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02918 Simulation of a pebble-bed heat regenerator

02918 Simulation of a pebble-bed heat regenerator

13 Space heating and cooling of air-conditioning, there is a report on how performance differs according to outdoor summer thermohygrometric design c...

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13 Space heating and cooling

of air-conditioning, there is a report on how performance differs according to outdoor summer thermohygrometric design conditions, such as those indicated by UN1 10339, by ASHRAE and by the processing of TRY data. Finally, this paper discusses the optimal choice of design conditions according to the type of application. 00102915 Performance comparative study of new alternatives to R-502 inside air/refrigerant enhanced surface tubing Sami, S. M. and Desjardins, D. E. Inrernarional Journal ofEnergy Research, 2000,

24, (2),

177-186.

In this paper the test results of a performance evaluation of new alternatives; R-407B, R-507, R-408A and R-404A as substitutes to CFC502 are presented. The test results were obtained using an air-source heat pump with enhanced surface tubing under standard AR conditions. The data demonstrated that, as an interim replacement, R-408A blend has a superior performance among the proposed blends including R-502, in the range investigated. Furthermore, the alternatives to R-502 are characterized by high discharge pressure compared to R-502. In particular, R-407B and R-408A have higher discharge temperatures compared to R-502. 00102916 Performance R-502 Sami, S. M. and Desjardins, 2000,

24, (4),

enhancement D. E. fnternarional

of some alternatives Jotrrnal

of Energy

to

Research,

279-289.

The results of an experimental study on the behaviour of some new alternatives to R-502 using heated suction accumulator are presented. The experimental set up was composed of a fully instrumented air-source heat pump with a capacity of 12 000 BTUH and equipped with a heated suction accumulator. The refrigerant temperatures were varied at the evaporator entrance to simulate various extreme conditions encountered in air-source heat pump applications. The primary parameters observed during the course of this study were mass flux, heat flux, quality evaporator and condenser thermal capacities, power consumed and pressure ratios for the azeotropic refrigerant mixtures under investigation. The test results showed that a heated suction accumulator enhanced the evaporation of more volatile component of ternary azeotropic refrigerant mixtures. Thus, increasing the mixture thermal capacity as well as the COP. Furthermore, experiments have also shown capacity increases of 27 per cent with a heat accumulator over an unheated accumulator at -15°C outside air temperatures. 00/02917 Performance of a thermal storage system of the vertical tube type Ismail, K. A. R. and Abugderah, M. M. Energy Conversion & Monagemenr, 2000, 41, (II), 1165-1190. A transient phase change thermal storage system of the vertical tube type is studied using a fixed grid numerical model. The solution of the system consists of solving the equations of the heat transfer fluid (HTF), the pipe wall and the phase change material (PCM) as one domain. The control volume finite difference approach is used to solve the equations describing the phase change thermal storage system. The SIMPLE scheme is used to solve for the pressure and velocity fields of the HTF. The radial temperature distribution, the phase change interface position and the latent and sensible heat accumulated along the system axial length are shown for different Reynolds and Stefan numbers, phase change temperature range and time periods. Also shown in this paper is the possibility of using the numerical model to solve problems with a single temperature phase change. The results obtained are important parameters for PCM thermal system performance investigation and design. 00102918 Simulation of a pebble-bed heat regenerator Choudhury, M. A. A. S. and Hossain, I. Inr. J. Energy Res., 2000, 24, 239250. A mathematical model to simulate the operational behaviour of a pebblebed heat regenerator has been developed and an experimental study performed to test the model predictions. The model is based on finite heat balances for the solid and the fluid applied to a bed which is divided into several sections insulated from each other. Within each section, there is no radial or axial temperature gradient, i.e. the temperature of all the pebbles in a given section are the same. As the fluid stream flows through the idealized compartmented bed, there is heat exchange in each section between the pebbles and the fluid. The model, which is applicable both to the heating and cooling cycles, has been used to simulate the behaviour of a heat regenerator. To test the predictions of the model, experiments have been performed on a 7 ft by 8 in cylindrical column using a hot ;ir stream of approximately 200°C at an average flow rate of 365 I min A special technique, wherein a pebble is fixed to a thermocouple, was used to measure the temperature at different bed positions. Experimental conditions were such that interesting results have been generated. The model was able to predict with good accuracy all the unusual operational behaviour encountered. The deviations between the model and the experimental results can be explained by the fact that the model does not consider heat loss from the column wall. 00102919 Sizing of air-conditioning plant for commercial buildings in Hong Kong Yu, P. C. H. and Chow, W. K. Applied Energy, 2000. 66, (2), 91-103

