Numerical Study of Multistage Serial and Parallel Configurations of Thermoacoustic Engines

2016 ◽  
Vol 8 (2) ◽  
Author(s):  
Adnan Poshtkouhian Badi ◽  
Hamid Beheshti
Keyword(s):  
Fluid Dynamics ◽  
Low Temperature ◽  
Cfd Simulation ◽  
Waste Heat ◽  
Numerical Study ◽  
Initial Pressure ◽  
Heat Pumps ◽  
Published Data ◽  
Pressure Amplitude ◽  
Thermoacoustic Engines

The focus of this study is on serial and parallel configurations of a multistage thermoacoustic engines (TAE). Thermoacoustics integrates fluid dynamics, thermodynamics, and acoustics to explain the interactions existing between heat and sound. Considerable amounts of waste heat are released to the environment in everyday industrial processes. This waste heat cannot be reused due to its low temperature. One way for reusing some of this waste heat is to employ a thermoacoustic heat pump. TAEs can be driven by waste heat and are capable of supplying the power to drive the thermoacoustic heat pumps. However, due to the low temperature of this waste heat, single-stage TAEs cannot provide the required temperature lifts. Multistage TAEs are advantageous because they can provide sufficient temperature lifts. In this study, a computational fluid dynamics (CFD) simulation is carried out to understand the conversion process of heat to sound and study the nonlinear conjugation of unsteady heat release and acoustic disturbances. The two main parameters evaluated in this simulation are the initial pressure disturbance and the stack's temperature gradient. Their effects on actuating limit cycle oscillations are examined in a 2D numerical model. The numerical simulation results indicate that the pressure amplitude varies through alteration made in these mentioned parameters. The present numerical results are validated by previously published data.

scholarly journals Local Heating Networks with Waste Heat Utilization: Low or Medium Temperature Supply?

Energies ◽  
2020 ◽  
Vol 13 (4) ◽  
pp. 954 ◽  
Author(s):  
Hanne Kauko ◽  
Daniel Rohde ◽  
Armin Hafner
Keyword(s):  
Low Temperature ◽  
Heat Pump ◽  
Urban Areas ◽  
Waste Heat ◽  
Local Heating ◽  
District Heating ◽  
Heat Pumps ◽  
Hot Water ◽  
Local Network ◽  
Medium Temperature

District heating enables an economical use of energy sources that would otherwise be wasted to cover the heating demands of buildings in urban areas. For efficient utilization of local waste heat and renewable heat sources, low distribution temperatures are of crucial importance. This study evaluates a local heating network being planned for a new building area in Trondheim, Norway, with waste heat available from a nearby ice skating rink. Two alternative supply temperature levels have been evaluated with dynamic simulations: low temperature (40 °C), with direct utilization of waste heat and decentralized domestic hot water (DHW) production using heat pumps; and medium temperature (70 °C), applying a centralized heat pump to lift the temperature of the waste heat. The local network will be connected to the primary district heating network to cover the remaining heat demand. The simulation results show that with a medium temperature supply, the peak power demand is up to three times higher than with a low temperature supply. This results from the fact that the centralized heat pump lifts the temperature for the entire network, including space and DHW heating demands. With a low temperature supply, heat pumps are applied only for DHW production, which enables a low and even electricity demand. On the other hand, with a low temperature supply, the district heating demand is high in the wintertime, in particular if the waste heat temperature is low. The choice of a suitable supply temperature level for a local heating network is hence strongly dependent on the temperature of the available waste heat, but also on the costs and emissions related to the production of district heating and electricity in the different seasons.

Numerical Study on Choked Flow of CO2 Refrigerant in Helical Capillary Tube

2018 ◽  
Vol 26 (03) ◽  
pp. 1850027 ◽  
Author(s):  
Pravin Jadhav ◽  
Neeraj Agrawal
Keyword(s):  
Fluid Dynamics ◽  
Present Model ◽  
Capillary Tube ◽  
Numerical Study ◽  
Fundamental Principle ◽  
Tube Diameter ◽  
Published Data ◽  
Flow Conditions ◽  
Pressure Drops ◽  
Choked Flow

This paper presents a numerical study on an adiabatic helical capillary tube employing homogenous and choked flow conditions of a CO2 transcritical system. The theoretical model is based on the fundamental principle of fluid dynamics and thermodynamics. The result of the present model validates with the previously published data. The influence of operating and geometric parameters on the performance of the capillary tube has been evaluated. Flow characterizations of choked and unchoked flow conditions are determined. As the evaporator pressure drops, from unchoked condition to choked state, the percentage change in mass flow rate is minimal. A simulation graph is developed which has been helpful for the design of the helical capillary tube. The choked flow condition in a capillary tube is avoided by either increasing tube diameter of the fixed length tube or decreasing the length of the fixed tube diameter.

