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Presented here is an effective low-cost method for the temperature calibration of infrared cameras, for applications in the 0-100 degrees C range. The calibration of image gray level intensity to temperature is achieved by imaging an upwelling flow of water, the temperature of which is measured with a thermistor probe. The upwelling flow is created by a diffuser located below the water surface of a constant temperature water bath. The thermistor probe is kept immediately below the surface, and the distance from the diffuser outlet to the surface is adjusted so that the deformation of the water surface on account of the flow is small, yet the difference between the surface temperature seen by the camera and the bulk temperature measured by the thermistor is also small. The benefit of this method compared to typical calibration procedures is that, without sacrificing the quality of the calibration, relatively expensive commercial blackbodies are replaced by water as the radiative source (epsilon approximately 0.98 for the wavelengths considered here). A heat transfer analysis is provided, which improves the accuracy of the calibration method and also provides the user with guidance to further increases in accuracy of the method.

An experimental study is presented of the Nusselt-Rayleigh and Sherwood-Rayleigh number relations for water undergoing free-surface natural convection, which is natural convection beneath an air/water interface. The focus of this work is on the Nu-Ra relationship. This relationship is typically studied using the traditional Rayleigh-Be´nard convection experiment where a fluid layer is bounded above and below by solid plates of different, but constant, temperatures. Hence, the boundary conditions are of the no-slip, constant-temperature type. Power laws are typically used in these studies to correlate the Nu-Ra data, and existing studies have given power law exponents that are usually close to 1/3. The experimental data obtained in this study yields a power law relation of the form: Nu=(0.0016)Ra0.328(1) for 107 < Ra < 1011. This result is surprising in that the effect of the free-surface boundary condition on the power law exponent is quite small when compared to the solid plate case. However, the prefactor in Eq. (1) is significantly smaller than for the solid plate case. The Sh-Ra data obtained in this study are also fit to a power law, giving: Sh=(0.0019)Ra0.329(2) where Sh is the dimensionless mass transfer coefficient for evaporation. The exponent of this power law differs from that which has been observed by prior researchers. However, the prior research on evaporation that utilizes this form for scaling the data is considerably smaller than for the heat transfer case. Possible explanations for the observed behavior are presented.

in Wiley Online Library (wileyonlinelibrary.com).Presented here is an experimental investigation of the effects of several surfactant monolayers on evaporation driven by natural convection in the air above a water surface. Experiments were performed in a controlled laboratory setting with tanks of heated water for the following cases: (1) a clean water surface, and for surfaces covered with monolayers of (2) oleyl alcohol, (3) stearic acid, and (4) stearyl alcohol. Evaporation rates were measured using a laser-based method, and the Sherwood and Rayleigh numbers, Sh and Ra, were computed from the data. Power law scalings of the form Sh ¼ BÁRa m were developed for each case which yielded, essentially, m ¼ 1/3 for all four surface conditions. The oleyl alcohol and stearic acid conditions give essentially the same value for B as for the clean surface case. For stearyl alcohol, B is smaller than for all other surface conditions; this result is attributed to the ability of the stearyl alcohol monolayer to inhibit evaporation by blocking the passage of water molecules through the monolayer: the barrier effect. The surface temperature is measured in this work enabling a separation of the effect of surfactants on evaporation due to a reduction in surface temperature from their effect on evaporation due to a true barrier effect. This has not been accomplished heretofore. V V C 2012 American Institute of Chemical Engineers AIChE J, 59: [303][304][305][306][307][308][309][310][311][312][313][314][315] 2013

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