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.

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.

The gain in popularity of freezing as a means of food preservation has created a need for additional refrigeration on the farm. Even with the wide selection of commercial equipment to choose from, many of the units purchased have proven to be inadequate in storage and freezing capacity. A practical solution to the problem of ample capacity and economy of installation and operation, in many cases is the walk-in type farm refrigerator which may be constructed in part by farm labor using locally available materials. Such a unit designed, constructed and extensively tested in the V.P.I. Agricultural Engineering Department. One of the major items in the initial cost of such a farm refrigerator is the installation of the refrigeration equipment. The nature of this type of installation is conductive to very inefficient use of labor, equipment and facilities. If shops equipped for refrigeration work were used to prefabricate the refrigeration equipment the labor could be used more efficiently because, (a) costly time involved in travel to and from the installation would be reduced to a minimum and (b) the assembly would be made in familiar surroundings with all of the necessary tools, equipment and supplies available. Furthermore, the supplier should be able to finish a more trouble-free installation because the assembly could be made under better working conditions and the equipment could be thoroughly inspected and adjusted before being released from the shop. All these advantages for prefabrication should make it possible for the farm operator to ger a more satisfactory installation at less cost. Also, he would have a unit that would be structurally separate from the refrigerator in which it was installed. In case of emergency such a unit could be removed for repair or replacement or for use in other refrigerators. Manufacturers of refrigeration equipment offer integral units for air conditioning installations, for use with milk coolers and in similar applications which have proven highly satisfactory. These units are designed for operation at an evaporator temperature considerably higher than that required in a walk-in refrigerator. While the gasoline powered units designed for operation on refrigerated transport trucks came closer than any of the other units studied to meeting the requirements for use with the walk in farm refrigerator, they were not considered to be fully satisfactory. In all cases commercial equipment currently available would require considerable modification before it could be used. Since the integral refrigeration units used for other purposes have proven satisfactory it seemed feasible that such a unit could be designed and used on a walk-in type farm refrigerator. / Master of Science

During World War II, with the armed forces waging war on several fronts and with the development of high altitude aircraft, the necessity for a great deal of low temperature testing was brought about. The production testing of various instruments and appliances, such as radios, cameras, clocks, and meters, which would be subjected to low temperatures in arctic climates or at high altitudes, was found necessary. This subject had been given very little consideration prior to the war. When it became necessary to test equipment at a low temperature, it was normally transported to a cold climate and there the tests were conducted. With the increased demand for low temperature testing, the expense and time delay encountered in such movements became prohibitive. During and since the war many low temperature test chambers have been built. The design problems encountered, such as load determination, defrosting, lubrication, refrigerant selection, proper staging, and control selection, have been similar, but the solutions have been different. Moore, Gellalles, and Young state: "Experience has shown that research requirements change so quickly and so radically that the original design specification cannot be much more than a hopeful guess.”(22) Mr. Coy W. Brown states: "Any systems requiring evaporating refrigerant temperatures below -40° F. should be attempted only by engineers experienced in this presently special field."(5) Since definite data on equipment for low temperature test rooms seems to be limited, it is believed that from a design of such a machine much valuable information can be gained. Two low temperature testing rooms have been constructed in the Mechanical Engineering Laboratory at The Virginia Polytechnic Institute. One will operate at temperatures down to 0° F. and the other will operate at temperatures down to -40° F. In addition to being used for low temperature research, it is anticipated that the refrigerating equipment for these rooms will be used by students taking Mechanical Laboratory in routine experiments. The object of this thesis is to design suitable refrigeration equipment for the two rooms. The design will include specifications, bill of material and equipment, detail and assembly drawings, and operating instructions. Available data on the design, control, and operation of low temperature refrigerating equipment will be assembled and correlated. This information, with interpretation thereof, will be used in solving a practical engineering problem which is, at the present, in a special field. / Master of Science

M.S.