A waste heat-driven cooling system based on combined organic Rankine and vapour compression refrigeration cycles

In this paper, a heat driven cooling system that essentially integrated an organic Rankine cycle power plant with a vapour compression cycle refrigerator was investigated, aiming to provide an alternative to absorption refrigeration systems. The organic Rankine cycle (ORC) subsystem recovered energy from the exhaust gases of internal combustion engines to produce mechanical power. Through a transmission unit, the produced mechanical power was directly used to drive the compressor of the vapour compression cycle system to produce a refrigeration effect. Unlike the bulky vapour absorption cooling system, both the ORC power plant and vapour compression refrigerator could be scaled down to a few kilowatts, opening the possibility for developing a small-scale waste heat-driven cooling system that can be widely applied for waste heat recovery from large internal combustion engines of refrigerated ships, lorries, and trains. In this paper, a model was firstly established to simulate the proposed concept, on the basis of which it was optimized to identify the optimum operation condition. The results showed that the proposed concept is very promising for the development of heat-driven cooling systems for recovering waste heat from internal combustion engines’ exhaust gas

Studies on a Double Poisson-Geometric Insurance Risk Model with Interference

This paper mainly studies a generalized double Poisson-Geometric insurance risk model. By martingale and stopping time approach, we obtain adjustment coefficient equation, the Lundberg inequality, and the formula for the ruin probability. Also the Laplace transformation of the time when the surplus reaches a given level for the first time is discussed, and the expectation and its variance are obtained. Finally, we give the numerical examples

The Gerber-Shiu Discounted Penalty Function of Sparre Andersen Risk Model with a Constant Dividend Barrier

This paper constructs a Sparre Andersen risk model with a constant dividend barrier in which the claim interarrival distribution is a mixture of an exponential distribution and an Erlang(n) distribution. We derive the integro-differential equation satisfied by the Gerber-Shiu discounted penalty function of this risk model. Finally, we provide a numerical example

Cavitating flows of organic fluid with thermodynamic effect in a diaphragm pump for organic Rankine cycle systems

Diaphragm pumps often experience cavitation and subsequent fluid flow oscillation when delivering an organic fluid in small/micro scale organic Rankine cycle (ORC). The cavitation behaviour of diaphragm pumps has rarely been investigated for organic fluids so far. Three-dimensional, unsteady cavitating flows of organic fluid R245fa in a diaphragm pump were simulated with ANSYS 2019R2-CFX in suction stroke in terms of the k- turbulence model, the ZGB cavitation model, rigid body motion model for one-dimensional motion of valve and moving mesh technique for the first time. The thermodynamic effect in cavitation of R245fa was considered. The vapour volume fraction threshold for cavitation inception was determined, and the cavitation inception and cavitation developed states were identified, and vortex production and entropy generation rate during cavitation were clarified. Cavitation inception emerges at the edge of the valve seat, then on the valve surface. With cavitating development, the pressure and force on the valve, valve opening, and velocity oscillate violently due to vapour bubble collapse cycles. Expansion cavitation and flow induced cavitation happen in sequent at different crank rotational angles. The maximum temperature depression is 0.549K in the cases studied. The volume-integrated entropy generation rate in the valve chamber correlates to cavitation states

Convective heat transfer in a thermal chimney for freshwater production in geothermal total flow systems

The convective heat transfer of air in a laboratory-scale thermal chimney with rectangular cross-section of constant area and two row electrical heaters simulating two heat exchangers was studied experimentally and numerically at 60–200 ℃ nominal temperatures of the top row heaters, 100 ℃ of the low row heaters and 20 ℃ ambient temperature to verify our design concept on freshwater production in geothermal total flow systems. Computational fluid dynamics simulations of air convective heat transfer were performed in ANSYS 2019R CFX based on the three-dimensional, steady Reynolds-averaged Navier-Stokes equations, Boussinesq buoyancy model, k-w turbulence model, and energy equation. The thermal radiation between heater surfaces and chimney walls was considered. The overall thermal and heat transfer characteristics, temperature and flow fields in the chimney were obtained. Effects of boundary condition of heater surface and thermal radiation between two row heaters on heat transfer were discussed. The thermal characteristics of the chimney with two row heaters are better than that with single row heaters. The predicted thermal power and convective Nusselt number agree with the experimental data, and the convective Nusselt number of the low row heaters is enhanced by (11.6–29.8) % compared with the single row heaters. The optimal operating nominal temperature of top row heaters should be higher than 140 ℃, and the optimal centre-to-centre row gap ratio is 5. Multiple jets in the gaps among the heaters and temperature jump crossing each row were observed. The maximum velocity and temperature jump rise with increasing heater nominal temperature

Heat transfer enhancement of water-cooled triply periodic minimal surface heat exchangers

