Carlos Rubio-Maya

Thermodynamic Analysis of Simultaneous Heat and Mass Transfer Systems

The direct heat exchange network (direct flow mixing network) and the indirect heat exchange network (exchanger network) are two of the elements that constitute a water network where heat and mass are transferred. When designing these systems, it is important to consider different aspects such as thermodynamics and equipment costs. This paper analyzes different design options within the framework of heuristic methodologies on a case study taken from the open literature. Two design methodologies are compared on the basis of exergy losses. It also enunciates a series of considerations in heuristic design for the heat and mass exchange networks. A very helpful tool in relation with the considerations set out herein is the composite curve; special focus will be given during its construction. This paper shows how to incorporate the exergy component in design seeking to minimize the thermal irreversibility.

Analysis of alternatives for a multiproduct system using geothermal energy under cascade utilization concept

Geothermal energy is one of the no fossil energy sources that has been utilized mainly for electricity generation, by using the so-called high enthalpy geothermal resource. Nevertheless, low and medium enthalpy geothermal resources are most abundant, but utilized in less extension due mainly to technological barriers or the thermal match between temperature of energy resources and the technology requirements. This work presents the analysis of alternatives for integrating a multiproduct system, producing sequentially electricity, ice and useful heating. For the purpose, the cascade utilization concept is considered for geothermal energy, utilizing low and medium enthalpy resources. To carry out the analysis, it is assumed availability of geothermal hot water with different temperatures typical of already drilled geothermal wells or studied geothermal reservoirs in Mexico. In order to produce electricity, ice and heating for further use (dehydration process or greenhouse heat supply), three cascade levels are proposed to operate sequentially and simultaneously. For electricity generation Organic Rankine Cycles are considered, and for ice production, thermally activated technologies are the best candidates. If necessary, supplementary heat is provided as a mean of geothermal energy upgrade; among the technologies to integrate are parabolic trough collectors, linear Fresnel collectors and biomass boiler. Particularly, with regard to Organic Rankine Cycles, are considered the ones that works with geothermal hot water in the range of 90 °C to 125 °C with rated power output between 25 kWe to 250 kWe. For ice production, two type of machines are under study, i.e. single-effect absorption machines with coefficient of performance around 0.6, and half-effect absorption machines with a value around 0.3 for the coefficient of performance. Absorption machines can be activated thermally with geothermal hot water with temperature in the range of 70 °C to 90 °C. Afterwards, a number of alternatives are proposed to integrate the multiproduct system, which are analyzed and compared both from the energy and economic point of view, obtaining in this way the main energy interactions of the systems, including electricity produced, amount of ice produced and heat availability. In the model, economic indicators are evaluated, obtaining for each alternative the capital cost, simple payback and net present value. Results shows quantitatively that cascade use of geothermal energy is a viable concept to increase the use of low and medium enthalpy geothermal resources with increase of energy performance and improvement of economical profit.Copyright

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 Nicolas 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 Nicolas 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.Copyright

Feasibility Analysis of a Hybrid Photovoltaic/Thermal Cogeneration System for Domestic Applications

A PV/T hybrid system is able to simultaneously produce electricity and heat from solar radiation. The feasibility of implementing PV/T systems depends primarily on climatic and economic characteristics of locations where are planned to be placed. Particularly in Mexico, there are only a few studies in the scientific literature which report the feasibility of using such innovative systems. Therefore, in this work the development of a techno-economic study is presented aiming to predict the performance and feasibility of implementation of this type of hybrid systems. Firstly, a PV/T system was designed to partially cover the needs of electricity and hot sanitary water in the domestic sector (considering a house of four inhabitants). Then, PV/T hybrid system operation was simulated using TRNSYS software over a full year using data from a typical meteorological year (TMY) of Morelia city (Michoacan State). Finally, an economic analysis was conducted, estimating the inherent cash flows and computing some economic indicators to determine the feasibility of implementation of PV/T system adapted to Mexican economic conditions. The simulation results show that the proposed system consisting of 1.55 m2 of collection area, will annually produce 1480.95 kWh and 393.57 kWh of thermal and electrical energy, respectively. The system is able to meet up to 51.2% of thermal energy and 29.2% of the electricity needed. The system reaches a total efficiency of 57.48%. The results of economic analysis indicate that in optimistic case, the proposed system has a simple payback period of 6.62 years, a net present value of

