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Effect of artificial coarseness on the performance of rectangular solar air heater duct: a comparative study

Dubey Manoj Kumar, Prakash Om

Archives of Thermodynamics

2023

Vol. 44, no 3

325--358

Solar air heater is regarded as the most common and popular solar thermal system and has a wide range of applications, from residential to industrial. Solar air heater is not viable because of the low convective heat transfer coefficient at the absorber plate which contributes to decreasing the thermal efficiency. Artificial coarseness on the plain surface is the most effective method to enhance heat transfer with a moderate rate of friction factor of flowing air in the design of solar air heater duct. The different parameters and different artificial coarseness are responsible to alter the flow structure and heat transfer rate. Over the years different artificial roughness and how its geometry affects the performance of solar air heater have been thoroughly studied. Various investigators report the correlations between heat transfer and friction factors. In the present study, a comparison of several artificial coarseness geometries and methods with a view to enhancing the performance of solar air heater has been made. A brief outline has also been presented for future research.

Thermal performance evaluation of an earth-to-air heat exchanger for the heating mode applications using an experimental test rig

Ahmad Saif Nawaz, Prakash Om

Archives of Thermodynamics

2022

Vol. 43, no 1

185--207

This paper presents the experimental investigation of an earth-to-air heat exchanger for heating purposes in the Patna region of India, using an experimental test rig. In the view of the author, real field experiments have several limitations such as lack of repeatability and uncontrolled conditions. It also takes more time for the response of parameters that depends on nature and climate. Moreover, earth-to-air heat exchangers may be expensive to fabricate and require more land area. Thus, in this work authors executed their experimental work in indoor controllable environments to investigate the thermal performance of an earth-to-air heat exchanger. The actual soil conditions were created and maintained the temperature at 26°C throughout the soil in the vicinity of pipes. Three horizontal PVC pipes of equal lengths and diameters of 0.0285 m, 0.038 m and 0.0485 m were installed in the test rig. The experiments were performed for different inlet air velocities at ambient air temperature. This study acknowledges that the maximum rise in outlet temperature occurs at a lower speed for smaller pipes. Also, the maximum effectiveness of 0.83 was observed at 2 m/s for the smallest diameter pipe.