3D Computational Analysis of Thermal and Hydraulic Performance of Louvered Fin Heat Exchanger With Variable Louver Angle and Louver Pitch

In the present study, 3-D numerical simulations on heat and fluid flow characteristics of double-row multi-louvered fins heat exchanger are carried out. The heat transfer improvement and the corresponding pressure drop amounts were investigated depending on louver angles in the range of 20° ≤θ≤ 30°, louver pitches of Lp = 2,7mm, 3,5mm and 3,8mm and frontal velocities of Uin between 1.22 m/s and 3 m/s. The results are reported in terms of Colburn j-factor, Fanning friction factor f and area goodness factor j/f based on louver angle, louver pitch and Reynolds number. To understand local behavior of flow around louvered fins and heat exchanger tubes, flow visualization results of velocity vectors and stream-lines with temperature counters are presented. It is investigated that increasing louver angle enhances convective heat transfer while hydraulic performance decreases due to increased pressure drop. The flow noticeably behaves louver directed for all louver angles The flow can easily travel between different fins. This case study has been done to design and manufacture an industrial louver fin heat exchanger.

Computational Analysis of Airfoil Merging and its Effect on Performance of Lift Based Vertical Axis Wind Turbine

In regions of low wind speed, overcoming the starting torque of a Vertical Axis Wind Turbine (VAWT) becomes a challenge aspect. In order to overcome this adversity, careful selection of airfoils for the turbine blades becomes a priority. This paper tries to address the issue utilizing an approach wherein by observing the effect of merging two airfoils. Two airfoils which are of varying camber and thickness are merged and their aerodynamic characteristics are evaluated using the software XFOIL 6.96. For a variation in angle of attack from 0 to 90°, aerodynamic analysis is done in order to observe the behavior of one quarter of the entire VAWT cycle. An objective function is developed so as to observe the maximum possible torque generated by these airfoils at Reynolds number varying from 15,000–120,000. Due to change in the value of CL observed at Low Reynolds Number using commercial CFD softwares, multiple objective functions are utilized to observe the behavior over a range of Reynolds number. An experimental co-relation between the cut-in velocity and the lift-coefficient of the airfoils is developed in order to predict the cut-in velocity of the interpolated airfoils. The airfoils used for this paper are NACA 0012, NACA 0018, FX 66 S196, Clark Y (smooth), PT 40, SD 7032, A 18, SD 7080, SG 6043 and SG 6040.

Thermal Analysis of Elemental Sulfur in a Shell-and-Tube Configuration for Thermal Energy Storage Applications

Currently, concentrated solar power (CSP) plants utilize thermal energy storage (TES) in order to store excess energy so that it can later be dispatched during periods of intermittency or during times of high energy demand. Elemental sulfur is a promising candidate storage fluid for high temperature TES systems due to its high thermal mass, moderate vapor pressure, high thermal stability, and low cost. The objective of this paper is to investigate the behavior of encapsulated sulfur in a shell and tube configuration. An experimentally validated, transient, two-dimensional numerical model of the shell and tube TES system is presented. Initial results from both experimental and numerical analysis show high heat transfer performance of sulfur. The numerical model is then used to analyze the dynamic response of the elemental sulfur based TES system for multiple charging and discharging cycles. A sensitivity analysis is performed to analyze the effect of geometry (system length), cutoff temperature, and heat transfer fluid on the overall utilization of energy stored within this system. Overall, this paper demonstrates a systematic parametric study of a novel low cost, high performance TES system based on elemental sulfur as the storage fluid that can be utilized for different high temperature applications.

Integrated Process for Textile Cotton Waste (TCW) Valorization: Waste-to-Energy and Wastewater Decontamination

