平壁矩形直肋装置肋化热阻系数曲线图

提供了工程计算用的平壁矩形直肋装置肋化热阻系数曲线图。从图上可清楚地看出肋厚、肋高和肋间距对肋装置传热性能的影响。     

平壁三角形直肋装置肋化热阻系数曲线图

提供了工程计算用的平壁三角形直肋装置肋化热阻系数曲线图。从图上可清楚地看出肋基厚、肋高和肋间距对肋装置传热性能的影响 ,有助于最佳尺寸的确定 ,简化传热计算。     

Experimental study of convective heat transfer on a finned rotating cylinder

In this study, the local convective heat transfer from a rotating finned cylinder to the surrounding air was evaluated using an infrared thermographic experimental set up. Solving the inverse conduction heat transfer problem allows the local convective heat transfer coefficient to be identified. We used the specification function method, along with spatio-temporal regularization, to develop a model of local convective heat transfer in order to take lateral conduction and 2D geometry into account. This model was tested using rotational Reynolds numbers (based on the cylinder diameter and the peripheral speed) between 4300 and 17 900. The local heat transfer on the fin surface was analyzed to determine the influence of the rotational Reynolds number and the influence of the height and spacing of the fins. In this paper, we propose an efficiency definition that allows the optimal geometrical configuration of the finned cylinder to be identified for the given operating conditions.     

Estimation of temperature dependent heat transfer coefficient in a vertical rectangular fin using liquid crystal thermography

This paper presents a methodology for the estimation of temperature dependent heat transfer coefficient for a vertical rectangular fin by using the inverse heat transfer method with Liquid crystal thermography (LCT) data. Steady state, laminar natural convection experiments have been done on a vertical rectangular fin of size 150 × 250 × 4, (L × w × t, all dimensions are in mm). The variation of heat transfer coefficient is considered as a power law function of temperature excess (h = a_oθ^b) and is derived from the basic Nusselt number equation used for laminar natural convection, Nu = aRa^b. With this functional form, the one dimensional fin equation in finite difference form is repeatedly solved using the Gauss–Seidel iterative method. Treating this as a one parameter estimation in ‘a’ the sum of the squares of the difference between the simulated and Thermochromic Liquid Crystal (TLC) measured temperatures is minimized with the Golden section search algorithm to retrieve ‘a’. Estimate of ‘a’ and the accompanying uncertainties are first reported for synthetically generated temperature distribution for assumed values of ‘a’. The effect of noise on the estimate of ‘a’ is discussed. This is followed by retrievals with experimentally obtained TLC temperature distribution for a range of heat inputs to the fin base. The required temperature distributions for accomplishing the retrievals over the surface are obtained using calibrated R40C5W Thermochromic Liquid Crystal (TLC) sheets. As an additional proof of the accuracy of the method, the retrieved value of ‘a’ is used to simulate the temperature distribution in the fin which is then compared with the actual TLC measured temperature distribution.     

Numerical analysis of natural convection heat transfer from rectangular shrouded fin arrays on a horizontal surface

The main aim of this investigation is to discover the effects of clearance parameters on the steady-state heat transfer. In order to solve the three-dimensional elliptic governing equations, a finite volume based CFD code was used. The clearance gap between fin tips and shroud, the base and fin temperatures and the size and configuration of the finned surfaces were varied during the parametric study. The numerical results have been compared to existing experimental values from the literature and the comparison shows a good agreement. It is found that the heat transfer coefficient increases with the increase in the clearance parameter and it approaches to the value of heat transfer coefficient obtained for unshrouded fin arrays.     

Prediction of convection from a finned cylinder in cross flow using direct simulation,turbulence modeling,and correlation-based methods

Direct numerical simulation (DNS), two shear-stress transport (SST) turbulence models, and three k-ε models are used to predict mixed convection associated with air in cross flow over an isothermal, finned cylinder. The DNS predictions reveal complex time-variation in the flow field. Convection heat transfer coefficients predicted by the SST models are in good agreement with those generated by DNS, whereas the k-ε models do not accurately predict heat fluxes. Correlation-based predictions of heat transfer coefficients are, in general, in poor agreement with the DNS and SST predictions. The impact of various geometrical modifications on convection coefficients is also presented.     

Using oscillations to enhance heat transfer for a circular cylinder

An experimental investigation into the effects of transverse oscillations on the heat transfer from a circular cylinder in cross-flow was carried out. The cylinder’s heat transfer coefficient was measured for a wide range of oscillation frequencies and amplitudes. Heat transfer enhancement was found to be strongly dependent on synchronization with harmonics of the natural shedding frequency, the cylinder wake mode, and the cylinder transverse velocity. For representative oscillation conditions, the velocity and temperature fields in the near wake were measured using digital particle image thermometry and velocimetry (DPIT/V). This revealed several mechanisms that explain the observed heat transfer enhancement.     

Forced convection heat transfer and pressure drop for a horizontal cylinder with vertically attached imperforate and perforated circular fins

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer experimentally investigated. Six millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Some experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at six different angular locations in order to determine the best angular location. In addition, a perforated finned heater was compared with an imperforate finned heater to observe the differences. In the cases of the Re above the critical value, Nusselt numbers for the perforated finned positions are 12% higher than the Nusselt numbers for the imperforate state. Moreover, a correlation has been obtained between the Re and Nu in the Re number above the critical value and the Re below the critical value. Meanwhile, correlations regarding pressure drops in the flow areas have been obtained.     

Exact,analytical heat transfer from longitudinal radiating fins of rectangular profile in a tube/fin ensemble

In this technical note, the problem concerning the quantification of heat transfer rates from an array of longitudinal radiating fins of rectangular profile in a tube/fin ensemble to a nonzero temperature sink is investigated. Radiating fins constitute essential elements in the thermal control of spacecrafts and satellites. We consider quasi one-dimensional heat conduction in the longitudinal radiating fins and neglect radiative exchange between the fins and the tubes carrying a hot fluid. It is demonstrated that the governing nonlinear differential equation of second order with constant coefficients and nonhomogeneous can be solved in exact, analytical implicit form. The pertinent temperature distributions eventually provide the magnitudes of heat transfer rates and fin efficiencies influenced by the radiation–conduction parameter and the sink temperature.