Conservation of energy by waste heat recovery is important not only for cost reasons, but also for reducing primary energy consumption as well as reducing carbon dioxide production. This paper explains and discusses the simulation, performance, and successful applications of thermosyphon heat exchangers (THE’s) for recovering waste heat from exhaust gases in industrial plants. The advantages of this system are compactness, flexibility of system size, ease of operation, and minimum maintenance requirements. The thermosyphon heat exchanger can satisfactorily act as a pre-heater of air in boilers and furnaces using the heat recovered from the exhaust. In this work, one successful industrial practice is explained using thermosyphon heat exchanger. The THE was simulated to recover waste heat from the exhaust of a nearly 7 ton boiler in the SAMEN company. The energy recovered from the flue gas is used to preheat the incoming air to the boiler. The average rate of waste heat recovery and thermal effectiveness obtained from computer simulation are 100 kW and 40%, respectively. The payback period was less than two years. The evaluation of the thermal performance of the THE was based on the effectiveness-NTU and LMTD methods to obtain the heat transfer characteristics.

In the present study, the impact of Heat Pipe Based Heat Exchangers (HPHEX) on the performance of an air-conditioning system in a library building was investigated. According to the fieldwork study, the air conditions established by the existing system are not within the comfort zone recommended by the ASHRAE. Therefore, enhancing the performance of the existing system by adding HPHEX was studied. HPHEX with different numbers of rows were examined in the system to determine the proper configuration. TRNSYS software was used to investigate the hourly effect of HPHEX on the system in terms of provided air conditions and energy consumption. According to the results, the system behavior in terms of provided air conditions is appropriate and marginally inside the comfort area with the added eight-row HPHEX. In addition, it was shown that by adding HPHEX to the system, a significant amount of energy recovery could be achieved.

The recovery of low-grade heat is crucial for energy conservation, particularly in manufacturing and process industries that discharge substantial waste energy into the atmosphere. This waste heat, varying from slightly above room temperature to several hundred degrees Celsius, can exist as liquids, gases, or a combination of both. Low-grade heat recovery, also known as waste heat recovery, involves capturing and transferring this energy using gas or liquid mediums, reintroducing it into the process as an additional energy source. This process is essential for improving energy efficiency and promoting sustainability, employing various techniques tailored to the waste heat temperature. Helical cone coils offer significantly enhanced heat transfer characteristics compared to straight tubes. These coils feature a secondary fluid flow running in planes parallel to the primary flow within their helical structure. This study focuses on designing and analyzing a shell and helical cone coil heat exchanger, highlighting its ability to reduce unit size compared to a standard shell-and-tube heat exchanger operating under the same thermal load. The experimental setup included a shell and helical cone coil configuration, utilizing diesel engine exhaust as the hot gas source and tap water as the cold fluid in a counterflow arrangement. The investigation revealed that helical cone coils extracted 15 to 20% more heat compared to conventional straight tubes, demonstrating improved effectiveness and compactness.

Exergy analysis emboldens in cases that all the inefficiencies and bottlenecks to improve energy systems are to be addressed. In this study, a novel vapor compression air dehumidifier integrated with an auxiliary heat exchanger in series arrangement with the main condenser in order to mitigate the reheat coil, and an extra mixing box to recover the ventilated air heat has been introduced. A comprehensive methodology for exergetic analysis of vapor compression heating ventilation and air conditioning systems has been presented. The quasi-dynamic component-by-component exergy analyses of both the conventional and novel air dehumidification systems have been conducted for a specific outside air fraction. Also, sensitivity analyses have been conducted on the exergy destruction and efficiency as a function of outside air fraction. Results denote that for the outside air fraction of 53%, exergy destruction of the novel air dehumidification system has decreases up to 32. 4% and exergy efficiency has ramped up by 53. 45%. Moreover, by rising the outside air fraction from none to 100%, exergy destruction in the novel air dehumidification system has declined by 46% to 30. 5 %, and exergy efficiency has undergone a 106% to 40. 3 % increase compared with the conventional system depending on the outside.

The thermal energy found in shower hot wastewater, which is usually dumped, can be recovered through heat exchangers and used to pre-heat shower cold-water, contributing to energy sustainability. The objective and novelty of this work are to present a computational fluid dynamics (CFD) model and a theoretical model based on literature correlations to evaluate the performance of a shower water horizontal heat exchanger with twisted tape inserts. CFD simulations are used to improve the shape of twisted tape in the setting of the turbulator. The findings suggest that the wastewater flow convection heat transfer coefficient is between the flow around a cylinder and the flow around a cylinder in a narrow channel. The results for the turbulator are consistent with theoretical data, except for twist ratios below 3. The most promising twisted tape design has a twist ratio of 4 and a thickness of 1 mm. A conclusion could be drawn that the efficacy of the twisted tape in the heat exchanger is greater at lower flow rates. The performance gain ranges from 18.1 % to 3.0 % for flow rates of 3–10 L/min. Future directions for this research should focus on the improvement of the external convection coefficient because it represents the highest thermal resistance in the shower wastewater horizontal heat exchanger.