scholarly journals Experimental Investigation of the Effect of a Recuperative Heat Exchanger and Throttles Opening on a CO2/Isobutane Autocascade Refrigeration System

Energies ◽  
2020 ◽  
Vol 13 (20) ◽  
pp. 5285
Author(s):  
Michał Sobieraj
Keyword(s):  
Heat Exchanger ◽  
Experimental System ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Condensation Process ◽  
Design And Optimization ◽  
Expansion Valve ◽  
Zeotropic Mixture ◽  
Recuperative Heat Exchanger ◽  
Discharge Pressure

An experimental evaluation of an autocascade refrigeration (ACR) system was carried out. A zeotropic mixture of isobutane and CO2 was employed as a working fluid in an autocascade refrigeration (ACR) system. An experimental system was designed and built to study the influence of the recuperative heat exchanger (RHX) and openings of the throttle valves on the system performance. The use of RHX facilitated the condensation process and improved the cycle characteristics. The working mass concentration of CO2 was higher, as it was closer to the nominal concentration and the discharge pressure was lower by 19% to even 39% when the RHX was employed in the system. An increase of up to 20% in the coefficient of performance (COP) was observed. Furthermore, the effects of the openings of the throttle valves on the system characteristics were studied. The change in the openings of the expansion valves affected the mass flows and the working mixture composition. The working CO2 mass fraction increased with higher openings of the evaporator throttle. The subcooling degree of liquid CO2-rich refrigerant increased with higher openings of the expansion valve under the phase separator. The results of the present work should be helpful for design and optimization of autocascade systems working with natural and synthetic refrigerants.

Converting Low-Grade Heat Into Power Using a Supercritical Rankine Cycle With Zeotropic Mixture Working Fluid

2010 ◽  
Author(s):  
Huijuan Chen ◽  
D. Yogi Goswami ◽  
Muhammad M. Rahman ◽  
Elias K. Stefanakos
Keyword(s):  
Rankine Cycle ◽  
Phase Region ◽  
Working Fluid ◽  
Condensation Process ◽  
Heating Process ◽  
Low Grade ◽  
Two Phase ◽  
Working Fluids ◽  
Zeotropic Mixture ◽  
Low Grade Heat

A supercritical Rankine cycle using zeotropic mixture working fluids for the conversion of low-grade heat into power is proposed and analyzed in this paper. A supercritical Rankine cycle does not go through two-phase region during the heating process. By adopting zeotropic mixtures as the working fluids, the condensation process happens non-isothermally. Both of the features create a potential in reducing the irreversibility and improving the system efficiency. A comparative study between an organic Rankine cycle and the proposed supercritical Rankine cycle shows that the proposed cycle improves the cycle thermal efficiency, exergy efficiency of the heating and the condensation processes, and the system overall efficiency.

Design and Optimization of Waste Heat Recovery Unit Using Carbon Dioxide as Cooling Fluid

2014 ◽  
Author(s):  
Geir Skaugen ◽  
Harald T. Walnum ◽  
Brede A. L. Hagen ◽  
Daniel P. Clos ◽  
Marit J. Mazzetti ◽  
...  
Keyword(s):  
Heat Exchanger ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Working Fluid ◽  
Design And Optimization ◽  
Power Cycle ◽  
Turbine Efficiency ◽  
Recovery Unit ◽  
Process Simulations

This paper describes design and optimization of a Waste Heat Recovery Unit (WHRU) for a power cycle which uses CO2 as a working fluid. This system is designed for offshore installation to increase gas turbine efficiency by recovering waste heat from the exhaust for production of additional power. Due to severe constraints on weight and space in an offshore setting, it is essential to reduce size and weight of the equipment to a minimum. Process simulations are performed to optimize the geometry of the WHRU using different objective functions and thermal-hydraulic models. The underlying heat exchanger model used in the simulations is an in-house model that includes the calculation of weight and volume for frame and structure for the casing in addition to the thermal-hydraulic performance of the heat exchanger core. The results show that the for a set of given process constraints, optimization with respect to minimum total weight or minimum core weight shown similar results for the total installed weight, although the design of heat exchanger differs. The applied method also shows how the WHRU geometry can be optimized for different material combinations.

