International Journal of Air-Conditioning and Refrigeration

Heating ventilation air conditioning (HVAC) design mainly deals with moisture and its control. The moisture may be present inside ducts, conditioned spaces, or outdoors. The process of humidification and dehumidification requires equipment for mass and heat transfer, where the transfer of energy and mass takes place at varying concentrations and temperatures. The exchange of mass or heat depends on the type of flow and is conceivably in the form of gas to liquid or liquid–vapor. This paper aims to review the effect of moisture in the buildings and modulate its effect with several humidifying and dehumidifying techniques as sustainable techniques depending upon the external weather conditions to maintain thermal comfort. Various humidification and dehumidification techniques have been discussed with both their merits, limitations, applications and future scope to meet sustainable energy demands.

A detailed literature review on the flow characterization of the capillary tubes is presented in this paper. The flow behavior is reviewed for straight, helically, and spirally coiled capillary tubes at different operating and geometric conditions by considering various aspects in the tube. This paper summarizes experimental and numerical study on the adiabatic and nonadiabatic straight and coiled capillary tubes at different geometries conditions. The vital information of the range of the tube geometry and operating conditions are discussed, which can be utilized for further studies on the capillary tube. Various methodologies with generalized correlations are indicated. It has been observed that there are even more studies need to do with environmentally friendly refrigerants with various practical aspects in the capillary tube. It would be interesting to find the coiling effect on the design and simulation of the capillary tube. In addition to that more experimental and numerical studies need to explore the nonadiabatic coiled capillary tube. It would be fascinating to study the metastable condition in the capillary tube and set suitable relations to present its effect on the mass flow rate.

The creation of new age refrigerants might be the answer to the issue of an Earth-wide rise in temperature. Hence, while choosing new refrigerants a careful process is required. The general effect of any refrigerant substance on global warming, energy efficiency, ozone depletion, cost-effectiveness, chemical stability, and safety ought to be assessed. This paper sums up the experimental and numerical investigations directed with the globally accepted R1234yf refrigerant. The paper’s principal points are to assess the capability of the hydro-fluoro-olefin (HFO) refrigerant mainly R1234yf utilized in the refrigeration system (vapor compression systems, domestic refrigeration system) and to explore its utilization as an eco-friendly refrigerant. In the vapor compression refrigeration system, the cooling capacity and coefficient of performance of R1234yf are found to be less, 9% and 11%, respectively compared to that of R134a. But the power consumption of the system with R1234yf increased between 1.6% and 6.7% when compared to R134a. This paper likewise assists with recognizing the gap in the past research works and explores the possibilities for additional works.

The human thermal comfort and the indoor healthy air quality in the houses and the offices have become a vital necessity, especially in the state of the development of the contagious virus as the COVID-19. In this study, the evaluation of the air distribution was investigated using a DHTT sensor connected to an ARDUINO card to benefit their simple use and their reasonable price comparing to other tools such as the infrared camera. The measurement of the temperature is made in 14 points divided on two directions: one near the sitting manikin and another in front with the cooling system. The impact of the heat sources was tested. In these conditions, the indoor temperature was examined for an empty room, a room occupied by one person and one computer, a room occupied by two persons and two computers and a lighted room. The experimental results prove that the indoor temperature increases with the multiplication of the heat sources. From a temperature equal to $T=32^{\circ }$C, the PMV curves move away from the comfort zone and the indoor climate becomes hot.

This study presents a coupled model to simulate the heat transfer process between the helical condenser coil and the water inside the tank. This coupled model was developed using ANSYS Fluent Computational Fluid Dynamics (CFD). The heat flux of the condenser coils is obtained from our experimental investigation and delivered as initial boundary conditions to the tank model. The results obtained are considered essential and are, in turn, capable of assessing the performance of the modified domestic refrigerator for the production of hot water. According to this model, the results confirmed that the coefficient of heat transfer and the performance of the system decreased with an increase in the heating time. The natural heat transfer coefficient Uc falls from 727.26W $\cdot$ m${}^{-2}$ $\cdot$ K${}^{-1}$ to 68.64W $\cdot$ m${}^{-2}$ $\cdot$ K${}^{-1}$ during the total heating cycle, and the water temperature rises from 20^∘C to 50.73^∘C. In addition, the impact of water temperature on the evaporating region was used in this analysis. Therefore, the temperature of the evaporator is unaffected by the development of hot water. As a result, these outcomes will be used for the development of the domestic refrigerator with immersed condenser coil.

An experimental investigation was carried out to study the performance evaluation of Modified Low-Temperature Cascade (MLTC) system, based on two-stage cascade type refrigeration system using the combination of R404A/R23 refrigerants. This system was developed using chilled water (CHW) in the condenser of high-temperature circuit (HTC) and pre-cooler (PC) in the low-temperature circuit (LTC). Isentropic compression efficiency is computed in this work and used here as an important parameter. Performance of MLTC system was compared with or without the introduction of PC into LTC. System’s coefficient of performance (COP) has also been compared with using CHW, cooling tower water (CTW), normal water (NW) into the HTC condenser. It has also been shown that COPs of the system are significantly affected by slight variation in the LTC and HTC evaporating temperatures. Presented parameters and comparisons are likely to help in developing a low-temperature (LT) refrigeration system with higher efficiency for industrial and other applications.

