Length Of Regenerator Research Articles

Energy, environmental and economic evaluations of a CCHP system driven by Stirling engine with helium and hydrogen as working gases

Abstract In this study, with a comprehensive approach, energy, economic, and environmental evaluations of a combined cooling, heating and power (CCHP) generation system driven by Stirling engine with working gases of hydrogen and helium were performed. This system can be used for residential applications. The engine was analyzed using the non-ideal adiabatic model, and two beta type Stirling engines were suggested in the CCHP system. Also, the energy analysis of the absorption chiller was presented with utilizing the waste heat of the engine. Then, the impacts of important specifications of the Stirling engine including: temperature of heater, length of regenerator, engine rotational speed, and type of working gases on the COP of absorption chiller, CCHP efficiency, Trigeneration Primary Energy Saving (TPES), Operational Cost Reduction (CR), and Trigeneration CO2 Emission Reduction ( TCO 2 ER ) relative to conventional energy supply systems were studied. Finally, at the appropriate conditions, the values for parameters of electrical power: 15.24 kW, 22.52 kW, heating capacity: 19.65 kW, 21.65 kW, cooling capacity: 12.65 kW, 14.43 kW, COP: 0.644, 0.667, CCHP efficiency: 70%, 72.29%, TPES: 24.05%, 31.3%, TCO 2 ER : 31.06%, 38% and CR: 75.53%, 78.8% were obtained for helium and hydrogen, respectively.

Entropy generation in a parallel-plate active magnetic regenerator with insulator layers

This paper proposes a feasible solution to diminish conduction losses in active magnetic regenerators. Higher performances of these machines are linked to a lower thermal conductivity of the Magneto-Caloric Material (MCM) in the streamwise direction. The concept presented here involves the insertion of insulator layers along the length of a parallel-plate magnetic regenerator in order to reduce the heat conduction within the MCM. This idea is investigated by means of a 1D numerical model. This model solves not only the energy equations for the fluid and solid domains but also the magnetic circuit that conforms the experimental setup of reference. In conclusion, the addition of insulator layers within the MCM increases the temperature span, cooling load, and coefficient of performance by a combination of lower heat conduction losses and an increment of the global Magneto-Caloric Effect. The generated entropy by solid conduction, fluid convection, and conduction and viscous losses are calculated to help understand the implications of introducing insulator layers in magnetic regenerators. Finally, the optimal number of insulator layers is studied.

СОВЕРШЕНСТВОВАНИЕ НИЗКОТЕМПЕРАТУРНОЙ СТУПЕНИ КРИОРЕФРИЖЕРАТОРА ГИФФОРДА-МАК-МАГОНА С РЕГЕНЕРАТОРОМ, ЗАПОЛНЕННЫМ ЦЕНОСФЕРАМИ

Creating Gifford-McMahon (GM) cryocoolers for cooling at temperatures below 4,2 K is a quantum leap in the development of techniques for obtaining helium temperatures. The paper provides a comparative analysis of different types of regenerator packing, which allow obtaining temperatures below 4,2 K. The advantages of cenosphere packing filled with helium are shown. Using a wave approach to modelling regenerator operation, we analyzed operation of a two-stage GM cryocooler, having a cooling capacity of 0,2 Watt at the temperature of 4,2 K. Calculated value of the length of the heat exchanger regenerator with the packing from cenosphere for such cryocooler was equal to 320 mm, i.e. substantially bigger than the length of the regenerator packed with intermetallic compounds of rare earth elements. The resulting length value does not exceed a technically possible size of regenerators for GM cryocoolers. Advantages of cenosphere packing can compensate for the increased size of a cryocooler.

Performance optimisation of room temperature magnetic refrigerator with layered/multi-material microchannel regenerators

A hybrid numerical model of the magnetic refrigerator with multi-material microchannel regenerator has been developed. The magnetocaloric effect was implemented using instantaneous temperature rise/drop (discrete method). Two pipe-in-pipe heat exchangers at two ends of the regenerator were treated using ε-NTU method. The commercially available compounds of LaFe13-x-yCoxSiy as well as hypothetical compounds of Gadolinium were considered as the magnetocaloric materials (MCMs) with different Curie temperatures. The predicted results of the present work for parallel-plate regenerators employing different compounds of LaFe13-x-yCoxSiy were broadly in good agreement with the available experimental data. The cooling capacity increases as the number of MCMs increase. However, for a given length of regenerator, an optimum number of MCMs was seen yielding the maximum performance of the refrigerator. For a given number of MCMs, a smaller Curie temperature difference ΔTCu between the MCMs was found to give higher performance.

