AIM

To design and analyze a finned-tube radiator capable of transferring heat from hot water to air and producing heated air suitable for drying applications.

BACKGROUND

Drying is one of the most widely used methods for preserving agricultural products. The efficiency of a drying system depends on its ability to supply hot air at a controlled temperature. A radiator acts as a heat exchanger that transfers thermal energy from hot water to air. By increasing the heat transfer surface area through fins and counter flow type the radiator can efficiently heat air before it enters the drying chamber. Therefore, proper radiator design is essential for achieving energy-efficient and uniform drying.

INTRODUCTION

A radiator is a heat exchanger designed to transfer heat from a hot fluid to a colder fluid without direct contact. In drying applications, hot water flows through tubes while ambient air passes over finned surfaces. Heat is transferred from the water to the tube walls, then through the fins, and finally to the air.

The use of fins significantly increases the available heat transfer area and arrangement of tubes breaks laminar resulting in higher thermal efficiency. The design of a radiator involves selecting appropriate tube dimensions, fin geometry, tube arrangement, and flow rates to achieve the desired outlet air temperature.

OBJECTIVES

  1. To understand the working principle of a radiator as a heat exchanger.
  2. To calculate the heat transfer rate required for air heating.
  3. To determine radiator dimensions such as tube length, tube diameter, fin spacing, and fin thickness.
  4. To evaluate the effect of airflow and water flow rate on heat transfer performance.
  5. To optimize the radiator design for maximum thermal efficiency.

WORKING

The radiator functions as a heat exchanger between hot water and air. Hot water enters the radiator tubes at a high temperature (around 80–90°C) and flows through the tube network. Simultaneously, ambient air is forced across the finned tubes using a blower or fan.

As the hot water flows inside the tubes, heat is transferred to the tube walls by convection. The heat then conducts through the tube material and spreads into the attached fins. Because fins provide a much larger surface area than plain tubes, they significantly enhance heat transfer to the surrounding air.

The moving air absorbs this heat and its temperature increases before entering the drying chamber. Meanwhile, the water temperature decreases as it releases heat, typically leaving the radiator at 50–60°C.

For improved performance, tubes are often arranged in a staggered pattern. This arrangement increases air turbulence, improves contact between air and the heat transfer surfaces, and enhances overall heat transfer efficiency.

The heat transfer process occurs are:

  1. Convection from hot water to the inner tube surface.
  2. Conduction through the tube wall and fins.
  3. Convection from the outer finned surface to the airflow.

Design Requirements and Parameters

Hot Water Side Parameters

  • Inlet water temperature: 80–90°C
  • Outlet water temperature: 50–60°C
  • Water flow rate: To be determined based on heat demand
  • Working fluid: Water
  • Operating pressure: As per system requirements

Air Side Parameters

  • Inlet air temperature: Ambient temperature
  • Desired outlet air temperature: Approximately 65°C
  • Air flow rate: Depends on drying capacity

Geometrical Parameters

  • Tube diameter
  • Tube wall thickness
  • Tube length
  • Number of tubes
  • Tube pitch
  • Number of tube rows
  • Fin thickness
  • Fin spacing
  • Fin height