2004 ANNUAL SCIENTIFIC SEMINAR 497 good contact and the entire apparatus is insulated. From the measured temperature differentials ATs i.e., (T2 -T0 and AT• i.e., (T3 -T2), the P• can be calculated by the equation R• = R• (AT•/ATs) Fig. 2 Schematic representation of Heat Transfer Apparatus. Heat Transfer Through Hair Assemblies: A hair assembly, 5mm in diameter was prepared by taking appropriate amount of hair tied together with hair fibers. The cross ties were placed at lcm distances along the length of the hair bundle. Two thermocouples were mounted on the tress, one at the surface, and the other at the center. In drying wet hair, water content of the tress was kept at 12-13%. A hair drier was placed at a distance of 15 cm from the tress with the impinging air temperature at 80øC. The increase in temperature of the tress was recorded over a period of time from 6-40 min. The effect of perming and application of products meant to protect the hair during thermal treatments was investigated. The outcome of this work will not be presented in this preprint because of lack of space but will be included in the conference presentatior[ Results and Discussion Drying of a Hair Tress: Typical cooling curve for a hair tress drying on the Gyrotherm is shown in Figure 3. The copper plate was heated to a temperature 20øC higher than the room temperature. The air velocity was 1.7m/s. The results show that the wet hair transfers heat to the copper plate much faster than dry hair, suggesting a conduction mechanism in addition to the convection and radiation mechanisms. From the data we could calculate the heat transfer coefficients. 25 20 • lO n,,.. E o -5 -10 dry hair (50% RH) •wat hair ......... • up to 78 % water loss upt 2o *8• waterlosg'"'•.. / 80 % water loss 0 400 800 1200 1600 2000 2400 2800 Time (s) Fig. 3 Typical cooling curves for the dry and wet hair observed during the cooling mode experiment.

498 JOURNAL OF COSMETIC SCIENCE Thermal Conductivity Measurements: The literature gives the thermal conductivity of haft as 0.37 Wm4K 4. However, the values determined for different samples of hair in the dry (50%RH) condition were in the range of 0.06-0.08 Wm4K 4. This clearly shows that the heat transfer through hair assemblies is dominated by convection through air spaces between the fibers, rather than conduction through the keratin material. More data will be presented to support this conclusion. Modeling of Heat Transfer: This was accomplished by solving the heat conduo, on equation as applied to a cylinder in the case of single hair and to a bundle of cylinders in the case of a hair assembly. Using the proper boundary conditions, temperature profiles within the hair fiber or the fiber assembly were generated. In the case of a haft assembly the outcome of the model calculations was checked by experiment, at least at the surface and the center of the assembly. These profiles will be included in the conference presentation.