Indian institute of technology delhi

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COURSE – Experimental Methods in Thermal Engineering (MEL - 705)

Title of study

Study of performance of a car radiator.

Experiment no.

Date of experiment

Date of submission

Course coordinator

# 8

Dr. PMV Subbarao (Professor)

Department of Mechanical Engg.

Applied Thermal Science Cycle


  • To understand functioning of an automobile radiator.

  • To evaluate overall thermal resistance of an automobile radiator.

  • To determine effectiveness of an automobile radiator.


The demand for more powerful engines in smaller hood spaces has created a problem of insufficient rates of heat dissipation in automotive radiators. Insufficient heat dissipation can result in the overheating of the engine, which leads to the breakdown of lubricating oil, metal weakening of engine parts, and significant wear between engine parts. A cooling system is used to remove this excess heat. A radiator is the most prominent part of the cooling system (because it dissipates heat) apart from water pump, electric cooling fan, radiator pressure cap, thermostat etc. As the coolant flows through the tubes of the radiator, heat is transferred through the fins and tube walls to the air by conduction and convection.

­One might expect the term "radiator" to apply to devices that transfer heat primarily by thermal radiation while a device which relied primarily on natural or forced convection would be called a "convector". In practice, the term "radiator" refers to any of a number of devices in which a liquid circulates through exposed pipes (often with fins or other means of increasing surface area), notwithstanding that such devices tend to transfer heat mainly by convection and might logically be called convectors. However, term "convector" refers to a class of devices in which the source of heat is not directly exposed.

A car radiator is a type of heat exchanger. It is designed to transfer heat from the hot coolant that flows through it to the air blown over it by the fan. A radiator is always a source of heat to its environment, although this may be for either the purpose of heating a space, or for cooling the fluid or coolant supplied to it e.g. engine cooling. Most modern cars use aluminum radiators. These radiators are made by brazing thin aluminum fins to flattened aluminum tubes. The coolant flows from the inlet to the outlet through many tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing over the radiator tubes.

Common types of heat exchanger flows include parallel flow, counter flow, and cross flow. In parallel flow, both fluids move in the same direction while transferring heat; in counter flow, the fluids move in opposite directions and in cross flow the fluids move at right angles to each other. When engineers calculate the theoretical heat transfer in a heat exchanger, they must contend with the fact that the driving temperature difference between the two fluids varies with position. To account for this in simple systems, the log mean temperature difference (LMTD) is often used as an 'average' temperature. In more complex systems, direct knowledge of the LMTD is not available and the number of transfer units (NTU) method can be used instead.

Experimental Precedure

  • Draw a neat skecth with all the major dimensions of the test rig and details of all the insturments available on the test rig. And enumerate all the assumptions made for the analytic model chosen for the study.

  • Measure steady state temperature and flow rates of the two heat exchanging fluids flowing across the heat exchanger.

  • Repeat the same exercise for two different air flow rates at three different water flow rates respectively.

Data Analysis

  • Determine overall thermal resistance and effectiveness of the heat exchanger for all combinations of water and air flow rates.

  • Uncertainty analysis.

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