Heat Recovery Device Research Articles

Experimental study on wet gas condensation heat transfer and flow resistance in horizontal intensified tube

The heat transfer and flow resistance characteristics of in-tube vapor condensation with high content non-condensable gas is significant for designing waste heat recovery devices of gas-fired boilers. In this paper, the forced convection condensation of wet gas in the horizontal tube is experimentally investigated with a non-condensable gas mass fraction of 83–95%. The condensation heat transfer coefficient, thermal resistance and pressure drop are compared between bare tube and two intensified tubes, i.e., the corrugated and spiral tube, under various Reynolds number, wall subcooling degree and inlet humidity. The results show that the in-tube condensation heat transfer coefficient increases with increasing Reynolds number and inlet humidity, but decreases with increasing wall subcooling degree. Compared with the bare tube, the heat transfer coefficient and pressure drop increase up to 47.13% and 16.00% respectively for the spiral tube, and 116.04% and 88.48% respectively for the corrugated tube. When combing the heat transfer and flow resistance factors, the maximum comprehensive performance coefficients are 1.71 and 1.44 for corrugated tube and spiral tube respectively. The superiority of corrugated tube in the wet gas condensation is benefit from effective breaking the non-condensable gas film and promoting the vapor diffusion on the interface.

Research on Multiple Energy-Saving Strategies for Existing Coach Stations: A Case of the Xi’an Area, China

In the context of China’s dual-carbon goals, energy efficiency in public buildings has become a focal point of public concern. As large-scale public transportation buildings, the indoor thermal comfort and the current state of energy consumption of coach stations are increasingly being emphasized. This research used existing coach stations in the Xi’an region as the object; through on-site investigations and field tests of indoor thermal environments in winter and summer seasons, it was found that the coach stations had energy waste and high energy consumption; the enclosure structures had poor thermal performance; and the stations lacked effective energy-saving measures. Energy-saving transformation strategies were proposed from two aspects: enclosure structures and renewable energy utilization. Using DeST-C for energy consumption, the external walls, roofs, insulation materials, and glass materials were simulated, and nine different combinations of energy-saving schemes were simulated using orthogonal experiments. The optimal scheme was selected based on the comprehensive energy-saving rate and economic analysis results, which included using 80 mm XPS external insulation for the external walls, low-e hollow glass for the windows (low transmittance type), and an 80 mm PUR board for the roof insulation. The energy-saving rate of this scheme was 26.84%. The use of rooftop solar photovoltaic power generation and fresh air heat recovery devices can effectively reduce building energy consumption, and the investment payback period is less than 5 years. The research applications have practical significance for improving the indoor environment of existing coach stations and saving energy consumption.

Analysis of direct expansion heat recovery ventilation devices by orthogonal optimization method.

Heat recovery ventilation devices include rectangular plate cross-flow, hexagonal plate combined counter and cross-flow, rotary wheel sensible, sorption rotor hybrid sensible and latent heat exchanger. Currently, existing studies have produced no clear findings on which climatic conditions latent heat recovery would be optimal, and therefore sought to determine in which climatic conditions it would be suitable to use devices that perform latent heat recovery. This study analysed the performance of different heat recovery devices in different climatic conditions in a ventilation project of a sample hotel building. In the case study, while there is a useful heat recovery between 44.01 and 58.68kW at low outdoor temperatures in devices with only sensible heat transfer, this value increases up to 158.42kW, as the outdoor temperature rises. In the heat recovery device providing latent heat transfer, the amount of useful heat recovery varies between 51.34 and 352.16kW at low outdoor temperatures, depending on the outdoor relative humidity, while this amount increases to 411.26 from 773.25kW at high outdoor temperatures. Outdoor temperature and humidity levels required for latent heat recovery was also determined by orthogonal optimization method. By using the orthogonal optimization, the study found that under conditions of high temperature that exceeds 35°C in outdoor ambient temperature, and high humidity that exceeds 60% relative humidity, usage of latent heat recovery devices caused significant differences in total heat recovery ratio. Analysis also concludes that these devices can be used under these conditions.

