Introduction

A radiator is a heat exchanger designed to transfer heat from a hot fluid to a colder fluid without direct contact. In drying, we envisage applications where 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

week 1 

Study the woeking principle of the cross flow radiator (Heat Exchanger)

  • Hot water from the solar water-heating system flows through 11 staggered copper tubes.
  • The copper tubes have an outer diameter of 10 mm and an inner diameter of 8 mm.
  • A fan/blower forces air across the tubes in a cross-flow direction.
  • Heat is transferred from the hot water to the flowing air through the copper tube walls.
  • The tubes are arranged in a staggered pattern with 30 mm horizontal spacing and 25 mm vertical spacing.
  • The staggered arrangement increases air–tube contact and improves heat transfer.
  • The heated air is then supplied to the drying chamber.
  • Tube diameter, wall thickness, and tube length affect water flow and heat transfer.
  • Number of tubes, tube pitch, and tube rows determine the total heat-transfer area and water distribution.
  • Fin thickness, fin spacing, and fin height increase the heat-transfer surface area and allow effective airflow.
  • Proper selection of all design parameters improves heat-transfer efficiency and produces a higher air outlet temperature.

Geometrical parameters

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

Design parameters fianilised, material selection and fabrication

  • Design parameters finalized: The heat exchanger has been designed for approximately 1 kW heat transfer capacity.
  • Material selection completed: Copper tubes and aluminium fins have been selected for efficient heat transfer.
  • Copper tube preparation completed: Tubes of 10 mm outer diameter, 8 mm inner diameter, and 200 mm length have been cut and prepared.
  • Aluminium fin preparation in progress/completed: Aluminium sheets of 0.16 mm thickness have been cut into the required fin size.
  • Fin drilling completed: Holes have been drilled according to the staggered tube arrangement, maintaining approximately 25 mm horizontal pitch and 30 mm vertical pitch.

week 2

Assembly preparation stage

  • Design parameters finalized for a 1 kW cross-flow radiator.
  • Copper tubes cut to the required 200 mm length.
  • Aluminium fins prepared with 0.16 mm thickness.
  • Holes made according to the required tube pitch.
  • Tubes arranged in a staggered pattern.
  • Tube–fin assembly completed with 4 mm fin spacing.
  • Radiator core fabrication is currently in progress.
  • Next step: Header connection.

header connection

  • Copper pipe was selected for the header  of assembly. 
  • The copper pipe was selected and cut to the required length.
  • Initially, the pipe had a circular cross-section.
  • The pipe was manually hammered and gradually reshaped.
  • The circular pipe was successfully converted into a rectangular-shaped pipe.
  • This shaped copper pipe will be used in the fabrication of the radiator-type heat exchanger.
  • Next step: Preparation of fins and assembly of the copper tubes with fins and headers.

Preparation of fins and assembly of the copper tubes with fins and headers.

  • Header Preparation: The reshaped copper header pipe was prepared for connecting the copper tubes.
  • Hole Making: Holes were made in the header according to the required tube arrangement.
  • Copper Tube Insertion: The copper tubes were inserted into the prepared holes of the header.
  • Fin Assembly: Aluminium fins were placed over the copper tubes to increase the heat-transfer surface area.
  • Core Assembly: The tubes, fins, and headers were assembled to form the radiator core.
  • Brazing Process: The tube-to-header joints are being brazed to make them strong and leak-proof.
  • Present Status: The radiator core fabrication is in progress, and the main components have been successfully assembled.
  • Next Step: Complete brazing, check for water leakage, align the fins, and perform thermal performance testing.

week 3

 Header & Fin Preparation

  • Copper header plates were cut.
  • Header plates were welded.
  • A plywood template was prepared.
  • 4 mm fin spacing was maintained

 Assembly & Sealing

  • The radiator was assembled.
  • M-Seal was applied to all joints.
  • Joints were checked for proper sealing.

Leakage Testing

  • The first leakage test was conducted.
  • Leakage points were identified.
  • Araldite was applied to repair the leakage.
  • The radiator was left for 24 hours to cure.
  • A second leakage test showed improved sealing.

Final Fabrication

  • Two remaining leakage points were sealed.
  • Araldite was again applied to repair the leakage.
  • The radiator was left for 24 hours to cure.
  • Metal side plates were welded.
  • The fins were protected and the structure was strengthened.
  • The prototype is ready for the third leakage test.

Third leakage test

  • The third leakage test was conducted.
  • The leakage points was corrected.
  • After cure for 24 hours.
  • leakages are now negligible.

Final Status

  • The radiator assembly was completed.
  • All leakage tests are conducted.
  • The leakages are negligible.
  • The radiator will be ready for performance evaluation.

Week 4

Fan Installation

 

  • Mounted the axial fan  of (90 cfm) on the heat exchanger casing.
  • Secured the fan with proper fastening by metal sheet casing.
  • Prepared the system for forced-air testing.

Heat Exchanger Assembly completed 

 

  • Completed the fabrication of the cross-flow heat exchanger. 
  • Connected the water inlet and outlet pipes.
  • Connection of the fan(90 cfm) is done.
  • Checked the overall assembly and structural alignment.

Performance Testing

 

  • Conducted the initial performance test using hot water  of (85 °c) circulation.
  • Measured the inlet and outlet water temperatures and air outlet temperature.
  • Observed stable operation and recorded experimental data for heat transfer performance and system capacity evaluation:-   

 

Parameters and values

Hot Water Inlet Temperature 

85°C

Hot Water Outlet Temperature

70°C

Air Inlet Temperature

26°C

Air Outlet Temperature

35°C

Maximum Air Velocity

3.3 m/s