scholarly journals Characteristics of R718 Thermal Systems and Possibilities for Implementation in Refrigeration / Heat Pump Systems in Buildings

2020 ◽  
Author(s):  
Aleksandar Gjerasimovski ◽  
◽  
Maja Sharevska ◽  
Natasha Gjerasimovska ◽  
Monika Sharevska ◽  
...  
Keyword(s):  
Heat Pump ◽  
Pressure Ratio ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Thermal Systems ◽  
Flow Rates ◽  
Isentropic Exponent ◽  
Volumetric Cooling ◽  
Phase Out ◽  
Optimum Application

Regulations for CFCs and HCFCs refrigerants phase out and HFCs and HFEs reduction and renewed interest in natural refrigerants (water R718, CO2 R744, ammonia R717, air, hydrocarbons etc.) are discussed. Thermodynamic properties of water (R718) are analyzed and benefits of applicationas well as challenges in the implementation of R718 systems are explained. Deep vacuum operating conditions and low specific volumetric cooling capacity of R718 are peculiarities that cause large and extremely large volumetric flow rates for the temperature range of refrigeration / heat pump air –conditioning applications. The required pressure ratio for a given temperature lift is high. The high value of the water isentropic exponent causes high temperature at the compressor discharge. The specifics in the R718 turbo compressors caused by that reasons are analyzed and the range of optimum application of R718 refrigeration / heat pump systems are estimated

scholarly journals Study of a Heat Pump for Simultaneous Cooling and Desalination

2016 ◽  
Vol 819 ◽  
pp. 152-159 ◽  
Author(s):  
Paul Byrne ◽  
Yacine Ait Oumeziane ◽  
Laurent Serres ◽  
Thierry Mare
Keyword(s):  
Heat Pump ◽  
Energy Demand ◽  
Energy Resource ◽  
Coupled System ◽  
Data File ◽  
Cooling Capacity ◽  
Membrane Distillation ◽  
Operating Conditions ◽  
Weather Data ◽  
Air Gap Membrane Distillation

Access to freshwater and energy resource management are two of the major concerns of the next decades. The global warming indicator, the decrease of rainfalls and the growing energy demand for cooling are correlated in the most populated agglomerations of the world. For industrial and social purposes, it seems vital to develop energy efficient systems for cooling and desalination. A heat pump can produce energy for space cooling and heat for desalination. Among the different desalination systems available, membrane distillation seems the most suitable solution to the condensing temperature level of a standard heat pump.This article presents the development of a model of heat pump for simultaneous cooling and desalination by air-gap membrane distillation. The model was first developed using EES software and validated with experimental results from our laboratory and from the literature. The desalination unit was then optimised by numerical means in terms of dimensions and operating conditions using a bi-dimensional model with Matlab. A coupled system with a heat pump was finally simulated. The objective is to estimate the freshwater production depending on the cooling loads of a refrigerator placed in a building submitted to the conditions given by a weather data file in the Trnsys environment. The energy consumptions are compared to those of a standard reverse osmosis plant producing the same amount of freshwater associated to a chiller of same cooling capacity as the heat pump. The results show that the heat pump for simultaneous cooling and desalination offers interesting perspectives.

scholarly journals Modelling of Refrigerant Distribution in an Oil-Free Refrigeration System using R134a

Energies ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4792 ◽  
Author(s):  
Xinwen Chen ◽  
Zhaohua Li ◽  
Yi Zhao ◽  
Hanying Jiang ◽  
Kun Liang ◽  
...  
Keyword(s):  
Global Warming ◽  
Pressure Ratio ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Percentage Error ◽  
Two Phase ◽  
Phase Form ◽  
Compact Heat Exchangers ◽  
Micro Channels ◽  
Low Global Warming Potential

