Ideal Coefficient Of Performance Research Articles

Limits of coefficient of performance of adsorption cooling cycle based on refrigerant’s type

This research work discusses how the thermodynamic properties of refrigerant constrain the upper limit of the coefficient of performance (COP) of adsorption cooling (AC) cycle. A mathematical model is developed based on the mass and energy balance across the adsorption bed and used to estimate the maximum COP. Langmuir model is used to derive the ideal COP. Besides, Carnot COP and exergy efficiency are derived to evaluate the adsorption cooling cycle further. These new parameters are applied to the available cycles in the open literature to assess how much room for improvement is still left in the adsorption technology based on the refrigerant type. Water, ammonia, methanol, ethanol, Butane, R134a, R32, CO2 and R1234ze are used in this study. The maximum cooling COP cannot exceed 1.0 for cooling applications and is always less than 2.0 for heat pumps. Results show that AC cycles using water or ethanol as refrigerants achieve the highest exergy efficiency. The AC cycle using water as an adsorbate and silica gel as an adsorbent has the highest relative COP, about 80 % at 85 °C regeneration temperature. In turn, CO2 exhibits the lowest one. This work is merely an attempt to save experimental effort and time by identifying the most suitable refrigerant based on its physical and thermal properties and the cycle operating conditions.

Experimental Study on the Water Selective Dense Membrane under an Absolute Pressure Difference with Simplified Test Method

Membrane-based vacuum dehumidification technology is currently being actively studied. In most studies, the performance of the membrane-based systems is evaluated under the assumption that the membrane can achieve ideal separation, which results in ideal coefficient of performance (COP) values. However, the performance factors for membranes vary depending on the experimental conditions and measurement methods. Therefore, relevant values can only be calculated if the data are measured in an environment close to that of the application conditions. The cup measurement method is a simple method to measure the permeability, however, there are limitations regarding adding variables during the experiment. To overcome these limitations, a new experimental device was constructed that combines pressurized cell with the cup method. Using the device, the performance of polyethylene-amide-bonded dense membranes was evaluated under conditions where absolute pressure differentials occurred before and after the membrane, such as in air conditioner dehumidification systems.

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.

Novel reduction of hysteresis loss controlled by strain memory effect in FeRh/PMN-PT heterostructures

As living standards increase, the energy consumption in refrigeration, such as air-conditioning and refrigerators, tremendously increases and intensifies global warming. As an alternative for the conventional vapor compression technique, solid state refrigeration based on magnetocaloric effect shows significant potential due to energy-saving and environmental-friendly properties. However, hysteresis loss is a longstanding problem seriously harming refrigeration efficiency. Here, we report novel enhancement of refrigeration efficiency controlled by strain memory effect in FeRh films grown on (011)-PMN-PT substrates. Utilizing nonvolatile strain triggered by a pulse electric field to engineer magnetization process of FeRh film, a nonvolatile large reduction of hysteresis loss, ∼56%, is achieved, consequently effective refrigeration capacity increases to ∼86%. The hysteresis loss can be expected to be eliminated and even turned out to be inverse through enhancing the strain memory effect. As a result, effective refrigeration capacity (RCeffe) can increase to a new height through introducing external mechanical work in a magnetic refrigeration cycle, and the ideal COP (coefficient-of-performance) would break through Carnot limit if only hysteresis loss and the contribution of mechanical work were considered.

Karakteristik Laju Pendinginan Dan Coefficient Of Performance (COP) KTE-2000EV Menggunakan Katup Ekspansi Otomatis Dan Katup Ekspansi Thermostatik

The purpose of the study was to determine the characteristics of the cooling rate and The ideal coefficient of performance (COP) is the KTE-2000 EV refrigeration machine using an automatic expansion valve and thermostatic expansion valves. Analysis of the cooling and COP rates is ideally done by measuring changes in room temperature and plotting data on temperature and compressor pressure on the suction side and press side (suction line and discharge line) in the P-h diagram for the type of refrigerant R-404a. The test results show the characteristics of the average KTE-2000 EV cooling rate using an automatic expansion valve is 0.035 oC / s with an ideal COP value between 1.91 to 2.02, while for the thermostatic expansion valve the cooling rate characteristics obtained are an average of 0.024 oC / s and the ideal COP value between 2.58 and 3.13.

Theoretical Limit on COP of a Heat Pump from a Sequential System

The theoretical limit on Coefficient of performance (COP), which is maximum and ideal one, is investigated with a sequential Carnot heat pump where multiple Carnot heat pumps are interconnected in parallel. Using fundamental relations from thermodynamics and heat transfer, the performance of a sequential Carnot heat pump is obtained analytically. The effect of major parameters of the system, such as the number of individual heat pumps in a sequential system, the number of transfer unit of heat exchangers, and temperatures of heat sources, on the performance is researched. Also, expressions for ideal COP derived by limit calculation when the system has an infinite number of Carnot heat pumps or infinite number of transfer unit are suggested. For example, the most ideal COP is the ratio of the final heat source temperature to the difference between the initial and final heat source temperature. To support the result of theoretical analysis, a simple simulation of sequential Carnot heat pumps is carried out with thermodynamic properties of real refrigerants. The result of a simulation quite accords with that of theoretical analysis.

