PDF Publication Title:
Text from PDF Page: 002
J. Sarkar et al. / International Journal of Refrigeration 27 (2004) 830–838 831 Nomenclature c specific heat (kJ kg21 K21) COP coefficient of performance e specific exergy (kJ kg21) ep output exergy (kJ kg21) h specific enthalpy (kJ kg21) i specific irreversibility (kJ kg21) m_ mass flow rate (kg s21) p pressure (bar) q specific heat transfer (kJ kg21) R gas constant (kJ kg21 K21) s specific entropy (kJ kg21 K21) t temperature (8C) T absolute temperature (K) T average temperature w specific work (kJ kg21) Greek h efficiency 1 effectiveness Subscripts 1–6 refrigerant state points 7–10 external fluid state points comp compressor cooling cooling mode ev evaporator evef evaporator external fluid exp expansion device gc gas cooler gcef gas cooler external fluid heating heating mode ihx internal heat exchanger is isentropic max maximum o ambient opt optimum r refrigerant II second law transcritical region. This has led to the development of transcritical carbon dioxide cycles with the condenser replaced by a gas cooler. It is found that the use of gas cooler with heat rejection taking place over an unusually large temperature glide offers several unique possibilities such as simultaneous refrigeration and hot water heating/ steam production, simpler control of capacity etc. Several theoretical and experimental studies have spurred further interest in carbon dioxide based systems in varied applications. Environment friendliness, low price, easy availability, non-flammability, non-toxicity, compatibility with various common materials, compactness due to high operating pressures, excellent transport properties are cited as some of the reasons behind the revival of carbon dioxide as a refrigerant. Past studies indicate that carbon dioxide based systems have great potential in two sectors—in mobile air conditioning and in heat pumps for simultaneous cooling and heating. Extensive applications of carbon dioxide heat pumps were reported by Neksa [5]. Neksa et al. [6] and Yarrall et al. [7] have carried out experimental studies on a transcritical carbon dioxide heat pump prototype. Several manufacturers (mainly Japanese) have announced plans to launch heat pump water heaters based on carbon dioxide and a few more have actually launched products in the market. Although a few studies related to system performance analyses and optimization have been reported [8 – 10], theoretical optimization studies of such systems for simultaneous heating and cooling applications are scarce in open literature. In the present study, the first and second law analyses have been carried out on a carbon dioxide system for simultaneous cooling and heating applications. A computer code has been developed to estimate thermo-physical properties of carbon dioxide for sub-critical and super-critical regions. Based on the results, optimization of the system in terms of COP and exergetic efficiency has been carried out. Correlations are obtained for optimum discharge pressure, optimum gas cooler inlet temperature and COP at optimum conditions in terms of evaporator and gas cooler exit temperatures. 2. Thermodynamic property estimation Span and Wagner [11] have developed a new funda- mental equation in the form of Helmholtz energy based on a comprehensive study on experimental data for thermo- dynamic properties of carbon dioxide. Based on this seminal work a computer code ’CO2PROP’ has been developed to estimate thermodynamic properties of carbon dioxide in sub-critical and super critical region. The code employs the technique based on the derivatives of Helmholtz free energy function. Efficient iterative procedures have been used to predict assorted state properties. A systematic comparison with the published property tables [11] calculated from the equation of state yields a maximum of 0.1% deviation. It may be mentioned that the present code performs much better than some of the available commercial software in the region around the critical point. 3. Process analysis and simulation A simplified sketch of a carbon dioxide based heating and cooling system with its main components is given inPDF Image | Optimization of a transcritical CO2 heat pump cycle
PDF Search Title:
Optimization of a transcritical CO2 heat pump cycleOriginal File Name Searched:
transcritical-co2-heat-pump.pdfDIY PDF Search: Google It | Yahoo | Bing
CO2 Organic Rankine Cycle Experimenter Platform The supercritical CO2 phase change system is both a heat pump and organic rankine cycle which can be used for those purposes and as a supercritical extractor for advanced subcritical and supercritical extraction technology. Uses include producing nanoparticles, precious metal CO2 extraction, lithium battery recycling, and other applications... More Info
Heat Pumps CO2 ORC Heat Pump System Platform More Info
| CONTACT TEL: 608-238-6001 Email: greg@infinityturbine.com | RSS | AMP |