Search Results (10)

To confirm the suitability of aluminum for the heat transfer surfaces as a heat exchanger material for ocean thermal energy conversion, the seawater corrosion resistance of aluminum plates in a plate heat exchanger was experimentally investigated. In this study, four different surface shapes with chevron angles of 45° and 60° and different treatment types of A1050 aluminum heat transfer surfaces were processed into herringbone patterns. Additionally, the surfaces of the test plates were either anodized or untreated. In continuously flowing deep ocean water, the surface conditions of the test plates were observed at 1, 3, 6, and 12 months using mass measurements, visual inspection, laser microscopy, and SEM. For the anodized A1050 plates, regardless of the surface shape, there was almost no change in the mass, laser microscopy, or SEM results even after 12 months. In contrast, the untreated plate mass decreased in the samples after 3 months or later, and the mass reduction rate was approximately 2–7%. In conclusion, untreated aluminum is not suitable for use in seawater and an anodizing treatment is necessary for its use in heat exchangers for ocean thermal energy conversion. Full article

The study investigates, by calculations, some ways to improve the thermal efficiency of plate heat exchangers (PHEs) used in the vegetable oil processing industry. The performance of these heat exchangers is limited by the heat transfer rate of the oil side and by the low thermal conductivity of the plate material. The study starts from a base case with vegetable oils cooled with water in plate heat exchangers, all with a chevron angle of 30° and a different number of channels and plate transfer areas. The change in one geometrical characteristic of the plates, namely the chevron angle, from 30° to 45° then to 60°, led to a significant increase in the overall heat transfer coefficients of 16.0% when changing from 30° to 45° and of 28.1%, on average, when increasing the angle from 45° to 60°. This is a significant increase accompanied by a rise in the pressure drops of the circuits, but the values are acceptable since they do not exceed 1 bar on the oil circuit and 1.4 bar on the cold fluid circuit, respectively. The use of Fe₃O₄–SiO₂/Water hybrid nanofluids with concentrations of 0.5% v/v, 0.75% v/v, and 1% v/v were investigated to replace the cooling water. An increase of 2.2% on average was noticed when using the 1% v/v nanofluid comparatively with water, which is not large but adds to the chevron angle increase. A supplementary 2.6% increase is possible by changing the manufacturing material for plates with aluminum alloy 6060 and also by adding to the performances obtained by previous modifications. The total increase for all sets of modifications can increase the performance by 34.2% on average. Thus, for the design of new PHEs, miniaturization of the equipment becomes possible. Full article

This paper studies how the correlation with the Nusselt number affects the final result of the efficiency, ε, and exergy efficiency, η_ex, of a chevron-type gasketed plate heat exchanger, which is installed in a typical small solar installation dedicated to single-family housing; the solar fluid is a TiO₂:SiO₂/EG:DI hybrid nanofluid with concentrations from 0% to 1.5% vol. The experimental model assumes constant flow of the solar fluid and varies on the domestic hot water side—from 3 lpm to 6 lpm. The inlet temperatures are 30 °C and 60 °C on the cold and hot sides of the heat exchanger, respectively. Of the six analysed correlations that showed similar trends, it is concluded that for the assumed flow conditions, geometry, and chevron angle of the plate heat exchanger, one model is the most accurate. The largest difference between the η_ex values for a given concentration is 3.4%, so the exergy efficiency is not affected by the chosen Nusselt model by very much. However, the choice of correlation with the Nusselt number significantly affects the efficiency, ε; the difference between the values obtained within a given concentration is more than 40% and depends on the Reynolds number and flow. Most research discusses the scenario with the nanofluid as a coolant. This paper considers the opposite situation in which the solar fluid is a hotter working medium that transfers heat to domestic hot water installation. Full article

The use of the phase change material (PCM) as a storage medium represents an important advance to store energy for the absorption cooling systems when solar energy is not available; however, the temperature of the storage tank is a key parameter for the adequate operation of the cooling system. This paper presents a parametric analysis of a flat and a commercial plate heat exchangers with MgCl₂·6H₂O as the PCM at absorption cooling conditions. The plate heat exchanger (PHE) is a chevron type with an angle of 45° and a plate area of 0.04 m². The governing equation was solved using the method of finite difference. The results showed that the corrugated plate improved the heat transfer than the flat plate; however, the flat plate obtained a higher operation time than the corrugated plate for the absorption cooling condition in the discharge process because the output temperature of the PHE was much higher than the operating conditions. Finally, the decrement of the PCM thickness and the increment of the input temperature and flowrate of the heating fluid improved the heat transfer of the PHE; however, the main thermal resistance was still in the PCM. Full article

This article presents the possibility of evaluating the efficiency of the heat exchange element with a special stamping plate, which is based on the results of computer simulation. The method is based on a comparative analysis of convective heat transfer models implemented in ANSYS using a k-ε turbulence model. To conduct the study, 3D models of three different types of cavity geometry formed between two heat exchange plates (flat plate, chevron plate, and plate with conical stampings) were built. Simulation was performed by finite element analysis in ANSYS for channels formed by the three types of plates, one of which is a new configuration. The results of hydrodynamic and heat exchange parameters allowed for establishing the efficiency of convective heat exchange for plates of known structures and to compare them with the proposed one. It was found that the plates with conical stamping form the smallest channels through which the fluid moves. The velocity of the coolant is uniform throughout the cross section of the channel and equal to 0.294 m/s; the value of the heat transfer coefficient is the largest of the three models and is 5339 W/(m K), while the pressure drop is 1060 Pa. Taking into account the simulation results, the best heat transfer parameters were shown by the channel formed by plates with conical stamping and the highest pressure drop. To increase the efficiency, indicated by the ratio of heat transfer coefficients to hydraulic resistance, the geometry of the plate with conical stamping was optimized. As a result of optimization, it was found that the optimal geometric parameters of the heat exchange plate with conical stamping were achieved at a 55° inclination angle and 1.5 mm height for the cone. The results of this study can be used in the design of heat exchange elements of new structures with optimal parameters for highly efficient heating of liquid coolants. Full article

