Waste Thermal Energy Research Articles

A review on using thermoelectric cooling, heating, and electricity generators in solar energy applications

Parallel with the rapid advances of solar technologies as the very crucial components of future energy systems, much interest has also been observed in scientists and commercial companies for the further development and use of thermoelectric systems during recent years. This has led to an interesting field of research combining solar systems/technologies and thermoelectric systems for a variety of purposes. Thermoelectric cooling, heating, and power generators are here proposed in different ways to enhance the performance of solar energy systems. In thermoelectric heating applications, the hot side of the thermoelectric module contributes to increasing the temperature of the solar working fluid in e.g. the desalination, water or air heater systems, etc. For the thermoelectric cooling case, the cold side of the module plays a supplementary or main role in reducing the temperature of e.g. PV panels, the condensation area of desalination units, etc. A thermoelectric power generator may be used to convert the waste thermal energy or the main heat flow output of a solar system to electricity. A combination of heating, cooling, and/or electricity generating thermoelectric units in solar systems could also be frequently seen in the literature. This article, presenting a summary and discussion of previous articles published recently in the literature, aims to make a review and assessment of the methods and impacts of thermoelectric devices on the performance of solar systems in various designs, and thereby, giving readers a good insight into the state-of-the-art and the gaps.

Optimization and Comparative Performance Analysis of Conventional Air Conditioning System and Desiccant Air Conditioning System with Complete Waste Heat Reclamation: Experimental Investigation

A desiccant air conditioning unit provides a compelling alternative to a conventional air conditioning system to eliminate moisture. In order to resolve the issue of more energy consumption for the regeneration of desiccant wheel, structures containing desiccant wheel can utilize full waste heat or thermal energy to restore desiccant material. Here, the performance of conventional and desiccant air conditioning systems have been evaluated. During experimentation, these two systems were operated and compared at process air inlet humidity ratios ranging (0.01580-0.01740 kg/kg) and process air inlet velocities ranging (1.5-4.5 m/s). Besides, the desiccant air conditioning system was regenerated by using complete waste heat from the condenser (50-58.8℃) for regeneration of the desiccant wheel at a minimum (2.5 m/s) and a maximum (4.5 m/s) regeneration air inlet velocity. Thus, optimization of performance parameters, i.e. VCOP, ECOP, DCOP, wheel effectiveness in the adsorption sector and regeneration sector, adsorption rate and regeneration rate have been examined for achieving maximum efficiency of conventional and desiccant air conditioning systems under the above operating conditions.

Carbide slag based shape-stable phase change materials for waste recycling and thermal energy storage

Massive accumulation of industrial carbide slag tend to cause ecological environment pollution and greenhouse gas emission. This innovative work proposed to fabricate shape-stable phase change materials (SSPCMs) with carbide slag to utilise industrial solid waste and protect precious natural resources. Seven SSPCMs were fabricated with different mass ratios of industrial carbide slag to sodium nitrate by cold-compression hot-sintering method, and key performance was investigated on the SSPCMs. Results showed that the SSPCM (sample CC6) with the mass ratio of 5:5 of carbide slag to sodium nitrate presented the best performance: sample CC6 achieved a high thermal energy storage density of 447 J/g in the range of 100–400 °C and reached a mechanical strength of 73.6 MPa; sample CC6 demonstrated a good thermal stability and chemical compatibility between carbide slag and sodium nitrate during the heating/cooling cycles; the thermal conductivity of sample CC6 was 0.93 W/(m•K), and elements distributed uniformly in sample CC6.

