A two-dimensional computational model has been developed as a pilot study for the multidimensional simulation of fixed bed underground coal gasification (UCG). The analysis is based on the finite element method and incorporates a moving boundary algorithm to model the permeation linked vertical well in a forward gasification mode. In order to account for the motion of the combustion front with time, an immobilization transformation of coordinates technique is introduced in the finite element formulation. A numerical case study is included to illustrate the capability of the model. Predictions on temperatures, gas composition, pressure, and coal consumption in space and time are possible by using this model.

The core cooling of upward flow MTR pool type Research Reactor (RR) at the later stage of pump coast down is experimentally handled to clarify the effect of some operating parameters on RR core cooling. Therefore, a test rig is designed and built to simulate the core cooling loop at this stage. The core is simulated as two vertical channels, electrically heated, and extended between upper and lower plenums. Two elevated tanks filled with water are connected to the two plenums. The first one constitutes a left branch, connected to the lower plenum, and is electrically heated to simulate the core return pipe. The second one constitutes the right branch, connected to the upper plenum, and is cooled by refrigerant circuit to simulate the reactor pool. Channel coolant and wall temperatures at different power and branch temperatures are measured, registered and analyzed. The results show that at this stage of core cooling two cooling loops are established; an internal circulation loop between the channels dominated by the difference in channel's power and an external circulation loop between the branches dominated by the temperature difference between branches. Also, there is a double inversion in core flow, upward-downward-upward flow. This double inversion increases largely the channel's wall temperature. Complementary safety analysis to evaluate this phenomenon must be performed.

In this study, a refrigeration system developed by phase change material, PCM, is compared to a conventional refrigerator. Equal thermal loads (i.e. water) are gripped by the evaporator cabinet at different height levels apart from the evaporator surface. In the modified refrigerator, different PCMs are attached to the bottom side of the stored products. Then a comparison between products of the conventional and modified refrigerator is held using multiple parameters such as: minimum approachable temperature and temperature fluctuation during cyclic operation. While, period factor and heat recovery gained are investigated at planned power outage intervals. The 01involved PCMs types are (i.e. C-18, RT-9, cooler shock) while paring both of (RT-9 and C-18) is developed. Tests performed at different heights with the lower evaporator surface as the reference point show that RT-9 PCM achieves the maximum net energy saving ratios of 23% at dimensionless heights of H=0.25 and 25% at H=0.375.

In an attempt to understand the built-up of natural circulation in MTR pool type upward flow research reactors after loss of power, an experimental test rig was built to simulate the loop of natural circulation in MTR reactors. The test rig consisting of two vertically oriented branches, in one of them the core is simulated by two rectangular, electrically heated, parallel channels. The other branch simulates the part of the return pipe that participates in the development of core natural circulation. In the first phase of the work, many experimental runs at different conditions of channel's power and branch's initial temperatures are performed. The channel's coolant and surface temperatures were measured. The measurements and their interpretation were published by the first three authors. In the present work the thermal hydraulic behavior of the test rig is complemented by theoretical analysis using RELAP5 Mod 3.3 system code. The analysis consisting of two parts; in the first part RELAP5 model is validated against the measured values and in the second part some of the other not measured hydraulic parameters are predicted and analyzed. The test rig is typically nodalized and an input dick is prepared. In spite of the low pressure of the test rig, the results show that RELAP5 qualitatively predicts the thermal hydraulic behaviour and the accompanied phenomenon of flow inversion of such facilities. Quantitatively, there is a difference between the predicted and measured values especially the channel's surface temperature. This difference may be return to the uncertainties in initial conditions of experimental runs, the position of the thermocouples which buried inside the heat structure, and the heat transfer package in RELAP5.

The global energy and environmental issues are promoting the development of innovative energy solutions. Thermoelectric generators (TEGs) are regarded as a promising alternative to conventional energy technologies. TEG is a device that converts thermal energy directly into electric power by exploiting Seebeck effect. It is essential to understand the behavior of thermoelectric devices during both thermal transient and steady state to accurately simulate and design complex and dynamic thermoelectric systems. So a comprehensive model for simulating the dynamic TEG performance is developed, taking into consideration all the thermoelectric effects (Seebeck, Peltier and Thomson), in addition to Joule heating and Fourier heat conduction. Additionally, the effects of temperature-dependence of thermoelectric materials are accounted. Computational results are retrieved using "MATLAB" software. To verify the integrity of the modeling processes, the predicted results are compared with data obtained from the experimental evaluation. It is found that the outcomes of the experimental analysis validated the accuracy of the developed model and the possibility to be used as a simulation tool. The dynamic performance characteristics of a TEG is experimentally studied under different operating conditions. The effect of input heat rate and the influence of utilizing extended surfaces (fins) on both transient and steady state performance of a TEG are experimentally investigated. The variation in the temperature of the TEG hot and cold sides in addition to the output voltage is taken as a denotation of the performance characteristics. Input heat rate of 15.0 W, 17.5 W, 20.0 W, 22.0W and 25.0 W are applied to the TEG hot side. Free air convection is the utilized for heat dissipation from the TEG module through the cold side. From the experimentation, it can be deduced that increasing the input heat rate provides higher temperature difference across the module sides leading to higher power output. Additionally, using fins to aid heat dissipations enhanced the TEG performance by lowering the temperature of cold side and increasing the temperature difference across the module. The experimental data obtained are compared with the data available by the TEG module manufacturer and excellent agreement is obtained.: ‫الملخص‬