Whether triply periodic minimal surface (TPMS) heat exchangers are applicable to cooling or cold storage systems as a cooler for supercritical carbon dioxide (SCO2) is undocumented. Here the conjugated heat transfer of SCO2 in TPMS Schoen-G heat exchanger and printed circuit heat exchanger (PCHE) was predicted based on three-dimensional steady turbulent Reynolds-averaged Navier-Stokes equations, energy equation and shear stress transport model using computational fluid dynamics software ANSYS CFX when SCO2 inlet temperature and pressure vary in 65-30 ℃ and (8-9)MPa. SCO2 in two heat exchangers is cooled under counter-flow conditions by a stream of cold water with given inlet temperature and mass flow rate. It was shown that the mean heat transfer coefficient of SCO2 in TPMS Schoen-G heat exchanger is larger than PCHE. As the inlet pressure rises, the friction factor increases and Nusselt number decreases in the heat exchangers due to decreased Reynolds number and Prandtl number, respectively. The friction factor ratio, Nusselt number ratio and performance evaluation criterion vary in the range of 0.38-0.50, 1.07-1.49, and 1.45-2.04 with Reynolds number and inlet temperature when the PCHE serves as a reference heat exchanger. The streamlines in TPMS Schoen-G heat exchanger are quite smooth even though the areas with a higher velocity appear. The streamlines in PCHE exhibit a spiral flow pattern to result in extra hydraulic loss. The heat transfer enhancement of TPMS Schoen-G heat exchanger is much better TPMS Schwarz-D heat exchanger at a Reynolds number higher than 16,000. The enhancement is attributed to a larger heat transfer surface area and more topological tortuosity without flow separation than PCHE

Correction of cavitation with thermodynamic effect for a diaphragm pump in organic rankine cycle systems

Diaphragm pumps are a sort of leakage-proof reciprocating pumps with low flow rate but high head and better efficiency, and can potentially find their applications in organic Rankine cycle (ORC) systems as the feed-pump of organic fluid to the evaporator. A diaphragm pump in an ORC system may suffer from cavitation in the pump suction chamber inevitably when the pump delivers an organic fluid. However, the cavitation performance of the pump has been a little known for organic fluids so far. In the article, the performance of a specific diaphragm pump was determined based on the existing performance charts provided by the pump manufactory in terms of pump rotating speed and inlet liquid pressure for cold water. The net positive suction head required (NPSHr) was predicted by involving thermodynamic effect in cavitation when the pump feeds the organic liquid R245fa to the evaporator in an ORC system at 480rpm rotational speed. The net positive suction head available (NPSHa) was calculated at 100 kPa and 141 kPa inlet liquid pressures, and the corresponding cavitation safety margins were addressed. The subcooling for the NPSHr and NPSHa as well as the safety margin were figured out. Two one-dimensional (1D) mechanical models for motion of the suction valve were built and solved at 480rpm and 100 kPa and 141 kPa inlet pressures. A preliminary experiment was performed to verify the analytical results. It turned out that the NPSHr is reduced to 2.02m from 3.02m NPSHr of cold water due to the thermodynamic effect in cavitation, and the corresponding subcooling is lowered to 8.28 C from 12.38 C. 100 kPa but 141 kPa inlet pressure can result in cavitation in the pump. The 1D mechanical models are subject to a rough spatial resolution for the flow field in the suction chamber, hence three-dimensional(3D) numerical simulations of the flow field are desirable

Development of Discoid Products Stacking Machine Based on PLC

Abstract. Binding the actual production of one sporting goods factory, in order to meet the needs of automatic production line of shooting flying saucer, the discoid products stacking machine was developed based on PLC, carried out mechanical system design of discoid products stacking machine and control system development based on PLC. After production testing proved reasonable structure of mechatronics systems, easy to operate, reliable, able to meet the requirements of automated production, with a strong practical and innovative, have some application value

An improved cavitation model with thermodynamic effect and multiple cavitation regimes

Mechanical feed pumps in organic Rankine cycle (ORC) power plants can suffer from cavitation to lose their normal feeding performance or even damage. Cavitation models for organic fluids in ORC systems are lacking presently. Hence, a new cavitation model with thermodynamic effect was proposed. Surface tension-controlled, inertia-controlled, intermediate and heat transfer-controlled cavitation regimes, and two key elements: vapour bubble growth rate and vapour bubble number density are included in the model. A known air or non-condensable gas concentration in the liquid was employed to determine cavitation nuclei number density. The model was coded in ANSYS CFX as user defined model and validated with cavitating flows of organic fluid R114 in a venturi, liquid nitrogen and liquid hydrogen on a tapered hydrofoil and warm water around a hydrofoil NACA 0015 in cavitation tunnels based on visualised cavity length. Two model constants, temperature depression, and minimal cavitation number were correlated to bulk liquid temperature, Reynolds number, and Jakob number. The temperature and pressure profiles of liquid nitrogen and hydrogen on hydrofoil surface were examined against the experimental data. The model was applied to simulate unsteady cavitating flows of organic fluid R245fa in a diaphragm pump. It was shown that the temperature depression and minimal cavitation number cannot be correlated to bulk liquid temperature, Reynolds number and Jakob number. Two model constants can be correlated fairly to Reynolds number. The model underestimates the thermodynamic effect by 43% for R114, 18.6% for liquid nitrogen and 32.6% for liquid hydrogen based on temperature depression. The predicted temperature and pressure profiles on hydrofoil surface agree with the experimental data for liquid nitrogen. The model can produce an expected curve of mean pump flow rate against net positive suction head available