Rotary Regenerator Research Articles

04/01701 A comparison of rotary regenerator theory and experimental results for an air preheater for a thermal power plant: Skiepko, T. and Shah, R. K. Experimental Thermal and Fluid Science, 2004, 28, (2–3), 257–264

04/01701 A comparison of rotary regenerator theory and experimental results for an air preheater for a thermal power plant: Skiepko, T. and Shah, R. K. Experimental Thermal and Fluid Science, 2004, 28, (2–3), 257–264

04/01708 Utilization of alternative fuels and raw materials (AFRs): Scheuer, A. Cement International, 2003, 1, (1), 52–57, 59–66

The aim of the paper is to compare results obtained based on theoretical modeling with directly measured experimental data on a full scale operating air preheater. First, the model of rotary regenerator energy transport involving longitudinal matrix heat conduction is formulated in the paper. Then a solution of the model equation system is presented with reference to authors’ former papers. The results representing temperature distributions of heat exchanging gases and continuously rotating matrix are illustrated by means of 3D charts. For the rotary air preheater of 5.3 m diameter, the temperature distributions computed are compared with experimental data. Right trends and a fair agreement between theory and experiments are found. Finally, the computed and experimental regenerator heat transfer effectivenesses are compared and found to be within ±3% agreement at about 88% regenerator effectiveness.

Analysis of heat and mass transfer in porous sorbents used in rotary regenerators

A new dimensionless formulation, that locally accounts for heat conduction and mass diffusion in solid sorbent materials occurring in either enthalpy exchangers or desiccant wheels has been developed. Governing equations were fully normalized using classical dimensionless groups for heat and mass transfer. The model was validated using previously published results, including experimental data. The proposed equations are easily adaptable to incorporate additional features such as the influence of a supporting structure or the effects of flow entrance regions. Finally, results of a test-case are presented, indicating a possible optimization to wheel construction and compactness by reducing the felt thickness.

Exergy analysis of carryover leakage irreversibilities of a power plant regenerative air heater

Energy recovery devices can have substantial impact on process efficiency and their relevance to the problem of conservation of energy resources is generally recognized to be beyond dispute. One type of such a device, which is commonly used in fossil-fired and air conditioning systems, is the rotary regenerator, in which a stream of hot waste gas exchanges heat with fresh atmospheric air through the intermediate agency of a rotating matrix. As there are gas streams involved in the heat transfer and mixing processes, then there are irreversibilities, or exergy destruction, due to mixing, pressure losses IΔP and due to temperature gradients IΔP. These principle components of total process irreversibility are not independent and there is a trade-off between them. Therefore the purpose of this case study is to demonstrate the importance of the use of exergy analysis in the minimization of carryover leakage irreversibilities of a symmetric balanced rotary regenerator. The chemical exergy Ėo and physical exergy Ėph are calculated and the ratio of chemical and physical irreversibilities has been evaluated for a rotary regenerator used for air preheating in a coal-fired power plant. A numerical finite difference technique has been used to calculate the fluid and matrix temperature distributions effect on the regenerator performance. The effects of variation of the principal design parameters on the irreversibilities and on the regenerator effectiveness are examined and recommendations are made for the selection of the most appropriate parameters.

Exergoeconomic optimisation of an air-conditioning rotary regenerator: effect of matrix thermal conductivity on its performance

The purpose of this paper is to demonstrate the importance of the use of exergoeconomic analysis in the optimisation of the geometry of a rotary regenerator. The optimum geometry of a rotary regenerator is determined using the unit cost of the exergy of the warm air delivered as the objective function. The running cost is determined using different unit costs for the pressure component of exergy, EΔP, and the thermal component of exergy, EΔT, which are evaluated separately. A mathematical model using a finite difference technique of matrix thermal conductivity and heat transfer is presented and the governing differential equations have been formulated in terms of the characteristic dimensionless groups (Πt, Λt and Ζt) and the effect of two different materials is examined. The effect of variation of the regenerator geometry on the objective function is examined and recommendations are made for the selection of the most appropriate parameters for a rotary regenerator. The results show that the effect of thermal conductivity on the minimum exergoeconomic objective function is slightly over 1% for mild steel and 3.374% for aluminium.

