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This paper investigated the cooling performance of a high-efficiency dew-point evaporative cooler with optimised air and water flow arrangement using the combined experimental and numerical simulation method. The experimental results showed that the wet-bulb efficiency of the dew-point evaporative cooler was increased by 29.3% and COP was increased by 34.6%, compared to the existing commercial dew point air cooler of the same capacity. An improved two-dimensional, multi-factor engaged numerical model which can scale up and optimize the size and capacity of the cooler was developed. The numerical predictions agreed well with the experimental results, indicating that the cooling rate of the dew-point evaporative cooler is influenced by the dew-point evaporative cooler structure. The cooling efficiency of the dew-point evaporative cooler with corrugated plates is more than 10% higher than with flat plates and the cooling efficiency of the dew-point evaporative cooler with the actual flow arrangement is only 62%–67% that of a dew-point evaporative cooler with an ideal counter-flow arrangement. The cooling efficiency can be improved by increasing the channel length and the air entrance length, and decreasing the channel width and channel gap within a reasonable range. [ABSTRACT FROM AUTHOR]

Swift assessment of evaporative cooling systems has become a necessity in practical engineering applications of this advanced technology. This paper bypasses details of the performance process and pioneers in developing a statistical model based on the multiple polynomial regression (MPR) to predict the performance of a dew point cooling (DPC) system. Thousands of numerical and experimental data are explored and the statistical model is produced. The developed statistical model correlates the performance parameters with the key operational parameters, including the flow and geometric characteristics. The selected operational parameters are, intake air conditions, including temperature, relative humidity and flow rate as well as the working air fraction over the intake air, while cooling capacity, coefficient of performance (COP), pressure drop, dew point and wet-bulb effectiveness are selected as performance parameters. The considered geometric characteristics are channel height, channel interval and number of layers in heat and mass exchanger. The model with different polynomial degrees is assessed by R2, MRE and MSE metrics. The 8th degree polynomial model is selected. The maximum relative error of the cooling capacity, coefficient of performance, pressure drop, dew point and wet-bulb effectiveness are 6.1%, 7.54%, 0.07%, 3.54% and 2.53% respectively. Finally, as examples, the model is used to predict the performance of the DPC system in random operating conditions and in a dry climate i.e. Las Vegas. Model developed in this study would enable the swift prediction of the DPC system. • A multiple polynomial regression model for a dew point cooler is developed. • The statistical model explores lots of numerical and experimental data. • Model is assessed by three metrics and a cross validation. • The average error of outputs by the model is less than 1.22%. [ABSTRACT FROM AUTHOR]

• A statistical model for a novel dehumidification system is developed. • A new application of Gaussian process regression (GPR) is presented. • Validity of the model for any random operating conditions is investigated. • Several applications of the model in performance prediction of the system are presented. Swift performance assessment of dehumidification systems, in design stage and while operation of the system is of substantial importance for commercialization and wide implementation of this technology. This paper presents a novel statistical model, employing Gaussian Process Regression (GPR) to investigate performance of a solar/waste energy driven dehumidification/regeneration cycle with a solid adsorbent bed. The statistical model takes thousands of operating conditions derived from a numerical model to predict the performance of the system. This predictive tool directly correlates the main operating parameters with the performance parameters of the system. The operating parameters considered in this study are: temperature, relative humidity and flow rate of process air, temperature of regeneration air, length of the desiccant bed, solar radiation intensity and operating time, and the selected performance parameters are: moisture extraction efficiency for the dehumidification cycle and moisture removal efficiency for the regeneration cycle. The model is evaluated by three metrics, namely: root mean square error (RSME), mean absolute percentage error (MAPE), and coefficient of determination (R2). The maximum RSME and MAPE for moisture extraction are only 0.045, 0.21%, and for moisture removal efficiencies are 0.082 and 0.39%, respectively, while the R2 value is derived as 0.97. The developed model is used to investigate the impact of four selected operating parameters on system performance. Additionally, the system performance is predicted for randomly generated operating conditions as well as warm and humid climates. The developed GPR model provides a swift and highly accurate predictive tool for design of the dehumidification systems and for commercialization of the investigated dehumidification systems. [ABSTRACT FROM AUTHOR]

• Three CPC-PV cell modules have been established. • Effect of bus-bar location on electrical performance of CPC-PV cells is indicated. • Effect of bus-bar number on the electrical performance of CPC-PV cells is indicated. • The optimal bus-bar location and number for CPC-PV cells are determined. • The electrical efficiency of the optimized CPC-PV is increased from 11.95% to 13.71%. The compound parabolic concentrator photovoltaic (CPC-PV) cell module is composed of two symmetrical mirrors and a crystalline silicon solar cell. In this study, two new CPC-PV cells based on known CPC-PV cell are established by changing the location and number of bus-bar in crystalline silicon solar cell. The effect of different location and number of bus-bar on the electrical performance of CPC-PV cells was investigated. The numerical simulation of three CPC-PV cells is performed using a two-dimensional finite element model. The electrical performance of three CPC-PV cells are compared, and surface voltage distribution, current density and internal current flow of the crystalline silicon solar cell for each CPC-PV cell are analyzed. The results show that compared with the known CPC-PV cell with bus-bar placed on the right side of the crystalline silicon solar cell, the electrical efficiency of the CPC-PV cell when the bus-bar is placed in middle region of the crystalline silicon solar cell is relatively improved by 14.76%. Finally, it is concluded that the bus-bar optimization based on the non-uniform illumination intensity distribution formed by the concentrator will help to improve the electrical performance of the CPC-PV cell. [ABSTRACT FROM AUTHOR]

Effective thermal management of photovoltaic cells is essential for improving its conversion efficiency and increasing its life span. Solar cell temperature and efficiency have an inverse relationship therefore, cooling of solar cells is a critical research objective which numerous researchers have paid attention to. Among the widely adopted thermal management techniques is the use of thermoelectric generators to enhance the performance of photovoltaics. Photovoltaic cells can convert the ultra-violent and visible regions of the solar spectrum into electrical energy directly while thermoelectric modules utilize the infrared region to generate electrical energy. Consequently, the combination of photovoltaic and thermoelectric generators would enable the utilization of a wider solar spectrum. In addition, the combination of both systems has the potential to provide enhanced performance due to the compensating effects of both systems. The waste heat produced from the photovoltaic can be used by the thermoelectric generator to produce additional energy thereby increasing the overall power output and efficiency of the hybrid system. However, the integration of both systems is complex because of their opposing characteristics thus, effective coupling of both systems is essential. This review presents the concepts of photovoltaics and thermoelectric energy conversion, research focus areas in the hybrid systems, applications of such systems, discussion of the most recent research accomplishments and recommendations for future research. All the essential elements and research areas in hybrid photovoltaic/thermoelectric generator are discussed in detailed therefore, this review would serve as a valuable reference literature. • A detailed review of photovoltaic thermal management is presented. • The role of thermoelectric generator in hybrid photovoltaic enhancement is explained. • Research focus areas in hybrid photovoltaic/thermoelectric generator are discussed. • Recommendations for future research on hybrid PV/TEG are presented. [ABSTRACT FROM AUTHOR]

For a solar collector with a heat pipe, the tilt angle is an important factor which has a direct impact on the orientation (surface azimuth angle) and affects the amount of solar radiation reaching the surface of the collector. The performance of the microchannel heat pipe (MCHP), as a highly efficient heat transfer device, can be influenced by gravity and two-phase flow pattern. The relationship between the performance of the MCHP and the tilt angles is nonlinear. In this paper, the effect of the evaporator temperature and tilt angle on the thermal performance of the MCHP, especially the temperature distribution along the heat pipe wall and the effective thermal conductivity, will be investigated. An experimental study with different evaporator temperatures and tilt angles is carried out. Additionally, thermal characteristics of the MCHP have been simulated and verified by the experimental results. In addition, the temperature distribution along the MCHP and the effective thermal conductivity for different working conditions have been performed. These results would provide many references for the solar collector with MCHP system design, optimization, and installation. [ABSTRACT FROM AUTHOR]

• A low-concentration PV module with different finger numbers is established. • The optimal number of fingers is determined. • Three low-concentration PV modules with different fingers spacing are established. • The optimal finger spacing is determined. • The influences of shading losses, finger resistance and lateral spreading resistance are analysed. Compared with conventional silicon solar cell, concentrating photovoltaic cell has a higher incident illumination intensity and non-uniform illumination intensity distribution. There is a close relationship between the illumination intensity and the resistance and shading losses of front metal fingers. In this paper, according to the non-uniformity of the illumination distribution formed by the concentrator, the effects of different finger numbers and spacing on the performance of low-concentrating photovoltaic cells were studied. First, low-concentrating photovoltaic cell modules with different finger numbers and spacing were established, and efficiency of these modules was compared to determine the optimal finger numbers and spacing of the front metal fingers. Then, effects of the shading losses, finger resistance and lateral spreading resistance on the performance of the low-concentrating photovoltaic cell were analyzed. Results show that for the specific illumination intensity distribution of the low-concentrating photovoltaic cell when the numbers and spacing of the front metal fingers are optimized, efficiency of the low-concentrating photovoltaic cell can be increased from 13.805% to 13.837%. Additionally, it can be concluded that the optimization of the number and spacing of the front metal fingers in the crystalline silicon solar cell is an efficient way to improve the electrical performance of the concentrating photovoltaic cell. [ABSTRACT FROM AUTHOR]

• Hybrid photovoltaic-thermoelectric systems with and without heat pipe are studied. • Comparison of the photovoltaic only and hybrid photovoltaic systems is presented. • Influence of concentration ratio, ambient temperature, wind speed is investigated. • Three-dimensional numerical simulation using finite element method is presented. Thermal management of photovoltaic cells is an essential research objective for increasing the conversion efficiency of the photovoltaic. Flat plate heat pipe is a passive cooling device capable of effectively reducing the solar cell temperature. Therefore, this study presents a numerical investigation of a hybrid photovoltaic-thermoelectric system with and without a flat plate heat pipe. A detailed comparative analysis of the electrical performance of the photovoltaic only, photovoltaic-thermoelectric and photovoltaic-thermoelectric-heat pipe systems is performed. The influence of solar concentration ratio, ambient temperature, wind speed and thermoelectric generator cold side temperature on the efficiency and power output of the photovoltaic only and hybrid photovoltaic-thermoelectric systems are studied using COMSOL 5.4 Multiphysics software. A three-dimensional finite element study is carried out and temperature dependent thermoelectric material properties are considered to increase the simulation accuracy. Results show that the photovoltaic-thermoelectric-heat pipe efficiency is 1.47% and 61.01% higher compared to that of the photovoltaic-thermoelectric and photovoltaic only systems respectively at a concentration ratio of 6. In addition, the photovoltaic-thermoelectric-heat pipe is recommended for highly concentrated systems because of its superior performance. Furthermore, the photovoltaic-thermoelectric system is a better alternative to the photovoltaic only system because of its enhanced performance which is second only to that of the photovoltaic-thermoelectric-heat pipe system. Results also show that ineffective cooling of the thermoelectric generator can adversely affect the performance of the hybrid systems. This study will proper valuable information on the feasibility of hybrid photovoltaic-thermoelectric systems with and without heat pipe. Finally, the three-dimensional nature of this study makes it very useful in understanding the actual temperature distribution in the hybrid systems. [ABSTRACT FROM AUTHOR]

• An innovative dew point cooling system was designed, constructed, installed and real live tested in live data centre. • The system can provide continuously stable cooling air and maintain the required temperature and humidity in data centre. • The average COP of 29.7 was achieved during the testing period. • 90 % energy saving can be achieved for data centre cooling. • Suitability, stability and reliability of the system used in data centre environment were proved. This paper presents the development and application of a super performance dew point cooling technology for data centres. The novel super performance dew point cooler showed considerably improved energy saving and carbon reduction for data centre cooling. The innovations of this technology are built upon a series of technological breakthroughs including, a novel hybrid flat/corrugated heat and mass exchanging sheets, an innovative highly water absorptive and diffusive wet-material for the sheets which enable an intermittent water supply with well-tuned water pressure and flow rate, and the optimised fan configurations. Following a list of fundamental research including theoretical, numerical and lab experimental testing of a small scale prototype system, a specialist 100 kW rated data centre dew point cooling system was dedicated designed, constructed, installed and real life tested in an operational live data centre environment, i.e., Maritime Data Centre at Hull (UK) to investigate its dynamic performance, suitability and stability for application in operational data centre environment conditions. During the testing period, the system showed its reliability and capability to remove a tremendous amount of heat dissipated from the IT equipment and maintain an adequate space temperature in the operational live data centre. The dynamic data collection and analysis during the continuous testing and monitoring period showed the average COP of 29.7 with the maximum COP of 48.3. Compared to the existing traditional vapor compression air conditioning system in the data centre, the energy saving using the super performance dew point cooling system is around 90 %. The work presented in this paper include detailed innovation aspects of the technology and the system operation, as well as the established bridging knowledges, methodology and technical procedure for bringing this new technology into real life operation which involve in data centre survey, optimum design and modularization of the specialist cooling system for data centre application, proven system installation, operating method and cooling air management for data centre as well as the assurance of the continuous sufficient cooling supply to the data centre. [ABSTRACT FROM AUTHOR]

In this study, a segmented asymmetrical thermoelectric generator (SASTEG) is numerically investigated to optimize its electrical performance and mechanical reliability under transient and steady state conditions. The thermal and electrical performance of the SASTEG and TEG under transient and steady state heating conditions are studied and compared. A three-dimensional numerical model is developed and solved using finite element method in COMSOL 5.3 Multiphysics software. Temperature dependent thermoelectric material properties are considered, and the elastoplastic behaviour of copper and solder is accounted for in the thermal stress analysis. The initial SASTEG geometry used in this study is subsequently optimized to reduce the maximum von Mises stress developed in its legs while maintaining its enhanced power output. Results obtained show that the optimized SASTEG provided a power output enhancement of 117.11% compared to that of the conventional TEG under rectangular pulsed heat condition. Also, the asymmetrical leg geometry used in the SASTEG n-type leg provided a reduced thermal stress of 39.21% in the lower segment (cold side) compared to the symmetrical leg geometry used in the p-type leg lower segment. This study will provide vital guidance in the design of high-performance TEG with improved mechanical reliability. • A thermoelectric generator with segmented materials and asymmetrical leg is studied. • Rectangular pulsed heating and steady state heating are applied to the TEG. • Geometry optimization is done to reduce thermal stress and enhance power output. • Comparison is made between the new TEG design and conventional TEG design. [ABSTRACT FROM AUTHOR]

