The feasibility of using vapor expander to recover the expansion work in two-stage heat pumps with a large temperature lift

2015 ◽  
Vol 56 ◽  
pp. 15-27 ◽  
Author(s):  
Nan Zheng ◽  
Li Zhao
Author(s):  
S. K. Abildinova ◽  
R. A. Musabekov ◽  
A. S. Rasmukhametova ◽  
S. V. Chicherin

The increase in production and modernization of existing heat pumps are global trends in the development and implementation of heat pump technology. Application of refrigerant with zero potential ozone depletion relative to fluorinetrichloromethane and minimum values of global warming potentials relative to carbon dioxide is environmentally justified in pumps. Prospective are stage compression heat pump units and, also, consecutive and cascade schemes of inclusion which provide higher temperature of the heat carrier in the system of heat supply. Improving the efficiency of the heat pump depends on the perfection of the thermodynamic cycle, on the choice of the working agent and on the quality of the operation of the unit in off-design conditions of a temperature mode. The article presents the results of a study of the performance of stage compression heat pump. The concepts of application of the heat pump of two-stage compression of the working agent are formulated. Experimental researches has been fulfilled with the use of Altal GWHP26Н heat pump of 24.2 kW capacity operating on an eco-friendly refrigerants of R134a and R600а. The results of comparative calculation of performance indicators of one- and two-stage heat pumps are presented. Various schemes of realization of a thermodynamic cycle for one- and two-stage heat pumps are considered. The efficiency of two-stage heat pumps that implement thermodynamic cycle with supercooling of condensate and regeneration of steam heat of the working agent has been proved. The two-stage thermodynamic cycle of the heat pump is accompanied by minimal losses during the throttling of the liquid refrigerant, and it solves the problem of useful heat use to increase the temperature of the heated coolant for heating and hot water supply systems. Steam regeneration of the working agent at the outlet from the evaporator through the use of regenerative heat exchanger also provides the additional effect of minimization of thermodynamic losses and improving efficiency of cycles with vapor compression heat pumps in the conditions of large temperature differences in the evaporator and the condenser.


2021 ◽  
Vol 11 (10) ◽  
pp. 4635
Author(s):  
Marcel Ulrich Ahrens ◽  
Maximilian Loth ◽  
Ignat Tolstorebrov ◽  
Armin Hafner ◽  
Stephan Kabelac ◽  
...  

Decarbonization of the industrial sector is one of the most important keys to reducing global warming. Energy demands and associated emissions in the industrial sector are continuously increasing. The utilization of high temperature heat pumps (HTHPs) operating with natural fluids presents an environmentally friendly solution with great potential to increase energy efficiency and reduce emissions in industrial processes. Ammonia-water absorption–compression heat pumps (ACHPs) combine the technologies of an absorption and vapor compression heat pump using a zeotropic mixture of ammonia and water as working fluid. The given characteristics, such as the ability to achieve high sink temperatures with comparably large temperature lifts and high coefficient of performance (COP) make the ACHP interesting for utilization in various industrial high temperature applications. This work reviews the state of technology and identifies existing challenges based on conducted experimental investigations. In this context, 23 references with capacities ranging from 1.4 kW to 4500 kW are evaluated, achieving sink outlet temperatures from 45 °C to 115 °C and COPs from 1.4 to 11.3. Existing challenges are identified for the compressor concerning discharge temperature and lubrication, for the absorber and desorber design for operation and liquid–vapor mixing and distribution and the choice of solution pump. Recent developments and promising solutions are then highlighted and presented in a comprehensive overview. Finally, future trends for further studies are discussed. The purpose of this study is to serve as a starting point for further research by connecting theoretical approaches, possible solutions and experimental results as a resource for further developments of ammonia-water ACHP systems at high temperature operation.