Activated carbon, silica-gel and calcium chloride composite adsorbents for energy efficient solar adsorption cooling and dehumidification systems

Composite adsorbents were synthesized from activated carbon, silica-gel and CaCl2. The optimized condition for adsorption cooling systems was obtained when raw activated carbon was impregnated by soaking in 10 wt.% sodium silicate solution for 48 h and then in 30 wt.% CaCl2 solution for 48 h. A 0.805 kg kg−1 of difference in equilibrium water uptake between 25 °C and 115 °C was recorded at atmospheric pressure. Besides, an adsorption rate test unit was built to study the adsorption isotherms and adsorption rates in which 0.23 kg kg−1 of adsorption capacity was recorded at 27 °C and a water vapor pressure of 900 Pa. The ideal coefficient of performance (COP) and the average specific cooling power (SCP) for an adsorption cooling system using the composite adsorbent were estimated to be 0.70 and 378 W kg−1 respectively. The results demonstrated that the composite adsorbents can be a good candidate for low temperature heat-driven adsorption cooling and dehumidification systems.

A combined double-way chemisorption refrigeration cycle based on adsorption and resorption processes

An innovative combined double-way chemisorption refrigeration cycle based on adsorption and resorption processes is presented. Two different reactive salts were used as sorbents and ammonia was utilized as the refrigerant in the proposed cycle. The useful cold was obtained from the evaporation heat of the refrigerant during the adsorption process and from the reaction heat of the low-temperature salt during the resorption process. The proposed combined double-way cycle has a distinct advantage of higher coefficient of performance (COP) in comparison with conventional adsorption cycle or resorption cycle. Experimental verification indicated that the advanced combined double-way cycle is feasible for refrigeration application, and the ideal COP of the basic cycle was about 1.24. Theoretical results showed that the proposed combined double-way cycle could improve COP by 167% and 60% when compared with conventional adsorption cycle and resorption cycle, respectively.

Performance analysis of an innovative multimode, multisalt and multieffect chemisorption refrigeration system

AbstractThe conceptual design of an innovative multimode, multisalt and multieffect solid‐gas chemisorption refrigeration system with evaporation and resorption processes is presented. In the proposed system, both the evaporation heat of the refrigerant during adsorption process and the reaction heat of the low‐temperature salt during resorption process are employed to provide useful cooling. The reaction heat of the high‐temperature salt is recovered for the regeneration process of the middle temperature salt. The presented system has the distinct advantage of larger cooling capacity per unit of heat input in comparison with other types of sorption refrigeration systems, based exclusively on evaporation or resorption. To identify the expected COP of the proposed system, two groups of working pairs containing metal chlorides and ammonia were analyzed. The ideal coefficient of performance (COP) can be improved by more than 59 to 169% if compared to the COP obtained with other kinds of cycle. When the sensible heats of the reactant, the refrigerant and the metallic part of the reactors are considered in the calculation of the COP, this figure can reach values between 0.91 and 1.80, according to the salts employed and the mass ratio between the metallic part of the reactor and the salt. © 2007 American Institute of Chemical Engineers AIChE J, 2007

New deep-freezing process using renewable low-grade heat: From the conceptual design to experimental results

An exergy-based analysis applied to ideal thermochemical dipoles allowed to design an original process that could use low-grade energy, produced from a thermal solar collector at around 70 °C, to provide low-temperature cold, below −23 °C, in order to store deep-frozen food. The ideal coefficient of performance (COP) of this system is 0.5 and the exergetic yield is 1. Taking into account the process enthalpies and the sensible heat of the reactants, the COPthermo is 0.17. The process functioning is described in this paper. It alternates between a regeneration mode during daytime and cold production mode during night-time. An experimental prototype was designed and built. It proved the feasibility of the concept and showed an experimental COP of about 0.06, which is similar to the up-to-date solar cooling systems, but at higher cold temperatures. The mean annual exergetic yield of the process is about 0.06.

Synthesis of Single Effect Solid-Gas Thermochemical Refrigerators

A systematic approach to the energy efficient design of single effect solid-gas Thermochemical Refrigerators (TR) using the appropriate choice of salt materials is proposed. The approach includes three major steps. The first one, the targeting step, is applied to the ideal thermochemical process. It allows identification of the energy performance targets (the ideal Coefficient of Performance, COP i ) as a function of external temperature conditions and the internal distribution of energy flows within a thermochemical system. Targets can be set without actually having to carry out the design of the system. This step characterizes only the thermodynamic feasibility of an ideal thermochemical process. A new graphical technique, a modified Carnot factor vs. heat diagram, is applied to determine the targets. In the second step, in order to achieve the targeted COP i value, the design options of ideal thermochemical systems using different salt materials are generated. The physicochemical feasibility of the options is ensured in this step on the Clausius–Clapeyron diagram. Finally, in the third step, the assessment of the thermodynamic irreversibilities produced within real thermochemical processes using the same materials as the ideal ones allows evaluation of the real COP values. This step is the traditional energy and exergy analysis that ensures the thermodynamic feasibility of the real thermochemical systems.