In this study, a modified auto-cascade refrigerating cycle is proposed. The cycle includes two evaporators and one compressor, and a separator is located after the refrigerator evaporator. The vapor phase from the separator is condensed through an internal evaporator and is mixed with some amount of the liquid phase taken from the separator. The condensed liquid is sent to the freezer evaporator at low pressure. Thermodynamic properties of the mixture R290/R600a, which is a zeotropic mixture as a cycle fluid, were determined using the REFPROP database. The variation of the cycle performance and total cooling capacity is investigated by changing the ratios of refrigerator and freezer loads. The results show that the volumetric cooling capacity increases and the compressor pressure ratio decreases as the load ratio of the refrigerator increases.

In this work, a cascade refrigeration system operating with four different ecological refrigerant pairs was modeled. This system uses R744 (Carbon dioxide) in the low-temperature cycle and operates with R290 (propane), R1234yf (2,3,3,3-tetrafluoropropene), R152a (1,1-difluorethane), and R717 (ammonia) in the high-temperature cycle. Energetic, exergetic, environmental, and economic performance of the cascade system was investigated to determine the most appropriate ecological refrigerant couple. The parameters used in each mentioned performance were COP (Coefficient of Performance), ${\eta }_{\mathrm{\text{exergy}}}$ (Exergy Efficiency), TEWI (Total Equivalent Warming Impact), ECOP (Ecological coefficient of performance), and ${Ċ}_{\mathrm{\text{total}}}$ (Total plant cost rate), respectively. The results showed that the cascade refrigeration system operating with R744/R717 provided the best performance for the thermodynamic conditions analyzed, presenting a COP of 2.10, ${\eta }_{\mathrm{\text{exergy}}}$ of 56.9%, ${Ċ}_{\mathrm{\text{total}}}$ of 24 334 USD/year, ECOP of 4.86, and TEWI of 25.67 tons of CO₂. Finally, evaluating the total plant cost rate of this cascade system, it was noted that the capital and maintenance cost rate $({Ċ}_{\mathrm{\text{CM}}})$ corresponds to 89.1% of the ${Ċ}_{\mathrm{\text{total}}}$ value, the operational cost rate $({Ċ}_{\mathrm{\text{op}}})$ corresponds to 10.27% of the ${Ċ}_{\mathrm{\text{total}}}$ value and the environmental cost rate $({Ċ}_{\mathrm{\text{env}}})$ corresponds to 0.63% of ${Ċ}_{\mathrm{\text{total}}}$.

Thermoacoustic refrigeration is an emerging green, novel and promising alternate technology compared to vapor compression refrigerator systems for domestic cooling. It uses environmentally benign gases like air or helium or the mixture of inert gases as working substances and has no moving parts, no lubrication and no vibration. The cooler is designed and optimized with helium and air as refrigerants operating at 10bar with 3% drive ratio for the temperature difference of 28K and stack diameter of 200mm using linear thermoacoustic theory. In this paper, the effect of gas blockage (porosity) of the spiral-stack heat exchanger system ranging from 45% to 85% on the theoretical performance of the cooler is discussed. The one-third and one-fourth wavelength convergent–divergent resonator designs are optimized with air and helium as working substances, respectively, to improve performance and power density. The optimized coolers show best performance with 85% porosity. The theoretical results are validated with DeltaEC software simulation results. The simulation results show the coefficient of performance and cooling capacity of 0.93 and 219W for helium and of 0.50 and 139W for air, respectively, at the cold heat exchanger temperature of 0^∘C.

In this paper, exergy destruction analysis of a heat-assisted ejector cooling system has been carried out using a modified Gouy–Stodola equation. The modified Gouy–Stodola equation provides a more accurate and realistic irreversibility analysis of the system than the conventional Gouy–Stodola formulation. The coefficient of structural bond (CSB) analysis has also been executed to find the component whose operating variables affect the system’s total irreversibility at the most. Exergy analysis revealed that the maximum exergy loss happens in the ejector followed by the generator and condenser. The model predicted 40.84% of total irreversibility in the ejector at the designed conditions. However, total exergy destruction is found to be the most sensitive to the evaporator temperature. The CSB value of 12.97 is obtained in the evaporator using the modified exergy method. The generator appears to be the second sensitive component with the CSB value of 2.42, followed by the condenser with the CSB value of 1.628. The coefficient of performance of the system is found to be 0.18 at the designed conditions. The refrigerant R1234yf is considered in the system.

A conventional vapor compression refrigeration system (VCRS) cascaded with a heat-assisted ejector refrigeration system (ERS) has been experimentally analyzed. Cascading allows the VCRS to operate at lower condenser temperatures and thus achieve a higher coefficient of performance. In this cascaded system, the condenser of the vapor compression system does not dissipate its heat directly to the evaporator of the ERS; instead, water circulates between the condenser of VCRS and the evaporator of ERS to exchange the heat. Seven ejectors of different geometries have been used in the ERS; however, all the ejectors could not maintain thermal equilibrium at the desired operating conditions. The compressor of the cascaded VCRS consumed 1.3 times less power than the noncascaded VCRS. Furthermore, the cascaded system provided a maximum 87.74% improvement in COP over the noncascaded system for the same operating conditions. The performance of the system remained constant until the critical condenser pressure of the ERS.