scholarly journals Impact of Employing Hybrid Nanofluids as Heat Carrier Fluid on the Thermal Performance of a Borehole Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2892
Author(s):  
Hossein Javadi ◽  
Javier F. Urchueguia ◽  
Seyed Soheil Mousavi Ajarostaghi ◽  
Borja Badenes
Keyword(s):  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Carrier ◽  
Pure Water ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Hybrid Nanofluid ◽  
Borehole Heat Exchanger ◽  
Carrier Fluid ◽  
Hybrid Nanofluids

In this numerical study, 4 types of hybrid nanofluid, including Ag-MgO/water, TiO2-Cu/water, Al2O3-CuO/water, and Fe3O4-multi-wall carbon nanotube/water, have been considered potential working fluid in a single U-tube borehole heat exchanger. The selected hybrid nanofluid is then analyzed by changing the volume fraction and the Reynolds number. Based on the numerical results, Ag-MgO/water hybrid nanofluid is chosen as the most favorable heat carrier fluid, among others, considering its superior effectiveness, minor pressure drop, and appropriate thermal resistance compared to the pure water. Moreover, it was indicated that all cases of Ag-MgO/water hybrid nanofluid at various volume fractions (from 0.05 to 0.20) and Reynolds numbers (from 3200 to 6200) could achieve better effectiveness and lower thermal resistances, but higher pressure drops compared to the corresponding cases of pure water. Nevertheless, all the evaluated hybrid nanofluids present lower coefficient of performance (COP)-improvement than unity which means that applying them as working fluid is not economically viable because of having higher pressure drop than the heat transfer enhancement.

Performance of A R22 split-air-conditioner when retrofitted with ozone friendly refrigerants (R410A and R417A)

2012 ◽  
Vol 23 (3) ◽  
pp. 16-22 ◽  
Author(s):  
Bukola Olalekan Bolaji
Keyword(s):  
Pressure Ratio ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Air Conditioner ◽  
Performance Study ◽  
Alternative Refrigerants ◽  
Air Conditioners ◽  
Average Coefficient ◽  
Compressor Power ◽  
Discharge Pressure

R22 that has been used predominantly in air conditioning and in medium and low-temperature applications contains ozone depleting chlorine atoms and hence will be phased out eventually. This paper presents the experimental performance study of a split-air-conditioner using ozone friendly alternative refrigerants. The existing split-air-conditioner originally designed for R22 as the working fluid was retrofitted with R410A and R417A respectively, and the performance of the system was evaluated and compared with its performance when R22 was used. Experimental results showed that with R417A, the system had 1.9% higher refrigeration capacity and 14.2% lower with R410A when compared to that of R22. The average discharge pressure of the compressor obtained with R417A and R410A were 3.8% lower and 10.3% higher, respectively, than with R22. The lowest compressor power consumption and pressure ratio were obtained with the R417A retrofitted system. The average coefficient of performance (COP) obtained using R417A is 2.9% higher, while that of R410A is 8.4% lower than that of R22. Generally, with R417A the system consistently had the best performance in comparison to both R22 and R410A, indicating that R417A would be a better choice for retrofitting existing split-air-conditioners originally designed to use R22 as working fluid.

scholarly journals Parametric Investigation of a Ground Source CO2 Heat Pump for Space Heating

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3563
Author(s):  
Evangelos Bellos ◽  
Christos Tzivanidis
Keyword(s):  
Heat Exchanger ◽  
Heat Pump ◽  
Heat Pumps ◽  
Geothermal Field ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Space Heating ◽  
Geothermal System ◽  
Parametric Investigation ◽  
Ground Source