Optimizing the thermal performance of the thermosyphon heat pipe for energy saving with graphene oxide nanofluid

A thermosyphon heat pipe (THP) involves a vacuum tube with a specific quantity of liquid. Due to its simplicity of design and structure, THP has many applications in heat recovery and renewable energy devices. Prior studies showed that using stable nanofluids can improve THPs' energy efficiency. In this evaluation, the effect of working fluid type, input heat, two types of surfactants, and nanoparticle concentration on the energy efficiency and thermal resistance of a THP was investigated and optimized. A magnetic stirrer and ultrasonic waves were used to create stability. Imaging and spectrophotometric analysis showed that graphene oxide (GO) nanofluid with SDS surfactant is more stable. The most notable decrease in thermal resistance at an input power of 100 W with GO nanofluids compared to distilled water at an F.R. of 50% was 12%. The highest decrease in the evaporator temperature section was achieved with GO and SDS surfactant at a weight ratio of 0.3% wt, equal to 12.3 °C. This was also confirmed by measuring the contact angle. The highest percentage increase in thermal efficiency of THP with the mixture of GO nanoparticles and SDS surfactant in distilled water with 0.3 wt percent and input heat of 200 W was 18% compared to distilled water. In the optimum condition, the highest percentage increase in thermal efficiency of THP with the mixture of GO nanoparticles and SDS surfactant in distilled water with 0.3 wt percent and input heat of 200 W was 18% compared to distilled water.

Designing of energy saving system with heat recovery and solar air collector

In this study, it is aimed to increase the efficiency of heat pump systems, which are generally used for heating in winter. A combined system was created by utilizing the heat pump system, solar air collectors and a heat recovery device. The coefficient of performance of the heat pump system was 6.4 and the efficiency of the solar air collector was 70% while 85% energy efficiency was acquired from the heat recovery device used in the system. The heat recovery device’s energy efficiency was calculated as 85%, while the exergy efficiency was calculated as 40%. The usage of these three systems, which has already high energy-efficiency at separately usage, together in one single system has prevented the decreasing that may occur in the energy efficiency of the systems during the day increased their efficiency. The outdoor air temperature in the winter season significantly reduces the efficiency of heat pump systems, and even many systems work defrost mode. The proposed and experimentally studied system, the operability of the heat pump has been ensured throughout the day. For this process, the system has been able to benefit not only from the solar air collector, but also from the energy of heat recovery device.

Physical Separation: Reuse Pollutants and Thermal Energy from Water

Conventional sewage treatment based on biological and chemical methods have made historical contributions to humans. However, it breaks the biogeochemical cycles of carbon, nitrogen, and phosphorus and cannot remove hazardous materials including viruses and nano/microplastics. Therefore, we rethought the conceptual revolution of principles of sewage treatment in the 1890s, that is, “the replacement of a philosophy that saw sewage purification as the prevention of decomposition with one that tried to facilitate the biological processes that destroy sewage naturally”. We proposed a promising sewage treatment system based on physical separation, which mainly consists of the source separators and the insoluble-pollutants separators, soluble-pollutants separators, and the wastewater heat recovery devices in wastewater treatment plants. By using the promising system, the carbon in wastewater will be recovered by sending biosolids directly into the soil after removing the hazardous materials and organic toxicity. The nitrogen and phosphorus in wastewater will be sent back into the soil or be used for hydroponics rather than be mineralized. The thermal energy in wastewater will be recovered and reused, and the hazardous materials will be removed. As a result, the promising system will turn the wastewater treatment system with high resource and thermal energy waste and high energy consumption into a no-chemicals, green factory. At present, nonetheless, it is still urgent to develop more advanced insoluble-pollutants separators and soluble-pollutants separators with high separation efficiency and low energy consumption, especially volume separators. Because the volume separators (e.g., functionalized sand filters) have the potential for replacing the surface separators (e.g., membranes).

Performance investigation of a biomimetic latent heat thermal energy storage device for waste heat recovery in data centers

Improving the power usage effectiveness of data centers has become a significant challenge for carbon peaking and carbon neutrality. To address this, here we propose a single-phase immersion cooling system with latent heat thermal energy storage (LHTES) devices to recover waste heat. Furthermore, an innovative LHTES device with palmate leaf-shaped fins is designed by bionic techniques. The phase change behavior and thermal transport patterns of biomimetic and traditional LHTES devices are investigated, and the effects of the arrangement and working conditions are revealed. Additionally, the proposed solution's application prospect and economy are presented. The results indicate that the performance of palmate leaf-shaped finned LHTES devices is significantly enhanced compared to traditional ones, whose charge and discharge durations reduce by 21.0 % and 38.2 %, respectively. Moreover, the natural convection development enhances the melting performance, but its effect on solidification processes is insignificant. Considering the trade-off between power consumption and LHTES efficiency, a horizontal biomimetic LHTES device with a flow rate of 20 L/min and a large heat-transfer temperature difference is suggested in practical engineering. Notably, the maximum reduction in annual power consumption for using biomimetic LHTES devices is 2397.4 kW·h, and the minimum payback period is only 2.0 years.

