Theoretical Coefficient Of Performance Research Articles

Thermodynamic analysis of adsorption cooling system using composite halide salts

AbstractIn the development of an adsorption cooling system, it has been observed that halide composites exhibit less hysteresis than pure halide salts. Therefore, it is important to thermodynamically analyze the composite salt‐based adsorption cooling system (ACS) to understand its performance. In this study, we conduct a thermodynamic first‐law and second‐law analysis of ACS using reactive salts such as BaCl2, BaCl2‐ENG, CaCl2‐ENG, SrCl2‐ENG, and MnCl2‐ENG, with ammonia as the refrigerant. We compared the coefficient of performance (COP) with that of a pure halide salt‐based ACS. The theoretical COP of the ACS at a mass ratio of 4 is estimated as 0.45, 0.4, 0.27, 0.37, and 0.22, and the second‐law efficiency is estimated as 44.28%, 38.76%, 20.71%, 16.26%, and 6.92% for BaCl2, BaCl2‐ENG, CaCl2‐ENG, SrCl2‐ENG, and MnCl2‐ENG reactive salts, respectively. Among the different salts, BaCl2 shows the highest COP. However, the COP values are lower than the maximum theoretical coefficient of performance (COPmax) due to the sensible mass of the reactor, and COP values decrease with an increase in the mass ratio due to an increase in sensible mass. It is noteworthy that the COP of the pure salt‐based ACS is higher than that of the composite salt‐based ACS because the ammonia uptake of pure salt is greater than that of the composite salt.

Analysis of the Coefficient of Performance (COP) on the Car’s Air Cooling System Using a Training Kit with Constant Rotation

The performance of the air condition system is strongly influenced by the compressor work, the condenser cooling temperature. So that the compressor working pressure (suction) and condenser cooling play a very important role in the performance of the air conditioning system which will have an impact on compressor work, compressor power, refrigeration impact, isentropic efficiency and coefficient of performance (COP) of the car air conditioning system. From the research, data will be obtained which include the pressure value on the refrigerant, namely P1 and P2, the temperature on the refrigerant, namely T1, T2, T3 and Tcabin, at the point of installation of the Manifold Gauge and Thermocouple. The research data is then processed and analyzed to obtain performance at constant rotation with variations in compressor working time both actual and theoretical as well as the efficiency of the ac system. From the results of the study, it was found that the compressor rotation was 2300 rpm with a constant rotation then measured the pressure and temperature of the refrigerant, then temperature data was obtained and analyzed to obtain the enthalpy value, thus obtaining the coefficient of performance (COP) of the car air conditioning system. The coefficient of performance (COP) of the resulting system is greater than the actual COP, the optimal COP occurs at P1 30 psi and P2 340 psi working pressures, the actual COP is 3.4848 and the theoretical COP is 4.1500, with an efficiency of 83.97% at 360 seconds.

Estimation of coefficient of performance of thermoelectric cooler using a 30 W single-stage type

Abstract In this study, a single stage thermoelectric cooler (TER, of size: 21 × 14.2 × 13.5 cm) with thermoelectric module (TEM, of type inbc1-127. 05 with size 40 × 40 × 4.0 mm) and applied electrical power of 30 W and current of 2.5 A, was adopted to estimate the coefficient of performance (COP) of thermoelectric refrigerator (TER). The TER uses a fan to cool the heat exchange region of the TEM. The temperature of the fruit/vegetable samples used in this study was taken before and after cooling for a specific period. The temperatures at both the hot and cold sides of the TEM were also taken at every specific cooling period. The experimented TER can cool vegetable/fruit from about 27 to 5°C within 3 h. The aim of this study is to determine the COP of TER to ascertain the possible applications. The temperature gradient at the heat exchange section of TEM was used to estimate the average theoretical COP to be 0.99, the heat extracted from the cooling chamber and the power supplied was used to estimate the average practical cooling COP to be 0.52; which is within 0.4–0.7 standard COP for a single stage type of TER.

