CHAPTER 3 EXPERIMENTAL SETUP AND PROCEDURE

Transcription

1 31 CHAPTER 3 EXPERIMENTAL SETUP AND PROCEDURE 3.1 DETAILS OF EXPERIMENTAL FACILITY The schematic diagram and photographic view of the experimental setup are shown in Figures 3.1 and 3.2 respectively. Experimental setup consists of a calming section, test section,, hot and cold water tanks and hot and cold water pumps. It consists of two concentric tubes in which hot water flows through the inner tube (d i = 25 mm and L = 2000 mm) and cold water flows in counter flow through annulus (D o = 54.5 mm and L = 2000 mm). Calming section with the dimension of 2000 mm long or 83 d i (Eiamsa-ard et al. 2010b), 25 mm ID and 28.5 mm OD is used to eliminate the entrance effect. The outer pipe is well insulated with two layers of asbestos rope tape wound and over the asbestos tape winding approximately 40 mm thickness of glass wool is lined and over which, another two layers of asbestos rope tape is wound to minimize the heat loss to the atmosphere. Three calibrated s having the accuracy of ±0.1 Lmin -1 and the flow range of one 0 2 Lmin -1 (Laminar flow) and other two with the flow ranges of 0 20 Lmin -1 are used to measure the hot and cold water flow rates. Seven calibrated RTD Pt 100 type temperature sensors with ±0.1 º C accuracy and digital indicator are used to measure the temperature of the hot and cold water sides. For the accurate temperature measurement, two

2 Figure 3.1 Schematic diagram of experimental setup 32

3 Panel board Manometer Calming section Test section Cold water pump Cold water tank Hot water pump Hot water tank Figure 3.2 Photographic view of experimental setup 33

4 34 sensors are used and average temperature is considered. Similarly, in the cold water side two sensors at the outlet and one at the inlet sides are used to measure the cold water temperature accurately. The water is heated using three electric heaters each with 1kW capacity and the desired temperature of the hot water is controlled by the temperature controller. Two centrifugal pumps are used to supply hot and cold water to the test section. The two pressure tapings one just before the test section and another just after the test section are provided, and attached to the U-tube manometer for pressure drop measurement. Proper care is taken to prevent leakage in all parts of the experimental setup. The summary of the technical specifications of the instruments and details of the experimental setup are given in Tables 3.1 and 3.2. Table 3.1 Technical specifications of the instruments Sl. Name of No. Instrument Specifications 1 Water pump Phase RPM HP Volts Single Hot Water Body Material Float Material Flow range in Lmin -1 Mfg. Name Model No (Laminar) Crystal SS, Bombay AB786MT instruments 3 Hot Water Crystal SS, Bombay Instruments AB786- MT (Turbulent ) 4 Cold water Crystal SS, Bombay Instruments AB786- MT 5 A mmeter Phase Make Current rating Single IMASTER 0-15 Amps 6 Volt meter Phase Make Voltage rating Single IMASTER Volts 7 Temperature Make controller MICRO SENSORS 8 Digital Number of Range Temperature channel Make Model No indicator º C 8 SANSEL VC14

5 35 Table 3.2 Details of the experimental set up Sl. No. Part 1 Test section 2 Calming section 3 Insulation material 4 Hot and cold water tanks Particulars (a) Inner tube (b) Outer tube Inner diameter mm Outer diameter mm Length mm Material - Copper Inner diameter mm Outer diameter mm Length mm Material - Galvanized iron Asbestos rope Glass wool Material Capacity - Stainless steel - 50 Liters Inner diameter mm Outer diameter mm Length mm Material - Galvanized iron 5 Temperature Sensor Accuracy No of sensors measurement RTD Pt 100 ±0.1 º C 7 6 Flow Instrument Accuracy Numbers measurement Rota meter ±0.1 Lmin Pressure measurement Instrument U-tube manometer Manometric liquid Dibutyl Phthalate (C 6 H 22 O 4 ) Carbon Tetra Chloride (CCl 4 ) 3.2 EXPERIMENTAL PROCEDURE To start with, the electric heater is switched on, and desired temperature is maintained by controlling the heater using a temperature controller. The hot water pump is switched on, the hot water flow rate to the test section is adjusted using by-pass valve and hot water flows to the inner tube of test section through a via control valve. During laminar flow, hot water flows through a of 0 2 Lmin -1 and for turbulent flow hot water flows through a of 0 20 Lmin -1. The cold water is pumped from a cold water tank and allowed to pass through an annulus

6 36 through a control valve in counter flow direction to hot water and excess cold water returns to the tank through bypass valve. The steady state is obtained within one hour for the first run and 25min for the subsequent runs. The inlet temperatures at the hot water and cold water sides are kept constant at 54 ± 1 º C and 30 ± 1 º C respectively. The cold water at room temperature constantly flows at 10 Lmin -1 whereas the flow rate of hot water is adjusted from 0.5 Lmin -1 to 1.5 Lmin -1 for laminar flow with 0.2Lmin -1 increments and for turbulent flow from 2Lmin -1 to 7 Lmin -1 with 0.5 Lmin -1 increments respectively. The inlet and outlet temperatures of hot and cold water are recorded only after temperature attains a steady state. During pressure drop measurement, air bubbles are removed from the manometer so that the liquid levels in both the limbs are equal when the flow is stopped. For laminar flow, Dibutyl Phthalate with specific gravity (S) of 1.048, and for turbulent flow Carbon Tetra Chloride of specific gravity (S) of 1.59 is used as the manometric fluids. The pressure drop measurements are also taken after attaining the steady state by varying the hot water flow rates under laminar and turbulent flows conditions. The heat transfer and friction factor data are collected for the entire range of flow rates for plain tube and subsequently by inserting P-TT, T-TT, S-TT, U-TT, V-TT with different depth and width ratios, VW-TT, HW-TT and WN-TT for both laminar and turbulent conditions. The experimental results are discussed in Chapter 7 and sample experimental data are tabulated in Appendix 1. The technical details of variant twisted tapes used in the present work have been discussed in the next Chapter.