An Experimental Approach for Enhancement of Heat Transfer Using TTHE : U Valve

The conventional double pipe heat exchanger has less heat transfer rate, so to overcome this problem, this paper focuses on establishing the Triple Tube Heat Exchanger (TTHE) is modified constructive version of double concentric tube heat exchanger by adding an intermediate tube for hot fluid. In this paper the experimental data obtained during the test in a double and triple concentric tube heat exchangers are very much impressive. However, U valve also fitted and were analyzed and the experiment results conforms the effectiveness of the triple tube heat exchanger. © 2020 Elixir All rights reserved. Elixir Thermal Engg. 141 (2020) 54290-54293 Thermal Engineering Available online at www.elixirpublishers.com (Elixir International Journal) A. Nayak et al./ Elixir Thermal Engg. 141 (2020) 54290-54293 54291 He concluded that 1) overall heat transfer coefficients and the temperature profiles are useful for designing a heat exchanger to meet the process requirements. 2) Overall heat transfer coefficients values may also be useful for determining the convective heat transfer coefficient values (h). S Radulescu [12] established an algorithm for the calculation of partial coefficient of heat transfer for a fluid which flows through an inner annular space of a triple concentric-tube heat exchanger in transition regime based on experimental results. He developed a new correlation for design purposes on heat transfer devices, such as triple concentric pipe heat exchanger. The correlation obtained is: NuH =2.718 ReH0.597 PrH1/3 (dh2/L1)2/3 It molds the heat exchange for Reynolds values that go from 2264 to 7893 and for the velocities values between 0.11 and 0.36 m/s. The practical applicability of the obtained correlation in the study applies for Prandtl values between 3.30 and 3.70. G.A. Quadir et al. [13] analysed performance of heat exchanger for two flow arrangements, called N–H–C and C–H–N, and for insulated as well as non-insulated conditions of the heat exchanger. The three fluids being considered are hot water, cold water and the normal tap water. Under N–H–C arrangement, normal water flows in the innermost pipe, hot water flows in the inner annulus, and the cold water flows in the outer annulus. All fluids flow parallel to each other. Cold and normal water are interchanged in the C–H–N arrangement keeping hot water flow unchanged. He concluded that the heat transfer between the three fluids considered is more effective in N–H–C arrangement of the heat exchanger as compared to that in C–H–N arrangement. Here N-H-C: Normal-Hot-Cold C-H-N: Cold-Hot-Normal This study was devoted to the analysis of the heat transfer phenomenon in a triple tube heat exchanger (TTHE). During the literature review on the subject, it was seen that no procedure is available for accurate calculation of overall heat transfer coefficients in a TTHE. Therefore, initial studies focused on developing a procedure for accurate computation of the overall heat transfer coefficients and temperature profiles of the fluids in a TTHE. An effective overall heat transfer coefficient concept was also established. However, another type heat exchanger are shell and tube type but they are mostly use in laboratories [14] Methodology A heat exchanger is a device that is used to transfer thermal energy (enthalpy) between two or more fluids, between a solid surface and a fluid, or between solid particulates and a fluid, at different temperatures and in thermal contact [14]. Heat exchanger have been classified in several ways, according to transfer process (direct contact, indirect contact), according to geometry of constructions (plate, tube, extended surfaces), according to heat transfer mechanisms (single phase, two phases), according to flow arrangements (parallel, counter, cross flow) [15-19]. The type of heat exchanger to be used is determined by the process and product specifications. Nevertheless, concentric tube heat exchanger play a major role in accomplishing the heat exchanger needs of food industry. The most common heat exchanger is double pipe heat exchanger [12]. A typical double pipes heat exchanger consists of one pipe places concentrically inside another of a large diameter pipe with appropriate fitting to direct the flow from one section to the next [13]. Introducing an intermediate pipe to a double concentric pipe heat exchanger provides triple pipe heat exchanger and the latter performs better compared to the prior one. Triple concentric pipes heat exchanger consists of three pipes of different diameters and three fluids exchange heats between them. Thus in this case, there are three sections: central pipe, inner annular space and outer annular space. In triple pipe heat exchangers, a thermal fluid is passed through an inner annular space and heat transfer mediums are passed through the central pipe and outer annular space. Diagram and line diagram of triple tube pipes were shown in fig. 1 & 2. Fig 1. Triple concentric pipes. Fig 2. Line diagram of triple tube. Triple concentric-pipes heat exchangers are used for food processing, pasteurization of viscous food products (milk, cream, pulpy orange juice, apple mash), sterilization, cooling, energy conversion, Refrigeration. The most common problems in heat exchanger design are rating and sizing. The rating problem is concerned with the determination of the heat transfer rate and the fluid outlet temperatures for prescribed fluid flow rates, inlet temperature, and allowable pressure drop of an existing heat exchanger. On the other hand, the sizing problem is concerned with determination of dimension of heat exchanger, that is, selecting an appropriate heat exchanger type and determining the size to meet the specified hot and cold fluid inlet and outlet temperatures, flow rates, and pressure drop requirements [14-19]. In this study, the sizing procedure of triple concentric pipe heat exchanger is presented, in which, length of the heat exchanger is calculated for the available dimensions of three pipes to meet the required temperature drop of hot water. Triple concentricpipes heat exchangers are used for food processing, pasteurization of viscous food products (milk, cream, pulpy orange juice, apple mash), sterilization, cooling, energy conversion, Refrigeration. 4.1.1 Outer tubeDimensionOuter diameter of the tube=0.0338m Inner diameter of the tube=0.0318m Thickness of the tube=0.001m Length of the tube=1.1176m A. Nayak et al./ Elixir Thermal Engg. 141 (2020) 54290-54293 54292 4.1.2 Intermediate tubeInter mediate tube is made up of copper material, which is used for the flow of hot water. The photographic image of the experimental setup shown in Fig. 3 DimensionOuter diameter of the intermediate tube=0.0179mnner diameter of the inter mediate tube=0.0159m Thickness of the inter mediate tube=0.001m Length of the inter mediate tube=1.3208m 4.1.3 Central tubeCentral tube is made up of copper materials, which is used for the flow of cold water. DimensionOuter diameter of the centre tube=0.0115m Inner diameter of the central tube=0.0095m Thickness of the central tube=0.001m Length of the central tube=1.524m Fig.3 photographic image of the experimental setup Results &Discussion The overall heat transfer coefficients of triple concentric pipe heat exchanger were found out using input parameters i.e. geometrical characteristics of three pipes, mass flow rates and thermo physical properties of three fluids. There are two overall heat transfer coefficients in triple pipe heat exchanger: one based on outside area of central pipe (U02) and second based on inside area of intermediate pipe (Ui1). The overall heat transfer coefficients based on outside area of central pipe and based on inside area of intermediate pipe were found to be different for different mass flow rate. The results were shown in table 1, 2 and 3 respectively. Theoretically the energy balance equation i.e. total heat transferred by hot fluid should be equal to the sum of heat received by both the cold fluids, but in practical case for different mass flow rate there is some difference in the energy transferred. The parallel flow counter flow and combination of both were shown in fig. 4, 5 & 6 respectively. The flow regimes in triple pipe heat exchanger were observed to be: Transition in the central pipe and inner annular space and laminar in outer annular space. Figure 4. Parallel flow heat exchanger Figure 5. Counter flow heat exchanger Table 1. Parallel flow heat exchanger