S. L. Cardoso

Measurement of the thermal properties of liquids using a thermal wave interferometer

In this paper we discuss the use of an alternative photothermal technique for measurements of thermal properties of liquids. The proposed technique is based upon the concept of thermal wave interferometry. The liquid sample is confined between two thin pyroelectric detectors. One of these detectors acts as a modulated absorber of light while the other is used for sensing the temperature fluctuations transmitted through the liquid layer. The good agreement between the values of the thermal properties we got with the present technique and those reported in the literature demonstrates the capability of the technique for full characterization of the thermal properties of liquids.

Optical and thermal properties of liquids measured by means of an open photoacoustic cell

A double-purpose open photoacoustic cell, suitable for optical and thermal characterization of liquid samples is described. An experimental method for the determination of very low concentrations of contaminants in liquid substances is proposed. The proposed technique was used to determine the concentration of Chromium (VI) in water via the measurement of its optical absorption coefficient. To test the suitability of the proposed technique for experimental determination of thermal properties of liquids, studies on ethanol were performed. The agreement between experimentally obtained thermal properties and values reported in the literature is good.

On the use of the thermal wave resonator cavity sensor for monitoring hydrocarbon vapors

A gas sensing device based on a thermal wave resonator cavity is outlined. It is experimentally tested by monitoring the presence of several hydrocarbon vapors in air via the measurement of the thermal diffusivity. It is also shown that its time-dependent response may be used to follow the vapor diffusion. It is shown that its characteristic response time is linearly correlated to the thermal diffusivity value of the mixture. The steps toward the development of a practical sensing device are further discussed.

Application of the thermal wave resonator to the measurement of the thermal diffusivity of gas mixtures

A gas analyzer device based on thermal wave interference in a cavity is presented. The thermal diffusivity of CO2:air mixtures as a function of the relative concentration is measured. It is demonstrated that different concentrations of CO2 in air can be detected with accuracy using the described experimental device. The results presented here open the possibility to perform routine measurements of thermal diffusivity of binary gas mixtures and using this parameter to monitor the relative gas concentration.

Characterization of the thermal properties of gases using a thermal wave interferometer

A method suitable for the thermal characterization of gases is described. It is based on thermal wave interference (TWI) in a cavity. A TWI device was constructed and the thermal diffusivity of different binary gas mixtures as a function of their relative concentration was measured. From these values, using a logarithm mixing model for the thermal conductivity of a two-phase gas system, the thermal properties of the corresponding pure gases were calculated. The data obtained for several test gases show good agreement with values reported in the literature.

Effect of heat treatment on ethylene and CO2 emissions rates during papaya (Carica papaya L.) fruit ripening

Ripening studies of nontreated and treated papaya (papaya L) are accomplished by monitoring the ethylene and CO2 emission rates of that climacteric fruit, to evaluate its shelf life. The treatments simulate the commercial Phitosanitarian process used to avoid the fly infestation. Ethylene emission was measured using a commercial CO2 laser driven photoacoustic setup and CO2, using a commercial gas analysis also based on the photothermal effect. The results show a marked change in ethylene and CO2 emission rate pattern for treated fruits when compared to the ones obtained for nontreated fruits and a displacement of the climacteric pick shown that the treatment causes a decrease of shelf life of fruit.

Measurement of mass diffusivity in air using thermal wave interference detection

A discussion on the use of the thermal wave interference (TWI) for the monitoring of the transient of hydrocarbon in air is presented. The thermal wave signal was modeled using the logarithm-mixing model for the thermal diffusivity of a two-phase gas system in which the hydrocarbon vapor concentration in the air-filled TWI cell is a varying function of time. The time varying hydrocarbon vapor concentration was described assuming the simple Fick’s model for mass diffusion of the hydrocarbon vapor in the stagnant air column of the TWI cell. The transient TWI signal amplitude data fitting yielded two parameters, namely, the saturation concentration and the characteristic diffusion time. From the corresponding values of the diffusion time the hydrocarbon mass diffusivities were straightforwardly obtained.

Determination of thermal and sorption properties of poly-3-hydroxy octanoate using photothermal methods

With the increasing human awareness in environmental problems, the development of new biocompatible and biodegradable materials has become of increasing importance. This work is concerned with the use of photoacoustic methodologies to study the thermophysical properties and diffusion coefficient of O 2 and CO 2 of poly-3-hydroxy octanoate samples.

On the use of the optothermal window technique for the determination of iron (II) content in fortified commercial milk

This work reports on the use of the optothermal window and a well-proven phenanthroline colorimetry method for determination of iron (II) content in a commercial fortified milk. Initially, iron (II) in distilled water was determined using a series of calibration samples with ferrous sulfate acting as the source of iron (II). In the following phase, this calibration methodology was applied to commercial milk as the sample matrix. The phenanthroline colorimetry [American Public Health Association, Washington, DC (1998)] was chosen in an attempt to achieve proper selectivity (i.e., to obtain the absorption band, the wavelength of which is centered near the radiation wavelength available for our experiments: Excitation wavelength at a 514-nm line of a 20-mW tunable Ar ion laser). Finally, samples of commercially available fortified milk were analyzed in an attempt to access Fe (II) content.

Monitoring of gas diffusion in air using the TWI technique: Thermal diffusivity measurements made easy

The thermal wave interference technique (TWI) has been explored in recent years for the investigation of the thermal and transport properties of gases and liquids. In this article we address ourselves to the quantitative understanding of the transient thermal wave interference signal of air:hydrocarbon vapor mixtures. This is the situation one faces when placing a given portion of liquid hydrocarbon inside an initially air-filled thermal wave interference. What is observed in this case is the thermal wave interference signal decay as a function of the time as a result of the change of the gas thermal diffusivity with time due to the increase of the hydrocarbon vapor concentration in air. In this article we show that value of the thermal diffusivity of the saturated mixture is readily obtained from the saturation value of the normalized signal amplitude, without the need of performing the conventional L scan.