Dynamic simulation of a solar ejector‐based trigeneration system using TRNSYS‐EES co‐simulator

AbstractIn this paper, a new configuration of a solar combined cooling, heating, and power (CCHP) system is proposed to recover the waste thermal energy of a steam power plant, which provides the cooling and heating needs of an apartment complex located in Tehran. The required energy of the system is supplied by the parabolic trough solar collectors (PTCs) and, if necessary, an auxiliary heater is also used. An ejector refrigeration cycle (ERC) and a steam Rankine cycle are used for cooling and power generation, respectively. The cycle is dynamically modeled over a year using a TRNSYS‐EES co‐simulator. It is found that the highest Rankine cycle efficiency is obtained in the cold months (January) because of the decrease of turbine backpressure. With increasing the turbine inlet temperature from 190 to 210°C, the Rankine cycle and the overall cycle efficiencies increased about 1% and 2%, respectively. The maximum cooling, heating, and power generation, as well as the maximum solar fraction, are obtained at the turbine inlet temperatures of 210°C, which are 185.46, 598.65, 680.49 kW, and 70%, respectively. The annual overall performance and the solar fraction of the proposed CCHP system are 32.5% and 9.5%, respectively, based on 3000 m2 collector aperture area. The exergy analysis indicated that the maximum annual exergy destruction is related to the solar collectors, which have comprised 27% of the total exergy destruction. In addition, the yearly exergy efficiency of the proposed system is 39.9%.

Simulation Analysis and Experimental Study of Piezoelectric Power Generation Device Based on Shape Memory Alloy Drive.

In order to solve the problem of waste heat collection from energy consumption, a thermal energy generation device combining shape memory alloy and piezoelectric materials has been designed. The shape memory alloy is heated and deformed to drive the drive wheel continuously, and the impact wheel is deformed against the piezoelectric cantilever beam during the rotation of the drive wheel to generate electricity. In this paper, the impact force generated by the impact wheel and the output voltage of the piezoelectric cantilever beam during the rotation process are given. Finally, the experimental test shows that the larger the radius of the drive wheel, the lower the impact force of the wheel and the lower the output voltage of the piezoelectric cantilever beam; the larger the diameter of the shape memory alloy wire, the higher the impact force of the wheel and the higher the output voltage of the piezoelectric cantilever beam; the more teeth of the drive wheel, the higher the impact frequency of the piezoelectric cantilever beam and the higher the output voltage. The maximum output voltage of the thermoelectric converter is 14.2 V, when the drive wheel radius is 13 mm, the shape memory alloy wire diameter is 1 mm and the number of impact wheel teeth is 6. The new structural design provides a new structural model for waste heat recovery and thermal energy generation technology. The new structural design provides a new approach and idea for waste heat recovery and thermal energy generation technology.

Multimodal electrochemistry coupled microcalorimetric and X-ray probing of the capacity fade mechanisms of Nickel rich NMC - progress and outlook.

Lithium nickel manganese cobalt oxide (NMC) is a commercially successful Li-ion battery cathode due to its high energy density; however, its delivered capacity must be intentionally limited to achieve capacity retention over extended cycling. To design next-generation NMC batteries with longer life and higher capacity the origins of high potential capacity fade must be understood. Operando hard X-ray characterization techniques are critical for this endeavor as they allow the acquisition of information about the evolution of structure, oxidation state, and coordination environment of NMC as the material (de)lithiates in a functional battery. This perspective outlines recent developments in the elucidation of capacity fade mechanisms in NMC through hard X-ray probes, surface sensitive soft X-ray characterization, and isothermal microcalorimetry. A case study on the effect of charging potential on NMC811 over extended cycling is presented to illustrate the benefits of these approaches. The results showed that charging to 4.7 V leads to higher delivered capacity, but much greater fade as compared to charging to 4.3 V. Operando XRD and SEM results indicated that particle fracture from increased structural distortions at >4.3 V was a contributor to capacity fade. Operando hard XAS revealed significant Ni and Co redox during cycling as well as a Jahn-Teller distortion at the discharged state (Ni3+); however, minimal differences were observed between the cells charged to 4.3 and 4.7 V. Additional XAS analyses using soft X-rays revealed significant surface reconstruction after cycling to 4.7 V, revealing another contribution to fade. Operando isothermal microcalorimetry (IMC) indicated that the high voltage charge to 4.7 V resulted in a doubling of the heat dissipation when compared to charging to 4.3 V. A lowered chemical-to-electrical energy conversion efficiency due to thermal energy waste was observed, providing a complementary characterization of electrochemical degradation. The work demonstrates the utility of multi-modal X-ray and microcalorimetric approaches to understand the causes of capacity fade in lithium-ion batteries with Ni-rich NMC.

