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Development and Performance Investigation of Parabolic Trough Solar Collector and Latent Heat Storage Units for Indoor Cooking Application

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Furthermore, the effect of the nanofluids on the thermal performance of the PTSC is investigated numerically. The effect of operating parameters on storage device performance is investigated using both experimental and numerical analyses.

Preface

In modern times, solar energy can be converted into electricity in two ways, viz. In the case of indirect conversion of solar energy into electricity, solar radiation is converted into thermal energy inside the boiler or receiver.

Fig. 1.1.Global potential for renewable energy resources [4]
Fig. 1.1.Global potential for renewable energy resources [4]

Solar Collector

Solar Cookers

Direct type of solar cookers

Direct types of solar cookers are easily made from inexpensive materials; as a result, they are the most commonly used systems in general [7]. These types of solar cookers are also more stable and can keep food warm for a long time.

Indirect type of solar cookers

As a result, the vaporized liquid rises directly towards the heat exchanger and transfers heat energy. The HTF flowing inside the tube transfers the energy from the receiver to the heat exchanger or cooking device.

Solar cookers with heat energy storage

In the case of concentrating-type solar cookers, either spherical or parabolic shape is used to concentrate the scattered solar radiation. A receiver connected by pipes to a heat exchanger is provided at the focal line or point of the collector.

Thermal energy storage (TES)

  • Sensible heat storage
  • Chemical heat storage (CHS)
  • Latent Heat Storage
  • Organic PCMs
  • Inorganic PCMs
  • Eutectic
  • Melting point temperature of PCMs

The total amount of energy stored in the medium can be described as mentioned below. Solid materials such as metals, rocks, bricks and sand can be used for low as well as high temperature thermal energy storage.

Fig. 1.5.Classification of thermal energy storage systems  1.4.1  Sensible heat storage
Fig. 1.5.Classification of thermal energy storage systems 1.4.1 Sensible heat storage

Motivation and objective of the study

The melting point of the selected phase change PCM for the current storage application is in the range of 117-120 0C. Several studies have reported the health effects of collecting and burning solid fuels.

Organization of the thesis

Furthermore, the effect of operating parameters on the thermal performance of the storage unit is discussed in detail. The performance of the LHS unit based on the thermal energy generated by PTSC from direct solar radiation is addressed in this chapter.

Introduction

Performing numerical modeling and simulation of LHS systems is an acceptable solution to overcome the above-mentioned problems. Therefore, several researchers have designed, developed, and performed numerical and experimental performance evaluations of PTSC and LHS systems under various operating conditions presented in the following sections.

Review on performance evaluation of solar collectors

Thermal efficiency improvement methods of PTSC

The solar radiation reaching the wide area of ​​the PTSC is reflected in the receiving tube. The collector receiver is built with porous disks to improve the heat transfer behavior of the receiver.

Review of LHS technologies development and performance analysis

Effects of natural convection and operating parameters on LHS

In the lower half of the LHS unit, the natural convection contribution is 0.4 times the conduction contribution. The inclusion of HTF tube yarns increases the natural convection during PCM melting and conduction during the solidification process [82].

Thermal performance enhancement techniques of LHS

The increase in thermal conductivity of the longitudinal fin in the PCM is examined by monitoring the outlet temperature of the HTF. It was reported that the presence of longitudinal fins improves the performance of LHS.

Review of solar cookers integrated with LHS

The system consisted of PTSC, double wall cooking unit, TES tank and pump. The overall heat balance of the system was estimated, which indicated that the average rate of heat obtained by oil was only 0.25 kW out of 2.45 kW supplied by the TES tank.

Literature closure and objectives of the present study

Research objectives

Investigation of the charging and discharging characteristics of multi-tube shell-and-tube type LHS units based on erythritol as PCM and using food waste oil as HTF. Conduct an experimental study of the LHS unit to evaluate its thermal performance by varying its operating parameters.

Introduction

As we know, the use of sustainable solar energy for cooking and other services may face a problem due to the absence of solar radiation. Thermal energy storage methods are employed to carry out cooking activity within the kitchen, independent of time.

Sizing and fabrication of lab scale PTSC

  • Solar insolation Estimation
  • Sizing of the PTSC
  • PTSC structure
  • The Reflecting Assembly
  • Solar Absorption System
  • PTSC Orientation

As a result, the effective area of ​​the collector (Ac) in m2 can be calculated using Eq. The effective area of ​​the collector in terms of the glass cover is mentioned below.

