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08:40   Session 9: Heat exchangers
Chair: Vijaya Sekhar Gullapalli
08:40
20 mins 		System-search DESIGN AND RATING OF AN EVAPORATOR FOR WASTE HEAT RECOVERY ORGANIC RANKINE CYCLE USING SES36
Alihan Kaya, Marija Lazova, Michel De Paepe
Abstract: The paper presents a design and rating study of a 4MW evaporator having plain horizontal carbon steel tubes having diameters of 25,4 mm, 31,8 mm and 38 mm, to be used in waste heat recovery via Organic Rankine cycle (ORC). SES36 is chosen as working fluid due to its low boiling point, which makes it suitable for low-grade waste heat recovery with subcritical ORCs. Waste heat carrier industrial air arrives at the evaporator bundle at 280°C. Inlet temperature of the working fluid is 40°C and the evaporation occurs at 125°C and 1,09 MPa. Furthermore, a design sensitivity analysis is made by means of using 13 different in-tube flow boiling correlations. The resulting design and rating parameters yielded by each correlation are compared to each other. By those means, a design error margin of various thermo-hydraulic heat exchanger parameters is revealed, when different in-tube flow boiling heat transfer calculation methods are used. The change in the error margins are investigated with respect to changing tube outer diameter, tube wall thickness, fin density and tube layout (staggered and inline).
09:00
20 mins 		System-search DESIGN OF A SUPERCRITICAL HEAT EXCHANGER FOR AN INTEGRATED CPV/T-RANKINE CYCLE
Marija Lazova, Dieter Daenens, Alihan Kaya, Marnix Van Belleghem, Henk Huisseune, George Kosmadakis, Dimitris Manolakos, Michel De Paepe
Abstract: The worldwide interest for low grade heat utilization by using Organic Rankine Cycle (ORC) technologies has increased significantly. An Organic Rankine Cycle can be combined with several renewable sources, such as solar energy. Concentrating solar power is a well proven technology and it can be efficiently combined with ORC technology for electricity generation. The goal was achieved by utilizing the excess heat source from PV collectors through a low temperature supercritical heat exchanger in the Organic Rankine Cycle. The motivation for working at supercritical state in the heat exchanger is the better thermal match between the heat source and the working fluid, leading to better overall cycle efficiency. In this paper measurements on the supercritical heat exchanger prototype are reported. It is a helical coil heat exchanger with R404a as working fluid flowing in the coil and the heat source fluid in the shell. The design of this heat exchanger was done using heat transfer and pressure drop correlations available from literature. There exists a large uncertainty on these correlations for the considered application because they were derived for working fluids water and CO2, more than ten years ago. In order to have good performance and heat transfer rate the heat exchanger was oversized by 20%. Next, the prototype was built and installed in a test set-up. The measurements on the prototype show that the heat exchanger is indeed oversized. Based on the measurements, a new heat transfer correlation is suggested. In future design this correlation can be used to make a less oversized (and thus cheaper) heat exchanger.
09:20
20 mins 		System-search HEAT STORAGE ORC SYSTEM FOR VEHICLE ICE EXHAUST HEAT RECOVERY
Tao Chen, Lei Zhang, Weilin Zhuge, Yangjun Zhang
Abstract: A new Organic Rankine Cycle (ORC) system for vehicle internal combustion engine (ICE) waste heat recovery (WHR) is presented in this paper, which can effectively reduce the influence of exhaust gas fluctuation caused by vehicle driving cycle. An evaporator with heat storage material inside is used in this system to make it possible that the ORC expander working under more stable condition, and the conceptual scheme of the heat-storage ORC system is presented. The dynamic model is established, and a heavy diesel engine exhaust experimental data is used as heat source in the performance simulation. The heat resistance effect and the heat capacity effect are the main effects of heat storage ORC system, and the influence of this two effects are analyzed and discussed, meanwhile, the system designing criteria is presented. Compared with conventional system, the fluctuation of ORC evaporator outlet temperature can be decreased by 50 % and the system overall efficiency can be increased from 6 % to 7 %. Key words: ORC; ICE; heat fluctuation; heat storage material
09:40
20 mins 		System-search ADVANCED CONTROLS OF ORGANIC RANKINE CYCLE FOR HIGHLY TRANSIENT FLUCTUATIONS DURING INITIAL STARTUP
Parsa Mirmobin, Chris Sellers
Abstract: Organic Rankine Cycles are typically utilized where steady heat source and condensing conditions prevail. In highly transient cases, the working fluid often undergoes violent phase transition within the evaporator. The resulting forces are experienced by the heat exchanger, expander, and associated piping. This ultimately results in premature and catastrophic component failure. This paper discusses pressure and flow instability which occurs during initial startup of an ORC. The instability is a result of a nonlinear pressure field within the evaporator interacting with the pressure source (centrifugal pump.) The phenomenon is characterized by a rapid oscillation in pressure and flow and resembles similar effects observed in low pressure boilers; the so called Ledinegg instability. Experimental data is examined and various methods for reducing or eliminating this effect are presented.