A Brief Model to Evaluate the Behaviour of R134a/R1234yf Mixtures on a Reciprocating Compressor

2129.0 Mexican pesos, and an internal rate of return of 14%, showing economic feasibility. The results show the great potential of the use of the hybrid PV/T systems for domestic water heating and electric production at particular locations in Mexico.Copyright

A Sensitivity Analysis for Effective Use of CO2 for Heat Mining in Geothermal Reservoirs

Transitioning from R134a refrigerant to a low global warming potential (GWP) refrigerant is a current issue of global importance. Although any refrigerant still has set; there are a few options to replace it such as the R1234yf. In this paper is presented a semi-empirical model to assess the energy performance of mixtures with R134a and its possible substitute R1234yf. The inputs variables to the computational model are: suction conditions (pressure and temperature), discharge pressure and rotation speed. With these variables the model must compute the following parameters: mass flow rate, discharge temperature and energy consumption. The model is validated with data obtained from an experimental facility; calculations are obtained within a relative error band of ±10% for mass flow rate and energy consumption, and an error of ±1 K for discharge temperature. Finally, the model is carried out to an energy simulation in order to predict the behavior of different mass fractions of R1234yf. Energy savings are found when R1234yf mass fraction is reduced from 1 to 0.9. Knowing that the mixture with y=0.9 may be used as its GWP is 150.Copyright

Technical and economic study for the integration of parabolic trough collectors coupled to a binary cycle

Carbon dioxide (CO2) emitted from various sources, mainly fossil fuel power plants, is considered responsible of the global warming effect. Many processes and techniques are still under research for CO2 capture and sequestration. On the other hand, it is proposed that the geothermal heat be mined from geothermal reservoirs using captured CO2. In this sense, some theoretical studies show feasibility of using supercritical carbon dioxide (sCO2) as a heat mining media in such geothermal reservoirs. In this work, it is carried out a set of numerical simulations to determine the most effective distance between injection and production wells for extracting geothermal energy utilizing sCO2 (Water is used for comparison). In the study, the permeability is considered in the range of 0.5 mD to 3.5 mD, with the aim of determining also the critical point in which sCO2 works better than water (H2O) as a working fluid. The remaining properties such as volume, density and other thermal properties remain fixed. Afterwards, it is constructed a numerical model which is implemented in TOUGH2 and PETRASIM 5 software to simulate the cases established. In the model, it is considered a simplified control volume, i.e. only one well for injection and one for production, assuming a constant flow rate at the inlet and at the outlet, meaning that sequestration is not taken into account. A length of 300 meter is defined for reservoir thickness, considering also a pressure and temperature of 100 bar and 200 °C, respectively. The energy mined is estimated for a period of twenty-five years. As typically, the sensitivity analysis is performed by varying only one property and keeping the remaining properties constant, isolating in this way the effect of such variable. Results show that for small permeabilities H2O works better than sCO2, but it is possible to assure that for permeabilities greater than 1 mD, sCO2 presents more advantages as extracting heat media instead of water. Both, H2O and sCO2 show a linear behavior. A deep analysis is necessary to carry out, because results shows that sCO2 works better in an intermediate zone (greater than 200 meter length, but smaller than 800 meter length). An unusual behavior is presented when the distances between the wells are varied; water shows a linear behavior increasing monotonically, while sCO2 shows a nonlinear behavior for some distances sCO2 works better. As expected, the more the distance, the greater the amount of the energy mined due to the volume related with each one of the distances.Copyright

Design optimization of a polygeneration plant fuelled by natural gas and renewable energy sources

In this paper, the preliminary technical and economic study for the integration of parabolic trough solar collectors to a geothermal binary cycle plan is presented, in order to maximize the use of medium enthalpy geothermal resource. It is proposed the use of solar collectors to increase the geothermal brine temperature and achieve design temperature of the plant. A study was conducted to determine the main features of the solar field and its coupling with binary cycle power plant. Subsequently, the thermodynamic models were established in order to obtain the main parameters of the hybrid plant. Additionally, a study was conducted to determine the economic feasibility of the plant including the determination of the levelized cost of electricity (LCoE).