A venturi meter is preferable to an orifice meter because the energy loss is less in a venturi meter compared to an orifice meter. The energy loss in a flow measurement device is an important consideration as it affects the accuracy and efficiency of the measurement.

Energy Loss in Venturi Meter:
1. The venturi meter operates on the principle of Bernoulli's equation, which states that the total energy of a fluid is constant along a streamline. This means that the sum of the potential energy, kinetic energy, and static pressure remains constant.

2. In a venturi meter, the fluid flowing through a converging section experiences an increase in velocity and a decrease in pressure. This change in velocity and pressure allows for the measurement of the flow rate.

3. The gradual change in velocity and pressure in a venturi meter minimizes energy losses due to turbulence and friction. The smooth transition from the converging section to the throat and then to the diverging section helps maintain the total energy of the fluid.

Energy Loss in Orifice Meter:
1. An orifice meter consists of a plate with a hole (orifice) inserted in a pipeline. The fluid passing through the orifice experiences a reduction in pressure and an increase in velocity.

2. However, due to the sudden contraction and expansion of the fluid flow, energy losses occur in the form of turbulence and eddies. These losses result in a decrease in the accuracy and efficiency of the flow measurement.

Comparison:
1. The venturi meter has a smoother flow path compared to the orifice meter, reducing the energy losses. This leads to higher accuracy and efficiency in flow measurement.

2. The orifice meter is cheaper and easier to assemble compared to a venturi meter. However, the energy loss in an orifice meter can be significant, impacting the reliability of the measurement.

Conclusion:
In conclusion, a venturi meter is preferable to an orifice meter because it has lower energy losses. While the orifice meter may be cheaper and easier to assemble, the accuracy and efficiency of the flow measurement are compromised due to higher energy losses. Therefore, in applications where accuracy is crucial, such as in industrial processes or water supply systems, a venturi meter is the preferred choice.