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Equilibrium moisture content
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<h2 id="equilibrium-moisture-content-of-grains">Equilibrium moisture content of grains</h2> <p>The moisture content of grains is an essential property in food storage. The moisture content that is safe for long-term storage is 12% for corn, sorghum, rice and wheat and 11% for soybean<a class="footnote-ref" id="fnref:1" href="#fn:1"><sup>1</sup></a> </p><p>At a constant relative humidity of air, the EMC will drop by about 0.5% for every increase of 10 °C air temperature.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a> </p><p>The following table shows the equilibriums for a number of grains (data from <a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>). These values are only approximations since the exact values depend on the specific variety of a grain.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <table><tbody><tr><th></th><th></th><th colspan="4">Corn kernels</th><th colspan="4">Soybean</th><th colspan="4">Sorghum</th><th colspan="4">Long Grain Rice</th><th colspan="4">Durum Wheat</th></tr><tr><th></th><td><a href="/facts/Celsius/okAEu1CA">°C</a></td><td>1.7</td><td>10.0</td><td>21.1</td><td>37.8</td><td>1.7</td><td>10.0</td><td>21.1</td><td>37.8</td><td>1.7</td><td>10.0</td><td>21.1</td><td>37.8</td><td>1.7</td><td>10.0</td><td>21.1</td><td>37.8</td><td>1.7</td><td>10.0</td><td>21.1</td><td>37.8</td></tr><tr><th><a href="/facts/Relative_humidity/Nwb28VlT">RH</a></th><td><i><a href="/facts/Fahrenheit/2TVmyJod">°F</a></i></td><td><i>35</i></td><td><i>50</i></td><td><i>70</i></td><td><i>100</i></td><td><i>35</i></td><td><i>50</i></td><td><i>70</i></td><td><i>100</i></td><td><i>35</i></td><td><i>50</i></td><td><i>70</i></td><td><i>100</i></td><td><i>35</i></td><td><i>50</i></td><td><i>70</i></td><td><i>100</i></td><td><i>35</i></td><td><i>50</i></td><td><i>70</i></td><td><i>100</i></td></tr><tr><th>25</th><td></td><td>9.3</td><td>8.6</td><td>7.9</td><td>7.1</td><td>5.9</td><td>5.7</td><td>5.5</td><td>5.2</td><td>11.5</td><td>10.9</td><td>10.2</td><td>9.3</td><td>9.2</td><td>8.6</td><td>8.0</td><td>7.3</td><td>8.3</td><td>8.0</td><td>7.7</td><td>7.2</td></tr><tr><th>30</th><td></td><td>10.3</td><td>9.5</td><td>8.7</td><td>7.8</td><td>6.5</td><td>6.3</td><td>6.1</td><td>5.7</td><td>12.1</td><td>11.5</td><td>10.8</td><td>9.9</td><td>10.1</td><td>9.5</td><td>8.8</td><td>8.0</td><td>8.9</td><td>8.7</td><td>8.3</td><td>7.7</td></tr><tr><th>35</th><td></td><td>11.2</td><td>10.4</td><td>9.5</td><td>8.5</td><td>7.1</td><td>6.9</td><td>6.6</td><td>6.2</td><td>12.7</td><td>12.1</td><td>11.4</td><td>10.5</td><td>10.9</td><td>10.3</td><td>9.5</td><td>8.7</td><td>9.6</td><td>9.3</td><td>8.9</td><td>8.3</td></tr><tr><th>40</th><td></td><td>12.1</td><td>11.2</td><td>10.3</td><td>9.2</td><td>7.8</td><td>7.6</td><td>7.3</td><td>6.9</td><td>13.3</td><td>12.7</td><td>12.0</td><td>11.1</td><td>11.7</td><td>11.0</td><td>10.3</td><td>9.4</td><td>10.2</td><td>9.9</td><td>9.5</td><td>8.8</td></tr><tr><th>45</th><td></td><td>13.0</td><td>12.0</td><td>11.0</td><td>9.9</td><td>8.6</td><td>8.3</td><td>8.0</td><td>7.5</td><td>13.8</td><td>13.3</td><td>12.6</td><td>11.7</td><td>12.5</td><td>11.8</td><td>11.0</td><td>10.0</td><td>10.9</td><td>10.5</td><td>10.1</td><td>9.4</td></tr><tr><th>50</th><td></td><td>13.9</td><td>12.9</td><td>11.8</td><td>10