Satyender Singh

Using an Analytical Approach to Investigate Thermal Performance of Double-Flow Packed-Bed Solar Air Heaters with External Recycle

AbstractIn the present study, the thermal and effective thermal efficiencies of a double-flow packed-bed solar air heater with an external recycle are investigated theoretically. An analytical model capable of predicting the thermal and effective thermal performances of the heater is presented. The effects of the mass flow rate, the recycle ratio, and the bed porosity on the thermal and effective thermal efficiencies of the heater are investigated. It is indicated that the recycle ratio significantly improves the thermal performance of a double-pass packed-bed solar air heater. The results revealed that the thermal and effective thermal efficiencies of the heater are about 21.3 and 25.4% higher when compared to a conventional-type solar air collector of the same size with an external recycle. The optimum values of the recycle ratio, the mass flow rate, and the bed porosity, at which the heater yields the maximum value of effective thermal efficiency, are identified and presented. The results of the therma...

A numerical evaluation of thermal performance of double flow packed bed solar air heaters

In this paper, double flow packed bed solar air heater was investigated theoretically and experimentally. A numerical model for the air heater was presented. Numerical calculations had been performed under Hamirpur (latitude, 31o25’ to 31o52’North) prevailing weather conditions. A mathematical models based on the volumetric heat transfer coefficient have been developed. To solve this model and to provide an iterative approach, forward difference method of finite difference scheme is employed. The theoretical predictions indicated that the agreement with the measured performance is fairly good. The effect of mass flow rates of air on thermal and effective thermal efficiencies of the double flow with and without packed bed solar air heaters were also investigated. The results showed that the double flow packed bed solar air heater is about 78.8% more efficient compared to the double flow without packed bed solar air heater.

Thermal and Thermohydraulic Efficiency of Recyclic-Type Double-Pass Solar Air Heaters With Fins and Baffles

This paper presents investigations related to the heat-transfer performance improvement of double-pass finned and finned with baffles solar air heaters. The analytical study has been carried out to see the effects of parameters such as mass flow rate, recycle ratio, fins thickness, number of fins, and baffles width on the heaters’ efficiencies. It is indicated that the mass flow rate and the recycle ratio are the most significant factors, which considerably increase the heaters’ efficiencies by increasing the fluid velocity. The theoretical results showed that the device with fins plus baffles can enhance the heat transfer rate compared with the device with fins under the same flow rate and working dimensions. The effect of the depth of the first channel on the thermal and thermohydraulic efficiency improvement is also delineated. To validate the proposed theoretical models, comparisons of the results are performed with those obtained from previous studies and show that good agreement is achieved.

Double Duct Packed Bed Solar Air Heater Under Combined Single and Recyclic Double Air Pass

The present work intended to investigate thermal and thermohydraulic efficiencies of two different models of recyclic double pass packed bed solar air heaters experimentally. Model-I consists of single air pass through two glass covers as well as double air pass caused due to recycle of the air exiting from the packed bed duct formed between the absorber plate and the glass cover through another duct integrated between the absorber and back plates to inlet of the packed bed duct. On the other hand, model-II consists of only double air pass originated due to recycle operation constituted between the similar solar air heater elements as that of model-I. Twelve numbers of wire mesh screens to form 95% bed porosity were used. Both solar air heater models were tested under the range of packed bed Reynolds number from 300 to 1500 for air mass flow rate and recycle ratio of 0.01 kg/s to 0.025 kg/s and 0.3 to 1.8, respectively. Results revealed that thermal performance of model-I is found to be 15% higher than that of model-II. The optimum value of the recycle ratio for model-I and model-II are obtained as 0.9 and 1.2, respectively, at a mass flow rate of 0.025 kg/s that yields the best thermohydraulic efficiency of 77% and 67%, respectively. Moreover, optimum solution for recycle ratio and air mass flow rate during off sun shine hours are also obtained and presented in the current work.

Thermal performance assessment of recyclic double-pass flat and V-corrugated plate solar air heaters

Double-pass solar air heaters occupy an important place among solar air heating systems, because of minimal heat loss and maximum thermal efficiency with marginal heater size and cost. In the present work, investigations related to the thermal performance predictions have been carried out for double-pass flat and V-corrugated absorber plate solar air heaters under recycle operation. The mathematical models proposed herein are solved using an analytical approach that uses an iterative solution procedure. Furthermore, based on simulation results obtained from the analytical study, the optimum value of the recycle ratio, the mass flow rate, the absorptivity and the emissivity at which the heaters yield the maximum value of the thermal efficiency have been identified and presented using response surface methodology (RSM). The results of RSM revealed that the mathematical models are significant. In addition, results of the present study are validated and compared with previous studies. A reasonable agreement and significant improvement have been achieved.

