The Experts below are selected from a list of 35178 Experts worldwide ranked by ideXlab platform
Jaroslav Šesták - One of the best experts on this subject based on the ideXlab platform.
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Thermal science and analysis
Journal of Thermal Analysis and Calorimetry, 2013Co-Authors: Jaroslav ŠestákAbstract:History of thermoscopy and thermometry is reviewed showing the role of temperature degrees including the forgotten logarithmic scale. The importance of natural laws of energy, motion, least action, and thermal efficiency is discussed. The meaning of idiomatic terms—thermal physics, thermodynamics, Thermostatics, thermotics, and thermal analysis—is specified and revealed within two parallel developed branches of thermal science. Itemized 105 references with titles.
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chapter 7 thermodynamics and Thermostatics
Science of Heat and Thermophysical Studies#R##N#A Generalized Approach to Thermal Analysis, 2005Co-Authors: Jaroslav ŠestákAbstract:In thermodynamics, the standard postulation approach does not provide direct numerical predictions. The heat exchange between the sample and its surroundings must be familiarized as a fundamental characteristic for the standard thermal analysis examinations, which specifies the experimental conditions of all thermal measurements. Changes in the thermal state of our system are, as a rule, accompanied by changes in nearly all macroscopic properties of the system and vice versa. A change in a macroscopic property results in a change in thermal properties. The course of a chemical reaction that takes place in a homogeneous (continuous) system, can be described by a pair of new quantities—extensive chemical variable, denoted as the thermodynamic extent of reaction; and intensive chemical variable, called the affinity and having a significance that is similar to the chemical potential. Thermoanalytical methods often solve questions connected with the study of oxidation and dissociation processes. Any process of a phase transition does not take place simultaneously within the whole (homogeneous) system, but proceeds only at certain energetically favorable sites, called nuclei. Every system bears certain degree of fluctuations around its equilibrium state. The general expressions describing the balance of mass, momentum and energy are retained, but are extended by a specific rate of energy supply leading to the disparity known as the Clausius-Duhem fundamental inequality.
Claude Amra - One of the best experts on this subject based on the ideXlab platform.
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Anisotropic conductivity rotates heat fluxes in transient regimes.
Optics express, 2013Co-Authors: Sébastien Guenneau, Claude AmraAbstract:We present a finite element analysis of a diffusion problem involving a coated cylinder enabling the rotation of heat fluxes. The coating consists of a heterogeneous anisotropic conductivity deduced from a geometric transformation in the time dependent heat equation. In contrast to thermal cloak and concentrator, specific heat and density are not affected by the transformation in the rotator. Therein, thermal flux diffuses from region of lower temperature to higher temperature, leading to an apparent negative conductivity analogous to what was observed in transformed Thermostatics. When a conducting object lies inside the rotator, it appears as if rotated by certain angle to an external observer, what can be seen as a thermal illusion. A structured rotator is finally proposed inspired by earlier designs of thermostatic and microwave rotators.
Sébastien Guenneau - One of the best experts on this subject based on the ideXlab platform.
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Anisotropic conductivity rotates heat fluxes in transient regimes.
Optics express, 2013Co-Authors: Sébastien Guenneau, Claude AmraAbstract:We present a finite element analysis of a diffusion problem involving a coated cylinder enabling the rotation of heat fluxes. The coating consists of a heterogeneous anisotropic conductivity deduced from a geometric transformation in the time dependent heat equation. In contrast to thermal cloak and concentrator, specific heat and density are not affected by the transformation in the rotator. Therein, thermal flux diffuses from region of lower temperature to higher temperature, leading to an apparent negative conductivity analogous to what was observed in transformed Thermostatics. When a conducting object lies inside the rotator, it appears as if rotated by certain angle to an external observer, what can be seen as a thermal illusion. A structured rotator is finally proposed inspired by earlier designs of thermostatic and microwave rotators.
