Theoretical Analysis of Overall Heat Loss Coefficient in a Flat Plate Solar Collector with an In-Built Energy Storage Us
Flat Plate Solar Heater is one of the most widely used devices to harness solar energy available in abundance. The collector efficiency can be improved by reducing the overall losses. Efficiency of the collector depends on overall loss coefficient which i
- PDF / 451,725 Bytes
- 10 Pages / 439.37 x 666.142 pts Page_size
- 37 Downloads / 188 Views
c cp I S L M T
Collector area (m2) Specific heat capacity (Jkg−1k−1) Intensity of solar radiation (Wm−2) Solar radiation reaching the absorber plate (Wm−2) Number of glass covers Mass flow rate (Kgs−1) Temperature (K)
R. Sivakumar (*) Department of Mechanical Engineering, MAM College of Engineering and Technology, 621 105 Tiruchirapalli, TamilNadu, India e-mail: [email protected] V. Sivaramakrishnan Department of Mechanical Engineering, Roever Engineering College, 621 212 Perambalur, TamilNadu, India e-mail: [email protected]
S. Sathiyamoorthy et al. (eds.), Emerging Trends in Science, Engineering and Technology, Lecture Notes in Mechanical Engineering, DOI: 10.1007/978-81-322-1007-8_13, © Springer India 2012
145
R. Sivakumar and V. Sivaramakrishnan
146
hw U L U T UB UE Q T QB QE Qo Qu FR F′
Wind loss coefficient (Wm−2K−1) Overall heat loss coefficient (Wm−2K−1) Top loss coefficient (Wm−2K−1) Bottom loss coefficient (Wm−2K−1) Edge loss coefficient (Wm−2K−1) Top heat loss (W) Bottom heat loss (W) Edge heat loss (W) Is the heat loss (W) Useful heat energy collected (W) Collector heat removal factor Collector efficiency factor
Greek α Absorptive τ Transitivity η Efficiency σ Stefan Boltzmann’s constant = (5.67 × 10−8 Wm−2K−4) β Collector tilt angle Subscripts a Ambient c Collector i Inlet o Outlet g Glass cover p Absorber plate
1 Introduction Time delay in availability of solar energy and utility of solar energy reiterates the need for use of Phase Change Materials (PCM) in Thermal Energy Storage Systems (TES). A conventional liquid flat plate collector consists of an absorber plate, tube, transparent cover, insulation, and collector box. The advantages are: it utilizes both diffused and direct component of solar radiation, does not require orientation towards sun, and requires minimum maintenance. The disadvantages are: it has no optical concentration, hence heat is lost from large area and low efficiency as a result, and can be used only during day time. A natural circulation solar water heater works on the principle of conduction, convection and radiation, and flow is because of density difference developed in the heater. A forced circulation solar water heater is provided with a pump to circulate water at a constant flow rate. The above mentioned Flat plate solar water heaters have limitation of usage only during sun shine. An inbuilt storage of heat in the Solar water heater by
Theoretical Analysis of Overall Heat Loss Coefficient
147
Table 1 Properties of Phase change materials considered [6] PCM
Melting Heat of fusion Thermal Density kg/m3 Specific heat point oC kJ/kg conductivity solid, liquid capacity— solid, liquid in Wm−1K−1 kJkg−1K−1
Paraffin wax Sunoco 50 P116 Glauber’s salt Na2SO4. 32 10H2O
190
0.21
930, 830
2.1, 2.1
251
2.25
1,460, 1,330
1.73, 3.3
Fig. 1 Energy balance of a flat plate collector adapted from Garg 1987 [2]
providing PCM under the absorber surface enables charging of heat during sunshine and discharge of heat to water even during night time. Th
Data Loading...