Fig. 3.3.Section of a linear parabolic concentrator showing major dimensions  𝑓 = 𝑎 2
Fig. 3.3.Section of a linear parabolic concentrator showing major dimensions 𝑓 = 𝑎 2

Lab-scale LHS unit sizing and fabrication

Sizing of LHS unit

In the case of latent heat storage, the amount of heat being stored depends on the mass and latent heat fusion of the PCM. The size of the tank depends directly on the maximum amount of energy to be stored and the physical properties of the circulating HTF.

LHS unit manufacturing

Both the front and rear of the tube sheets are drilled with 19 holes so that the working fluid is restricted to move from the front to the rear head via the copper tubes. Therefore, the ends of the tubes pass through the holes of the front and back side tube sheets and are joined by welding.

Fig. 3.8.Principal and pictorial view of LHS unit  3.3.2.1  Storage tank
Fig. 3.8.Principal and pictorial view of LHS unit 3.3.2.1 Storage tank

Experimental setup layout

Measuring instruments

The temperature from different locations of the PTS and LHS units is recorded with thermocouples.

Summary

This chapter details the theoretical and numerical formulation, analytical and numerical results, solar data calculation, and experimental results of the PTSC developed during the fabrication of the solar cooker.

Optical and thermal modeling of PTSC

Modified Thermophysical properties Nanoparticles /Nano fluids

Adding a volume fraction of nanoparticles to the base heat transfer fluid (HTF) increases the thermal efficiency of the collector system. The thermal properties of a nanofluid are derived from the corresponding base fluid and nanoparticle volume fraction [125] as follows.

Solar data input calculation

The hourly diffuse, beam, and total radiations on June 15, June 22, October 13, October 18, December 21, and March 22 are estimated using incident angle and solar constant and are presented in Fig. As expected, radiation is highest on June 15, June 22, and March 22.

Fig. 4.5.Diffuse radiation, beam radiation, total solar radiation and incidence angle variation  versus LST
Fig. 4.5.Diffuse radiation, beam radiation, total solar radiation and incidence angle variation versus LST

Analytical and Numerical results

Analytical performance evaluation of the PTSC

They concluded that the thermal efficiency of the PTSC decreases as the flow rate and inlet temperature increase. Furthermore, the effect of the HTF inlet temperature on the thermal efficiency and heat loss of these two HTFs is exhibited in Fig.4.11.

Fig. 4.8.Effects of mass flow rate variation versus thermal efficiency
Fig. 4.8.Effects of mass flow rate variation versus thermal efficiency

Numerical Analysis of PTSC

The intensity flux density is variable around the circumferential direction of the absorber tube and glass cover. The non-uniform heat flux distribution leads to temperature gradients on the wall of the receiver pipe and glass envelope.

Fig. 4.12. Physical model of the receiver system
Fig. 4.12. Physical model of the receiver system

Experimental Results

Experimental setup procedure of PTSC

Experimental test results

Performance Curve of the PTSC based on ASHRE standard

Summary

Furthermore, the performance of PTSC based cooking waste oil (CWO) HTF is compared with the commonly used Syltherm 800 (S-800) HTF. It is found that the performance of PTSC improvises when CWO is used as HTF.

Introduction

Experimental Result Analysis

  • Materials preparation
  • Geometric details of the LHS unit
  • Experimental Procedure
  • Experimental error
  • Experimental temperature evaluation
  • HTF volume flow rate effect
  • Effect of HTF inlet temperature
  • Outlet temperature variation

For experimental and numerical evaluation of LHS, the inlet temperature of the HTF must remain the same. The rate of temperature increase varies in the radial and axial directions of the LHS unit.

Fig. 5.1.Physical modeling representation of the LHS unit and thermocouples locations (a) front  (b) side view
Fig. 5.1.Physical modeling representation of the LHS unit and thermocouples locations (a) front (b) side view

Numerical results

Numerical formulation

Numerical analysis of governing equations

Under the aforementioned assumptions, Eq. 5.9) The source term of the momentum equation is only valid for the PCM domain and is not considered for the HTF analysis [137]. The outer surface of each HTF tube is in direct contact with. longitudinal fins and the thermal resistance between the contact surfaces is minimal.