Energy and exergy analyses of an experimental open-cycle desiccant cooling system

A procedure is developed for the energy and exergy analyses of open-cycle desiccant cooling systems and it is applied to an experimental unit operating in ventilation mode with natural zeolite as the desiccant. The same procedure and formulations may easily be applied to the units operating in recirculation mode. Energy-based performance parameters such as the coefficient of performance (COP) of the unit and the effectiveness’ of system components are presented. Exergy destruction and exergy efficiency relations for the system and its components as well as the reversible COP of the system are derived. The energy and exergy formulations are applied to the experimental unit using the data collected during a typical operation of the unit. The unit has a COP of 0.35, a reversible COP of 3.11, and an exergy efficiency of 11.1%. Desiccant wheel has the greatest percentage of total exergy destruction with 33.8% followed by the heating system with 31.2%. Rotary regenerator and evaporative coolers account for the remaining exergy destructions. The analysis shows that an exergy analysis can provide useful information with respect to the theoretical upper limit of the system performance, which cannot be obtained from an energy analysis alone. The analysis allows us to identify and quantify the sites with the losses of exergy, and therefore showing the direction for the minimization of exergy losses to approach the reversible COP.

Evaluation of Combined Heat and Mass Transfer Effect on the Thermoeconomic Optimization of an Air-Conditioning Rotary Regenerator

The purpose of this paper is to demonstrate the importance of the use of the exergy analysis in the optimization of the geometry of a periodic-flow regenerator. The optimum geometry of the regenerator is determined using the unit cost of exergy of the warm air delivered as the objective function. The running cost is determined using different unit costs for the pressure component of exergy E˙ΔP and the thermal component of exergy E˙ΔT, which are evaluated separately. The ratio of the two unit costs has been calculated for an air-conditioning application in which the regenerator is used. A mathematical model of condensation, evaporation, thermal conductivity and heat transfer is presented for calculating the fluid and matrix temperatures effect on the regenerator performance. The governing differential equations have been formulated in terms of the characteristic dimensionless groups (Πt,Λt, and Zt).

Design of Regenerative Heat Exchangers

Rotary regenerators are used widely for energy recovery, both in industrial and air-conditioning applications, because of the advantages they have over other types of heat exchangers. In this study, a mathematical model for the design of rotary regenerators is presented. The method is valid for all kinds of channel geometries that form the matrix of a rotary regenerator and can be used for all rotational speeds. The validity of the method is tested with the experimental and numerical results available for rotational speeds between 0.05 and 7 rev/min. A good agreement between the model and the experimental numerical results is obtained. The method presented can therefore be recommended for the safe design of rotary regenerators.

A comparison of rotary regenerator theory and experimental results for an air preheater for a thermal power plant

The aim of the paper is to compare results obtained based on theoretical modeling with directly measured experimental data on a full scale operating air preheater. First, the model of rotary regenerator energy transport involving longitudinal matrix heat conduction is formulated in the paper. Then a solution of the model equation system is presented with reference to authors’ former papers. The results representing temperature distributions of heat exchanging gases and continuously rotating matrix are illustrated by means of 3D charts. For the rotary air preheater of 5.3 m diameter, the temperature distributions computed are compared with experimental data. Right trends and a fair agreement between theory and experiments are found. Finally, the computed and experimental regenerator heat transfer effectivenesses are compared and found to be within ±3% agreement at about 88% regenerator effectiveness.