The increasing of world population, industrialization and global consuming, existing market products existed in the along with diversification of raw materials, are responsible for an exponential increase of wastes. This scenario represents loss of resources and ultimately causes air, soils and water pollution. Therefore, proper waste management is currently one of the major challenges faced by modern societies. Textile industries represents, in Portugal, almost 10% of total productive transforming sector and 19% of total employments in the sector composed by almost 7.000 companies. One of the main environmental problems of textile industries is the production of significant quantities of wastes from its different processing steps. According to the Portuguese Institute of Statistics (INE) these industries produce almost 500.000 tons of wastes each year, with the textile cotton waste (TCW) being the most expressive. It was estimated that 4.000 tons of TCW are produced each year in Portugal. In this work an integrated TCW valorisation procedure was evaluated, firstly by its thermal and energetic valorisation with slow pyrolysis followed by the utilization of biochar by-product, in lead and chromium synthetic wastewater decontamination. Pyrolysis experiments were conducted in a small scale rotating pyrolysis reactor with 0.1 m3 of total capacity. Results of pyrolysis experiments showed the formation of 0,241 m3 of biogas for each kilogram of TCW. Results also demonstrated that the biogas is mostly composed by hydrogen (22%), methane (14 %), carbon monoxide (20%) and carbon dioxide (12%), which represents a total high calorific value of 12.3 MJ/Nm3. Regarding biochar, results of elemental analysis demonstrated a high percentage of carbon driving its use as low cost adsorbent. Adsorption experiments were conducted with lead and chromium synthetic wastewaters (25, 50 and 100 mg L−1) in batch vessels with controlled pH. It was evaluated the behaviour of adsorption capacity and removal rate of each metal during 120 minutes of contact time using 5, 10 and 50 g L−1 of adsorbent dosage. Results indicated high affinity of adsorbent with each tested metal with 78% of removal rate in chromium and 95% in lead experiments. This suggests that biochar from TCW pyrolysis may be appropriated to wastewaters treatment, with high contents of heavy metals and it can be an effective alternative to activated carbon.

Energy Consumption Modeling of a Heat Pump System for Combined Space Conditioning and Residential Water Heating in a Typical Household in Quito, Ecuador

This research develops a detailed model for a Water to Water Heat Pump Water Heater (HPWH), operating for heating and cooling simultaneously, using two water storage tanks as thermal deposits. The primary function of the system is to produce useful heat for domestic hot water services according to the thermal requirements for an average household (two adults and one child) in the city of Quito, Ecuador. The purpose of the project is to analyze the technical and economic feasibility of implementing thermal storage and heat pump technology to provide efficient thermal services and reduce energy consumption; as well as environmental impacts associated with conventional systems for residential water heating. An energy simulation using TRNSYS 17 is carried to evaluate model operation for one year. The purpose of the simulation is to assess and quantifies the performance, energy consumption and potential savings of integrating heat pump systems with thermal energy storage technology, as well as determines the main parameter affecting the efficiency of the system. Finally, a comparative analysis based on annual energy consumption for different ways to produce hot water is conducted. Five alternatives were examined: (1) electric storage water heater; (2) gas fired water heater; (3) solar water heater; (4) air source heat pump water heater; and (5) a heat pump water heater integrated with thermal storage.

Performance Evaluation of an Asymmetric Hybrid Solar Collector: Effect of Nanofluids on the Electrical and Thermal Energy Production

The scope of this work is the analysis of the electrical and thermal performance of an asymmetric hybrid solar collector PVT and the prospect of the installation of a system consisting of these collectors in the Mediterranean region. For the purpose of this work, the Solarus V11 PVT collector (readily available in our laboratory) was chosen and numerically modeled. The main asset of this collector is its asymmetric reflector that consists of a circular and a parabolic part leading to a maximum thermal energy production even in winter as the solar radiation is concentrated in the edge of the reflector rather than in the center of it. Using a software developed in Matlab, the calculated data are presented for both thermal and electrical energy and they are compared with the hot water and electrical energy requirements (per month) around the Mediterranean territory. Furthermore, a parametric study is conducted in order to investigate the effect of the mass flow rate and the PVT array configuration on the thermal and electrical production, as well as the efficiency of the solar cells of the system. Moreover, in order to increase the PV cell efficiency, nanofluids, i.e. mixtures of nanometer size particles well-dispersed in a base fluid, are proposed as heat transfer fluids and the analysis for the performance evaluation is conducted for different nanoparticle loadings.

Design and Construction of a Heated Garden System Utilizing Steam Condensate From an On Site Boiler

Municipal District Heating Services and Combined Heat and Power (CHP) systems can produce waste heat in the form of steam condensate and hot water. The authors have demonstrated (IMECE2014-39066) the potential of open field heating of green roofs to reduce thermal pollution, save potable water, and while increasing plant growth. Subsequent research in both Iceland and New York City using similar systems has resulted in the growth of out of region plants. The latest plant growth results are detailed. The latest research has indicated additional potential impediments, including the need for an additional CHP system pump. A thorough structural analysis on existing older roofs is necessary to avoid an overstressed roof. Substantial UV shielding of the plastic piping and upgrading of the pipes from braided PVC to PEX(a) was also needed. The details of selecting an appropriate heat exchanger were analyzed for a specific building and associated construction details are provided.

