A resonantly-coupled ��-Stirling (RCAS) cooler was designed and constructed. Tests on air and helium were performed with constant driving displacement over a range of frequencies. The effects of changing driving amplitude and charged pressure were studied. The use of stainless steel bellows in place of pistons eliminated the problem of piston seals and relaxed the construction tolerances. The fatigue life of the bellow is, however, a problem. The experimental optimization based on Taguchi methods was performed on regenerator mass, regenerator wire diameter, vibrating mass, and damping coefficient. Driven by a voice coil actuator, the characteristic phase shift of the Stirling cycle cooler was demonstrated where the hot-end displacement led the cold-end displacement. The 90�� phase shift was selected as the natural frequency. The pressure-volume diagrams for each working space were plotted and the indicated powers were determined. The compression powers in the hot and cold-ends show maximum values near the natural frequency. The mechanisms are different. At the hot-end where the displacement was kept constant, operation near the natural frequency gave a maximum pressure ratio and also maximized the compression power. The phase shifts in the cold-end were, however, relatively constant. The maximum pressure ratio and amplitude gave the maximum expansion power near the natural frequency. The expansion powers in the cold-end as indicators of cooling potential were approximately 2-4 watts for the air case, and 3-7 watts for the helium case. In both air and helium tests, the value of the parasitic losses reached 12 watts. The temperature difference developed across the regenerator is considered an indication of the cooling capacity. Good correlations were found between the indicated cooling capacity in the expansion space and the temperature difference. For a given size of cooler, the use of helium offered higher cooling capacity due to smaller pressure drop loss and smaller amplitude ratio. Higher cooling performance was also attained from helium at elevated pressures. / Graduation date: 1998

In United Arab Emirates (UAE), a huge proportion of electrical energy consumed in buildings is used to run air conditioning equipments. This is because UAE’s climate is characterized by very high ambient temperatures and high humidity, especially during summer periods. There is need to promote air conditioning systems that are run by renewable energy based power because of the environment threats and energy security negative issues associated with conventional fossil fuel – energy powered systems. The huge buildings’ cooling loads occur during periods of high solar insolation; this creates a huge potential of using solar powered cooling systems for air conditioning applications. However, the solar air conditioning systems still face a number of challenges in UAE which include; the availability of cheap electricity from fossil fuel resources and lack of government incentives to promote renewable energy resources. In order to understand the potential of applying solar cooling systems for air conditioning applications versus conventional systems, there was a need to experimentally and/or theoretically evaluate the performance of pilot solar cooling systems in UAE.      In this project, the performance of a 10 TR solar cooling system in Ras Al Khaimah (RAK) Emirate of UAE was evaluated by both experiment and theoretical simulation. TRNSYS, a transient – systems simulation software that was developed by Solar Energy Laboratory – University of Winsconsin, was used for the purpose of the theoretical simulations of the system. The solar cooling absorption equipment used for this study is an R&D system that was developed by CSEM – uae in RAK for the purpose of assessing the potential of applying solar cooling systems in UAE. The solar cooling system is based on absorption chilling technology run by hot water produced by a field of evacuated tube solar collectors. Experimental results were compared with TRNSYS – theoretical simulations results and areas of possible improvements in the solar cooling system were recommended. Results of the study show that the solar cooling system runs with a COP in the range of 0.60 – 0.80, with an average COP of 0.70. It was also observed that the inlet cooling and hot water temperatures to the absorption chiller have a huge impact on the performance of the solar cooling system. A need to isolate the absorption chiller hot water circuit from the hot water stratified tank by incorporation of a heat exchanger between the chiller and the stratified tank was also identified. This will help to improve the degree of stratification during the operation of the solar cooling system. Theoretical performance evaluation of the system using a typical TMY2 weather data shows that the system can meet its cooling requirement for at least eight (8) months of the year. In conclusion, this study has indicated that solar cooling for air conditioning application in UAE has a huge potential. However, further research is necessary to enable improvement of the performance of solar cooling systems and to assess the possibility of commercialization of such systems.

No description available.

The research focuses on testing the film cooling effectiveness on a gas turbine blade suction side surface. The test is performed on a five bladed cascade with a blow down facility. Four different blowing ratios are used in this study, which are 0.5, 1.0, 1.6, and 2.0; mainstream flow conditions are maintained at exit Mach number of 0.7, 1.1 and 1.3. Nitrogen is injected as the coolant so that the oxygen concentration levels can be obtained for the test surface. Based on mass transfer analogy, film cooling effectiveness can be computed with pressure sensitive paint (PSP) technique. The effect of blowing ratio on film cooling effectiveness is presented for each testing condition. The spanwise averaged effectiveness for each case is also presented to compare the blowing ratio and mainstream effect on film cooling effectiveness. Results show that due to effects of shock, the optimum blowing ratio is 1.6 for exit Mach number of 1.1 and 1.3; however; without the effects of shock, the optimum blowing ratio is 1.0 for exit Mach number of 0.7.

