Comparative study of advanced heat pumps

A numerical simulation study is reported on the thermodynamic performance of several non-CFC refrigeration devices. The study includes complex compound absorption, Brayton, Stirling, and thermoelectric devices. Comparisons are made to the more commonly applied vapor compression systems, including those using R-134a. The study examines the effect of thermal resistances between the device and the heat rejection or heat absorption space. A cool side temperature difference between 0 and 20{dollar}\sp\circ{dollar}C is investigated, and this temperature difference accounts for both thermal resistance and cooling load. An outside temperature ranging between 35{dollar}\sp\circ{dollar}C and 46{dollar}\sp\circ{dollar}C is considered in the calculations, with a cooled space temperature of 22{dollar}\sp\circ{dollar}C assumed throughout. Evaluations of the coefficients of performance for each of the units show the vapor compression machines demonstrate superior performance over the complete range of operating conditions examined. However, additional requirements, such as maintenance and environmental factors, indicate other desirable options

Cycle basics of thermally driven heat pumps

Part of: Thermally driven heat pumps for heating and cooling. – Ed.: Annett Kühn – Berlin: Universitätsverlag der TU Berlin, 2013 ISBN 978-3-7983-2686-6 (print) ISBN 978-3-7983-2596-8 (online) urn:nbn:de:kobv:83-opus4-39458 [http://nbn-resolving.de/urn:nbn:de:kobv:83-opus4-39458]Thermally driven heat pumps (TDHP) work at three temperature levels. Driving heat Q2 is supplied at a high temperature level. Useful cold (cooling operation) or low temperature heat (heating operation) Q0 is supplied at a low temperature level. The sum of the heat supplied is released at a medium temperature level. Q1 is the useful heat in heating operation. In cooling operation, it is usually released to the environment. However, medium and low temperature heat can also be used simultaneously for heating and cooling purposes. (...

Overview of Deployment of Magnetic Refrigeration in Heat Pump Systems

The majority of cooling systems are based upon vapor-compression refrigeration technology. Its principle has been unchanged for more than a century. Miniaturization and competitiveness have been gained, but there’s still a need of alternative technologies, which can operate with better efficiency, lower energy consumption and better environmental safety. One of the most promising alternatives to a conventional vapor compression system is magnetic refrigeration. In this article, an overview of the current state of development of a room-temperature magnetic heat pump is reported

Modeling of thermal losses in Vuilleumier machines

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) “Παραγωγή και Διαχείρηση Ενέργειας

Stirling engine design manual, 2nd edition

This manual is intended to serve as an introduction to Stirling cycle heat engines, as a key to the available literature on Stirling engines and to identify nonproprietary Stirling engine design methodologies. Two different fully described Stirling engines are discussed. Engine design methods are categorized as first order, second order, and third order with increased order number indicating increased complexity. FORTRAN programs are listed for both an isothermal second order design program and an adiabatic second order design program. Third order methods are explained and enumerated. In this second edition of the manual the references are updated. A revised personal and corporate author index is given and an expanded directory lists over 80 individuals and companies active in Stirling engines

Theoretical and experimental investigation of a Solar Free-Piston Stirling Engine (FPSE) using a flexible bellow for water pumping/power generation

Fossil fuels are the primary energy source globally and currently represent more than 80% of the overall energy consumption. Fossil fuels such as natural gas, oil and coal remain the principal fuels for supply and off-grid power generation in remote areas. Concerns over the negative environmental impact of greenhouse gases emission have shifted toward deploying and developing renewable and low carbon energy technologies. In the last decades, many sustainable and clean energy alternatives have been exploited to make energy and power generation clean and affordable to mitigate the negative impact of fossil fuels on the environment. The Stirling engine is considered one of the most promising solutions of sustainable power technologies to generate electricity from external heat sources. This research develops the computer model of a free-piston Stirling engine (FPSE) prototype operated by a solar simulator for small-scale power generation. The mathematical model was based on solving the working fluid's mass, energy and momentum conservation equations in different engine components. The engine's performance was evaluated based on the other three models: Schmidt, Adiabatic and Simple analysis. It is found that Simple analysis gave the most accurate result because the model considers the heat losses of the Stirling cycle. This research also investigated a novel design of a solar Free-piston Stirling engine for power generation and water pumping, which can be used in remote world regions. The design incorporates flexible bellows or diaphragm working as a power piston and two pre-compressed springs to support the displacer. This mechanical arrangement of the moving components in the engine reduces mechanical friction and air leakage. The experimentally testable FPSE was carried out, including a linear electric generator to develop and validate the theoretical simulation model. It was demonstrated the engine could operate successfully at an input heat temperature of 300C°, at 1 bar pressure and a frequency of 10 Hz. Moreover, a novel design is added to the engine to convert the linear motion to rotary motion. Overall, the engine's measured power and efficiency are low, and more tests of increasing the pressure of the engine for more than 1 bar are required to obtain better performance

Handbook of external refrigeration systems for long term cryogenic storage

Handbook of external refrigeration systems for long term cryogenic storag

Theoretical and experimental investigation of a Solar Free-Piston Stirling Engine (FPSE) using a flexible bellow for water pumping/power generation