Numerical investigation of a solar air heater comprising longitudinally finned absorber plate and thermal energy storage system

In the present work, the thermal performance of a double glazed single pass solar air heater consisting of a longitudinally finned absorber plate on its top surface and attached to a phase change material (PCM) with its bottom surface is investigated, theoretically. Paraffin wax (Rubitherm RT42) is used as a PCM. The main idea of this solar air heater design is to use it during nocturnal hours or off sunshine hours. A computational heat transfer and fluid dynamics solution using an implicit scheme has been developed and employed to study the effects of the mass flow rate and number of fins on its thermal performance under transient conditions. The maximum outlet air temperature of the finned type solar air heater with latent heat storage is achieved as 40 °C, 37 °C, and 35 °C for mass flow rates of 0.01, 0.015, and 0.02 kg/s, respectively, and it is predicted that the system can be used for 14, 12, and 10 h after sunset at respective mass flow rates. The maximum daily average thermal efficiency is predicted to be 62.4% at a mass flow rate of 0.02 kg/s which is higher than the other designs considered in the present investigation.In the present work, the thermal performance of a double glazed single pass solar air heater consisting of a longitudinally finned absorber plate on its top surface and attached to a phase change material (PCM) with its bottom surface is investigated, theoretically. Paraffin wax (Rubitherm RT42) is used as a PCM. The main idea of this solar air heater design is to use it during nocturnal hours or off sunshine hours. A computational heat transfer and fluid dynamics solution using an implicit scheme has been developed and employed to study the effects of the mass flow rate and number of fins on its thermal performance under transient conditions. The maximum outlet air temperature of the finned type solar air heater with latent heat storage is achieved as 40 °C, 37 °C, and 35 °C for mass flow rates of 0.01, 0.015, and 0.02 kg/s, respectively, and it is predicted that the system can be used for 14, 12, and 10 h after sunset at respective mass flow rates. The maximum daily average thermal efficiency is predict...

Thermal and thermo-hydraulic performance investigation of double-pass packed bed solar air heaters under external recycle

In the present investigation, two types (Type A and Type B) of the double-pass packed bed solar air heater under external recycle are investigated theoretically. In Type A, the porous media is considered in the upper channel, whereas in Type B, the porous media is considered in the lower channel. Iron scraps are used as a packed bed material (porous media) to strengthen the convective heat transfer coefficient for air flowing through the packed bed. The mathematical model for these two air heaters operating under forced convection mode is presented. The results revealed that the thermal and thermo-hydraulic efficiencies of Type A are higher as compared to Type B. In order to validate the models, the theoretical results obtained from the conventional model of Type B are compared with the theoretical results obtained from the previous investigation and showed that good agreement is achieved.

Fluid flow and heat transfer characteristics within a rectangular microchannel array of different manifold shapes – modelisation and optimisation using CFD and response surface methodology

Different manifold shapes of microchannel device are investigated for the pressure drop characteristics under the effect of varying microchannel depth, width and spacing. The response surface methodology is applied to optimise the operating conditions of different microchannel systems. Four operating parameters, the channel width, depth, spacing and the inlet Reynolds number are considered in this study. The individual effects of these operating parameters and the combined effects of multiple operating conditions on pressure drop characteristics are examined using CFD. The semi-elliptical manifold shapes results the high level of fluid flow uniformity within microchannels and lower pressure drop. The maximum percentage reduction in the pressure drop across the microchannel device is 70%, obtained for semi-elliptical manifold shape as compared to other. The heat transfer analysis is also carried out in the extent of the study.

Thermal Performance Analysis of a Rectangular Longitudinal Finned Solar Air Heater With Semicircular Absorber Plate

Thermal performance of a single-pass single-glass cover solar air heater consisting of semicircular absorber plate finned with rectangular longitudinal fins is investigated. The analysis is carried out for different hydraulic diameters, which were obtained by varying the diameter of the duct from 0.3–0.5 m. One to five numbers of fins are considered. Reynolds number ranges from 1600–4300. Analytical solutions for energy balance equations of different elements and duct flow of the solar air heater are presented; results are compared with finite-volume methodology based numerical solutions obtained from ansys fluent commercial software, and a fairly good agreement is achieved. Moreover, analysis is extended to check the effect of double-glass cover and the recycle of the exiting air. Results revealed that the use of double-glass cover and recycle operation improves the thermal performance of solar air heater.