Tag Archives: Thermal Conductivity

Comparison Analyses of Different Models used to Determine Soil Thermal Conductivity and Diffusivity at Nimex Site, Ibadan (Published)

Soil thermal properties regulate the separation of energy fluxes at the ground surface and they control the exchange of energy and mass between the soil and the atmosphere. The knowledge of these properties is needed in order to ascertain the heat flux distribution in the soil under steady and non-steady conditions. In this study, which lasted for 11 months starting from March 2006 to January 2007, we estimated soil thermal conductivity and thermal diffusivity at Nigeria Mesoscale Experiment (NIMEX) site, Ibadan using Johansen and Kersten  models and Horton Numerical method. The aim of this work is to compare the results obtained from these models and to ascertain the level of agreement of the results. The result showed that for Johansen and Kersten models, the highest mean values of thermal conductivity and thermal diffusivity were obtained in the month of September 2006. For Johansen model the values are 4.18±0.08 Wm-1K-1 and 4.56±5.57*10-8m2s-1 for thermal conductivity and thermal diffusivity respectively and for Kersten model the thermal conductivity and thermal diffusivity values are 1.00±0.05 Wm-1K-1 and 1.07±0.22*10-8 m2s-1 respectively. This may be due to the observed increase in the soil moisture content within this month. The result obtained using Horton Numerical method showed that the highest mean thermal conductivity and thermal diffusivity values of 9.76 ±3.00 Wm-1K-1 and 10.70±3.30*10-8m2s-1 respectively were obtained in the month of December 2006 while the lowest mean values of -0.44 ±14.68 Wm-1K-1 for thermal conductivity and 0.10±12.70*10-8m2s-1 for thermal diffusivity were obtained in the month of September contrary to the results obtained with the first two models. The negative mean thermal conductivity value of -0.44 ±14.68 Wm-1K-1 obtained in the month of September 2006 using Horton Numerical method was probably due to the increase in soil moisture content which is as a result of increase in the amount of rainfall within this month that lowered the temperature at the near soil surfaces. Kersten model is in agreement with Johansen model but has low values making it unsuitable for very low soil moisture. Johansen model is likely the best model for estimating thermal conductivity and diffusivity.

Keywords: Soil moisture content, Thermal Conductivity, Thermal Diffusivity, Volumetric Heat Capacity

Temperature Variations and Soil Thermal Properties at the Nigeria Mesoscale Experiment Site, Ibadan, Nigeria (Published)

Soil temperature has been observed to depend on a number of factors, which also determine the surface temperature. In this study, soil temperature at the Nigeria Mesoscale Experiment (NIMEX) site, Ibadan (7.4398° N, 3.8930° E) was investigated and the soil thermal properties were estimated for the period of March, 2006 to January, 2007 using Kersten model. The rainy seasons had increased the soil moisture content and soil thermal properties while the dry seasons had low soil moisture content and soil thermal properties. The maximum temperature of 32.10° C at the 30cm depth was measured in November 2006 during the dry season and the minimum temperature 26.80° C was measured at 5cm depth in September 2016 during the wet/rainy season. Soil moisture, thermal conductivity, thermal diffusivity and volumetric heat capacity had their maximum value of 20.52m3m-3, 1.006 Wm-1K-1, 1.07*10-8m2s-1 and 0.91*108Jm-3K-1 in September 2006 respectively. The minimum values for soil moisture, thermal conductivity and volumetric heat capacity occurred in January, 2007 with values of 15.75 m3m-3, 0.90 Wm-1K-1 and 0.91*108Jm-3K-1 respectively, and the minimum value of 0.85*10-8m2s-1 for thermal diffusivity occurred in July 2006.