Proposed application of a geothermal heat pump technique to address frost damage of embankments in cold regions

This study proposes a novel frost-proof heating method, which uses a ground source heat pump (GSHP) to generate artificial heating and prevent frost damages of embankment filling materials in cold regions. A direct expansion-GSHP (DE-GSHP) apparatus for embankments was designed and manufactured for experimentation. Consequently, the prototype of the new system demonstrated high performance with daily average heating temperatures above 50 °C in winter and low energy consumption with a theoretical coefficient of performance more than 3.0. The internal temperature in the test soil platform increased, and the calculated thermal influencing radius was 0.87 m and 2.03 m on days 1 and 5, respectively. Frost heave of embankments can be rapidly treated by heating the embankment through distribution of DE-GSHPs with a heat supply capacity of 1.0–2.0 kW and spacing of 2.0–4.0 m. The findings of this study provide significant insights into the methods suitable for thermal maintenance of embankment filling materials using the GSHP, thereby providing a feasible and energy-efficient solution during embankment construction in cold regions to prevent frost heave damages.

Development of an effective TE cooler box for food storage

The development of a cooling system with a low power supply and evenly distributed temperature for food storage is challenging. This paper proposed a thermoelectric (TE) cooler box that adopt both conduction and convection heat transfer to solve the problems. The cooler box is made of three-layer wall, six TE modules (TEC1-12706), six inner heatsinks with fan, six outer heatsinks with fan, six top fans, two-power supply, a contactor, a switch, and a thermostat. With the six TE modules power consumption of 37.7 W at 3.18 A, the obtained results showed steady temperature distributions with time at various points of the layers including the cold and hot region. Meanwhile, the cooling capacity changes and became steady with the time. The conduction heat transfer is the dominant of the total heat transfer (Qc). The theoretical COP(coefficient of performance) using Carnot decreases with constant time, where COPsink of heatsink is approximately 1.6 higher than COPc of TE module. Furthermore, the experimental COPexp increases sharply before actualizing stability with experimental time compared to previous findings. Therefore, the TE cooler box is applicable for fruits and vegetable storage, and in areas of limited power supply.

ENERGY EFFICIENCY IN CONSTANTA HARBOR- A THEORETICAL ASSESSMENT OF THE PERFORMANCE OF A HEAT PUMP FOR HEATING NEEDS, FOR A LESS POLLUTANT ADMINISTRATION OFFICE

In accordance with the present energetic exigencies, the energy consumption in port buildings is of a vital importance. From this perspective, heat pumps are less pollutant and more energy efficient options than the traditional heating technologies. This study focuses on an air source heat pump (ASHP), operating in an administration office located in Constanta harbor, Romania, in order to supply heated water during December of 2020. Electrically driven heat pumps are seen as a successful alternative to classical expensive heating means, such as electrical heating or the one based on fossil fuels combustion. Within this research, are investigated influences of the heated water temperatures and exterior air temperatures on the theoretical Coefficient of Performance, the compression ratio and the discharge temperature. The cycle is working with R134a, with 50C superheating and sub cooling. It will be considered that the heated water is supplied in the range (40-50) 0C, while the outdoor air temperature varies in the range (0-10) 0C. Obtained results show that the highest efficiency of the ASHP is obtained for the lowest value of the heated water temperature and for the highest value of the outdoor air temperature. This situation corresponds also to the good working of the compressor of the refrigeration plant, since are seen lowest values of the compression rate and the discharge temperature, as well. This means that the compressor do not consume high amounts of energy and the oil is not damaged because of high temperatures of the refrigerant vapors.

Performance analysis of adsorption refrigeration system using silicagel/methanol pair: experimental & analytical approaches

An adsorption refrigeration system (ARS) working on silica-gel/methanol pair has been investigated analytically and experimentally. By applying the mass balance in the adsorber bed the mechanism of adsorption in the thermal compressor with respect to time and bed length was determined. An experimental analysis was performed using a thermal gravimetric analyzer (TGA) to evaluate the mass transfer coefficient and optimum cycle time for silica-gel/ methanol pair at different working temperatures. The Diffusion coefficient Ds and Activation energy Ea for silica-gel/methanol pair were found 2.55 × 10–4 m2/s and 83.08 KJ/mol. Further, the results of variation of regeneration temperature on the performance of the system in terms of COP (Coefficient of Performance) and SCP (Specific Cooling Power) was evaluated; the maximum average theoretical COP and SCP achieved by the system was 0.5 and 102 W/kg near about 127°C regeneration temperature.

Electrocaloric cooling over high device temperature span

Summary Electrocaloric cooling demonstrates direct electricity utilization and high energy efficiency, and is often proposed as an environmentally benign, solid-state alternative to the conventional vapor compression cooling technology. As a result, the fabrication of effective electrocaloric materials and engineering of electrocaloric cooling devices have attracted increasing attention in the cooling community. However, the limited material adiabatic temperature change under safe operation field poses a major challenge to practical electrocaloric cooling device development, since real-world applications usually require device temperature span over 20 K. This perspective presents recent efforts devoted to design electrocaloric cooling devices based on active heat regeneration and cascading approaches; both strategies have achieved significant device temperature lift ~10 K with adiabatic temperature change of 2~3 K. The strategies discussed in this work are broadly applicable to the design of efficient and compact cooling systems.

