Driving Heat Source Temperature Research Articles

Compression-assisted absorption refrigeration cycle employing organic working pairs for ultra-low grade heat recovery

Solar absorption refrigeration technology is considered an ideal alternative to energy-intensive refrigerated warehouses due to its decarbonization and environmental friendliness. However, it faces challenges in competing with vapor compression refrigeration, such as high driving heat source temperature (>100 °C) and a long payback period. In this paper, we address these challenges by focusing on cycle structure and working pair, and propose a compression-assisted absorption refrigeration cycle (CARC) using R32/dimethylacetamide (DMAC) as working pair. The aim is to significantly reduce driving heat source temperature by adjusting absorption pressure utilizing an auxiliary compressor, enabling the cycle to be connected to low-cost and efficient non-concentrating solar collectors, thereby effectively shortening its payback period. This cycle includes two operating modes: CARC mode powered by solar energy during the daytime and vapor compression refrigeration cycle mode driven by off-peak electricity at night, ensuring 24-hour cooling capacity for refrigerated warehouses. The results indicate that this cycle can flexibly utilize 60∼80 °C solar hot water easily obtained as driving heat source and its evaporation temperature decreases to -20 °C. To assess its performance benefits, a compression-assisted absorption refrigeration system is developed and implemented. By utilizing the limited roof area of a refrigerated warehouse, it can achieve an 18.2 % reduction in electricity consumption and a 24.2 % reduction in carbon emissions compared to the vapor compression one annually. Additionally, during peak electricity demand periods in summer, the system exhibits significant energy-saving effects, and its payback period is about 4.2 years. Ultimately, this cycle provides a viable solution for energy-saving and emission reduction in refrigerated warehouses.

Experimental investigation and thermodynamic modeling of adsorption equilibria of MSC30 with R32 for supercritical adsorption cooling systems

In the present study, the adsorption isotherms of difluoromethane (R32) on the activated carbon (MSC 30) throughout a temperature range of 25 °C to 150 °C and pressures up to 3000 kPa are measured for possible application in adsorption cooling systems. The Dubinin-Astakhov model was used to fit the experimental data. A thermodynamic model is proposed in this study to investigate the adsorption potential under supercritical conditions. The model is validated using the isotherm data from the experiments and literatures for different working pairs. The validation results exhibited a good agreement between the proposed model and the experimental data, signifying the precision and dependability of the model. The corresponding adsorption isosteric heat model was derived and verified, taking into account both the inclusion and exclusion of the adsorbed volume correction. Furthermore, the developed models were utilized in the equilibrium analysis of an adsorption heat pump to evaluate the performance of the system in terms of the theoretical coefficient of performance (COP) and specific cooling energy (SCE). The analysis covered the driving heat source temperature ranging from 30 °C to 150 °C, with different evaporation temperatures and adsorption temperatures. The results showed that the maximum COP value of 0.47 for the adsorption heat pump system employing the MSC30+R32 pair was achieved at a desorption temperature of 115 °C, at which the SCE was 315.5 kJ·kg−1. The results can potentially improve the accuracy of predicting adsorption behavior and contribute to the development of more efficient and effective adsorption systems.

Ammonia-based hybrid chemisorption-compression heat pump for high-temperature heating

Conventional compression heat pumps employing natural refrigerant of ammonia can barely meet the requirement of high-temperature heating above 90 °C, while ammonia-based chemisorption heat transformers characterised by high-temperature heating require driving heat source temperature above 80 °C. To address these issues, a novel ammonia-based hybrid chemisorption-compression high-temperature heat pump employing SrCl2-NH3 as the working pair is designed and established in this paper. Particularly, a conventional normal temperature compressor instead of an expensive high-pressure ammonia compressor can be adopted to upgrade the abundant 50–80 °C waste heat to 90–120 °C high-temperature heat. Simultaneously, due to that chemisorption reaction heat is larger than condensing heat of refrigerant, this heat pump has significant potential for improving coefficient of performance (COP). For the first time, regulation strategies of key parameters such as sorption pressure, desorption pressure, and sorption reaction exothermic time are proposed, and these provide the theoretical support for the stable and efficient operation of the heat pump. Moreover, its performance is evaluated by varying operating conditions. The results indicate that at heat output temperature of 100 °C, the optimal sorption pressure and reaction exothermic time are 1.70 MPa and 22 min, respectively. At waste heat temperature of 70 °C and heat output temperature of 110 °C, the COP of the heat pump is 4.58, i.e., its efficiency is 14.5% more than that of R245fa compression one.

