Reciprocal trade agreements in gravity models: a meta-analysis

Over the time a large number of reciprocal preferential trade agreements (RTAs) have been concluded among countries. Recently many studies have used gravity equations in order to estimate the effect of RTAs on trade flows between partners. These studies report very different estimates, since they differ greatly in data sets, sample sizes, and independent variables used in the analysis. So, what is the “true” impact of RTAs? This paper combines, explains, and summarizes a large number of results (1460 estimates included in 75 papers), using a meta-analysis (MA) approach. Notwithstanding quite an high variability, studies consistently find a positive RTAs impact on bilateral trade: the hypothesis that there is no effect of trade agreements on trade is easily and robustly rejected at standard significance levels. We provide pooled estimates, obtained from fixed and random effects models, of the increase in bilateral trade due to RTAs. Finally, information collected on each estimate allows us to test the sensitivity of the results to alternative specifications and differences in the control variables considered.Free Trade Agreements; Gravity equation; Meta-regression analysis; Publication bias.

FDI and growth: what cross-country industry data say

Foreign Direct Investment, Economic Growth, Capital Intensity, Technological Progress, Total Factor Productivity

Determinants of trade: the role of innovation in presence of quality standards

This paper analyses the role that quality standards and innovation play on trade volume, by using a gravity model. The role of innovative activity and quality standards in enhancing trade performance is widely accepted in the literature. However, in this paper, we argue that the net effect of quality standards on trade depends on the producers’ ability to innovate and comply with these requirements. In particular, by using a sample of 60 exporting countries and 57 importing countries, for a wide range of 26 manufacturing industries over the period 1995-2000, we show that the most innovative sectors are more likely to enhance the overall quality of exports, and then gain a competitive advantage. We also find that this effect depends on the level of technology intensity at sector-level and on the level of economic development of exporting country

A brine evaporative cooler/concentrator for autonomous thermal desalination units

In recent years growing attention has been paid to the problem of brine disposal due to the raising awareness of significant environmental issues related to the use of desalination processes for fresh water production. This is particularly relevant when desalination units are located in remote sites, characterised by major complexity in the construction and management of intake and outfall structures. In the present work a novel device, named brine evaporative cooler/concentrator (BECC, patent pending), has been developed for coupling with small-scale thermal desalination plants in order to reduce the problem of brine disposal. Such device fulfils two different functions: i) cooling of the recirculating brine (which is often mixed with cold seawater to feed the unit, acting first as a cooling medium for the condensation of the vapour) and ii) concentration of the brine to de disposed. The BECC device is based on the principle of evaporative cooling, i.e. a primary liquid stream is cooled by means of a secondary liquid stream (by-pass stream), which in turn evaporates in contact with atmospheric air, thus being cooled naturally. The two streams are separated by a heat-conductive surface, through which heat is transferred from the primary stream to the cooling-evaporating by-pass stream. A lab scale BECC pilot unit has been designed, constructed and tested. Geometrical and operating features have been studied in order to allow the operation with concentrated brines, to minimise problems of corrosion, scaling and fouling. The first results have demonstrated the feasibility of the technology and a larger scale prototype unit has been designed for the installation within a 5 m3/d solar membrane distillation unit to be constructed in Pantelleria Island, Italy

