Optimal Fin Thickness Research Articles

Energy and exergy analysis of a bidirectional solar thermoelectric generator combining thermal energy storage

In this paper, energy and exergy analysis of a bidirectional solar thermoelectric generator (STEG) coupled to a latent heat storage and cooling system (LHSCS) has been carried out. The effect of various parameters of LHSCS on energy and exergy efficiencies of STEG have been analysed under climatic conditions of Chile’s Atacama Desert. It is found that the most relevant design parameter to improve the energy and exergy efficiencies of the thermoelectric generator (TEG) is the container insulation, followed by heat sink at the TEG hot side, fin thickness and the aspect ratio of the container. The results showed that an optimally designed insulation container can improve the energy and exergy efficiencies of LHSCS by 30% and 200%, respectively, and the TEG conversion efficiency by 30% during nighttime. Further, inclusion of heat sink at TEG hot side during reverse operation of TEG at night can improve the TEG efficiency by 20%. The optimal fin thickness can improve the TEG conversion efficiency by 20% during the night and LHSCS energy and exergy efficiencies by 30% and 23%, respectively. The container geometry should have higher aspect ratios. This study may help in optimal design of LHSCS for solar energy conversion applications in the desert locations.

Performance optimization of a finned shell-and-tube ice storage unit

The solidification enhancement of the finned shell-and-tube ice storage (STIS) unit with water is numerically analysed with consideration of natural convection. An unsteady model of the discharging process is presented to investigate the role of fin geometry in ice storage performance, which is validated by a discharging experiment in a finned STIS unit. The temperature response and ice front evolution in a finned STIS unit are analysed and compared with a corresponding unit without fins. The effects of structural parameters on the solidification performance are comprehensively discussed, including fin height, fin thickness, and fin number. Furthermore, a new evaluation criterion of the dimensionless cooling power mass penalty is proposed to optimize fin geometry. The results indicate that the natural convection is not conducive to the solidification performance. The addition of fins effectively enhances the energy discharging performance of STIS units due to the coupling effect of natural convection suppression and thermal conduction enhancement. It is highly efficient to increase fin height for better energy discharging performance since fin height is the most important parameter. Fin thickness and fin number also affect ice storage performance. Considering the trade-off between the weight and ice storage performance of STIS units, the optimal fin thickness and fin number in this paper are respectively recommended to be 3 mm and 8 to achieve the largest performance enhancement with the least mass penalty.

Performance of a guided plate heat sink at high altitude

In the present study, the thermal performance of an enhanced air-cooled heat sink system, comprising of a parallel plate-fin heat sink (PPFHS) with a guide plate installed to alter the bypass flow, was analyzed for fan-driven convection conditions at various altitudes from sea level to 12,000 m. Numerical simulations were carried out using ANSYS Fluent 16.0 with the κ-ω SST turbulence model to analyze the airflow and assess the thermal performance. After validation by experimental data in the literature, numerical results of the flow and temperature fields were obtained for different environmental pressures, several fan speeds and PPFHS design parameters. The measured characteristic fan curves at different altitudes show that the fan delivers approximately the same volume flow rate at different altitudes. For high-altitude operation, using the PPFHS only configuration could lead to electronic failure due to the larger temperature increase compared to using the PPFHS/guide plate configuration. For both configurations, the optimum fin number ranges between 20 and 32, which depends on the environmental pressure and fan speed. Improper use of highly dense PPFHS may lead to inadequate electronic cooling and will add extra weight for high-altitude operation. The optimal fin thickness depends on the fan speed, and the minimum thermal resistance occurs with low fin thickness at the lower fan speeds. Weight optimization procedures were conducted to obtain a considerable decrease in the PPFHS/guide plate weight and to achieve optimal thermal resistance at lower fan speeds.

Longitudinal-Fin Heat Sink Optimization Capturing Conjugate Effects Under Fully Developed Conditions

We develop a method requiring minimal computations to optimize the fin thickness and spacing in a fully shrouded longitudinal-fin heat sink (LFHS) to minimize its thermal resistance under conditions of hydrodynamically and thermally developed laminar flow. Prescribed quantities are the density, viscosity, thermal conductivity and specific heat capacity of the fluid, the thermal conductivity and height of the fins, the width and length of the heat sink, and the pressure drop across it. Alternatively, the length of the heat sink may be optimized as well. The shroud of the heat sink is assumed to be adiabatic and its base isothermal. Our results are relevant to, e.g., microchannel cooling applications where base isothermality can be achieved by using a heat spreader or a vapor chamber. The present study is distinct from the previous work because it does not assume a uniform heat transfer coefficient, but fully captures the velocity and temperature fields by numerically solving the conjugate heat transfer problem in dimensionless form using an existing approach. We develop a dimensionless formulation and compute a dense tabulation of the relevant parameters that allows the thermal resistance to be calculated algebraically over a relevant range of dimensionless parameters. Hence, the optimization method does not require the time-consuming solution of the conjugate problem. Once the optimal dimensionless fin thickness and spacing are obtained, their dimensional counterparts are computed algebraically. The optimization method is illustrated in the context of direct liquid cooling.

Closed form correlations for thermal optimization of plate-fin heat sinks under natural convection

In the present paper, closed form correlations that allow for thermal optimization of vertical plate-fin heat sinks under natural convection in a fully-developed-flow regime are suggested. Analytical solutions for velocity and temperature distributions for high channel aspect ratios, high conductivity ratios, and low Rayleigh numbers are presented using the volume averaging approach. To validate the analytical solutions, both experimental and numerical studies are performed, and it is shown that the analytical solutions are applicable to the range of H/wc >> 1, ks/kf > 10, and Ra″<1000. From the analytical solutions, explicit correlations for optimal fin thickness and optimal channel width, which minimize thermal resistance for given height, width, and length of heat sink, are proposed. The correlations show that the optimal fin thickness depends on the height, the solid conductivity, and the fluid conductivity only and is independent of the Rayleigh number, the viscosity of the fluid, and the length of the heat sink.