322

Fuel and Energy Abstracts

September

2000

Results of a survey indicate that 89% of the respondents use PC-based software packages to size their air-conditioning plant; 67% of them care about the building energy use; 83% adopt either ASHRAE standards or CIBSE guides in their design work; 67% intentionally oversize; and 87% use central air-conditioning plant with primary air fan-coil (PAF) systems in their recently completed commercial building projects, 00102920 Substituting propane R290 for R22 in household air conditioner Yan, L. Nanjing Ligong Da-we Xuehao. 1999, 23, (2), 170-173. (In Chinese) The cubical equation of state is used to calculate the thermodynamic properties of R290 and R22. Their theoretical cool circulation properties are compared under the standardized working conditions of the conditioners. A test was made on substituting R290 for R22 in a KF-22GM air conditioner. The test results showed that R290 and R22 have almost the equal refrigerant capacity without any change of the conditioner and with the proper amount of refrigerant. 00/02921 Thermal analysis of electric heating floor panels with daily heat storage Amir, M. e/ a/. Inr. J. Therm. Sci., 1999, 38, (2), 121-131. (In French) During peak winter periods, it is known for electric heating of buildings to result in considerable overloads of the distribution grid. One way to alleviate this problem is to store electricity as thermal energy during offpeak hours and to discharge it during peak hours. In the present study, the thermal behaviour of two electric heating floor panels containing water and n-octadecane paraffin respectively in a concrete structure was examined. In the first case, off-peak electricity is stored as sensible heat in the water and concrete, while in the second case it is primarily stored as latent heat in the paraffin. The choice of dimensions and operating characteristics for each panel were made with the aid of a transient one-dimensional model, validated analytically and experimentally. The one containing paraffin is more compact than that with water (134 mm thickness versus 152 mm), stores more energy (2 880 kJ mm2 versus 2 415 kJ mm*) and provides more comfort since the daily temperature fluctuations at its surface are less significant (1.3”C versus 2.8”C). 00/02922 Thermodynamic analysis of refrigeration systems with monocomponent two-phase fluids Bisio, G. and Pisoni, C. Energy Environ., Proc. Trcrhzon Int. Energy Environ. Edited by Dincer I. and Ayhan T. Symp.. 2nd 1998, 1999, 495-500. The research of a meaningful reference cycle to which actual cycles may be compared for the evaluation of their ‘fitness degree’ is displayed. Vapourliquid and gas-liquid cycles, with and without regeneration, are considered. Also, non-azeotropic mixtures are examined in addition to monocomponent working fluids. 00102923 Thermodynamic modeling of absorption chiller and comparison with experiments Ng, K. C. et al. Heat Transfer Eng.. 1999, 20, (2), 42-52. This paper presents a simple and accurate thermodynamic model for a fourheat-reservoir, absorption chiller. The performance of chillers, as described by l/COP (coefficient of performance), is expressed in terms of the dominant external and internal losses that stem from the finite-rate heat transfer and internal entropy generation in the absorber, condenser, generator and evaporator. It is found that the relative contributions from these losses of absorption chillers govern their behaviour over a wide range of cooling capacities. The successful formulation of the thermodynamic model, as presented in this article, implies that all previous endo-reversible approaches are inadequate because they cannot portray the real behaviour of absorption chillers accurately. At best, these models give only the upper bounds of experimental realities and thus they can be viewed only as subsets of the generic thermodynamic approach described here. To this end, evidence from an experimental facility is given to show that true absorption chiller behaviour is governed by the presence of three key competing losses, namely, the finite-rate heat transfer losses, the internal dissipative losses, and heat leaks. 00102924 Two-phase flow boiling characteristics of alternatives to R-22 inside air/refrigerant enhanced surface tubing Sami, S. M. and Desjardins, D. E. Internarional Journal of Energy Research, 2000.

24, (Z),

109-I

19.

In this paper, an experimental study on the heat transfer characteristics of two-phase flow boiling of alternative zeotropic refrigerant mixtures to R-22, on air/refrigerant horizontal enhanced surface tubing is presented. The new alternatives considered in this study are: R-507, R-404A, R-408A, R-407C and R-410A.The experimental data showed that R-22 has the highest heat transfer rate compared to the other blends in the range investigated. Furthermore, it was also quite evident from these data that R-410A has the highest pressure among the blends under investigation for Reynolds number greater than 3.5 x 10,. However, for Reynolds number less than 3.6 x 104, it appears from the data that R-22 has the highest pressure drop compared to other refrigerants under investigation. 00/02925 Two-phase flow heat transfer correlations for refrigerant-oil mixture flows inside augmented tubes Usmani, G. I. and Ravigururajan, T. S. Enhanced Hear Transfer, 1999, 6. (6).

405-418.