Many models for accurately predicting the performance of gasket plate heat exchangers were developed in the last decades, grouped in three categories: empirical, semi-analytical or theoretical/numerical, with the view to saving materials and energy through correct design of industrial equipment. This work addresses one such model, namely Lévêque correlation modified by Martin and by Dović, which is promising due to the correct assumption of the flow in sine duct channels and the consideration of energy losses caused by flow reversal at plate edges and the flow path changing when entering the chevron angle. This model was validated by our own experimental data under industrial conditions for vegetable oils processing, both in laminar flow (Re = 8–42) and fully developed turbulent flow (Re = 446–1137). Moreover, in this study, particular values for constants/parameters of the model were determined for the corrugation inclination angle relative to vertical direction equal to 30°. Through statistical analysis, this study demonstrates that this particularized form of the generalized Lévêque correlation can be used with confidence. Full article

An experimental study regarding the thermofluid characteristics of a shell-and-plate heat exchanger with different chevron angles (45°/45°, 45°/65°, and 65°/65°) with a plate diameter of 440 mm was carried out. Water was used as the working fluid on both sides and the corresponding temperatures ranged from 30–70 °C. The flow rate on the plate or shell side ranged from 10–60 m³/h. The effects of chevron angles on the heat transfer and fluid flow characteristics of shell-and-plate heat exchangers were studied in detail. With regard to the heat transfer performance on the plate side, a higher chevron angle (65°/65°) resulted in a significantly better performance than a low chevron angle (45°/45°). The effect of the chevron angle became even more pronounced at high Reynolds numbers. Unlike the plate side, an increase in the chevron angle had a negative effect on the heat transfer performance of the shell side. Additionally, this opposite effect was more prominent at low Reynolds numbers due to the comparatively large contribution of the manifold. The friction factor increased appreciably with the increase in the chevron angle. However, when changing the chevron angle from 45°/45° to 65°/65°, the increase in the friction factor was about 3–4 times on the plate side while it was about 2 times on the shell side. This can be attributed to the presence of the distribution/collection manifold on the shell side. Empirical correlations for the Nusselt number and friction factor were developed for different combinations of chevron angles with mean deviations of less than 1%. Full article

Few experiments have been performed to investigate the hydraulic performance in a chevron brazed plate heat exchanger (BPHE) with the narrow channel at lower Reynolds number. The hydraulic characteristics of seven types of chevron BPHEs were investigated experimentally and numerical simulation revealed the effects of structural parameters on hydraulic performances. The correlations between friction factor f and Re were fitted out based on more than 500 sets of pressure drop data. The research results show that there is a power-law between f and Re; which has a similar trend but a different amplitude for different plates, and the exponent of the power-law could be approximate to a constant. Numerical results show that the pressure drop Δp is positively correlated with the corrugated angle and spacing, however, negatively correlated with the corrugated height. Research on the hydraulic performance is significant for the optimal design of BPHE. Full article

The present study numerically investigates thermal performance and turbulent flow characteristics of chevron-type plate heat exchangers with sinusoidal, trapezoidal, triangular, and elliptical corrugation profiles. The commercial code of ANSYS Fluent (v. 17.0) is used for computational fluid dynamics (CFD) simulation with the realizable k-ε model. In particular, we focus on the influence of configuration shape on a substantial change in flow direction near the contact point, yielding local vorticity. As a result, secondary vortical motions are observed in the flow passage with vorticity that is distributed locally and which changes near the contact point. Higher flow mixing generated and distributed by the secondary vortical motions contributes to the increase of the Colburn j-factor as well as the friction factor. The highest Colburn j-factor and friction factor are obtained for an elliptical profile, compared to other shapes, because of the increase in the vortex strength near the contact point. Full article

A multiobjective optimization of an organic Rankine cycle (ORC) evaporator, operating with toluene as the working fluid, is presented in this paper for waste heat recovery (WHR) from the exhaust gases of a 2 MW Jenbacher JMS 612 GS-N.L. gas internal combustion engine. Indirect evaporation between the exhaust gas and the organic fluid in the parallel plate heat exchanger (ITC2) implied irreversible heat transfer and high investment costs, which were considered as objective functions to be minimized. Energy and exergy balances were applied to the system components, in addition to the phenomenological equations in the ITC2, to calculate global energy indicators, such as the thermal efficiency of the configuration, the heat recovery efficiency, the overall energy conversion efficiency, the absolute increase of engine thermal efficiency, and the reduction of the break-specific fuel consumption of the system, of the system integrated with the gas engine. The results allowed calculation of the plate spacing, plate height, plate width, and chevron angle that minimized the investment cost and entropy generation of the equipment, reaching 22.04 m² in the heat transfer area, 693.87 kW in the energy transfer by heat recovery from the exhaust gas, and 41.6% in the overall thermal efficiency of the ORC as a bottoming cycle for the engine. This type of result contributes to the inclusion of this technology in the industrial sector as a consequence of the improvement in thermal efficiency and economic viability. Full article