Plate Micro-Fins in Natural Convection: Experimental Study on Thermal Effectiveness and Mass Usage

This is the author accepted manuscript. The final version is available from the publisher.International Conference on Polygeneration 2015 (ICP 2015), Chennai, India, 18-20 February 2015Every year, micro-technologies are gaining more attention among researchers and industries. Although they are already applied for cooling purposes in several installations, the researches on the thermal performance of micro-fins in natural convective conditions are yet limited. The correlations between heat transfer coefficients and geometry have already been investigated. The present study merges the results of an original experimental investigation with the data available in literature, in order to give an overview of the behavior of micro-fins in terms of different heat sink metrics: the fin effectiveness and the mass specific heat transfer coefficient. The introduction of micro-fins is found not to be always beneficial in terms of heat transfer, although always positive in terms of the material usage and can be considered advantageous in those applications that requires a minimized weight of the heat sinks.The financial support provided by the EPSRC-DST through the BioCPV project is duly acknowledged

Experimental comparison of micro-scaled plate-fins and pin-fins under natural convection

This is the final version of the article. Available from the publisher via the DOI in this record.The present work analyses, for the first time, the heat transfer from pin micro-fins. The scope of the present paper is comparing thermal performance of plate micro-fin and pin micro-fin arrays under natural convection conditions in air. Two fin geometries are considered: plate and pin fin arrays with the same thermal exchanging surface are tested. The investigation shows that the pin micro-fins can improve the thermal performance compared to plate micro-fin arrays. Indeed, pin micro-fins are found to have higher heat transfer coefficients and lower thermal resistances, as well as a better material usage. This makes pin micro-fins able to achieve both thermal enhancement and weight reduction. The radiative heat transfer is calculated: a new model to determine the radiative view factors of pin fins is proposed and is used in the analysis. The effect of the orientation is considered as well.The financial support provided by the EPSRC-DST through the BioCPV project (Ref No: EP/J000345/1) is duly acknowledge

Plate micro-fins in natural convection: an opportunity for passive concentrating photovoltaic cooling

This is the final version of the article. Available from Elsevier via the DOI in this record.70th Conference of the Italian Thermal Machines Engineering Association, ATI2015The raise in temperature is a non-negligible issue for concentrating photovoltaics (CPV), where the sunlight is concentrated up to thousands of times and a large amount of heat is collected on the solar cells. Micro-fins have been identified as one of the most promising solution for CPV cooling: despite its potentials, the number of publications on this subject is still limited. The present paper resumes the state-of-the-art of the research on micro-fins, in order to identify the most convenient fin geometry for CPV applications. The results of the investigation conducted in this work show that, compared to a conventional heat sink, micro-fins can improve the thermal performance and, at the same time, lower the weight of a system. For this reason, they are particularly beneficial for tracked systems, such as CPV, where a reduced weight means a reduced load for the tracker. The heat transfer coefficients measured through an experimental setup are used to predict the performance of a micro-finned CPV system in natural convection: an optimized fin array is found able to enhance the mass specific power up to 50% compared to an unfinned surface.This work was financially supported by the EPSRC-DST funded BioCPV project (EP/J000345/1)

Optimization of finned solar photovoltaic phase change material (finned pv pcm) system

This is the final version. Available on open access from the publisher via the DOI in this recordHeat generation during the operation of the photovoltaic (PV) cell raises its temperature and results in reduced electrical output. The heat produced in the process can be removed by attaching phase change material (PCM) at the back of the PV panel which can contain the PV temperature substantially and increase its efficiency. Fins can be used inside the PCM container to enhance the heat transfer. In literature, it is observed that as soon as PCM is melted completely, the heat extraction rate of PCM reduces which again leads to increase in PV temperature. However, the study carrying out the optimization of Finned-PV-PCM system to keep PV temperature low during operation for different solar irradiance levels is not available in literature. Thus, in the current study, the most suitable depth of PCM container is calculated for different solar irradiance levels. In addition, how it is affected with spacing between successive fins, fin length and fin thickness has been studied. The best fin dimensions are also calculated. The results show that the most suitable depth of PCM container is 2.8 cm for ∑I T = 3 kWh/m 2 /day and 4.6 cm for ∑I T = 5 kWh/m 2 /day for the chosen parameters. The best spacing between successive fins (to keep PV temperature low) is 25 cm, best fin thickness is 2 mm and best fin length is the one when it touches the bottom of the container. PV, PV-PCM and Finned-PV-PCM systems are also compared. For PV-PCM system (without fins), the most suitable depth of PCM container is 2.3 cm for ∑I T = 3 kWh/m 2 /day and 3.9 cm for ∑I T = 5 kWh/m 2 /day.The authors gratefully acknowledge the financial support from EPSRC-DST funded Reliable and Efficient System for Community Energy Solution - RESCUES project (EP/K03619X/1

Numerical investigation of micro-channel based active module cooling for solar CPV system

