Exergy Analysis of a Flat Plate Solar Collector in Combination with Heat Pipe

ABSTRACT: The use of solar collectors in combination with heat pipes is rapidly growing in recent years. Heat pipes, as heat transfer components, have undeniable advantages in comparison with other alternatives. The most important advantage is their high rate of heat transfer at minor temperature differences. Although there have been numerous studies on the heat analysis or first thermodynamic analysis of flat plate solar collectors in combination with heat pipes, the exergy analysis of these collectors is needed to be investigated. In this work, energy and exergy analysis of a flat plate solar collector with a heat pipe is conducted theoretically. Next, the exergy efficiency of pulsating heat pipe flat plate solar collectors (PHPFPSC) is compared with conventional collectors by using the experimental data. The results indicate that the use of heat pipes for heat transfer from the absorption plate to the water reservoir has significantly higher availability and exergy efficiency than the case with conventional collectors with intermediate fluid

Investigation of a radiative sky cooling module using phase change material as the energy storage

Radiative sky cooling (RSC) systems have enjoyed a privileged position in the research community due to generating cooling energy without consuming electricity using the open atmospheric window and infrared emission to the sky. However, the system's justification occurs when it reaches a temperature below the minimum 24-hour ambient temperature. This study utilizes phase change materials (PCM) as the energy storage of a hybrid daytime photovoltaic-thermal and nighttime RSC module and investigates the nocturnal cooling energy-saving potential of the system at different phase transition temperatures. After being validated by the experimental data in the literature, the simulated model was used for examining the exergy and energy efficiencies of PCMs with varying phase transition temperatures. The comparison of the exergy efficiency in the radiative sky cooling systems was performed for the first time, revealing the simultaneous effect of the temperature drop and cooling power to specify the optimal operative point of the system. Based on the climatic conditions of the simulation site, the PCM with phase transition temperatures of 18 °C revealed the peak and average exergy efficiencies of 42.8% and 33.7%, respectively. Likewise, the 23 °C PCM recorded the maximum cooling power of about 49.9 W/m2, and the 15 °C PCM achieved the highest temperature drop of about 14.8 °C

EXPERIMENTAL STUDY OF EVAPORATOR SURFACE AREA INFLUENCE ON A CLOSED LOOP PULSATING HEAT PIPE PERFORMANCE

ABSTRACT Pulsating Heat Pipes are an effective mean for heat removal with the potential for a widespread application in electronic packaging

Simultaneous power generation and heat recovery within a novel thermosyphon heat pipe: An experimental study and correlation development

The unique concept of generating electricity from a thermosyphon heat pipe (THP) utilizing an oscillating magnet in the adiabatic section was successfully examined experimentally. Generating electrical power while the THP operates is a revolutionary approach to improving its performance. In this regard, an energy harvesting module, including a magnet, was designed, built, and installed into the adiabatic section of the THP. The investigation was performed for four filling ratios ranging from 10 to 40%, while water served as the working fluid. In addition, the effect of variation of heat input on the performance of both THP and oscillating magnet thermosyphon heat pipe (OM-THP) was studied. Results demonstrated a negligible difference between the thermal resistances of OM-THP and THP before dry-out. The presence of the oscillating magnet causes dry-out to occur sooner; however, OM-THP still has electrical power generation during stable operation in the range of 50–125 W of heat inputs. According to the results, raising the filling ratio delays the drying of OM-THP. At 20% filling ratio and 100 W heat input, the highest average peak-to-peak open circuit voltage was 1 V. Besides, new correlations are presented to predict the induced voltage and thermal performance of the THP and OM-THP. The proposed correlations can predict the thermal resistances of THP and OM-THP, and the induced voltage of OM-THP with RSQ values of 0.91, 0.79, and 0.94, respectively

Experimental evaluation of a vapor compression cycle integrated with a phase change material storage tank based on two strategies

In this survey, the integration of a vapor compression cycle with a phase change material (PCM) storage tank has been evaluated experimentally during the hottest days of five cities with different weather conditions: Tehran, Ramsar Hamedan, Bushehr, and Ahvaz. The temperature conditions for outdoor (condenser, compressor, etc.) and indoor (evaporator) air conditioning units are provided with the help of two separated test chambers and a controller system. The desired system has been examined based on two scenarios. In each scenario, the system is assessed for the conventional air conditioning (AC) system (with no PCM involved) and the AC plus PCM unit. Based on scenario 1 operating strategy, the results indicate that adding the PCM tank decreases the total daily COP compared to the conventional AC unit, which varies from 32.07% for Bushehr city to 17.23% for Tehran city. Whereas the AC plus PCM system’s performance enhances during on-peak hours compared to the conventional AC system, which varies from 65.99% for Hamedan city to 12.84% for Bushehr city. Based on scenario 2 operating strategy, adding the PCM storage tank to the conventional AC unit increases total electric energy consumption over 24 h, which varies from 29.35% for Bushehr city to 5.49% for Tehran city. While it leads to shaving the electric peak load from 45.11% to 67.02% in which the highest peak load shaving belongs to Tehran and the least is related to Bushehr city

Optimization approach for MoS2-water ethylene glycol mixture nanofluid flow in a wavy enclosure

The mixed convective heat transfer in a two-dimensional enclosure containing ethylene glycol-water mixture-based MoS2 nanofluid in the presence of magnetic field and thermal radiation is evaluated, adopting Galerkin standard finite element method. The Boussinesq approximation is applied to simulate natural convection. The partial differential governing equations with the appropriate boundary conditions are numerically handled using FlexPDE software. In order to validate the implemented numerical method, results were compared against outcomes obtained from the previous studies. Afterward, the influences of key indicators such as Hartmann number (Ha), Radiation parameter (Rd), Volume fraction (φ), and Shape factor of nanoparticles (Sf) on the profiles of local Nusselt number, temperature, and velocity are discussed. Furthermore, the streamlines and isothermal lines for the various values of considered control factors are demonstrated to assess a nanofluid hydrothermal behavior. Finally, the Taguchi method is undertaken to achieve the optimum condition, in which the mean Nusselt number is maximum. The obtained results reveal that in the existence of thermal radiation, augmenting Ha from 0 to 60 leads to an increment in the Nuave up to about 17%. Based on the analysis of variance (ANOVA), the nanoparticles’ volume fraction is the most influential factor affecting the average total Nusselt among the investigated control parameters, with a contribution of 56.9%