The objective of the present study is the parametric investigation of a ground source heat pump for space heating purposes with boreholes. The working fluid in the heat pump is CO2, and the geothermal field includes boreholes with vertical heat exchangers (U-tube). This study is conducted with a developed model in Engineering Equation Solver which is validated with data from the literature. Ten different parameters are investigated and more specifically five parameters about the heat pump cycle and five parameters for the geothermal unit. The heat pump’s examined parameters are the high pressure, the heat exchanger effectiveness, the temperature level in the heater outlet, the flow rate of the geothermal fluid in the evaporator and the heat exchanger thermal transmittance in the evaporator. The other examined parameters about the geothermal unit are the ground mean temperature, the grout thermal conductivity, the inner diameter of the U-tube, the number of the boreholes and the length of every borehole. In the nominal design, it is found that the system’s coefficient of performance is 4.175, the heating production is 10 kW, the electricity consumption is 2.625 kW, and the heat input from the geothermal field is 10.23 kW. The overall resistance of the borehole per length is 0.08211 mK/W, while there are 4 boreholes with borehole length at 50 m. The parametric analysis shows the influence of the ten examined parameters on the system’s performance and on the geothermal system characteristics. This work can be used as a reference study for the design and the investigation of future geothermal-driven CO2 heat pumps.

scholarly journals Heating Performance and Ammonia Removal of a Single-Stage Bioscrubber Pilot Plant with Integrated Heat Exchanger under Field Conditions

Energies ◽  
2021 ◽  
Vol 14 (20) ◽  
pp. 6484
Author(s):  
Manuel S. Krommweh ◽  
Hauke F. Deeken ◽  
Hannah Licharz ◽  
Wolfgang Büscher
Keyword(s):  
Heat Exchanger ◽  
Thermal Energy ◽  
Ammonia Removal ◽  
Coefficient Of Performance ◽  
Air Treatment ◽  
Process Stage ◽  
Heating Performance ◽  
Recuperative Heat Exchanger ◽  
First Time

In this study, biological exhaust air treatment was combined with a recuperative heat exchanger in one process stage. The aim of this plant development and testing is not only to reduce ammonia from the exhaust air of pig houses but also to recover thermal energy at the same time. This is intended to offset the high operating costs of exhaust air treatment with savings of heating costs in cold seasons and to use the plant more efficiently. This system was tested for the first time under practical conditions in a pig fattening house in southern Germany. Three different assembly situations of the heat exchanger were examined for 13 days each and then compared with each other. The heating performance of the plant is primarily dependent on the outside air temperature and secondarily on the scrubbing water temperature. Depending on the assembly situation of the heat exchanger, an average heating performance of between 6.0 and 10.0 kW was observed; the amount of recovered thermal energy was between 1860 and 3132 kWh. The coefficient of performance (COP) ranked between 7.1 and 11.5. Furthermore, ammonia removal up to 64% was demonstrated. A long-term investigation of the system under practical conditions is recommended to validate the data collected in this study.

Investigation of Thermal Performance of Primary and Secondary Thermoelectric Modules

2008 ◽  
Author(s):  
Simranjit Khalsa ◽  
A. G. Agwu Nnanna
Keyword(s):  
Heat Exchanger ◽  
Integrated Circuits ◽  
Integrated Circuit ◽  
Heat Sink ◽  
Thermoelectric Module ◽  
Experimental System ◽  
Cooling Capacity ◽  
Coefficient Of Performance ◽  
Measured Temperature ◽  
Thermoelectric Modules

This paper reports the findings of an investigation on application of secondary thermoelectric (TE) module as a heat exchanger for the primary TE module. The experimental system consists of two commercially available thermoelectric modules arranged thermally in series with a heat sink and an integrated circuit (IC) chip. Heat produced from the IC chip is transferred to the heat sink via the TE modules. A total of nine experimental setups were analyzed using measured temperature data to assess the efficacy of the setups. Experimental evidence shows that the secondary TE module provides additional cooling advantage. The cooling capacity for a system with secondary TE module is 10.95W compared to 3.5W for systems where secondary modules are non-existent. The respective coefficient of performance, COP = Qc/Qp are 2.43 and 0.78. The use of a secondary TE module as a heat exchanger for the primary thermoelectric module is ineffective when compared with liquid-cooled heat exchanger. Results further showed that during early stages of heating and cooling processes, there exists lag in response time between the integrated circuits chip. This could result in over-heating or under-cooling the IC chip.

