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This study investigates the thermal performance of an evacuated U-tube solar collector (ETSC) using different tube geometrical configurations. The effect of tube geometry on the overall collector efficiency is numerically analyzed and compared with experimental results. Three different ETSC configurations made of copper viz., Model 1 (M1) having one inlet and two outlets, Model 2 (M2) having one inlet and three outlets, and Model 3 (M3) having one inlet and four outlets are considered. An overall rise in temperature of heat transfer fluid at the outlets for each model is predicted and compared with a conventional U-tube (CT) for different mass flowrates and solar insolations to evaluate the collector performance. In comparison with the CT, the outlet temperature of the M3 and M1 is higher by 46.2% and 40.3%, respectively. M2 gives a nearly similar fluid outlet temperature as M1. A maximum of 35.4% enhancement in heat gain compared to the CT is observed for M3 (which is best among modified configurations) under similar operating conditions. However, at 788 W/m2 solar insolation and a constant mass flowrate of 0.0167 kg/s, the estimated thermal efficiency of M1 is higher among the three models which is 33.5% higher than the CT. The experimental results closely approximate the numerical predictions with a deviation of ± 1.1 °C. From the economic evaluation of the modified collectors, a minimum payback period of 2.5 years was observed for Model 1 which is the shortest among the investigated ETSC systems.

Maintaining human thermal comfort and extensive power consumption of the conventional heating ventilating and air-conditioning systems drive the researchers to look for an alternative dehumidification system. Among the potential alternatives, the liquid desiccant dehumidification system has evolved as a long-term renewable and less power consuming system due to its effective controlling capability of humidity. In the present study, an experimental investigation is carried out to demonstrate the performance of lithium bromide (LiBr) and potassium formate (HCOOK) desiccant solution mixture in a spray type counterflow-packed bed adiabatic dehumidifier. Subsequently, ternary plots and 3D-contour trade-off paradigms are patterned to assess the performance parameters using an optimal mixture design methodology. Additionally, empirical correlations are developed to pattern the performance parameters (moisture removal rate (MRR), enthalpy effectiveness (ξh) and moisture effectiveness (ξm)) as a function of blend combinations. Further, the present study endeavours to explore the application of offline calibration methods based on a balanced optimum mixture design-centred desirability approach for optimizing the mixture proportion to obtain the optimal performance parameters (i.e., MRR, ξh and ξm). The wettability area is explained based on the static contact angle on a plane glass. The results showed that the contact angle was decreased from 47.3° to 44.1° for the optimum mixture of LiBr solution (37.2%-LiBr +17.8%-HCOOK), which further confirmed the higher MRR. Lastly, the tuning effect of the liquid to gas flow rate on the dehumidifier performance and economic viability of LiBr-HCOOK blends are studied.

Current research in dehumidification systems is mainly focused on thermally driven liquid desiccant systems. However, the selection of proper desiccant solution has a greater significance on the performance of a dehumidifier. In this perspective, current work is presented with governing equations of energy, mass and species balance to study the performance of a dehumidifier. The governing equations are solved using finite difference method coupled with Jacobi’s model for an air–desiccant contact system of a cross-flow packed bed adiabatic dehumidifier operating with different desiccant blends of lithium chloride (LiCl) and calcium chloride (CaCl2) solution. The effect of variation in blend proportion on outlet parameters of a packed bed dehumidifier is patterned under various desiccant to air (L/G) mass flow rate ratios. It is observed that the addition of CaCl2 desiccant solution into LiCl changes the nature of thermo-physical properties of blends‚ which are predicted using non-random two liquid (NRTL) equation. Further, a trade-off analysis among the performance parameters is presented. It demonstrates that dehumidifier performance paradox such as enthalpy effectiveness (ɛh), moisture removal rate (MRR) and moisture effectiveness (ɛm) have a tendency to be optimal for 35% LiCl with 5% CaCl2 blend (BL1) among all blends at L/G ratio of 2. The variation of thermodynamic properties (air temperature, humidity, desiccant temperature and desiccant concentration) inside the dehumidifier module is visualized in terms of contour plots. Furthermore, the irreversibility in heat and mass transfer operation for the optimal blend is investigated in terms of physical and chemical exergy destruction paradigm. The result of such investigation elucidated that the maximum chemical exergy destruction is 0.88 kW, whereas the physical exergy destruction is 0.06 kW.

