International Journal of Air-Conditioning and Refrigeration

Heat pump tumble dryers, air-vented dryers and condenser dryers are widely used as clothes dryers. Clothes dryers use hot air to absorb moisture from textiles to get them dry after a wash by passing drying air through the drum. To simulate the drying process of clothes in the drum and to obtain the moisture evaporation rate, it is necessary to use an accurate model to predict the moisture transfer coefficient from the textile to the air in the drum as well as the mass transfer area between the drying air and the textile. In this study, a comprehensive review of the literature on the prediction of the moisture evaporation rate inside the drum of a clothes dryers was conducted. It was found that researchers generally used constant values, fitting models, dimensionless correlations, and Chilton–Colburn analogy to predict the area–mass transfer coefficient. Moreover, few researchers used the effectiveness model for the prediction of moisture evaporation rate. The comprehensive review of the literature showed that all of the previous models for prediction of the moisture evaporation rate have some limitations in terms of generality or accuracy. Therefore, the development of a new accurate model for prediction of the moisture evaporation rate inside the drum of clothes dryers is crucial.

This work is a contribution to the improvement of the thermal and the dynamic fields of a natural convection indirect solar dryer, composed of a solar flat air heater and a drying chamber, intended for drying agricultural products and medicinal plants. We have studied the effects of size and position of the outlet on the distribution of air and temperature within the drying chamber, containing the figs as a product to be dried. To be more realistic, we have used a user defined function (UDF) subroutine written in $C++$ to integrate the unsteady evolution of a day’s climate data in the Oujda region.

This study was achieved by numerical simulations using the ANSYS FLUENT software, in order to optimize the distribution of air and temperature inside the drying chamber, and to choose the best outlet’s position and size for the best efficiency of the dryer.

The results show that the optimal outlet position found is in the right corner with a size range of 0.07 to 0.15m. The effects of the position and size of the outlet on the air deflection along the trays were also presented and discussed.

Numerical simulation of a mini-channel, flat-tube, louvered fin, automotive condenser is performed to study the heat rejection rate, pressure drop and performance of the heat exchanger. The simulation study is carried out for the refrigerant R1234yf. The properties of R1234y are obtained from REFPROP software. The moist air properties are calculated from those of dry air and water vapor using suitable correlations. To select the input data, the cycle performance is carried out for a standard vapor compression refrigeration system working with R1234yf between the temperature limits of $-10^{\circ }$C on the low-pressure side and $40^{\circ }$C on the high-pressure side. The condensation process is taken into account in three sections, namely, the superheated, two-phase and the subcooled regions. A custom code is prepared in MATLAB to solve the simultaneous equations of heat transfer from refrigerant to inside tube wall, inside tube wall to outside tube wall and outside tube wall to moist air. The simulation results show the sensible heat transfer during desuper heating to be very small compared to the condensing region. Results are reported for the pressure variation along the refrigerant flow passage in the desuper heating, two-phase and subcooling regions. The heat-transfer coefficient is found to be the highest in the two-phase region for higher dryness fractions. The effect of inlet air velocity is less compared to that of the inlet air temperature on the heat rejection rate.

The world is now living in an energy crisis. Refrigeration and air-conditioning systems have become the basics of daily life in various fields and accordingly, it cannot be dispensed. Refrigeration machines and air-conditioning systems are the most energy-consuming systems, independent on the application whether it is domestic, commercial, industrial or medical. Therefore, using cooling systems which are powered by thermal energy, e.g., solar energy, can save a lot of electrical energy. Absorption refrigeration system is an example of a refrigeration system powered by heat energy. However, the system problem here is that it has low coefficient of performance (COP). The objective of this research is to improve the COP of the ammonia absorption cycle. This is done in the absorber unit by improving the absorption of the refrigerant ammonia into the ammonia–water solution. The absorption efficiency is improved by using (1) a stirrer pump to improve mixing, (2) sprayers to increase the contact area between ammonia and ammonia–water solution and (3) continuous cooling of the solution during the absorption process via an external heat exchanger. The COP of the ammonia absorption cycle has increased from 0.48 to 0.715, i.e., by 49%. This is due to the improvement of the absorption of the ammonia into the ammonia–water solution.

