Mathematical modelling and simulation of multiphase flow in a flat plate solar energy collector

Abstract

a b s t r a c tNon-conventional collectors where organic fluid or refrigerant experience a phase change have many advantages over conventional collectors which have either air or relatively high temperature boiling liquid. Increase in heat transfer coefficient and system efficiency, corrosion prevention and freeze protection are the main benefits of the first type. In this study, a detailed numerical model of a flat plate collector is developed to investigate the fluid mean temperature, useful heat gain and heat transfer coefficient along the collector tube. The refrigerant HFC-134a was used in the simulation as the working fluid of the collector. The model can both predict the location where the fluid undergoes a phase change in the tube and the state at the exit under given inlet conditions. The effect of boiling on the heat transfer coefficient of the fluid is also investigated. Simulations were performed at three different mass flow rates (0.001, 0.005 and 0.01 kg/s) and three different operating pressures (4, 6 and 8 bar) to be able to see the effect of mass flow rate and pressure on plate temperature, heat loss coefficient, efficiency of the collector and the heat transfer coefficient of the fluid. The simulation results indicate that the heat transfer coefficient of the fluid increases from 153.54 W/m 2 K to 610.27 W/m 2 K in multiphase flow region. In the liquid single phase region, the collector efficiency rises from 60.2% to 68.8% and the heat transfer coefficient of the fluid increases from 39.24 W/m 2 K to 392.31 W/m 2 K with an increased flow rate whereas the collector efficiency decreases from 72.5% to 62.3% as the operating pressure increases from 4 bar to 8 bar. In order to validate the simulation model an experimental test rig was built and the experiments were performed with HFE 7000 as working thermo-fluid. A new simulation model utilizing HFE 7000 has been developed and the outlet temperature of the fluid was compared with the measured outlet temperature. Both measured and simulated results have shown close conformity.

A numerical investigation of laminar forced convection in a solar collector with non-circular duct

“…In fact, the fully developed laminar Nusselt number is found to be independent of the length of the duct, the Prandtl number Pr and the Reynolds number Re, but dependent on the duct geometry and boundary conditions [13,14]. The considered non-circular geometries include several common shapes, such as regular polygons, ellipses and Cassini ovals.…”

“…In this paper the H1 condition is considered: T = const, at Lh (constant peripheral wall temperature). The H1 condition has found many applications with negligible normal wall thermal resistance [14], such as in tube heat exchangers and in solar energy collection [4,13]. Details of the solution of Poisson's equations (2-3) using the boundary element method can be found in the literature [15].…”

“…Dehghan et al [12] investigated the effects of radiation heat transfer on the forced convective heat transfer mechanism in solar heat exchangers filled with a porous medium. Helvaci and Khan [13] analysed multiphase flow in a flat plate solar energy collector.…”

A Theoretical and Experimental Study of HFE-7000 in a Small Scale Solar Organic Rankine Cycle As a Thermofluid

“…[24]. Initially, the solar energy on the absorber plate (Q p ) and the useful energy (Q u ) are calculated by using the formulas below;…”

“…The collector specifications, the description of the iterative method for the fluid and plate temperature calculations, heat gain of the fluid and the collector heat loss determinations were described comprehensively in Ref. [24]. Once the, working fluid mass flow rate was calculated, the expander calculations were started to determine the built-in volume ratio and the expander designed outlet pressure with the help of Eq.…”