Boundary conditions

Numerical procedure

In addition, to ensure the reliability of the developed CFD numerical code, a numerical simulation was performed and compared with the practical results of Agyen et al [29]. For validation, the same PCM properties, similar initial and boundary conditions as in the experimental study were used.

Numerical Analysis

  • Optimization of the numbers of HTF tubes and fins
  • Temperature evaluation
  • Charging/discharging average temperature
  • Convective flow analysis
  • Liquid fraction evaluation
  • Charging/discharging liquid fraction variation curve
  • HTF volume flow rate effect
  • HTF inlet temperature effect
  • Stored/discharged energy
  • Experimental and numerical results comparison

The rate of heat addition and removal is so high at the beginning of the melting and solidification processes respectively. The impact of variation in the HTF flow rate on the melting progress of the PCM was investigated.

Fig. 5.14.Determination of number HTF tubes (a) 15 tubes (b) 17 tubes (c) 19 tubes and (d) 21  tubes
Fig. 5.14.Determination of number HTF tubes (a) 15 tubes (b) 17 tubes (c) 19 tubes and (d) 21 tubes

Thermal performance enhancement of LHS system using nanoparticles additives

The transient temperature and liquid fraction curves of the nano-PCM and pure PCM are shown in Fig. 1, respectively. 5.33 and 5.34. The comparison of the stored energy for the pure PCM and nano-PCM for 5% values ​​of the volume fraction is shown in Fig.

Fig. 5.33.Transient temperature curves of the nano-PCM and pure PCM
Fig. 5.33.Transient temperature curves of the nano-PCM and pure PCM

Summary

On the other hand, the energy storage capacity of the storage device is reduced by about 23% when nanoparticles are included in the PCM. On the other hand, the energy storage capacity of the storage device is reduced by approximately 23% when nanoparticles are included in the PCM.

Introduction

Advantage of hybrid energy systems

Solar powered power supply is less reliable as the power generated depends on weather conditions and time of day. The objective of this study is to evaluate the performance of the LHS unit powered by hybrid renewable energy sources.

Description and experimental setup procedure

However, instead of the biogas cylinder, an electric heater is used and an experimental and numerical study of the performance of the storage unit is performed. For safety reasons, cooking is usually done in the kitchen and can be done at any time of the day.

Charging performance of the LHS based on the PTSC system

Since the intensity of solar radiation is constantly decreasing, the rate of heat generation in the absorber tube also decreases. At this moment, the thermal charging rate of the LHS becomes uniform and the rate of temperature rise is recorded to be minimal.

Numerical evaluation of the proposed LHS unit powered by PTSC and auxiliary Energy

At the beginning of the charging process, the rate of heat addition is fast and the differences between all points are insignificant. However, the temperature increase of point H is the largest compared to the other points.

Fig. 6.3.Temperature variation of the LHS powered by PTSC and auxiliary energy sources  Fig.6.3 illustrates temperature variation of PCM at selected monitoring points
Fig. 6.3.Temperature variation of the LHS powered by PTSC and auxiliary energy sources Fig.6.3 illustrates temperature variation of PCM at selected monitoring points

Summary

After this period, the storage device experiences an extended period of slow heating until the end of the process. To conclude, the PTSC developed in the proposed work seems unable to melt the PCM placed inside the storage unit alone.

PTSC system

Therefore, the numerical and experimental study of the PTSC is carried out using CWO as the HTF medium. The experimental results of selected four days of the months of June and October are presented.

LHS unit

For the numerical study of the storage unit, a 3D LHS computer model is developed using ANSYS-Fluent that emulates the actual unit. The effect of operating parameters on storage unit performance is investigated using both experimental and numerical analysis methods.

PTSC and LHS Hybrid system

Future Scope

Groulx, “Experimental study of the phase change heat transfer within a horizontal cylindrical latent heat energy storage system,” Int. Meyer, “Numerical analysis of the thermal and thermodynamic performance of a parabolic trough solar collector using SWCNTs-Therminol ® VP-1 nanofluid,” vol.

Figure

Fig. 1.5.Classification of thermal energy storage systems  1.4.1  Sensible heat storage
Fig. 3.2.Pictorial view of the PTSC system  3.2.1  Solar insolation Estimation
Fig. 3.5. Pictorial view of PTSC during construction (a) and profile of the steel frame (b)  3.2.4  The Reflecting Assembly
Fig. 3.8.Principal and pictorial view of LHS unit  3.3.2.1  Storage tank
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References

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