Increasing number of refrigeration units has led to an increase of CO2 emissions and the destruction of the ozone layer. Using low global warming potential (GWP) refrigerants, improving the efficiency of vapour compression refrigeration (VCR) units, and minimising refrigerant leakages can reduce the global warming effect. Investigating the refrigerant distribution under varied operating conditions can provide a deeper understanding of refrigerant charge optimization. This study proposed a model of refrigerant mass distribution in a prototype oil-free VCR system using a linear compressor with variable strokes and R134a. The absence of the oil lubricant allows the adoption of compact heat exchangers, such as micro-channels, so that the total refrigerant charge can be reduced significantly. The predicted total refrigerant charge has a Mean Absolute Percentage Error (MAPE) of 3.7%. The simulation results indicate that refrigerant distributed in the condenser is most sensitive to operating conditions and total refrigerant charges. The refrigerant accumulated in the condenser is 6.8% higher at a total refrigerant charge of 0.33 kg than that of 0.22 kg. For a total refrigerant charge of 0.33 kg, 72.1% of the total refrigerant can accumulate in the condenser. At a fixed pressure ratio, the refrigerant as a two-phase form in the condenser decreases slightly with the increase of compressor strokes, resulting in a larger mass flow rate, thus cooling capacity. The present model can be adapted for optimization of a refrigeration unit and its components.

Heat exchanger design optimization for mitigation of diesel engine exhaust fouling

2020 ◽  
pp. 1-36
Author(s):  
Victor C. Aiello ◽  
Girish Kini ◽  
Marcel Staedter ◽  
Srinivas Garimella
Keyword(s):  
Design Optimization ◽  
Heat Pump ◽  
Waste Heat ◽  
Large Data ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Component Level ◽  
Pressure Drops ◽  
Single Tube ◽  
Wide Range

Abstract The design optimization of a diesel exhaust coupled heat and mass exchanger that drives a 2.71 kW cooling capacity absorption heat pump is presented in this study. Fouling layer thermal resistance and pressure drops from single-tube experiments are used to develop a thermodynamic, heat transfer, and pressure drop model for the exhaust coupled desorber. A parametric study is performed to select a desorber design that meets system performance while minimizing footprint. Experimental heat duties and pressure drops are within 10% and 3%, respectively, of the model predictions. Thus, large data sets from single-tube experiments with representative geometries are successful in accounting for fouling effects at the component level. Desorber design optimization based on this approach ensures continued heat pump performance after fouling. This study, along with the single tube experiments, presents a systematic approach to design exhaust-coupled heat exchangers while considering the effects of fouling. These results are applicable for a wide range of waste-heat recovery applications and this method can be extended to different geometries and operating conditions.

Compact Diesel Engine Waste-Heat Driven Ammonia-Water Absorption Heat Pump Modeling and Performance Maximization Strategies

2021 ◽  
pp. 1-28
Author(s):  
Christopher M. Keinath ◽  
Jared Delahanty ◽  
Srinivas Garimella ◽  
Michael A. Garrabrant
Keyword(s):  
Heat Exchanger ◽  
Water Absorption ◽  
Heat Pump ◽  
Waste Heat ◽  
Cooling Capacity ◽  
Operating Conditions ◽  
Heat Transfer Fluid ◽  
Ammonia Water ◽  
Absorption Heat Pump ◽  
Wide Range

Abstract An investigation of the best ways to achieve optimal performance from a waste-heat-driven ammonia-water absorption heat pump over a wide range of operating conditions is presented. Waste-heat is recovered using an exhaust gas heat exchanger and delivered to the desorber by a heat transfer fluid loop. The absorber and condenser are hydronically coupled in parallel to an ambient heat exchanger for heat rejection. The evaporator provides chilled water for space-conditioning with a baseline cooling capacity of 2 kW. A detailed thermodynamics model is developed to simulate performance and develop strategies to achieve the best performance in both cooling and heating modes over a range of operating conditions. These parametric studies show that improved coefficients of performance can be achieved by adjusting the coupling fluid temperatures in the evaporator and the condenser/absorber as the ambient temperature varies. With the varying return temperatures, the system is able to provide the 2 kW design cooling capacity for a wide range of ambient temperatures.