PublishedConference Proceeding4th International Conference on Advances in Energy Research 2013, ICAER 2013Concentrating photovoltaic (CPV) technology is one of the fastest growing solar energy technologies achieving higher electrical conversion efficiencies. The increase in temperature of solar CPV cell significantly reduces the performance; the efficiency of a CPV system can be improved by introducing effective thermal management or cooling system. This paper presents the design and numerical analysis of a heat sink based on micro-channels for efficient cooling of a commercial high concentration photovoltaic (HCPV) cell. A combinatory model of an array of micro-channels enclosed in a wide parallel flow channel design is developed. The optimized geometry of the micro-channel heat sink was found by using commercial CFD software ANSYS 13. Based on numerical simulations, it is found that the optimum configuration of micro-channel with 0.5mm width and aspect ratio of 8. The micro-channels provided high heat transfer over heat generations spots and parallel flow channels resulted in lower pressure drop. The temperature rise across the micro-channel is estimated as10K in CPV module of 120 × 120 mm2 and with a pressure drop of 8.5 kPa along a single channel with six such channels in each modules at a flow rate of 0.105 liter/s. © 2014 The Authors

Optimization of fins fitted phase change material equipped solar photovoltaic under various working circumstances

This is the final version. Available on open access from Elsevier via the DOI in this recordData availability: in support of open access research, all underlying article materials (such as data, samples or models) can be accessed upon request via email to the corresponding author.The present work aims at the optimization of fins fitted phase change material equipped photovoltaic system under different working circumstances for proper power enhancement. Setup has been modelled and the best deepness of fins fitted phase change material enclosure has been computed for a range of daily collective solar flux at photovoltaic panel surface, wind pace, wind azimuth, surroundings temperature, melting point, successive fins distance, fins deepness and fins width in order to analyse the influence of working circumstances. It is shown that the change in wind pace from 0.2 m/s to 6 m/s results in reduction of best deepness of phase change material enclosure from 5.2 cm to 3.7 cm, 5.6 cm to 4.0 cm, 5.8 cm to 4.2 cm, 5.9 cm to 4.3 cm and 5.9 cm to 4.3 cm for successive fins distance of 1 m, 1/2 m, 1/3 m, 1/4 m and 1/5 m respectively for daily collective solar flux at photovoltaic panel as 5000Wh/m2. The change in wind azimuth from 0° to 75° results in increment in the best deepness of enclosure from 3.9 cm to 4.8 cm, 4.3 cm to 5.2 cm, 4.5 cm to 5.4 cm, 4.6 cm to 5.5 cm and 4.6 cm to 5.5 cm for respective fins distances. The power production is increased from 125 W/m2 to 137 W/m2, 140 W/m2, 142 W/m2, 143 W/m2 and 143 W/m2 with fins width of 0 mm, 0.5 mm, 1 mm, 2 mm and 4 mm respectively.Engineering and Physical Sciences Research Council (EPSRC

Review of high concentration photovoltaic thermal hybrid systems for highly efficient energy cogeneration

This is the final version.Available on open access from Elsevier via the DOI in this recordConcentrated photovoltaic/thermal hybrid systems are a combination of concentrated photovoltaics and photovoltaic/thermal hybrid systems which capture waste heat for later application. Higher concentrations lead to higher energy fluxes over smaller areas which is beneficial for several reasons. Firstly, less photovoltaic material is required, instead using relatively cheap optics. This allows more efficient types of PV material to be used effectively. Secondly, the concentrated heat flux easily allows for a high outlet temperature which in turn increases the applicability. Point focused systems have experimentally achieved cogeneration efficiencies of 86.47% (excluding system losses) and concentrations of over 1000 suns, but the technology still faces challenges. The design of the cooling system must be optimised to maximise both electrical and thermal efficiency. Furthermore, the optics and cell interconnections must mitigate the effects a non-uniform focal image for high electrical efficiencies. These challenges must be faced while minimising the thermal stresses the system undergoes to ensure the system has a substantial lifetime. This review provides an in depth understanding of the challenges and function of point focused concentrated photovoltaic/thermal systems. From the literature, it is clear more focus should be put on microchannel/impinging jet hybrid cooling systems for use in dense array concentrated photovoltaic/thermal systems. More physical experimentation is needed, especially full model systems which include the output image of the optics, along with consideration to alternative cooling fluids (particularly nanofluids).Engineering and Physical Sciences Research Council (EPSRC

Optical Losses and Durability of 4-Domed Optic for Concentrator Photovoltaics

This is the author accepted manuscript.The use of optical elements to focus light onto a smaller area of semiconductor material can enhance the cost effectiveness and electrical performance. Enabling ultrahigh concentration ratios for photovoltaic systems requires an optic bonded directly to the solar cell to further concentrate and homogenise the illumination, as well as to improve the acceptance angle. For many optical materials manufacture flaws are common, and difficult to prevent. An estimation of the effective external quantum efficiency of the receiver based on the material’s transmissivity tells us the effect of added absorptivity from manufacture defects. Evaluating the module under a solar simulator under various angles yields information on how scattered light changes the optic’s concentration ability. This study suggests sapphire has higher optical losses due to its higher refractive index compared to slygard184. Thus, the need for a higher refractive index material must be considered carefully and matched with anti-reflective coatings if needed. The effective concentration of slygard-184 notably suffers when flaws are present, dropping up to 48.2%. Further, the optimum angle is difficult to predict. Minor flaws could be deemed acceptable in performance when high acceptance angles are not the primary design requirement.Engineering and Physical Sciences Research Council (EPSRC