Keywords: Soil moisture content, Thermal Conductivity, Thermal Diffusivity, Volumetric Heat Capacity, soil temperature

Temperature Variations and Soil Thermal Properties at the Nigeria Mesoscale Experiment Site, Ibadan, Nigeria (Published)

Soil temperature has been observed to depend on a number of factors, which also determine the surface temperature. In this study, soil temperature at the Nigeria Mesoscale Experiment (NIMEX) site, Ibadan (7.4398° N, 3.8930° E) was investigated and the soil thermal properties were estimated for the period of March, 2006 to January, 2007 using Kersten model. The rainy seasons had increased the soil moisture content and soil thermal properties while the dry seasons had low soil moisture content and soil thermal properties. The maximum temperature of 32.10° C at the 30cm depth was measured in November 2006 during the dry season and the minimum temperature 26.80° C was measured at 5cm depth in September 2016 during the wet/rainy season. Soil moisture, thermal conductivity, thermal diffusivity and volumetric heat capacity had their maximum value of 20.52m3m-3, 1.006 Wm-1K-1, 1.07*10-8m2s-1 and 0.91*108Jm-3K-1 in September 2006 respectively. The minimum values for soil moisture, thermal conductivity and volumetric heat capacity occurred in January, 2007 with values of 15.75 m3m-3, 0.90 Wm-1K-1 and 0.91*108Jm-3K-1 respectively, and the minimum value of 0.85*10-8m2s-1 for thermal diffusivity occurred in July 2006.

Keywords: Soil moisture content, Thermal Conductivity, Thermal Diffusivity, Volumetric Heat Capacity, soil temperature

Experimental Investigation of Thermal Conductivity of Woods by Linear Regression Approach (Published)

This research tries to study the experimental investigation  on thermal conductivity of Melina and wall nut  woods using linear regression approach .From the thermal conductivity investigation of woods by linear regression approach , test results show that the values of thermal conductivity for Melina wood falls in the range of  K between  0.002w/mk-1 to 0.007w/mk-1 which is on the low side and the wall nut between 0.0001w/mk-1 to 0.041w/mk-1 which is on the high side .It therefore depicts that Melina has a better  thermal conductivity than wall nut since thermal conductivity of  it (Melina) agrees with the literature that thermal conductivity is better with lower values of K.

Keywords: Linear Regression, Modified Lee Disc, Thermal Conductivity

EFFECTS OF DYNAMIC COMPRESSION ON THE THERMAL CONDUCTIVITIES OF SELECTED WOOD PRODUCTS OF DIFFERENT PARTICLE SIZES (Published)

The study examines the effects of dynamic compression on the thermal conductivity of five different wood species of the families of Sterculiaceae, Moraceae and Ulmaceae. These species are; Nesogordonia papaverifera, Milicia excelsa, Antiaris africana, Celtis zenkeri and Celtis phillipensis. The results showed that, increase in compacting pressure resulted to increase in the thermal conductivities of the wood samples. It was also noted that, the thermal conductivity decreases with increase in the particle sizes of the wood material. The thermal conductivity values obtained for the samples fall within the range 0.0890 – 0.1534
Wm−1 K −1 for wood materials. This range lies within the thermal conductivity values of common material used in Asbestos, Rubber, Diatomite and Chlorinated poly- ether. In addition, 850 µ m of Nesogordonia papaverifera (Danta) pose the best insulation among the particle sizes considered Hence, the selected wood materials could find useful applications in industrial insulating devices and could also serve as good potential devices as heat resistant.

Keywords: Dynamic compression, Particle sizes, Thermal Conductivity

THERMAL PROPERTIES OF THREE MAJOR LANDFORMS IN AKWA IBOM STATE, NIGERIA (Published)

The thermal properties of some selected soil samples collected from three landforms, namely Beach Ride Sand (BRS), Coastal Plane Sand (CPS), Sandstone/Shale Hill Ridges (SHR) from Akwa Ibom State of the Federal Republic of Nigeria were measured, such as; thermal conductivity (K), thermal diffusivity (λ), thermal absorptivity (α) and thermal resistivity (R); the result obtained shows that K falls within the range of 0.272 – 0.501w/mk, λ = 4.9 x 10-6 – 11.4 x10-8 m2 S-1, α = 17.86 – 27.24m-1 and R also falls within the range of 1.996 – 3.676mkw-1 for all the soil samples, which shows that SHR would make the best soil for building and construction while CPS and BRS are best for planting root crops.

Keywords: Soil Samples, Thermal Absorptivity, Thermal Conductivity, Thermal Diffusivity, Thermal Resistivity