A Critical Review of Real Gas Effects on the Regenerative Refrigerators

The regenerative refrigeration is an important reverse work-heat conversion cycle with a theoretical coefficient of performance (COP) identical to the Carnot efficiency. Practical regenerative refrigerators are capable of working down to 4 K and largely fulfill the refrigeration requirement of modern technologies in many fields, especially for space applications. However, the enthalpy flow associated with the pressure dependence, abbreviated as pressure-induced enthalpy flow, brought about by real gas effects degrades the theoretical COP of the refrigerator to below about 30% of the Carnot efficiency at the temperatures of below the critical point. This paper reviews the long history of exploring the real gas effects which dates back to the 1970s and continues to now. Important explorations of uncovering the loss mechanism and reducing such losses are summarized. The theories that are in accordance with experimental results and simulation results are expounded. We further carry out analyses on the expansion components, including the pulse tube and the clearance gap. Several inferences are made in order to explore the long-lasting puzzles about real gas effects. It is emphasized that the underlying cause of the loss in the regenerator is an indirect effect of the real gas properties. Further study about carrying out a direct verification of the theory is proposed.

Adsorption thermodynamics and performance indicators of selective adsorbent/refrigerant pairs

Adsorbed phase thermodynamics and isosteric heat of adsorption of adsorbent/refrigerant pairs have immense importance in predicting the system performance of an adsorption heat pump. In this study, six potential adsorbent/adsorbate pairs - Maxsorb III/ethanol, PR_KOH4/ethanol, SAC2/R32, Maxsorb III/R152a, H2-treated Maxsorb III/ethanol, and Maxsorb III/propane are compared using a well-established model for determining heat of adsorption. Temperature-entropy (T-s) maps as a function of pressure, temperature, and adsorption uptake were plotted. It was observed that at a fixed temperature (303 K) the adsorbed phase entropy had an increasing trend with the increment of adsorbate uptake for all the studied pairs. Adsorption cooling cycles were plotted in the temperature-entropy maps for a specific cooling condition. Moreover, the entropy flow for different pairs suggested the minimum required driving force. The theoretical coefficient of performance and specific cooling effect were computed for all the pairs. This comparative analysis is important for choosing the suitable adsorbent/adsorbate pair for a particular heat pump application.

Analysis and assessment of partial re-liquefaction system for liquefied hydrogen tankers using liquefied natural gas (LNG) and H2 hybrid propulsion

Boil-off gas (BOG) is inevitable on board liquefied hydrogen tankers and must be managed effectively, by using it as fuel, re-liquefying it or burning it, to avoid cargo tank pressure issues. This study aims to develop a BOG re-liquefaction system optimized for l60,000 m3 liquefied hydrogen tankers with an LNG and hydrogen hybrid propulsion system. The proposed system comprises hydrogen compression and helium refrigerant sections with 2 J–Brayton cascade cycles. Cold energy recovery from the fuels and feed BOG exiting the cargo tanks was used. The system exhibits a coefficient of performance (COP) of 0.07, a specific energy consumption (SEC) of 3.30 kWh/kgLH2, and exergy efficiency of 74.9%, with the hydrogen BOG entering the re-liquefaction system at a feed temperature of −220 °C. The theoretical COP and SEC values at ideal conditions were 0.09 and 2.47 kWh/kgLH2, respectively. The effects of varying the hydrogen compression pressure, inlet temperature of the hydrogen expander, feed hydrogen temperature and helium compression pressure were investigated. Additionally, the LNG-to-hydrogen fuel ratio was adjusted to satisfy the Energy Efficiency Design Index (EEDI) Phase 2 and 3 emission requirements.