The rising need for thermal comfort has resulted in a rapid increase in refrigeration systems’ usage and, subsequently, the need for electricity for air-conditioning systems. The ejector system can be driven by a free or affordable low-temperature heat source such as waste heat as the primary source of energy instead of electricity. Heat-driven ejector refrigeration systems become a promising solution for reducing energy consumption to conventional compressor-based refrigeration technologies. An air-conditioning system that uses the ejector achieves better performance in terms of energy-saving. This paper presents a study on the combined driven refrigeration cycle based on ejectors to maximize cycle performance. The experimental setup is designed to determine the coefficient of performance (COP) with ejector nozzle sizes 1.8, 3.6, and 5.4mm, respectively. In this system, the R-134a refrigerant is considered as a working fluid. The results depict that the efficiency is higher than that of the conventional refrigeration method due to comparing the performance of the conventional refrigeration cycle and the combined driven refrigeration cycle. The modified cycle efficiency is better than the vapor compression cycle below 0^∘C, which implies sustainability at low temperatures by using low-grade thermal energy. For the improvement of mechanical efficiency, proposed cycle can be easily used.

The Natural Gas Liquids (NGL) recovery unit is one of the processes that requires cooling. The sweetened gas enters this unit after the dehydration stage, and the final product called NGL Product is stored and ready for consumption or export. In this research, the first, one of the NGL units, is simulated with HYSYS software. Three types of processes with different cooling systems are studied using the exergy analysis method. Joule–Thomson’s combination with the expander is selected for its high exergy efficiency, and the exergy efficiency function has been selected as the objective function 1 to optimize this process mathematically based on this study’s findings. The critical term in this objective function is the work of the compressors and turboexpanders in the process. After defining the optimization problem, the problem is optimized by two genetic algorithms and SQP, considering the process constraints and the process’s initial conditions. Finally, using the genetic algorithm’s data application to the simulated process, a 15% increase in the plant’s exergic efficiency was observed.

A Turbine Inlet Air Conditioning (TIAC) system can chill the inlet air of the turbine to maintain maximum turbine performance at all ambient temperatures. However, turbine characteristics, performance guarantees and bell-mouth icing considerations require accurate prediction of the chilling coil performance over a wide range of operating conditions. A modified wet-surface model (MWSM) is developed to more accurately predict the chilling coil performance. The higher accuracy of the model is demonstrated by applying the model to simulate performance data of two different coils. The data covered a wide range of operating conditions with ambient temperature vary from $43.3^{\circ }$C to $9.7^{\circ }$C dry bulb and $27.2^{\circ }$C to $6.1^{\circ }$C wet bulb. The turbine flow rate varies from 100% to 43% with chilled air temperature in the range of 3.3–$14^{\circ }$C and chilling load variation of 100% to 5%. The chilled water flow rate varies from 100% to 32% with supply glycol-water temperature in the range of $-$2.2–$6.1^{\circ }$C. The MWSM uses 11 empirical parameters evaluated from the coil performance data and is able to correlate the data with an adjusted coefficient of determination ($R_{\mathrm{\text{adj}}}^2$) of over 99%. The higher accuracy of the modified model enables the development of a more robust controls strategy required to maintain the inlet air temperature at the set point with varying ambient temperatures and chilling load conditions. The model can also be applied to other chilling and dehumidification applications especially those experiencing wide variations in operating conditions and load or those requiring close control of the chilling and dehumidification process.

This research study compares the thermodynamic performance of 10kW lithium chloride–water (LiCl–H₂O) and lithium bromide–water (LiBr–H₂O) absorption cooling systems through first and second law of thermodynamics. Further, the exergy degradations happening in each component have been split into unavoidable and avoidable exergy degradations as well as endogenous and exogenous exergy degradations through advanced exergy analysis. Pressure–temperature–concentration ($P$–$T$–$X)$ diagrams are drafted to clarify the real, ideal, and unavoidable cycles for LiCl–H₂O and LiBr–H₂O absorption cycles. Moreover, this paper exhibits the sensitivity of various system components towards the generator, condenser, and absorber temperature for both pairs. Energetic observation proves that LiCl–H₂O pair is 10% more efficient as compared to LiBr–H₂O pair. Exergetically, LiBr–H₂O cycle struggles with additional (nearly 13.45%) exergy destruction than LiCl–H₂O cycle. The major contribution (around 70% to 80%) of irreversibility comes from the generator and absorber. Comprehensively, the parametric partitions of irreversibility rate in each component provide broad indications to prioritize the system components for enhancements.

