Francis Meunier

Solid sorption heat powered cycles for cooling and heat pumping applications

Heat powered solid sorption is a feasible alternative to electrical vapour compression. However, the emergence of that technology takes time. In this review, the possibilities and limits of this technology are analysed. The performances are shown to be very interesting and in progress, and right now applications are foreseen. The use of waste heat for solid sorption air-conditioning may be an attractive application, but, for a large dissemination, higher efficiencies as well as cost reduction are required. With respect to primary energy and global warming, sorption cooling and heat pumping is coherent, except for waste heat or solar applications, only if the cooling COP is larger than about 1 or 1.2 depending on operating conditions. Technical results are close to that point which provide a wider perspective.

Numerical analysis of adsorptive temperature wave regenerative heat pump

Abstract An adsorptive heat pump system with the temperature wave heat generation is numerically analysed, using a two-dimensional model which takes into account both heat and mass transfer processes inside the adsorber. In the model, the gaseous phase flow is described by Darcys law. The adsorber is heated or cooled by an external thermal fluid which is considered as one-dimensional. The mathematical model is numerically solved using the ADI finite difference method. Numerical simulations are performed on two adsorption systems: zeolite NaX-water and activated carbon AX21-ammonia. The effects of the operating parameters, such as cycle time, permeability and heating temperature, on the cooling coefficient of performance and the power of cold production are discussed. Finally, the temperature wave regenerative heat pump system is compared to the basic adsorptive heat pump process.

Use of roadsides by diurnal raptors in agricultural landscapes

In a 2772 km survey in western France, we compared the relative abundance and activity of diurnal raptors along motorway verges and secondary roads to those in open cropland, during different seasons and hours of the day. Motorway verges, and to a lesser extent secondary road verges, were used significantly more than adjacent areas by buzzards (Buteo buteo), kestrels (Falco tinnunculus) and black kites (Milvus migrans), but not by harriers (Circus aeruginosus, C. cyaneus, C. pygargus). There was a seasonal shift in the use of roadsides by buzzards and kestrels, with a high use of motorway verges in winter and a low use in summer. Although kestrels and buzzards clearly used verges for hunting, their abundance along roads was not directly related to the relative abundance of small mammals. The supply of perching sites, allowing a less energy-demanding hunting behaviour than flight-hunting, and the width of the verges, appeared important factors in the attractiveness of roadsides for these species. This study shows that roadsides, particularly wide motorway verges, can be managed with respect to the conservation and abundance of raptor species in agricultural landscapes, in providing stable prey habitats and perching sites.

Bird communities of highway verges: Influence of adjacent habitat and roadside management

Abstract We have investigated the effects of landscape traversed and roadside structure on the use of highway verges by birds. Three contrasted landscapes were chosen in terms of human land use and vegetation structure: an intensive farmland, a pine plantation, and a matoral. The roadside sections varied in vegetation structure, width and profile. We recorded birds present in roadsides and adjacent habitats by transect counts over all seasons. Roadside bird species appeared for a great part similar to those of adjacent habitats. However, diversity and abundance in verges did not depend on that of adjacent habitats. Woody roadsides were comparable to hedges, as trees (and shrubs) in verges enhanced species richness and abundance of birds in the farmland and woodland sites. Width and profile of verges had less influence. In all sites, typical species of the habitat traversed partly avoided roadsides. On the contrary, numerous species associated with ‘rare’ habitats in one site preferred roadsides, provided that verge vegetation contrasted with the dominant habitat. It is concluded that birds responses to highways can vary greatly with landscape traversed and verge vegetation. Highway verges could be favorable to birds, if they constitute a complementary habitat to the dominant habitat within a landscape.

Adsorption heat pump modeling: the thermal wave process with local equilibrium

Abstract This paper describes a model for a thermal-wave adsorption heat pump cycle. Local equilibrium is assumed, providing the asymptotic best-case performance. The model is utilized to examine the performance of adsorption refrigeration cycles powered by low temperature waste heat sources of 373–393 K. The impact of varying system temperatures, bed cycling frequency, valve positioning, and sectioning of the bed are examined. Cycle coefficients of performance (COPs) were greater than 1.2 for the base case of a 393 K heat source, 303 K condenser temperature, and 278 K evaporator temperature for a cycle utilizing a water/NaX zeolite adsorbate/adsorbent pair. As an effect of the small temperature changes during the cycle, for some regions of the bed, the loading change was opposite of that expected; i.e., from the start to the end of the entire heating process some portions of the bed experienced loading increases. The location of the inlet/outlet valves in the bed was found to have an impact on the shape of the temperature and loading fronts. The introduction of partitions within the bed was found to have only a small impact on the performance of the cycle for the temperatures examined, with sections of the bed undergoing pressurization in a non-sequential order.

Second-law analysis of adsorptive refrigeration cycles: The role of thermal coupling entropy production

Abstract The reason why the performance of adsorptive refrigeration cycles is always less than that of the Carnot cycle corresponding to the same heat reservoir temperatures is analysed. This analysis is performed using the entropy production concept and introducing numbers of entropy production which are a direct measure for the efficiency degradation. The thermal entropy production due to the external thermal coupling of the isothermal heat reservoirs to the temperature varying adsorbers is important in all cases considered. It prevails for the basic uniform temperature cycle (about 95% of the total entropy production). For n-adsorber uniform temperature cycles, internal thermal entropy production (due to heat recovery between adsorbers) may reach 50% of the external thermal entropy production. The entropy production due to the refrigerant flow inside the unit does not depend on the process and is small (less than about 10%) in all cases. For thermal wave cycles, the origin of the entropy production depends highly on the cycle time. For very short cycle times, the external thermal entropy production is very small but an important internal thermal entropy production is observed in the adsorbers. For long cycle times, it is the opposite, the external thermal entropy production becomes very large while the internal thermal entropy production in the adsorbers does not increase.

A comparison of experimental and theoretical adsorption kinetics of dichloromethane vapour by active carbon under non-isothermal conditions

The kinetics of the adsorption of dichloromethane vapour by a typical active carbon have been measured at 288 and 323K and for spherical granules of 0.25 and 1.0 mm in diameter. The data have been analysed within the framework of a model for adsorption by bidispersed systems and under non-isothermal conditions. Micropore diffusion is the rate-controlling step, and direct measurements show that the process is not isothermal. However, thermal effects do not seem to influence significantly the kinetics of adsorption. Good agreement can be found between experimental and calculated data, and the model leads to micropore diffusivities and heat-transfer coefficients for the system under investigation.

Entropic Analysis of Regenerative Adsorptive Refrigeration Cycles

An entropic analysis of regenerative adsorptive refrigeration cycles shows that the thermal coupling of adsorbers to heat reservoirs generates entropy which is responsible for the COP to be much less than the Carnot COP. This analysis shows that with both regenerative processes studied up to now, the COP is improved as compared to the intermittent cycle because of the reduction of the external thermal entropy production but those regenerative processes generate internal thermal coupling entropy production.