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The heat sink is considered one of the most critical issues in designing and operating light-emitting diode (LED) lamps. The manufacturers in the technical catalogs indicate the maximum temperature tolerable by LED chips, which causes the light to drop and the color of the lamp output to change when this temperature range is not met. The selection and design of the cooling system usually affect the costs associated with the construction of the heat sink. This paper introduced a new heat sink system incorporating concave fins for the LED lamp cooling system. The numerical method was applied to solve the governing heat balance equations to examine this heat sink’s capability. The optimum geometry was determined to achieve minimum electronic chip temperature and heat sink weight at different LED lamp capacities based on the coupled numerical solution of heat transfer and particle swarm optimization (PSO) optimization algorithm. A comprehensive database was created and used as input for genetic planning tools based on two objective optimal solutions for different LED lamp capabilities. Based on genetic programming results, an analytical relation was presented to determine the optimal geometric parameters for LED power. Therefore, it is possible to determine the optimum geometry for a given power without numerical resolution and optimization. The efficiency and volume of sinks are significantly improved in optimal heat sinks with concave fins compared to fixed cross-sections based on the results. [ABSTRACT FROM AUTHOR]

This work provides a theoretical and non-dimensional numerical analysis of the dynamics of gas-borne unipolar charged particles flowing through a cylindrical tube at high number concentrations. It is discovered that above a threshold input particle number concentration, the concentration at the exit of the tube is nearly constant and independent of further increase in the input. Based on a maximum of 2% sensitivity of the system, the threshold input number concentration is quantified for a tube of any length more than 40 × the radius. The theoretical analysis developed in this work is used to derive correlations for the threshold input concentration and the exit concentration, as well as show that the exit particle concentration is lower than the threshold input value by a factor of 20/ P D , where P D is the well-known diffusive particle penetration. The analysis demonstrates that a constant concentration can occur if and only if the ratio of non-dimensional electric particle mobility to the Gormley-Kennedy diffusion parameter is above 74, which is a hitherto unexplored regime of charged aerosol flow dynamics. It is shown that the constant concentration can occur in compact tube designs (L/R <100) as long as the mass Peclet number of the particles is high and reducing the mass Peclet number to around 10 or below makes it impossible to obtain an input-independent number concentration. It is also shown that the Reynolds number of the flow has very little effect on the charged transport dynamics, where the order of magnitude of the input-independent number concentration is not highly sensitive to the Reynolds number, provided the system remains laminar. Finally, practical examples for designing instrumentation to generate a constant concentration of charged particles are discussed. • Flowing sufficiently high number density of charged particles results in input-independent output number density in compact tubes (L/R < 100). • The threshold input number density must be at least 20/ P D times the desired constant output, P D being the diffusive particle penetration. • Number densities of 30-120 nm particles in the order of 106/cm3 are possible using 15-30 mm diameter tubes & flows of ∼100 ml/min. • For mass Peclet numbers of ∼10 or less, the regime of input-independent output disappears for compact tubes (L/R < 100). • For laminar flows, Reynolds number has very little effect on the conditions to produce the desired number concentrations. [ABSTRACT FROM AUTHOR]

The heat transfer characteristics in a smooth tube are studied. Based on the available experimental data, a new correlation is proposed to predict the heat transfer coefficients inside tubes of different lengths. The predicted results show that for a range of L/D from 26.31 to 58.14, the heat transfer coefficient may be reduced by 20.56% and increased by 13.31% at the beginning and at the end of this range, respectively. The results obtained from the proposed correlation are compared with other analytical and experimental data, and satisfactory agreement is found. [ABSTRACT FROM AUTHOR]

Starting from the definition of the average specific heat capacity for chosen temperature range, the analytic dependence between the real and the mean specific heat capacities is obtained using differential and integral calculation. The obtained relation in differential form for the defined temperature range allows for the problem to be solved directly, without any special restrictions on its use. Using the obtained relation, a general model in the form of a polynomial of arbitrary degree in the function of temperature was derived, which has more suitable and faster practical application and is more general in character than the existing model. New graphical method for solving the problem is obtained based on differential geometry and using the derived equation. This may also have practical significance since many problems in thermodynamics are solved analytically and graphically. This result was used in order to obtain the amount of specific heat exchanged using an analytical model or a planimetric method. In addition, this graphical solution was used for the construction of the diagram showing the dependence between the specific heat exchanged and temperature. This diagram also gives a simple graphical procedure for the calculation of the real and the average specific heat capacity for arbitrary temperature or temperature interval. The confirmation for all graphic constructions is obtained using the differential properties between thermodynamic units. In order for the graphical solutions presented to be applicable in practice, suitable ratio coefficients have been determined for all cases. Verification of the model presented, as well as the possibilities of its application, were given using several characteristic examples of semi-ideal and real gas. Apart from linear and non-linear functions in the form of polynomials, the exponential function of the dependence between specific heat capacities and temperature was also analysed in this process.

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