Experimental and Numerical Study of Thermal Performance of an Innovative Waste Heat Recovery System

One of the biggest challenges the world is facing these days is to reduce the greenhouse gases emissions in order to prevent the global warming. Since a significant quantity of CO2 emissions is the result of the energy producing process required in industry or buildings, the waste heat recovery is an important aspect in the fight for preserving the planet. In this study, an innovative waste heat recovery system which can recover waste heat energy from cooling liquids used in industry or in different processes, was designed and subjected to experimental investigations. The equipment uses heat pipes to capture thermal energy from the residual fluids transiting the evaporator zone and transfer it to the cold water transiting the condenser zone. The efficiency of the heat exchanger was tested in 9 scenarios, by varying the temperature of the primary agent to 60, 65 and 70 °C and the volume flow rate of the secondary agent to 1, 2 and 3 L/min. The temperature of the secondary agent and the volume flow rate of the primary agent were kept constant at 10 °C, respectively 24 L/min. The results were later validated through numerical simulations, and confirmed that the equipment can easily recover waste thermal energy from used water with low and medium temperatures at very low costs compared to the traditional heat exchangers. The results were promising, revealing an efficiency of the equipment up to 76.7%.

Feasibility of Boosting Low-Energy-Quality Steam by Using Wave Rotor

Owing to the difficult utilization of the low-pressure level in the process industry, the low-energy-quality steam is often condensed to recover the demineralized water or just discharged directly, causing a huge waste of thermal energy. A novel technology of enhancing the steam’s energy quality by using the wave rotor based on the principle of moving shockwave compression is proposed. The supercharging ability of 3-port wave rotor is studied by meaning of 1-dimension unsteady theory and computational fluid dynamic. A practical thermodynamic flowsheet of boosting the low-pressure steam driven by high-pressure steam is also proposed and analysed in detail. As an example, to boost the saturated steam of pressure 1.0 MPa to 1.953 MPa, a three-stage wave rotor solution is proposed and is verified its feasibility. The high supercharging ratio and entrainment ratio of the wave rotor are much higher than the traditional steam ejector shows the feasibility of enhancing energy-quality of low-pressure steam.

An Experimental and Comparative Performance Evaluation of a Hybrid Photovoltaic-Thermoelectric System

The majority of incident solar irradiance causes thermalization in photovoltaic (PV) cells, attenuating their efficiency. In order to use solar energy on a large scale and reduce carbon emissions, their efficiency must be enhanced. Effective thermal management can be utilized to generate additional electrical power while simultaneously improving photovoltaic efficiency. In this work, an experimental model of a hybrid photovoltaic-thermoelectric generation (PV-TEG) system is developed. Ten bismuth telluride-based thermoelectric modules are attached to the rear side of a 10 W polycrystalline silicon-based photovoltaic module in order to recover and transform waste thermal energy to usable electrical energy, ultimately cooling the PV cells. The experiment was then carried out for 10 days in Lahore, Pakistan, on both a simple PV module and a hybrid PV-TEG system. The findings revealed that a hybrid system has boosted PV module output power and conversion efficiency. The operating temperature of the PV module in the hybrid system is reduced by 5.5%, from 55°C to 52°C. Due to a drop in temperature and the addition of some recovered energy by thermoelectric modules, the total output power and conversion efficiency of the system increased. The hybrid system’s cumulative output power increased by 19% from 8.78 to 10.84 W, compared to the simple PV system. Also, the efficiency of the hybrid PV-TEG system increased from 11.6 to 14%, which is an increase of 17% overall. The results of this research could provide consideration for designing commercial hybrid PV-TEG systems.

Thermogalvanic and Thermocapacitive Behavior of Superabsorbent Hydrogels for Combined Low-Temperature Thermal Energy Conversion and Harvesting

Around two-thirds of the energy generated by the society is lost as waste heat. Thermogalvanic cells can continuously convert thermal energy directly into electrical energy. Conversely, thermocapacitors can convert and store thermal energy as thermocapacitance. Here, we report two superabsorbent monolithic polymer hydrogel matrices designed through vessel-templated synthesis, which act as soft host materials for extremely high concentrations of redox-active ions, namely, [Fe(CN)6]3–/4– and Fe2+/3+. These highly charged superabsorbent hydrogels were found to improve both electrocatalysis and ohmic resistance of the hosted redox couples, preventing electrolyte leakage, and enable the ability to perform both thermogalvanic conversion and thermocapacitive storage. An unoptimized maximum thermogalvanic power density was observed at ca. 95 mW m–2 (ΔT of 20 K), on par with other reported gelled systems. An optimized thermocapacitance density of ca. 220 F cm–2 was achieved, which is 15-fold higher than the highest previously reported. These novel systems therefore present new possibilities in both the harvesting and storage of low-grade waste thermal energy.

Experimental Investigation of unused heat recovery using ORC cycle in a passenger car

The internal combustion engines of automobiles generally operate around 25-40 percent conversion efficiency. The productivity of the engine can be improved by using the dissipated waste heat by the automobile cooling jacket. An ORC (Organic Rankine Cycle) unit can be installed to recover the waste heat in engine cooling jacket of a passenger car. The installation of this unit shall reduce part load from the engine by reducing the load acting directly on the alternator. The System shall increase the overall efficiency and also improves the fuel economy by using the waste thermal energy. A Thermodynamic cycle analysis and prototype fabrication of model has been considered for the experimental evaluation of the efficiency and effectiveness of ORC system. The cycle is considered using an Automotive Air-conditioning Scroll compressor as the turbine expander and also as an feed pump. Low temperature heat source from a heater is considered for the heat source in the boiler setup. The ORC turbine shall be coupled with and Electric Generator and then to the battery for recharging. The whole Setup is considered for mass production of ORC Units for cheaper price and light weight. Owing to the fact that this setup is a prototype the efficiency of the cycle can be improved further in order to careful adjustment of the critical parameters such as pressure, temperature, flow rate of the refrigerant of the thermodynamic cycle and the flow rate of the coolant according to the actual performance of the vehicle.

Seawater Desalination via Waste Heat Recovery from Generator of Wind Turbines: How Economical Is It to Use a Hybrid HDH-RO Unit?

Over recent years, the concept of waste heat recovery from the generators of wind turbines for driving a thermal-driven desalination system was introduced, and its advantages were highlighted. However, any selection of a bottoming thermal-driven desalination system among different existing technologies should be taken under consideration before making an ultimate recommendation. Unfortunately, no comprehensive comparison is available in the literature to compare the performance as well as the cost aspects of using the waste thermal energy of the generator of a wind turbine for desalinating seawater, comparing them with those of a layout where the power of the wind turbine is directly supplied to a mechanically driven desalination system for the same amount of drinkable water production. This study aims at analyzing the economic aspects of waste heat recovery from the generators of wind turbines for seawater desalination via the humidification-dehumidification (HDH) approach, versus the reverse osmosis (RO) unit. For this purpose, a closed-air water-heater HDH unit, directly coupled with a RO unit (called a hybrid HDH-RO unit) is employed, in which thermal energy is provided by the heat dissipating from the generator of the wind turbine while its power is supplied directly by the wind turbine. The energetic and exergetic performance, along with the cost aspects of a hybrid HDH-RO unit driven by the wind turbine, are compared with those of a solo RO unit. The results of the study were extended for six different types of wind turbines, and we concluded that the unit cost associated with the freshwater produced by the waste heat recovery approach is astronomically higher than that of the solo RO system for all wind turbine models, and hence is not practically feasible. It was found that more power can be recovered from the discarded brine from the solo RO unit than the hybrid HDH-RO unit. In addition, the solo RO desalination system, working directly with the power of the wind turbine, has a less complex configuration, and hence its investment cost rate is significantly lower than that needed for setting up an HDH-RO unit. At high wind speeds, however, the cost penalty associated with the freshwater produced by the HDH-RO unit decreases, but it is still huge. Among all screened wind turbines, the GW-136/4.8 is most appealing in terms of greater power generation, but its investment cost rate is the highest among all models due to its high rated power value. However, the freshwater unit cost of the GW-136/4.8 is significantly lower than the values obtained for other models. Finally, the two locations of Manjil and Zabol are selected as a benchmark and the results of the simulation are extended for these locations.

Comparative Study of Thermal Waste Recovery Systems Deployed in Three Different Chemical Units

Waste thermal energy is enough amount of energy that is rejected to the atmosphere in the form of flue gases, streams of air, and liquid rejected from industries. It arises from the equipment, less efficient processes, and limitations due to the laws of thermodynamics on operations. It is obvious that it is not possible to regenerate all waste energy but most of the time some waste heat can be used to achieve useful purposes. Waste heat recovery is the most important key to carry out most of the research areas. The major areas of research and it is necessary to make the process more energy-efficient in chemical industries. To save energy Heat Exchanger Network’s synthesis (HEN) is essential. They are designed to reach energy targets. HEN design is the thermal integration between cold and hot utilities by pinch analysis at minimum temperature difference. HENs are important for utility saving because it helps in recovering heat from hot streams to others which reduces the utility consumption and requirement. The heat exchangers design with simplified models for different industries using pinch technology by which most thermal recovery is obtained and then some HEN network is required for a particular targeted area. In this research improvements in energy recovery systems and HENs, synthesis helps in capital savings and pollutant emission can also be reduced.

Modeling of thermal energy sharing in integrated energy communities with micro-thermal networks

This investigation focuses on the potential of harvesting heat rejected from the cooling and refrigeration systems of buildings with high year-round cooling and refrigeration demand (e.g., ice arenas and grocery stores) and using it to heat other nearby buildings. Integrating a small group of buildings with diverse thermal demands via a low-temperature micro-thermal network effectively allows wasted thermal energy to be harvested and shared among the buildings with minimal thermal and mechanical losses. This paper presents a reduced model that shows the potential of harvesting thermal energy between buildings by calculating the amount of heat energy simultaneously shared between the connected buildings on a five-minute time resolution. The model also evaluates changes in greenhouse gas (GHG) emissions and the amount of energy that is still required from supplemental heating sources after harvesting relative to conventional stand-alone building systems. This study shows that changing the operating temperature of the micro-thermal network when primarily sharing between diverse thermal demand buildings has a minor effect on GHG emissions but can have a larger effect on electrical energy consumption. The model is applied using actual utility energy consumption at one of the potential clusters in Ontario, with results showing that approximately 48% of the cluster’s total heating requirements can be covered by instantaneous sharing between buildings, and an additional 12% can be covered by daily short-term thermal storage. This reduced heating demand results in an approximately 74% reduction in total GHG emissions.

Performance optimization of an integrated adsorption-absorption cooling system driven by low-grade thermal energy

• Thermal characteristics of integrated absorption - adsorption systems were studied. • Optimal intermediate pressure and LiBr solution concentration were investigated. • Effect of heating and cooling flow arrangement on system performance was evaluated. • The integrated system produced a greater cooling capacity with a reliable high COP. • The AB-bottom-AD-top system performed better than the AD-bottom-AB-top system. The integrated adsorption-absorption system is a novel technology to convert low-temperature waste thermal energy into useful cooling, which substantially improves energy utilization efficiency and lowers environmental pollution. This novel system incorporates the adsorption cycle into the absorption cycle so that the generation/adsorption pressure can be adjusted to enhance the system performance at low-temperature heat sources. In this paper, the thermal characteristics of the integrated system are theoretically evaluated. The optimization of the key parameters (e.g. cycle time, switching time, intermediate pressure and solution concentration) are conducted to achieve the best system performance. Furthermore, different configurations of the integrated system and the effect of the heating and cooling flow arrangements on the system performance are also investigated. The results showed that the coefficient of performance of the proposed system was as high as 0.4 at a heat source temperature of 50 °C. As the heat source temperature increased from 50 to 85 °C, an optimal intermediate (generation/adsorption) pressure varied gently from 2.36 to 2.16 kPa while the optimal solution concentration increased from 52.4 to 65% to achieve the best system coefficient of performance. The results also showed that the maximum specific cooling power is 193.7 W/kg when the heating and cooling water flow arrangement are both in parallel. In contrast, the lowest specific cooling power is 157.9 W/kg for both heating and cooling water flow arrangements in series. When compared the two different configurations, the cooling capacity and coefficient of performance of the configuration with absorption-cycle as the bottom cycle and adsorption-cycle as the top cycle were about 5 and 15% higher, respectively than those of the configuration with adsorption-cycle as the bottom cycle and absorption-cycle as the top cycle.

Thermoelectric Energy Harvesting from Single-Walled Carbon Nanotube Alkali-Activated Nanocomposites Produced from Industrial Waste Materials.

A waste-originated one-part alkali-activated nanocomposite is introduced herein as a novel thermoelectric material. For this purpose, single-walled carbon nanotubes (SWCNTs) were utilized as nanoinclusions to create an electrically conductive network within the investigated alkali-activated construction material. Thermoelectric and microstructure characteristics of SWCNT-alkali-activated nanocomposites were assessed after 28 days. Nanocomposites with 1.0 wt.% SWCNTs exhibited a multifunctional behavior, a combination of structural load-bearing, electrical conductivity, and thermoelectric response. These nanocomposites (1.0 wt.%) achieved the highest thermoelectric performance in terms of power factor (PF), compared to the lower SWCNTs’ incorporations, namely 0.1 and 0.5 wt.%. The measured electrical conductivity (σ) and Seebeck coefficient (S) were 1660 S·m−1 and 15.8 µV·K−1, respectively, which led to a power factor of 0.414 μW·m−1·K−2. Consequently, they have been utilized as the building block of a thermoelectric generator (TEG) device, which demonstrated a maximum power output (Pout) of 0.695 µW, with a power density (PD) of 372 nW·m−2, upon exposure to a temperature gradient of 60 K. The presented SWCNT-alkali-activated nanocomposites could establish the pathway towards waste thermal energy harvesting and future sustainable civil engineering structures.

Strain-induced electronic, stability and enhancement of thermoelectric performance of 2D Si2C3 monolayer: An emerging material for renewable energy

Strain engineering is a highly efficient technique to improve the electronic, mechanical, and thermoelectric characteristics of two-dimensional materials. Inspired by a recent study on the most stable structures of the silicon-carbon monolayer [Li. P. et al., Nanoscale, 2014, 11685], we have carried out systematic investigations for 2D Si2C3 monolayer (ML) on electronic, dynamical, mechanical, thermal stability and thermoelectric properties by applying the biaxial tensile strain using density functional theory combined with semi-classical Boltzmann transport theory. The calculated results demonstrate that biaxial tensile strain can change the position of the conduction band minimum (CBM) or valence band maximum (VBM), which produce significant effects in the thermometric parameters. The enhanced power factor strongly suggests that biaxial tensile strain is a compelling way to improve the thermoelectric (TE) performance of 2D Si2C3 ML, making it an ideal candidate for thermoelectric applications. Such strain sensitive thermoelectric response in 2D Si2C3 ML couldopen pathways for a wide range of applications in the emerging renewable energy such as thermoelectric power generation and waste thermal energy harvesting.

