C. Garnier, J. I. Currie* and T. Muneer

Napier University, Scottish Energy Centre, 10 Colinton Road, Edinburgh AH10 5DT, UK
* Corresponding Author, j. currie@napier. ac. uk scientific. comm@eurosun2008.org

Abstract

A simple low cost integrated collector storage solar water heater (ICS-SWH) which has the potential to substantially reduce domestic energy use was proposed for simulation. The system takes the form of a rectangular-shape incorporating the solar collector and storage tank into a single unit. The incorporation of extended surface fins are a good way of enhancing the construction for an inexpensive SWH and to achieve an increase in efficiency of the system. The thermal performance of the systems is critically dependant on the convective heat transfer coefficient occurring on the waterside of the inclined absorber plate and fins. A Computational Fluid Dynamic (CFD) study was undertaken to model flow and heat transfer in the three-dimensional (3D) SWH geometry. A first analysis was undertaken for a four fins collector designed at Napier University, Scotland, in order to improve its performance. The 3D CFD analysis allowed the optimisation of fin spacing to improve the ICS-SWH performance to create a new ICS-SWH design. Global water temperature in the collector was found to increase without impeding the flow between the fins. A minor decrease in temperature gradient was observed but stratification remained.

Keywords: CFD Modelling, Solar Energy

1. Introduction

Computational Fluid Dynamic (CFD) in simple terms is the use of computer and numerical methods to solve and analyse problems involving fluid flow. It is very often used in product concept, product development and also virtual prototyping as it provides complementary information about environmental performances and significantly reduces the amount of experimental work needed. CFD-Fluent software, based on the finite volume method offering a wide array of physical 2D and 3D models, was used for this study. Recent studies indicate an increase in the use of CFD tools for analysing and optimising design and performances of solar collector. A pioneering study on cavities used a finite element method to solve the flow in a square cavity [1]. In the 1980’s the knowledge of flows was extended by numerical investigation of 3D aspects [2] and the influence of varied fluid properties and radiation were inspected [3]. Recent work has been done [4] on inclined cavities based on laminar natural convective flow in inclined rectangular glazing cavities. However the work on flow pattern inside the storage tank of integrated collector storage solar water heater (ICS-SWH) is still largely unexplored. To date only two studies [5-6] from the author’s knowledge have been recorded. A 2D CFD analysis involving both radiation and convection in a solar collector to compare with experimental results showed that CFD model results underestimated experimental data [5]. The second phase of research involved intensive 3D CFD analysis on ICS-SWH on flow behaviour of air and water cavities for different angles and different boundary conditions in order to optimise the design of the ICS-SWH [6].

Based on published research [6-11], a 3D CFD study was undertaken to model flow and heat transfer in a simple low cost ICS-SWH geometry. This model provided useful information about collector performance and was a useful tool for design improvements providing detailed pictures of fluid movements and stratification occurring in our collector.

2. Preliminary