Experimental and sensitivity analysis of a rotary air preheater for the flue gas heat recovery

Energy saving is one of the key issues, not only from the viewpoint of fuel consumption but also for the protection of global environment. A rotary regenerator (also called an air preheater or a heat wheel) is a sizeable porous disk, fabricated from some materials having a fairly high heat capacity, which rotates between two side-by-side ducts; one for the cold gas; the other for the hot stream. Its application is in a wide range of temperature waste heat recovery systems. In this work, a rotary regenerator is simulated by solving a developed mathematical model and optimized with the experimental design method. In this method, the effect of dimensionless parameters on the effectiveness of rotary heat exchangers was investigated. Numerical results were obtained by solving continuity, momentum and energy equations, and a two-step, predictor–corrector procedure is used. Experimental results are obtained by using a lab-scale rotary type regenerator and factorial design of experiments was performed for the analysis of the data. The simulation results have been compared with the experimental data and good agreement has been obtained.

An analytical solution for a cyclic regenerator in the warm-up period in presence of an axially dispersive wave

Regenerative heat exchangers are important components of energy intensive sectors such as chemical process, power, metallurgical and cryogenic industry. The challenge of simulating regenerators accurately is considerable in view of the transient cyclic process taking place in it. The simulation of warm-up period is even more challenging due to the change in temperature profiles after each cycle. In the present work a modern technique based on the “axial dispersion model” has been utilized to simulate the regenerative heat exchanger both in the warm-up and pseudo-steady state operation. The advantage of this model is that it takes all the flow maldistribution and backmixing effects into consideration instead of idealizing the flow to be so called “plug flow”. In contrast to previous studies with dispersion, in the present study the dispersion is considered to propagate with a finite propagation velocity following a hyperbolic law which is physically more consistent. The effect of different parameters on the cyclic response has been brought out and the results have been verified by comparing results of a rotary regenerator available in literature. The technique utilized in the present study can act as a tool for modelling regenerators where non-uniformity in flow distribution is significant.

Influence of leakage distribution on the thermal performance of a rotary regenerator

A comprehensive modeling is proposed for leakages and thermal performance of rotary regenerators in this paper. It represents a substantial refinement over that available in the literature. Two separate models are proposed for the energy transfer in the regenerator. The first refers to the heat transfer and pressure drop process. The second, based on a gas flow network, represents modeling of leakage distribution within the regenerator. The solution to both models is obtained iteratively with proper input data and yields the thermal/flow design parameters of a rotary regenerator. These models use experimental correlations describing the Nusselt number, friction factor and seal discharge coefficients. A design procedure is outlined for the rating problem and details are referenced. Keeping the pressure leakage factor constant, the rating problem has been solved for different distributions of leakages through radial, peripheral and axial seals. The results clearly demonstrate that a significant reduction could occur in the thermal energy transfer to the cold fluid even with reasonably small (5% or so) individual leakages.

Analysis of the gas turbine rotary regenerator

Recent solution of the ‘Hausen’ regenerator and conjugate heat transfer problems invites a fresh look at the Ritz rotary regenerator. The approach deals readily with the reflux phase (‘hold-up’, flushing or ‘residence time’) and with the effects of friction (re-heating and pressure drop). There is no necessity to assume constant Stanton number, Nst, and friction factor, Cf. With accurate temperature and flow solutions available, recovery ratios in terms of operating parameters are a fait accompli. Optimization for specified duty becomes possible.

Indirect Estimation of Leakage Distribution in Steam Boiler Rotary Regenerators

Leakages are inherently associated with the heat transfer process in a rotary heat exchanger, owing to clearances brought about by construction difficulties and rotor-housing thermal distortions. The method proposed permits one to evaluate leakage distributions within steam boiler rotary regenerators. In principle, the method is based on a gas flow diagram of the regenerator, where gas streams are arranged into a network in which the corresponding mass flow rates are governed by pressure drops in the seals and matrix rotation. Moreover, energy and mass balances are taken into account where appropriate. On this basis, a nonlinear equation system modeling gas flows within the rotary regenerator is derived. Supplementing this system with data determined experimentally, one obtains a closed form of the gas flow problem, the solution of which gives particular gas mass flow rates within the regenerator and the leakage distribution resulting from it. On the basis of experiments carried out on real devices, the approach presented is exemplified with two particular cases accompanied by evaluation of uncertainties in the final results. A comparison of the results presented with those available by another method concludes the article.

