M.Ing. (Electrical And Electronic Engineering) / The feasibility of various alternative methods for obtaining air conditioning in internal combustion vehicles is examined from literature studies. It is concluded that adsorption cooling which utilises the hot exhaust gases appears to be the most promising and the combination zeolite-water is chosen for further research. A synopsis of the state of the art as documented in the literature is given and typical unresolved problems are identified. A description of the basics of adsorption cooling and the properties ofthe material zeolite is elaborated upon. The requirements for a design to be successful is explained. A finite difference computer spreadsheet model is developed to aid in the calculation ofthe heat transfer process that is necessarily part ofthe sorption processes. Laboratory tests on three sorbers of proprietary design are described and the test methods are refined to the point where satisfactory results are obtained. It is concluded from the tests and computer simulations that adsorption cooling as an alternative method of vehicle air conditioning appears a viable proposition, but that further research is required.

An investigation into economical energy usage in freeze tunnels was conducted. Freeze tunnels are commonly used in the food processing industry to freeze products, and in some cases may use large amounts of electricity. An actual freeze tunnel was observed and modeled on a computer. A parameter study was conducted. The results of the parameter study indicated the efficiency and energy costs in freeze tunnels may vary widely. Important parameters included the Nusselt number, air temperature, and the ratio of fan work divided by the useful refrigeration effect. Although no single set of optimum conditions were found, methods for improving the effectiveness of freeze tunnels, both in existing and future designs, were discussed. It was also concluded that the ratio of fan work to the freeze tunnel's useful refrigeration effect was a dominant factor in the energy cost of operating a freeze tunnel.

M.S.

A series of tests was run to determine the performance characteristics of the 2-1/2 ton steam jet refrigeration unit. The first series of tests was run to determine the nozzle position relative to the throat of the diffuser at which best performance was obtained. This series included tests with two methods of introducing the warm water into the evaporator, namely by spraying the warm water into the evaporator by means of commercial spray nozzles and by spraying the warm water into the evaporator through small holes in a straight piece of pipe. A series of tests was run to determine the effect of the evaporator water level on performance. A series of tests was also run with inlet steam pressures lower and higher than design in combination with outlet pressures at and lower than design. Lastly, one test was run in an effort to reduce the amount of liquid carryover into the ejector. From the results of the above tests the following was concluded: 1. Use of a 62% entrainment efficiency and a 65% diffuser efficiency to give a greater steam flow rate did not enable the design capacity to be met. 2. Best performance of the unit was obtained with the nozzle exit 7-1/2 inches from the entrance to the diffuser throat. 3. Better performance was obtained from the unit by introducing the wara water into the evaporator by means of the commercial spray nozzles than was obtained by introducing the warm water into the evaporator by means of small hole in a straight pipe. 4. Lowering the evaporator water level did not effect performance of the unit greatly. However, control of the unit was greatly enhanced by using a low evaporator water level. 5. Performance of the unit was unstable at inlet steam pressures above design and outlet pressure below design. The capacity of the unit dropped sharply under these condition 6. The design evaporator outlet velocity was too high to enable a sufficiently large amount of liquid carryover to be baffled out. 7. The compression process in the diffuser did not occur as assumed in the design procedure. 8. The throat area of the diffuser should be increased to reduce the fluid velocity in the throat and thereby improve performance of the unit. This is necessary to make the normal shock occur at the throat section of the diffuser. / M.S.

M.S.

The investigation is concerned with the effect of entrained oil on the heat transfer characteristics of a direct expansion evaporator coil. A modified refrigeration system, in which the oil content of the refrigerant could be varied, was used in conjunction with an air conditioning system, which supplied the evaporator load. The heat transferred to the refrigerant was measured for different concentrations of oil in the refrigerant. The load to the evaporator was supplied by 500 cfm of air maintained at 80°F dry bulb and 61°F wet bulb by a washer and an electric heater. The heat transferred to the refrigerant was determined by measuring the temperature of the liquid refrigerant entering the expansion valve and the suction temperature and pressure of the superheated vapor at exit from the evaporator. A sample of the liquid refrigerant flowing to the evaporator during the test was trapped in a sample collector and channeled to an expansion chamber, where the oil and refrigerant were separated and the oil concentration was determined. The results of the investigation showed that oil tends to reduce heat transfer across the evaporator tube wall. At 25°F suction temperature, the reduction in the heat transferred was 5% with an oil concentration of 0.84% by volume compared to the refrigerant with an oil concentration of 0.063%. At 30°F suction temperature the reduction in the heat transferred was 3% with an oil concentration of 1.52% by volume. The range of suction temperatures for the investigation was from 24°F to 31.9°F, The maximum average oil concentration obtained during the investigation was approximately 1.75% by volume of oil in the refrigerant. / Master of Science

M.S.

The use of an ejector to improve the performance of a vapor compression refrigeration system was investigated. The ejector harnesses kinetic energy developed during the throttling process and returns it to the compressor in the form of a pressure boost. An ejector was designed taking into account the expected nonequilibrium behavior in the motive nozzle, and assuming equilibrium conditions in the other components. A standard vapor compression system using R-12 was modified to test the ejector. Included in the resulting ejector cycle was a hot gas bypass arrangement which was found to effectively control the condenser and evaporator flowrate. Hot gas bypass was used instead of a throttling valve, which would have undermined the benefit of the ejector. Experiments were conducted by running the ejector cycle at varying amounts of hot gas bypass flow. Performance results for the ejector and the overall cycle were obtained which showed that while the ejector recovered some of the kinetic energy of the expansion process, its design needed optimization. Recommendations were made for a more in-depth study of the ejector cycle. / Master of Science

In 1947, Professor H. S. Miles, Jr. of the Mechanical Engineering Department at the Virginia Polytechnic Institute, presented a thesis (1) on the design of a 65 ton steam jet refrigeration unit. Miles recommended that a small unit be constructed in the Mechanical Laboratory so that the soundness of his design be confirmed. With this in mind, Messrs. A. W. Howard and C. W. Vogelsang (2) built a 5 ton unit in the laboratory in 1948. It is the purpose of the authors of this report to determine why the steam jet refrigerating unit constructed in the Mechanical Laboratory at the Virginia Polytechnic Institute in 1948 did not reach design capacity. / M.S.

M.S.