I. Pilatowsky

Thermodynamic analysis of monomethylamine–water solutions in a single-stage solar absorption refrigeration cycle at low generator temperatures

A theoretical analysis of the coefficient of performance COP was undertaken to examine the efficiency characteristics of the monomethylamine–water solutions for a single-stage absorption refrigeration machine, using low generator temperatures (60–80°C), which allows the use of flat plate solar collectors. The thermodynamic analysis considers both, basic and refined cycles. The refined absorption cycle included a sensible heat recover exchanger (that is a solution heat exchanger). The thermal coefficients of performance COPh for the basis cycle and COPSHE for the refined cycle were calculated using the enthalpies at various combinations, at the operating temperatures and concentrations. The flow ratio FR has been calculated as additional optimization parameter. Due to the relative low pressure and the high coefficients of performance, the monomethylamine–water solutions present interesting properties for their application in solar absorption cycles at moderate condenser and absorber temperatures (25–35°C), with temperatures in the evaporator from −10°C to 10°C which are highly usable for food product preservation and for air conditioning in rural areas.

Mathematical simulation of a solar ejector-compression refrigeration system

This paper presents a mathematical simulation for the dynamic thermal behavior of a solar ejector-compression refrigeration system with a capacity production of 100 kg of ice per day. It consists of an evacuated tube solar collector array, a thermal storage unit and an ejector-compression refrigeration unit. Due to the change in climate, the collector efficiency varies and, therefore, so does the system efficiency. This fact makes it necessary to evaluate the design of the system not just for a whole day but also for a whole year. The ejector-compression refrigeration system was designed to work with Freon R142b as the working fluid at condenser temperature (Tc) of 30°C, generation temperature (TG) of 105°C, evaporator temperature (TE) of −10°C, with a required generator heat load (QG) of 5.6 kW and an obtained evaporator heat load (QE) of 2 kW, the corresponding COP was 34%. With these conditions, the ejector geometry was fixed and curves for QG, QE and COP as a function of TC and TG were obtained. A plot of the daily history of system storage tank temperature for two days of the year (one in January and one in June) is presented. Also graphs for the monthly average ice production, COP, collectors and system efficiencies are presented. The annual average values for COP, collector efficiency and system efficiency were 0.21, 0.52 and 0.11, respectively.

Solar assisted cooling with sorption systems : status of the research in Mexico and Latin America

Abstract Solar refrigeration projects both national and international with sorption and other refrigeration systems have been developed in Mexico and other Latin American countries in the last 15 years. A review of the main projects, both for solar cooling and refrigeration and the results obtained are presented in this paper. A methodology where 19 solar technologies for cooling were identified is also presented. Although solar cooling is still not an economically viable technology, the advances made and the experience gained in the projects described and the improved systems envisaged, will make solar refrigeration systems play an important role in the future.

Thermodynamics of Fuel Cells

In this chapter the basic thermodynamic and electrochemical principles behind fuel cell operation and technology are described. The basic electrochemistry principles determining the operation of the fuel cell, the kinetics of redox reactions during the fuel cell operation, the mass and energy transport in a fuel cell, etc., are described briefly to give an understanding of practical fuel cell systems. The ideal and practical operation of fuel cells and their efficiency are also described. This will provide the framework to understand the electrochemical and thermodynamic basics of the operation of fuel cells and how fuel cell performance can be influenced by the operating conditions. The influence of thermodynamic variables like pressure, temperature, and gas concentration, etc., on fuel cell performance has to be analyzed and understood to predict how fuel cells interact with the systems where it is applied. Understanding the impact of these variables allows system analysis studies of a specific fuel cell application.

Thermodynamic design data for absorption heat pump systems operating on ammonia-lithium nitrate—part three. Simultaneous cooling and heating

Abstract The free choice of operating temperatures in absorption systems is limited by the Gibbs phase rule and the thermodynamic properties of the working pair. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance have been presented for ammonia-lithium nitrate absorption systems for simultaneous cooling and heating. The interactions of operating temperatures have been illustrated graphically.

State of the Art of Sorption Refrigeration Systems

Sorption cooling systems have been used commercially for some decades for different applications including air conditioning and refrigeration, using a diverse range of thermodynamic cycles and technologies for many size and capacities. However, their use has been limited mainly because of their low efficiency and high investment costs, at least compared with compression systems that are widely used all over the world. Because of this, sorption and desiccant systems have been used, in general, only when large amounts of waste thermal energy that can be used as the energy supplied to the system are available, and recently with, for example, solar and geothermal technologies.

Cogeneration Fuel Cells – Air Conditioning Systems

As already discussed in Chapter 1, energy is a finite resource and its rational use implies an increase in energy efficiency. The electric generation efficiency is always less than 100% due to resistive, transmission and distribution losses, which can be quantified as heat sent to the environment. This waste heat determines the quantity of energy that can be used by other systems in order to improve the process efficiency.

Thermodynamic design data for absorption heat pump systems operating on monomethylamine-water. Part II: Heating

Abstract The Gibbs phase rule and thermodynamic properties of the working pair limit the choice of operating temperatures. For any combination of temperatures, the concentrations in the absorber and the generator and hence the flow ratios are fixed. For any particular working pair, the coefficient of performance is related to the flow ratio. Tables of possible combinations of operating temperatures and concentrations, including flow ratios, Carnot coefficients of performance and enthalpy-based coefficients of performance have been presented for monomethylamine-water absorption systems for cooling. The interactions of operating temperatures have been illustrated graphically.

Energy and Cogeneration

The word energy is derived from the Greek in (in) and ergon (work). The accepted scientific energy concept has been used to reveal the common characteristics in diverse processes where a particular type of work is produced. At the most basic level, the diversity in energy forms can be limited to four: kinetics, gravitational, electric, and nuclear.

Potential Applications in Demonstration Projects

Fuel cells are devices where electrical energy is produced by redox electrochemical reactions of hydrogen or enriched hydrogen fuels and oxygen, or simply air. Powerful fuel cells or stacks have emerged as potential replacements for the internal combustion engine in automobile vehicles, because the use of fuel cells implies clean and efficient use of energy, and the unique by-products are water and heat when pure hydrogen is used as fuel.