Performance analysis of a double-effect absorption refrigeration cycle using a low-temperature ethanol solution as the working pair

In this paper, a double-effect absorption refrigeration system using a low-temperature working pair, lithium bromide (LiBr)+1-butyl-3-methylimidazolium bromide ([BMIM]Br)/ethanol (C2H5OH), was proposed to reduce the driving heat source temperature and enlarge the operation range to subzero temperatures. Based on the measured thermal properties, the thermodynamic performance of the double-effect absorption refrigeration cycle under different working conditions was calculated by Matlab and compared with that using LiBr/H2O working pair. Results showed that the generation temperature of the refrigeration system using LiBr-[BMIM]Br/C2H5OH was reduced by about 30 K in comparison to LiBr/H2O under the same operating condition. The temperature in the absorber with LiBr-[BMIM]Br/C2H5OH was 40 K higher than its crystallization temperature, whereas LiBr/H2O was only less than 20 K. Moreover, the system using LiBr-[BMIM]Br/C2H5OH was able to successfully work under 273.15 K without crystallization. At a typical operating condition, the COP of the double-effect absorption refrigeration cycle with LiBr-[BMIM]Br/C2H5OH reached 1.47, which was 0.10 higher than that using LiBr/H2O. As a low-temperature working pair, LiBr-[BMIM]Br/C2H5OH showed a great potential in utilizing solar energy and the low-temperature waste heat under severe operating conditions. Furthermore, compared with LiBr/H2O, the refrigeration system had a better economic performance with LiBr-[BMIM]Br/C2H5OH working pair.

Techno-economic performance of multi-generation energy system driven by associated mixture of oil and geothermal water for oilfield in high water cut

Geothermal energy is an important renewable energy. Oilfields in high water cut stage are also geothermal fields. We propose a geothermal cascade utilization system, including organic Rankine cycle (ORC) power generation, Li-Br absorption refrigeration, oil gathering and transportation heat tracing (OGTHT) and heat. Associated geothermal water from abandoned oil wells is used as a renewable heat source. The thermodynamic and economic analysis of the cascade utilization system is carried out by establishing a mathematical model. In ORC system, we use two-stage series evaporation to reduce irreversible losses. The results show that there is an optimum evaporation temperature to maximize the net output power, thermal efficiency and exergy efficiency. It is found that the mass flow of the working fluid has a great impact on the system performance. In economic analysis, we find that both cost and benefit increase with the increase of geothermal water temperature (Tgw in) and driving heat source temperature. We use the payback period (PBP) as a comprehensive evaluation index of economy. The results show that there is an optimal temperature combination to minimize PBP. The smallest payback period occurs at the Tgw in is 383 K and the driving heat source temperature is 363 K, which is 3.07 years.

Energy, exergy and exergoeconomic analysis of an ultra low-grade heat-driven ammonia-water combined absorption power-cooling cycle for district space cooling, sub-zero refrigeration, power and LNG regasification

