Junichi Fujino

Numerical and experimental studies on the measurement of thermal conductivity of a silicone rubber plate as a reference material

Silicone rubber is used as a reference material to examine the accuracy of measuring apparatus. However, the thermal conductivity of silicone rubber has been reported as ranging from 0.20 to 0.25 W/(m·K) at 293.15 K; thus an engineer cannot determine the accuracy of measuring apparatus. In order to obtain the exact value for the thermal conductivity of silicone rubber, the authors have developed a measuring apparatus according to the Guarded Hot Plate method. The dimensions of the test sample were 100 mm x 100 mm x 10 mm. This is sufficient to measure thermal conductivities ranging from 0.18 to 0.26 W/(m·K). The thermal conductivity obtained for a silicone rubber plate in this study was close to 0.25 W/(m·K). It was found that deformation of the silicone rubber has an effect on the thermal conductivity. The accuracy of our thermal conductivity measurement is estimated to be within ±3.5%.

Assessment of thermal damage in total knee arthroplasty using an osteocyte injury model

Polymethylmethacrylate bone cement has been widely used for the anchorage of artificial implants in various orthopedic surgeries. Although it is one of the most successful biomaterials in use, excess heat generation intrinsically causes thermal damage to bone cells adjacent to the bone cement. To estimate a risk of thermal injury, a response of bone cells to cement polymerization must be elucidated because of the occurrence of thermal damage. Thermal damage is affected not only by maximal temperature but also by exposure time, temperature history, and cell type. This study aimed at quantifying the thermal tolerance of bone cells for the development of a thermal injury model, and applying this model for the estimation of thermal damage during cement polymerization in total knee arthroplasty. Osteocytes, osteoblasts, and fibroblasts were respectively subjected to steady supraphysiological temperatures ranging from 45 to 50°C. Survival curves of each cell and temperatures were used to formulate the Arrhenius model. A three‐dimensional heat conduction analysis for total knee arthroplasty was conducted using the finite element model based on serial CT images of human knee. A maximal temperature rise of 50°C was observed at the interface between the 3‐mm thick cement and the tissue immediately beneath the tibial tray of the prosthesis. The probability of thermal damage to the osteocyte, which was calculated using the Arrhenius model, was negligible at a distance of at least 1 mm away from the cement–bone interface.

Study on Guarded Hot Plate Apparatus for Measurement of Thermal Conductivity of Small Polymer Specimens

The aim of this work is to develop a guarded hot plate test apparatus for measuring the thermal conductivity of polymer specimen, the size of which is smaller and thicker than that recommended by the ISO and JIS. The authors made three experimental apparatus suitable for the different sizes of specimen 50×50, 100×100 and 200×200 mm2 in area, measured the thermal conductivity of polymer as homogeneous materials, which ranged from 0.2 to 0.6 W·m−1 ·K−1 , and carried out the numerical analysis. The uncertainty for the measurement of the thermal conductivity of the polymer specimens is estimated to be within ±4% using our test apparatus. For the test apparatus suitable for the specimen 50×50 mm2 , the gap has an effect on the measurement of the thermal conductivity. In addition, the temperature difference ΔTg of the heat source has a direct influence on the deviation in the thermal conductivity data. The influence of the aspect ratio of the specimen and gap width on the measurement is estimated to be within 0.9% for the specimens 50×50 mm2 used in the present study.Copyright