摘要:

AbstractDuring the past seven years, the Florida Solar Energy Center (FSEC) has conducted extensive experimental research on radiant barrier systems (RBS). This paper presents recent research on the development of mathematical attic models and results from a sensitivity analysis of RBS performance parameters.Two levels of modelling capability have been developed. A very simplified model based on ASHRAE procedures is used to study the sensitivity of RBS performance parameters, and a very detailed finite‐element model is used to study highly complex phenomena, including moisture adsorption and desorption in attics. The speed of the simple model allows a large range of attic parameters to be studied quickly, and the finite‐element model provides a detailed understanding of combined heat and moisture transport in attics.This paper concentrates on the sensitivity analysis of attic RBS performance parameters using the simplified model. The development of the model is described, and results of the analyses are presented and discussed. Results from the finite‐element model are also presented and compared with measurements from a test attic to illustrate the effects of moisture adsorption and desorption in common attics.The simplified steady‐state model shows excellent agreement with measured steady‐state data when thermal stratification of the attic air is modelled. Results of the sensitivity analysis using this model show that the radiant barrier surface emittance and the attic ventilation inlet air temperature are the most sensitive performance parameters for attic radiant barrier systems.The detailed, finite‐element model shows that moisture sorption phenomena can have significant effects in attics. The daily temperature extremes in attics are significant, and they induce a moisture flux at the surfaces of the materials bounding the air zone(s). If this moisture flux is not accounted for in detail (i.e. with fully coupled heat and moisture transport equations) inaccurate surface temperature predictions are like

ISSN:0363-907X    

DOI:10.1002/er.4440160102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe economic viability of air heating for grain drying with the aid of heat pumps and the viability of replacing existing heating methods (i.e. direct electrical heaters and diesel burners) with heat pumps are investigated. The energy costs of different types of heating apparatus to dry grain are calculated and, taking the different capital costs into account, the life cycle costs of the heating methods can be predicted. On comparing the life cycle costs of the different heating methods, it is concluded that heat pumps are more economical than other methods of heating provided that the apparatus is used for more than a minimum period per year. Drying of grain is usually done for periods shorter than this minimum; the result is that the use of heat pumps cannot be economically justified for the drying of grain only.

ISSN:0363-907X    

DOI:10.1002/er.4440160103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe paper describes the integration of a chemical and a vapour‐compression heat pump for energy storage applications. The vapour‐compression system is designed to operate using the UK cheap rate ‘Economy 7’ electricity tariff. The system is characterized thermodynamically using various refrigerant/absorbent pairs in the chemical storage circuit and an ozone‐friendly refrigerant, R134a, in the vapour‐compression circuit. Results indicate that the H2O/Na2S pair provides a high energy storage density and is the most suitable for use in this system. The paper also describes the design features of a domestic‐sized version of this heat pump system. Air in the sunspace (conservatory) of a house was used as a heat source for

ISSN:0363-907X    

DOI:10.1002/er.4440160104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this paper a systematic method of choosing the gain parameter of the wind turbine generator pitch control is presented using the Lyapunov technique that guarantees stability. A comprehensive digital computer model of a hybrid wind–diesel power generation system including the diesel and wind power dynamics with a superconducting magnetic energy storage (SMES) unit for stability evaluation is developed. The effect of introducing an SMES unit for improvement of stability and system dynamic response is studied. Analysis of stability has further been explored using an eigenvalue sensitivity technique. The eigenvalues of the system with and without an SMES unit are studied and the effect of variation of the SMES unit parameters on eigenvalue locations are plotted. The dynamic response of the power system to random load changes with optimal gain setting is also presente

ISSN:0363-907X    

DOI:10.1002/er.4440160105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe combined free convection and mass transfer flow in a plume over a vertical needle is studied. This mixed type of flow is produced from a point heat‐mass source at the tip of the needle. A numerical solution of the similarity equations of the problem under consideration is obtained. The velocity, temperature and concentration profiles are shown for different values of the dimensionless parameters entering into the problem under consideration. The flow field is greatly influenced by the dimensionless parameters α (heat‐source strength) and β (mass‐source st

ISSN:0363-907X    

DOI:10.1002/er.4440160106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractMolten steel produced in an electric arc furnace is poured into a ladle and transported to a continuous casting machine. In order to minimize the heat losses during transportation, the inner surface of the ladle is lined with refractory material. Also, this inner surface needs to be preheated to prevent the cooling of the molten steel below the casting temperature. The paper describes a dynamic model for a ladle preheater with the objective of predicting the heat‐up time. It has been validated by experiments performed on an existing ladle in an iron and steel mill. The results predicted by the model are sufficiently accurate for practical use. The model is further used to investigate several important operating parameters that are expected to shorten the heating time, conserve energy and increase the productivit

ISSN:0363-907X    

DOI:10.1002/er.4440160107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAn experimental investigation was made to study the effect of some operating parameters on the bed‐to‐wall heat transfer in a 5.25 m‐tall circulating fluidized bed having a 102 mm‐square cross‐section with a bed temperature varying from 350 to 1173 K, a superficial velocity from 4 to 8 m/s, and a bed inventory from 15 to 40 kg of sand with a mean particle diameter of 309 μm. Two heat flux probes were used at two different locations in the furnace for measuring the heat transfer coefficient. The experimental results were compared with those of other investigators and also with the data predicted from a proposed theoret

ISSN:0363-907X    

DOI:10.1002/er.4440160108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAn energy audit was performed to determine the energy patterns of the cement industry in United Arab Emirates (UAE). A macro‐energy analysis revealed that the cement industry consumes annually 467,000 tons of oil equivalent (TOE). The thermal energy consumption represents 81–91% of the total utilized energy. The breakdown of the overall energy requirements among the most important unit processes was determined covering the cement production lines in the UAE and was compared with published values in the literature.A micro‐energy analysis was also carried out for one of the cement production lines to determine the thermal energy disposition by type. The study revealed that the thermal losses via the exit gases and the radiation losses account for 25 and 13%, respectively, of the total input thermal energy.Opportunities for energy conservation such as a change from expensive liquid fuels to relatively cheap natural gas and the modification of existing energy consuming systems are disc

ISSN:0363-907X    

DOI:10.1002/er.4440160109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAn analytical study is performed to examine the thermal diffusion characteristics of free convection and mass transfer flow in a non‐Newtonian fluid (Walters, 1962: liquid B') past a uniformly accelerated infinite vertical plate in the presence of thermal diffusion. The expression for the velocity field is obtained by the Laplace transform technique. The influence of the Soret number (a thermal diffusion parameter) on the velocity field is extensively discussed with the help of graph

ISSN:0363-907X    

DOI:10.1002/er.4440160110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:0363-907X    

DOI:10.1002/er.4440160111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY