This paper discusses two advanced heat pipe mechanisms that have the potential of achieving heat flux capabilities over 300W/cm2. The mechanisms include Combined Pulsating and Capillary Transport (CPCT) and Graded Wick Transport (GWT) mechanisms. Theoretical models were developed to predict the performance of the advanced heat pipe mechanisms. Prototype heat pipes were tested to verify the heat flux capability of the mechanisms and the accuracy of the theoretical models. The advanced heat pipe mechanisms are feasible approaches to removing increasing heat dissipation densities in electronic equipment.
The two phase closed thermosyphon are highly efficient heat transfer element. At present, however, actual applications are mostly limited for thermosyphon using smooth tube as its container. In the present work, a corrugate tube was used as its container and distilled was used as the working fluid. The corrugated container is flexible and it has several features to allow the thermosyphon to be used in a wide range of application. In the first step of our study , the influence of inclination angle and fluid charge ratio on the heat transfer performance were studied. A useful formula to calcurate the heat transfer coefficient in the evaporator accounting for the effect of the liquid charge and inclination angle has been derived. In the second step, the condensation heat transfer coefficient is proposed as a function of the modified Nusselt theory by three parameters: the Lockhart-Martinelli parameter, inclination angle of the thermosyphon and fill ratio of the working fluid.
Air-side heat transfer enhancement mechanisms in three types of interrupted surfaces: parallel-plate, louvered and convex-louvered fins in compact heat exchangers are analyzed. It is found that boundary layer restarting is the major enhancement mechanism in all these interrupted surfaces. Vortex shedding can be generated at sufficiently high Reynolds numbers. However, vortex shedding may or may not provide additional enhancement in heat transfer, depending on the type of interrupted surface employed. Effects of varying geometric parameters have been studied in these interrupted surfaces. In the parallel-plate fins, vortex shedding occurs at much lower Reynolds numbers in the inline and one offset geometry than that in another offset geometry. Different flow characteristics in the louvered fins have been analyzed and the important geometric parameters such as fin pitch to louver pitch ratio have been identified. This study also shows that other mechanisms such as flow impingement seen in convex-louvered fins can provide additional heat transfer enhancement. However, the enhanced heat transfer is usually associated with increased pressure drop penalty, especially, with the more aggressive enhancement mechanisms.
In the present work, the possibility of spent nuclear fuel rejuvenation in fusion reactors is investigated for different fuels and coolants. Cumulative Fission Fuel Enrichment (CFFE) and neutronic performances of the (D,T) driven hybrid blankets, fueled with U308 and UF4, are investigated under first wall load of 5 MW/m2. Fissile fuel zone is considered to be cooled with three coolants, flibe (Li2BeF4), Natural Lithium (Li) and Eutectic Lithium (Li17Pb83) respectively. In the fuel zone is considered to be cooled with the different coolants mentioned above with volume fraction of 45.5%, ε = 1:1, for each coolants. Again, the behavior of the fuels mentioned above are observed during 48 month for discrete time intervals of Δt =15 days and by a plant factor of 75%. At the end of the operation time, calculations have shows that (CFFE) values have varied between 4.51% and 8.49% depending on the fuel and coolant type. The best enrichment performance is obtained in Li2BeF4 coolant blankets for each fuels. CFFE reach maximum value (8.49%) in UF4 fueled blanket (in Row# 1) after 48 months. The lowest CFFE value (4.51%) is in U3O8 fueled blanket (in Row# 8) and Natural Lithium coolant at the end of the operation period. So, the enrichment would be sufficient for LWR reactor. The best Tritium Breeding Ratio (TBR), 1.5054, is obtained in U308 fueled blanket with Eutectic Lithium (Li) coolant. At the beginning of the operation, TBR values were 1.2942 in U3O8 fueled blanket 1.2175 in UF4 fueled blanket. At the end of the operation, TBR reach 1.5034 in U308 fueled blanket and 1.4510 in UF4 fueled blanket.
Heat transfer in a porous medium subjected to the effect of internal heat sources is considered. Macroscopic equations are obtained from the method of volume averaging. Both local equilibrium and non-local equilibrium conditions are considered. It is shown that homogeneous sources can simply be taken into account by introducing averaged values in the macroscopic equations. The heterogeneous source term corresponding to heat sources at the interface between the two phases requires a different treatment. The average source is distributed in the two macroscopic equations of the local non-equilibrium model through a distribution coefficient, which is given by a local "closure problem". This closure problem is solved numerically for different representative unit cells, and for different values of the thermal conductivity ratio and Peclet number. Numerical experiments are performed to test the theory, and results show a good agreement between theoretical and "experimental" predictions.
Experiments on high-enthalpy water blowdown through a short converging nozzle were preformed to measure the critical discharge flowrate under different stagnation conditions. Two-phase critical flow models were reviewed and three of the simple predictive models were described. The test results were compared with the simple predictive models. It was found that the Henry-Fauske Model provided the best overall agreement with the experimental data. Photographic studies of the two-phase flashing jet revealed the presence of three distinct regions in the jet. These regions are consistent with the jet geometry proposed in previous studies.
In the present paper work is reported which was carried out at the Technical University Hamburg-Harburg (TUHH) in connection with the retrofitting project of the sewage sludge incinerator of the city of Ulm. In order to keep the emission limits under a variety of operating conditions different primary measures of emission control were examined at TUHH's pilot-scale bubbling fluidized bed combustor (150 mm diameter, height of combustion chamber 9m). In the first phase of the investigations it was shown that the emissions of the pollutants CO and NOx measured at the test rig compare well with those measured at the existing large-scale combustor if operating conditions were chosen according to similarity rules. The main part of the work consisted then of a systematic investigation of the various means to influence the combustion process and the pollutants generating and reducing reactions inside the combustion chamber. In particular, the influences of predrying of the sludge, excess air ratio, staging of the combustion air and flue gas recirculation were investigated. Furthermore, the influence of a mixing element in the freeboard on the emissions was examined. The results which are described in detail in the paper have given valuable advice for the design of the new incinerator. The knowledge of the various influences and interdepences will furthermore allow the operator to choose suitable measures to minimize the emissions and keep the regulation limits under all possible operating conditions.
