Solar thermal energy is currently used for low temperature heating applications using flat plate collectors. The absorbed solar energy is transferred to the working fluid flowing in the pipe. The performance of the system is influenced by heat transfer from tube to working fluid, with minimum convective losses, which has to be considered as one of the primary design factor. In tube and channel flows, to enhance the rate of heat transfer to the working fluid, passive augmentation techniques such as twisted tapes and swirl generators are used in the fluid flow path. In this paper, convective heat transfer analysis for a horizontal circular pipe with fluid in mixed laminar flow range is performed using experimental simulation under constant heat flux boundary condition. The variation of heat transfer coefficient and pressure drop in the pipe flow for water and water based Al2O3 nanofluids at different volume concentrations and twisted tapes are studied. The dependence of particle concentration and Reynolds number for enhancement in heat transfer and increase in the pumping power due to pressure drop is analysed in the range of parameters considered

Humidification–dehumidification (HDH) desalination is a simple technique to produce desalinated water from saline water. Dehumidifier is a key component in the HDH system, which influences the desalination yield. In the current work, a three-dimensional multiphase numerical simulation study is carried out on third dehumidifier alone to evaluate its performance using computational fluid dynamics (CFD) code. The simulation result is validated with experimental readings, and it is found that there exists a very close agreement between the predicted and the experimental readings. The key parameters influencing the dehumidifier performance are chilled water temperature, humid air temperature, and volume fraction. Experiments are carried out on the combined two stage HDH plant at different hot water temperature and flow rates. A detailed study of dehumidification process is carried out using ansys cfx 15.0 tool by solving the governing equations, namely, mass, momentum, and energy, with turbulence modeled through shear stress transport (SST) k–ω model of closure. Multiphase is solved using a free-surface multiphase model. The measured average cooled air temperature and relative humidity (RH) at the exit of third dehumidifier are 21 °C and 67%. The desalinated water produced at a hot water flow of 100 LPH is found as 2205 ml/h from the experiments. The CFD results are deviated by 0.41%, 6.45%, and −0.70% with that of experimental results at the dehumidifier for air temperature, velocity, and chilled water temperature, respectively.

The desalination yield in humidification-dehumidification (HDH) process is increased by proposing cooling plant integration with two stage operation. The current work is targeted on the investigation of vapor absorption refrigeration (VAR) parameters on overall energy utilization factor (EUF). The dephlegmator heat is recovered internally in VAR instead of rejecting to environment. This work can be used to control the operational conditions of VAR to enhance the desalination and cooling together. The studied process parameters in VAR are strong solution concentration, separator or generator temperature, dephlegmator effectiveness, circulating water inlet temperature and evaporator temperature. Out of these five variables, lower limit of separator temperature, upper limit of dephlegmator effectiveness and lower limit of circulating water temperature are fixed in the specified range to attain the optimum strong solution concentration and optimum evaporator temperature. At the specified boundaries of three variables, the optimized strong solution concentration and evaporator temperature are 0.47 and 10°C respectively. At this condition, the maximized cycle EUF is 0.358