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05023 Predicting flow boiling heat transfer of refrigerants in microfin tubes
13 Minimizing throttling losses in the refrigeration 97lO5014 cycle Domanski, P. A. Proc. Int. Congr. Refrig., 19th, 199.5, 4I3, 766-773. The molar heat capacity at given reduced temperatures in the evaporator and condenser is the major determining factor in throttling losses. The potential for improving the system COP increases with the atmosphere of throttling losses for ail three modified cycles. The economizer and ejector cycle increase the COP for all fluids. The improvement results from both the increased capacity and reduced work, the latter having a more significant effect. The COP of the ejector cycle is very sensitive to the ejector efficiency. Due to limited knowledge of two-phase ejectors, it is unclear what efficiency level they can achieve. When the single-phase component efficiencies (0.8.5 for a nozzle, 0.7 for a diffuser) were used in simulations for R-134a at two operating regimes, the economizer cycle had a marginally better COP than the ejector cycle. Modification test of staged pulse tube refrigerator 97105015 for temperatures below 4 K Chen, G. et ul. Cryogenics. 1997, 31, (9), 529-532. Both to improve the performance of and to further simplify a staged pulse tube refrigerator, structure modification tests were completed. The influence of operation parameters on cooling effect has also been tested. A double-orifice configuration was used to enhance the phase shift effect and as a result liquid helium temperatures were reached by a two-stage pulse tube refrigerator. Experimental results are presented and evaluated. Numerical analysis of 4 K pulse tube coolers: Part I. 97105016 Numerical simulation Wang, C. Cryogenicy. 1997, 37, (4). 207-213. The development of a computer program for numerical simulation of 4 K pulse tube coolers is described. The program takes into account non-ideal gas properties of “He, the properties of the magnetic regenerative material, and the heat transfer in the heat exchanger and regenerator. The presented modelling is very efficient for visualizing physical processes in 4 K pulse tube coolers. The numerical predictions are compared with the performance of existing pulse tube coolers for liquid helium temperature and reasonable agreement was found. Numerical analysis of 4 K pulse tube coolers: Part 97105017 II. Performances and internal processes Wang, C. Cryogenics, 1997, 37, (4). 215-220. Numerical simulation was used to analyse the processes and performance of two configurations of 4 K pulse tube coolers and a G-M cooler. A configuration of the pulse tube cooler where the phase sifter is located at room temperature does not lead to an efficient phase shifting of the moving liquid helium at the cold end. Effects of double-inlet operation and structure parameters of the 4 K regenerator are also analysed. Numerical model for the behaviour of a salt97105016 gradient solar-pond greenhouse-heating system Badran, B. B. et al. Applied Enerp, 1997, 58, (1). 57-72. A parametric study is presented of a salt-gradient solar-pond greenhouseheating system under Jordanian climatic conditions using a one-dimensional numerical model which has been solved using a definite difference technique. The model makes use of several empirical correlations for calculating solar fluxes and heat losses from the solar pond. The surface area of the pond, the non-convective zone (NCZ) and the lower convectivezone (LCZ) thicknesses, the inclination wall angles of the pond, the greenhouse area, the greenhouse cover transmittance, and the thermal load extracted are some of the parameters considered. Under Jordanian climatic conditions, the solar pond can provide 30% of the heating load for the greenhouse. Optimal operation of an embedded-piping floor 97105019 heating system with control input constraints Zaheer-Uddin, M. et al. Energy Cowem. Mgmt, 1997, 38, (7). 713-725. The paper explores the dynamic modelling and optimal control of an embedded-piping floor heating system. The system consists of a single zone with serpentine tubes embedded in the floor slab. A gas-fired boiler supplies hot water in the tubes. The input energy to the boiler and the mass flow rate of hot water circulating in the tubes is modulated. A numerical solution to the 24-hour optimal control problem, taking into consideration the capacity constraints of the floor heating system, is found. Results show that, by proper choice of objective function, the energy input to the boiler can be minimized while maintaining good zone temperature control. The implementation of the optimal trajectories using Pl controllers is also shown. Optimum dimensions of plate fins for fin-tube heat 97105020 exchangers Kundu. K. and Das. P. K. Fluid and Heat Flow, 1997. 18, (5). 530-537. This study determined the optimum dimensions of the fin fo; the fin-tube heat exchangers for both rectangular and equilateral triangular arrays of tubes. For a fixed fin volume, maximum heat dissipation was obtained for a particular value of pitch length or fin thickness. The optimization is done by the classical derivative method. Design curves, based on the mathematical analysis, have been constructed for the design of optimum fins. It is confirmed that the concept of equivalent annular fin can be extended to calculate the optimum fin dimensions.
