Development of Solar thermal Refrigerator

Over the past few decades, energy is the backbone of technology and economic development. In addition to men, machines, and money, ?energy? is now the fourth factor of production. The primary focus of this project would be utilizing solar energy to design and study the environmentally friendly vapor

Project Title

Development of Solar thermal Refrigerator

Project Area of Specialization

Mechanical Engineering

Project Summary

Over the past few decades, energy is the backbone of technology and economic development. In addition to men, machines, and money, ‘energy‘ is now the fourth factor of production. The primary focus of this project would be utilizing solar energy to design and study the environmentally friendly vapor absorption cycle. We will mainly focus on heat/thermal energy received from the sun to heat the refrigerant. The heating of refrigerant is achieved by using evacuated tubes. The vapor absorption system consists of two fluid systems comprising ammonia and water and it has three phases: Evaporation, Absorption, and Regeneration. In this refrigeration system, the refrigerant having a low boiling point evaporates, taking heat away with it. Hence, this provides the cooling effect and finally changes gas back into liquid. The compressor has been replaced by the absorber and generator in the system.

Project Objectives

Objective:

The objective of our project is to design and fabricate a portable solar thermal refrigerator based on the vapor absorption cycle which means that we will be heating the refrigerant via the thermal energy of the sun.

Methodology:

Solar Thermal Refrigerator is designed in a way that its working principle is the cycle that starts from the evaporator where the refrigerant ammonia gains heat and turns into vapors. The vapors are then supplied to the absorber tank where they mix with water and the ammonia-water solution is formed. Afterward, the solution is pumped into the evacuated tubes in which the solution changes its state from liquid to vapors. The superheated vapors are then supplied to the rectifier. Rectifier serves two functions firstly it separates NH3 vapors from H2O vapors, secondly, it throttles weak solution to the absorber tank. The ammonia vapors from the rectifier enter the condenser where they change their state from vapors to liquid rejecting heat from the atmosphere. The liquid refrigerant now is throttled to evaporator pressure and enters the evaporator tank. The refrigerant provides cooling in the evaporating chamber and this cycle continues.

Project Implementation Method

Solar refrigeration engages a system where solar power is used for cooling purposes. Solar energy can provide cheap and clean energy for cooling and refrigeration applications all over the world. According to the reports, the implementation of a solar-driven cooling system can save the Mediterranean countries approximately 50% of their energy costs. Solar energy also has vast applications for the agricultural sector for example maintaining and storing crops is very difficult where electricity is unavailable; solar refrigeration can play an important role. Moreover, some sub-Saharan countries that have very good solar potential can use solar refrigeration for storing medicines and vaccines at lower temperatures, and these systems can be made portable if needed, as their energy source is the sun. Solar refrigeration has become more attractive for cooling purposes today because of the use of desiccant gases, such as LiCl (lithium chloride) and LiBr (lithium bromide), or water instead of harmful Freon gas. Furthermore, the high demand for air conditioning and refrigeration is relentlessly increasing across the globe mainly due to climate change (Global Warming), improvement in living standards, industrialization, and general population growth. This demand peaks during warm weather periods. The refrigeration requirements in the food-processing field and the conservation of pharmaceutical products in developing countries are leading the interest in air-conditioning and refrigeration systems powered by renewable energies, especially solar thermal, which work efficiently, and in certain cases, approach competitiveness with conventional cooling systems.

Benefits of the Project

Solar energy is the most abundant source of energy in Pakistan. It receives about 1KW of solar energy per square meter of its landmass for 6-7 hours on the average per day having the number of sunshine hours amount almost to 3000-3300 per year, but unfortunately, we don’t have efficient technology to utilize this energy source into the various application. This makes it one of the most promising unconventional energy sources. In addition to its size, solar energy has two other factors in its favor. Firstly, unlike fossil fuels and nuclear power, it is an environmentally clean source of energy. Second, it is free and available in adequate quantities in almost all parts of the world where people live. Solar cooling can be divided into two main categories that are PV operated refrigeration cycle and solar thermal refrigerator. PV involves the direct conversion of solar radiation to direct current using semiconducting material. The inverter then converts DC to AC for running the compressor of a vapor compression refrigeration system, still, the PV panel has the disadvantage that 65% of energy is wasted as heat and only 35% is used for generating electricity. In addition, losses in battery, inverter, and wires are also present. This was the factor that leads us of introducing solar cooling using the thermal energy of the sun. Moreover, it can help reduce the electricity peak demand associated with conventional cooling, as maximum solar radiation usually occurs when cooling is needed. Solar thermal cooling can also operate in the evening by using thermal storage. Our focus is to design the refrigerator in such a way that it would fulfill domestic needs as well as commercial needs in sub-Saharan areas. Domestically it can be used to store food, drinks, vegetables, etc. while commercially it can be used to store medicines and vaccines.

Technical Details of Final Deliverable

The foremost task was to select the refrigerant. The refrigerant used should be pollution-free, noncorrosive, and cost-effective, secondly to maintain the low circulation rate of the refrigerant, it should have a high concentration and latent heat within the absorbent and the solution should be chemically stable, non-toxic, and non-explosive. Lithium Bromide water (LiBr-H2O) solution and Ammonia water (NH3-H2O) solutions are the two widely used refrigerants used in the vapor absorption refrigeration cycle. In LiBr-H2O solution, water is the refrigerant, and LiBr acts as absorbent while in NH3-H2O solution, ammonia is the refrigerant while water acts as an absorbent. Since we are doing refrigeration we need to maintain the temperature of the cooling space near 0 deg. Celsius therefore we selected the NH3-H2O solution. If we had selected LiBr-H2O solution it would restrict our cooling space temperature to 10 deg. Celsius because below it LiBr forms crystals. That’s why LiBr-H2O solution is used in air conditioning where cooling space temperature lies between 16-22 deg. Celsius. The next task was quite challenging as we need to calculate the heat energy required in the generator, which is essential for the refrigerant, to convert it from liquid to vapor state. To heat the refrigerant, we need solar thermal devices such as a Flat plate collector, Evacuated tubes, Parabolic trough, Fresnel lens, or Parabolic dish. Considering the requirements, we end up choosing Evacuated tubes. This is because a Flat plate collector provides less temperature change compared to Evacuated tubes. Max temperature that the Evacuated tube can reach is between 120 deg. Celcius-140 deg. Celsius. To bring the refrigerator into operation we need an absorber tank, generator tank, and rectifier tank that will be fabricated using specified dimensions. The material that is required to make them is mild steel. An auto Diaphragm DC Pump is required that is used to pump the fluid/refrigerant from the absorber tank to the generator. A PV panel is required for operating the pump. For cooling, the refrigerant wire and tube condenser are used hence refrigerant is cooled by air. An expansion valve is also used in between the condenser and evaporator, to reduce the condenser pressure to evaporator pressure. Other than that copper coil is used for assembling these parts.

Final Deliverable of the Project

Hardware System

Core Industry

Energy

Other Industries

Core Technology

Clean Tech

Other Technologies

Sustainable Development Goals

Affordable and Clean Energy, Climate Action

Required Resources

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