International Journal of Air-Conditioning and Refrigeration

In this paper, a model of a water-cooled centrifugal chiller system is developed and its control performance is studied. The overall system consists of three control loops: (i) a compressor speed control; (ii) an inlet guide vane control and (iii) a condenser liquid-level control. The model is validated by comparing the simulation results with the experimental data under steady state conditions. The results match to within 10% accuracy. A multi-mode control strategy was designed to simulate the operation of the centrifugal chiller as it transitions between start-up, speed control mode, IGV control mode and shutdown mode during a typical day operation. COP of the chiller was studied by conducting simulation runs under a wide range of operating conditions. The results showing the coefficient of performance of the system at different cooling loads as a function of cooling water temperature under IGV control mode and compressor speed control mode are presented.

The adsorbent coated exchangers are the main part of adsorption refrigeration systems. Although coated exchangers are commercially available, the coating technique and the binder used are seldom revealed and left as a challenge for researchers. Dip-coating is the most commonly used coating technique. However, the variety of binders used indicates that choosing the appropriate binder is still a matter of trial-and-error. A series of experiments were performed to introduce acrylic latex emulsion (ALE) and bitumen emulsion as the new binder for coating silica-gel powder on aluminum. The results indicate coats created by both emulsion binders are stable but the bitumen emulsion keeps its stability for about 10min after mixing with water and silica-gel powder. The effect of ALE binder and water concentrations on water vapor equilibrium and desorption kinetics was investigated. The outcomes indicated that the sample containing 0.8g water/g silica-gel, 0.08g ALE binder/g silica-gel shows the fastest desorption kinetic and the minimum capacity loss. The mechanical stability of this sample was evaluated by the shear test and the pull-off test. The measured values show that the prepared laminate withstands up to 27N/cm² shear stress and 18N/cm² tensile stress.

In this study, heat-transfer and friction characteristics of newly developed nonsymmetric slit-finned-tube heat exchangers are experimentally investigated. The newly developed slit fin had more slits in the second row than the first row. As a result, different row effect on $j$ factor than that of conventional enhanced finned-tube heat exchangers was observed. In other words, two-row configuration yielded larger $j$ factor than the one-row configuration. Comparison with conventional louver fin or slit fin heat exchangers revealed that the present slit fin heat exchangers show superior heat-transfer characteristics, especially at the second row. The reason was attributed to the many narrow slits that formed at the second row, which maintain thin water film along the slits and smooth the condensate flow.

When water chillers are arranged in series-series counterflow (SSCF), the compressor lift of each chiller is decreased in comparison with that of water chillers in parallel. This means that the compressor power of SSCF chillers is lower than that of parallel chillers. In this paper, models of the main components in an air conditioning system were developed and verified to predict the behaviors of the whole system with respect to SSCF chillers. The results showed that performance was maximized with three SSCF chillers when the system was operated with normal set points. The performance was further improved to 26% and decreased with the number of SSCF chillers when the system was operated with optimal set points. The SSCF chiller system also demonstrated higher exergy efficiency regardless of the number of SSCF chillers. The irreversibility of components in SSCF chillers was rather low. However, the irreversibility of the cooling tower and cooling coil was slightly higher and lower, respectively, than those in the parallel chiller system.

The current study assesses the thermo-economic performance of a H₂O$+$[EMIM][DMP] (1-ethyl-3-methylimidazolium dimethyl phosphate) working fluid-based absorption machine coupled with various solar collectors to cater the cooling load to business building at Gandhinagar city, India. H₂O$+$[EMIM][DMP] could be an alternative to conventional LiBr$+$H₂O working fluid pair of absorption machines as it can operate without problem of crystallization which is perquisite for the continuous operation of the system. A mathematical model is developed to simulate the proposed system with 10kW cooling capacity at 5^∘C. The sensitivity assessment is carried out to find the effect of various parameters including heat source temperature on the coefficient of performance (COP) and exergetic efficiency for each collector case. The optimum SCOP of parabolic trough collector (PTC)-based system is 11.43% higher compared to ETC-based system, whereas the ETC-based system is 25.10% economical than the PTC-based system. Furthermore, payback period for ETC-based system is only one month higher than FPC-based system, which altogether exhibits the superiority of ETC-coupled H₂O$+$[EMIM][DMP] absorption refrigeration system over FPC-based system.

This paper reports the design and implementation of genetically optimized fuzzy logic controller (GAFLC) for split air-conditioner based on the principle of Fanger’s Predicted Mean Vote (PMV) index. The proposed control strategy is aimed at improving the indoor thermal environment (ITE) at houses, offices, libraries, hotels, etc. because it plays a vital role in determining the health, physical and mental productivity of the occupants. The GAFLC has been implemented in MATLAB Simulink for computer simulation and also on hardware platform using the commercially available 8-bit ATmega-328 microcontroller through embedded C-coding for real practice. One part of the designed control algorithm examines the values of activity level, clothing insulation, air velocity, and relative humidity and decides the comfort temperature value to be set such that the PMV and PPD indices get satisfied. The other part generates a control signal to the air-conditioner compressor to maintain that temperature. From the simulation results it is seen that the generated comfort temperature values are in the range of 24.4^∘– 26.55^∘C for various combinations of environmental and personal parameters, which are well above the general temperature set value of 20^∘C. This indicates the scope for reducing energy consumption to a greater extent. Also the PMV index lies in the range of $-$0.23 to +0.36 with untuned fuzzy inference system (FIS), and in the range of $-$0.32 to +0.14 with genetic algorithm (GA)-tuned FIS, which are acceptable comfort levels that human physiology can endure with more satisfaction. The experimental results show that GAFLC has generated a comfort temperature value for specified input parameters and also maintained the room temperature at that value to keep the thermal ambience more satisfactorily.