Space heating and cooling
97105021 Performance analyses of sensible heat storage systems for thermal applications Dincer, 1. et al. Int.J. Energy Res., 1997, 21, (12), 1157-1171. Sensible heat storage (SHS) systems and performance evaluation techniques aie studied in this work. A detailed investigation is presented of the availability of SHS techniques for solar thermal applications, selection criteria for SHS systems, the economics of SHS systems, the main issues in evaluating SHS systems, the viability of SHS systems, the environmental impacts of SHS systems and criteria for SHS feasibility studies, as well as energy saving options. In addition to energy and exergy analyses, several definitions of energy and exergy efficiency for the performance of SHS Systems are provided with an illustrative example. 97105022 Polybranched regenerative GAX cycles for combined power and cooling production Staicovici, M. D. Proc. Int. Congr. Refrig., 19th, 1995, 4A, 542-551. A great potential for primary energy saving and environment progress is offered by this combined power and cooling production, using advanced absorption technology. Cogeneration of power and cooling is modelled in order to compare absorption with mechanical vapour compression. The polybranched regenerative generator-absorber heat exchange (PBR GAX) cycles were considered for absorption. These new cycles have far better COP values than all others published GAX or double and triple-effect cycles, for similar working parameters. For the mechanical vapour compressor, two well-designed ammonia compressors with one and two stages are considered. According to the present study, the specific absorption cooling effect (MJ/kg of extracted steam) is 2-2.5 times higher than that achieved through compression, for a wide range of cooling working parameters. The economic assessments show attractive, less polluting, investments in PBR GAX based cogeneration operated cooling equipments. 97105023 Predicting flow boiling heat transfer of refrigerants in microfin tubes Kandlikar, S. G. and Raykoff, T. Enhanced Heat Transfer, 1997, 4, (4). 257-268.
To make use of the information available on microfin performance in the design of equipment, it is necessary to correlate this data into a readily usable form. Kandlikar presented a correlation scheme to correlate flow boiling data for augmented tubes and compact evaporators and in this work the Kandlikar correlation is modified to correctly account for the Reynolds number exponent in the single-phase flow. Also the missing (k/D) ratio is introduced in the single-phase heat transfer correlation. The augmented tube correlation scheme was applied to five sets of microfin tube flow boiling data available in literature. A single set of constants was found to correlate different refrigerant data sets obtained with the same microfin tube geometry. Parametric trends in heat transfer coefficient for microfin tubes obtained from the correlation are presented. Microfin geometry was found to influence the enhancements in the nucleate boiling and the convective boiling contributions in the microfin tubes. A single-phase heat transfer data should be obtained for the tube over a wide range of Reynolds number in order to improve its correlation capability. 97105024 Prediction of pool boiling heat transfer with new refrigerants based on thermodynamic similarity Golobic, 1. and Gaspersic, B. Proc. Int. Congr. Refrig., 19th, 1995, 4A, 230237.
A method of predicting the pool boiling heat transfer coefficient based on thermodynamic similarity was developed. The coefficient for fluids, especially new refrigerants, where thermodynamic and transport properties over the temperature range are not known, can be determined with only fluid protection constants such as molecular weight, critical temperature, critical pressure and normal boiling point. 97105025 Pulse tube coolers for HTS devices Evans, B. E. and Richardson, R. N. Cryogenics, 1997, 37, (10). 695-697. Where thermal loads are relatively small, cryocoolers offer a convenient means of cooling, particularly where bath cooling is not required and the load may be attached directly to the cold head. Depending on the type of cooler and number of stages, it is possible to reach temperatures of 4 K and below. Unlike either Gifford-McMahon (G-M) or Stirling coolers, pulse tubes have no active components operating at low temperature. Therefore, they offer the potential of high reliability together with an absolute minimum of microphonics at the cold station. Their simplicity means that they could probably be produced at relatively low cost if there was sufficient demand. Applications already under consideration include the cooling of processor chips and other semiconductor devices, but pulse tubes obviously hold considerable potential in high-temperature superconductor (HTS) device applications. 97l95026 Pulse tube refrigerator with low temperature switching valve: concept and experiments Liang, J. el al. Cryogenics, 1997, 37, (9). 497-503. A new type of pulse tube refrigerator is proposed, with low temperature switching valve. Industrial applications requiring greater refrigeration powers will benefit from this new concept. In place of a regenerator, this refrigerator uses a recuperative heat exchanger and a switching valve is installed at the cold end of an orifice pulse tube. The adiabatic expansion efficiency of the orifice pulse tube with low temperature switching valve has
Fuel and Energy Abstracts
November
1997
435