Air conditioning systems are used to control the air dry-bulb temperature and humidity level for human thermal comfort. In order to control the humidity level, air dry-bulb temperature needs to be brought down below its dew point temperature to condense out the moisture from the air. This eventually consumes a significant amount of total building energy in terms of electricity. Therefore, to minimize the energy consumption, researchers are stimulating their study towards an alternative latent heat load control system. In this regard, desiccant based sorption technologies are more effective compared to the conventional vapor compression system. Therefore, it is necessary to analyze the different desiccants' individual properties and their physical behavior in material perspective. In this study, an effort is devoted to explore the thermo-kinetic properties of pure LiBr, CaCl2, as well as their mixtures (LiBr:CaCl2 of 90:10; 85:15; 80:20 and 75:25) by X-ray diffraction (XRD), thermo-gravimetric (TG) and absorption rate, analyzes through numerous control experiments. The XRD study confirmed that peaks of CaCl2 and LiBr were shifted slightly for LiBr and CaCl2 mixtures due to interaction effects. The results of present investigation elucidated that mixtures of LiBr and CaCl2 showed less moisture regeneration cost than pure CaCl2 and all the mixtures revealed more rate of moisture absorption than pure LiBr and CaCl2. Further, 85:15 mixture of LiBr:CaCl2 showed higher rate of moisture absorption when compared to other prepared samples.

Solar collectors are efficient in utilising solar thermal energy for heating applications as their efficiency is quite high even in the medium temperature range, which motivated to design a high efficient collector system. In this study, an experimental investigation is carried out by developing a series of evacuated tube solar collectors with U-tube configuration using water as a working fluid. The performance of the collector system is continuously measured throughout the day. A trade-off study is carried out considering all the performance parameters. On the basis of experimental datasets, a multilayer perceptron (MLP) architecture is developed to predict thermal efficiency, useful heat gain and water outlet temperature of the evacuated tube collector as a function of solar irradiation, mass flow rate of water and water inlet temperature. It is demonstrated that the MLP model has an excellent agreement with experimental data as the mean square error is very low (

In this paper, an experimental investigation for predicting the performance of evacuated U – tube solar collector is presented. A simplified numerical model is developed for predicting the working fluid outlet temperature of a single evacuated U – tube solar collector and also for the whole solar collector system. The model predictions are compared with the experimental data and noticed a good agreement exists between them. It is observed from the experimental and numerical analyses that evacuated U – tube solar collector manifolds connected in series provides higher temperature rise of working fluid at higher solar intensities and lower working fluid inlet temperatures and flow rates. The working fluid transition time in an evacuated U – tube solar collector is defined for analysing the time taken by a working fluid to attain a steady state condition. Based on experimental analysis, three empirical correlations for predicting working fluid transition time, energy efficiency and exergy efficiency are developed as the function of operating parameters and ambient temperature. Data predicted from these correlations match with the experimental data with maximum errors of ± 12.7%, ± 6.9% and ± 7.8% for working fluid transition time, energy efficiency and exergy efficiency of an evacuated U – tube solar collector, respectively.

Recently, sorption technology has taken significant attention as an alternative process to mechanical air conditioning systems for dehumidification of air without lowering the air dry-bulb temperature below its dew point temperature. In this perspective, an aqueous lithium chloride (LiCl) is considered as a more effective desiccant in desiccant sorption systems due to its higher moisture absorption capability. In the present study, an effort is made to develop a simple correlation to predict the vapour pressure of LiCl solution as a function of solution temperature and concentration. Based on the developed correlation, an Othmer chart is constructed for LiCl solution in the concentration range of 20–40% and 15–50 °C temperature range. A trade-off analysis has also been carried out among the performance parameters. It is shown that venture of optimum outcome is observed at solution to air flow rate ratio of 8.5 with a condensation rate, moisture and enthalpy effectiveness of 0.234 g/s, 71.5% and 72.5%, respectively. Subsequently, empirical regression models are developed for predicting the performance parameters, which reveals that the developed models are robust for surrogate modelling in dehumidifier testing paradigms.

