Variable temperature effects on TEG performance

The present paper presents an experimental investigation of the variable temperature effects on the performance of a Thermoelectric Generator (TEG). In the conducted experiments, a sample TEG is analyzed by imposing variable temperature patterns on the cold side, while keeping the temperature uniformon the hot side. The achieved local temperature variations on the cold side has approximately been about 8% of the temperature difference between the hot and cold sides. The results reveal that the TEG performance shows some variation with the applied variable temperature patterns, which remains, however,rather small for the applied temperature variations. For achieving a more clear answer to the present question, further experiments need to be designed where more substantial temperature variations canbeobtained.

Thermoacoustic Refrigerator for High Temperature Gradient

Leakage of HFCs, thermal shocks to sensitive devices, moving mechanical components which in turn require more maintenance, are some of the cons of a conventional vapor compression system .The newest field in refrigeration overcoming such flaws is Thermoacoustic refrigerator (TAR), where the sound energy is used to generate a temperature difference which can be used for refrigeration. TAR are environment friendly, do not use any kind of refrigerants, and as the compressor and expander are not used, hence, its life is more than a conventional VCR. The objective is to obtain a substantial temperature gradient using a Thermoacoustic Refrigerator. The methodology is to choose the suitable material and design the prototype. A large part of this project is devoted to explore the different designs for thermo acoustic refrigerators, and select the optimum one for maximum utility. With the present system, it was possible to achieve a temperature difference across the stack of 14 K.

Protocol for disentangling the thermally activated contribution to the tunneling-assisted charge transport. Analytical results and experimental relevance

In this paper we present results demonstrating that the charge transport by tunneling in molecular junctions can exhibit a substantial temperature dependence.

Multi-Layer Thermionic-Tunneling Structures for Power Generation

A new method for power generation based on nano-engineered interface design with partially filled gap is proposed. The device combines electron thermionic emission and tunneling to enhance electron transport. Thermal radiation and tunneling contribute to heat transfer in the device, which can be minimized using selected materials. The largely reduced heat transfer coupled with use of multi-layer structures enable a substantial temperature difference between heat source and heat sink or two electrodes, thereby maximizing heat source utilization. Detailed analyses are provided for the solid device operating either as a power generator or as a cooler.

Moisture Variations in Brine-Salted Pasta Filata Cheese

A study was made of the moisture distribution in brine-salted pasta filata cheese. Brine-salted cheeses usually develop reasonably smooth and predictable gradients of decreasing moisture from center to surface, resulting from outward diffusion of moisture in response to inward diffusion of salt. However, patterns of moisture variation within brine-salted pasta filata cheeses, notably pizza cheese, are more variable and less predictable because of the peculiar conditions that occur when warm cheese is immersed in cold brine. In this study, cold brining resulted in less moisture loss from the cheese surface to the brine. Also it created substantial temperature gradients within the cheese, which persisted after brining and influenced the movement of moisture within the cheese independently of that caused by the inward diffusion of salt. Depending on brining conditions and age, pizza cheese may contain decreasing, increasing, or irregular gradients of moisture from center to surface, which may vary considerably at different locations within a single block. This complicates efforts to obtain representative samples for moisture and composition testing. Dicing the entire block into small (e.g., 1.5 cm) cubes and collecting a composite sample after thorough mixing may serve as a practical sampling approach for manufacturers and users of pizza cheese that have ready access to dicing equipment.

Modelling of Heat Conduction and Thermal Stresses in Multilevel Interconnects

The effects of metal Joule heating in interconnects were studied numerically. Particular attention is devoted to the multilevel nature of interconnects in modem microelectronic devices. Heat conduction analyses were carried out to quantify the temperature rise in structures composed of various levels of metal lines under different electric current densities. Two types of metallization (aluminum and copper) and two types of interlevel dielectric (silicon dioxide and polyimide) were considered. It was found that increasing the total number of metal level and/or switching the dielectric from silicon dioxide to polymer-based low-k dielectrics can cause substantial temperature increases, pointing out that interconnect Joule heating can become a major reliability threat in future applications. Thermal stresses induced by the nonuniform temperature field were also analyzed.

Air Temperature Rises in Compressor and Turbine Stator Wells

This paper considers the fluid dynamic principles determining the consequences of mainstream fluid ingressing to the comparatively shallow space between the rotor disc and the ring used in many designs of axial-flow turbo-machine, especially compressors, to support the stator blades at their inner ends. Windage power due to friction between this fluid and the bounding walls of this annular space, or ‘stator well’, can lead to substantial temperature rises in this region. The feasible range of flow regimes is first developed, especially as influenced by leakage through the internal seals beneath the stators separating adjacent wells. Using published data, on windage coefficients and the effects of geometry on the flow through the wells, very little of which has been obtained from truly representative flow conditions or geometries, calculations have been made to estimate the likely rises in temperature to be anticipated in realistic well designs. Leakage rates appear, not unexpectedly, to be crucial in determining these temperature rises, but the geometries of the system are little less critical, in particular the ratio of the outer to inner radiuses of the stator well and the outer peripheral clearances between rotor and stator surfaces. Leakage into a well from its adjacent neighbour is shown to lead to higher temperature rises downstream of the labyrinth seal and the possible effects of recirculation through stator wells from the mainstream boundary layer could be significant.