.6</td><td>9.4</td><td>9.1</td><td>8.8</td><td>8.3</td><td>14.4</td><td>13.8</td><td>13.2</td><td>12.3</td><td>13.3</td><td>12.5</td><td>11.7</td><td>10.7</td><td>11.5</td><td>11.2</td><td>10.7</td><td>10.0</td></tr><tr><th>55</th><td></td><td>14.8</td><td>13.7</td><td>12.6</td><td>11.3</td><td>10.3</td><td>10.0</td><td>9.7</td><td>9.1</td><td>15.0</td><td>14.4</td><td>13.8</td><td>12.9</td><td>14.1</td><td>13.3</td><td>12.4</td><td>11.3</td><td>12.2</td><td>11.9</td><td>11.4</td><td>10.6</td></tr><tr><th>60</th><td></td><td>15.7</td><td>14.5</td><td>13.4</td><td>12.0</td><td>11.5</td><td>11.1</td><td>10.7</td><td>10.1</td><td>15.6</td><td>15.1</td><td>14.4</td><td>13.6</td><td>14.9</td><td>14.0</td><td>13.1</td><td>12.0</td><td>13.0</td><td>12.6</td><td>12.1</td><td>11.3</td></tr><tr><th>65</th><td></td><td>16.6</td><td>15.4</td><td>14.2</td><td>12.8</td><td>12.8</td><td>12.4</td><td>11.9</td><td>11.3</td><td>16.3</td><td>15.7</td><td>15.1</td><td>14.3</td><td>15.7</td><td>14.8</td><td>13.8</td><td>12.7</td><td>13.8</td><td>13.4</td><td>12.8</td><td>12.0</td></tr><tr><th>70</th><td></td><td>17.6</td><td>16.3</td><td>15.0</td><td>13.6</td><td>14.4</td><td>14.0</td><td>13.5</td><td>12.7</td><td>17.0</td><td>16.5</td><td>15.8</td><td>15.0</td><td>16.6</td><td>15.7</td><td>14.6</td><td>13.4</td><td>14.7</td><td>14.3</td><td>13.7</td><td>12.8</td></tr><tr><th>75</th><td></td><td>18.7</td><td>17.3</td><td>16.0</td><td>14.5</td><td>16.4</td><td>16.0</td><td>15.4</td><td>14.5</td><td>17.8</td><td>17.3</td><td>16.7</td><td>15.9</td><td>17.6</td><td>16.5</td><td>15.5</td><td>14.2</td><td>15.8</td><td>15.4</td><td>14.7</td><td>13.8</td></tr><tr><th>80</th><td></td><td>19.8</td><td>18.5</td><td>17.0</td><td>15.4</td><td>19.1</td><td>18.6</td><td>17.9</td><td>17.0</td><td>18.8</td><td>18.2</td><td>17.6</td><td>16.9</td><td>18.6</td><td>17.5</td><td>16.4</td><td>15.1</td><td>17.1</td><td>16.6</td><td>16.0</td><td>15.0</td></tr><tr><th>85</th><td></td><td>21.2</td><td>19.8</td><td>18.2</td><td>16.5</td><td>22.9</td><td>22.3</td><td>21.6</td><td>20.5</td><td>19.9</td><td>19.4</td><td>18.8</td><td>18.0</td><td>19.8</td><td>18.7</td><td>17.5</td><td>16.1</td><td>18.8</td><td>18.3</td><td>17.6</td><td>16.5</td></tr><tr><th>90</th><td></td><td>22.9</td><td>21.4</td><td>19.8</td><td>17.9</td><td>28.9</td><td>28.2</td><td>27.3</td><td>26.1</td><td>21.4</td><td>20.9</td><td>20.3</td><td>19.6</td><td>21.3</td><td>20.1</td><td>18.9</td><td>17.4</td><td>21.3</td><td>20.7</td><td>20.0</td><td>18.8</td></tr></tbody></table> <h2 id="equilibrium-moisture-content-of-wood">Equilibrium moisture content of wood</h2> <p>The <a href="/facts/Moisture/vubw4SpX">moisture</a> content of wood below the <a href="/facts/Fibre_saturation_point/8rfkn7pk">fiber saturation point</a> is a function of both <a href="/facts/Relative_humidity/Nwb28VlT">relative humidity</a> and <a href="/facts/Temperature/QyGe4gmj">temperature</a> of surrounding air. The moisture content (<i>M</i>) of wood is defined as: </p> M = m − m o d m o d {\displaystyle M={\frac {m-m_{od}}{m_{od}}}} <p>where <i>m</i> is the mass of the wood (with moisture) and m o d {\displaystyle m_{od}} is the oven-dry mass of wood (i.e. no moisture).