Effect of Hydrofluorocarbons and Hydrofluoroolefins in a Household Refrigerator as a Substitute for R134a

2019 ◽  
Vol 969 ◽  
pp. 199-204
Author(s):  
Shaik Mohammad Hasheer ◽  
Kolla Srinivas
Keyword(s):  
Cooling Capacity ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Condensation Temperature ◽  
Outlet Temperature ◽  
Refrigeration System ◽  
Volumetric Cooling ◽  
Work Done ◽  
Theoretical Results ◽  
Hfc 152A

Now a days R134a can be used in domestic refrigerators and in air conditioning of automobiles. As per Kyoto protocol the usage of R134a is restricted due to their higher GWP value. The GWP value of this refrigerant is around 1430. So in this article, thermodynamic analysis of HFC-152a, HFO refrigerants-1234ze(E) and 1234yf was done in a household refrigeration system as direct substitute to HFC-134a.The performance of the household refrigerator was compared in terms of outlet temperature of the compressor, volumetric cooling capacity (VCC), refrigeration effect, work done by the compressor and coefficient of performance (COP). The entire analysis is carried out at various operating conditions of condenser and evaporator temperatures i.e. condensation temperature of 25°C,35°C & 45°C and evaporating temperatures ranging between −20°C to 10°C.From the theoretical results, it can be concluded that R1234yf can be used as a direct substitute to R134a.

Comparing Water (R718) to Other Refrigerants

2006 ◽  
Author(s):  
Amir A. Kharazi ◽  
Norbert Mu¨ller
Keyword(s):  
High Pressure ◽  
Water Vapor ◽  
State Of The Art ◽  
Pressure Ratio ◽  
Cooling Capacity ◽  
Specific Work ◽  
High Pressure Ratio ◽  
Current State ◽  
Two Factors ◽  
Volumetric Cooling

Even though water (R718) is one of the oldest refrigerants, state of the art technology is required to use water as a refrigerant in compression refrigeration plants with turbo compressors. To compare water (R718) to other refrigerants, a code is developed in which all refrigerants can be compared in a single p-h, T-s, or p-T diagram. Using the code, the COP isolines of water (R718) and any refrigerant can be generated in a graph to determine which refrigerant has a better COP for a certain evaporation temperature and temperature lift. In regard to using water (R718) as a refrigerant, some specific features complicate its application in refrigeration plants with turbo compressors. Because the cycle works at very low pressure, the volumetric cooling capacity of water vapor is very low. Hence, huge volume flows have to be compressed with relatively high pressure ratios. Therefore, the use of water (R718) as a refrigerant, compared to classical refrigerants, such as R134a or R12, requires approximately 200 times the volume flow, and about twice the pressure ratio for the same applications. Because of the thermodynamic properties of water vapor, this high pressure ratio requires approximately a two to four times higher compressor tip speed, depending on the impeller design; while the speed of sound is approximately 2.5 times higher. Reynolds numbers are about 300 times lower and the specific work transmission per unit of mass has to be around 15 times higher. Two factors are introduced to compare the irreversibilities of R718 and other refrigerants and the main source of irrevercibility in R718 cycle is identified. Finally, the current state-of-the-art R718 is reviewed.

Design of a Centrifugal Turbo Compressor With the Working Fluid Water for the Operation in a Hybrid Sorption/Compression Heat Pump Cycle

2016 ◽  
Author(s):  
Thomas Eckert ◽  
Leo Dostal ◽  
Martin Helm ◽  
Christian Schweigler
Keyword(s):  
Heat Pump ◽  
High Speed ◽  
Fluid Dynamic ◽  
Pressure Ratio ◽  
Lithium Bromide ◽  
High Volume ◽  
Heat Pumps ◽  
Operating Conditions ◽  
Working Fluid ◽  
Turbo Compressor

In various applications the use of sorption chillers and heat pumps is limited by the available temperature level of the driving heat source or the heat sink for export of reject heat. These constraints can be overcome by integrating an efficient high-speed transonic turbo compressor into the internal cycle of a thermally driven water/lithium bromide absorption heat pump. The operation in a hybrid heat pump with the refrigerant water implies specific challenges for the design of the compressor: Saturation pressures in the sub-atmospheric range, low vapor density, high volume flows and a targeted pressure ratio of 3 result in high impeller tip speeds with machine Mach numbers close to 1. Here the authors present a theoretical design study based on a numerical simulation of a centrifugal compressor, targeted at the given operating conditions. Evaluation of the results is conducted with regard to the relevant thermodynamic and fluid mechanic figures. The optimization of the impeller geometry comprises both fluid dynamic behavior and structural stability.

