Moisture Content In Porous Materials Research Articles

Comparison of microwave moisture evaluation quality in time and frequency domain

The article presents the comparison of two methods of microwave data analysis for evaluation of moisture content in porous materials. The content of the paper covers the short description of microwave technique for moisture evaluation and the description of the two methods of microwave data analysis – the time domain and frequency domain. In the second part, the dependences between red brick moisture and apparent permittivity are presented. Apparent permittivity values are determined by microwave antenna and calculated in time and frequency domain. With the calculated values, regression models were estimated and quality of both evaluated. Using the analyzed data, the advantages and disadvantages of both techniques were defined and the measuring potential evaluated.

Measuring moisture content in building insulation materials by a hot film

In a humid environment, porous insulation materials can acquire large amounts of moisture, which worsens the materials’ performance and causes corrosion. Current thermal methods to measure moisture content in porous materials require that a temperature sensor be placed some distance away from a heating element. As a result, the measurement is very sensitive to the distance between the heating element and the sensor. In addition, the required large heat flux induces unwanted convection and radiation heat transfer that interfere with the measurement. To solve these problems, this investigation proposed a hot film with two thermocouples attached to measure the moisture content. The hot film was embedded in the test material for a constant heating of 90 s. The sensed temperature rise rate for the final 50 s was obtained to infer the volumetric heat capacity for moisture content. The proposed method was used to measure moisture in sponge blocks with different moisture contents. By comparing the measured moisture contents with those determined by gravimetric weighing, it was found that the hot film method accurately measured the moisture in porous materials. The hot film method was more sensitive to low moisture content in porous materials than to high moisture content.

Measuring moisture content in porous insulation materials based on transient temperatures over a period of 100 seconds

Porous materials can absorb large amounts of moisture under high-humidity conditions. Numerous methods have been developed to determine moisture content, but a rapid, inexpensive and accurate measurement method is lacking. The current investigation proposed the measurement of moisture content in porous materials based on transient temperature responses over a period of 100 seconds. A lacquered nichrome wire was used as the heating element, and the transient temperatures were monitored by two highly sensitive fiber-optic sensors. Through curve-fitting of the transient temperature responses with the composite heat conduction theory, the volumetric heat capacity (product of the density with the specific heat) of the tested material was inferred. The moisture content was determined from the difference in the volumetric heat capacity of the material with respect to its dry state. The above method was used to quantify the moisture content of sponge blocks with volumetric moisture mass ranging from 0 to 75 kg/m3. Two series of isolated tests were conducted to evaluate the repeatability of the measurements. The maximum difference in the measured volumetric moisture mass between the proposed method and the gravimetric method was less than 7 kg/m3, and this accuracy is sufficient for engineering applications.

Time-Domain Reflectometry for the Prediction of Loblolly Pine and Sweetgum Moisture Content

Time-domain reflectometry (TDR) can be used to predict the moisture content in porous materials, including soil, and is an exciting tool that could be used to measure the moisture content in wet-stored wood. Three-rod probes with 127 mm- or 152 mm-long rods were inserted into 62 loblolly pine and 34 sweetgum saturated bolts. The bolts were air dried over a span of five weeks. TDR waveforms and moisture content were periodically recorded. In total, 534 and 482 readings were taken for the loblolly pine and sweetgum bolts, respectively. An algorithm in R was written to automatically analyze the apparent length of the TDR rods. Calibration models were developed between moisture content and X (apparent length / actual rod length). A three-parameter logistic model was developed for loblolly pine (R2=0.64) and sweetgum (R2=0.84). The process was repeated using shorter bolts and 152 mm-long rods, resulting in improved models for loblolly pine (R2=0.99) and sweetgum (R2=0.97). Overall, TDR and the algorithm written to analyze the waveforms were accurate in predicting moisture content and could be used to monitor moisture in wet-decks.

Measuring moisture content in a porous insulation material using a hot wire

Porous insulation materials may easily acquire a large amount of moisture when they are exposed to high-humidity conditions. The acquired moisture can cause degradation of insulation performance, micro-organism growth, corrosion, etc. Currently, there is lack of an accurate, simple and inexpensive method for in-situ, nondestructive and rapid measurement of the moisture content in porous materials. This investigation proposes measuring the moisture content by means of the material's volumetric heat capacity using a hot wire. The moisture content is inferred from the change of the volumetric heat capacity before and after the moisture acquirement, which is the ratio of the thermal conductivity to the thermal diffusivity. To evaluate the measurement performance, the method was applied to determine both liquid water and ice content in sponge blocks. The results indicate that the discrepancies in the measured moisture mass content are within ±4% (w/w) between our proposed hot-wire method and the benchmark gravimetric method using a precision balance. Unlike the measurement of the thermal conductivity or the thermal diffusivity, the hot-wire method is insensitive to the contact resistance when measuring the volumetric heat capacity. This method may even be extended to detect foreign substances in porous materials if there is a meaningful difference in the measured volumetric heat capacity before and after the substance intrusion.

Determination of critical moisture content in porous materials by IR thermography

This study is focused on the improvement on the porous material characterisation, measuring the transition stage between the saturated and dry phases, which has been defined in literature as the critical moisture content (Θc). This study develops a procedure based on Quantitative IR Thermography (QIRT) determining the effective Θc, as a physical property for the porous material. The Θc for San Marco bricks were examined in laboratory by QIRT and the standard gravimetric method (SGM). It was seen that QIRT can be used to determine the Θc and was also found to be more practical and sensitive than the SGM. The results obtained in the laboratory were promising to give the hints of methods for quantitative moisture content measurements and in-situ QIRT investigations.

Detection of water deposits and movement in porous materials by infrared imaging

Since a large amount of damage in porous materials arises as a direct or indirect consequence of moisture (static and dynamic phenomena), detection and monitoring of moisture in porous materials is important, in an attempt to determine the actual damage, as well as the deterioration rate. The most common methodology to assess the moisture content in porous materials is to collect representative samples from the sites investigated and then weigh them before and after drying. In this research, infrared thermography, an indirect moisture assessment technique, was used in the investigation of various porous stones in the laboratory during capillary rise tests. Supplementary investigation of the stones in terms of their microstructure (mercury intrusion porosimetry) and isothermic behaviour (water sorption) was also performed. Finally, an in field diagnostic survey on historic structures was carried out. The results of this study indicate that infrared imaging provides significant information in the study of moisture in porous materials.

住宅の結露防止,結露被害防止に対する吸放湿材貼付効果に及ぼす外界気象の影響 : 暖房室における吸放湿材内含湿特性の把握と一定外気温湿度による評価

住宅の結露防止,結露被害防止に対する吸放湿材貼付効果に及ぼす外界気象の影響 : 暖房室における吸放湿材内含湿特性の把握と一定外気温湿度による評価