Comparative Performance Analysis of Exhaust Air Heat Recovery Devices Based on Microchannel heat pipe

In response to the problem of low recovery efficiency of sensible heat recovery devices, this paper designs a microchannel heat pipe heat recovery device (MHPHRD) and compares its heat transfer performance during summer use through experiments and simulation calculations. The experimental results show that the microchannel heat pipe (MHP) has strong temperature uniformity, and the temperatures of the evaporation and condensation sections are basically the same. When the inlet temperature of fresh air changes between 32°C and 40°C, the recovery efficiency of the device varies between 67%-80%, and the linear relationship between the two is obvious. The established calculation model has high accuracy, with a maximum error of 0.7% between measured and simulated values. Simulation calculations show that the cooling capacity recovery efficiency of the MHPHRD is 4%-16% higher than that of the cylindrical heat pipe heat recovery device (CHPHRD), and 24%-30% higher than that of the plate heat recovery device (PHRD). The research in this article can provide reference for the practical application of the device.

Experimental study of the influence of external factors on the functionality of a regenerative decentralized ventilation unit

The article presents an experimental field study of the influence of environmental factors on the functionality of a commercial decentralized ventilation device for regenerative utilization of heat from the exhaust air, intended for installation in an external wall of buildings. The experiments included measurements during the winter and summer seasons. Real operating situations with two regenerative heat exchange matrices are presented and tested. The results of the experiments show that the functionality of the ventilation and heat recovery device does not meet the characteristics that the device shows under standard laboratory conditions.

Waste Heat Recovery from a Drier Receiver of an A/C Unit Using Thermoelectric Generators

Thermoelectric generators (TEGs) are considered promising devices for waste heat recovery from various systems. The Seebeck effect can be utilized to generate power using the residual heat emitted by the filter dryer receiver (FDR) of an air conditioning (A/C) system, which would otherwise go to waste. The study aims to build a set of thermoelectric generators (TEG) to collect the waste heat of the FDR and generate low-power electricity. A novel electrical circuit with two transformers is designed and fabricated to produce a more stable voltage for operation and charging. The thermoelectric generator (TEGs) was installed on the FDR of the A/C unit. The test showed that climate conditions have a significant impact on the output power generated from the system. The results showed that the peak voltage recorded in the current study is 5.2 V per day (wet, cold, and wind weather) with an output power of 0.2 W. These values are acceptable for powering the load and charging a single battery with 3.5 V as the voltage increases battery 0.1 V/20 min charge. A case study of operating the emergency signs in a building was considered. The current heat recovery system is deemed to be easily installed and can be connected to a network of TEGs to produce more power.

Thermal and Economic Evaluations of a Drain Water Heat Recovery Device under Transient Conditions

Thermal and Economic Evaluations of a Drain Water Heat Recovery Device under Transient Conditions

Heat transfer enhancement by diamond nanofluid in gravity heat pipe for waste heat recovery

Waste heat recovery is significant for improving energy utilization, reducing carbon emissions, and neutrality. The gravity heat pipe (GHP) has excellent thermal performance due to the cyclic phase transformation of the working fluid. As an important thermal management device for waste heat recovery, the heat transport capacity of GHP improves, the efficiency and performance of the waste heat recovery increase, and more wasted heat can be stored more quickly. Nano-diamond has the highest thermal conductivity and can be dispersed in water to form a diamond nanofluid, enhancing the thermal performance of GHP. In contrast, the study on the heat transfer behavior of the diamond nanofluid in GHP is insufficient. Besides, the influences of filling ratio (FR), mass fraction (MF), and heat flux on thermal performance are in demand for further study. In this article, the heat transfer behavior is investigated by studying the flow patterns of diamond nanofluids. The influences of filling ratio and mass fraction on flow patterns are analyzed. An orthogonal experiment is conducted; the heat flux has the most significant effect on the thermal performance, followed by the filling ratio and mass fraction. The thermal performance is the best when the optimal parameters (FR = 20%, MF = 1 w.t.%) are selected under a heat flux of 20 × 104 W/m2. The equivalent heat transfer coefficient reaches 3485 W/(m2·°C). This article can achieve a deeper understanding of the diamond nanofluid heat transfer mechanism in GHP and enhance the thermal performance of GHP for better waste heat recovery.

