Transcritical

A steady state simulation model has been developed to evaluate the system performance of a transcritical carbon dioxide heat pump for simultaneous heating and cooling. The simulated results are found to be in reasonable agreement with experimental results reported in the literature. Such a system is suitable, for example, in dairy plants where simultaneous cooling at 4 8C and heating at 73 8C are required. The optimal COP was found to be a function of the compressor speed, the coolant inlet temperature to the evaporator and inlet temperature of the fluid to be heated in the gas cooler and compressor discharge pressure. An optimizing study for the best allocation of the fixed total heat exchanger inventory between the evaporator and the gas cooler based on the heat exchanger area has been carried out. Effect of heat transfer in the heat exchangers on system performance has been presented as well. Finally, a novel nomogram has been developed and it is expected to offer useful guidelines for system design and its optimisation. q Elimination des cristaux de givre sur une plaque froide: effets des fréquences stationnaires et de balayage des champs électriques

In his ambitious 2001 book Toransukuritīku: Kanto to marukusu (translated into English in 2003 as Transcritique: On Kant and Marx), Karatani Kojin formulates what he calls a 'transcritique' by drawing on the work of Kant and Marx. In his own words, it is an undertaking that “forms a space of transcodings between the domains of ethics and political economy, between the Kantian critique and the Marxian critique” by “read[ing] Kant via Marx and Marx via Kant” in a manner which will “recover the significance of the critique common to both.” According to Karatani's reading, both Marx and Kant employ a transcritical perspective which, when faced with an antinomy or antagonism between two (or more) elements, recognises that the locus of radical critique lies not on one side (reductionism), nor beyond both sides (dialectical synthesis), nor even on all sides (relativism), but rather, to borrow a line from Žižek's exegesis of Karatani's book, in “the irreducible gap between the positions – the purely structural interstice between them.” It is in this space that it is possible to carefully oscillate between seemingly contradictory perspectives in a manner that is both transcendental (but not transcendent) and transversal, and thus form a transcritique. This paper will sketch out a reading of Foucault which identifies him as a practitioner of transcritique, and argue that the much-maligned contradictions in his oeuvre reflect a restless yet strategic oscillation between critical positions. It will then suggest that the operation of transcritique should also be performed between different thinkers in order to illuminate the shadows cast by each. The Foucauldian and Karatanian critiques, in particular, can be fruitfully deployed together in the sphere of genealogy – that is, the space in which radical histories of the present can and must be written.

With the ever-growing need for climate change mitigation, CO2 as the sole refrigerant (R744) has become an appealing future-proof option for several refrigeration and heat pump solutions. Currently transcritical CO2 systems offer, by far, the best energy and environmental performance in various medium-and large-capacity applications, provided that some of the available expansion work is recovered via two-phase ejectors. However, although similar benefits are expected for small-scale units (e.g. condensing units), at present no appropriate capacity control strategy is available for two-phase ejectors in these solutions. The aim of this work is to bridge this knowledge gap by presenting the first experimental results related to an innovative capacity control technique for two-phase ejectors in transcritical CO2 condensing units. The novel capacity control methodology is based on the pulse-width modulation (PWM) of the refrigerant flow through the ejector. At the compressor speed of 40 Hz, water temperature at the gas cooler inlet of 35 °C and ethylene glycol temperature at the evaporator inlet of 5 °C, it was found that the high pressure and the cooling capacity can be increased by up to about 20 bar and 17%, respectively. Furthermore, at the optimal operation condition the solution relying on the PWM ejector offered an increase in coefficient of performance (COP) by 14% compared to the unit with passive ejector and by about 29% over the standard system. In addition to the encouraging results obtained, the proposed strategy features low cost, simplicity, low vulnerability to clogging, no need to vary the nozzle throat area for flow control and major potential than its currently available competitors. Having no practical size or application constraints, the suggested capacity control mechanism could possibly lead to lay robust foundations for a significantly more sustainable future in the whole cooling and heating sector.