CFD-Simulation of Oscillatory Flow Around the Heat Exchangers of Thermoacoustic Devices

2014 ◽  
Author(s):  
Olusegun M. Ilori ◽  
Xiaoan Mao ◽  
Artur J. Jaworski
Keyword(s):  
Heat Exchangers ◽  
Oscillatory Flow ◽  
Cfd Simulation ◽  
Waste Heat ◽  
Oil And Gas Industry ◽  
Cooling Power ◽  
Maximum Pressure ◽  
Curvature Radius ◽  
Computational Domain ◽  
Pressure Amplitude

Thermoacoustic systems rely on conversion between thermal and acoustic (i.e. mechanical) forms of energy. The technology lends itself to various applications such as waste heat recovery to produce useful electricity or cooling power or gas liquefaction and regasification in oil and gas industry. Detailed understanding of the fluid flow processes within the internal structures of thermoacoustic systems, especially the heat exchangers, is seen as one of the ways by which the performance of next generation of thermoacoustic systems can be improved. The current study uses 2-D computational fluid dynamics (CFD) model to perform numerical investigations of thermoacoustic heat exchangers placed in an oscillatory flow induced by a standing wave. The computational domain is chosen from a thermoacoustic rig that is built for characterisation of heat exchangers for thermoacoustic applications. Validation of the present numerical approach is first established. Then the numerical analysis is extended by modifying the geometrical and operating parameters. The geometrical parameter considered is the curvature radius of the aerodynamic shapes attached to the entrance and exit of gas channels of the heat exchangers, mainly to modify the flow characteristics. Cases are run for the drive ratios (i.e. the ratio of maximum pressure amplitude to the mean pressure) ranging from 0.3–3.0%. Turbulent model as suitable for thermoacoustic analysis is selected from the literature. Results are discussed based on velocity profiles and the pressure difference obtained as functions of phase angles in the acoustic flow cycle.

Numerical Optimization of a Piece-Wise Conical Contraction Zone of a High-Pressure Wind Tunnel

2015 ◽  
Author(s):  
Karsten Hasselmann ◽  
Felix Reinker ◽  
Stefan aus der Wiesche ◽  
Eugeny Y. Kenig
Keyword(s):  
Fluid Dynamics ◽  
Wind Tunnel ◽  
Low Temperature ◽  
Flow Field ◽  
Waste Heat ◽  
Design Guidelines ◽  
Optimal Shape ◽  
Geometrical Approach ◽  
Separation Criterion ◽  
The Ideal

The Organic Rankine Cycle (ORC) offers a great potential for recovering waste heat and using low-temperature sources for power generation. However, the ORC thermal efficiency is limited by the relatively low temperature level, and, therefore, designing ORC components with high efficiencies and minimized losses is of major importance. Such an approach requires the use of a specially designed closed cascade wind tunnel. This contribution presents the design of the contraction zone shape. The ideal shape can be defined by a sixth order polynomial yielding a smooth curve for the nozzle profile. Due to pressure vessel costs, it is not possible to realize the whole contraction zone as one piece for this wind tunnel. Instead, a piece-wise conical design approach is chosen. Classical nozzle design guidelines do not offer an analytical solution to this flow problem. Therefore, computational fluid dynamics (CFD) in combination with Stratford’s separation criterion is used for an optimization study of a piece-wise conical contraction zone. Different combination of numbers of components, length, and inflection points are investigated. The optimization minimizes the flow deviation of the chosen profile to the optimal shape in two steps: a geometrical approach to the optimal shape and an optimization of the flow field within the contraction zone. The geometrical optimization yields a profile with minor deviation to the ideal shape. For the flow field optimization, a CFD analysis is used to minimize flow separations at the break points between the single conical pieces, especially those at the far end of the contraction zone. All shapes are investigated by Stratford’s separation criterion, which is adopted to conical pieces. The presented analysis indicates that the flow field optimization yields a much better approach for the fluid dynamics of the wind tunnel than the geometrical approach.

scholarly journals Waste heat recovery in low temperature networks versus domestic heat pumps - A techno-economic and environmental analysis

Energy ◽  
2021 ◽  
Vol 219 ◽  
pp. 119675 ◽  
Author(s):  
Monica Arnaudo ◽  
Johan Dalgren ◽  
Monika Topel ◽  
Björn Laumert
Keyword(s):  
Low Temperature ◽  
Environmental Analysis ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Heat Pumps

scholarly journals Enhancing Heating Performance of Low-Temperature Air Source Heat Pumps Using Compressor Casing Thermal Storage

Energies ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 3269 ◽  
Author(s):  
Zhongbao Liu ◽  
Fengfei Lou ◽  
Xin Qi ◽  
Yiyao Shen
Keyword(s):  
Low Temperature ◽  
Heat Pump ◽  
Waste Heat ◽  
Thermal Storage ◽  
Heat Pumps ◽  
Coefficient Of Performance ◽  
Pump System ◽  
Heat Pump System ◽  
Discharge Temperature ◽  
Vapor Injection

Air source heat pumps (ASHPs) are widely recognized as energy-saving and environmentally friendly heating and air-conditioning equipment with broad applications. However, when conventional ASHPs are operated at a low ambient temperature, they suffer from problems such as high discharge temperature and low heating efficiency. To address these problems, this study designed a new type of dual evaporator combined with a compressor casing thermal storage heat pump system (DE-CCTS) on the basis of a low-temperature air source heat pump water heater with enhanced vapor injection (EVI). The proposed DE-CCTS used thermal storage phase change material (PCM), which was filled in the secondary evaporator (the thermal storage heat exchanger), to recover the waste heat of the compressor casing. Unlike that in the original system under different ambient temperatures, the suction temperature increased by 0.1–1 °C, the discharge temperature decreased by 0.1–0.5 °C, and the coefficient of performance (COP) of DE-CCTS increased by 0.85–4.72% under the proposed system. These effects were especially evident at low temperatures.

CFD Simulation of a Sliding Vane Expander Operating Inside a Small Scale ORC for Low Temperature Waste Heat Recovery

2014 ◽  
Author(s):  
Gianluca Montenegro ◽  
Augusto Della Torre ◽  
Angelo Onorati ◽  
Dalia Broggi ◽  
Gerd Schlager ◽  
...  
Keyword(s):  
Low Temperature ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Cfd Simulation ◽  
Waste Heat ◽  
Small Scale
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