In this study, density, specific heat, thermal conductivity, and thermal diffusivity were measured experimentally along the lengths of human cadaveric femora. Fresh and dry bone samples were selected from both male and female specimens, and for different age groups varying between 44 and 73 years old. Measured values for specific heat vary between 1.14 and 2.37 J/gm degrees C; for thermal conductivities the range is from 0.16 to 0.34 W/m degrees C; and for thermal diffusivities the range is from 0.10 to 0.23 cm2/sec, depending on whether the bone samples were fresh or dry, cancellous or cortical. The experimental results are presented in non-dimensional coordinates and are compared with the few other data available in the literature.
This paper describes the laser cutting and the amount of laser energy needed to remove a unit mass of compact or cancellous human cadaveric bones ("heat-of-removal") by using a CO2 laser. Data are collected under different operating conditions, such as laser power, scanning speed, and lens focusing for fresh and fixed human bones from male and female femora and tibiae samples with ages varying between 28 and 73 years old. The aim of the present experiments was to demonstrate the feasibility of laser osteotomy, to find the energy requirements for given groove depths or bone removal rates, and to shed some light on optimum conditions for laser osteotomy. Only cadaveric bones were used in this study, since the present aim did not include the investigation of heating rates and the extent and effect of thermal necrosis adjacent to the cut. In vivo properties may be somewhat different from those of cadaveric material. While blood circulation within the living bone may contribute to the laser cutting characteristics, it cannot be addressed here. Experiments showed that very deep cuts are difficult to achieve with a CO2 laser, as at high-power/low-scan-speed the groove becomes rather wide, with unacceptable thermal damage adjacent to the cut, while multiple passes do not easily attain large depths. There was no significant difference for the laser heat-of-removal for different age groups and for male and female samples. The laser heat-of-removal was found to be higher for compact bone than for cancellous bone samples. Comparison of cross-sections of the cuts with an existing model gave good agreement.
An experimental investigation was carried out to measure local and average heat transfer coefficients for horizontal tubes located in freeboard region of air fluidized beds. Tests were carried out at room temperature and atmospheric pressure in a rectangular fluidized bed, with mean particle diameters of 275 to 850 μm.Both local and average heat transfer coefficients were found to vary with particle diameter, flow rate, static bed depth, and elevation in the freeboard region.
Gas-fluidized beds are operated with a wide particle size range, and the entrainment of particles into the freeboard region above the dense bed is of practical importance. For example, heat transfer coefficients in the freeboard region are a strong function of void fraction and solid holdup. As a result the heat transfer coefficient is reduced an order of magnitude in the freeboard region as compared to in-bed values (Biyikli et al., 1983). The objective of this investigation was to determine the local and average void fractions that may be experienced by a heat transfer tube located in the freeboard region of gas-fluidized beds.
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