DESIGN AND PERFORMANCE EVALUATION OF AN EVAPORATIVE HEAT EXCHANGER A.O. MURITALA, S.O. OBAYOPO, S.K. FASHOGBON, O.T. POPOOLA*, S.A ADIO Department of Mechanical Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria. International Conference on Innovations in Engineering and Technology (IET 2011) UNIVERSITY OF LAGOS, FACAULTY OF ENGINEERING, AKOKA, LAGOS, Nigeria

INTRODUCTION

Evaporative Cooling The increased air filtration qualities Simplified operation and maintenance Lower costs Lower energy usage Less greenhouse gas No CFC's or HFC's

Evaporative Cooler Cabinet Reservoir Tank Pad Blower Electric Motor Pump Fig 1: Schematic diagram of an evaporative cooler

Objective To design and construct an evaporative cooler. To evaluate the performance of the cooler.

DESIGN

General Reduction in the discomfort index by 90% Required fan power is linearly dependent on the floor area to be cooled. Building heat balance (EC sizing) SOLAR HEAT + HEAT FROM EQUIPMENT & PEOPLE = HEAT REMOVED BY EAC

Cabinet Reservoir Tank Galvanized iron sheet 50x55x70 cm 3 One sided Cabinet Reservoir Tank Inlet Outlet (50 x 55 x 23) cm 3

Evaporative Pads Aluminum fins 35 x 47 x 10 cm 3 Blower

Electric Motor half-horse power connected by a direct drive 2 speed motor 220 V Pump re-circulating surface pump 0.5 horse power Water pump screen

Plate 1: The evaporative cooler housing cabinet Plate 2: The designed evaporative cooler

EVALUATION

Monitored Parameter Room size 305 x 254 x 203 cm³ Outside air temperature Evaporative cooler inlet air temperature and humidity Evaporative cooler outlet air temperatures and humidity Water temperature in the evaporative cooler reservoir Evaporative pad surface temperature Air speeds & mass flow rate

RESULTS Inlet db temp (°C) Inlet HR (kg/kg) Outlet db temp (°C) Outlet HR (kg/kg) Humidity gain(kg/kg) Inlet wb temp (°C) Reservoir water temp(°C ) Table 1: Dry and Wet Bulb Temperature, Humidity Ratio humidity gain and Saturation Effectiveness

Saturation Effectiveness & External Dry-Bulb Temperature increase in saturation effectiveness as the external db temp increases evaporative cooler is more efficient at higher outside air db temp

Saturation Effectiveness & Humidity Gain The saturation effectiveness increased as the humidity gain increases

Humidity Gain & External Dry Bulb Temperature increased gain in humidity ratio at higher external db temp Fig 4.3: Humidity gain as a function of external dry bulb temperature

Speed (m/s) db Temp ( 0 C) Water flow rate Air Flow rate(m 3 /s) LOW MEDIUM HIGH

CONCLUSION The saturation effectiveness of pad determined from the experimental result falls between the ranges of %. the pad employed for the construction of the cooler is efficient and reliable. The designed evaporative coolers can maintain cooled spaces at temperatures below ambient air temperatures. The performances of the evaporative cooler were significantly affected by weather conditions. The overall cooled room temperature depression from ambient air temperature reached up to 11 0 C, and ambient air temperatures varied between 22–33 0 C.

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