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How to Design and Make the ''One Stove with Double Pots''

Jin Zong-wu Shanghai Municiple Agricultural Bureau

Introduction

For many years, the source of the energy for daily use was seriously short but at the same time, a lot of straw was was-cd in Shanghai suburbs. The Peasants lack straw (main fuel for peasants in Shanghai) or two or three months each year. The stoves the peasants used are old-fashioned. The heat efficiency is only about 10%.

In order to solve this problem, we began to design and make a new type of stove called "One Stove with Double Pots" in December 1982 and it was appraised by Shanghai Municiple Authorities on December 24, 1984.

The heat efficiency of the new stove is 34.46%. The obvious advantage of the stove is that it enjoys the profit of one stove with double pots. Because of the high efficiency, lower cost and convenient usage, it was warmly welcomed by the users when we popularized it.

The Reformation of the Pot's Material

To improve the heat efficiency, the most Important thing, we think, is to change the pot's material. Usually, the peasants use iron-pots instead of aluminium ones. But if you use aluminium pots, you can surely save not only time but also fuel (straw).

The Structure of the Stove

Whether you succeed or not depends on the structure. Because it has the close relationship with heat efficiency and also can decide if our popularizing of the stove will be successful or not. Here is the structure of the chamber:

a) The distance be-weep the grate and the pots:

Dish pot 6cm; rice pot 16cm. This data of the height is especially suitable in Shanghai suburbs. Because in Shanghai suburbs, the straw which has higher flame while burning, is the main fuel for cooking, and the distance can ensure the top flame to touch the bottom of the pot directly in order to raise the efficiency of the heat.

The shape of the stove's chamber:

It's share is just like a boat and gradually upward from the entrance to the end. The rice pot cannot be lower than the top of the stove door. In this case the flame can spread out equally.

c) Fire-return-way:

In order to reinforce the fire-return-way, under the surface of the stove a reinforce-bar is needed between the two pots. While burning, the flame and the smoke spread from the first pot to the second pot and then return to the first pot through the fire-return-way and at last go into the chimney. Thus, 'he flame and the smoke which is with heat can circle equally in the chamber of the stove and the temperature that may be pulled out can be controlled. The stove can make the full use of the heat existed in the smoke and ash fire.

d ) The fire-blocking iron board

Put an iron board (0.5cm thick; 25cm long; 20cm wide and crescent moon like) between the entrance of the chimney and the upside of the stove-door. The board should leave a space of 2cm from the bottom of the rice-Dot so that the flame and smoke with heat cannot rush to the chimney directly.

FIRST INTERNATIONAL SYMPOSIUM ON FUEL-EFFICIENT STOVES


Figure 3 Drawings of Twin-Pot Fire-Returning Stove

e) The size of the stove door:

The size of the stove door is 18cm x 15cm (50%) smaller than the old-fashioned one). This perfect size can reduce the excess air to enter the chamber.

f ) Heat preservation method:

Using slaked lime to decorate the inside of the chamber can preserve the heat and the surface looks smooth.

The Design of the Grate and the Place Where Ash can Drop

The grate should be made of pig iron with seven holes. The size is 16cm x 32cm; the size of ash-dropping place is 4cm x 18cm. Installing a grate can make more oxygen while burning. According to the speciality of the stove, the grate should be put under the rice pot. With the ash-down room, the ash can drop directly, not through the grate.

Ventilating Passage Design

The height of the passage is 39cm and the width is 18cm. The passage should be vertical with the central line of the pot. When the ash drops from the chamber, it can heat the air and the heated air can not only offer oxygen to help burning, but also prevent the cold air from entering the chamber.

The Chimney

The section size of single-stove-chimney is 2 x 12 sq. cm. and that of the puble-stove-chimney is 18 x 12 sq. cm the fight is 300 cm. It is estimated that with the new type chimney, the speed of smoke caving is [m/second, the temperature of smoke is about 100 degrees centigrade. so that the loss will be less.

The height of the stove 75cm is suitable for most of the people.

Heat Function Analysis

In order to ensure the accuracy of the data, e invited the engineer from Shanghai Institute of Energy Research to make the project of determination and be rheologist.

A result of the testing is that everything OK according to the standard in "The casting Method of the Heat Function of civil e Stove and Oven'' made by the People's public of China. Following is the result the testing (One Stove with Double pots ).


Table

"1" stands for: the speed of temperature increasing.

"2" stands for: the speed of water evaporating.

"3" stands for: the speed of the heat returning .

"FX" stands for: Fengxian One Stove with Double Pots.

From. the table above, we can see that the index of each heat function is more advanced. And the total heat efficiency has reached to 34.46%. Compared with the old-fashioned one, the heat efficiency has increased 2.4 times.

Economical Efficiency

"One Stove with Double Pots" has higher economical efficiency because of the reasonable structure; quick conduction of heat; equally spersed flame; higher heat efficiency.

1. Reasonable price.

To make a new stove only costs about 30 yuan to buy some bricks, lime cement and a grate.

2. Convenient and economical.

The new stove can save 60% straw and ;0% time compared with the old one. Each family can save 54.45 yuan in the purchasing of fuel.

Conclusion

1. This stove enjoys advanced heat function, is suitable for various of straw (wood) and can save time and fuel.

2. Convenient and reasonable price.

It is warmly welcomed by the peasants. It can relax the energy tension. So it is worth popularizing wider.

3. Reasonable structure.

Because of the high technology, the workers who make it should strictly do as the design requires.