Modelling Load Profiles of Heat Pumps

Approximately one quarter of energy-related emissions in Germany are caused by the domestic sector. At 81%, the largest share of these emissions is due to heat supply. Many measures are available to reduce these emissions. One of these measures, which is considered to play an important role in many studies, is the replacement of fossil-fired boilers with electric heat pumps. In order to be able to analyse the impact of high penetrations of heat pumps on the energy system, the coefficient of performance (COP) must be modelled with high temporal resolution. In this study, a methodology is presented on how to calculate high-resolution COPs and the electrical load of heat pumps based on thermal load curves and temperature time series. The COP is determined by the reciprocal Carnot factor. Since heat pumps are often designed bivalently due to the cost structure, the methodology described can also be used for evaluating the combination of immersion heater and heat pump (here for the air/water heat pump). As a result the theoretical hourly COPs determined are calibrated with annual performance factors from field tests. The modelled COPs show clear differences. Currently, mostly air source heat pumps are installed in Germany. If this trend continues, the maximum electrical load of the heat supply will increase more than would be the case with higher shares of ground source heat pumps.

Attainability of the Carnot efficiency with real gases in the regenerator of the refrigeration cycle

Improving efficiency is an enduring effort for all work-heat conversion cycles. Ideal regenerators working with ideal gases bring about a lossless work and heat transfer over a temperature gradient, but real gases give rise to an “intrinsic” heat loss in regenerators because of the time-averaged enthalpy flow associated with the pressure dependence. Real gas effects play a vital role on the coefficient of performance (COP) of regenerators of refrigeration cycles working at the temperatures close to or below the critical point. The “intrinsic” heat loss of real gases degrades the theoretical COP of regenerators to as low as 1% of the Carnot efficiency. In this paper, an approach of heat input or removal aiming to improve the COP is proposed. The theoretical analysis of this approach reveals the underlying mechanism. It is shown that the theoretical COP of an ideal regenerator working with a real gas applying this approach is identical to the Carnot efficiency. A simplified approach of heat input is further analyzed. The Carnot efficiency can be attained under certain circumstances, and it is possible to obtain over 90% of the Carnot efficiency with a discrete method. The theory of improving the COP with the approach of heat input in discrete regenerator locations is supported by the experiment results found in the relevant literature. This new approach provides a potential way to significantly improve the efficiency of the regenerator of the refrigeration cycle working at the temperatures close to or below the critical point. This approach may further provide a reference for studies of the heat pump cycle and the engine cycle working with real gases.

Research on a Household Dual Heat Source Heat Pump Water Heater with Preheater Based on ASPEN PLUS

This article proposes a dual heat source heat pump bathroom unit with preheater which is feasible for a single family. The system effectively integrates the air source heat pump (ASHP) and wastewater source heat pump (WSHP) technologies, and incorporates a preheater to recover shower wastewater heat and thus improve the total coefficient of performance (COP) of the system, and it has no electric auxiliary heating device, which is favorable to improve the security of the system operation. The process simulation software ASPEN PLUS, widely used in the design and optimization of thermodynamic systems, was used to simulate various cases of system use and to analyze the impact of the preheater on the system. The average COP value of a system with preheater is 6.588 and without preheater it is 4.677. Based on the optimization and analysis, under the standard conditions of air at 25 °C, relative humidity of 70%, wastewater at 35 °C, wastewater flow rate of 0.07 kg/s, tap water at 15 °C, and condenser outlet water temperature at 50 °C, the theoretical COP of the system can reach 9.784 at an evaporating temperature of 14.96 °C, condensing temperature of 48.74 °C, and preheated water temperature of 27.19 °C.

Experimental and theoretical study on a novel double evaporating temperature chiller applied in THICS using R32/R236fa

A novel chiller with double evaporating temperatures is proposed in this paper, which can be applied in temperature and humidity independent control system (THICS). A zeotropic mixture R32/R236fa is selected as the refrigerant, and chilled water with two different temperatures is produced. The experimental coefficient of performance (COPexp), theoretical coefficient of performance (COPth), and second law efficiency (η) of the chiller are studied. The performance of the chiller is studied by varying the mass fraction of R32 in the R32/R236fa (W(R32)), chilled water temperature, and the flow rates of the heat transfer media (chilled water and cooling water). The results show that the high temperature chilled water (TH,out) can be at 15–18 °C, and the low temperature chilled water (TL,out) can be at 6–8 °C. When TH,out is 17 °C and TL,out is 7 °C, the maximum COPth and COPexp are 4.73 and 3.97, respectively. Second law efficiency, η, increases to 31% as W(R32) increases from 0.3 to 0.6.