Regenerator Effectiveness During Transient Operation

Current designs of regenerative gas turbines include high-effectiveness rotary regenerators. The regenerators make the gas turbines highly efficient during steady-state operation. During engine transients, however, engine efficiency can be low because high-effectiveness regenerators tend to have large cores with large thermal masses, and it can take a long time (minutes for example) for these regenerators to reach their steady-state effectivenesses. The following criterion determines the response time of regenerators: τss˜(mc)R/Cx, where τxx (S) is the time period of transient operation; (mc)R (J/K) is the heat capacity of the core; and Cx (W/K) is the heat-capacity rate of the exhaust. This criterion has been verified through analysis and experimentation. The criterion enables the designer to estimate the fraction of an operating cycle during which the regenerator will have reduced effectiveness.

Low-leakage and High-Flow Regenerators for Gas Turbine Engines

The preliminary analysis and development of two new forms of regenerative heat exchanger that seem to promise greatly improved performance characteristics is described. To reduce drastically the usually high leakage and high seal wear rates suffered by present rotary regenerators, discontinuous rotation of the matrix has been studied, with seals that clamp the matrix during the stationary periods. To enable the regenerative gas turbine cycle to be used at high powers, regenerators consisting of movable ceramic modules are being investigated. The potential applications of the discontinuous-rotation type are particularly to small lightweight gas turbine engines such as those for automotive applications and to helicopters and light turboprop aircraft. The modular regenerator is being studied in application to burning coal and biomass of gas turbine engines and to larger marine and stationary base-power engines with power outputs of up to (and possibly beyond) 100 MW.

Second-law optimization of regenerative heat exchangers, including the effect of matrix heat conduction

The effects of heat conduction in a regenerator matrix and unbalanced heat-capacity rates on the second-law efficiency of rotary regenerators are documented. The results show that the maximum second-law efficiency increases as the ratio of the heat-capacity rate increases. The overall number of transfer units NTU o corresponding to this optimum also increases with heat capacity rate C ∗ . Including the effect of heat conduction in the regenerator matrix lowers the second-law efficiency and increases the NTU o required to obtain the maximum second-law efficiency. These results can be used to design and optimize the performance of a regenerator considering both heat transfer and pressure drop effects.

TRANSIENT TEMPERATURE DISTRIBUTION IN ROTARY REGENERATOR HEAT EXCHANGER

The purpose of this study is to analyse dynamic response of rotary regenerator for dynamic simulation of automotive gas turbine using a simplified method. Exit temperatures of working fluids in rotary regenerator depend on time, position of core, inlet temperature of working fluid and initial temperature of core. We tried to simplify the calculation model of rotary regenerator, as a counter flow heat exchanger and show that they give good results compared to the available analytical solution.

Some Essential Principles for Adjustment of Seal Clearances in Rotary Regenerators

Abstract In the present study, attention is paid to some indispensable principles for making a useful adjustment of seal clearances in a rotary regenerator, illustrated by means of examples. First, the effect of leakages and their distribution within such a heat exchanger on the efficiency of a steam power plant is presented. In this way it is shown that not only total leakage but also the distribution of the leakages within the rotary regenerator have an important influence on the efficiency. An interesting conclusion appears here—reduction in total leakage may even bring about a drop in power plant efficiency if distribution of leakages changes unfavorably. Second, in order to show in which rotor state seal clearances should be adjusted, appropriate examples of experimental results concerning radial seal clearances in the hot and cold rotor state are compared. Next, on the basis of a leakage network and some experimental data before and after reduction in radial seal clearances, the effect of reduction ...

The effect of wall conduction on the performance of regenerative heat exchangers

The effect of heat conduction in the wall on the effectiveness of rotary regenerators is described. In order to document the effect of wall conduction, it is assumed that the thermal conductance of the solid is finite, both parallel and perpendicular to the gas flow. Two parameters introduced for modeling conduction effects are the Biot numbers in the y(Bi y ) and x(Bi x ) directions. Our results show that for certain values of Bi x and Bi y , the effectiveness including wall conduction can deviate substantially from results obtained when wall conduction is neglected.