Development and performance mapping of a multi-ejector expansion work recovery pack for R744 vapour compression units, AbstractA multi-ejector expansion pack, intended as a substitute for a standard high-pressure electronic expansion valve (HPV), was designed, manufactured and experimentally investigated. Four different ejector cartridges were sized to enable a discrete opening characteristic with a binary profile for a parallel-compression R744 system. The system is rated for 70 kW at a 35 °C gas cooler outlet temperature and a -3 °C evaporation temperature. High values of ejector efficiency, exceeding 0.3 over a broad operation range, were recorded for all four of the cartridges tested under vapour compression conditions. The applicability of the multi-ejector pack as a main flashing device was verified experimentally. Similar profiles of the discharge pressure control error were recorded for both alternative options: expansion purely in the HPV vs. HPV-assisted expansion in the multiejector pack.

A hindcast wave database and a wave database based on future climate scenarios for the Baltic Sea, Kattegat and Skagerrak is under development. The wind force used for the wave simulation is coming form the RCA model and the future wind from RCA is based on global climate model ECHAM4 for one emission scenario (IPCC SRES A2)The phase averaged spectral model SWAN (Simulated WAves Nearshore) model is used for simulating the wave field. The model is driven by atmospheric forcing and it simulates waves generated by the wind and their propagation both in deep water and near shore areas. When realistic winds are provided the model has an outstanding performance.Winds from the Mesan reanalysis and the RCA model were used as forcing for the SWAN model simulating short hindcast storms for the validation of the wave model in connection with the winds. RCA results appeared to underestimate extreme winds. A correction was introduced which used an empirical relation between 3-second gust and the wind velocity.The model data were compared with observational data. Statistical parameters like scatter index, bias and symmetric slope were used to judge the quality of the data. The performance of the wave model with Mesan is very good. Model and observed data appear to have a good correlation. The performance with RCA is worse and it underestimates the wave height during extreme wind events. The performance when using corrected RCA winds is improved and data give better statistical values when they are compared with observations. The reason for using RCA forcing was the length of RCA data, 40 years of hindcast, and the 50 years of future winds based on global climate scenarios. The corrected coefficient was applied to the RCA and used to force SWAN. Only one year of hindcast has been performed initially while the 40 year run is planned to be performed in the near future. Moreover, a run based on future scenario has been performed. Six month is 1970 were run as control period and 6 months in 2020 as a future projection, giving insight to some of the possible changes in the future wave climate. Thirty years of control run and thirty years of future projection are in progress.

The adoption of the EU F-Gas Regulation 517/2014 and the resulting development of the multi-ejector concept have led carbon dioxide to take center stage as the sole refrigerant (R744) in several applications. Therefore, a knock-on effect on the number of supermarkets relying on “CO2 only” refrigeration systems has been experienced. Additionally, a global consensus of commercial multi-ejector based R744 units is also intensifying as a consequence of both the promising results obtained and the other measures in force for environment preservation. Furthermore, the multi-ejector concept is expected to offer significant energy savings in other high energy-demanding buildings (e.g., hotels, gyms, spas) as well, even in warm climates. In this investigation, the evolution of R744 ejector supported parallel vapor compression system layouts for food retail applications was summed up. Furthermore, their technological aspects, the results related to the main theoretical assessments and some relevant field/laboratory measurements were summarized. Also, the experience gained in the adoption of the multi-ejector concept in transcritical R744 vapor-compression units aimed at other energy intensive applications was presented. Finally, the persistent barriers needing to be overcome as well as the required future work were brought to light.

The present paper presents an experimental and numerical study of partial wave reflection and transmission for monolithic rectangular submerged breakwaters located in the nearshore region. The study is based on large-scale experiments that have been conducted in Universitat Politecnica de Catalunya, Laboratory de Ingeneria Maritima in Spain. Both irregular and regular waves are tested under breaking and non-breaking conditions. The experimental findings confirmed that the wave breaking due to the presence of the structure is a main energy dissipation mechanism which significantly affects wave transmission. The numerical approach of the problem is based on a higher-order Boussinesq type of equations for breaking and non-breaking waves with improved linear dispersion characteristics. The energy loss due to eddy motions near the sharp corners of the structure is introduced in the model by using a hydraulic loss formula. The breaking criterion proposed by Okamoto and Basco was introduced in the numerical model. The comparison between model results and experimental data shows that the model is able to describe breaking and non-breaking wave deformation passing over a submerged breakwaterwater depth d + depth immediately downstream (or upstream) of the structure E incident incident wave energy E reflected reflected wave energy E transmitted transmitted wave energy F submerged depth f friction coefficient H ins incident wave height H rms root-mean-square wave height L wave length m c computational slope T wave period

No abstract