<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> If the wood is placed in an environment at a particular temperature and relative humidity, its moisture content will generally begin to change in time, until it is finally in equilibrium with its surroundings, and the moisture content no longer changes in time. This moisture content is the EMC of the wood for that temperature and relative humidity. </p><p>The Hailwood-Horrobin equation for two hydrates is often used to approximate the relationship between EMC, temperature (<i>T</i>), and relative humidity (<i>h</i>):<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a><a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> M e q = 1800 W [ k h 1 − k h + k 1 k h + 2 k 1 k 2 k 2 h 2 1 + k 1 k h + k 1 k 2 k 2 h 2 ] {\displaystyle M_{\mathrm {eq} }={\frac {1800}{W}}\left[{\frac {kh}{1-kh}}\,+\,{\frac {k_{1}kh+2k_{1}k_{2}k^{2}h^{2}}{1+k_{1}kh+k_{1}k_{2}k^{2}h^{2}}}\right]} <p>where <i>M</i>eq is the equilibrium moisture content (percent), <i>T</i> is the temperature (degrees Fahrenheit), h is the relative humidity (fractional) and: </p> W = 330 + 0.452 T + 0.00415 T 2 {\displaystyle W=330+0.452\,T+0.00415\,T^{2}} k = 0.791 + 4.63 × 10 − 4 T − 8.44 × 10 − 7 T 2 {\displaystyle k=0.791+4.63\times 10^{-4}\,T-8.44\times 10^{-7}\,T^{2}} k 1 = 6.34 + 7.75 × 10 − 4 T − 9.35 × 10 − 5 T 2 {\displaystyle k_{1}=6.34+7.75\times 10^{-4}\,T-9.35\times 10^{-5}\,T^{2}} k 2 = 1.09 + 2.84 × 10 − 2 T − 9.04 × 10 − 5 T 2 {\displaystyle k_{2}=1.09+2.84\times 10^{-2}\,T-9.04\times 10^{-5}\,T^{2}} <p>This equation does not account for the slight variations with wood species, state of mechanical stress, and/or <a href="/facts/Hysteresis/9M2pwR62">hysteresis</a>. It is an empirical fit to tabulated data provided in the same reference, and closely agrees with the tabulated data. For example, at T=140 deg F, h=0.55, EMC=8.4% from the above equation, while EMC=8.0% from the tabulated data. </p> <h2 id="equilibrium-moisture-content-of-sands-soils-and-building-materials">Equilibrium moisture content of sands, soils and building materials</h2> <p>Materials such as stones, sand and ceramics are considered 'dry' and have much lower equilibrium moisture content than organic material like wood and leather. <a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> typically a fraction of a percent by weight when in equilibrium of air of <a href="/facts/Relative_humidity/Nwb28VlT">Relative humidity</a> 10% to 90%. This affects the rate that buildings need to dry out after construction, typical cements starting with 40-60% water content. This is also important for construction materials such as render reinforced with organic materials, as modest changes in content of different types of straw and wood shavings have a significant influence on the overall moisture content<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> <h2 id="bibliography">Bibliography</h2> <ul><li><a href="/facts/R._Bruce_Hoadley/QrkTo8C0">Hoadley, R. Bruce</a> (2000). <i>Understanding Wood: A Craftsman's Guide to Wood Technology</i> (2nd. ed.). <a href="/facts/Taunton_Press/XQVeXhjd">Taunton Press</a>. <a href="/facts/ISBN_(identifier)/15AdSPa9">ISBN</a> 1-56158-358-8.</li> <li>Robert J. Ross, ed. (2010). <a href="https://web.archive.org/web/20170213231240/https://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf"><i>Wood Handbook: Wood as an Engineering Material</i></a> (PDF). US Forest Products Laboratory. pp. 4-3 – 4-4. General Technical Report FPL–GTR–190. Archived from <a href="http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf">the original</a> (PDF) on 2017-02-13. Retrieved 2016-05-19.