Theme 1: Basic thermal drawings of energy devices and methods for their preservation How to determine the scheme of a thermal unit

Theme 1: Basic thermal drawings of energy devices and methods for their preservation
How to determine the scheme of a thermal unit
When determining the scheme and equipment of a heat point, they rely on the technical characteristics of the local heat consumption system, the external branch of the network, the mode of operation of the systems and their sources.
In this section, you will get acquainted with the heat carrier flow charts - the thermal scheme of the thermal unit.
Detailed consideration will allow you to understand howconnection to a common collector is made, the pressure inside the network and relative to the coolant, the indicators of which directly depend on the heat consumption.

Important! In the case of connecting a thermal unit not to a collector, but to a heat network, the flow rate of the coolant of one branch is inevitably reflected in the flow rate of the other.

Analysis of the thermal unit scheme in detail

The figure shows two types of connections: a - in the case of connecting consumers directly to the collector; b - when joining a branch of the heating network.

he drawing reflects graphical changes in coolant flow rates in the event of such circumstances:

A - when connecting heating and water supply systems (hot) to the heat source collectors separately.
B - when connecting the same systems to an external heating network. Interestingly, the connection in this case is characterized by high rates of pressure loss in the system.
Considering the first option, it should be noted that the indicators of the total flow rate of the heat carrier increase synchronously with the flow rate for hot water supply (in mode I, II, III), while in the second, although the increase in the flow rate of the heating unit takes place be, along with it, the heating consumption indicators are automatically reduced.
Based on the described features of the thermal scheme of the thermal unit, we can conclude that as a result of the total flow rate of the coolant considered in the first variant, when it is applied in practiceis about 80% of the consumption when using the second prototype scheme.


The place of the scheme in design
When designing a scheme for a thermal heating unit in a residential area, provided that the heat supply system is closed, pay special attention to the choice of a scheme for connecting hot water heaters to the network. The selected project will determine the estimated flow rates of heat carriers, functions and control modes, etc.


Features of substation equipment
In order for the heat supply network of the house to function properly, the heating points are additionally installed:

• 
  valves and valves;
  
• 
  special filters that trap dirt particles;
  
• 
  control and statistical instruments: thermostats, pressure gauges, flow meters;
  
• 
  auxiliary or standby pumps.
  

Scheme symbols and how to read them

Thermal schemes of thermal units
The figure above shows a schematic diagram of a thermal unit with a detailed description of all the constituent elements.
1-three-way valve, 2-valve, 3-plug tap, 4-12-mud, 5-return valve, 6-throttle washer, 7-v-fitting for thermometer, 8- thermometer, 9-manometer, 10-elevator, 11-teplometer, 13- water meter, 14- water flow controller, 15-sub-steam regulator, 16-valves in the system.

Exercise 1. Find the in-plane effective thermal conductivity, and the normal thermal resistance for a component covering a 37.537.5 mm² area, in a PCB of 1501001.5 mm³, made of a single FR-4 layer, with a top copper layer of 70 m with 20 % of metal, and a bottom copper layer of 70 m with 100 % of metal.
^{Sol.: PCB one-side area A}PCB^{=150100=15·10-3 m2; main-component area A}comp^{=37.537.5=1.4·10-3 m2. As copper only covers 20 % of the top layer (the other 80 % can be neglected for thermal conduction), applying (9) and (10) with k}FR4^{=0.25 W/(m·K)
across, k}FR4^{=0.5 W/(m·K) along, and k}Cu^{=400 W/(m·K), we get:}


Exercise 2. Find the effective thermal conductivity and the effective thickness of the ribbed aluminium (A-7075) plate sketched in Fig. E3, machined from a 5005005 mm³ uniform plate, with six equi-spaced parallel grooves 60 mm wide and 3 mm deep were milled, leaving 7 equip-spaced ribs 20 mm wide.