A generalized thermodynamic model is developed to describe combined cooling, heating, and power generating systems. This model is based on reversible power generation and refrigeration devices with practical, irreversible heat exchanger processes. It provides information on a system’s performance and allows easy comparisons among different systems at different loading conditions. Using both the first and second laws as well as the carbon dioxide production rate allows one to make a first-order system assessment of its energy usage and environment impact. The consistency of the exergy destruction rate and the first law performance ensures that the thermodynamic system boundaries are correctly and completely defined. The importance of the total thermal load to the required power ratio (HLRP) as a scaling parameter is demonstrated. A number of trends for limited conditions can be delineated even though the reported results confirmed that generalized trends are not identifiable because of the systems’ complexities. The results demonstrate that the combined vapor compression∕absorption refrigeration has higher first law utilization factors and lower carbon dioxide production rate for systems with high refrigeration to total thermal load ratios for all HLRP values. Fuel cell systems outperform engine systems for large refrigeration load applications. An illustration of combining these results to an economic analysis is presented.
The thermal performance of a graphic module on graphic card is theoretically and experimentally investigated. Unlike prior benchmark studies, this study involves a practical electronic device operating in a real software environment. The temperatures at five locations on the module and at one point on the board are measured as a function of time during the operation of a series of computer games. The theoretical model is developed using Flotherm to simulate the transient thermal response. There is close agreement from 3% to 10% between the numerical steady state case prediction and test data. The calculated transient trends using Flotherm model closely agree with experimental results and demonstrate the rapid increase in temperature as the number of module operations increases during the games. The results for the maximum temperature are directly linked to the software operation and exhibit a superposition type behavior in which the observed maximum operating temperature can exceed that estimated by steady state conditions. As expected, the results demonstrate that a carefully constructed thermal simulation can accurately predict the thermal response of a module under actual operating conditions.
Many regions in the United States, especially in the Northeast coastal and Southern California regions, and in arid parts of the world are facing fresh water shortages while having access to salt or brackish water. At the present time, the reverse osmosis process is the most prevalent means of converting salt to fresh water. However, as energy prices continue to climb there is evidence that solar desalination may provide a more economical and sustainable means of converting salt water to fresh water. The following paper presents a design of unique modular solar distillation units that provides a mobile, flexible installation for addressing water shortages. The solar still is designed such that the condensation surface is on the shady side of the unit while the absorbing surface is designed as a series of cascading trays that significantly increases the evaporation surface area. Fresh water is produced in this device from the condensate. This design is intended to convert sea water into fresh water that is introduced into a community’s reservoir system to augment traditional water sources. The analysis of the solar distillation unit is performed for the Boston, Massachusetts, USA over a day period in the months of December and July to determine performance at the maximum and minimum ambient conditions. The performance of the proposed device is comparable with reported solar stills in the literature, without optimizing the number of trays or heat rejection surfaces.
A relatively new form of alternative energy known as reverse electrodialysis (RED) appears to be one of the promising energy sources of the future. This technology harvests the energy stored in the salinity gradient between two different liquids, and converts it directly into electric power. This power is generated by pumping water through an array of alternating pairs of cation and anion exchange membranes called cells. An experimental system was designed and assembled with cells 61 cm × 16.5 cm. Along with having much larger dimensions than the prototype systems reported in the literature, the design has an adjustable number of cells in the stack, allowing users to obtain test results at a variety of settings. Comparing the output of systems with few cells to systems with a higher number of cells will help us to optimize the stack size in terms of hydrodynamic losses. Tests results have shown a voltage output of 1.98V, 83% of the predicted output. The current and power produced by the system did not meet theoretical output levels, but our group believes a redesign of the electrode rinse system will bring these values up to expectations. Future works will benefit from the learning experience.
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