M. Zaheeruddin - One of the best experts on this subject based on the ideXlab platform.
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dynamic simulation and analysis of a water chiller refrigeration system
Applied Thermal Engineering, 2005Co-Authors: M. ZaheeruddinAbstract:In this paper, a lumped-parameter dynamic model of a water chiller refrigeration system based on mass and energy balance principles is developed. First the component models for an evaporator, compressor, condenser and a thermostatic expansion valve (TEV) were derived. These models were integrated to develop an overall model of a water chiller system. A control-oriented approach to model development was taken and the effect of control inputs such as compressor operational frequency and TEV opening fraction on the output performance of the system was investigated. The transient response characteristics show that the thermal system responses are much slower than pressure and mass flow rate responses revealing a two time-scale property of the system. Steady state performance of the system is also analyzed and graphical relationships between refrigerant mass flow rate, suction vapor superheat temperature, operation frequency and thermostatic expansion valve opening fraction are presented.
Rita Mastrullo - One of the best experts on this subject based on the ideXlab platform.
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Performance of thermostatic and electronic valves controlling the compressor capacity
International Journal of Energy Research, 2006Co-Authors: Ciro Aprea, Rita Mastrullo, Carlo RennoAbstract:The performance of the energy consumption of an electronic valve and a classical thermostatic valve has been compared when these expansion valves are adopted in a vapour compression plant subjected to a cold store. The main aim is to verify experimentally which type of expansion valve would be preferable from energy point of view when a classical thermostat or a fuzzy logic algorithm are used as the control system for the refrigeration capacity. The fuzzy logic-based control is able to modulate continuously the compressor speed through an inverter. The results show that with a fuzzy algorithm, the thermostatic expansion valve allows an energy saving of about 8% in comparison with the electronic valve. When on–off control is used, the electric energy consumption obtained both with the electronic valve and with the thermostatic valve is comparable. Copyright © 2006 John Wiley & Sons, Ltd.
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An experimental evaluation of the vapour compression plant performances in presence of R407C leaks using an electronic expansion valve
Applied Thermal Engineering, 2002Co-Authors: Ciro Aprea, Rita MastrulloAbstract:Chlorofluorocarbons and hydrofluorocarbons (HFCs) used as working fluids in the vapour compression plants, have to be replaced by new substances because of their ozone depletion potential. Zeotropic mixture of HFCs refrigerants that are environment-friendly substances are often employed. The zeotropic mixtures with a large glide temperature could cause problems in the refrigeration control system when a leak occurs because their composition modifies. This paper presents a comparison of the energetic performances, in presence of leaks, when a thermostatic valve and an electronic expansion valve are used in a refrigeration plant, working with the zeotropic mixture designated as R407C (R32/R125/R134a 23/25/52% in mass)—this is the most suitable substitute of the HCFC22. The vapour leaks are simulated at the inlet of the evaporator and at the liquid receiver. Experimental results show that a good adaptability to mixture leaks is related to the electronic expansion valve, while better energetic performances are obtained using the thermostatic expansion valve as long as it is usable.
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Experimental evaluation of electronic and thermostatic expansion valves performances using R22 and R407C
Applied Thermal Engineering, 2002Co-Authors: Ciro Aprea, Rita MastrulloAbstract:An experimental study to evaluate the energetic performances in steady-state and in transient operating modes of an electronic and thermostatic expansion valve is presented. Both valves have been assembled to feed an air cooled evaporator connected to an experimental vapour compression plant with a water cooled condenser operating with a semihermetic compressor. The performances of the valves have been examined at different conditions when the experimental plant works with R22 and with a substitute as the non-azeotropic blend R407C that is chlorine free. Indeed the HCFC designated as R22 contains chlorine that is harmful for the ozone layer and must be replaced in the future. The final results of this study show an overall better performance of the electronic expansion valve compared with the thermostatic expansion valve under transient conditions while in steady-state conditions both the valves are equal in performance. These results apply to both R22 and R407C.