Thermal Performance of Parabolic Trough Collector for Cooling Applications in Residential Buildings in UAE

This paper addresses the potential of integrating Parabolic Trough Collectors (PTC) with a double-effect absorption chiller for the purpose of space cooling in residential buildings. The proposed model was designed such to provide a continuous cooling while in the absence of sun, the bio-mass heater was used as an auxiliary heating source. In this study, the thermal performance was investigated and a feasibility study was conducted in order to assess the system’s economic and environmental impacts. The obtained model was implemented on a case study represented by a four-floored residential building based in Dubai with a net cooling load requirement of 366 kW. The obtained results from the numerical simulation were analyzed to identify the optimum configuration in terms of feasibility and potential savings. It was found that a hybrid system with 40% solar contribution is the optimum solution compared to other alternatives. The proposed system achieved Annual Energy Consumption savings (AEC) of about 556061 kWh and a reduction by 69% in the annual operating costs. Moreover; the system reduced the Carbon-dioxide emissions by 344 tons/year. The payback period of the proposed system was found to be 2.42 years only.

Numerical Study of Thermochemical Storage Using Ca(OH)2/CaO: High Temperature Applications

Thermal energy storage by reversible gas-solid reaction has been selected as a thermochemical energy storage system. Simulations are conducted to investigate the dehydration of Ca(OH)2 and the hydration of CaO for thermal energy storage and retrieval, respectively. The rectangular packed bed is heated indirectly by air used as a heat transfer fluid (HTF) while the steam is transferred through the upper side of the bed. Transient mass transport and heat transfer equations coupled with chemical kinetics equations for a two dimensional geometry have been solved using finite element method. Numerical results have been validated by comparing against results of previous measurements and simulations. The effect of geometrical and operational parameters including the material properties on overall storage and retrieval process has been investigated. The co-current and counter-current flow arrangements for steam and heat transfer fluid have been considered.

Numerical Analysis of Geothermal Heat Exchangers to be Implemented in a Geothermal-Solar Hybrid Power Plant for Electricity Production in Mexico

The Mexican government due to the need of developing and creating cutting-edge technology for application of renewable energy has created renewable energy centers to develop research projects related to solar, wind and geothermal energy. In particular, geothermal energy has been of great interest due to high geothermal energy potential reported for the country. Regarding the projects approved by the Mexican government, the Universidad Michoacana de San Nicolás de Hidalgo, has been granted with fundings to carry out the design and implementation of a geothermal-solar hybrid plant for electricity production. This project is being developed in the community of San Nicolás Simirao (Michoacan State) where geothermal energy is available and exploited from an existing geothermal well. Initially, the well ran through induction, but fluid flow was not constant for long periods and was not sufficient to obtain a full operation of the geothermal-solar hybrid power plant. Therefore, it was necessary to explore new techniques to extract geothermal energy effectively, meeting design conditions of power plant. One solution might be a geothermal heat exchanger to extract heat from the rock and carry it to the surface. Literature reports two basic configurations of geothermal heat exchangers: one of them is the Downhole Coaxial Heat Exchanger and the other one is Borehole Heat Exchanger. Before making a decision to implement one type or another, several studies were carried out by the authors of this work to determine what type of configuration was most suitable, considering in such studies technical and economic aspects that provided information to continue or not the project. Therefore, in this paper the numerical analysis of both configurations (Downhole Coaxial Heat Exchanger and Borehole Heat Exchanger) is presented. The study was conducted to determine what type of geothermal exchanger presents the best trade-off between maximum heat extraction rate and minimum length to minimize costs. A minimum temperature of 125°C was proposed to reach at the hot fluid heat exchanger outlet, allowing a normal operation of the geothermal-solar hybrid plant. Through numerical analysis was determined that the Borehole Heat Exchanger configuration did not present good heat extractions rates, obtaining that for 100 m length the outlet temperature of the hot fluid was even lower to that of entering into the well. This behavior was attributed to heat loss in the return pipe. For the same configuration, but using a length of 500 m, a temperature of 117.21°C was reached at the heat exchanger outlet. On the other hand, the Downhole Coaxial Heat Exchanger configuration reached a temperature of 118.35°C for a length of 100 m. For a length of 200 m a temperature of 131.25°C was obtained, whereby the facility can operate with the minimum necessary conditions. Finally, for a length of 500 m, a temperature of 134.67°C was reached, showing that this type of configuration is the most suitable to be installed in the geothermal well. Thus the Downhole Coaxial Heat Exchanger configuration has more advantages than the Borehole Heat Exchanger configuration from a technical and economic (by pipe cost) point of view.