The Comparative Water Boiling Test for Wood
The Comparative Water Boiling Test (CWBT) is an adaptation by Jean-François Rozis of the test method and procedure of the international standard Water Boiling Test (WBT), modified to account for the real customs and habits of cooking in Cambodia. CWBT is only for comparing stoves’ Potential Fuel Savings under similar conditions of use, which eliminates error sources from fuel heat value calculations.
The CWBT is designed to duplicate as closely as possible real cooking conditions. As well, the CWBT is designed to be simple – it requires minimum equipment easily available in Cambodia and is easy to conduct in the field. The CWBT also simplifies the calculation at the end of the test.
The CWBT is designed for Cambodia, but its general procedure could be adapted for use in other countries.
Procedures presented here are for testing of wood. The following two sets of procedures are also available:
Minimum Recommended Equipment: - A digital watch with second precision
- An accurate platform scale (ratio between precision of the measure and maximum weight should be lower than or equal at 1%), a simple balance almost available in all villages (like Tanita 2 kg balance made in Vietnam and accurate within 10 grams).
- Digital thermometer with thermocouple probes, if possible, or other type of thermometer able to indicate temperature in water until 100 °C (accuracy of 1 °C)
- A form for recording data
- Cylindrical aluminum pots/pans with flat/round bottom and with lids: diameter of the pot rim and bottom should be 23,8 cm, the height should be 11 cm, and the thickness of the pan should be 2 mm. Two pan lids should allow for the thermocouple probes to be fixed through the insulated cap in the center of lids and 1 cm above the internal bottom of the pot to permit measurement of the water temperature.
- Around 25 grams of local resin (from dipterocarpus alatus) used traditionally as fire starter.
- 1 kilogram of split wood for 3 liters of water (to be Comparative following fuel consumption of the stove, to obtain reasonable TTB –around 20 minutes-and TTT – around 60 minutes)
Moisture range of wood: Without any specific instruments for measuring the wood moisture content, the following procedure is recommended: split the wood and dry it (can be stored inside the kitchen or sun dried) for at least 2 months. According to the CFSP test, if the freshly cut wood (65% of moisture content) is split and dried for 2 months either in storage or via the sun (hygroscopic equilibrium), the average moisture content is in the range of 10 to 15%.
Test principle for a one-pot hole: - Weigh the recommended amount of wood (1 kg) prepared as above presented
- For comparative information, register the room temperature.
- The stove should be cold and clean, installed in a room protected from the wind in the direction to the fire door.
- Two similar pots placed above the potholes with probe instrumented pot lids 1 cm above the internal bottom of the pan.
- The fire is ignited with a fixed quantity of resin. The fuel is managed in such a manner as to obtain the maximal output power possible during the high power phase, so as to reach as quickly as possible the boiling point in the first pot. The boiling point is reached when the temperature is stabilized, around 99 °C, after 10 seconds.
- Time to Boil (TTB) is recorded.
- After reaching the boiling point in the pot, high power phase is maintained during 5 minutes to respect the traditional way of cooking.
- Then, the fire is maintained to keep water simmering in the pot in a range of two degrees around boiling point (97 – 99 °C), avoiding dying flames. The temperature is recorded every 3 minutes. When all remaining wood is burned, and as soon as the temperature falls under 97 °C, Total Time Test (TTT) is recorded. If the temperature exceeds the range by five degrees during the simmering period, the test should be rejected.
- For comparative information, weigh the remaining charcoal and water in the pot. Remaining wood has to be absent, so ensure the fire consumes all the wood before the water temperature begins to drop; only remaining charcoal has to be observed (max 20 grams).
- Note for re-fuelling of the wood. For first firings, prepare 500 grams of wood. Maintain the water temperature in a range of five degrees. When the temperature seems to be going down (do not wait until 2 degrees less), than refuel with 200 gram of wood (around two sticks of split fire wood).
NB: If this is the first time the cookstove to be tested has been used, make two to three cooking processes before initiating any comparative test to take out any moisture content in the stove body.
Analysis of the test measurements The test should be conducted at least three times (CWBT 1, CWBT 2, CWBT 3); be aware of the similar initial conditions (e.g., cold at ambient temperature, clean stove, no wind, same amount and type of wood, water, pot). If the test is conducted with two stoves at the same time, then change the instrumented pots between the two stoves to reduce experimental error.
As above, if each TTT is greater than or equal to [calculated average – 5 minutes] and lower than or equal to [calculated average + 5 minutes], accept the test series. If not, conduct an additional test and select from the four those three that respect this level of precision around the calculated average of the three selections.
- Calculation of Useful Energy (UE)
Useful energy depends on the quantity of water, the starting water temperature and the amount of water evaporated water:
For example, UE [in KJ]= 1068 + 2257* (3-remaining water [in Kg])
- Potential Fuelwood Savings (PFS) Compared With Old Design
Percentage of Fuelwood Savings is the difference between Useful Energy of the New Stove Design and Useful Energy of the Old Stove Design, divided by Useful Energy of the Old Stove. If negative, then the new design is consuming more fuel for the same purpose than is the old design.
So, PFS [in %]= 100*(UE new stove – UE old stove)/UE old stove
Related topics - The Water Boiling Test based on VITA 1985 - the 'International Standards'.
- The Indian standard WBT procedures developed by the Bureau of Indian Standards, for measuring the efficiency of the cookstoves.
- The Chinese standard WBT procedures developed by the State Standards Organization of the People's Republic of China - "Testing Method for the Heat Properties of Civil Firewood Stoves".
Contributors User:Erin Boyd 20 March 2006
Comments / Questions on this page
|