An ultra low-grade waste heat (≤100 °C) driven ammonia-water combined absorption power-cooling (APC) cycle-based multi-generation system with liquefied natural gas (LNG) cold exergy recovery is thermodynamically and exergoeconomically investigated for sustainable district cooling (DC) at two different temperature levels, and electricity generation in coastal hot climate regions serviced by LNG regasification terminals. At 70 °C heat source temperature, the system yields a specific net equivalent power output of 51.4 kWh/tonLNG at a cooling-to-power ratio of 7.3, and effective first-law and effective exergy efficiencies of 39% and 36%, respectively. Per million ton per annum (MTPA) LNG regasification capacity, the system would deliver 9.4 MW of space cooling, 6.5 MW of sub-zero refrigeration, and 2.2 MW of electricity for the district, while saving 8.4 ktons of natural gas and 19.3 kt of CO2-equivalent emissions per year, compared with conventional cooling, power and regasified LNG provision systems. The LNG refrigeration heat exchanger and APC absorber-evaporator are the most important components from exergoeconomic viewpoints. In addition to enhancing overall cooling and power generation capacity, the use of LNG as a cold source/sink reduces the minimum APC driving heat source temperature and rectification requirements, relative to an ambient water-cooled absorber sink. Additional benefits include the avoided use of conventional refrigerants, and reduced impact of LNG regasification on marine ecosystems.

Study on a Quaternary Working Pair of CaCl2-LiNO3-KNO3/H2O for an Absorption Refrigeration Cycle.

When compared with LiBr/H2O, an absorption refrigeration cycle using CaCl2/H2O as the working pair needs a lower driving heat source temperature, that is, CaCl2/H2O has a better refrigeration characteristic. However, the crystallization temperature of CaCl2/H2O solution is too high and its absorption ability is not high enough to achieve an evaporation temperature of 5 °C or lower. CaCl2-LiNO3-KNO3(15.5:5:1)/H2O was proposed and its crystallization temperature, saturated vapor pressure, density, viscosity, specific heat capacity, specific entropy, and specific enthalpy were measured to retain the refrigeration characteristic of CaCl2/H2O and solve its problems. Under the same conditions, the generation temperature for an absorption refrigeration cycle with CaCl2-LiNO3-KNO3(15.5:5:1)/H2O was 7.0 °C lower than that with LiBr/H2O. Moreover, the cycle’s COP and exergy efficiency with CaCl2-LiNO3-KNO3(15.5:5:1)/H2O were approximately 0.04 and 0.06 higher than those with LiBr/H2O, respectively. The corrosion rates of carbon steel and copper for the proposed working pair were 14.31 μm∙y−1 and 2.04 μm∙y−1 at 80 °C and pH 9.7, respectively, which were low enough for engineering applications.

Development of a novel unbalanced ammonia-water absorption-resorption heat pump cycle for space heating

Ammonia-water absorption-resorption heat pump (ARHP) is a promising technology for promoting efficient utilization of low-temperature thermal for space heating. This paper proposes a novel unbalanced ARHP cycle by replacing the condenser and evaporator in the conventional absorption heat pump (AHP) cycle with a high-pressure absorber and a low-pressure generator, respectively. The proposed cycle can work just depending on the concentration difference of ammonia-water solution under different pressure levels. A numerical model has been developed to investigate the feasible high-pressure/low-pressure (PH/PL) values to effect the thermodynamic cycle. The cycle's coefficient of performance (COP) under different PH/PL pair values and other given working conditions are studied. The maximum COP is 1.550 and the corresponding optimum PH/PL pair to effect the cycle is 1.40 MPa/0.38 MPa at a heat source temperature of 95 °C. When PH/PL pair value is 1.40/0.38 MPa, heat supply temperature of 44.5 °C and COP value of 1.331 can be obtained, which can basically meet the temperature demand of building floor heating. In addition, effects of different PH/PL pair values on solution circulation ratios and vapor discharge scopes of generators are discussed. It is concluded that the ideal PH/PL candidates yield large concentration difference between the inlet and outlet of generators and absorbers. Meanwhile, the solution circulation ratios of the two generators at ideal PH/PL pairs are acceptable values between 2.0 and 12.0. The cycle can work when the ambient temperature is above −7.5 °C and the driving heat source temperature is larger than 85 °C, which is potential in efficient utilization of commonly used stationary solar collectors for winter heating.