</li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20150610231137/https://www.imagepermanenceinstitute.org/resources/newsletter-archive/v4/moisture-equilibration">"The Who, Why, When and How of Moisture Equilibration"</a>. <i>Image Permanence Institute</i>. Rochester Institute of Technology. Archived from <a href="https://www.imagepermanenceinstitute.org/resources/newsletter-archive/v4/moisture-equilibration">the original</a> on 10 June 2015. Retrieved 7 October 2013.</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Sadakam, Samy Grain Drying Tools: Equilibrium Moisture Content Tables and Psychrometric Charts. Univ. Arkansas, FSA1074 <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>FAO. 2011. Rural structures in the tropics. Design and development. Chapter 16: Grain crop drying, handling, and storage. Rome. http://www.fao.org/docrep/015/i2433e/i2433e10.pdf <a href="http://www.fao.org/docrep/015/i2433e/i2433e10.pdf" target="_blank">http://www.fao.org/docrep/015/i2433e/i2433e10.pdf</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Sadakam, Samy Grain Drying Tools: Equilibrium Moisture Content Tables and Psychrometric Charts. Univ. Arkansas, FSA1074 <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>FAO. 2011. Rural structures in the tropics. Design and development. Chapter 16: Grain crop drying, handling, and storage. Rome. http://www.fao.org/docrep/015/i2433e/i2433e10.pdf <a href="http://www.fao.org/docrep/015/i2433e/i2433e10.pdf" target="_blank">http://www.fao.org/docrep/015/i2433e/i2433e10.pdf</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>What is Equilibrium Moisture Content? http://www.wagnermeters.com/wood-moisture-meter/moisture-content-and-equilibrium-determined-by-relative-humidity/ <a href="http://www.wagnermeters.com/wood-moisture-meter/moisture-content-and-equilibrium-determined-by-relative-humidity/" target="_blank">http://www.wagnermeters.com/wood-moisture-meter/moisture-content-and-equilibrium-determined-by-relative-humidity/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Hailwood, A.J.; S. Horrobin (1946). "Absorption of water by polymers: analysis in terms of a simple model". Trans. Faraday Soc. 42B: 84–102. <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Rasmussen, E.F. (1988). Forest Products Laboratory, U.S. Department of Agriculture. (ed.). Dry Kiln Operators Manual. Hardwood Research Council. <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Eleotério, Jackson Roberto; Clóvis Roberto Haselein; Nestor Pedro Giacomini. "A Program to Estimate the Equilibrium Moisture Content of Wood" (PDF). Ciência Florestal. 8 (1): 13–22. doi:10.5902/19805098347. ISSN 0103-9954. Archived from the original (PDF) on 2009-07-11. Retrieved 2008-11-14. <a href="https://web.archive.org/web/20090711024227/http://www.ufsm.br/cienciaflorestal/artigos/v8n1/art2v8n1.pdf" target="_blank">https://web.archive.org/web/20090711024227/http://www.ufsm.br/cienciaflorestal/artigos/v8n1/art2v8n1.pdf</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Leivo, Virpi & Rantala, Jukka. (2003). Moisture Behavior of Slab-On-Ground Structures <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>An experimental investigation on equilibrium moisture content of earth plasters with natural reinforcement fibres for straw bale buildings Taha Ashour, Heiko Georg, Wei Wu <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> </ol>