4E analysis is used on a Brayton–Rankine combined cycle power plant (CCPP) with a dual pressure heat recovery steam generation (HRSG) system. A multi-objective genetic-based evolutionary optimization has been used to estimate the most optimal exergy efficiency status, exergy cost reduction, carbon emission reduction, and NOx emission reduction. For the validation of the data, the simulation results are compared with the plant’s data. This study investigates the effect of every decisive parameter on the objective performance parameters of the CCPP. The primary estimated results are the emission rates, efficiencies, and the exergoeconomic cost of the system. At the optimum operational state, the exergy efficiency may increase by 10%, while the total emissions may decrease by 14.6%. The conventional technical measures’ effectiveness to improve the combined cycle power plant’s energy performance is applied to the simulated case study. Results have shown that the main source of the exergy destruction in this system is the HRSG and the combustion chamber, and also the overall performance of the plant shows great sensitivity to the ambient air temperature. This fact has shown that climate change and global warming are effective in thermal power plants’ performance. Therefore, the effect of the climate change on the ambient air temperature impact on the power plant and the 4E performance of the simulated combined cycle power plant is also studied. The results show that, due to the global warming effect, the exergy efficiency of the CCPP unit is decreased by over 0.2% in the last two decades, which can be generalized to all thermal electricity generation units throughout the world based on the mean global temperature rise in the last decades.

Refrigeration and air conditioning cycles consume a large amount of electrical energy and the shortage in traditional sources of energy is the main reasons for governments to use renewable energy. The most power consuming part in the Vapor Compression Cycle (VCC) is the gas compressor. Therefore, the objective of this research is to increase the cooling rate of the VCC using the same compressor, and that is done by heating the refrigerant coming out from the compressor. The proposed cycle is similar to the VCC except that the compression processes is done in two stages, the first stage via a gas compressor and in the second stage by heating the refrigerant under constant volume. The heating process can be done using solar energy. An experimental setup has been developed to study the influence of heating the refrigerant on the cooling rate of the VCC. The heating process is performed after the compressor, and it is done under constant volume in order to increase the pressure of the refrigerant. Four experiments have been performed; the first experiment is a normal VCC, i.e., without heating, while in the second, third and fourth experiments, the refrigerant has been heated to 50^∘C, 100^∘C and 150^∘C, respectively. It has been found that the cooling power increases with the heating temperature. Heating increases the pressure of the refrigerant in VCC, and consequently increases the mass flow rate of the refrigerant that results in an increase in the refrigeration power for the same compressor power. However, the disadvantage of heating the refrigerant is that it increases the evaporator temperature, which limits the possibility of the VCC to be used in freezing applications.

Air curtains are installed to reduce heat loss due to drafts intruding into the indoor through the open doorways, and play the role of separating two climatic zones and different environmental zones. It is also used to protect the workplace from impurities or to reduce the spread of cigarette smoke in restaurants. Recently, aircraft to provide the individual air barrier by the vertical blowing air curtains have installed a physical barrier in the breathing zone between adjacent seats to protect passengers from COVID-19. The main factors affecting the sealing performance (SP) of the air curtain are the difference of temperature and pressure between indoor and outdoor, and are used to make the proper jet flow an air barrier with the high airtightness. Until now, various types of air curtains are manufactured and sold. Air curtains with the improved SP do not only have a discharge port but also a suction port. This study was conducted to evaluate the SP of the horizontal blowing air curtain according to the discharge pressure, and to select the minimized volume flow rate required for creating the proper zone separation. The volume flow rate of outdoor air intruding into the indoor through the doorways is used to evaluate the SP of the air curtain, and is calculated using the SVE4 proposed by Murakami in this study.