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This paper deals with an experimental study of free convective heat transfer from fins and fin arrays attached to a heated horizontal base. The technique of differential interferometry has been utilised and experiments have been carried out under steady state conditions. Local values of heat flux, temperature, heat transfer coefficients, local and overall Nusselt numbers have been estimated. An attempt has been made to discuss in detail the flow and heat transfer mechanisms for three cases namely an isothermal vertical flat plate, a single fin attached to a heated horizontal base and a fin array in the light of the experimental findings. Correlations are presented relating the overall Nusselt number with the relevant non-dimensional parameters in these cases.

Experimental work has been carried out on horizontal fin arrays using the differential interferometric technique. The local variations of heat flux and temperature in the central fin of a three fin array have been studied in the transient heating and cooling regimes. The average values of heat transfer coefficients in the transient state have been calculated for three spacings of 10 mm, 15 mm and 25 mm and with two materials namely aluminum and mild steel under constant heat input to the system. The results have been compared with experimental findings in the cases of a single fin attached to a base and a vertical isothermal flat plate. Attempt has been made to explain the differences between these cases in relation to the physical mechanism of heat and fluid flow about a fin array.

Abstract:  This paper presents an analysis of the problem of a thin fin of finite thermal conductivity, with an isothermal line source at the base, dissipating heat to the surrounding air by natural convection. The horizontal surface to which the fin is attached is adiabatic so that heat is dissipated only through the fin. The temperature and velocity distributions in the field, the temperature profile in the fin, local Nusselt numbers along the fin and the average heat transfer coefficient of the fin are obtained by solving the governing equations in the field and the heat transfer equation in the fin simultaneously, using an explicit unsteady Finite Difference formulation leading to the steady state result. Numerical experiments are performed to study the influence of parameters namely the fin height, temperature of the heating source and the fin material on the average heat transfer coefficient. Comparison is made with fins of infinite thermal condutivity and the vertical isothermal flat plate.

This paper deals with experimental investigations on a 1–2 shell and tube heat exchanger, to study the effect of spiral turbulators on its performance. The heat exchanger has its tubes wound with copper wire, so that the winding acts as an augmenting device. Experiments were conducted with various winding wire diameters and pitches and the heat transfer coefficients were evaluated for a wide range of temperature levels and flow rates of the shell side fluid. The experimental results are discussed in detail and correlations are proposed to predict the shell side Nusselt number of the exchanger with varying winding pitches and diameters. The existence of optimum winding is also discussed in this paper. The present results are based on over 250 experimental observations made in the laminar range of flow.

In this paper the optical methods in heat transfer applications are described briefly. In particular, interferometric methods are discussed in detail as applied to the study of natural convection heat transfer. Of the most popular interferometers, viz. the Mach Zehnder Interferometer (mzi) and the Differential Interferometer (di), thediis considered in detail. The theoretical and constructional features of adiare outlined. The procedures of heat transfer measurement and the temperature profile estimation are explained. The advantages and limitations of the two interferometers are compared with the help of a sample calculation. The experimental analyses of three cases, viz. (1) isothermal vertical flat plate, (2) single vertical fin attached to a heated horizontal base, and (3) horizontal fin array, are described. Typical heat transfer and temperature profile results are presented. Using the estimated temperature profiles isotherms are plotted. It is possible to get fairly good heat transfer and temperature profiles using adi. The instrument is specially useful in applications involving short optical path lengths because of its superior resolution as compared tomzi.

The research reported here presents the results of an experimental investigation of the adsorption performance of different combinations of activated carbon and multi-walled carbon nanotubes mixtures (7.5–25%), as an adsorbent material for refrigerant R-134a, with the application potential in vapor adsorption refrigeration systems. The specific adsorbance was found to increase with the addition of carbon nanotubes to activated carbon. The experimental data were used to calculate the isosteric heat of adsorption using the Clausius–Clapeyron equation, and study its variation with the specific adsorbance for the mixture with the highest percentage of carbon nanotubes, and compare the results with that for activated carbon. The increase in the specific adsorption capacity upon addition of carbon nanotubes was interpreted as due to an increase in the pore volume, which in turn increases the specific surface area of the adsorbent material.