DETERMINATION OF HEAT TRANSFER EFFICIENCY IN THE CONDITIONS OF FORCED CONVECTION FROM PIPES WITH SPECIAL RIBS

Today, heat transfer processes are present in almost all technological processes of various industries. In heat exchange processes, shell-and-tube heat exchangers are quite effective and easy to manufacture, as the long-term practice of using these devices has shown. Therefore, intensification of heat transfer processes, improvement and development of appropriate equipment is a very urgent task. The object of research is a heat-exchange element with special finning on heat-exchange tubes. The subject of research is the heat transfer processes implemented in a heat exchange element with special finning. The aim of the study is to determine the efficiency of heat transfer of the finned surface of the heat exchange element under conditions of forced convection and to evaluate its efficiency by means of experimental and computer research. This article presents a computer simulation that allows to adequately assess the efficiency of using various designs of finning elements of heat exchange equipment. This is confirmed by the convergence of the experimental data and the results of computer simulation (the discrepancy between the results of the experiment and computer simulation does not exceed 5 %). Experimental and computer studies have shown that the proposed technical solution is more effective than standard ones and can be used in the design of new equipment or improvement of the existing one.

Physical Dimensions as a Design Objective in Heat Transfer Equipment: The Case of Plate and Fin Heat Exchangers

To incorporate exchanger dimensions as a design objective in plate and fin heat exchangers, a variable that must be taken into consideration is the geometry of the finned surfaces to be used. In this work, a methodology to find the surface geometry that will produce the required heat transfer coefficient and pressure drop to achieve the design targets was developed. The geometry of secondary surfaces can be specified by the fin density, which represents the number of fins per unit length. All other geometrical features, as well as the thermo-hydraulic performance, can be derived from this parameter. This work showed the way finned surfaces are engineered employing generalised thermo-hydraulic correlations as a part of a design methodology. It also showed that there was a volume space referred to as volume design region (VDR) where heat duty, pressure drop, and dimensions could simultaneously be met. Such a volume design region was problem- and surface-specific; therefore, its limits were determined by the heat duty, the pressure drop, and the type of finned surface chosen in the design. The application of this methodology to a case study showed that a shell and tube heat exchanger of 227.4 m2, with the appropriate fin density using offset strip-fins, could be replaced by a plate and fin exchanger with any combination of height, width, and length in the ranges of 0–0.58 m, 0–0.58 m, and 0–3.59 m. The approach presented in this work indicated that heat exchanger dimensions could be fixed as a design objective, and they could effectively be achieved through surface design.

Optimisation of the Geometric Parameters of Longitudinally Finned Air Cooler Tubes Operating in Mixed Convection Conditions

The results of optimisation calculations presented in the article are related to longitudinally finned tubes of a heat pump evaporator operating under natural wind-induced flow of outdoor air conditions. The finned surface is characterised by an unusual, wavy fin shape. The article presents the methodology applied to seeking optimal geometric parameters of the finned tube in which thermal calculations were performed by modelling a mixed convection process on the finned surface using the finite volume method. In the case of maximising the heat flow with the minimum mass of the fins, the optimal solution was dominated by the minimum mass of the fins and thus geometric parameters correspond to the number of fins n = 6, fin height h = 0.065 and fin thickness s = 0.0015 m. Optimisation calculations made for maximum efficiency of the exchanger at constant mass indicated that the tube with ten fins (n = 10) with a height of h = 0.11 m and a thickness of s = 0.0018 m allowed maximum heat flow at the assumed mass of the fins in the exchanger tube model. The article proposes a simplified method of determining the optimal geometric parameters of the profile for any mass and maximum thermal efficiency.

An Experimental Investigation Into Frost Accumulation Over Vertical Finned and Unfinned Surfaces During Impinging Air Flow

Frost formation on evaporators negatively affects the cooling performance of refrigerators. It increases the thermal resistance between the refrigerant and air leading to a reduction in the system cooling capacity. In this study, the effect of frost accumulation over a bare and finned surface on the convective thermal resistances has been experimentally investigated under impinging flow conditions. The surfaces are vertically positioned in a horizontal wind tunnel. The convective resistances have been measured with an in-house developed heat flux measurement system. Finally, the effectiveness of the finned surface was derived from the measurements for dry, condensing flow and as well as for frosting conditions. Under frosting conditions, the effectiveness of the finned surface is measured as 1.4 that is by a factor of 2X lower compared to the effectiveness of the same finned surface operating under dry conditions. It has been observed that the frost accumulation initially takes place at the tip of the fins and leads to a 45% drop in the heat transfer rate when the fin tips are completely covered with frost. Further frost accumulation on the fin base does not result in an additional drop in the heat transfer rate. In this regard, the study emphasizes the importance of the fin tip design for the heat sinks operating under frosting conditions.

Optimization of Vortex Promoter Parameters to Enhance Heat Transfer Rate in Electronic Equipment

In this paper, optimization of the location and the geometry of a vortex promoter located above in a finned surface in a channel with eight heat sources is investigated for a Reynolds number of 12,500 < Re < 27,700. Heat transfer rates and the corresponding Nusselt number distributions are studied both experimentally and numerically using different vortex promoter geometries (square, circular, and triangular) in different locations to illustrate the effect of vortex promoter on the fluid flow. Optimization study considered a range of following parameters: blockage ratio of 0.30 < (y/C) < 0.45 and interpromoter distance ratio of 0.2277 < (x/L) < 0.3416. Results show that fins over which rectangular and circular promoters are integrated perform better in enhancing the heat transfer. According to the numerical and experimental results, higher blockage ratios cause significantly higher heat transfer coefficients. According to the observations, as the interpromoter distances increase, shedding gains strength, and more turbulence is created. All vortex promoters enhance heat transfer resulting in lower temperature values on the finned surface for different (y/C) and (x/L) values and Reynolds numbers. The use of promoters enhances the heat transfer, and the decrease in the maximum temperature values is recorded on the finned surface changing between 15% and 27%. The biggest decrease in maximum surface temperature value is 500 K–364 K and observed in circular promoter case with (y/C) = 0.43, (x/L) = 0.3416, and Reynolds numbers of 22,200.