Fresh water production using underground cooling of humid air and solar energy

Master's Thesis

Mechanical Engineering of Energy Conversion

Abstract

Due to the lack of fresh water resources, it is of great importance to discover new ways of water production. One of the new methods of producing fresh water in low capacities is the use of air humidity, which is known as the condensation water production system. In this method, the flow of hot and humid air is directed into the pipes buried in the ground, the air along the pipe gradually cools due to heat transfer with the soil, and at a temperature lower than the dew point, the steam in it appears on the surface of the pipe in the form of water droplets. In this research, potable water production systems have been studied and investigated with the aim of obtaining the optimal length and evaluating the effective parameters on the amount of water produced in condensation systems. For this purpose, first, the governing equations of the problem, its boundary and initial conditions for a sample condensing water production system were extracted, and then its discretization is described using the finite volume method. In the following, an example of drinking water production system is modeled in MATLAB software in one day and night. Numerical results show that in a pipe with a diameter of 0.2 meters, at a depth of half a meter from the ground and a length of fifteen meters, where the temperature of the incoming air is 70 degrees Celsius and the relative humidity is 70%, approximately 2.1 kg of water will be extracted per day. Sensitivity analysis on different parameters and soil type has also been done. The results of the analysis show that air temperature and relative humidity have the greatest effect on the amount of water produced, and sand, gravel, wet soil and clay produce the most water, respectively. The modeling of the cooling of condensation systems during the night also shows that the soil can reach almost the initial temperature of the previous day after 12 hours of night cooling.

Key words: condensation water production systems, hot and humid air, soil, sensitivity analysis, cooling during the night

Introduction

Water is the source of life and the source of life. One of the ways to develop countries is the optimal use of God-given natural resources. One of the most important and vital resources that plays a great role in the daily life of people, countries and the continuity of production is water resources. Water is a vital substance that is not uniformly available on the surface of the earth and many different parts of the earth face water shortage. Water is important from both economic and health aspects because it drives the wheel of industry and boosts agricultural activities. Also, healthy water guarantees human health.

In the last two decades, especially in the last years of the 20th century, water has been an important issue in the center of international discussions and negotiations. The phenomena caused by the way water resources are exploited and managed have reached the highest levels of decision-making at the national, regional and international levels. Developing countries account for a large share of the world's population. At the end of the 20th century, water shortage has become one of the important issues in these countries. Due to the climatic conditions, a large part of their area naturally suffers from a lack of rainfall. Many of the health problems in developing countries are the lack of safe drinking water. Without providing safe water, the health and well-being of the society will be endangered [1].

Given the ever-increasing growth of the world's population and the stability of water resources, it can be concluded that the problem of water shortage will become a big problem in the future. As a result, new and reliable solutions must be taken to maintain available water resources as well as to produce and purify fresh water. According to a report published by the Pacific Institute of Oakland, California [2], if no preventive decision is taken, more than 76 million people will die in 2020 due to diseases caused by contaminated water, and diseases caused by contaminated water threaten the health of the global community more than AIDS. Therefore, it is necessary to use new technologies and solutions to provide fresh water.

1-1 Water situation in the world

The volume of the earth's water is about 1.386 billion cubic kilometers, which covers about 70% of the planet.A small part of the available water can be used for sanitary and agricultural purposes. The water of oceans, seas and most lakes is unusable for health, agricultural and industrial purposes due to excessive salinity and mineral salts [1 and 3]. Only 2.5% of the world's water is fresh, and most of them are located in the form of ice and snow in mountains and poles. Humans get the fresh water they need from rivers, lakes and underground water. Water available for humans is about 11 million cubic kilometers [1 and 3]. The distribution of fresh water is shown in Figure (1-1) [4].

(Images are available in the main file)

At present, more than 25 countries in the world are facing water shortage crisis. About 5.1 billion people do not have access to safe drinking water. 7.1 billion are on the verge of water shortage crisis. By the year 2025, it is estimated that two-thirds of the world's population will face a water shortage [5]. 1-2 Classification of fresh water consumption: Usually, fresh water consumption is divided into the following three general categories: 1- Domestic use (drinking, cooking and hygiene): 8 It accounts for 10% of the global consumption.

2- Industrial uses: It accounts for about 20% of the global fresh water consumption, and since 1950, the consumption of this area has been increasing.

3- Agricultural uses: It is the largest consumer of fresh water resources in the world, and since the beginning of the 20th century until now, due to the increase in the world population, the consumption of this area has been increasing. It has increased almost 7 times. It is predicted that the water demand for the agricultural sector will increase by 20% by 2025.

In order to provide food for the growing world population, the development of agricultural land is necessary. With the development of agricultural lands, irrigation and its new methods become important. Traditional methods such as flooding, in addition to increasing costs, cause the destruction of agricultural lands [1]. As can be seen, countries like India and Egypt, which have dry lands, consume the most water in the field of agriculture [5].

1-3 Status of water resources and per capita in Iran

The country of Iran occupies 1.1% of the total area of ??the world, but it only has 0.43% of the water in the world. Iran has a dry and semi-arid weather climate and the amount of rainfall in it is 0.25 of the average rainfall in the world and the per capita consumption of each Iranian is 0.25 per capita in the world. According to the above figures, Iran is one of the poorest countries in the world in terms of per capita water resources. The methods of combating the water crisis in the country are:

The reform of water consumption in the country should be changed in such a way as to reduce the share of agricultural water consumption from 92% to 87% in the next twenty years.

The efficiency of water in the agricultural sector per cubic meter of water should increase from the current situation to double in the next twenty years.

The priority of water consumption should be allocated for drinking, health, industry and agriculture, respectively.

Compliance with national standards for the quality protection of water resources by consumers should be required.

The use of desalination and other modern methods to produce fresh water should be common.

Drinking water should be separated from other uses. [1].

1-4 overview of common water desalination methods in the country

According to the climate of the country, the supply of fresh water is one of the most important concerns of the country, especially in dry areas. To deal with the problem of drinking water supply in Iran, it is not possible to provide fresh water from surface and underground water for the areas that need drinking water with the usual methods, because in many cases a lot of money has to be spent.