Fossil fuels are the primary energy source globally and currently represent more than 80% of the overall energy consumption. Fossil fuels such as natural gas, oil and coal remain the principal fuels for supply and off-grid power generation in remote areas. Concerns over the negative environmental impact of greenhouse gases emission have shifted toward deploying and developing renewable and low carbon energy technologies. In the last decades, many sustainable and clean energy alternatives have been exploited to make energy and power generation clean and affordable to mitigate the negative impact of fossil fuels on the environment. The Stirling engine is considered one of the most promising solutions of sustainable power technologies to generate electricity from external heat sources. This research develops the computer model of a free-piston Stirling engine (FPSE) prototype operated by a solar simulator for small-scale power generation. The mathematical model was based on solving the working fluid's mass, energy and momentum conservation equations in different engine components. The engine's performance was evaluated based on the other three models: Schmidt, Adiabatic and Simple analysis. It is found that Simple analysis gave the most accurate result because the model considers the heat losses of the Stirling cycle. This research also investigated a novel design of a solar Free-piston Stirling engine for power generation and water pumping, which can be used in remote world regions. The design incorporates flexible bellows or diaphragm working as a power piston and two pre-compressed springs to support the displacer. This mechanical arrangement of the moving components in the engine reduces mechanical friction and air leakage. The experimentally testable FPSE was carried out, including a linear electric generator to develop and validate the theoretical simulation model. It was demonstrated the engine could operate successfully at an input heat temperature of 300C°, at 1 bar pressure and a frequency of 10 Hz. Moreover, a novel design is added to the engine to convert the linear motion to rotary motion. Overall, the engine's measured power and efficiency are low, and more tests of increasing the pressure of the engine for more than 1 bar are required to obtain better performance

Development of a solar powered refrigeration system: Stirling-cycle based

Solar refrigeration has been tirelessly studied since the 1970s. Yet, no renewable technology has been superior to the conventional grid powered technology for household applications. However, Photovoltaic (PV) powered vapour compression coolers and thermal collector powered sorption technologies are affordable in the market for off-grid cooling. The Stirling cycle is more than 200 years old technology but had limited success. For solar powered applications, it is complex, expensive and only commercially feasible at high-temperature differences in both motoring and refrigeration modes. That’s because high power machines need efficient, compact and hence complex heat exchangers, high temperature materials, pressurised light gases, complex driving mechanism, expensive solar tracking and solar thermal coupling mechanism. In this study, the Stirling-cycle machine is thermodynamically and technologically studied and designed to work with input temperatures between 450 K and 600 K that can be achieved by line-focus solar collectors. The Franchot-type machine, which is a double acting Stirling machine that uses one hot and one cold cylinder to form 2 alpha-type Stirling machines, has been redesigned to use long and direct-heated and cooled cylinders at low temperature differences. In addition to the polytropic processes, a novel simple isothermaliser was presented to improve the power density of the Franchot machine. The isothermaliser is either passive or active if it is thermally insulated or connected to external heat source, respectively. A simple balanced compounding mechanism, where compression pistons are mechanica l ly coupled to expansion ones, is suggested and studied theoretically. A novel thermal coupling mechanism with evacuated tube collectors is suggested for the solar-powered engine. To minimise material use, unpressurised ambient air and short regenerator connections are only considered with the suggested Stirling-cycle machine. In this study, the Franchot machine is mathematically studied in the Matlab/Simul ink environment using the second order model for the three-control volume machine, assuming the expansion and compression are polytropic processes. In the initial study, the model is built on ideal processes in order to understand the response of the machine for changes in the speed, gas pressure, phase angle, dead volume and geometry. In successive chapters, introduction of different non-ideal processes and effects is considered and coupled to the ideal model. It is found that the Stirling cycle performance can be improved by the optimisation of load, losses, gas pressure, engine speed, phase angle and geometrical parameters (e.g. cylinder diameter, length and dead volume). Increasing the gas pressure and engine speed enhances the power as they increase Reynolds’ number which in turn improves the in-cylinder heat transfer. Varying the phase angle and dead volume at a given speed can maximise the power approaching the Curzon and Ahlborn efficiency, which is the efficiency of any heat engine at maximum power. On the other hand, the Stirling-cycle refrigerator has a monotonic response approaching Carnot efficiency at very low cooling power and maximum cooling density at very low efficiency. Therefore, the optimised engine parameters at maximum power generation is used for the refrigera tor. In comparison to the Stirling engine with adiabatic cycle, the polytropic model of the isothermalised engine predicts about 275% and 211% power density improvements at the maximum power point for the active and passive isothermalisers, respectively. Similarly, in comparison to the adiabatic cycle refrigerator, the isothermalised refrigerator could have about 250% and 190% cooling power improvements at a COP of 3.25 for the active and passive isothermalisers, respectively. Conceptually, the suggested balanced compounding mechanism generates low side forces, reduces the machine length and complexity and adds self-starting capability. Simplicity and compactness are also enhanced by the removal of complex heat exchangers and using of a novel thermal coupling mechanism with the line solar collector. The solar refrigerator could deliver a specific cooling power peak of 367.5 W/m2 for air conditioning relative to a peak solar irradiance of 1 kW/m2. This number can be approximately computed by multiplying solar irradiance by Curzon efficiency, COP of 4 and solar collector efficiency of 50%. Therefore, the solar Stirling refrigera tor might have the potential to compete with the vapour compression cycle for domestic applications