CFD analysis of the fluid flow behavior in a reverse electrodialysis stack

Salinity Gradient Power by Reverse Electrodialysis (SGP-RE) technology allows the production of electricity from the different chemical potentials of two differently concentrated salty solutions flowing in alternate channels suitably separated by selective ion exchange membranes. In SGP-RE, as well as in conventional ElectroDialysis (ED) technology, the process performance dramatically depends on the stack geometry and the internal fluid dynamics conditions: optimizing the system geometry in order to guarantee lower pressure drops (DP) and uniform flow rates distribution within the channels is a topic of primary importance. Although literature studies on Computational Fluid Dynamics (CFD) analysis and optimization of spacer-filled channels have been recently increasing in number and range of applications, only a few efforts have been focused on the analysis of the overall performance of the process. In particular, the proper attention should be devoted to verify whether the spacer geometry optimization really represents the main factor affecting the overall process performance. In the present work, realized within the EU-FP7 funded REAPower project, CFD simulations were carried out in order to assess the effects of different parameters on the global process efficiency, such as the choice of spacer material and morphology, and the optimization of feed and blowdown distribution systems. Spacer material and morphology can affect the fluid dynamics inside each channel. In particular, the appropriate choice of net spacer material can influence the slip/no-slip condition of the flow on the spacer wires, thus significantly affecting the channel fluid dynamics in terms of pressure drops. A Unit Cell approach was adopted to investigate the effect of the different choices on the fluid flow along the channel. Also, the possibility of choosing a porous medium to substitute the net spacer was theoretically addressed. Such investigation focused on the porosity and the fiber radius required to respect the process constrains of pressure drops and mechanical stability. On the other hand, the overall pressure drops of a SGP-RE or ED stack can be considered as resulting from different contributions: the pressure drop relevant to the feed distributor, the pressure drop inside the channel, and the pressure drop in the discharging collector. The choice of the optimal stack geometry is, therefore, strongly related to the need of both minimizing each of the above terms and obtaining the most uniform feed streams distribution among the stack channels. In order to investigate such aspects, simulations were performed on a simplified ideal planar stack with either 50 spacer-less or 50 spacer-filled channels. The effect of the distribution/collector channel thickness and geometry on single-channel flow rates and overall pressure drops in the system was analyzed and a significant influence of distributor layout and size on the overall process performance was found

Experimental Analysis via Thermochromic Liquid Crystals of the Temperature Local Distribution in Membrane Distillation Modules

A reliable and optimized design of channels for Membrane Distillation (MD) requires knowledge of local temperature distributions within the module. This information is essential to measure the temperature polarization, choice the module configuration (net spacer features, channel size, etc) providing the best process performance. Notwithstanding such crucial aspects, only few studies have been devoted to the experimental characterization of MD channels and none of them includes data on the local temperature distribution. In the present work, an experimental technique based on the use of Thermochromic Liquid Crystals (TLCs) and digital image processing, previously proposed by the authors (Pitò et al., 2011), was further developed and employed in order to measure the temperature and local heat transfer coefficient distribution on the membrane surface in a MD spacer-filled channel. The performance of different types of commercial net spacers were tested. The channel provided with the symmetric net spacer was found to be the configuration leading to the best heat transfer and to the lowest temperature polarization

Towards 1 kW power production in a reverse electrodialysis pilot plant with saline waters and concentrated brines

Reverse electrodialysis (RED) is a promising technology to extract energy from salinity gradients, especially in the areas where concentrated brine and saline waters are available as feed streams. A first pilot-scale plant was recently built in Trapani (Italy), and tested with real brackish water and brine from saltworks. The present work focuses on the scale-up of the pilot plant, reaching more than 400 m2 of total membrane area installed and representing the largest operating RED plant so far reported in the literature. With a nominal power capacity of 1 kW, the pilot plant reached almost 700 W of power capacity using artificial brine and brackish water, while a 50% decrease in power output was observed when using real solutions. This reduction was likely due to the presence of non-NaCl ions in relatively large concentration, which negatively affected both the electromotive force and stack resistance. These results provide relevant and unique information for the RED process scale-up, representing the first step for the feasibility assessment of RED technology on large scale

Dense Solid-Liquid Off-Bottom Suspension Dynamics: Simulation and Experiment

Dense solid-liquid off-bottom suspension inside a baffled mechanically agitated stirred tank equipped with a standard Rushton turbine is investigated. Dynamic evolution of the suspension from start up to steady state conditions has been inspected by both visual experiments and computational fluid dynamics. A classical Eulerian-Eulerian Multi Fluid Model along with the “homogeneous” k-epsilon turbulence model is adopted to simulate suspension dynamics. In these systems the drag inter-phase force affects both solids suspension and distribution. Therefore, different computational approaches are tested in order to compute this term. Simulation results are compared with images acquired on the real system and a good agreement is found