56 Journal of Advanced Thermal Science Research, 2020, 7, 56-69 E-ISSN: 2409-5826/20 © 2020 Avanti Publishers Comparison of the Critical Mass Flow Rates for Two Serpentine Designs of the Photovoltaic Solar Thermal Collector Sakhr M. Sultan * , C.P. Tso and M.N. Ervina Efzan Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450, Melaka, Malaysia Abstract: A recent analysis on the photovoltaic (PV) cell efficiency for the photovoltaic solar thermal collector (PVT), cooled by forced fluid flow, revealed that there is, in general, a critical mass flow rate that corresponds to the maximum PV cell efficiency for a PVT. The derived new equations are applicable for laminar and transition or turbulent flow regimes and could yield directly the critical mass flow rate as compared with existing methods that use repeated computational trials. To demonstrate further the generality of the method, this paper reports results on comparing the critical mass flow rates for two serpentine designs with different technical details, namely Design A and Design B, using the new equations. It is shown that Design A and Design B have critical mass flow rates of 0.041 and 0. 014 kg/s, respectively. The corresponding Reynolds numbers are 4078 and 2785 for Design A and Design B, respectively. It is shown that the critical mass flow rate is different from one design to another. The importance of the critical mass flow rate is summarized. Keywords: Solar energy, Photovoltaic solar thermal collector, Surpentine collector design, Critical mass flow rate, Pumping requirement, Photovoltaic cell efficiency. 1. INTRODUCTION The grouping of photovoltaic (PV) together with solar thermal collector technologies leads to the formation of photovoltaic solar thermal collectors (PVT) [1]. The major advantages of a PVT are the generation of both electricity and heat. Generally, a PVT is divided into two types; a water or air-based photovoltaic solar thermal collector. The main components of a water- based PVT are a PV and a solar collector that circulates the cooling water with a pump [2-3]. An insulation material is usually incorporated to reduce heat loss from the system, as shown in Fig. ( 1). A PVT utilizes the collector for absorbing and transferring heat to the water, which can then be utilized, and more importantly, the heat withdrawn from the PV will enhance the PV performance [4-6]. Garg and Agarwal [8] studied a closed-loop PVT that operated over a day with varying solar radiation and ambient temperature. Then, using simulations, the time-averaged daily cell efficiency was plotted, at various flow rates, from which it was found that there was a daily optimum flow rate identifiable by observation. The pump was operated based on an on/off switch and depended on the changes of the solar radiation and ambient temperature. At the optimum efficiency, the coolant mass flow rate called the critical mass flow rate, ṁ , was 0.03 kg/s, when the maximum PV efficiency was 8.1 %. *Address correspondence to this author at the Faculty of Engineering and Technology, Multimedia University, Jalan Ayer Keroh Lama, 75450, Melaka, Malaysia; E-mail: mas2007_eng@yahoo.com The experimental measurements showed that the electrical and thermal efficiencies of the proposed design were 0.7 % higher than the conventional PV efficiency and 44.37 %, respectively. It was concluded that the overall efficiency of the glass to glass PVT was improved. The evaluation of the electrical performance of a water-based PVT was carried out [9]. The artificial neural networks (ANNs) for machine learning and neuro-fuzzy were applied for improving the simulation models of a PVT. The parameters such as solar radiation, mass flow rate & inlet temperature were considered as the input variables in the proposed model. Experimental measurements were carried out for a novel PVT design. A good agreement was achieved between the proposed model results and the experimental measurements. It was concluded that the proposed method can solve the problem associated with the experimental setup such as time and cost. A new PVT liquid type was proposed [10]. A phase change material (PCM) tank was integrated into PV’s backside. As a result, the PV performance could be improved due to PV’s temperature control during the process of the phase change. The effect of dispersing copper (Cu) and alumina (Al 2 O 3 ) nanoparticles in pure water on the perfor- mances of a PVT was investigated [11]. The numerical model was developed which is derived from the energy balance equations. Experimental measurement was conducted and compared with the analytical results and they were in good agreement. Results showed that Cu-water nanofluid provided a better PVT performance as compared with Al2O3. To overcome the drawback of