The stress generated due to the temperature difference is called thermal stress. Generally, the temperature gradients, thermal shocks, and thermal expansion or contraction are most effective contributors to thermal stress. The improper temperature profile of a body results in the formation of cracks, fractures, or plastic deformations at single or multiple spots depending upon two factors (i.e., the magnitude of temperature distribution or other variables of heating and material properties). So, this chapter analyses the causes of thermal stress and their measurement techniques. However, as most of the engineering problems, the thermal stress is due to the thermal expansion or sudden temperature changes happening in the body. Therefore, a brief analysis of temperature measurement devices with their proper data capturing methodology is also discussed.

Liquid desiccant dehumidification is a promising energy-extensive process for air dehumidification, which can easily be driven by any waste or renewable heat sources. In the current study, a hybrid method is proposed by combining the solar evacuated tube collectors as a regeneration source to drive liquid desiccant system in a close-loop. Subsequently, an experimental setup has been fabricated to assess the performance of the overall system using a novel desiccant mixture. The overall energy balance between the ambient air and the liquid desiccant was also studied. Effects of independent parameters such as solution to airflow rate, solution concentration and temperature on the dehumidifier-regenerator performance parameters such as latent heat ratio, condensation rate, desiccant mass fraction index, evaporation rate, latent and enthalpy effectiveness were analyzed. The result of present investigation showed that high solution to airflow (S/A) ratio enhanced the dehumidification and low S/A ratio enhanced the liquid desiccant regeneration rate. The maximum latent heat ratio for the dehumidifier at the design condition was 0.92, and the thermal coefficient of performance of the system was found as 1.1. The airside pressure drop in the dehumidifier/regenerator was also estimated at different flow rates of desiccant. Further, adaptive neuro-fuzzy inference system (ANFIS) prediction models are developed to predict the system performance as a function of system-independent parameters. The model results exhibited a good agreement with the experimental outcomes. The latent heat ratio and evaporation rate are predicted within a mean absolute percentage error (MAPE) of 2.7% and 2.3%, respectively.

In last few decades, a substantial advancement has been observed in dehumidifier modules for their energy-conservative and environment-friendly nature; however, still uncertainty in decision-making is of concern in selection of optimum input parameters to attain an effective performance. In this perspective, an experimental study is performed in an adiabatic packed bed, counter-flow liquid desiccant dehumidifier fuelled with the blend of lithium bromide and calcium chloride solution at various operating conditions with different control settings. It is observed that air mass flux rate (Fa), solution concentration (ζ) and air specific humidity (ωa) have significant impact on condensation rate (CR), whereas, air mass flux rate (Fa) and solution temperature (Ts) are the most effective parameters for moisture effectiveness and latent heat factor, respectively. The experimentally obtained results for multiple response performance characteristics are represented based on inlet process parameters using gene expression programming (GEP). The proficiency of developed GEP meta-models is provided by statistical parameters, Taylor diagram and Theil uncertainty. Subsequently, GEP meta-model based fuzzy logic is developed for optimising dehumidifier inlet process parameters in terms of multi-responsive performance characteristics using Genetic Algorithm. The optimisation results showed that dehumidifier performance characteristics have a tendency to become optimal at Fa = 0.766 kg/m2-s, Ta = 30.745 °C, ωa = 0.023 kgwv/kgda, Fs = 1.812 kg/m2-s, Ts = 24.01 °C, and ζ = 48.1%. Finally, experiments were conducted at optimum conditions and observed proximity between the predicted and experimental outcomes, which further validates the current optimisation approach.