PERFORMANCE COMPARISON OF A NOVEL THERMOFLUIDIC ORGANIC-FLUID HEAT CONVERTER AND AN ORGANIC RANKINE-CYCLE ENGINE

asme-orc2015 Tracking Number 159

The Up-THERM engine is a novel vapour-phase heat engine with a single moving part (a vertical solid piston) that relies on the phase change of a suitable working fluid to produce sustained thermodynamic oscillations and reciprocating displacement, which can be converted to useful work. In this paper a model of the Up-THERM engine is developed, based on lumped dynamic descriptions of each engine sub-component and by using electrical analogies founded on previously developed thermoacoustic principles [1,2]. This is extended here to include a description of phase change analogous to that used in the model of a similar thermofluidic oscillator known as the Non-Inertive-Feedback Thermofluidic Engine (NIFTE) [3,4] and also to include non-linear descriptions of important sub-components [5]. The predicted efficiency and power output from the Up-THERM model are compared with those of a sub-critical ORC engine, obtained by using a previously developed mathematical model [6]. Both systems are optimized for operation between the same heat sources and sinks, and using the same working fluids; common organic working fluids such as refrigerants and hydrocarbons (and their mixtures) are considered. In some cases, including mixtures, empirical fluid-property data are unavailable; here we employ the SAFT-VR Mie equation of state [6]. Preliminary results indicate that the Up-THERM engine underperforms its ORC counterpart in terms of efficiency and power output. However, owing to its mode of operation and lack of moving parts, the Up-THERM engine does offer a much simpler and more cost-efficient solution than an ORC engine, and is therefore a competitive alternative in terms of cost of electricity or power per unit cost in low-power applications, especially for remote, off-grid settings or those in developing countries where minimising upfront costs is crucial. REFERENCES [1] S. Backhaus, G.W. Swift, “A thermoacoustic-Stirling heat engine: Detailed study”, J Acoust. Soc. Am., v. 107, pp. 3146-3166, 2000. [2] B.J. Huang, M.D. Chuang, “System design of orifice pulse-tube refrigerator using linear flow network analysis”, Cryog., v. 36, pp. 889-902, 1996. [3] C.N. Markides, T.C.B. Smith, “A dynamic model for the efficiency optimization of an oscillatory low grade heat engine”, Energy, v. 36, 6967-6980, 2011. [4] R. Solanki, A. Galindo, C.N. Markides, “The role of heat exchange on the behaviour of an oscillatory two-phase low-grade heat engine”, Appl. Therm. Eng., v. 53, pp. 177-187, 2013. [5] C.N. Markides, A. Osuolale, R. Solanki, G.-B.V. Stan, “Nonlinear heat transfer processes in a two-phase thermofluidic oscillator”, Applied Energy, v. 104, pp. 958-977, 2013. [6] O.A. Oyewunmi, A.I. Taleb, A.J. Haslam and C.N. Markides, “On the use of SAFT-VR Mie for assessing fluorocarbon working-fluid mixtures in organic Rankine cycles for Waste-Heat Recovery”, J. Eng. Gas Turb. Power, revision under review, (2015).