Performance improvement of the electric water heater by a waste heat recovery method with the thermoelectric effect

In this study, a waste heat recovery method based on the thermoelectric effect was proposed to improve the thermal performance of electric water heaters. The method collected the surplus thermal energy in the high-temperature zone and released heat for reuse in the low-temperature zone through the thermoelectric element. A heat-recovery device using a thermoelectric element was designed and conducted experimentally to verify the method's feasibility and energy conservation effect. The device performance of heat absorption and heat release were investigated under various working thermal states. The experimental results showed that the heating COP of the system could be improved to 1.2–2.3 under different temperature conditions, which means the device can save energy than using electric power directly. The heat flux through the device can be actively controlled for an optimal effect of heat recovery. The source-sink matching effect of the device was investigated, and the results indicated that the device's energy efficiency could be higher than 75%. The thermal performance of an improved electric water heater using the heat recovery device was investigated numerically under a specific working condition. The results verified that the heat recovery device reduced heat dissipation and simultaneously increased the temperature of the water outlet.

Thermodynamic analysis of power recovery of marine diesel engine under high exhaust backpressure by additional electrically driven compressor

Marine diesel engines can be exposed to high backpressure conditions, because various aftertreatment systems and waste heat recovery devices have been applied to reduce emissions and some exhaust outlets are below sea level. The engine performance deteriorates sharply under high backpressure. This paper aims to study power recovery method under high backpressure based on thermodynamic analysis. Firstly, thermodynamic model is established and validated by experimental data. Next, effects of turbocharger efficiency and turbine area on power recovery are studied. The results show that feasible turbine performance are limitations for power recovery. If energy of compressor can be increased without changing turbine area, limitations can be overcome. Thirdly, additional electrically driven compressor as a solution is proposed to recover engine power. A comparative study of different electrically driven compressor schemes is carried out. The most suitable scheme is the series scheme at low-pressure stage because operating points for original compressor and electrically driven compressor are within a reasonable range. Finally, research on power recovery is carried out on optimal electric compressor scheme. The results show that when backpressure is 0.65 bar, engine net power can be increased by 49.4% and exhaust temperature drops by about 77 K, which largely reduces turbine thermal load.

Regulation strategies and thermodynamic analysis of combined cooling, heating, and power system integrated with biomass gasification and solid oxide fuel cell

A solid oxide fuel cell combined cooling, heating, and power system integrating biomass gasification is proposed. The hybrid system consists of the biomass gasifier, solid oxide fuel cell-gas turbine, and waste heat recovery device. The system can be divided into different configurations by adjusting the valve opening to change the waste heat mode. The thermodynamic model is established and validated; the system evaluation indicators and the thermodynamic, economic and environmental performance are researched under design conditions. The influences of several crucial parameters on syngas composition and system performance under the different configurations are investigated. This paper also evaluates the scope of system regulation and energy output to meet the energy demand side. The analysis results indicate that system power efficiency is 58.92% at the preferred configuration, and the system energy and exergy efficiency can attain 86.70% and 50.45%. The system total cost rate and the CO2 emission rate are relatively lower, at 19.6$/h and 0.4722kg/kWh. By implementing different configuration strategies, the system exergy efficiency is between 46.55% and 50.45%. The system heating to power ratio and cooling to power ratio can vary from 0 to 0.58 and 0 to 0.77.

Global sensitivity analysis and optimal design of heat recovery ventilation for zero emission buildings

Energy-efficient building services are necessary to realise zero-emission buildings while maintaining adequate indoor environmental quality. As the share of ventilation heating needs grow in well-insulated and airtight buildings, heat recovery in mechanical ventilation systems is increasingly common. Ventilation heat recovery is one of the most efficient and viable means to reduce ventilation heat losses and save energy. Highly efficient heat exchangers are being developed or applied to maximise the energy-saving potential of heat recovery ventilation. Nevertheless, the effects of practical operating conditions and the constraints of heat recovery – such as variations in ventilation rates, frost protection, and the prevention of an overheated air supply over a long-term period, which may significantly influence realistic recovery rates – have been less considered in efforts to maximise the energy savings. It is unclear which design parameters for heat recovery devices have the greatest effect on the annual energy savings from ventilation.This study proposes annual efficiency and annual net energy saving models for heat recovery ventilation that consider ventilation rate variations, the longitudinal heat conduction effect and operating controls. We use a global sensitivity analysis to quantify the contributions of various design input parameters to the variation in annual recovery efficiency and annual net energy savings. We identify the most influential parameters and their significant interaction effects for the annual energy performance of heat recovery ventilation. More attention should be paid to these most influential parameters during the design process. Furthermore, the optimal designs for rotary heat exchangers (as identified by a pattern-search optimisation algorithm) can improve annual net energy savings in demand-controlled ventilation by 33–48%, depending on the building areas. In combination with the reference year analysis presented in this study, heat recovery and demand-controlled ventilation can help to meet the need for highly efficient ventilation systems and zero-emission buildings.

