N2O represents a popular oxidizer for hybrid rocket motors for a variety of reasons, including safety, ease of access and self-pressurization. It is often used as a saturated two-phase fluid in these applications to t...N2O represents a popular oxidizer for hybrid rocket motors for a variety of reasons, including safety, ease of access and self-pressurization. It is often used as a saturated two-phase fluid in these applications to take advantage of self-pressurization. Recent interest in using this oxidizer in regeneratively cooled engines requires a detailed heat transfer process analysis to the coolant, in order to quantify performance. Since the injection of N2O typically takes place in the two-phase region, our study focuses on heat transfer rates in this region, and extends the region to include superheated vapor. This analysis is critical for these cooling applications, because the exothermic decomposition nature of N2O also means that unchecked heating in the superheated region may result in a runaway reaction in the cooling passages. Furthermore, provided that sufficient heat transfer rates are available, N2O is expected to accelerate in the cooling passages due to Rayleigh flow effects much like those of a calorically perfect gas. The proximity of superheated N2O to its saturated vapor curve, at the conditions studied here, makes the suitability of a perfect gas model questionable, but that benchmarks is still useful. This paper presents the development of an experimental apparatus （a ＂Rayleigh tube＂）, specifically designed to study this problem, and test the analytical methods developed to model it. Since we focus on the development of the apparatus, the data presented were uses primarily calorically perfect gas surrogates, but the goal is to apply the apparatus and method to N2O. The design and construction of the Rayleigh tube is presented, along with preliminary results with perfect gases. Finally, we present preliminary results on heated N2O flow. Using a simple model for predicted dry-out point, we investigate where superheating may be expected to occur. We present estimates of critical heating and compare them to the heat required to achieve self-decomposition.展开更多
文摘N2O represents a popular oxidizer for hybrid rocket motors for a variety of reasons, including safety, ease of access and self-pressurization. It is often used as a saturated two-phase fluid in these applications to take advantage of self-pressurization. Recent interest in using this oxidizer in regeneratively cooled engines requires a detailed heat transfer process analysis to the coolant, in order to quantify performance. Since the injection of N2O typically takes place in the two-phase region, our study focuses on heat transfer rates in this region, and extends the region to include superheated vapor. This analysis is critical for these cooling applications, because the exothermic decomposition nature of N2O also means that unchecked heating in the superheated region may result in a runaway reaction in the cooling passages. Furthermore, provided that sufficient heat transfer rates are available, N2O is expected to accelerate in the cooling passages due to Rayleigh flow effects much like those of a calorically perfect gas. The proximity of superheated N2O to its saturated vapor curve, at the conditions studied here, makes the suitability of a perfect gas model questionable, but that benchmarks is still useful. This paper presents the development of an experimental apparatus （a ＂Rayleigh tube＂）, specifically designed to study this problem, and test the analytical methods developed to model it. Since we focus on the development of the apparatus, the data presented were uses primarily calorically perfect gas surrogates, but the goal is to apply the apparatus and method to N2O. The design and construction of the Rayleigh tube is presented, along with preliminary results with perfect gases. Finally, we present preliminary results on heated N2O flow. Using a simple model for predicted dry-out point, we investigate where superheating may be expected to occur. We present estimates of critical heating and compare them to the heat required to achieve self-decomposition.