Numerical Analysis of Transport Phenomenon inside a Pulse Tube Refrigerator Coupled with Fuzzy Logic Controller

This research article illustrates a numerical study of single stage coaxial as well as inline Inertance-Type Pulse Tube Refrigerator (ITPTR). In this present work a computational fluid dynamic (CFD) approach has been adopted for numerical simulation purpose. The detail analysis of cool down behaviour, heat transfer at the cold end and the pressure variation inside the whole system has been carried out by using the most powerful computational fluid dynamic software package FLUENT. A number of cases have been solved by changing the porosity of the regenerator from 0.5 to 0.9 while the rest of the considered parameter is remains unchanged. The operating frequency for all the studied cases is (34 Hz) while the other system dimensions and the boundary conditions are considered unchanged for all cases. The results show that the porosity value of (0.6) produces a better cooling effect on the cold end of the pulse tube refrigerator. The variations of the pressure inside the pulse tube refrigerator during the process are also analysed. In this work an attempt has been made to make a thermally non-equilibrium model applied numerically to the porous region by considering two different energy equations to the solid matrix and for the fluid inside the porous medium and the results are compared with the thermally equilibrium model. In fact, to get an optimum parameter experimentally is a very tedious for iterance pulse tube refrigerator job, so that the CFD approach gives a better solution which is the main purpose of the present work. In the next part the fuzzy logic approach is applied to optimize the different component parameters that affect the cooling performance of the ITPTR. The investigation is performed with different design parameters such as the length and diameter of pulse tube and regenerator given as an input to the fuzzy controller while the output from the controller is the cold end temperature. The predicted optimum results have been verified by performing the confirmation tests.

Experimental study of honeycomb regenerator system for oxy-fuel combustion

An experimental study of a honeycomb regenerator for oxy-fuel combustion has been performed. A laboratory-scale test rig is set up and various experimental parameters such as cell density and length of the honeycomb regenerator, switching time, and bypass effect are investigated. The typical temperature trend of the heating and regenerating process is obtained for the oxy-fuel combustion. The regenerative characteristics for various combinations of these parameters are shown. It is found that part of the exhaust gas should be bypassed to use waste heat more efficiently and to optimize the efficiency of the honeycomb regenerator system for oxy-fuel combustion.

A new tapered regenerator used for pulse tube refrigerator and its optimization

The results of numerical simulation and theoretical analysis of the local heat transfer coefficient and the average remaining gas mass with the length of a uniform cross-sectional regenerator are presented in this paper. It was found that there are some serious thermodynamic limitations in the uniform cross-sectional regenerator and thus the efficiency of the regenerator can not fully exert. In order to further reduce the loss of the regenerator and improve the heat transfer of the cold end, the authors bring forward a design principle: the variation trend of the cross-section of the regenerator will be consistent with the direction of the temperature gradient, and introduce two kinds of tapered regenerators including convergent and divergent in order to improve the performance of the pulse tube refrigerator. Two models were introduced with governing equations to simulate two kinds of pulse tube refrigerators with tapered regenerator. The simulation results showed that there exist an optimum cone angle for tapered regenerator. When the cone angle is close to a certain value, the pulse tube refrigerator with convergent type regenerator can improve the performance which means increasing the cooling power, decreasing the working power, and eliminating the DC-flow rate. But the divergent type regenerator deteriorates the performance. In order to further validate the feasibility of this structural design, based on the enthalpy flow theory, the mechanism of the improvement of the performance of a PTR with tapered regenerator is systemically analyzed.

Optimizing impedances in the traveling wave heat engine

Thermal coupling between solid surfaces and an acoustic working fluid in a regenerator is essential to the operation of a thermoacoustic engine, while the associated viscous coupling, also between the surfaces and the working fluid, is detrimental to the engine's performance and efficiency. The Prandlt number (roughly 0.7 for most gases over a considerable range of temperatures and pressures) fixes the ratio of these two types of coupling for a thermoacoustic engine with a continuous regenerator. This ratio of couplings can be improved in several ways in traveling wave heat engines with short regenerators [P. H. Ceperley, J. Acoust. Soc. Am. 66, 1508–1513 (1979) and P. H. Ceperley, J. Acoust. Soc. Am. 77, 1239–1244 (1985)]. This paper will discuss the optimization of the flow resistance and length of a short regenerator and also resonant impedance enhancement using split mode excitation [P. H. Ceperley, U.S. Patent 4,686,407 (1987)] to significantly reduce the viscous losses while maintaining good thermal coupling.

Flow and heat transfer characteristics of stirling engine regenerator in oscillating flow.

For the design of stirling engine, the basic data on various regenerator materials are required to be offered which have to be incorporated to the design by computerized simulation. The, pressure loss and gas temperature were instantaneously measured for various regenerator materials installed in oscillating fluid flow. Hydraulic diameter is used as the representative length defined by friction factor and Reynold's number, and flow characteristics of different materials were able to be unifomly adjusted. It was found that heat regeneration loss was able to be evaluated by utilizing the hydraulic diameter, length of regenerator, mean temperature on both side of regenerator, mean heat flow. Such simple eavaluation method is effective when it is applyed to actual engine. By using the frictional loss factors and heat regenerating loss obtained by this study, the effect of wire diameter and length of regenerator on indicated thermal efficiency was clarified. 14 refs., 12 figs., 1 tab.