Pool Boiling Heat Transfer of Water on Finned Surfaces at Near Vacuum Pressures

This research paper presents a study of boiling heat transfer from longitudinal rectangular-finned surfaces immersed in saturated water at low vapor pressures. Finned surfaces with assorted fin spacing, fin thicknesses, and fin heights on a copper based surface have been investigated. All the finned surfaces were found to increase both boiling heat transfer coefficients and critical heat fluxes. An optimal fin thickness was found for a configuration, and heat transfer coefficients have been obtained at the pressures. Factors affecting the boiling characteristics have been identified and the optimal enhancement requires a balance of the active nucleation sites, bubble flow resistance, natural convection, thin film evaporation, liquid superheating, heat transfer area, bubble coalescence, and liquid reflux resistance. High speed visualization of vapor plug and vapor film generation on the boiling surfaces has revealed significant insights into the boiling mechanisms at low saturation pressures.

Closed-form correlations for thermal optimization of microchannels

In the present paper, closed-form correlations which allow for thermal optimization of microchannels are suggested. Asymptotic solutions for velocity and temperature distributions for the high channel-aspect-ratios, high conductivity ratios, and low Reynolds numbers are presented using the averaging approach. From the asymptotic solutions, explicit correlations for the optimal channel width and the optimal fin thickness are proposed.

Optimal Arrays of Pin Fins and Plate Fins in Laminar Forced Convection

This paper reports the optimal geometry of an array of fins that minimizes the thermal resistance between the substrate and the flow forced through the fins. The flow regime is laminar. Two fin types are considered: round pin fins, and staggered parallel-plate fins. The optimization of each array proceeds in two steps: The optimal fin thickness is selected in the first step, and the optimal thickness of the fluid channel is selected in the second. The pin-fin array is modeled as a Darcy-flow porous medium. The flow past each plate fin is in the boundary layer regime. The optimal design of each array is described in terms of dimensionless groups. It is shown that the minimum thermal resistance of plate-fin arrays is approximately half of the minimum thermal resistance of heat sinks with continuous fins and fully developed laminar flow in the channels.

Heat exchanger design: Optimal thickness (under natural convective conditions) of vertical rectangular fins protruding upwards from a horizontal rectangular base

Steady-state rates of heat transfer from an array of vertical, rectangular polished duralumin fins under natural convective conditions have been measured. The horizontal base, which was manufactured of the same material, was kept at the uniform temperature of either 20·0 (±0·2)°C or 40·0 (±0·2)°C above the local air temperature of 20 (±0·2)°C. The optimal thickness of the fins in this array, corresponding to a maximum rate of heat dissipation, was deduced. For a base of width 190 mm and length 500 mm, the optimal thickness for fins of 60 mm protrusion rose from 2·0 mm to 4·5 mm when the fin separation was increased from 20 mm to 60 mm. This optimal fin thickness was almost invariant with respect to the change of the considered base temperature.

Natural-Convective Heat Exchanger with Vertical Rectangular Fins and Base: Design Criteria

Steady state rates of free-convective, conductive and radiative heat transfer from a polished, duralumin and extended-plate, heat exchanger through air have been measured. When its vertical base was maintained at 40.0 (±0.2) K above the local air temperature (=15.5 ± 0.4°C) in the laboratory, optimal values of the vertical-fin array's geometrical parameters, corresponding to achieving maximum rates of heat loss, were deduced. For a base of width 190 mm and length 250 mm, the optimal uniform separation between 3 mm thick fins rose from 9.5 to 11.1 mm as the fin protrusion was decreased from 90 to 30 mm: it was almost independent of temperature within the range considered. For a base of width 190 mm and length 500 mm, the optimal uniform thickness for fins of 60 mm protrusion rose from 1.5 to 3.6 mm as the fin separation was increased from 15 to 55 mm, the optimal fin thickness being almost invariant with respect to changes in the fins' base temperature. No generalized quantitative recommendations emerge from the present investigation with respect to the optimal values for the fins' length or fins' protrusion. These would have to be evaluated, by making additional due allowances for the weight and cost of material involved in each proposed heat exchanger, according to each particular application envisaged. Nevertheless, it can be concluded that the use of two separated heat exchangers of the considered type, rather than a single one of similar design but whose length is the sum of the lengths of the previous two, should be considered when attempting to enhance the heat-transfer performance.

Heat-exchanger design: Optimal uniform thickness of Vertical rectangular fins protruding perpendicularly outwards, at uniform separations, from a Vertical rectangular ‘Base’

The effects of varying the fin thickness on the steady-state rate of heat loss from the fin array have been measured experimentally for free-convection conditions. The duralumin fin array had a base area of 500 mm (vertical) × 190 mm (horizontal), and the fins protruded 65 mm proud of, and perpendicularly out from, the base. The experiments were performed with five different fin thicknesses, namely 1, 3, 6, 9 and 19 mm, for base temperatures of 20·0 (±0·1)°C and 40·0 (±0·1)°C above that of the ambient environment, which was maintained at 20 (±0·2)°C. There is an average optimal uniform fin thickness equal to 3·0 ± 0·5 mm, corresponding to the maximum rates of heat loss, for the range of conditions stated when the uniform separations between the adjacent fins exceeds 20 mm. For 20 mm ≤ s ≤ 50 mm, the optimal fin thickness decreases slightly as either (i) the fin separation or (ii) the base temperature is reduced.