The design of high-temperature thermal conductivity measurements apparatus for thin sample size

This study presents the designing, constructing and validating processes of thermal conductivity apparatus using steady-state heat-transfer techniques with the capability of testing a material at high temperatures. This design is an improvement from ASTM D5470 standard where meter-bars with the equal cross-sectional area were used to extrapolate surface temperature and measure heat transfer across a sample. There were two meter-bars in apparatus where each was placed three thermocouples. This Apparatus using a heater with a power of 1,000 watts, and cooling water to stable condition. The pressure applied was 3.4 MPa at the cross-sectional area of 113.09 mm2 meter-bar and thermal grease to minimized interfacial thermal contact resistance. To determine the performance, the validating process proceeded by comparing the results with thermal conductivity obtained by THB 500 made by LINSEIS. The tests showed the thermal conductivity of the stainless steel and bronze are 15.28 Wm-1K-1 and 38.01 Wm-1K-1 with a difference of test apparatus THB 500 are −2.55% and 2.49%. Furthermore, this apparatus has the capability to measure the thermal conductivity of the material to a temperature of 400°C where the results for the thermal conductivity of stainless steel is 19.21 Wm-1K-1 and the difference was 7.93%

Empirical investigation to explore potential gains from the amalgamation of Phase Changing Materials (PCMs) and wood shavings

The reduction of gained heat, heat peak shifting and the mitigation of air temperature fluctuations are some desirable properties that are sought after in any thermal insulation system. It cannot be overstated that these factors, in addition to others, govern the performance of such systems thus their effect on indoor ambient conditions. The effect of such systems extends also to Heating, Ventilation and Air-conditioning (HVAC) systems that are set up to operate optimally in certain conditions. Where literature shows that PCMs and natural materials such as wood-shavings can provide efficient passive insulation for buildings, it is evident that such approaches utilise methods that are of a degree of intricacy which requires specialist knowledge and complex techniques, such as micro-encapsulation for instance. With technical and economic aspects in mind, an amalgam of PCM and wood-shavings has been created for the purpose of being utilised as a feasible thermal insulation. The amalgamation was performed in the simplest of methods, through submerging the wood shavings in PCM. An experimental procedure was devised to test the thermal performance of the amalgam and compare this to the performance of the same un-amalgamated materials. Comparative analysis revealed that no significant thermal gains would be expected from such amalgamation. However, significant reduction in the total weight of the insulation system would be achieved that, in this case, shown to be up to 20.94%. Thus, further reducing possible strains on structural elements due to the application of insulation on buildings. This can be especially beneficial in vernacular architectural approaches where considerably large amounts and thicknesses of insulations are used. In addition, cost reduction could be attained as wood shavings are significantly cheaper compared to the cost of PCMs

Numerical simulation of an instrument to determine the thermal conductivity of conductive solids

In this paper the design of a cut bar system to determine the thermal conductivity of conductive solid materials is presented. The system works under the comparative method, therefore two reference samples with known thermal conductivity are needed. The thermal design consisted on defining the physical configuration of the thermal system, materials to use and their dimensions, in order to evaluate their thermal performance by varying these parameters to calculate the maximum percentage design error. Given that the thermal design was parametric, the finite volume method was used to solve the heat conduction equation in the cut bar system, which allowed us to vary the different parameters that make up the thermal system such as length and diameter of the bars, insulation thickness, type of reference material, etc. The numerical code developed was verified with one analytical solution. It was found that, the thermal design of a cut bar instrument to determine the thermal conductivity of solid materials within the interval 0.58 ⩽ λ ⩽ 429 W.m-1.K-1 shows a maximum design error of 3.77% associated to the length of the sample material. The results in this paper allow one to kwon the error by design which can be taken into account as a source of uncertainty when determining the thermal conductivity of solid materials

Thermal Performance of a Concrete Cool Roof under Different Climatic Conditions of Mexico

AbstractA cool roof is an ordinary roof with a reflective coating on the exterior surface which has a high solar reflectance and high thermal emittance. These properties let the roof keep a lower temperature than a standard roof under the same conditions. In this work, the thermal performance of a concrete roof with and without insulation and with two colors has been analyzed using the finite volume method. The boundary conditions of the external roof surface were taken from hourly averaged climatic data of four cities. For the internal surface, it is considered that the building is air-conditioned and the inside air has a constant temperature. The interior surface temperature and the heat flux rates into the roofs were obtained for two consecutive days in order to assess the benefits of a cool roofs in different climates

Thermal potential of a geothermal earth-to-air heat exchanger in six climatic conditions of México

In this paper, the thermal and ventilation potential of a geothermal Earth-to-Air Heat exchanger (EAHE) is studied for six weather in Mexico. The cities for the study and their climate were Villahermosa (hot-humid), Merida (hot-sub humid), Monterrey (dry), Juarez City (very dry), Zacualtipan-Hidalgo (warm-humid) and Mexico City (warm-sub-humid). The thermal behavior of the EAHE was modeled numerically for the corresponding warmest and coldest days of the year for each city and three values of Reynolds number. The 24 hrs simulations were carried out with an in-house code using data every 10 minutes. To get the results, 5,184 computational runs were necessary. The results showed that the EAHE has poor ventilation potential for climates with high levels of humidity such as Villahermosa, while for cities with low levels of humidity such as Chihuahua, the ventilation potential increases significantly, the rest of the cities fall in between. As for its application in Mexico, the results show that the EAHE is highly recommended for dry climates such as at the north of the country and not recommended for humid climates such as at the south and south-east of the country