scholarly journals Thermodynamic investigations of Zeotropic mixture of R290, R23 and R14 on three-stage auto refrigerating cascade system

2016 ◽  
Vol 20 (6) ◽  
pp. 2073-2086
Author(s):  
Mayilsamy Sivakumar ◽  
Periasamy Somasudaram
Keyword(s):  
Mass Fraction ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Cascade System ◽  
Environment Friendly ◽  
Mass Fractions ◽  
Zeotropic Mixture ◽  
Efficiency Defect ◽  
Low Temperature Refrigeration ◽  
System Operating

The zeotropic mixture of environment friendly refrigerants (hydrocarbons and hydrofluorocarbons) being the only alternatives for working fluid in low temperature refrigeration system. Hence, three-stage auto refrigerating cascade system was studied for the existence using four combinations of three-component zeotropic mixture of six different refrigerants. The exergy analysis confirmed the existence of three-stage auto refrigerating cascade system. The performances of the system like coefficient of performance, exergy lost, exergic efficiency, efficiency defect, and the evaporating temperature achieved were investigated for different mass fractions in order to verify the effect of mass fraction on them. In accordance with the environmental issues and the process of sustainable development, the three-component zeotropic mixture of R290/R23/R14 with the mass fraction of 0.218:0.346:0.436 was performing better and hence can be suggested as an alternative refrigerant for three-stage auto refrigerating cascade system operating at very low evaporating temperature in the range of ?97?C (176 K), at coefficient of performance of 0.253 and comparatively increased exergic efficiency up to 16.3% (58.5%).

The Reversed Brayton Cycle Heat Pump—A Natural Open Cycle for HVAC Applications

1979 ◽  
Vol 101 (1) ◽  
pp. 162-167 ◽  
Author(s):  
F. Sisto
Keyword(s):  
Heat Exchanger ◽  
Gas Turbine ◽  
Heat Pump ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Heating Effect ◽  
Prime Mover ◽  
Total Potential ◽  
Open Cycle

Using reasonable assumptions for turbomachinery efficiencies and heat exchanger effectivenesses, the Coefficient of Performance (COP) and Specific Heating Effect (SHE) of the regenerated and unregenerated cycles are computed and optimized. Only heating data are presented and both open and closed cycles are considered. An effort is made to indicate those cases where (the working fluid being air) the cycle may be appropriately open to combine the heating function with ventilation. When driven by an appropriately small direct Brayton cycle prime mover, the total potential for a new and widespread gas turbine application of literally millions of units becomes defined.

Experimental studies on the performance of mobile air conditioning system using environmental friendly HFO-1234yf as a refrigerant

2019 ◽  
pp. 095440891988123 ◽  
Author(s):  
Prabakaran Rajendran ◽  
Shaji Sidney ◽  
Iyyappan Ramakrishnan ◽  
Mohan Lal Dhasan
Keyword(s):  
Heat Exchanger ◽  
Air Conditioning ◽  
Exergy Analysis ◽  
Coefficient Of Performance ◽  
Air Conditioning System ◽  
Environmental Friendly ◽  
Hfc 134A ◽  
Expansion Valve ◽  
Suction Line ◽  
Suction Line Heat Exchanger

In this work, the experimental investigation on the performance and exergy analysis of mobile air conditioning system with suction line heat exchanger using environmental friendly HFO-1234yf was carried out under varied evaporator air flow rates. The performance was compared with existing HFC-134a results. The performance analysis showed that the cooling capacity and the coefficient of performance of the system with HFO-1234yf were lower than that of the HFC-134a by upto 2–11%. The power consumption and the volumetric efficiency of the compressor with HFO-1234yf were found to be 14.02% and 11.2% higher than that of HFC-134a. From the exergy analysis, it was observed that the major exergy destruction occurred in the compressor, followed by the condenser, evaporator, thermostatic expansion valve, and suction line heat exchanger for both refrigerants. The exergy efficiency of the system with HFO-1234yf was 2.4–12.6% lower than that of HFC-134a. From this study, it was observed that the losses experienced in the compressor, thermostatic expansion valve and evaporator lead to poor performance with HFO-1234yf.

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