非共沸混合作動流体を用いたオーガニックランキンサイクルの熱力学的サイクルシミュレーション

The study performed cycle simulation of organic Rankine cycles with zeotropic mixtures as working fluid. A conventional Rankine cycle was modeled and thermodynamic state changes of each process was solved with the aid of Engineering Equation Solver. Thermophysical properties of working fluids were taken from REFPROP. The net thermal efficiency was calculated under the conditions of the driving heat source temperatures of 50 degree C and 90 degree C, and the heat sink temperature of 30 degree C. The results showd that the zeotropic mixtures achieved higher net thermal efficiency under the driving heat source temperature of 50 degree C. When the driving heat source temperature was raised to 90 degree C, pure materials with large latent heat resulted in higher net thermal efficiencies.

Experimental investigation and thermodynamic analysis of CO2 adsorption on activated carbons for cooling system

In the present study, the adsorption isotherms of CO2 on three commercially available activated carbons are measured for possible application in cooling systems. The adsorption isotherms are measured using a Sievert’s type experimental setup at various temperatures from 273 to 358K. Experimental data of CO2 adsorption isotherms is modelled using Dubinin-Astakhov model. Pseudosaturation pressure of CO2 plays a significant role in the estimation of thermodynamic properties for supercritical gas adsorption, and it is evaluated using adsorption isotherms data. The thermodynamic properties namely isosteric heat of adsorption at surface loading, Gibbs free energy, and entropy are evaluated using classical Clausius-Clapeyron equation and Dubinin-Astakhov model for both subcritical and supercritical phase of CO2 respectively. Adsorbed phase specific heat capacity, entropy, and enthalpy are also estimated. These thermodynamic properties are used for the thermodynamic analysis of CO2-AC based adsorption cooling system. The cooling system performance parameters like specific cooling effect (SCE) and coefficient of performance (COP) are estimated for the driving heat source temperature of 80°C at four cooling temperatures of 0, 5, 10 and 15°C with a fixed adsorption/condenser temperature of 25°C. All the three activated carbons are found suitable for developing CO2-AC based cooling system. The maximum SCE and COP are obtained as 25.87kJ/kg and 0.09 respectively.

Highly porous activated carbon based adsorption cooling system employing difluoromethane and a mixture of pentafluoroethane and difluoromethane

This paper presents a simulation for a low-grade thermally powered two-beds adsorption cooling system employing HFC-32 and a mixture of HFC-32 and HFC-125 (HFC-410a) with activated carbon of type Maxsorb III. The present simulation model adopts experimentally measured adsorption isotherms, adsorption kinetics and isosteric heat of adsorption data. Effect of operating conditions (mass flow rate of hot water, driving heat source temperature and evaporator temperature) on the system performance has been studied in detail. The simulation results showed that the system could be powered by low-grade heat source temperature (below 85 °C). AC/HFC-32 and AC/HFC-410a adsorption cooling cycles achieved close specific cooling power and coefficient of performance values of 0.15 kW/kg and 0.3, respectively at a regeneration temperature of 90 °C along with evaporator temperature of 10 °C. The investigated semi continuous adsorption cooling system could produce a cooling power of 9 kW.

Performance investigation of a waste heat driven pressurized adsorption refrigeration cycle

This article presents performance investigation of a waste heat driven two bed pressurised adsorption refrigeration system. In this study, highly porous activated carbon (AC) of type Maxsorb III has been selected as adsorbent while n-butane, R-134a, R410a, R507a and carbon dioxide (CO2) are chosen as refrigerants. All the five refrigerants work at above atmospheric pressure. Among the five pairs studied, the best pairs will be identified which will be used to provide sufficient cooling capacity for a driving heat source temperature above 60°C. Results indicate that for a driving source temperature above 60°C, AC-R410a pair provides highest cooling capacity while AC-CO2 pairs works better when the heat source temperature falls below 60°C.

