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The present article aims to cover the most recent advancements in heat recovery technology in heating, ventilation, and air conditioning and identify areas that have not been thoroughly investigated. Extensive information is available on heat recovery technologies and exchangers in central systems. Furthermore, the research examines both direct and indirect evaporative cooling approaches. The literature discusses how the heat recovery process is influenced by climatic conditions, air flow rate, and the type of heat exchanger employed. The latest studies contributing to enhancing the performance of heat exchangers were also considered. The results of the study indicate that recent years have witnessed great interest from researchers in the field of lost energy recovery; the experimental, theoretical, and numerical studies have focused on studies of the influencing factors that contribute to improving the performance of the energy recovery process. The current project involves doing an analytical and comparative analysis of the newest research about enhancing the efficiency of thermosyphon heat exchangers and various forms of evaporative cooling.

This work presents an adaptive model predictive control (MPC) strategy to suppress the vibration in a laminated composite beam. The control method incorporates a system identification algorithm to estimate the system parameters online, which provides a precise simulation of system dynamics. A fixed-free cantilever composite beam equipped with piezoelectric actuators was used to evaluate the efficacy of the control method. The sensors and actuators are securely bonded to the upper and lower surfaces at arbitrary locations along the beam’s length. A unified mechanical displacement field is applied to all layers, while displacements are considered independently for each layer. The beam is composed of eight layers of material, each with a thickness of 0.2 mm and orientations specified as (90°/0°/90°/0°). To achieve the best performance, the parameters of the MPC were adjusted numerically. The numerical analysis revealed that placing the actuator near the clamped end at the fixed end resulted in superior control outcomes, with a settling time of approximately 1.8 s. Conversely, the longest settling time occurred when the actuator was positioned at the free end, taking around 4 s. This model could potentially be expanded to address vibration in more intricate beams exhibiting nonlinear characteristics. The deflection readings measured at the end of the beam have been utilized as feedback control signals for predicting future behavior over a predetermined control horizon. The subsequent cost function is minimized through a quadratic equation to determine the sequence of optimal yet constrained control inputs. The suggested active vibration control system is then implemented and assessed numerically to examine the effectiveness of the control method.

Air conditioners (ACs) are more commonly used nowadays in residential and commercial buildings to achieve thermal comfort in the summer season. Due to the high outside temperature, condenser pressure was highest and ultimately resulted in high electricity consumption. One of the ways to reduce the energy consumption of AC systems and increase cooling capacity is by reducing air temperature entering the condenser by using the evaporative cooling principle. This article presents an experimental and theoretical investigation of improving the performance of the conventional air conditioning unit supported by a direct evaporative cooling system to increase the cooling capacity and reduce the consumption of power in hot and dry climates. A window-type AC unit was implemented in the experiment where the AC system is modulated to provide a wide range of various weather conditions. The results show that using evaporative cooling assist enhanced the system to overcome the many challenges by which the refrigeration capacity was increased in the range of 10–20%. Also, the results show a decrease in outlet temperature by 6–10°C, and the power consumption was reduced by about 3%. MATLAB program was used to analyze different data that were obtained. The input parameters for this program are the inlet conditions such as the weather conditions of the located city, namely the outdoor dry temperature and the outdoor relative humidity. The effectiveness and cooling capacity were calculated based on the frontal air velocity and the inlet air temperature. A comparison between the experimental and theoretical work showed a good agreement, as the relative difference is less than 9%.

Recently, solar thermal energy has been considered the main type of renewable energy used widely to provide heat energy and produce electrical power. Evacuated tube solar collectors (ETSCs) are used in various weather circumstances such as clear, cloudy, windy, hot, and cold weather, and their efficient system supplies latent heat storage fluid with higher temperature and lower heat energy loss compared to the flat-plate solar collectors (FPSCs). This review paper is considered an investigation on adding nanofluid particles to the evacuated tube solar collector-PCM, indicating future evacuated tube solar collector designs and predicting the suitable high- or low-temperature PCM for various types of applications. Also, three main types of ETSCs, heat pipe, Thermosyphon, and U-pipe, with their applications are reviewed, and the factors that influence the collector performance and efficiency are discussed. Moreover, the properties that affect the selection of the PCM and the usage of various types, sizes, and volumetric concentrations of nanofluid as a working fluid for each ETSC are investigated with their enhancements for each type. Lastly, this paper provides future ideas for using additive nanofluid materials as a working fluid to improve the performance and efficiency of ETSCs. [ABSTRACT FROM AUTHOR]

The generation of entropy and mixed convection in a nanofluid-filled 3D wavy tank containing a rotating cylinder is investigated. The top wavy surface of the tank is heated and all vertical surfaces are assumed to be adiabatic, while the bottom horizontal surface remains isothermally cold. The tank contains a solid cylinder and is saturated with an Al2O3–water nanofluid. The numerical simulations using the FEM are performed for the Richardson number ( 0.01 ≤ R i ≤ 100 ), nanoparticle volume fraction ( 0 ≤ ϕ ≤ 0.04 ) and number of oscillations ( 0 ≤ N ≤ 4 ). The numerical results of the present work are given in terms of 3D streamlines, isotherms and local entropy generation, as well as average heat transfer and Bejan number. The results show that for low values of the Richardson number and oscillation, heat transfer enhancement can be achieved by increasing the nanoparticle volume fraction. [ABSTRACT FROM AUTHOR]

Convective heat transfer of laminar forced convection in a wavy channel is studied in this paper. Numerical simulations of the 3D steady flow of Newtonian fluid and heat transfer characteristics are obtained by the finite element method. The effects of the Reynolds number (10 ≤ Re ≤ 1000), number of oscillations (0 ≤ N ≤ 5) and amplitude of the wall (0.05 ≤ A ≤ 0.2) on the heat transfer have been analyzed. The results show that the average Nusselt number is elevated as the Reynolds number is raised, showing high intensity of heat transfer, as a result of the intensified effects of the inertial and zones of recirculation close to the hot wavy wall. The rate of heat transfer increases about 0.28% with the rise of the number of oscillations. In the transfer of heat along a wavy surface, the number of oscillations and the wave amplitude are important factors. With an increment in the number of oscillations, the maximal value of the average velocity is elevated, and its minimal value occurs when the channel walls are straight. The impact of the wall amplitude on the average Nusselt number and dimensionless temperature tends to be stronger compared to the impact of the number of oscillations. An increase of the wall amplitude improves the rate of heat transfer about 0.91% when the Reynolds number is equal 100. In addition, when the Reynolds number is equal 500, the rate of heat transfer grows about 1.1% with the rising of the wall amplitude. [ABSTRACT FROM AUTHOR]