Accurate prediction of the friction factor and consequently the pressure drop of two-phase flow in small channels is still an issue. Many correlations exist for the determination of the viscosity and the friction factor that appear in the frictional pressure drop and their combination often determined the degree of disagreements between the experimental data and predicted outcomes. Demands for environmentally friendly refrigerants have further posed a challenge to find compatible alternatives with as good a performance as the current coolants. Despite the many available correlations developed to date, many more are studied in effort to reduce the discrepancies. This paper presents the outcomes of a study comparing the optimized conditions when three different viscosity equations are paired with eight different friction factor correlations to minimize the frictional pressure drop. The approach used multi-objective genetic algorithm (MOGA) to assist in selecting the best pairing. Comparison is then completed with available experimental data. The study showed that the Blasius friction factor paired with the Dukler viscosity produced the least percentage difference for R22, while when paired with the McAdams viscosity produced a lower difference for R290, an environmentally friendly refrigerant being considered to replace R22.

This paper experimentally investigates the effect of pressure resistance distribution by using perforated grilles with different porosities ($F=100$%, 58% and 35.4%) in a container data center. The inlet and outlet temperature distribution, rack cooling index (RCI) and supply heat index (SHI) are used to evaluate the cooling performance under semi-contained and fully contained configurations. As a result, the airflow reversal phenomenon at the top cabinets is found, which is especially conspicuous for the case without perforated grilles due to the extremely low pressure resistance in the cabinet. By implementing perforated grilles at lower three cabinets, the airflow reversal can be eliminated, however, it cannot be completely removed. By applying perforated grilles with $F=35.4$% at the top three cabinets can increase the pressure resistance at the cabinets $S1$ where the airflow reversal is eliminated thoroughly. Yet, the performance of cabinets at rack $A1$ may degrade rapidly due to much stronger hot-exhaust recirculation. Hence, the fully contained configuration is applied. Note that the airflow reversal is more severe for the case without perforated grilles. By arranging the perforated grilles with $F$ = 35.4%, the corresponding RCI and SHI may reach the ideal values of 100% and zero, respectively. Therefore, the perforated grilles with $F$ = 35.4% are more reasonable for simulated racks under semi-contained and fully contained configurations when airflow reversal occurs.

This paper presents the development of a numerical, iterative and nonisentropic model for the thermodynamic processes of a reciprocating compressor of a refrigeration system operating at steady state. The mathematical model was implemented using the scientific software Engineering Equation Solver (EES) and it is based on the application of the energy equations in four regions of the compressor: inlet duct and chambers of pre-compression, compression, and post-compression. The model was validated with experimental data collected from an open-drive reciprocating compressor, operating with the refrigerant R-134a at different suction and discharge pressures and with different compressor rotational speeds. Model validation was made comparing the values of the mass flow rate and the discharge temperature of the compressor generated by the model with their corresponding experimental values for 33 experimental tests, the mean relative difference was $-$0.2% for the discharge temperature and 2.9% for mass flow rate. In this validation, the output variables of the model were calculated considering the uncertainties from the input variables. The theoretical mean standard uncertainty is 2% for discharge temperature and 6% for mass flow rate. An analysis of the capacitive and thermal performance of the compressor was made using the model, which demonstrates a decrease in the capacitive and thermal efficiencies for increasing the pressure ratio or clearance volume.

This paper studies the performance of vapor compression refrigeration system using hydrocarbon refrigerant (HCR) mixture (R600a and R290), hydrocarbon nanorefrigerant mixture (R600a and R290/TiC) and cryogenically treated hydrocarbon nanorefrigerant mixture (R600a and R290/Cryo TiC). The COP of HCR (R600a and R290) system is 1.2960, whereas, COP of R600a and R290/TiC nanorefrigerant system is 1.5223. The TiC nanopowder is cryogenically treated at $-196^{\circ }$C for 24h. The treated TiC is dispersed in HCR mixture. Hence, the COP of R600a and R290- Cryo TiC system is further increased to 1.5801. The energy consumption of R600a and R290-TiC is reduced by 10.3% when compared with HCR. Further, it is reduced by 12.69% with respect to cryogenically treated refrigerant (R600a and R290/Cryo TiC) system. The COP is enhanced due to deep cryogenic of TiC nanopowder.

In this study, energy and exergy analysis was used to evaluate the performance of a vapor compression refrigeration system with a flooded evaporator and the causes of high temperatures of beverage during the production process determined. Subsequently, the components of the operation that require modification were identified in order to improve the system performance. The actual operating parameters related to energy and exergy analysis of the investigated beverage manufacturing plant were measured, the thermal properties of the beverage were determined from a calorimeter experiment, and mathematical models were developed based on the first and second laws of thermodynamics from the literature. The system energy and exergy efficiencies were 57.46% and 21.17%, respectively, whereas the system exergy destruction was 695.71kW. The highest exergy destruction among the components of the refrigeration system occurred at the cooling plate, followed by the ammonia compressor. The cooling plate also experienced a loss in the refrigerating effect of 43.59kW. Therefore, the cooling plate is the area with the highest potential for improvement. The ammonia compressor presents another potential area of improvement, which includes operating the compressor at a high compression ratio and high superheated temperature. However, the reduction of beverage inlet mass flow rate at the cooling plate offers the best opportunity to achieve a low beverage temperature between 1.00^∘C and 2.00^∘C and decreasing the system exergy destruction without incurring additional investment costs.