Energies ◽  
2020 ◽  
Vol 13 (3) ◽  
pp. 635 ◽  
Author(s):  
Limei Gai ◽  
Petar Sabev Varbanov ◽  
Timothy Gordon Walmsley ◽  
Jiří Jaromír Klemeš

To date, research on heat pumps (HP) has mainly focused on vapour compression heat pumps (VCHP), transcritical heat pumps (TCHP), absorption heat pumps, and their heat integration with processes. Few studies have considered the Joule cycle heat pump (JCHP), which raises several questions. What are the characteristics and specifics of these different heat pumps? How are they different when they integrate with the processes? For different processes, which heat pump is more appropriate? To address these questions, the performance and integration of different types of heat pumps with various processes have been studied through Pinch Methodology. The results show that different heat pumps have their own optimal application range. The new JCHP is suitable for processes in which the temperature changes of source and sink are both massive. The VCHP is more suitable for the source and sink temperatures, which are near-constant. The TCHP is more suitable for sources with small temperature changes and sinks with large temperature changes. This study develops an approach that provides guidance for the selection of heat pumps by applying Process Integration to various combinations of heat pump types and processes. It is shown that the correct choice of heat pump type for each application is of utmost importance, as the Coefficient of Performance can be improved by up to an order of magnitude. By recovering and upgrading process waste heat, heat pumps can save 15–78% of the hot utility depending on the specific process.


2019 ◽  
Vol 62 (9) ◽  
pp. 1596-1604 ◽  
Author(s):  
Jun Pei ◽  
LiangLiang Li ◽  
DaWei Liu ◽  
BoPing Zhang ◽  
Yu Xiao ◽  
...  

2018 ◽  
Vol 232 ◽  
pp. 695-703 ◽  
Author(s):  
Wenjie Nie ◽  
Ke Lü ◽  
Aixi Chen ◽  
Jizhou He ◽  
Yueheng Lan

2009 ◽  
Vol 1218 ◽  
Author(s):  
Jani Oksanen ◽  
Jukka Tulkki

AbstractWe propose a solid state heat pump based on photon assisted heat transfer between two large-area light emitting diodes coupled by the electromagnetic field and enclosed in a semiconductor structure with a nearly homogeneous refractive index. Ideally the thermophotonic heat pump (THP) allows heat transfer and electricity generation at the Carnot efficiency, but in reality there are several factors that limit the efficiency. We present a numerical model that accounts for the most important losses of the thermophotonic heat pump to study the operating regimes and the fundamental limitations of the THP structure. The results show that the thermophotonic heat pump has potential to outperform heat pumps based on the thermoelectric effect especially for heat transfer across large temperature differences. In energy harvesting applications the performance of the THP is good for small power densities, but drops at high power densities unless the losses in the structure can be efficiently minimized.


2019 ◽  
Vol 86 (3) ◽  
pp. 30902 ◽  
Author(s):  
Bin Liu ◽  
Lin Chai ◽  
Aiqiang Chen ◽  
Fuhui Tang ◽  
Khellil Sefiane ◽  
...  

Heat pumps are widely investigated for their versatile use in a wide range of applications. In this study, three types of heat pumps were experimentally compared. These heat pumps include an one-stage without injection vapor heat pump, an one-stage injection vapor heat hump and a two-stage injection vapor heat pump with an economizer. The results showed that the heating capacity of all three variants of heat pumps decreases with the decrease of the evaporation temperature. However, the attenuation ratio of the heating capacity is found to be different from one pump to another. On the one hand, the largest attenuation rate is found to be 68.84% for evaporating temperatures ranging from −1 °C to −23 °C and for the case of one-stage heat pump. On the other hand, the smallest attenuation rate is found to be 31% for the two-stage injection vapor heat pump in the same temperature range. It is worth noting that the heating efficiency is improved by the amount of vapor injection, nevertheless, there is a maximum value due to the limitations of the economizer. The two-stage injection vapor heat pump can exhibit an enhanced heating efficiency of 127% compared to the one-stage without injection vapor heat pump and 13% compared to the one-stage injection vapor heat pump for an evaporating temperature of −23 °C.


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