Modeling and Sizing of a MW Solar DSG plant

Direct Steam Generation (DSG) Concentrated Solar technology, based on Linear Fresnel Reflectors (LFR) and aimed at supplying saturated steam to industrial processes, is a promising application; nevertheless, nowadays few case studies and very few installations have been developed. A methodology for the design optimization of a MW solar DSG plant is presented in this article and applied to a real case study of a Brazilian tire manufacturing facility. A steady-state model, with spatial discretization of the ordinary equations, allows characterizing the physical phenomena such as pressure drop and heat transfer, and therefore to determine the pressure and specific enthalpy trend along the recirculation loop. For each receiver tube of the solar collectors, the occurring single or two-phase flow pattern is calculated based on specific empirical equations developed for evaporation in horizontal tubes. Two reference operating conditions have been identified for the present case study, at which the optimal field layout results to be a series connection of all the collectors, and the optimal nominal flow rate to avoid possible harmful operating conditions for the absorber tubes is 1.0 kg/s. © 2016 The Authors

Air dehumidification by cooled adsorption in silica gel grains. Part I: Experimental development of a prototype

This work deals with the development and testing of a fixed-bed adsorption dehumidifier, designed to manage the latent load in air conditioning. The system is based on the batch operation of two finned tube heat exchangers, where silica gel grains are packed between the fins. The water flow in the tubes provides the required heat supply and rejection, allowing a quasi-isothermal operation. As a result, the heat supply temperature can be reduced below 55 °C, fostering the use of waste heat and solar thermal collectors. Moreover, the inversion of the air flow direction between the operating stages is not needed to achieve suitable levels of dehumidification, enabling a design simplification. The test campaign has shown that the electric and thermal performances of the low-cost prototype highly depend on the operating conditions, but both reach very promising values under the worst environmental conditions, when the energy consumption is higher. © 2016 Elsevier Lt

Modelling and experimental validation of an in-tube vertical falling film absorber with counter flow arrangement of solution and gas

In the present study, an in-tube vertical falling film absorber with gas and falling film in counter-current flow arrangement, which utilizes NH 3 −H 2 O pair as the working fluid, has been built and is then integrated with a single effect absorption heat pump. Twelve sets of tests have been designed and conducted, taking into account the standard operating range of these types of heat pumps. The results obtained from performing a testing procedure on this experimental setup have been utilized to assess the accuracy of a developed mathematical model in simulating the corresponding absorption phenomenon. The obtained results demonstrate an acceptable agreement between the values simulated by the model and the experimental data, while addressing various heat duties. Furthermore, it has been shown that the transfer coefficients between the liquid film and the interface are order/s of magnitude higher than the ones between the gas and the interface and therefore, the absorption process is controlled by the heat and mass transfer coefficients between the film and the interface. Moreover, it has been revealed that in falling film absorber modelling, insignificant errors in the evaluation of rate of absorption can lead to a notable miscalculation of the absorber size. It is concluded that the effect of hydrodynamic of the film on the heat and mass transfer process should be considered for future enhancement of the model

Porosity and pressure drop in packed beds of spheres between narrow parallel walls

This is a theoretical and experimental study on porosity and pressure losses in a packed bed of spheres between parallel walls. It is focused on small values of the ratio of the distance p between the walls to the average diameter dav of solid particles: p/dav <= 2. We report a semi-empirical formula for the prediction of porosity of monodisperse packings made by randomly pouring the spheres between narrow parallel walls. Concerning the more general case of polydisperse lattices, characterized by a statistical distribution of diameters in the range dmin-dmax, we show how to determine a range p = f(dmax)- f(dmin) which ensures that the maximum value of the solid volume fraction, and thus of pressure losses, is less than a specific target. Lastly we present a new semi-empirical formula for the prediction of pressure losses of an air flow through random packings of spheres between narrow parallel walls, by adapting the Ergun equation to the peculiar geometry at issue