Combined absorption power and refrigeration cycles using low- and mid-grade heat sources

This article presents several combined absorption cycles proposed for the simultaneous and/or alternative production of power (mechanical or electrical) and refrigeration. The cycles are classified into two groups according to their driving heat source temperature range as low-grade (<200°C (392°F)) and mid-grade (<300°C (572°F)) combined absorption cycles. The thermodynamic performance of these cycle configurations were evaluated based on energetic and exergetic performance criteria that consider the thermodynamic quality of their useful outputs in both performance criteria. One particularly interesting application of such types of cycles could be the efficient utilization of solar thermal collector installations throughout the year to produce variable amounts of electricity and cooling according to a given building demand to minimize the consumption of primary energy.

Thermodynamic modelling and performance study of an engine waste heat driven adsorption cooling for automotive air-conditioning

Waste heat from engine can be utilized to drive an adsorption cooling system for air conditioning purposes in the vehicle cabin, which not only improves the fuel economy but also reduces the carbon footprint. It is also important to reduce the size of the adsorption bed to adopt the adsorption technology for air-conditioning applications in passenger cars, buses and trucks or even trains. In this article, we present a two stage indirect exhaust heat recovery system of automotive engine employing an effective lumped parameter model to simulate the dynamic behaviors of an adsorption chiller that ranges from the transient to the cyclic steady states. The thermodynamic framework of adsorption chiller is developed from the rigor of mass and energy balances of each component of the system and experimentally confirmed isotherms and kinetics data of various adsorbent–adsorbate pairs. The performance factors are calculated in terms of COP (Coefficient of Performance) and SCP (Specific Cooling Power) for different operating parameters such as cycle time, exhaust gas temperatures, cooling water temperatures and flow rates. From the simulation results, it is found that the exhaust energy of a six cylinder 3000 cc private car is able to produce nearly 3 kW of cooling power for the car cabin. It is also observed that the driving heat source temperature does not remain constant throughout the cycle time unlike the conventional adsorption chiller, and the hot water temperatures as driving source vary from 65 to 95 °C. CaCl2-in-silica gel–water system is found better in terms of COP and SCP as compared with other adsorbents – water systems.

Transient behavior of a cylindrical adsorbent bed during the adsorption process

A transient two dimensional local thermal non-equilibrium model is developed to investigate the influences of heat transfer and operating parameters on the dynamic behavior of a cylindrical adsorbent bed during the adsorption process. Local volume averaging method is used to drive the macro scale governing conservation equations from the micro scale ones. In the model, linear driving force model and Darcy’s equation are considered to account for the resistances to internal and external mass transfer, respectively. Silica gel–water pair widely used in the adsorption cooling systems is chosen to be an adsorbent–adsorbate working pair. The parameters of interest are convective heat transfer coefficient, solid phase thermal conductivity, bed thickness, evaporator pressure, condenser pressure, driving heat source temperature and cooling source temperature. It is found that amount of refrigerant circulated through the system increases with increasing evaporator pressure-driving heat source temperature and decreasing condenser pressure-cooling source temperature. The duration of adsorption process is more sensitive to heat transfer resistances than to mass transfer resistances. The conductive and convective resistances need to be reduced to reach the equilibrium conditions in a short period of time and hence to have a better specific cooling power.

Development of Novel Type of Two-stage Adsorption Chiller with Different Adsorbents

Adsorption refrigeration has attracted considerable efforts over the past few decades. Adsorption refrigeration is considered as green refrigeration technology, which is driven by low grade heat source. Intensified efforts were promoted to improve the adsorption chiller performance in recent years. Two stages with different adsorbents adsorption chiller working principle and test were proposed in this paper. The novel adsorption chiller contains 4 pieces adsorbers and evaporator and condenser. Zeolite and actived carbon were applied for adsorbents in the two-stage cycle and two adsorbers were packed with zeolite and other adsorbers with actived carbon. The two-stage cycle can be operated effectively with 50°C, even with 45°C. Coefficient of performance (COP) and volumetric cooling power (VCP) of two-stage adsorption chiller with different operation conditions were investigated in this paper. The results showed that VCP increases firstly and then decreases with increasing the elapsed time and the maximum of VCP with driving heat source temperature of 50°C and cooling water temperature of 30°C and chilled water temperature of 15°C was about 0.2kW/L. The COP with driving heat source temperature of 45°C was much higher than that of 50°C.