Parametric Study on the Performance of Combined Power Plant of Steam and Gas Turbines

Abstract This paper deals with aspects of the combined power and power (CPP) plants. Such plants consist of two major parts: the steam turbine and gas turbine plants. This study investigates the efficiency of CPP under the effect of several factors. CPP plants including an open cycle gas turbine and a bottoming cycle steam turbine can achieve the highest thermal efficiency obtained with turbomachinery up to date. In this cycle, the anticipated waste thermal energy of the exhaust of gas turbine is used to generate high-pressure steam to empower the steam turbine in the steam cycle. By systematically varying the main design parameters, their influence on the CPP plant can be revealed. A comprehensive parametric study was conducted to measure the influence of the main parameter of the gas and steam cycles on the performance of CPP. The results exhibit that the overall plant thermal efficiency is significantly greater than that of either of the two turbines. Due to the high thermal efficiency, a significant reduction in the greenhouse effect can be achieved. It is found that the regenerative steam cycle will reduce the overall efficiency of the combined cycle. On the other hand, using the reheat steam cycle in the CPP plant will lead to an increase in both the thermal efficiency of the plant and the dryness factor of steam at the exit of the steam turbine.

Latent Heat Phase Change Heat Transfer of a Nanoliquid with Nano–Encapsulated Phase Change Materials in a Wavy-Wall Enclosure with an Active Rotating Cylinder

A Nano-Encapsulated Phase-Change Material (NEPCM) suspension is made of nanoparticles containing a Phase Change Material in their core and dispersed in a fluid. These particles can contribute to thermal energy storage and heat transfer by their latent heat of phase change as moving with the host fluid. Thus, such novel nanoliquids are promising for applications in waste heat recovery and thermal energy storage systems. In the present research, the mixed convection of NEPCM suspensions was addressed in a wavy wall cavity containing a rotating solid cylinder. As the nanoparticles move with the liquid, they undergo a phase change and transfer the latent heat. The phase change of nanoparticles was considered as temperature-dependent heat capacity. The governing equations of mass, momentum, and energy conservation were presented as partial differential equations. Then, the governing equations were converted to a non-dimensional form to generalize the solution, and solved by the finite element method. The influence of control parameters such as volume concentration of nanoparticles, fusion temperature of nanoparticles, Stefan number, wall undulations number, and as well as the cylinder size, angular rotation, and thermal conductivities was addressed on the heat transfer in the enclosure. The wall undulation number induces a remarkable change in the Nusselt number. There are optimum fusion temperatures for nanoparticles, which could maximize the heat transfer rate. The increase of the latent heat of nanoparticles (a decline of Stefan number) boosts the heat transfer advantage of employing the phase change particles.

Applicability of indirect evaporative cooler for energy recovery in hot and humid areas: Comparison with heat recovery wheel

The indirect evaporative cooler (IEC), used as a novel energy recovery component for central air-conditioning (AC) systems, can cool and dehumidify the fresh air by capturing the waste thermal energy of exhaust air. To facilitate its implementation in hot and humid areas, the applicability of the hybrid AC system integrated with IEC needs to be addressed. This study quantitatively evaluated the cooling and energy-saving potentials of an IEC for energy recovery and compared it to a traditional hybrid AC system with a heat recovery wheel (HRW). On-site performance measurements were conducted in a wet market located in Hong Kong, where two air-handling units were integrated with a newly-designed IEC prototype and a commercial HRW respectively. Simulation models of the two hybrid AC systems were established based on TRNSYS platform by incorporating the numerical model of IEC and HRW respectively. The field-measurement data was used to validate the component models, and further calibrate the system models. To compare the regional adaptability of the two systems, annual simulations were conducted among 8 selected cities in southern China. Results showed that the total cooling capacities of IEC and HRW are closely related to local ambient relative humidity. Compared with the baseline AC system, the AC + IEC provides an annual energy saving intensity of 64.2–73.4 MJ/m2 for cities with hot and moderate humid climates, which is more competitive than the AC + HRW (45.5–51.8 MJ/m2). The annual energy saving ratios of the two types of hybrid systems range from 14.4% to 26.4%.