Space heating and cooling
97105021 Performance analyses of sensible heat storage systems for thermal applications Dincer, 1. et al. Int.J. Energy Res., 1997, 21, (12), 1157-1171. Sensible heat storage (SHS) systems and performance evaluation techniques aie studied in this work. A detailed investigation is presented of the availability of SHS techniques for solar thermal applications, selection criteria for SHS systems, the economics of SHS systems, the main issues in evaluating SHS systems, the viability of SHS systems, the environmental impacts of SHS systems and criteria for SHS feasibility studies, as well as energy saving options. In addition to energy and exergy analyses, several definitions of energy and exergy efficiency for the performance of SHS Systems are provided with an illustrative example. 97105022 Polybranched regenerative GAX cycles for combined power and cooling production Staicovici, M. D. Proc. Int. Congr. Refrig., 19th, 1995, 4A, 542-551. A great potential for primary energy saving and environment progress is offered by this combined power and cooling production, using advanced absorption technology. Cogeneration of power and cooling is modelled in order to compare absorption with mechanical vapour compression. The polybranched regenerative generator-absorber heat exchange (PBR GAX) cycles were considered for absorption. These new cycles have far better COP values than all others published GAX or double and triple-effect cycles, for similar working parameters. For the mechanical vapour compressor, two well-designed ammonia compressors with one and two stages are considered. According to the present study, the specific absorption cooling effect (MJ/kg of extracted steam) is 2-2.5 times higher than that achieved through compression, for a wide range of cooling working parameters. The economic assessments show attractive, less polluting, investments in PBR GAX based cogeneration operated cooling equipments. 97105023 Predicting flow boiling heat transfer of refrigerants in microfin tubes Kandlikar, S. G. and Raykoff, T. Enhanced Heat Transfer, 1997, 4, (4). 257-268.
To make use of the information available on microfin performance in the design of equipment, it is necessary to correlate this data into a readily usable form. Kandlikar presented a correlation scheme to correlate flow boiling data for augmented tubes and compact evaporators and in this work the Kandlikar correlation is modified to correctly account for the Reynolds number exponent in the single-phase flow. Also the missing (k/D) ratio is introduced in the single-phase heat transfer correlation. The augmented tube correlation scheme was applied to five sets of microfin tube flow boiling data available in literature. A single set of constants was found to correlate different refrigerant data sets obtained with the same microfin tube geometry. Parametric trends in heat transfer coefficient for microfin tubes obtained from the correlation are presented. Microfin geometry was found to influence the enhancements in the nucleate boiling and the convective boiling contributions in the microfin tubes. A single-phase heat transfer data should be obtained for the tube over a wide range of Reynolds number in order to improve its correlation capability. 97105024 Prediction of pool boiling heat transfer with new refrigerants based on thermodynamic similarity Golobic, 1. and Gaspersic, B. Proc. Int. Congr. Refrig., 19th, 1995, 4A, 230237.
A method of predicting the pool boiling heat transfer coefficient based on thermodynamic similarity was developed. The coefficient for fluids, especially new refrigerants, where thermodynamic and transport properties over the temperature range are not known, can be determined with only fluid protection constants such as molecular weight, critical temperature, critical pressure and normal boiling point. 97105025 Pulse tube coolers for HTS devices Evans, B. E. and Richardson, R. N. Cryogenics, 1997, 37, (10). 695-697. Where thermal loads are relatively small, cryocoolers offer a convenient means of cooling, particularly where bath cooling is not required and the load may be attached directly to the cold head. Depending on the type of cooler and number of stages, it is possible to reach temperatures of 4 K and below. Unlike either Gifford-McMahon (G-M) or Stirling coolers, pulse tubes have no active components operating at low temperature. Therefore, they offer the potential of high reliability together with an absolute minimum of microphonics at the cold station. Their simplicity means that they could probably be produced at relatively low cost if there was sufficient demand. Applications already under consideration include the cooling of processor chips and other semiconductor devices, but pulse tubes obviously hold considerable potential in high-temperature superconductor (HTS) device applications. 97l95026 Pulse tube refrigerator with low temperature switching valve: concept and experiments Liang, J. el al. Cryogenics, 1997, 37, (9). 497-503. A new type of pulse tube refrigerator is proposed, with low temperature switching valve. Industrial applications requiring greater refrigeration powers will benefit from this new concept. In place of a regenerator, this refrigerator uses a recuperative heat exchanger and a switching valve is installed at the cold end of an orifice pulse tube. The adiabatic expansion efficiency of the orifice pulse tube with low temperature switching valve has
Fuel and Energy Abstracts
November
1997
435