subjected to two boundary condition limits of constant heat flux and constant wall temperature is examined numerically. The working fluid is electrically conducting fluid (i.e. liquid metal). The central finite difference scheme is used to discretize the governing equations and the resulting equations are solved by MatLab using the iterative Gauss-Seidel method. The solutions for these heat transfer limits, the constant temperature boundary condition (with non-linear energy equation) and the constant heat flux boundary condition (with linear energy equation) are compared with previous work done for ducts of circular cross section subjected to constant heat flux boundary condition. The results show that the circular duct with constant heat flux exhibits the highest heat transfer rate whereas the square duct with constant temperature has the lowest heat transfer rate.

Modified–Thermal Borehole Shear Test Device and Testing Procedure to Investigate the Soil-Structure Interaction of Energy Piles

The intermittent operation of heat pumps connected to energy piles causes cyclic variation of temperature in the pile and surrounding soil, affecting the soil-pile interaction in ways that have not been fully investigated or directly measured. The temperature variation and cycles produce expansion and contraction of the pile in both the axial and radial directions and affect soil properties. In this study, a fully automated modified–thermal borehole shear test (Modified-TBST) device was developed to measure the thermo-mechanical behavior of the soil-pile interface properties considering the effects of radial expansion/contraction and temperature variation and cycles. Unlike other devices, the developed Modified-TBST device is fully automated and capable of combining the effects of temperature cycles with radial expansion/contraction (displacement) cycles or separating their effects. This paper describes the testing device, including the control method for expansion/contraction displacement cycles, the calibration of the shear head under non-isothermal conditions, and the measured load and displacement controls during the shearing stage. Furthermore, the paper presents procedure recommendations for performing the soil-pile interface tests, simulating energy piles and presenting preliminary results of shear stress-vertical displacement (t-z curves), considering temperature and displacement effects.

Ground Response to Global Warming

Owing to the awareness of the impact of global warming, there has been a growing interest in studying the relationship between the climatic changes and human activities. An increased global mean air temperature leads to an increase of the ground temperature. Therefore the analysis of borehole temperature depth profile (BTDP) has become an accepted method for detecting the past climatic changes. Mathematical models have been suggested to simulate deviation of BTDP in order to detect the warming level and time elapsed since warming started. Unlike previous studies, the aim of the current study was to derive a new equation that gives the ground temperature increase in areas where the warming is identified. A comparison of the solution suggested in the current study with other solutions established in other studies shows excellent agreement. The suggested solution is characterized by the fact that it is more user-friendly compared to other solutions. Furthermore, the obtained solution was used to get a very simple expression for the heat retained by a column of earth during the warming event. In addition it was used to determine the average change of ground temperature over a particular depth. This average change of ground temperature is of great importance in the borehole system.

Combined Effect of Global Warming and Buildings Envelope on the Performance of Ground Source Heat Pump Systems

Heating and cooling systems as well as domestic hot water account for over 50 % of the world’s energy consumption. Due to their high thermal performance, ground source heat pump systems (GSHP) have been increasingly used to reduce energy consumption. The thermal performance of GSHP systems strongly depends on the temperature difference between indoor and ground operation temperature. This temperature difference is a function of mean annual air temperature and energy demand for heating and cooling over the year. The thermal load of a building, on the other hand is influenced by the thermal quality of the building envelope (TQBE) and outdoor temperature. Over the time, there is a change in heating and cooling load of buildings due to two reasons; improving the comfort requirements and outdoor temperature change. The overall aim of the current work is to study the impact of climatic changes in combination with TQBE on driving energy of GSHP. This was achieved by comparing the driving energy of the GSHP for different global warming (GW) scenarios and different TQBE. Under climate conditions of selected cities (Stockholm, Roma, and Riyadh), the current study shows that GW reduces the driving energy of GSHPs in cold climates. In contrast, GW increases the driving energy of GSHPs in hot climates. Also it was shown that buildings with poor TQBE are more sensitive to GW. Furthermore, the improvement of TQBE reduces the driving energy more in cold climates than in hot or mild climates.

Potential of Geothermal Energy for Electricity Generation in Qatar

There is general acceptance that climate change, which is the most important challenge facing humanity, is anthropogenic and attributed to fossil fuel consumption. Therefore, improving the performance of our existing energy systems and deploy more renewable energy resources is an urgent issue to be addressed. Geothermal refers to existing of heat energy in deep rock and sedimentary basins. This energy can be used to drive a power turbine to generate electricity. Traditionally, geothermal has been exploited in places with the plentiful hot water at relatively shallow depth. In the light of fact that ground temperature increases with the depth everywhere on the Earth, engineered geothermal systems (EGS) can be installed in any place to exploit the geothermal in generating energy. Unfortunately, the high exploration and drilling costs of boreholes is the main barrier to commerciality of EGS worldwide. In addition, there are technical problems associated with drilling big depth. In oil producing countries such problems can be addressed by utilizing whether active or abandoned oil or gas wells and, consequently, EGS can produce power at profit. The current study presents an analysis of a binary geothermal power generation system for commercial electricity generation in Qatar. For this purpose, two binary cycles are assumed the main difference between them is that the first one is air cooled while the other will be water cooled. The performance of the two cycles and the possibility of improvement has been shown. Economic analysis the power plant shows that the levelized costs of electricity is 3.6US¢/kWh and the pay-back time is less than 8 years.