Of various attempts to improve the performance of the vapour compression refrigerating machine, two modified cycles are investigated. One of them is the multiple effect cycle, and the other the Plank cycle. In Part I the theory of the multiple effect cycle satisfying the law of heat balance is established. To facilitate the solution of the problem, groups of curves of the separator pressure, the total and heat of the refrigerant just after the multiple effect injection and before the compression in the compressor cylinder, are drawn in on the φ-I chart of the refrigerant. So far as the writer is aware, any investigation on the area of the multiple effect injection port has been made by nobody ; this problem is studied by the writer. A new needle regulating valve for the port is introduced, which is found to be effective in improving the efficiency of the multiple effect cycle. The construction of the compressor cylinder is very much simplified owing to the fact that only one small port is sufficient. In Part II the best intermediate pressure of the low pressure compressor of the Plank cycle, is studied. The best pressure is represented in a curve on the chart of the refrigerant. A new auxiliary compressor of an adjustable effective volume is designed to suit the condition required to obtain the maximum efficiency. The auxiliary high pressure compressor is constructed like a pump with a large clearance of about 135 per cent., for the reason that the refrigerant in it has a very small compressibility and resembles more to a liquid than to a vapour. With the multiple effect cycle, chief gain is in its capacity, and with the Plank cycle it is in its efficiency. With the simultaneous application of the multiple effect and the Plank cycle, both the capacity and the efficiency can be increased. Experiments were carried out to testify these theories on an experimental refrigerating machine which can be operated on any of the three cycle, the ordinary, the multiple effect, or the Plank cycle.
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