Highlights • A segmented annular thermoelectric generator (SATEG) is studied numerically. • The thermoelectric and mechanical performance of SATEG is investigated. • Comparison between SATEG and annular thermoelectric generator (ATEG) is presented. • The effect of thermoelectric geometry on SATEG and ATEG performance is studied. Abstract Annular thermoelectric generators can eliminate the thermal contact resistance formed due to geometry mismatch when flat-plate thermoelectric generators are used with round shaped heat source or heat sink. Therefore, in this study, the numerical simulation of a segmented annular thermoelectric generator (SATEG) is investigated using three-dimensional finite element analysis. The thermoelectric and mechanical performance of the segmented annular thermoelectric generator is studied by considering temperature dependent thermoelectric material properties and elastoplastic behaviour of copper and the welding layer (solder). The influence of segmented pin geometry on the performance of the segmented annular thermoelectric generator is investigated and comparison is made with non-segmented annular thermoelectric generators. COMSOL 5.3 Multiphysics software is used to investigate the effects of heat source temperature, thermoelectric leg length and leg angle on the electrical and mechanical performance of the segmented and non-segmented annular thermoelectric generators. Results show that the segmented annular thermoelectric generator has a greater efficiency compared to the annular thermoelectric generator (ATEG) with Bismuth telluride material when the temperature difference is greater than 100 K. In addition, the efficiency of the SATEG is found to be 21.7% and 82.9% greater than that of the Bismuth telluride ATEG and Skutterudite ATEG respectively at 200 K temperature difference. Finally, the results show that increase in thermoelectric leg length can reduce the thermal stress and electrical performance of the segmented and non-segmented thermoelectric generators. Results obtained from this study would influence the design and optimization of segmented annular thermoelectric generators. [ABSTRACT FROM AUTHOR]

The Rankine Cycle is a thermodynamic process widely applied to power plants such as coal-fired power plants or nuclear reactors. The thermal efficiency of a power plant is largely dependent upon the temperature difference between a heat source and a cold source; an increased temperature difference leads to the significant increase in the thermal efficiency and power generation rate of the power plant. Integrating the dew point cooler, i.e., Maistosenko Cycle system, into the traditional Rankine Cycle is an effective approach to reduce the temperature of the cold source (i.e. condenser), and thus, increase the thermal efficiency and power generation rate of the power plant. The paper presents a close overview of the combined Rankine/Maisotsenko Cycle, concerning with: (1) current development of Rankine Cycle power systems and Maisotsenko Cycle evaporative cooling technologies; (2) existing pre-cooling technologies for the cooling tower; and (3) thermal efficiency of the combined Rankine/Maisotsenko Cycle and its relevant impact factors. It is concluded that the combined Rankine/Maisotsenko Cycle can overcome the limit of the existing similar technologies, has great energy-saving potential and is economically viable. The further research should focus on a number of critical issues which require effective solutions to enable the energy efficient power generation. These include: (1) Optimisation of the combined Rankine/Maistsenko cycle using advanced multi-objective evolutionary optimisation algorithms; (2) Prediction of the future operational performance of the combined Rankine/Maistsenko cycle based power plant using future weather forecast scenarios and associated machine learning algorithms; (3) Analysis of thermal economics performance of the combined cycle using entropy and exergy analytic approach; and (4) Analysis of energy costs of the combined cycle using the exergo-economic and emergoeconomic analytical methods. This benefit also thanks to the recent development of the dew point cooling technology with highly enhanced COP, especially in hot and dry climates. • Current development of Rankine Cycle and Maisotsenko Cycle was investigated. • Combined Rankine/Maistsenko Cycle has a higher thermal efficiency than Rankine Cycle. • Combined Rankine/Maistsenko Cycle is applied to both the dry and wet cooling towers. • Optimisation and performance prediction of the combined cycle are required. • Thermal economics and energy costs of the combined cycle are to be investigated. [ABSTRACT FROM AUTHOR]

Among all available solar technologies, solar-assisted heat pump (SAHP) is the most popular technology for low- and medium-temperature applications, i.e., drying, space heating, and water heating. This paper presents a critical review of the SAHP, leading to identification of the key technological challenges with the current SAHP technology, including (1) poor energy performance at low ambient temperatures; (2) difficulty in coupling solar thermal panels with heat pumps to achieve increased operational time and reduced electrical energy usage; (3) mismatch between heat demand of the building and heat supply of the SAHP system; and (4) lack of multi-functional modelling tool. A recently developed SAHP technology is introduced, which can effectively tackle the challenges with the current SAHPs, thus achieving enhanced solar efficiency, improved heat pump energy efficiency, and fast responsive time to the heat demand of buildings. The future research directions of the SAHP were identified: (1) multi-source heat pump; (2) heat pump defrosting capacity using waste heat and renewable energy; (3) advanced heat storage and exchange unit (HSEU) technology; and (4) advanced machine learning and multi-objective evolutionary optimisation models for performance prediction and optimisation of the SAHP using big datasets. • Current development of Solar Assisted Heat Pump was investigated. • A recently developed SAHP technology was introduced. • The new SAHP has 30% higher COP and 8–15% higher solar efficiency. • The new SAHP achieves the fast response to building's heat demand. • The future research directions of the SAHP were identified. [ABSTRACT FROM AUTHOR]