Abstract The experiments was studied on a rotating ribbed square duct from two different impingement position of air jets (termed as Type A and B) and at rotational speeds of 0,300 and 600 rpm¡CThe jet impinged on two different geometric types of rib (square and semi-circular ribs). The study covered jet Reynolds number 5000 to 9000 and the jet rotation number was varied from 0 to 0.0053. Results are presented and focused on the effect of two of circular jet arrangements and different geometric of ribs. Significant heat transfer enhancement was found for Type A configuration and square ribs within the ranges of operating parameters considered in the study. However, rotation induced Coriolis and centrifuged forces decreased the Nusselt number values (up to 20%) which is quitely conincided with those of previous studies.

Two evaporative-cooling materials were studied which are (i) salt hydrates and (ii) polyacrylic acid for the purpose showing proof of concept of being able to put evaporative-cooling materials into a composite with the Air Force polyimide AFR-PEPAN. The salt hydrates were observed to absorb water and then evaporate water, but due to having a collapsible lattice, made them incapable of reabsorbing water. Polyacrylic acid was mixed into an epoxy sheet at polacrylic acid weight percentages of 5, 10, 12.5. For each weight percentage there was a hydrated epoxy specimen and a dry epoxy specimen. All specimens were individually shot with a hot air stream (temperature approximately 1300C). Temperature readings were taken for each sheet. The hydrated specimen exhibited greater evaporative cooling over its dry counterpart. 12.5 wt% was shown to have the best evaporative cooling mechanism. Experiments were repeated to show that the polyacrylic could reabsorb water. This study illustrates proof of concept utilizing polyacrylic acid as an evaporative cooling material.

Continued development of highly compact and powerful electronic components has led to the need for a simple and effective method for controlling the thermal characteristics of these devices. One proposed method for thermal control involves the use of a micro heat pipe system containing a working fluid with physical properties having been speciffcally selected such that the heat pipes, as a whole, vary in effective thermal conductance, thereby providing a level of temperature regulation. To further explore this possibility, a design scenario with appropriate constraints was established and a model developed to solve for the effective thermal conductance of individual heat pipes as a function of evaporator-end temperature. From the results of this analysis, several working fluids were identified and selected from a list over thirteen hundred that were initially analyzed. Next, a thermal circuit model was developed that translated the individual heat pipe operating characteristics into the system as a whole to determine the system level effects. It was found that none of the prospective fluids could completely satisfy the established design requirements to regulate the device temperature over the entire range of operating conditions. This failure to fully satisfy design requirements was due, in large part, to the highly constrained nature of problem definition. Several fluids, however, did provide for an improved level of thermal control when compared to the unmodified design. Suggestions for improvements that may lead to enhanced levels of thermal control are offered as well as areas that are in need of further research.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 138-155).

Electricity-driven air-conditioning is energy-intensive and puts a strain to many grids during hot periods in warm climates. Solar thermal cooling could be an alternative to conventional cooling, using a renewable energy source and supplying the most energy during peak demand periods with insignificant effect to the electric grid. Office buildings in warm climates have high cooling loads, naturally peaking during daytime because of occupancy and ambient temperature. Thus, office buildings have a seemingly advantageous relationship between the possible supply of solar thermal energy and cooling demand. With this background, solar cooling systems for two office buildings with the same dimensions are investigated, placed in a tropical- and a sub-tropical location. There are great differences in the design conditions for solar cooling systems in the tropics and the sub-tropics, between the chosen locations Manila and Abu Dhabi more specifically. Manila has a quite evenly distributed cooling load while Abu Dhabi has a strongly pronounced summer season with very high maximum cooling loads, while the winter temperatures are relatively low. The prior described conditions creates a big difference between loads throughout the year, making a thermal chiller less effective in this aspect. However Abu Dhabi is expected to have an overall smoother- and ultimately a more high performance solar cooling system due to lower humidity, which facilitates the important cooling of the chiller. Evacuated tube collectors were used at both sites, where the collectors in Manila needs to be larger relative to the chiller cooling capacity, in order to compensate for the irregularity of direct solar radiation. The electricity price in Abu Dhabi is too low for the solar cooling system to be economically feasible compared to a conventional system, where the net values over 20 years are 163 000 € and 127 000 €, respectively. Manila has on its hand a very high price for electricity, making the 20-year net values for both the solar cooling- and the conventional system approximately 170 000 €.

No description available.