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Rate of Moisture Loss and Air Drying Time of 10 Indigenous Wood Species of Bangladesh Under Two Conditions of Exposure.

M. A. Sattar
Director (Ex.)
Seasoning and Timber Physics Division, Bangladesh Forest Research Institute, Chittagong.

Abstract/ Executive Summary:

The rate of moisture loss and drying time of ten Bangladesh wood species were investigated under two exposure conditions. Drying was most rapid in the first month and five species reached 20% moisture content during that period. After first month, drying practically stopped due to monsoon. Variation of total drying time between the species was found to be statistically significant. Drying was faster under the open drying condition in all cases. It is recommended to air-dry these timbers in outside shed during active drying period.

Keywords: Air drying, Seasoning timber, Drying schedule, Rate of moisture loss.

Location:

Start Date: 00-04-1962

End Date: 00-03-1963

Program Area: Postharvest and Agro-processing

Commodity: Wood

Objectives:

(1) To study the rate of moisture loss of 10 different species under open air drying and shed drying conditions and

(2) To derive the time schedules for these species.

Methodology:

The following species of timber were employed for the study :

Garjan (Dipterocarpus spp.)
Champa (Michelia champaca)
Chapalish (Artocarpus chaplasha)
Sil koroi (Albizzia procera)
Gamar (Gmelina arborea)
Civit (Swintonia floribunda)
Guteguttya (Bursera serrata)
Bhadi (Lannea cormandelica)
Suruj (Cedrela toona)
Simul (Salmalia malabarica)

Fifteen cubic feet of each species of timber were procured including 4 sample boards of 1¹/₄” ´ 8” ´ 8’ size for each exposure condition. The experimental material was fresh sawn and free from decay. The sample boards were placed species wise in two consecutive tiers in the interior of the pile employing 1¹/₂” ´ 1” ´ 16” stickers so that the boards could be removed once a month for measurements. Three tiers of buffer lumber were employed at the bottom and top of the sample tiers. Two buffer piles were constructed out of the remaining lumber employing 24” long stickers. All the species were stacked in one pile to save large quantities of timber which would have been required if a separate pile was made for individual species. The pile foundation consisted of bricks and 12” ´ 12” galvanized iron sheet with the outer three inches bent toward the ground at an angle of 45⁰ to prevent subterranean termites from constructing tunnels up the side of the pile foundation. One pile was located in the open air drying yard and was roofed with the treated lumber. The other pile was placed inside the air drying shed.

Collection and analysis of data:

The air drying was started in the beginning of April, 1962 and the observation was continued till March, 1963. Each sample board was weighed once every month to the nearest one tenth of a pound. Moisture content and specific gravity determinations were made on each sample board at three positions at two feet intervals at the end of the experiment. Monthly moisture contents were computed on the basis of the final moisture contents. These values were averaged for the species under each set of drying condition .The climatological data as obtained from the Forest Research Institute’s meteorological observatory are represented.

Monthly rate of moisture loss was calculated by taking the difference of moisture content values between two successive months. The rate values are given in the text. Typical rate curves for gutguttya and chapalish under open air drying and shed drying conditions are shown in text. Linear regression equation was derived from the observed data on moisture content and square root of drying time. The regression equations together with the correlation coefficient (R²) are tabulated in the text. From the regression equations, The time required to dry from green to 15% moisture content was calculated for each species under each drying condition. The mean specific gravity and total drying time to reach 20% and 15% moisture contents are presented in the text.

Source of Information: Bano biggyan patrika, Vol : V (1), January 1973, 28-42

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The rate of drying was maximum for the first month for all the species under both exposure conditions.The drying rate as evidenced from the regression co-efficient was faster under open air drying condition in all cases. Five out of ten species dried to 20% moisture content in about a month. Gutguttya and bhadi were the slowest to dry. There was close agreement between the observed and calculated drying time at 15% moisture content. The between species variation in total drying time to attain 15% moisture content and also the exposure conditions were found to be highly significant. The derived drying periods appeared to be much higher for all the species under both open air drying, and shed drying conditions because of unfavorable weather condition during the middle of drying. Drying, in fact, stopped in many cases after the first month of piling. This is due to the fact that from the second month upto the fourth month (i.e., June-August) there was high relative humidity resulting from rainfall during these months. If the timber were stacked during the active period, the drying time would have been reduced appreciably.

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