Centrifugal turbo chiller using water as refrigerant and lubricant

2020 ◽  
pp. 095440892093819
Author(s):  
Tadayoshi Shoyama ◽  
Bunki Kawano ◽  
Takeshi Ogata ◽  
Masaru Matsui ◽  
Masato Furukawa ◽  
...  
Keyword(s):  
Heat Pump ◽  
High Speed ◽  
Pressure Ratio ◽  
Control Valve ◽  
Cooling Capacity ◽  
Flow Control Valve ◽  
Pump System ◽  
Heat Pump System ◽  
High Pressure Ratio ◽  
Turbo Compressor

Water refrigerant heat pump system with a water vapour turbo compressor is developed. Water (R718) is an ideal refrigerant that is considered perfectly environment friendly. Although water refrigerant heat pump is studied extensively, the development of turbo compressors of high pressure ratio is still a technical challenge, in terms of both aerodynamics of the impellers and high-speed rotordynamics. In this study, the high-speed rotor is supported by journal bearings lubricated with water refrigerant. Additionally, other system components such as sprayed direct intercooler heat exchanger and anti-cavitation flow control valve have to be designed and developed with the new requirements as well. An experimental test rig of closed-loop heat pump is constructed which achieves the cooling capacity of 100 kW on the rated condition with COP = 5. The experimental results and the experienced challenges and their undertaken solutions are discussed in terms of the efficiency and the vibrations of the turbo compressor and the heat pump system.

scholarly journals Investigation of the Environmentally-Friendly Refrigerant R152a for Air Conditioning Purposes

2018 ◽  
Vol 9 (1) ◽  
pp. 119 ◽  
Author(s):  
Evangelos Bellos ◽  
Christos Tzivanidis
Keyword(s):  
Heat Pump ◽  
High Performance ◽  
Environmentally Friendly ◽  
Cooling Capacity ◽  
Heat Pumps ◽  
Operating Conditions ◽  
Coefficient Of Performance ◽  
Cooling Systems ◽  
Detailed Model ◽  
Ambient Temperatures

Heat pumps are efficient and well-established technologies for providing the proper cooling load in the building sector. The objective of this work is the parametric investigation of a heat pump operating with the promising refrigerant R152a for different operating conditions. More specifically, the heat pump is studied for different ambient temperatures, different indoor temperatures and various compressor rotational speeds. The cooling capacity and the coefficient of performance (COP) are the most important parameters which calculated in every scenario. A detailed model is developed in Engineering Equations Solver (EES) and it is validated with literature data. According to the final results, the system can operate in nominal conditions with 5 kW cooling capacity and a COP equal to 6.46. It is found that the COP can be ranged from 4 to 12 and the cooling capacity, while the cooling capacity can reach up to 9 kW. Moreover, a regression equation about the performance of the system is suggested. The obtained results indicate that the use of the R152a leads to high performance and so it can be an environmentally friendly choice for the cooling systems.

Nitrogen Removal from Anaerobically-Treated Leachate

1984 ◽  
Vol 19 (1) ◽  
pp. 87-100
Author(s):  
D. Prasad ◽  
J.G. Henry ◽  
P. Elefsiniotis
Keyword(s):  
Nitrogen Removal ◽  
Air Flow ◽  
Operating Conditions ◽  
Air Flow Rate ◽  
Flow Rates ◽  
Anaerobic Filter ◽  
Ph Values ◽  
Wide Range ◽  
Ammonia Desorption ◽  
Effects Of Ph

Abstract Laboratory studies were conducted to demonstrate the effectiveness of diffused aeration for the removal of ammonia from the effluent of an anaerobic filter treating leachate. The effects of pH, temperature and air flow on the process were studied. The coefficient of desorption of ammonia, KD for the anaerobic filter effluent (TKN 75 mg/L with NH3-N 88%) was determined at pH values of 9, 10 and 11, temperatures of 10, 15, 20, 30 and 35°C, and air flow rates of 50, 120, and 190 cm3/sec/L. Results indicated that nitrogen removal from the effluent of anaerobic filters by ammonia desorption was feasible. Removals exceeding 90% were obtained with 8 hours aeration at pH of 10, a temperature of 20°C, and an air flow rate of 190 cm3/sec/L. Ammonia desorption coefficients, KD, determined at other temperatures and air flow rates can be used to predict ammonia removals under a wide range of operating conditions.

Sign in / Sign up

Export Citation Format

Share Document