• Photovoltaic-thermoelectric with flat plate micro-channel heat pipe is presented. • Energy and exergy analysis of the hybrid system is performed. • Comparison is made between the hybrid system and photovoltaic only system. • Feasibility of the hybrid system is demonstrated experimentally. Effective cooling of the photovoltaic can enhance electrical conversion efficiency of a photovoltaic system. The combination of photovoltaic and thermoelectric generator provides unique advantages because of their complementary characteristics. In addition, hybrid photovoltaic-thermoelectric can utilize a wider solar spectrum thereby harvesting more energy from the sun. Heat pipes are passive devices that can transfer heat efficiently over a long distance. Therefore, this study presents an experimental investigation and exergy analysis of a photovoltaic-thermoelectric with flat plate micro-channel heat pipe. The experiment is performed in a laboratory using a solar simulator and water-cooling is used for the thermoelectric generator. The effect of thermoelectric load resistance, micro-channel heat pipe back insulation and solar radiation on the performance of the hybrid system is presented and a comparison with a photovoltaic only system is provided. Results show that the hybrid system provides an enhanced performance compared to the photovoltaic only system and absence of insulation behind the micro-channel heat pipe enhances electrical performance of the hybrid system. Furthermore, results show the feasibility of the hybrid system for generating electricity and small hot water. This study will provide valuable guidance for design of photovoltaic-thermoelectric systems with heat pipe and verifies the feasibility of such systems. [ABSTRACT FROM AUTHOR]

• Comprehensive photovoltaic-thermoelectric model with contact resistance is provided. • Three-dimensional numerical study of photovoltaic-thermoelectric is presented. • Ignoring contact resistances leads to a 7.6% overestimation of power output. • Optimum load resistance in hybrid system is different from that in thermoelectric. A consequence of the integration of photovoltaic module and thermoelectric generator is the presence of thermal contact, which affects the heat transfer in the hybrid system. Thermal and electrical contact are inevitable in a thermoelectric generator and their effects on the performance of the thermoelectric generator can be significant if not properly managed. Therefore, this study presents a comprehensive three-dimensional numerical investigation on the effect of contact resistances on the performance of concentrated photovoltaic-thermoelectric using COMSOL 5.4 Multiphysics software. Four contact resistances are studied including thermoelectric thermal contact resistance, thermoelectric electrical contact resistance, photovoltaic-thermoelectric interface thermal contact resistance and thermoelectric generator-heat sink interface thermal contact resistance. Twelve contact resistance cases are considered, and a comparison study is presented to investigate the most important contact resistance. In addition, a parametric optimization study is performed to investigate the optimum values for thermoelectric leg height, load resistance, concentration ratio and convective heat transfer coefficient. Results show that ignoring all contact resistances in the hybrid system causes an overestimation of overall power output and efficiency by 7.6% and 7.4% respectively using the base values considered in this study. In addition, the thermal contact resistance between the thermoelectric generator and heat sink, and that between the photovoltaic-thermoelectric interface are found to be the most important contact resistances, which should be reduced. Furthermore, results show that the optimum thermoelectric external load resistance in a hybrid system is lower than that of the thermoelectric generator only system. This study will provide valuable guidance on photovoltaic-thermoelectric accurate modelling. [ABSTRACT FROM AUTHOR]