ANS:C - radiation heat transfer by increasing the temperature and reducing the emis-sivity.

A reduction in thermal resistance during heat transfer does not occur in radiation heat transfer by increasing the temperature and reducing the emissivity. Explanation:

1. Convection heat transfer by stirring the fluid and cleaning the heating surface: This statement is true. Convection heat transfer involves the transfer of heat between a surface and a moving fluid (liquid or gas). Stirring the fluid and cleaning the heating surface can enhance convection heat transfer by promoting better fluid flow and reducing boundary layer effects, ultimately reducing thermal resistance.
2. Conduction heat transfer by reduction in the material thickness and increase in the thermal conductivity: This statement is true. Conduction heat transfer occurs through a solid material and is governed by factors such as material thickness and thermal conductivity. A reduction in material thickness and an increase in thermal conductivity both lead to reduced thermal resistance and improved heat transfer.
3. Radiation heat transfer by increasing the temperature and reducing the emissivity: This statement is incorrect. Radiation heat transfer occurs between surfaces due to the emission, absorption, and transmission of electromagnetic radiation. Increasing the temperature of the radiating surface can increase the rate of radiation heat transfer according to the Stefan-Boltzmann law. Similarly, reducing the emissivity of a surface can decrease its ability to emit thermal radiation. However, neither of these actions directly reduces thermal resistance in radiation heat transfer. In fact, increasing the temperature may increase the thermal resistance due to the potential for greater temperature differences between surfaces.