S. Tundee, N. Srihajong* P. Sakulchangsatjatai, and P. Terdtoon

Department of Mechanical Engineering, Faculty of Engineering,

Chiang Mai University, Thailand 50200.

Tel. +66-53-944151 Fax. +66-53-226014, Email: suratundee2000@yahoo. com

Department of Mechanical Engineering, Faculty of Engineering, Rajamangala University of
Technology Isan Khon Kaen Campus, Thailand.

Abstract

Solar pond is one type of solar collector with the ability to store thermal energy for long period of time and lower cost of construction compared with the other type of solar collector. An alternative method of heat extraction from solar ponds. This paper presents the thermal analysis of heat extraction process from solar pond by using the heat pipe. The numerical analysis was done by small pond has an area of 7.0 m[1] [2] and a depth of 1.5 m. The heat pipe is made of copper tube which has 21 mm. inside diameter and 22 mm. outside diameter. The lengths of evaporator and condenser section are 800 mm and 200 mm. respectively. The working fluid used in the experiment was R-134a. which located at the North-Eastern Thailand from where Khon Kaen is the site selected for this study (16° 27′ N 102° E). The simulation was done by using the energy equation and solar radiation data at the above location. The solution of energy equation for solar pond can be obtained by the numerical method. The heat transfer capacity of the sized thermosyphon will be accordingly determined. The thermal efficiency of solar pond — thermosyphon system was defined by the ratio of the amount of heat extraction by thermosyphon by solar energy input in solar pond. The frame work of estimation of heat extraction from solar pond by using thermosyphon was revealed in this research. The performance of heat exchanger is investigated by varying the air velocity which receives the removed heat at condenser section. Air velocity was found to have a significant influence on the effectiveness of heat exchangers. The effectiveness decreased with increasing air velocity. The calculated results from this theoretical model have good agreement to those from the experimental data.

temperatures increasing up to 700C at a depth of 1.32 m at the end of the summer. The minimal temperature were 260C during early spring. Of which compare ambient temperature with higher than the others. The idea of solar energy collection was conduct by creating artificial solar pond hinted by Kalecsinsky.

A solar pond generally consists of three regions, the upper convective zone (UCZ), the non — convective zone (NCZ), and the lower convective zone (LCZ), Akbarzadeh et. al.[1]as shown in Figure.1

Fig. l.The salt gradient solar pond configuration (Akbarzadeh)

1. The upper convective zone (UCZ) is the topmost layer of the solar pond. It is a relatively thin layer which consists almost wholly of fresh water.

2. The non — convective zone is just below the upper convective zone and has an increasing concentration relative to the upper convective zone, and it also acts as insulation on the lower convective zone.

JCZ

NCZ

LCZ

3.

The lower convective zone is the layer in which the salt concentration is the greatest, and there is no concentration gradient in it. If the concentration gradient of the NCZ is great enough, no convective motion will occur in this region, and the energy absorbed in the bottom of the pond will be stored in the LCZ.

When solar radiation was incident upon the solar pond, a part of the ray is reflected on the surface and most of the incident ray transmits through the working fluid. Also, apart of the transmitted ray is more absorbed by each thin layer of NCZ and LCZ and, the part of transmitted ray, which reached the LCZ, is changed into the heat and stored in the LCZ.

There are many research studies on solar pond. Hillel Rubin et. al.[3]. establish the mathematical model to predict solar pond performance by using the energy equation. Later, Kurt et. al. [2] model the temperature profile in solar pond. They present the concentrate distribution behavior of solution in solar pond by means of mass transfer equation.

Two above research perfectly concluded the concept of solar pond heat capacity estimation. In side of, solar pond application, Jaefazadeh (Article in press) study the solar pond heat extraction by using the heat exchanger with water as working fluid. In this research, there are two heat exchangers. The first is installed in LCZ, the second receive heat from the first and transfer heat to the air. The fresh water is used as working fluid between both of heat exchangers.

Andrew et. al. [5] increase the solar pond performance by increasing heat transfer surface. Their works were done by installation of additional heat exchanger in NCZ and remain heat exchanger in LCZ. We can see from literature review that solar pond heat extraction process, generally, was done by using a change in sensible heat of working fluid. There is no any research of heat extraction by using a change in latent heat. This paper, thus, presents the thermal possibility to apply thermosyphon, the heat exchanger which using phase change of working fluid, in solar pond in heat extraction process. This work will show the method to estimate temperature profile and heat capacity of solar pond by using Rubin model. The simulation of solar pond heat extraction by using thermosyphon will, later, be inducted.