Analysis of the use of adsorption processes in trigeneration systems

Abstract The trigeneration systems for production of cold use sorption refrigeration machines: absorption and adsorption types. Absorption systems are characterized namely by better cooling coefficient of performance, while the adsorptive systems are characterized by the ability to operate at lower temperatures. The driving heat source temperature can be as low as 60-70 °C. Such temperature of the driving heat source allows to use them in district heating systems. The article focuses on the presentation of the research results on the adsorption devices designed to work in trigeneration systems.

Modeling and simulation of an activated carbon–CO2 four bed based adsorption cooling system

In this study, a transient mathematical model of a 4-bed adsorption chiller using Maxsorb III as the adsorbent and CO2 as the refrigerant has been analyzed. The performances of the cyclic-steady-state system are presented for different heating and cooling water inlet temperatures. It is found that the desorption pressure has a big influence in the performances due to the low critical point of CO2 (Tc=31°C). With 80kg of Maxsorb III, the CO2 based adsorption chiller produces 2kW of cooling power and presents a COP of 0.1, at driving heat source temperature of 95°C along with a cooling temperature of 27°C and at optimum desorption pressure of 79bar. The present thermal compression air-conditioning system could be driven with solar energy or waste heat from internal combustion engines and therefore is suitable for both residential and mobile air-conditioning applications.

Performance Comparison of Three-Bed Adsorption Cooling System With Optimal Cycle Time Setting

This article presents the optimal cycle time and performance of two different types of silica gel–water-based three-bed adsorption chillers employing mass recovery with heating/cooling scheme. A new simulation program has been developed to analyze the effect of cycle time precisely on the performance of the systems. The particle swarm optimization (PSO) method has been used to optimize the cycle time and then the optimum performances of two chillers are compared. Sensitive analysis of cycle time has been conducted using the contour plot of specific cooling power (SCP) with driving heat source temperature at 80°C. It is found that the center point of the contour indicates the maximum SCP value and optimal cycle time, which are comparable with the quantitative values obtained for the PSO method. Both three-bed mass recovery adsorption cycles can produce effective cooling at heat source temperature as low as 50°C along with a coolant at 30°C. The optimal SCP is similar for both cycles and is greater than that of the conventional two-bed adsorption system employing the same adsorbent–refrigerant pair. Consequently, the proposed comparison method is effective and useful to identify the best performance of adsorption cycles.

PERFORMANCE STUDY AND EXPERIMENTAL CYCLES OF TWO STAGE SOLAR HYBRID ADSORPTION REFRIGERATION SYSTEM

The performance parameters and experimental cycles of a solar adsorption refrigeration system working with the activated carbon-methanol working pair are presented here. Such a system has been fabricated and tested under the conditions of National Institute of Technology Calicut, Kerala, India. The performance parameters such as specific cooling power (SCP), coefficient of performance (COP), solar heating COP, solar cooling COP, uptake efficiency and exergy efficiency are studied. The dependency between the exergy efficiency and cycle COP with the driving heat source temperature for two thermal compressors is also studied. The optimum heat source temperature for the thermal compressor one is determined as 71.4oC and for the other thermal compressor it is 68.20C. The system has a mean cycle COP of 0.196 during day time and 0.335 for night time. The mean SCP values during day time and night time are 47.83 and 68.2, respectively. Experimental results also demonstrate that the adsorption refrigerator has cooling capacity of 47 to 78 W during day time and 57.6 W to 104.4W during night time. This study also presents the analysis of experimental thermodynamic cycle of solar adsorption refrigeration system. Two cycles have been analysed experimentally, one with clear sky and the other with partly cloudy. Use of artificial neural network model is proposed in order to predict the performance of the system. After training, it was found that LM algorithm with 9 neurons is most suitable for modeling solar adsorption refrigeration system. The ANN predictions of performance parameters are in good agreement with the experimental values with R2 values close to one and maximum percentage of error less than 5%. The RMS and covariance values are also found to be within the acceptable limits.