Vanguard (Lagos)

Nigeria: Research and Devt - Our Solar Refrigerator Ready for Commercialisation - Prof Enibe


If Nigeria must progress, her industrial base needs to be strengthened. Talk of the great nations of the world; they are nations with great industrial bases. Although Nigerian scientists are doing their bit in their laboratories, but the people seem not to feel the impact.

In this chat with Vanguard Learning, Professor Samuel Ogbonna Enibe, a professor of Mechanical Engineering at the University of Nigeria, Nsukka spoke on his research work on solar refrigerator and says there is usually a problem between laboratory work and the market place. Excerpts:

Using the energy of the sun to provide cooling:

Said Prof. Enibe: "Most of my research works centre on energy both renewable and conventional and more recently, the modelling of systems and dissemination of the information to the general public."

Prof. Enibe started his work on solar refrigerator by building on an earlier work done by his colleague, Prof. O. C Iloeje who did experimental work using calcium chloride (similar to common salt) which has the capacity to absorb a gas called ammonia at ordinary temperatures.

"He then developed a system such that we built a solar collector so that when you expose the calcium chloride that has absorbed ammonia to the solar collector, the solar collector heats it up to the extent that the temperature becomes very high. We got temperatures of up to 100oC. At that temperature, the gas will leave the salt (the absorbent) and act as a refrigerant.

"In a conventional refrigerator, there is a gas inside called a refrigerant, so in this case, ammonia can be used as such a gas. Once you release that ammonia from the salt at very high temperature and pressure, it becomes a very useful raw material.

"We then developed another circuit where that gas will go and change into liquid. When it changes to liquid, it will be like when alcohol touches your hand, it evaporates and cools the hand. So in the same way, the ammonia passes through the inside of a refrigerator coil and cools whatever is there and produces ice," he said.

System modeling:

Not satisfied with that achievement, Prof. Enibe went further to study and understand the system more. He said: "These days, we do not stop at building a system. After building a system, you will like to understand the internal dynamics of that system. What will happen if you change the temperature or pressure or environment or like this one that is powered by solar energy, what will happen if the sun is not enough or when it is too much?

Although you can usually find out these things by doing experiments, but in our modern world, we normally back up experiments with what we call modeling. What I did was to study this system that has been built and tested, study all its components and then convert the performance of each component into mathematical equations. That is modeling. For each component, you write mathematical equations to describe the performance, all the input and output, you model them mathematically and at the end of it all, you write a computer software that will calculate everything from the beginning to the end for may be, one year.

Having written the computer programme which was the topic of my PhD thesis, we compared the results we got with experimental data because when you have done a mathematical model, you convert it to computer algorithm, whatever results you get (since we believe more in the things we can see), you compare it with the experiment and that gives you the assurance that you have done the model correctly.

So when we did that and found that the results generated by the experimental model and the computer model were in agreement, we were very happy. Next, we used the computer model we have built to find out how the system will perform in various parts of the world. When you have done a good model, sometimes you may not even need to take it to a physical location, once you get data for that location, you can test the performance of that system for that location.

Testing the product:

With the computer model we developed, we tested the performance of the refrigerator in all parts of Nigeria for the entire year and then we extended it to major cities in Africa. We did not have to carry the refrigerator from town to town. Because we built the computer model, we were able to test it in Sudan, South Africa, Egypt and all the major climatic areas in Africa. We confirmed that it will perform in most of the places. Of course, there were areas - the very cold areas - that it could not do well like Cape Town during winter. In places like Juba, Sudan which has high temperatures, the performance was quite good," he stated.


Continuing, Enibe said they went on to optimize. "In optimization, what you do is that having tested something by experiment or computer programme over a very wide range of conditions, you will want to find out the best set of operating conditions that will give you best performance. Example, those who make cars have to make the car first, it has to be beautiful so that those who like good things will appreciate it.

"At the same time, the price has to be low enough so that ordinary people can afford it because if you have a very beautiful car but it is too expensive, then it will not sell. You look at all the input materials, all the things that affect it and put them all together and find out what you really want. Do you want something at very low cost or very high performance etc? So we found out the conditions under which the refrigerator will perform optimally."


He regretted that although the refrigerator was ready for commercialisation "but it has not been commercialised because in Nigeria, there is usually a problem between laboratory work and the market place. Many times, you do a very fine job in the laboratory and you are sure the thing works but bringing it to the market often requires an industrial base and our industrial base is weak so that is what is delaying the commercialisation of a number of things that have proven technically feasible. But we have worked out the technical things and they are okay but because of lack of industrial base, we have not brought it to a stage whereby it will be available in every market," he stated.

"Other things we have done are in the area of energy consumption modeling in Nigeria which as an oil-producing nation, doesn't consume much. We compared the energy consumption of the average person in Nigeria with that of others in many countries of the world and we discovered that the per capita energy consumption in Nigeria is very low, lower than Ghana, South Africa, Egypt etc.

The reason is that industrial production base is very low and in most countries, the key energy consumer is industrial production like automobile and steel factories. Because the heavy industries are not operating here, the nation's energy consumption is low.

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