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Thermal Capacities (thermal + capacity)

Distribution by Scientific Domains

Engineering	80%

Selected Abstracts

Computational energy analysis of an innovative isothermal chamber for testing of the special equipment used in the transport of perishable products

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2004
S. K. Chatzidakis
Abstract This paper describes an improved numerical simulation study of an isothermal chamber recently constructed at Zografou Campus of the National Technical University of Athens (NTUA) for the testing of special equipment used for transporting perishable foodstuffs in accordance with the United Nations ATP agreement. Using a transient finite difference model, a simulation is developed for a modern ATP test chamber and a typical specimen refrigerated vehicle to be tested. The simulation results are compared to experimental measurements taken under real conditions by a data acquisition system and a refrigerated semi-trailer as specimen. Proportional,integral control is employed for the regulation of the cooling and heating system. The impact of various parameters on the time required to reach the set-point temperature (tset) is investigated and the energy consumption is simulated for a period of 22 h. In particular, the impact of specimen insulation thickness and the thickness of the chamber insulation floor are considered in detail. The total energy consumption increases by approximately 16% when the concrete floor layer thickness is increased from 8 to 16 cm for typical initial conditions and desired chamber and specimen temperatures of 32.5 and 7.5°C, respectively. Using a floor insulation of 6 cm extruded heavy strain-resistant polystyrene reduces the energy consumption by at least 13%. Specimen insulation thickness increase from U -value of 0.35 W m,2 K to 0.75 W m,2 K result to an increase in energy consumption by a percentage of 28%. Thermal capacity, temperature of car body and specimen dimensions are also treated as variables that affect the total duration of an ATP test and its total energy consumption. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Application of dynamic rating to increase the available transfer capability

ELECTRICAL ENGINEERING IN JAPAN, Issue 4 2009
Masaki Miura
Abstract As the deregulated environment of power systems has spread worldwide, it is essential to operate power systems efficiently and economically. With the advance of communication technologies and sensors, so-called dynamic rating is now to be realized. Dynamic rating is a method which determines accurate ratings by utilizing real-time information such as conductor temperatures, ambient temperatures, and wind speeds. The dynamic rating is considered to increase the thermal capacities of overhead transmission lines and therefore take on importance in the deregulated electric power industry. The importance of the dynamic rating lies mainly in the area of Available Transfer Capability (ATC) improvement. In this paper, the validity of the proposed dynamic rating application is shown from the viewpoint of ATC, especially ATC with thermal constraints. In addition, the possibilities of ATC estimations using sensitivities are verified for the purpose of reducing calculation time, considering the importance of real-time simulation of ATC. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(4): 40,47, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20537 [source]

Behaviour of new refrigerant mixtures under magnetic field

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2005
Samuel M. Sami
Abstract The behaviour of some new alternative refrigerant mixtures such as R-410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point and consequently on the thermophysical properties. Furthermore, the use of magnetic field appears to have a positive influence on the thermal capacities of the condenser and the evaporator depending upon the refrigerant mixture's thermophysical properties. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Effect of magnetic field on the performance of new refrigerant mixtures

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2003
Samuel M. Sami
Abstract Performance test results of new alternative refrigerant mixtures such as R-410A, R-507, R-407C, and R-404A under various conditions of magnetic field are discussed, analysed and presented. The test results were obtained using an air-source heat pump set-up with enhanced surface tubing under various magnetic field conditions. Performance tests were conducted according to the ARI/ASHRAE Standards. The test results demonstrated that as magnetic field force increases, compressor head pressure and discharge temperature slightly increase as well as less liquid refrigerant is boiling in the compressor shell. This has a positive effect in protecting the compressor. The effect of magnetic field on mixture behaviour varies from one mixture to another depending upon the mixture's composition and its boiling point. Furthermore, the use of magnetic field appears to have a positive influence on the system COP as well as thermal capacities of condenser and evaporator. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Assessment of tracheal temperature and humidity in laryngectomized individuals and the influence of a heat and moisture exchanger on tracheal climate

HEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 8 2008
J. Karel Zuur MD
Abstract Background The beneficial function of heat and moisture exchangers (HMEs) is undisputed, but knowledge of their effects on intra-airway temperature and humidity is scarce. The aim of this study was to evaluate the clinical applicability of a new airway climate explorer (ACE) and to assess the HME's influence on tracheal climate. Methods Intratracheal temperature and humidity were measured with and without HME in 10 laryngectomized patients. Results An HME causes the intratracheal mean humidity minima to increase with 3.2 mg H2O/L (95% CI: 1.5,4.8 mg H2O/L; p <.001), from 21.4 to 24.6 mg H2O/L, and the mean temperature minima to decrease with 1.6°C (95% CI: 0.9,2.4°C; p <.001) from 28.5°C to 26.9°C. Relative humidity values suggest that the tested HME keeps inspired air (nearly) fully saturated during the full course of inspiration. Conclusion Assessment of intratracheal temperature and humidity, and evaluation of HME effectiveness is feasible with the ACE. The tested HME significantly increases the intratracheal humidity, but decreases the intratracheal temperature. Relative humidity calculations suggest that increasing the thermal capacity of this rehabilitation device can further increase the heat and moisture exchange efficiency. © 2008 Wiley Periodicals, Inc. Head Neck, 2008 [source]