Experimental study on influence of high exhaust backpressure on diesel engine performance via energy and exergy analysis

Marine diesel engines can be exposed to high backpressure conditions, because various aftertreatment systems and waste heat recovery devices have been widely applied to reduce the emission level, and the outlet of its exhaust manifold is normally below sea level. This article aims to understand the influence of exhaust backpressure on turbocharged engine performance. Diesel engine tests under high backpressure was conducted and it has been found that engine output power drops sharply. To explore the reasons and further study the recovery method, analysis of energy and exergy was carried out. With the increase of backpressure, turbo expansion ratio reduces sharply. But the energy upstream turbine doesn't decrease necessary due to the increase of exhaust temperature. Simultaneously, the exhaust exergy gradually increases by 10.3% when the backpressure increases from 0 bar to 0.55 bar at 75% load, leading to improved energy grade. The turbine output power reduces 56.7% because of the combination results of reduced expansion ratio and increased exhaust energy grade. The method of power recovery should balance these two factors. The study can enlighten the method of power recovery of diesel engine confronted by high backpressure conditions.

Hybrid Indirect Evaporative Cooling-Mechanical Vapor Compression System: A Mini-Review

The hybrid indirect evaporative cooling-mechanical vapor compression (IEC-MVC) process is deemed a promising cooling system for hot and humid areas. It possesses the merits of high energy efficiency and strong capability of temperature and humidity control. Herein, we provide an overview of the state-of-the-art investigations over different aspects of the hybrid IEC-MVC process. Firstly, we evaluate the potential of IEC as a pre-cooler and heat-recovery device. Then, we compare the energy efficiency of IEC-MVC with standalone MVC and summarize its long-term energy-saving potential under specific weather conditions. Subsequently, we discuss the economic viability and water consumption of the hybrid process. These studies form a solid foundation for the future installation of the IEC-MVC system.

A Drying system for Rhizoma et Radix Baphicacanthis Cusiae Based on multi-source coupling and efficient energy storag

The traditional Chinese Herbal Medicine Rhizoma et Radix Baphicacanthis Cusiae mostly grows in Southwest China. However, due to the lack of technology, the key drying process in the production of Rhizoma et Radix Baphicacanthis Cusiae has the problems of low efficiency, long time and uneven quality. The paper designed a drying system of Rhizoma et Radix Baphicacanthis Cusiae based on multi-source coupling and efficient energy storage by investigating the production of Rhizoma et Radix Baphicacanthis Cusiae in southwest China and studying the natural effects of geographical advantages and light conditions in the region. The main body of the system is composed of a two-position water tank heat circulation system, a hemispherical Fresnel lens array, an air source heat pump, a dehumidification and waste heat recovery device, a temperature and humidity sensor, and a heat exchange tube group. The drying system can better meet the drying needs of Chinese herbal medicine Rhizoma et Radix Baphicacanthis Cusiae. It has the advantages of high efficiency, energy conservation and environmental protection, stable operation, and can independently adjust according to the drying temperature. It has strong practicability. While saving energy, it saves high drying cost for farmers, and meets the special requirements of building intelligent agriculture and enriching rural economic business forms.

Low-Carbon Economic Dispatching of Multi-Energy Virtual Power Plant with Carbon Capture Unit Considering Uncertainty and Carbon Market

Multi-energy virtual power plants (MEVPPs) effectively realize multi-energy coupling. Low-carbon transformation of coal-fired units at the source side and consideration of demand response resources at the load side are important ways to achieve carbon peak and carbon neutralization. Based on this, this paper proposes a low-carbon economic dispatch model for the MEVPP system considering source-load coordination with comprehensive demand response. Combined with the characteristics of organic Rankine cycle (ORC) waste heat power generation and comprehensive demand response energy to increase the flexibility on both sides of the source and load, the problem of insufficient carbon capture during the peak load period in the process of low-carbon transformation of thermal power units has been improved. First, the ORC waste heat recovery device is introduced into the MEVPP system to decouple the cogeneration unit’s “heat-based electricity” constraint, which improves the flexibility of the unit’s power output. Secondly, we consider the synergistic effect of the comprehensive demand response and ORC waste heat recovery device and analyze the source-load coordination low-carbon dispatch mechanism. Finally, an example simulation is carried out in a typical system. The simulation example shows that this method effectively improves the carbon capture level of carbon capture power plants, takes into account the economy and low carbon of the system, and can provide a reference for the low-carbon economic dispatch of the MEVPP system.