Capacitive deionization regeneration as a possible improvement of membrane regeneration method for absorption air-conditioning system

Driven by renewable energy and being environment friendly, the absorption air-conditioning system is a good choice for green buildings. Concentrating the absorbent solution with electrodialysis method, the membrane regeneration absorption system has higher performance than the traditional absorption system. Its theoretical coefficient of performance can approach 6 under certain working conditions. However, the experimental data in this paper reveals the actual coefficient of performance of the membrane regeneration system is about 1–2, much lower than expected. It is caused by the energy loss in heating and electrochemical reactions. To improve, a capacitive deionization regeneration method is proposed: strong absorbent solution and pure water are acquired with the joint work of two units. Analysis has been made on the absorption air-conditioning system adopting this method. The mass and energy equations have been developed and some parameters have been investigated for performance optimization. Even with conservative prediction, the results show the capacitive deionization method has better performance than the membrane regeneration method. The coefficient of performance can be enhanced by 100% with the energy recovery strategy. Capacitive deionization method also has advantages on the cost and maintenance, which makes it a promising choice for the absorption air-conditioning system.

Measurement of thermodynamic properties of ammoniated salts and thermodynamic simulation of resorption cooling system

The adsorption and desorption pressure-concentration isotherms (PCIs) of ammonia on NaBr and MnCl2 salts are measured at different temperatures. Significant hysteresis is observed between adsorption and desorption PCIs. From PCI data, van't Hoff plots are constructed to estimate the enthalpies of formation for different ammonia concentrations. Substantial variation in reaction enthalpy during adsorption and desorption is noticed from beginning to the end of the processes. The average values of ΔH for NaBr and MnCl2 are −28.59 kJ mol−1 and −60.17 kJ mol−1 respectively for adsorption and 29.16 kJ mol−1 and 65.62 kJ mol−1 respectively for desorption. The resorption cooling system is thermodynamically analyzed using measured equilibrium data. The coefficient of performance (COP) and specific cooling power (SCP) of resorption system is evaluated to be 0.31 and 52 W kg−1 at refrigeration, regeneration and ambient temperatures of −15 °C, 170 °C and 25 °C respectively at a mass ratio of 4. About 49.18% decrease in COP is noticed in comparison with maximum theoretical COP in which 32.78% and 16.36% reductions are due to hysteresis effect and thermal capacity of metallic mass respectively.

Experimental verification of the variable effect absorption refrigeration cycle

A variable effect absorption refrigeration cycle is proposed which can obtain a rising COP (Coefficient of Performance) versus the rising generation temperature. This novel cycle could be applied for solar absorption cooling efficiently. In this paper, a 50 kw variable effect (also named as 1.n effect) absorption chiller using LiBr-water as working fluid was designed. Its rated condition is generation temperature of 125 °C, condensation temperature of 40 °C, absorption temperature of 35 °C and evaporation temperature of 5 °C. The variable effect absorption chiller was then manufactured and tested. Data from the experiment showed that the chiller can get a rising COP from 0.69 to 1.08 under generation temperature from 95 °C to 120 °C as it was expected. The average error between theoretical COP and experimental COP was 7.3%. Feasibility of the variable effect absorption chiller and the effectiveness of the design have been verified.

F201 低GWP冷媒を用いた多段型吸着冷凍サイクルの静的解析(OS10 外燃機関・廃熱利用技術(1))

A high pressure adsorption refrigeration cycle, which uses activated carbons as adsorbent and low GWP refrigerant (R 1234ze) as refrigerant, was proposed and the theoretical performance was investigated by static analysis. The coefficient of performance (COP) of multi-stage cycles was compared with that of single stage cycle under the desorption temperature of 80-120℃, adsorption/condensation temperature of 50℃, and evaporation temperature of 15℃ The medium pressure levels of the multi-stage cycles were optimized to maximize the COP. It was shown that two stage cycle had advantage in theoretical COP with desorption temperature lower than 100℃.

A two-stage deep freezing chemisorption cycle driven by low-temperature heat source

A two-stage chemisorption cycle suitable for deep-freezing application driven by low-temperature heat source was proposed. Through two-stage desorption processes, the two-stage cycle can break through the limitations of the heating temperature and ambient cooling temperature. The two-stage cycle based on CaCl2/BaCl2-NH3 working pair can utilize the heat source with a temperature of above 75°C, and simultaneously realize deep-freezing all the year round. Experimental results and performance prediction show that the adsorption quantity of calcium, theoretical coefficient of performance (COP) and optimized specific cooling power (SCP) of the CaCl2/BaCl2-NH3 chemisorption system are 0.489 kg/kg (salt), 0.24 and 120.7W/kg, when the heating temperature, ambient cooling temperature, pseudo-evaporating temperature and mass ratio of reacting salt and expanded graphite are 85, 30, −20, and 4:1, respectively.